Non-Maxwellian velocity distributions and non-Gaussian profiles of H atoms in low-pressure hydrogen discharges

摘要

In this paper we present a theoretical model to determine non-Maxwellian velocity distributions and non-Gaussian profiles of ground-state H atoms in low-pressure hydrogen discharges. The analysis has been conducted with the aim of discussing the validity of determining the H atom temperature from the full-width at half-maximum of one-dimensional (1D) distributions strongly departing from Gaussian functions. For this purpose, we analyze the effects on profile broadening of the 1D distribution of ground-state atoms produced by (i) electron-induced dissociative excitation, and (ii) the exothermic reaction producing H atoms, H~+ _2 + H_2 → H ~+ _3 + H + ΔE, in which the energy defect is ΔE = 1.56 eV. In the latter case, we show results from an updated version of our model. Here, the reactant species are assumed with different temperatures and the rapid decrease in the reaction cross section, at energies larger than ～1 eV, is taken into account in the model. The profiles obtained for the 1D velocity distributions of H atoms are much flatter and squarer than Gaussian functions, leading us to discuss the validity of determining the H atom temperature from the width of such profiles.