User manual
Contents
1. which allows the user to change the look of the traces Each ire spectrum can be represented using lines markers or both or be EE hidden completely Lines can have different widths colors and styles whereas markers have options for marker type size color border width and border color Each spectrum can also have an associated legend text This is shown if a legend is used see mmm Legend Properties below and can be different from the spectrum name Plot Properties ee The look of the background is changed using this option The zaj fom Plot Area encompasses the region within the axes whereas vepe oo sms the Chart Area includes those outside as well Both areas can e i have backgrounds consisting of a single color or have gradient or hatch patterns where a Secondary Color has to be specified eal ax o D z The areas can be surrounded by borders with different widths iren colors and dash styles and the user can also add a shadow to Ei mek the plot area defined by an offset and a color Legend Properties A legend can be added to the plot by s isa jenen eu Fort Moo Sana Sadi Fnni Meast Sana San Grind Shy Cor ec als dicho Hone E De selecting the Show Legend box on a c ne Bharat Rape Shack the top left The legend has many Ln Cte RR Oa 0 E m om ce NN options as seen to the figure on the 7 dL e 9 Neg Canter hm Styl2. This is a comment The Comments tab lets the user add comments to each spectrum in text format The entered comments are associated with the currently selected spectrum in the Calculated Spectra area Analyzing an experimental spectrum might involve calculating many spectra in an iterative process The comments section is there to help the user keep track of ideas or information above and beyond the Calculation Options which are saved automatically 2 4 2 Populations ET TT TE ETT Populations Electronic populations Nz State Population cm 3 Degen QVE AlS5IGGt 0 290ET18 1 0O 120E 04 ASSIGU 0 589E 06 3 0 221ET04 B3PIG 0 381ET04 amp 0 174ET04 E alPIe 0 507ET01 z 0 179ET04 C3PIU 0 115E 03 amp 0O 142E 04 blPIU 0 847E 07 z 0 302ET04 b l1SIGU t 0 135E 07 1 O 457E O4 c 45IGU 0 251E 08 1 0 130E 04 W3DELU 0 640ET04 amp 0 306E 04 The Populations tab displays among other variables the calculated electronic populations 2 4 3 Units s Comments Populations tl Units Units of emission spectra Spectrum computed with no slit function mW cm sr um Spectrum convolved with a slit function whose maximum intensity is normalized to unity mW cm sr To obtain a convolved spectrum in units of mW cm sr um divide the above spectrum by the equivalent FWHM in um of the slit function Units of absorption spectra The quantity plotted is the absorption coefficient in cm
3. Ho 3460 a Max 610 Min 350 4 Calculation Sett 0 L TT cpm 350 370 390 410 430 450 470 490 510 530 550 570 590 610 Generate m no Slit function conve Wavelength nm Spectral ster 0 00C Speed displ on Width of sist 1 4 Comments Area M Deere Figure 2 The Specair user interface 2 1 Menu Bar Specair 3 0 untitled praje Ele Edit View Data Plot Tools Help 2 1 1 File menu Specair 3 0 untitled project iim File Edit View Data Plot Tools Help New Project Ctrl N 2 Open Ctrl O lp Save Ctrl S Save As Import spectrum Ctrl Shift O Export spectrum Ctrl Shift S Save as image m Print graph Ctrl P Exit New Project Ctrl N Create a new Specair project This clears all the calculated spectra The program will ask you if you want to save the current project before closing it Open Ctrl O Open an existing Specair project A Specair project contains all calculated spectra and the options used to calculate them as well as any imported files Save Ctrl S Save the current project to a Specair data file Save As Save the project as a new Specair data file Import spectrum Import a data file containing a spectrum Most commonly use file formats are supported such as Galactic spc and JCamp DX jdx For a text file the data should be listed in two columns wavelength in nm and intensity separated by spaces o
4. specair User manual Version 3 0 Table of contents Table of VldinLc 1 DS DECANE mo MINUTOS x5onabacsihe tein abn us n e AM 3 1 Introduc on to SBeCalE iioi eve e t d SEE EVE Yo ee oeR Sev DX RU SEE A 6 2 XheSpecair User Interface cccecccccieccscesssavsdscssinsvacccucesucsssssvesssevevscsvansdeceseusdecasstsvesssucsssess 7 2 1 NIU BOE decuit td eo mb eS oU mI M d NUR I AM lene D LL RU 8 PAPAA O56 DINNER 18 PASS ME PIO aa AN ict Rr ee eC Ee eR Rey Ce ten RN RES ONCE Re Cea RON ee MTEC Tar Ce eee en Cm 19 Zo C MING TING Ted boue setas Moe toe eii bM EDO EPI NIME E ena 20 2 5 AIC ALCO DCC ira EEEE stance et E Maa M MOMMSEN M CC OEEM CDM 21 2 0 Opt ons or Calculated SPCC bas su crete rian a A el de ane Geiagain ete tea outa 21 PTUS Roles st E OPONE RT uu un 23 3 he SIC EUnDctIOD ood t eed EE oor Ort ND dI LEM oE DARE NU EEU DIETE ames 26 3S To Trapezoidal st Eunctloll epo eti E docu a oaes or ed E deno isse d aea rob ede e Saiviousa 26 232 Iniported SIT Ete HOID dcc e etet ceo puo mu etu eos aout etop a 26 Eli nceiscibiiti E PPORR 28 S Eciam ToC d 28 2 2 Pinde EEGOSTUOTDIS Soie dies dte Staind eed a LIN S LSU DR Cu eh ae UD dd 30 LAO GS DINE UU T TENTER 32 5 The physical model for radiation used in Specair eee e eee e ee eere eene 34 x S NI SIT ESAME SINE EN TR 34 3 2 DI epu eL LEM EE MM DE E 34 3 9 95S E IE C HOT Ule Senec sebo odo RU EC UR TM C LE 35 Dod
5. Once a sufficient change is detected the program proceeds to the regular fitting 4 1 3 Outputs For each iteration the iteration number the value used in the calculation and the residual 1s displayed in the Log section to the right This allows the user to directly observe the convergence and the improvement between successive fitting attempts The magnitude of the residual will depend on both the overall magnitude of the spectra and the wavelength range and is thus experiment specific 29 Under the section Add Spectra the user can choose to calculate and display both the spectrum and the residual spectrum using the values found during fitting The residual spectrum can be very informative when looking for underlying minor peaks or wavelength mismatches 4 1 4 Fitting methodology Due to the large number of parameters and the relatively long time for calculation a brute force approach is often inadequate for spectral fitting Any spectrum could in principle be fit by successively minimizing the residual for each parameter in an iterative manner but in practice the number of calculations grow exponentially with the number of variables So if four different temperatures are used in combination with several species and transitions a guided approach is often superior For a simple spectrum the recommended order is to start with the dominant Radiative Transition The experimenter should use previous knowledge about the condi
6. The rotational energy is a function of the total angular momentum rotational quantum number J As seen above Q is the projection of J on the internuclei axis which gives that J can never be less than Q 5 3 Selection rules For spontaneous transition between two states to occur the transition has to fulfill the following conditions e AS 0 e AA 0 1 e ue 9 e Yor ory ory eeorf gt f e AJ 40 ef l eeorfo f All other transitions are so rare that their emission has no significant importance for the detected radiation As we can see selection rules limit the possible transitions between different electronic states and rotational levels There are no such limits for the transition between different vibration levels between these levels everything goes 5 4 Example Figure 3 below an image from Herzberg p 267 illustrates transitions between states It represents the energy level diagram for a II X band where only the levels for J between 10 5 and 15 5 are included K stands for the total angular momentum apart from spin The broken line branches are satellite branches and the dotted branches do not appear in a strict Hund s case b A type doubling is present in the IT state Hund s cases distinguish different modes of coupling of the angular momenta 35 KE Amr 15 Fx 14 15 Ft 14 i Lr Dre PEN LIAE m Ft RENE FP E I LH i S PIA I 11 12 pa i did dh mh Er rn Inn m nme i Hm 10 11 S8
