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Updated: Dec 31, 2025

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
Published on: February 4, 2017
Deducing rotational quantum-state distributions from overlapping molecular spectra
Jan Voráč1, Lukáš Kusýn1, Petr Synek1
1Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic.
Abstract:
A novel method for fast and robust calculation of Boltzmann plots from molecular spectra is presented. Its use is demonstrated on the OH(A-X) spectrum near 310 nm. A limitation of the method is identified: for overlapping spectra of the OH(A-X) and N2(C-B, Δv = 1) band sequence, the calculation may often fail due to insufficient number of measured points. This is solved by introducing experimentally determined bounds for the N2(C) rotational distribution. Three cases are presented: (i) with undisturbed OH(A-X) emission, (ii) with strong emission of N2(C-B) in the said spectral range, and (iii) with weak but not negligible nitrogen emission. In case (ii), the data in the spectral range 306-320 nm are sufficient for the analysis. In case (iii), information from another spectral range with undisturbed N2(C-B) emission is necessary. These illustrate all relevant cases often encountered in laboratory plasmas. The calculated Boltzmann plots are not further analyzed in this article but can be used for development and validation of kinetic models with rotational resolution. The implementation of the reported method using the massiveOES software package written in the Python language is available in the supplementary material.
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