Molecular bands

Supported Bands

The molecules module allows the identification of some molecular band structures. For a subset of them, we support the calculation of simulated spectra (using Moose/MassiveOES) which can be fit to the data to obtain rotational and vibrational temperatures ($T_{rot}$, $T_{vib}$).

The following molecular bands are supported for fitting:

• C₂ Swan
• N₂ (C-B)
• N₂⁺ (B-X)
• NH (A-X)
• NO (B-X)
• OH (A-X)

For the sake of identification, further molecular bands can be shown, but do not allow variation of $T_{rot}$ and $T_{vib}$ for the sake of fitting. These were precalculated using LIFBASE. If you need to fit any of these molecular bands, you can use LIFBASE to do so. The following bands can be shown for identification:

• NO (A-X, C-X, D-X)
• CH (A-X, B-X, C-X)
• SiH (A-X)
• CF (A-X, B-X, C-X, D-X)
• CN (B-X)

Usage

Select which bands you want to see and then press "Show" at the bottom to display them. By default, OES toolbox will only show those band structures that fall within the range of the experimental data. For example, if your measured spectrum ranges from 280 nm to 350 nm, but you select "NO (B-X)" to be displayed, nothing will happen since there is no NO (B-X) emission in this range. If necessary, you can change this behavior by setting wavelength range limits or by removing the experimental spectrum from the graph view in the middle to show the entire wavelength range.

For the supported molecular bands, changing rotational and vibrational temperatures will change the calculated spectrum after pressing "Show" again. When fitting a structure, the values set in the menu are used as starting values, so it's a good idea to first adjust them to a good agreement between data and calculation. This includes the wavelength shift at the bottom of the graph view.

The line broadening can be adjusted in the spectrometer settings in the left pane (as shown in the picture). This is very important for getting a proper fit and can be adjusted by repeatedly changing the value and fitting the results until a proper fit is reached.

For fitting, it is a good idea to limit the wavelength range and allow the fit algorithm to shift the wavelength position. If the spectrometer is not perfectly wavelength calibrated, allowing the wavelength axis to stretch might also help. All of this can be adjusted by the settings in the middle of the module.

Once the proper initial values and settings are found, pressing "Fit" will start the fit process. The result will be shown in the graph view and the optimized values are placed in the table at the bottom of the module tab. By default, all spectra shown in the graph view are fitted, allowing multiple spectra to be analyzed at once. This behavior can be changed to instead fit the spectra of all files selected by a checkmark in the file list (dropdown menu "Fit all displayed" -> "Fit all selected").

Note that multiple band structures can be fit at once, which is important in case they overlap, as in the example above. You can then optionally allow the fit algorithm to use different $T_{rot}$ and $T_{vib}$ for each band. However, they will use the same start values.

The right-click context menu of entries in the results table at the bottom of the module tab allows to plot them in the graph view or remove them.

The complete table can be exported using the "Save data" button or the File -> Export menu in the menu bar at the top of the window.

Citations

Please see the dedicated wiki article on how to cite the proper sources when publishing results obtained with this module.