7. The Units tab displays the different intensity units in Specair The possibility of concurrently displaying many spectra of different origins such as imported spectra and spectra calculated with or without convolving with a slit function precludes a default intensity unit Instead the Unit tab provides a quick access to the Specair units and conversion factors 20 2 5 Calculated Spectra All spectra calculated and imported are listed in the Calculated Spectra area at the top right of the Specair window New calculated spectra are automatically named New Spectrum plus a number and imported spectra also have imported added to their names The user can manually enter a new name after anced Options p clicking on an already selected spectrum x Delete Permanently delete all selected spectra from the current project PG Hide P Show Hide or show selected spectra in the Plot Area 2 6 Options for Calculated Spectra The Options for Calculated Spectra are located at the bottom right of the Specair window and display properties a selected spectrum in the Calculated Spectra area All spectra both calculated and imported have three properties that can be changed Color Visibility and Width Color Spectra are automatically assigned a color which is used when it is displayed in the Plor Area This color can be manually changed by clicking on the drop down menu see figure to the right Visib
8. Use selected temperature I Fix To 10000 electronic fld spectra Use existing temperatures Spectrum with final settings Wavelengths Residual spectrum Wavelengths from input Use existing settings Update and close Cancel ic s 4 3 Global fit The Global fit window accessed under the Tools menu and shown in the figure below is an interface combining the basic fitting and the transition finder to streamline the fitting process As described above a general fitting procedure consists of adding transitions one at a time while optimizing all variables between each step In the Global fit both the addition of 32 transitions and the optimizations can be done automatically significantly reducing the active time for the user The transitions are added by pressing the Add button which launches the Find transition functionality described above If the Add transitions automatically is selected the transition finder uses the first choice among its suggestions Otherwise the user can verify that the right transition is chosen and also manually change the transition The Peak wavelength tolerance nm and resolution selector are the same as in the transition finder More than one transition can be added automatically with the number selected in the drop down menu This will add transitions in order of prominence if Optimize after adding is also selected The added transitions are listed belo
9. box opeed display With this option turned on the calculated spectra are returned with a resolution matching the Slit Function see also Speed display options above This significantly improves the speed and memory requirements without impacting the practical quality and is the default option The full resolution is returned with this option turned off but this is not recommended as the program can quickly run out of memory Wavelengths The returned wavelengths as observed in air or vacuum The standard value is air as spectroscopic detectors are usually placed in room air Width of slab Indicate the width of the plasma in cm along the line of sight of the spectrometer The value determines the intensity of the calculated spectrum and is important when comparing absolute intensities with experimental data 2 5 Mole Fractions The relative amount of each species is indicated here For plasma consisting of only one species the value should be 1 otherwise use fractional values For example use 0 5 for N and 0 5 for CO for two equal concentrations of these species For a non zero result the Mole Fractions for 24 the species responsible for the selected transitions see below have to be greater than zero The species are written without subscript 1 e N2 N gt 2 6 Radiative Transitions The spectroscopic transitions to model are selected by entering a 1 To exclude a transition set its value
10. copy Slit function F3 Open a dialog box for defining and selecting a slit function For more details please read the Slit Function section below Spectrum type Specair can calculate both emission intensities and absorption coefficients Both options use the same input parameters in the Calculation options The spectrum types are displayed similarly in the plot area but their units will differ Speed display options Specair automatically uses an optimal spectral resolution in its calculations This resolution is usually far greater than that offered by the experimental equipment as defined by the spectrometer s slit function By selecting the Speed display found in the Calculation options only a small subset of all points will be imported from the calculations to speed up the subsequent manipulation of the calculated spectra This option displays a certain number of points for each slit function full width half maximum FWHM as defined by this Speed display option 10 or 20 points is often sufficient Temperatu re loop Temperatures in loop Translational Electronic Temperature loop 7 4 Rotational The temperature loop allows the user to make many calculations in 4 ux one batch while varying one or more statistical temperatures The user defines the Start Temperature the Step which is the E incremental increase in temperature and the number of spectra to 7mm calculate The temperatures not
11. degeneracy of the electronic level e k is Boltzmann s constant is the electronic energy is the vibration energy and is the rotational energy for the state T el I and T are the temperatures associated with the electronic vibrational and the rotational levels respectively Finally pA A is the line shape function 36
12. does go to zero in the wings The center of the imported slit function will be detected automatically based on center of the line indicating the FWHM and it is advisable to verify that this is done correctly since an error in this value produces shifts in the spectral peak wavelengths In addition the FWHM is displayed to aid in the calculation of absolute intensities A spectrum calculated with an imported slit function will have intensities given in mW cm sr if the slit function 1s normalized to unity This normalization can be done directly in the slit function window by pressing the Normalize button with a value of 1 for the Enter new peak value entry A different peak value can be used if desired As in the case of a trapezoidal slit function the above spectrum can be divided by the FWHM in um to obtain units of mW cm2 sr um Specair calculates both the FWHM and the equivalent FWHM The latter is defined as the integrated area under the slit function divided by the peak value of the slit function To obtain spectra in units of mW cm sr mm compute your spectrum with a slit function normalized to a maximum value of 1 and divide the obtained spectrum by the equivalent FWHM Set Slit Function Use trapezoidal slit function Width of the base nm 1 Width of the top nm Intensity at the peak 1 Define own slit function C slit functiont txt mm The imported slit function is normalized by Specair to a
13. existing transitions is selected the user can choose to Keep existing mole fractions as well There is also an option Optimize new mole fraction which automatically optimizes the mole fraction as described in the Basic fitting section above Once a mole fraction has been set the temperatures and mole fractions can be further optimized These selections are listed under Optimize after closing The Fix Tetectronie option is similar to that above intended to keep the electronic temperature high for reasonable intensities even if the other temperatures are low as in the case of electric discharges The other option Tetectronic Tio Sets the electronic temperature to be equal to the rotational temperature before fitting the mole fraction This could be used if a fixed electronic temperature was used previously while trying to optimized the rotational temperature at a high intensity The final options under Add spectra can be selected to automatically calculate both the final spectrum after optimization for example and the corresponding residual spectrum i e the difference between the input spectrum and the calculated one Update settings e Add transitions amp Selected transition only Species Set mole fraction 0 1 3 All transitions for this species Existing transitions and species Optimize after closing w Clear existing transitions MES iv Temperatures Keep existing transitions Fix T dectronic Temperatures amp
