Cl-Loss Dynamics of Vinyl Chloride Cations in the BA″ State: Role of the CA' State.

The dissociative photoionization of vinyl chloride (CHCl) in the 11.0-14.2 eV photon energy range was investigated using threshold photoelectron photoion coincidence (TPEPICO) velocity map imaging. Three electronic states, namely, AA', BA″, and CA', of the CHCl cation were prepared, and their dissociation dynamics were investigated. A unique fragment ion, CH, was observed within the excitation energy range. TPEPICO three-dimensional time-sliced velocity map images of CH provided the kinetic energy release distributions (KERD) and anisotropy parameters in dissociation of internal-energy-selected CHCl cations. At 13.14 eV, the total KERD showed a bimodal distribution consisting of Boltzmann- and Gaussian-type components, indicating a competition between statistical and non-statistical dissociation mechanisms. An additional Gaussian-type component was found in the KERD at 13.65 eV, a center of which was located at a lower kinetic energy. The overall dissociative photoionization mechanisms of CHCl in the BA″ and CA' states are proposed based on time-dependent density functional theory calculations of the Cl-loss potential energy curves. Our results highlight the inconsistency of previous conclusions on the dissociation mechanism of CHCl.