Velocity Relaxation of Fast Hydrogen Atoms by Collisions with Rare Gases, N2, O2, and N2O

Abstract

Quenching energetic atoms by elastic and inelastic collisions with surrounding bath gases is one of the fundamental processes taking place in the upper atmosphere and in chemical reactors as well. The energetic atoms are often generated by photodissociation, photoelectron impact dissociation, dissociative recombination, and so forth. Velocity relaxation of fast hydrogen atoms colliding with rare gas atoms, N{sub 2}, O{sub 2}, and N{sub 2}O molecules has been investigated by measuring Doppler broadened H atom spectra. The fast hydrogen atoms were generated by photodissociation of H{sub 2}S at 243.2 nm, and the H atom spectra were measured by two photon absorption laser induced Lyman-{alpha} fluorescence. The H atom spectra show an anisotropic velocity distribution with the anisotropy parameter, {beta} = {minus}1.0 {+-} 0.05, without any colliding gases. Degradation of the anisotropy of the angular distribution was measured as a function of pressure of the colliding gases, He, Ar, Kr, N{sub 2}, O{sub 2}, and N{sub 2}O and the collision cross sections for velocity direction change were measured.