14. iP o TT WS a i P ert Epa i to L jud d ala ME i od ec a on L et ml m m ji e a a y s sme Siglo s 5 i RAS mee RENE P alalla TEL app trj S e Atha Ha aS i iy fil Wal les kal des j id ro eem s uj EMI atia aoo dg 1 it iube haere yy Wy l l iler pri por t l F ibbati rr pal La 15 m i Hr 7 P 14 14 i 13 19 E NEN Fis T 12 12 I 11 2 m mune aaa DU AE P O Figure 3 Energy level diagram from p 267 Herzberg G Molecular Spectra and Molecular Structure Volume I Spectra of Diatomic Molecules Krieger Publishing Company 5 5 Emission intensity The emission intensity due to a transition from the upper energy level e v J to the lower energy level e v J 1s expressed as v v S J I A n vJ const gt Re Y 2 T UE os E sp A Hu Ay d The expression gives the emission intensity as a product of the number of molecules in the upper state e v J the probability for spontaneous transmission from the upper state to the lower state and the energy difference between the two states The probability constants y Re j and S are both tabulated values and are not calculated by Specair The population in the upper state 1S calculated with the expression E Ep TE B z g 2S 1e kT KT kT evij TE Ey TEs g 25 1 e kT kT kT evJ where N is the total number of molecules g is the
15. oS onl a omen ener su eros E liec t Apis M A e bi een AO ee 35 IEMS ONIN ENS osea Acsi d Es tds tt os puris ras dE te dot tds Ea Ee dte 36 Specair in 3 minutes Specair is a program for calculating emission or absorption spectra of air plasma radiation It can calculate display and save spectra based on a wide range of user input parameters The main user interface sections of Specair are indicated in Figure 1 below To create a new spectrum the user specifies the input parameters for a new spectrum in the Calculation Options area to the left and presses the Calculate spectrum button in the top left corner The new spectrum will be displayed automatically in the Plot area in the center Comments to individual spectra can be added in the Comments Area at the bottom and the appearance of the spectrum can be changed in the Calculated Spectra area to the right or under the Plot menu By selecting a spectrum at the top of this area the user can see the used Calculation Options in the area to the bottom right In addition to calculating spectra Specair can import experimental spectra in most of the commonly used file formats Using Specair the user can manipulate both imported and calculated spectra by selecting the spectrum in the Calculated Spectra area and choosing among the options in the Data menu The data can be exported to other applications either by choosing Export spectrum in the File menu or by selecting Display Data in t
16. peak value of 1 Enter new peak value 1 Normalize Slit function Imported slit function Interpolated slit function Spectral step 0 001 nm Center 632 849 nm FWHM 0 325 nm Equivalent FWHM 0 375 nm D o g cz aal LLL 631 63222 6033 44 634 66 635 88 637 1 nm Make sure that the slit function goes to zero in the wings It is also advised to cut off the wings beyond the points where the slit function is equal to zero ok Gee al 27 4 Spectral fitting 4 1 Basic fitting 4 1 1 Introduction to fitting Fitting to experimental spectra is central to plasma spectroscopy The conditions in which the plasma was generated can be understood by finding the parameters that replicate the measurements This is a difficult and iterative process as a complex plasma is described by tens of variables Specair provides a numerical fitting routine which can greatly speed up the process The option can be accessed by selecting a spectrum to fit hereafter called the experimental spectrum and then selecting Fit to Spectrum in the tools menu This opens the window shown in the figure below Fit to spectrum I Temperatures C Mole Fractions F og Fi Ti perat ES Bu 5s Optimizing temperature Blectronic 2500 0 teration Temperature Residual 1 3500 6 671495169121 Rotational 2500 0 2 500 44 6960822728596 0 3 7427 540 283905813921 Translational 2500 4 2573 0 032631749392
17. slit L 0 2 G gt 0 025nm 0 25 nm slit 368 999800051976 373 999800051976 378 999800051976 383 999800051976 0 1 nm 1 nm slit 0 25 nm 2 5 nm sit ol i 0 5 nm 5 nm slit Transtion lt Close If a transition has been found the user can press the Update settings button to use the information for updating the calculation options or for fitting This opens the Update settings window see figure below The user can add the selected transition or all the transitions associated with the found species For example if N 1 was identified the user can also add N 2 at the same time This can be done while alsso Clearing existing transitions 1 e setting all Radiative transitions to O in the Calculation options 3l The temperatures can be updated to that selected in the transition finder There is an option to Fix Tetectronic Which is useful for example when studying plasmas from electric discharges Even though the plasma is cold the electronic temperature is high which is needed to see a meaningful intensity The min and max wavelength in the calculation settings will be updated to those indicated in the transition finder unless the user chooses to Use existing settings The wavelengths in the transition finder are those of the input spectrum by default but can be changed by the user Under Species the user can specify the new value for the mole fraction associated with the selected transition If Keep
18. than the second and third a minimum exists in the region around the initial value and the routine will proceed If instead there is a trend toward the second or third value the routine will keep extending the region by the Initial Step percentage until a minimum has been bracketed This means that a smaller Initial Step is preferable is the Initial Value is close to the final fit result whereas a larger Initial Step is better if the final value could be within a large unknown range The third option is the Accuracy which is the threshold for stopping further iterations It is given as a percentage of the final value such that 0 1 returns an answer within a 1 Kelvin range for a final temperature of 1000 K Lower accuracy such as 1 or 2 requires fewer iterations and hence leads to faster fitting Unlike the temperatures which are often between 300 and 12000 K the mole fractions in a plasma can vary by many orders of magnitude To quickly find a good starting point for fitting the user can select Find initial mole fraction This option starts by making a calculation at a very low mole fraction specified under First iteration Further calculations are then performed while increasing the mole fraction by an order of magnitude until a noticeable change in the residual is detected The change in mole fraction between iterations is indicated under Multiply by with 10 being the default and the Min residual change is normally 0 1
19. with respect to the operator 7 which inverts the coordinates of the nuclei and the electrons relative to the molecule s center of mass The letter g indicates that the wave function is symmetric gerade and a u indicates that it 1s not 34 66 66 For states a or a is showed to the right of the term This indicates if the electronic wave function is symmetric relative the operator o which corresponds to a mirror reflection through a plane containing the internuclear axis To designate the spin substates the notation e is often used Q is the quantum number associated with the projection of the total angular momentum J along the internuclear axis For diatomic molecules the total angular momentum exclusive of nuclear spin is the vector sum of orbital L spin S and rotational R angular momenta J R L S The projection of R on the internuclear axis is zero the projection of L is units of momentum the projection of S is X and the total projection of J is Qh For a L I state eq esp 2 this gives us four possible values of Q 3 2 1 2 1 2 3 2 A common notation is to just give the absolute value of Q and distinguish the positive values from the negative by their parity We use e f as parity notation and this gives the following notation for the four spin substates of the II state 2 2 2 2 It I It and Hs For rotational levels the notation F F2 Fz2s 1 is used to designate the 2 1 spin substates
