Dynamics at conical intersections: The influence of O–H stretching vibrations on the photodissociation of phenol.

Comparing the recoil energy distributions of the fragments from one-photon dissociation of phenol-d5 with those from vibrationally mediated photodissociation shows that initial vibrational excitation strongly influences the disposal of energy into relative translation. The measurements use velocity map ion imaging to detect the H-atom fragments and determine the distribution of recoil energies. Dissociation of phenol-d5 molecules with an initially excited O–H stretching vibration produces significantly more fragments with low recoil energies than does one-photon dissociation at the same total energy. The difference appears to come from the increased probability of adiabatic dissociation in which a vibrationally excited molecule passes around the conical intersection between the dissociative state and the ground state to produce electronically excited phenoxyl-d5 radicals. The additional energy deposited in electronic excitation of the radical reduces the energy available for relative translation. [ABSTRACT FROM AUTHOR]