Quantum Wave Packet Propagation Study of the Photochemistry of Phenol: Isotope Effects (Ph-OD) and the Direct Excitation to the 1πσ* State

An earlier time-dependent quantum wave packet propagation study of the photochemistry of Ph-OH [J. Chem. Phys. 2005, 122, 224315] is extended to investigate isotope effects (for Ph-OD) and the dynamics initiated by direct (vibronically induced) excitation to the (1)pi sigma* state. The isotope effect is significant only when the initially excited state is (1)pi pi*, that is, there are noticeable changes not only in the time scale but also in the branching ratio ((A) over tilde/(X) over tilde) for the electronic states of the product Ph-O radical. In contrast, the isotope effect on the dynamics initiated by direct excitation to the (1)pi sigma* state is very small. Our most important observation for the dynamics initiated by direct excitation to the (1)pi sigma* state is that the initial excitation of the OH stretch mode does not result in a noticeable enhancement of the product Ph-O radical in the A state, which corresponds to a dissociating H atom with low kinetic energy. The initial excitation of the CCOH torsion mode is the main reason for the enhancement of the product Ph-O radical in the A state that was observed in a vibrationally mediated two-photon experiment [J. Chem. Phys. 2008, 128, 104307].