20. 5838 0 5 2000 1 39253160952392 Vibrational 2500 6 2476 0 00418027373743118 0 T 2498 0 000826623 73468 7828 D 8 2500 0 000805426 1602337778 5 2502 0 0008314750092604 77 ae 0 VEE EES Final 2500 0 000805426160233778 initial Value 5000 D Initial Step 75 30 Accuracy 0 1 0 0 Add spectra 0 Spectrum with final settings C Residual spectrum 1E 10 10 0 1 m Specair implements Brents method to minimize a residual the root mean square of the difference between the experimental spectrum and the calculated spectrum The spectra are calculated based on the current settings in the Calculation Options including the slit function which are held constant as either temperatures or mole fractions are varied until a minimum is found Please note that all experimental spectra are normalized in the process of fitting This means it is advisable to make a copy within Specair of any imported spectra It also means that for a spectrum with a single electronic transition the actual spectrum being fit is independent of the electronic temperature which only changes the intensity Similarly the result will be independent of the mole fraction if only one species is present in the plasma The results from fitting are only as good as the starting point the experimental spectrum Specair automatically interpolates this spectrum before calculating the residual It is advisable to 28 correct any drift or offset after an initial round of fitting
21. Comments Ctrl Alt C Show the Comments 2 1 4 Data menu Specair 3 0 untitled project MEM RR NI File Edit View Data Plot Tools Help gt Calculate spectrum EA Normalize Normalize at Wavelength 3 Calculation options oy eras Find Minimum Electronic 40 Find Maximum Rotational 401 Translational 401 Set X Values Vibrational 401 Set Y Values 4 2 Pressure comme 1 Subtract Baseline Pressure Unit bat Crop 4 3 Wavelength Rang Max 611 Add Spectra Min 351 4 4 Calculation Settin Subtract Spectra Absorption thid Multiply Spectra Ge t le fi Divide Spectra Slit function cot Speed display on Average Spectra Wavelengths air Width of slab 4 Integrate 4 5 Mole Fractions y c 0 Convolve with Slit Function c o E Display Data c2 1 The data menu provides a number of operations that can be performed on both imported and calculated spectra These functions are useful for correcting experimental spectra for drift imperfect calibrations or different scaling They also give the user a way to compare spectra integrate them and to access the numerical data for further processing Normalize Normalize all the selected spectra to a maximum value of 1 Normalize at Wavelength Open a dialog box for normalizing selected spectra at a given i Normalize S wavelength The wavelength is initially set by the vertical marker but Moaien am can be changed by the user All spectra will be divided by the
22. OK to subtract a segment defined by the start and end obeeme values X value Y value 610 00 2 3 Crop ok Canca Open a dialog box for reducing the wavelength range of Crop spectrum a spectrum This can be useful for example to a small minX nm maxX nm Crop between 432 32409 and 555 82504 segment of an imported spectrum The wavelength Create new spectrum range is selected using the cursors in the plot area before selecting Crop but can also be changed in the Crop window If Create new spectrum is selected a ag pop 7 aeaii new cropped copy will be generated leaving the original spectrum intact Add Spectra e spectra Open a dialog box for adding two or more spectra A new EE spectrum with the name specified by the user will be Se created with y values at each wavelength being the sum of 5 all corresponding points in the selected spectra The wavelength x values are the same as one of the input spectra as determined by the user The y values for the other spectra are interpolated values at the same wavelengths before the addition allowing the user to quickly add spectra from different sources Subtract Spectra Open a dialog box for subtracting one of two LJ selected spectra from the other A new spectrum ss B iria with the name specified by the user will be minus New Spectrum 2 v created with y values at each wa
23. avelength Rar co 0 610 E 0 in 350 N 0 AValculation Sett N 0 Absorption thin N2 0 0 ZI Air Lambda air N2 0 350 370 390 410 430 450 470 490 510 530 550 570 590 610 Generate m no NH 0 Slit function conve NO 0 Wavelength nm Spectral ster 0 00 o 0 Speed displ on O 0 Width of slat 1 oe e Comments Output ls Units Comments Area gem i c2 1 pem x co 0 E 0 Figure 1 Screen shot of Specair Copyright 2012 SpectralFit S A S 5 Rev 1 0 0 1 Introduction to Specair Specair is a computer program that models radiative spectra for plasmas The areas of applications include analysis of plasma spectra and heat flux calculations and it has been verified by numerous experiments The calculations in Specair are based on a quantum mechanical model that describes each energy level of the species included The species are the most important radiating atoms ions and diatomic molecules present in air plasmas e g N2 O2 NO N7 N O C The spectra of diatomic molecules are computed as described in Laux C O Optical Diagnostics and Collisional Radiative Models VKI Course on Hypersonic Entry and Cruise Vehicles Stanford University June 30 July 3 2008 The latest iteration of Specair combines a fast engine for calculations with an intuitive and versatile Windows based user interface The engine is written in Fortran for maximal performance and can calculate a high resolution spectrum within a few seconds on a m
24. e Norse right The legend style includes a on _OK Gres options for the text associated with each trace such as font and color The geometry of the legend is defined by its style column or row and its docking and alignment The docking defines which side of the graph the legend is placed on and the alignment selects whether it is placed in the 13 middle or a specific corner The legend can be placed inside the Plot Area 1 e within the axes The legend can have its own title with options for font color background color and alignment This means that the title 1s associated with its own area separated from the rest of the legend by a separator which can also be defined in terms of style and color The legend can have its own background including gradients and hatch styles just like the plot area see above Similarly it can have a border and a shadow Title Properties A title can be added to the plot Like the legend and plot areas it can have background effects a border and a shadow The title can be aligned to the left middle or center and the text orientation 1s variable The title also has a few text styles such as shadowing Axis Properties The axis properties window can change one or both axes in the ss plot area Each axis has an axis title which can be changed along with its font alignment and orientation The axis range can be c7 7 defined manually as can the crossing if the user pre
25. ex spectrum with Es j remi nm alt several species and transitions miim The global fit incorporates both the Fit to Spectrum and z NEU ED mE NE x E A stink ante en r L oa Find Transition functionalities to successively add new species and transitions and then fit both temperatures and mole fractions in an iterative manner For more information see the section about curve fitting below 16 2 1 7 Help menu File Edit View Data Plot Tools Help gt Calculate spectrum GF Wh c e Optid 2 Specair User Manual pdf Specair Website a About Register This menu contains resources for help and registration 3 Calculation options 4 1 Temperatures Electronic Ratatinnal Specair User Manual pdf Open the Specair User Manual this document An external pdf reader must be installed Specair Website Open the Specair Website www spectralfit com in the default browser About Display the current version and copyright information Register Specair is available in a shareware version with limited z egistration capabilities The full version is enabled by entering the Pise enteryouricense number and registration key Licence number and Registration key obtained when Registration key purchasing a license For more information about licenses sesse send vestes please visit the Specair website www spectralfit com o
