Effects of π*−σ* coupling on dissociative-electron-attachment angular distributions in vinyl, allyl, and benzyl chloride and in chlorobenzene

Abstract

We report on a velocity map imaging study of ${\mathrm{Cl}}^{\ensuremath{-}}$ anions resulting from the dissociative electron attachment to four unsaturated chlorohydrocarbons. In all four molecules, this process is mediated by the formation of the lowest shape resonance. The choice of the molecules was motivated by the different character of this resonance. In the planar compounds chlorobenzene and vinyl chloride, it is a ${\ensuremath{\pi}}^{*}$ resonance, which is not dissociative along the C-Cl bond without distortion of the planar geometry. In the nonplanar compounds benzyl chloride and allyl chloride, the shape resonance has a mixed ${\ensuremath{\pi}}^{*}\text{\ensuremath{-}}{\ensuremath{\sigma}}^{*}$ character and is directly dissociative without the need for any additional distortion. Our motivation was to find out whether the dissociation-allowing nuclear motion has a common imprint in the resulting fragment angular distributions. In spite of the expected similarities between the two classes of compounds, the resulting images are quite different for all four molecules. We interpret the results, especially the imprints of the bending dynamics, with the aid of a single-electronic-state model in the axial recoil approximation.