Dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules

Abstract

In a combined experimental and theoretical effort, we have investigated dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules. Using the laser photoelectron attachment method, we have measured the energy dependence of the cross section σ DA (E) for dissociative electron attachment (Cl- formation) over the range 0-195 meV with an energy width of 1-3 meV and for Rydberg electron transfer at high principal quantum numbers (n > 67). Near zero energy, the cross section shows a behaviour compatible with the threshold law for p-wave attachment via the 2 Σ + u resonance, reaches a maximum around 50 meV and declines towards higher energies. These findings are in good agreement with the results of semi-empirical R-matrix calculations. Measured rate coefficients k nl for Cl- formation due to electron transfer from K**(nl) Rydberg atoms were found to be nearly constant for high principal quantum numbers (n > 67) in contrast to the behaviour expected within the quasi-free electron model for p-wave attachment. The R-matrix calculations are extended to describe electron attachment through the 2 Π g and 2 Π u resonances, and recommended absolute cross sections for dissociative attachment to chlorine molecules at room temperature are provided over the energy range 0-9 eV. Furthermore, we predict cross sections for vibrationally inelastic electron scattering through the 2 Σ + u, 2 Π g and 2 Π u resonances.