Modeling Kinetic Shifts for Tight Transition States in Threshold Collision-Induced Dissociation. Case Study: Phenol Cation

A threshold collision-induced dissociation (CID) study is performed on the phenol cation dissociation, investigating the CO-loss channel. Quantum chemical calculations are performed on the system to investigate the details of the potential energy surface and to provide the molecular parameters necessary for CID cross-section modeling. The effects of kinetic shifts on the CID threshold determinations are investigated using a model that incorporates statistical unimolecular decay theory. The model is tested using unimolecular dissociation rate constants as a function of energy provided by earlier photoelectron−photoion coincidence (PEPICO) experiments. Calculations indicate that the rate-determining step is an initial enol−keto isomerization. When the calculated transition state that corresponds to this step is used in the unimolecular decay model, the PEPICO rates are reproduced very well. The dissociation thresholds derived from CID data are in reasonable agreement with the ones derived from fitting the P...