Vibrational excitation of H 2 and HCl by low-energy electron impact. An isotope scaling law

Abstract

We examine the mass dependence of cross sections for resonant vibrational excitation by electron impact (from ν i to ν f) in H 2 and its isotopes. Excitation cross sections, for both inelastic and superelastic collisions, using numerical potential curves in a nonlocal resonance theory are presented and seen to obey the scaling law σ∝μ −|ν i−ν f|/2, where μ is the reduced nuclear mass of the isotope. This scaling law is also observed to hold for HCl, DCl, and TCl. We also present a supporting analytical argument for this isotope scaling law using a simple resonance model in which the neutral and resonant anion nuclear potential energy curves are taken as equal-frequency linear harmonic oscillators.