26. fers the other Oeming m axis to be placed somewhere in the middle of the plot The uu Mm o default setting is for the crossing to be at the minimum of the axis og Seale Orato fat range The x axis can be reversed and both axes can use a log ME ne scale provided that all values are greater than zero mg Ses Be on The width color and dash style of the axes can be modulated ci e The labels can be removed and their font color and orientation peor OK cue can be changed Reset Axes F5 Set the axis range for both axes to encompass all visible spectra Set Axes Graph Axis X axis Set the axis ranges manually This has the same effect as changing it Sa aw under Axis Properties see above but the values can be preset using 7 the plot markers Mn Max 1 72 8 640 ok Cms 14 2 1 6 Tools menu File Edit View Data Plot Tools Help D Calculate spectrum 7 Wh GQ Calculate Spectrum F2 Duplicate Spectrum Ctrl D 2 Calculation options 2 i apake Slit Function F3 3000 Spectrum Type gt a s Speed display options gt r rim aaa Temperature Loop Pressure 1 Eit to Spectrum Penn Unit Beer Find Transition 4 3 Wavelength Range nm Max 360 E Global Fit Min ann o Calculate Spectrum F2 Calculate and display a new spectrum based on the current settings in the Calculation options Duplicate Spectrum Ctrl D Create identical copies of all selected spectra The new spectra have the suffix
27. h which resolution The following sections explain each of these input parameters 2 7 1 Temperatures In Specair the populations of molecules in specific energy states are assumed to follow Boltzmanns distributions at the electronic vibrational or rotational temperature The levels of atomic species follow a Boltzmann distribution at the electronic temperature The fourth temperature is the translational temperature which together with the pressure defines the total density of the plasma as well as the line broadening coefficients Specair includes in general Doppler collisional Stark and natural broadening See the section below on the physical model for more information Electronic The electronic temperature determines the populations of electronic levels Boltzmann distribution at Tetectronic Rotational The rotational temperature determines the population of rotational levels Boltzmann distribution at Tyotational Translational The translational temperature is the classical thermodynamic temperature and determines together with the pressure the overall population of molecules in the plasma as well as the Doppler and collisional broadening widths Vibrational The vibrational temperature determines the population of vibrational levels Boltzmann distribution at Tyiprational 2 2 Pressure Pressure The pressure determines with the temperature the number density of species and therefore the absolute inte
28. he Data menu and the use Copy and Paste to for example MS Excel An actual plasma emission spectrum consists of many sharp lines each broadened by several mechanisms including Doppler collisional natural or Stark broadening In reality however the resolution of the collected data 1s determined by the instrumental broadening specific to each experimental setup In Specair instrumental broadening is taken into account by convolving the plasma emission spectrum with a Slit function The slit function represents the broadening caused by the spectrometer slit width pixel width grating dispersion and can be changed by selecting Slit Function from the Tools menu The user can either use a trapezoidal slit function or import an experimental file The imported file should be in a commonly used file format Specair has about 60 input parameters all set in the Calculation options which together determine the wavelength and intensity for each peak in the spectrum The peaks which correspond to various transitions between the internal energy states of atoms or molecules are determined by the population of plasma species in the various energy levels the energy differences and transitions rules between the excited states and the radiative transition probabilities 1 Temperatures The electronic rotational translational and vibrational temperatures in Kelvin define the respective Boltzmann population distributions of the internal energy level
29. i 8 747E 12 0 206907601030067 8 573E 12 0 206893598192774 0 5 nm 5 nm slit 8 660E 12 0 206867791456479 Optimize Optimize ee Remove Number of iterations 3 v Tm m eee 0 CO 0 N2 01 NO 0 Fit Parameters C2 0 E 0 N2 866E O 0 a Tempeaue CN 0 N 0 NH 0 02 0 Accuracy 1 3978 OH 0 Cancel 33 5 The physical model for radiation used in Specair 5 1 Energy levels Specair simulates emission intensities for a number of diatomic molecules Emission occurs during molecule transitions from higher to lower energy levels The energy of a level can be expressed as the sum of the electronic energy the vibration energy and the rotational energy E he T G v F J st The term st is a small term due to lambda doubling and spin splitting which will be discussed later The energy of the electronic levels hcT is often tabulated Spectroscopy literature frequently expresses the vibration energy as the polynomial expansion 1 1 1 1 hcG v 6 vit x vt y v z v e V 2 2 eve 9 e e 2 where the polynomial coefficients are tabulated The energy of the rotational levels FE J is calculated using a similar expression F J B J 1 D I J Y H 791 hc The polynomial coefficients are normally tabulated However for most transitions considered in Specair the above expressions are not used Instead for the sake of accu
30. le Set visibility of the spectrum in the Graph Area Changing this property from True to False is identical to clicking the Hide button above Wiath Change the line width in pixels for the spectrum in the Plot Area The standard value is 1 but higher values are possible 2 6 1 Calculated spectra The remaining options for calculated spectra are a copy of the 4 Spectrum properties Calculation Options used for the calculation of that specific spectrum T Tue E Width 1 see figure to the right These entries cannot be changed manually but 4 4 Temperatures serve as a quick reference ipei Translatio 4000 Vibrations 4000 4 2 Pressure Pressure 1 Fressure L bar Ao 7 MEA moron Darman Pore 21 2 6 2 Imported spectra Imported spectra have no Calculation Options Instead the name and path of the imported file is displayed see figure to the right Visible False Width 4 4 2 File properties File Name asdf dat Full Path C UsersohanDe 27 2 7 Calculation Options The Calculation Options found in the left of the Specair window represent all the variable input parameters for spectrum calculations There are about sixty independent variables in total all displayed in a single list Some variables such as temperature pressure and mole fractions represent the physical conditions of the simulated plasma Others let the user specify what to include in the calculations over which range and wit
31. magnification Click on the round button at the left or top of the scrollbar to return to the previous magnification for the x or y axis respectively Edit View Data Plot Tools Help gt Calculate spectrum j Gi GB Options B Spectra la Comments eeu Edit View Data Plot Tools Help D Calculate spectrum E kel amp GB Options X Spectra la Comments gt X 354 333248947889 Y 0 148308158541586 Y 0 148308158541586 0 78 0 52 0 26 we 9 o o o o a LL o Uu a oO LL o gt Uu S 9 w D Lu Emission intensity or absorption coefficient 0 du d 3 353 M 355 356 m 38 39 380 Wavelength nm Wavelength nm 2 3 2 Tracking Specair automatically displays the coordinates of a data point when the mouse pointer is placed on top of it The coordinates are displayed the top right corner of the Plot Area see figure below and the units are identical to the axis units nm for x and intensity for y C Specair 3 0 untitled project e File Edit View Data Plot Tools Help gt Calculate spectrum EF lal c3 GB Options B Spectra Comme SN 356 577671010834 Y 0 241179125321837 0 78 0 52 0 26 Emission intensity or absorption coefficient 350 1 352 1 354 1 356 1 358 1 Wavelength nm 19 2 4 Comments Area The Comments area consists of three tabs Comments Populations and Units 2 4 1 Comments
32. mplified one in the shape of a trapezoid If the trapezoid is normalized to unity 1 e the intensity is 1 the calculated spectrum will have the intensity given in mW cm sr To obtain a spectrum in units of mW cm sr um divide the above spectrum by the FWHM in um which is indicated in the graph in the Slit function window see figure below Set Slit Function Use trapezoidal slit function Width of the base nm N Ww Width of the top nm Intensity at the peak Define own slit function Slit function FWHM 1 5nm Trapezoidal slit function 2 o g E Cancel _ 3 2 Imported Slit Function An experimental Slit function can be imported in the Slit function window by selectig Define own slit function and then pressing the button to open a file dialog box The format of the 26 imported slit function should be a text file with two columns wavelength in nm and intensity separated by tabs or spaces The imported slit function will be displayed in the graph below in orange together with a linear interpolation in blue The interpolation uses the same spectral step as that defined by the user in the Spectral step box and Specair uses this version during the calculations IMPORTANT It is strongly advised to cut off large wings of a slit function such as those included in the example figure below to avoid artifacts Also it is imperative to make sure the slit function
