Comparative studies of dissociative electron attachment to methyl halides

Authors

R. S. Wilde, University of Nebraska-Lincoln
Gordon A. Gallup, University of Nebraska-LincolnFollow
Ilya I. Fabrikant, University of Nebraska-LincolnFollow

Date of this Version

11-1-2000

Comments

Published in Journal of Physics B: Atomic Molecular and Optical Physics 33 (2000), pp. 5479–5492. Copyright © 2000 Institute of Physics/IOP Publishing Ltd. Used by permission. http://www.iop.org/EJ/journal/JPhysB

Abstract

The dissociative electron attachment cross sections for the methyl halides vary in an enormous range from the virtually unmeasurable 10⁻²³ cm² for CH₃Cl at room temperature to 10⁻¹⁴ cm² for CH₃I. In this paper we supplement our previous studies by calculations of dissociative electron attachment to CH₃Br and compare results for all methyl halides studied so far. The rate as a function of temperature for CH₃Cl and CH₃Br exhibits an exponential dependence on 1/T (Arrhenius law) with the activation energy lower for CH₃Br. CH₃I does not obey the Arrhenius law since the crossing point of the neutral and anion potential curves occurs near the lowest vibrational levels. The cross section as a function of electron energy for all of the methyl halides studied here exhibits structure at the vibrational excitation thresholds that is associated with a vibrational Feshbach resonance like that observed recently in CH₃I by Schramm et al (Schramm A, Fabrikant I I, Weber J M, Leber E, Ruf M-W and Hotop H 1999 J. Phys. B: At. Mol. Opt. Phys. 32 2153).