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

Abstract

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 + E, in which the energy defect is E = 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.

Relaxation of electronic excitation in nitrogen/oxygen and fuel/air mixtures: fast gas heating in plasma-assisted ignition and flame stabilization

“…Dissociation of hydrogen molecules by electron impact e + H2(X 1  )  e + H( 1 S) + H( 1 S) + εH occurs through excitation of pre-dissociating electronic state of H2(b 3 Σ  u ), either directly or by excitation of states of H2(B 1 Σ  u ), H2(C 3 Пu), H2(a 3 Σ  g ), H2(d 3 Пu) etc., followed by a radiation-collision transition to H2(b 3 Σ  u ). Energy εH equal to the difference between the excitation energy of H2(b 3 Σ  u ) (εb = 8.9 eV) [137] and dissociation energy of H2 molecules, εdiss = 4.478 eV [93], is released to gas heating [137].…”

Kinetic modelling of atom production and thermalization in CCRF discharges in H2

“…Perrin et al [15] estimated the thermalization rate constant of hot H atoms of a given energy using relations from kinetic theory; however, such a simple estimate is not informative about the fraction of high-energy atoms still reaching the walls and the reactivity of hot H atoms in the gas phase. A simplified kinetic model to determine non-Maxwellian velocity distributions and non-Gaussian profiles of groundstate H atoms in low-pressure hydrogen discharges has been developed recently by Loureiro and Amorim [16]. This issue is best addressed by a Monte Carlo (MC) approach, which avoids most simplifications necessary in other approaches.…”