33. n Convolve one or more selected spectra by the current slit function Performing this operation on a non convoluted spectrum is equivalent to selecting convolution for the Slit function option in the Calculation options This menu option only works for spectra calculated in Specair Display Data Open a window with data for the selected spectrum see right figure The data is represented as two columns Wavelength nm and Intensity and can be copied to other programs such as MS Excel Click in the top left corner to select all data 12 2 1 5 Plot menu B Specair 3 0 untitled project RN File Edit View Data 3 Calculation options 4 1 Temperatures Electronic 3000 Rotational 3000 Translational 3000 Vibrational 3000 4 2 Pressure gt Calculate spectrum 7 b Plot Tools Help Spectrum Properties Plot Properties Legend Properties Title Properties Axis Properties Reset Axes F5 Set Axes Pressure 1 The plot menu contains all the options for modifying the plot area and the displayed spectra This gives the user the option of creating professional looking graphics for presentation purposes directly within Specair The options for changing the properties can also be accessed directly by clicking on elements in the plot such as the axes or the spectrum traces Spectrum Properties All the selected spectra will be changed when using this option
34. n coefficients and to the population in the upper state of the transition Although calculations should normally be performed with these parameters set to one any other numerical value can also be used For example choosing a value of 2 is a convenient way to multiply the population of the emitting level by a factor of 2 This could be useful to determine the extent of nonequilibrium in the population of excited states Room air absorbers to consider This section lets the user specify experimental conditions compensating for absorption in the air between the plasma and the spectrometer Note that the absorbing species are considered to be at room temperature for this option Set species to On to include them in the calculations and specify the path length of air in cm and the relative mole fractions 0 21 for 21 oxygen in air etc File Edit View Data Plot Tools Help P Calculate spectrum id cd A 3 Calculation options 4 1 Temperatures a Electronic Rotstionsl Translational Vibrational 4 2 Pressure Pressure Pressure Unit bar i 4 3 Wavelength Range r 388E n Calculation Options pee me Options for Calculated p ces tronic 4000 Wavel 2 68E 03 Spectra tions 4000 Width o sistions 4000 4 Plot Area Vibrational 4000 c 2 2 Pressure C 0 B Pressure 1 c2 1 E Pressure Uni bar jj e 0 uj 34E 05 3 W
35. nsity of the spectrum Pressure Unit This entry specifies the unit used for the number in the pressure entry The most common units are available Pa bar mbar atm and torr 2 3 Wavelength Range nm Specair calculates spectra over a wide range of wavelengths from the UV to the IR 23 Max The maximum wavelength of the calculated spectrum in nm Min The minimum wavelength of the calculated spectrum in nm 2 4 Calculation Settings Generate mole fractions Specair will automatically calculate mole fractions in air plasmas if this value is set to yes The generated mole fractions for air at 1 atm pressure with 300 ppm COs are based on the temperatures If this option is turned on the mole fractions entered manually in section 5 Mole Fractions will not be considered The calculated mole fractions are displayed in the Calculated Spectra section self absorption When this option relating to the radiative transport is on Specair takes into account self absorption of radiation within the length of the plasma slab see entry on width of slab below Turning it off means instead that all radiation produced will leave the plasma Slit function With the Slit function option set to no slit function Specair returns a spectrum with only Doppler collisional Stark and natural broadening When set to convolution the spectrum will be convolved with the slit function specified in the Slit Function dialog
36. odern desktop computer While spectra can be exported for advanced analysis or presentation purposes the Specair interface provides many basic functions for immediate analysis 2 The Specair User Interface The Specair user interface see Figure 2 offers many functions which are detailed in the subsequent sections After specifying the Calculation options for a spectrum the user starts the calculation by pressing the Calculate spectrum button by selecting Spectrum gt Calculate Spectrum from the menu bar or by pressing the F2 button Once calculated the spectrum will be displayed and ready to work with using the functionalities described below B Specair 3 0 untitled project ofS mz M H File gt Calculate spectra View Data Plot Tools Help id d Boros seer 2 Toolbar 5 Calculated Spectra 3 Calculation options 4 1 Temperatures Ew Spectrum 1 Electronic 4000 Rotational 4000 Translational 4000 Vibrational 4000 Big 4 2 Pressure 1 36E 04 Pressure 1 J o Pressure Unit bar E 4 3 Wavelength Range r o ta Delete Hide 4 Spectrum proper 7 Calculation 1 02E 04 p mE Options n 6 Options for e M peratures ectonic 4000 2 68E 03 Calculated Spectra tational 4000 8 t ansistions 4000 c 3 Plot Area Vibrational 4000 c o 4 2 Pressure C B Pressure 1
37. r send an email to license spectalfit com 17 2 2 Toolbar P Calculate spectrum 2 be GG Options Be Spectra Comments ep 1 S The toolbar provides a quick way to access some of the most used functionalities which are also found in the Menu Bar see above gt Calculate spectrum Calculates and displays a new spectrum based on the current settings in the Calculation Options a Open an existing Specair project lal Save the current Specair project ca Open a print dialog box for printing of the current view in the Graph Area 3 Options Show hide the Calculation Options bb Spectra Show hide the Calculated Spectra lka Comments Show hide the Comments cT Reset the axes Zoom in when selecting an area in the plot Enable the markers The markers can be used to select an area without zooming for use when cropping the spectrum for example Zoom out This button is only available when the user has zoomed into an area 18 2 3 Plot Area The Plot Area displays calculated and imported spectra as line charts Wavelength in nm is displayed on the x axis and intensity on the y axis 2 3 1 Zooming The user can zoom in on a region of interest by selecting that region with the mouse while pressing the left mouse button see figure right below Scroll bars will appear along the two axes see figure left below allowing the user to move within the graph at the current
38. r tabs Export spectrum Export the spectrum selected in the Calculated Spectra area For an ASCII text file output the file will contain two columns wavelength in nm and intensity separated by tabs Specair also supports other commonly used file formats used in other applications Save as image Save the current view in the Graph Area to an image file Several of the most popular image file formats are available Bitmap JPG EMF PNG GIF TIFF Print graph Ctrl P Open a print dialog box for printing of the current view in the Graph Area Exit Exit Specair 2 1 2 Edit menu Specair 3 0 untitled proj File Edit View Data Plot Tools Help P Cald amp Cut Ctrl X a 53 Copy Ctrl C ae AL Paste Ctrl V Ja Copy Image to Clipboard 4000 Rotational D s a E Cut Ctrl X Cut the current field Works with most text fields Copy Ctrl C Copy the current field Works with most text fields Paste Ctrl V Paste the clipboard content to a field Copy Image to Clipboard Copy the current view in the Plot Area to the Clipboard The image can be pasted into other programs such as MS Office 2 1 3 View menu Specair 3 0 untitled proj File Edit View Data Plot Tools Help gt Calculate sp Options Ctrl Alt O B Spectra Ctrl Alt G Comments Ctrl Alt C Options Ctrl Alt O Show the Calculation Options Spectra Ctrl Alt G Show the Calculated Spectra
