MASSIVEOES: PUSHING THE LIMITS – DISENTAGLING THERMAL N2(C-B) AND NON-THERMAL OH(A-X) ROTATIONAL DISTRIBUTION BY COMBINED STATE-BY-STATE AND BOLTZMANN SIMULATION APPROACH
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| Year of publication | 2018 |
| Type | Conference abstract |
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| Description | massiveOES is a free open source spectroscopic software with unique features of batch processing and state-by-state fitting for high-precision and high-speed construction of molecular Boltzmann plots recently developed at Masaryk University. Handling high number of overlapping spectra with thermal distribution was achieved in diagnostics of power modulated microwave surfatron plasma jet. Non-thermal distribution of OH(A-X) spectra in a surface barrier discharge in argon atmosphere in contact with liquid water was revealed by the novel approach of state-by-state fitting, allowing observation of features like iso-energetic vibrational energetic transfer. The state-by-state fitting method utilizes the linear nature of the problem, allowing the evaluation of the populations of quantum states with rotational and fine-structure resolution in a fraction of a second. This approach requires an overdetermined problem, i.e. the number of measured spectral positions (e.g. pixels) needs to be greater than the number of states to be evaluated. There are, however, cases, when this assumption is not met, such as in discharges ignited in argon with water vapor, containing nitrogen admixtures. In this contribution we introduce spectra from a volume barrier discharge developed originally for atomization of hydrides and subsequent atomic absorption spectroscopy for analytical purposes. The plasma is ignited in humidified argon and mixes with ambient air,introducing both excited hydroxyl OH(A) and nitrogen N2(C). The measured spectrum has 1024 pixels, and 2588 possible quantum states affecting this wavelength range by at least one spectral line. This is consequently an underdetermined problem that cannot be solved by conventional least-squares fitting. The proposed solution is measuring the N2(C) rotational temperature separately in another spectral window (e.g. around 337 nm) and treating the whole N2(C, Trot) as a single quantum state, reducing the number of quantum states to be evaluated to 226. This procedure is applied to spectra measured along the discharge axis from points with different concentration of air admixture. |
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