Cl-Loss Dynamics of Vinyl Chloride Cations in the B2A″ State: Role of the C2A' State.

The dissociative photoionization of vinyl chloride (C2H3Cl) 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, A2A', B2A″, and C2A', of the C2H3Cl+ cation were prepared, and their dissociation dynamics were investigated. A unique fragment ion, C2H3+, was observed within the excitation energy range. TPEPICO three-dimensional time-sliced velocity map images of C2H3+ provided the kinetic energy release distributions (KERD) and anisotropy parameters in dissociation of internal-energy-selected C2H3Cl+ 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 C2H3Cl+ in the B2A″ and C2A' 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 C2H3Cl+.