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

Abstract

In a combined experimental and theoretical effort, we have investigated dissociative attachmentand vibrational excitation in low-energy electron collisions with chlorine molecules. Using the laserphotoelectron attachment method, we have measured the energy dependence of the cross sectionσDA(E) for dissociativeelectron attachment (Cl− formation) over the range 0–195 meV with an energy width of 1–3 meVand for Rydberg electron transfer at high principal quantum numbers(n>67). Nearzero energy, the cross section shows a behaviour compatible with the threshold law for p-wave attachmentvia the 2Σu+ resonance, reaches a maximum around 50 meV and declines towards higherenergies. These findings are in good agreement with the results of semi-empiricalR-matrix calculations. Measured rate coefficientsknl forCl− formation due toelectron transfer from K**(nl) Rydberg atoms were found to be nearly constant for high principal quantum numbers(n>67) incontrast to the behaviour expected within the quasi-free electron model for p-wave attachment. TheR-matrix calculations are extended to describe electron attachment through the2Πg and 2Πu resonances, and recommended absolute cross sections for dissociative attachment to chlorinemolecules at room temperature are provided over the energy range 0–9 eV. Furthermore, wepredict cross sections for vibrationally inelastic electron scattering through the2Σu+,2Πg and 2Πu resonances.