State-by-state emission spectra fitting for non-equilibrium plasmas: OH spectra of surface barrier discharge at argon/water interface

Abstract

Optical emission spectroscopy applied to non-equilibrium plasmas in molecular\ngases can give important information on basic plasma parameters, including the\nrotational, vibrational temperatures and densities of the investigated\nradiative states. In order to precisely understand the non-equilibrium of\nrotational-vibrational state distribution from investigated spectra without\nlimiting presumptions, a state-by- state temperature-independent fitting\nprocedure is the ideal approach. In this paper we present a novel software tool\ndeveloped for this purpose, freely available for scientific community. The\nintroduced tool offers a convenient way to construct Boltzmann plots even from\npartially overlapping spectra, in user-friendly environment. We apply the novel\nsoftware to the challenging case of OH spectra in surface streamer discharges\ngenerated from the triple-line of argon/water/dielectrics interface. After the\nbarrier discharge is characterised by ICCD and electrical measurements, the\nspatially and phase resolved rotational temperatures from N$_2$ (C-B) and\nOH(A-X) spectra are measured, analysed and compared. The precise analysis shows\nthat OH(A) states with quantum numbers (v' = 0, 9 $\\leq$ N' $\\leq$ 13) are\noverpopulated with respect to the found two-Boltzmann distribution. We\nhypothesise that fast vibrational-energy transfer is responsible for this\nphenomenon observed here for the first time. Finally, the vibrational\ntemperature of the plasma and the relative populations of hot and cold OH(A)\nstates are quantified spatially and phase resolved.\n