39. raction The mole fraction for carbon dioxide in air The standard value is 0 00036 corresponding to 360 ppm O2 Set value to on to include VUV i e below 200 nm absorption by oxygen in the air gap The default value is off O2 Length The optical path length in cm for the absorption by oxygen in the air The path length refers to the total distance 25 O2 Mole Fraction The mole fraction for oxygen in the gap The standard value in atmospheric air is 0 21 or 21 3 The Slit Function The slit function is a measure of the broadening of spectral lines due to instrumental broadening The slit function can be determined for example by measuring a laser with a well defined wavelength usually a HeNe at 632 8 nm In Specair the user can import such a measurement and use it in calculations to simulate a real measured spectrum A user defined trapezoidal slit function the simplest approximation of a true slit function can also be used Note that a Gaussian slit function is well simulated by a triangular slit function 1 e a trapezoid of top 0 To convolve a spectrum with the slit function select convolution for the Slit function entry in the Calculation Options and specify the slit function by selecting Slit Function in the Spectrum menu or by pressing F3 which opens the slit function window 3 1 Trapezoidal Slit Function In the absence of an experimental slit function the user can specify a si
40. racy most energy states are computed in Specair by inverting Hamiltonian matrices This method also allows the modeling of perturbations for several systems of importance in Specair such as N first and second positive N57 first negative NO alpha beta gamma delta More details about Specair can be found in the following publication Laux C O Optical Diagnostics and Collisional Radiative Models VKI Course on Hypersonic Entry and Cruise Vehicles Stanford University June 30 July 3 2008 The general notation for an electronic level is A S is the quantum number associated with the total electron spin and A is the quantum number associated with the absolute value of the projection of the orbital angular momentum along the internuclear axis A takes the values 0 1 2 3 associated with the Greek letters Z II A db The number 25 1 is called the spin multiplicity and the notation for each state is usually preceded by an identifying letter often X for the ground state 5 2 Spin Each electronic level is split into 2S 1 spin substates spin splitting and for all A 2 1 every spin substate is split in two A substates A doubling This gives us the degeneracy for each electronic level as g 25 T e 0 a where is the usual Kronecker delta For diatomic molecules with nuclei of equal charges a u or a g is written to the right of the term This indicates if the electronic wave function is symmetrical or not
41. s 2 Pressure The pressure can be set using several different units and determine radiation intensity and the level of absorption 3 Wavelength Range nm This specifies the wavelength range over which the spectrum will be computed Calculation Settings The calculation settings allows the user to change certain aspects of the calculations such as whether to include absorption to generate Mole fractions automatically or to convolve the spectrum with a slit function to replicate experimental conditions The Speed display option is recommended as it reduces lowers the resolution to match that of the slit function Mole Fractions The relative amount of each species is indicated here For plasma consisting of only one species the value should be 1 otherwise use fractional values For example use 0 5 for N2 and 0 5 for CO for two equal concentrations of these species If the sum of the mole fractions of the species defined in your calculations exceeds unity the program will still compute the spectrum but a warning message will be given Radiative Transitions Specair includes most of the common transitions for air plasmas but also for plasmas containing carbon species The naming of the transitions conforms to the standard spectroscopy conventions The spectroscopic transitions to model are selected by entering a 1 To exclude the transition set the value to 0 The numerical value is used as a multiplier to the Einstein emissio
42. s the dimensionality of the minimization problem and it is often the case that repeated cycles are necessary until the method has fully converged The Global fit function in Specair see below can automate these steps in many cases and is a recommended approach for complex spectra 4 2 Finding transitions Specair includes an automated method for finding underlying transitions in a spectrum With a spectrum selected The Find Transitions window see figure below is accessed under the Tools menu The transition finder is intended to be a starting point for analysis to be followed by further optimization and it uses an extensive database of pre calculated spectra at different temperatures and with slit functions of different widths In the Find Transitions window the user can browse all available transitions and temperatures by sliding the horizontal scroll bars This is an intuitive way of finding the right transition and 30 the proper temperature range that 1s much faster than calculating plenty of candidates from scratch The transition finder can also find the best candidates automatically by searching the database for spectra that match the highest peak within the specified wavelength range When pressing the Find transition button suggestions are returned in order of best fits The Peak wavelength tolerance nm number indicates the small wavelength range around the main peak that will be considered Increasing the range returns more hi
43. selected at the top will be held sew 3009 constant at the values entered in the bottom text fields An example E of the temperature loop for the C2 Swan transition is shown in the cancel figure below 15 2 5E 04 430 450 470 490 510 530 550 570 590 Wavelength nm Fit to Spectrum Specair can perform successive calculations to fit a selected experimental spectrum The user can fit temperatures and mole fraction using several options For more information see the section about curve fitting below Find Transition This option helps finding unknown transitions in a spectrum either by m automatically matching peaks or by S manually scrolling through a number of zc precalculated spectra at various temperatures and resolutions The user can use a selected spectrum as input or B T rene T am at the residual from subtracting a selected spectrum and one calculated from the current settings The second option is useful for identifying smaller peaks under a spectrum that has already been fit The resolution is changed to most closely match that of the selected slit function The Find Transition function is intended only for finding starting points for further fitting and the absence of a hit does not mean that a transition is not present in the spectrum Global Fit The Global Fit function or fit SENHIIEIRAEEEE wizard can be used in some E cases where the user wants to mm n fit a compl
44. since a small offset in wavelength can lead to large residuals as sharp peaks no longer overlap 4 1 2 Input parameters The basic fitting routine normally minimizes the residual with respect to a single variable A group of variables sharing the same value such as all statistical temperatures under local thermal equilibrium LTE can also be used The user manually selects Temperatures or Mole Fractions All temperatures are fit simultaneously by default but any combination of temperatures can be fixed while the others are varied This is useful if the experimental plasma was not in LTE such that vibrational and rotational temperatures for example have different values The mole fractions on the other hand are fixed by default and the user selects the specific mole fraction s to vary by deselecting the check box Several mole fractions can be fit together but this is rarely useful in practice The minimization works by bracketing a minimum residual and narrow the range using inverse quadratic interpolation There are three general parameters by which the user can specify the starting conditions and the end point listed to the left below the temperatures The first is the Initial Value which is the temperature or mole fraction which will be used in the first calculation The second parameter is the Initial Step which specifies in percent of the Initial Value the second and third calculations If the first residual 1s lower
