Low-energy electron collisions with CH3Br: the dependence of elastic scattering, vibrational excitation, and dissociative attachment on the initial vibrational energy

Abstract

Using the laser photoelectron attachment (LPA) method at an energy width of 1–2 meV, the Br− yield due to dissociative electron attachment to the molecule CH3Br has been measured over the energy range 1–180 meV at a gas temperature of 600 K. The data clearly exhibit the vibrational Feshbach resonance predicted by Wilde et al (2000 J. Phys. B: At. Mol. Opt. Phys. 33 5479) and associated with the v3 = 4 vibrational level of the C–Br stretch mode in the neutral molecule. We also report the dependence of the rate coefficient for Rydberg electron attachment (measured at high principal quantum numbers n ≈ 150) on gas temperature and find an Arrhenius-type behaviour compatible with the results of R-matrix calculations and with earlier findings of electron swarm experiments. With the aim to stimulate experiments, we report absolute cross sections for elastic scattering and vibrationally inelastic scattering involving the C–Br stretch mode v3 of CH3Br for several initial vibrational levels in the range v3 = 0–4; they were obtained with R-matrix calculations based on the same potential input as that involved in the computations of the cross sections for dissociative attachment.