Vibrational excitation of H2 and HCl by low-energy electron impact. An isotope scaling law

✍ Scribed by D.E. Atems; J.M. Wadehra

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 391 KB
• Volume: 197
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(92)85810-w

✦ Synopsis

We examine the mass dependence of cross sections for resonant vibrational excitation by electron impact (from z+ to ur) in H2 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 ucc,~~"~-"~~~*, where n is the reduced nuclear mass of the isotope. This scaling law is also observed to hold for HCI, DCI, 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.

Cross sections for vibrational excitation by lowenergy electron impact of Hz [ l-5 ] and of HCl [ 6-9] have been measured by several different investigators. The absolute cross section values for excitation from the y = 0 level of Hz are fairly consistent with each other to within 20%30%. Vibrational excitation of the heavier isotopes of H2 and HCl has been much less studied experimentally. Vibrationally excited D2 and other isotopes of H2 are of interest as a source of production of negative ions Hand D-through the process of dissociative electron attachment. It is therefore desirable to understand the dependence of vibrational excitation cross sections on the isotope mass. The purpose of this paper is to present an isotope scaling law for vibrational excitation of H2 and its isotopes from an arbitrary low-lying vibrational level. We also observe that this relationship holds approximately for the family of isotopes XCl, where X is one of H, D, or T. The cross sections are obtained by treating vibrational excitation as a resonant process which occurs through the formation of a temporary anion state, and numerically solving the nonlocal integrodifferential