45. tions if possible or use Specair s transition finder which contains a database of spectra for individual transitions at a few temperatures Once a candidate species and transition combination has been identified the mole fraction is set to a number between zero and one and the user selects the Fit to spectrum option in the Tools menu First the temperatures are fit together unless the experimenter knows some of the temperatures a priori If the user believes that the selected transition accounts for the entire signal the next step 1s to fit each temperature separately This is done by fitting primarily the vibrational and the rotational temperatures in an alternating fashion until both of them remain roughly constant between each round If more species are found in the spectrum the next step is instead to add the most prominent one followed by the optimization of the corresponding mole fraction Adding more species and transitions will change the optimal temperature so the next step is to once more fit the temperatures and subsequently all the mole fractions in order of importance This cycle is repeated until a true global minimum is found If necessary the various temperatures can also be optimized in a similar fashion When the residual stops improving between successive alternation between temperatures and mole fractions the user can add even more species and transitions or declare victory It is clear that each added variable increase
46. to 0 In the code this numerical value is actually used as a multiplier to the Einstein emission coefficients or to the number density of the emitting state Thus using a value of 2 would be equivalent to computing a spectrum with twice the population given by the Boltzmann distribution This feature is left open such that the user can simulate a non Boltzmann distribution for the emitting state of the selected transition Specair includes most of the common transitions for plasmas made of N O and C compounds The naming conforms to the standard spectroscopy literature 2 f Room air absorbers to consider Specair can include the effects of room air absorption in the calculations This is useful when analyzing experimental data collected with an air filled gap between the plasma and the detector H2O Set value to on to include IR absorption by water molecules in a humid air path The default value is off H2O Length The optical path length in cm for the absorption by water molecules in the air gap The path length refers to the total distance H2O Mole Fraction The mole fraction for water in air The standard value is 0 002 corresponding to 0 2 CO2 Set value to on to include IR absorption by carbon dioxide in the air gap The default value is off CO2 Length The optical path length in cm for the absorption by carbon dioxide in the air The path length refers to the total distance CO2 Mole F
47. ts and can be useful if the experimental spectrum has an offset but it also increases the number of false positives The default setting for the comparisons is to use the spectrum that was selected when opening the window The user can also choose to Use residual from settings where a calculated difference spectrum is used A spectrum is calculated based on the current Calculation options and the difference between this spectrum and the selected imported spectrum is displayed making it easier to find smaller peaks below larger ones that have already been fit To further refined the search the user can limit the overall wavelength in which to search for a transition The spectra can be normalized either at their main peaks or at a given wavelength as indicated by a vertical pointer in the graph Finally the resolution as defined by a spectral step slit function width combination can be changed using the slider in the bottom left corner A triangular slit function is implemented here 1 Find Transitions Find transitions Peak wavelength tolerance nm 1 2 1 0 8 NENNEN jn N2 2 2000 K EN a uo EMEN Next Suggestion of 4 N2 2 3500 K Residual 4 609 Residual Use original graph Use residual from settings Nomalize n Nomalize at peak TA Normalize at pointer LI Wavelenaths zx QqAMPTS Lo ooo o Resolution 0 01 nm 0 1 nm
48. value 38 the specified wavelength determined by interpolation if necessary Canos j Find Minimum Find the minimum value among the data in the selected spectra The cursor is placed at that point and the coordinates are displayed in the top right corner until the mouse enters the plot area Find Maximum Finds the maximum point similarly to the Find Minimum above Set X Values Open a dialog box to perform basic arithmetic on e one or several selected spectra see right figure Operation on X V l 1 1 T P Eb i Select an operator in the first field and enter a value i nod in the second The operation will be performed on Create new spectrum the X Nue eene for each point in the spectra which will be replotted in the graph area If _ Create new spectrum is selected a new spectrum will be created and displayed in the plot area leaving the original spectrum intact 10 Set Y Values Same as Set X Values above except that the arithmetic operation will be performed on the Y value emission intensity or absorption coefficient Subtract Baseline Open a dialog box for subtracting a linear baseline from a Svbtect Baseline selected spectrum see right figure This can be used for Subtract Baseine from example to compensate for background noise in the Statof baseline i X value Y value experimental apparatus used to measure imported spectra 350 09 1 Press
49. velength being the difference between the points in the top Name ofnewspectum Subtraction anias Cancel d spectrum and the bottom spectrum as determined by the user in the drop down menus The wavelength x values are the same as one of the input spectra as determined by the X values from option The y values for the other spectrum are interpolated values at the same wavelengths allowing the user to quickly subtract for example a calculated spectrum from an imported one to assess their agreements Multiply Spectra Multiplies the points in selected spectra Similar to Add Spectra above 11 Divide Spectra Divides the points in one selected spectrum by those in a second selected spectrum Similar to Subtract Spectra above Average Spectra Averages the y values for two or more spectra and creates a new spectrum This can be used for example to consolidate data from several experiments under identical conditions This operation is equivalent to Add spectra above followed by a division by the number of input spectra Integrate Display the result of the numerical integration of the selected 5 spectrum A trapezoidal integration using the wavelengths is used Integrated Spectrum and the units are dependent on the input spectrum The average y Average Value value equal to the area divided by the wavelength range is also 6s6e o11 displayed Convolve with Slit Functio
50. w the graph window and they can be removed using the Remove button After one or more transitions have been added the user can refine all parameters by pressing the Optimize button The program will execute the basic fitting routine outlined above for all relevant variables based on the last temperature used The starting value for the mole fractions can be changed manually in the text boxes Note that all plasmas have to be in Local Thermal Equilibrium Tetectronic T transiational rotational vibrational When using the Global fit For different temperatures a manual fitting has to be done To reach a global minimum many cycles determined by the Number of iterations should be performed The figure below shows an example where the peaks of N 2 and N 1 were identified and fit automatically This particular spectrum was found to be out of Local Thermal Equilibrium Global fit Add transition Add v Optimize after adding v Add transitions automatically Residual 0 667907282975674 3978 0 206867791456479 5909 0 683588037935186 4335 0 230178455169191 Peak wavelength tolerance nm 4044 0 207645391905715 1 3938 0 207286558707637 Resolution 3978 0 206867791456479 0 01 nm 0 1 nm sii Optimizing mole fraction 0 025 nm 0 25 nm slit Iteration Mole fraction Residual 6 062E 12 0 2398705043593 0 1nm 1nm sit 8 660E 12 0 206867791456479 1286E 11 0 292500810059414 0 25 nm 2 5 nm si
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