Photodissociation of the vinoxy radical through conical, and avoided, intersections

摘要

The mechanism for predissociation of the vinoxy radical after the excitation X~2A:->B~2A~" is studied theoretically. Critical points on the A~2A' and B~2A" potential energy surfaces are determined at the multireference configuration interaction level using expansions of five million configuration state functions. A mechanism consisting of a sequence of internal conversions to the ground state is proposed. B~2A" - A~2A' conical intersections are shown to be too high in energy to participate in this process. The B~1A"-A~2A' radiationless transition is enabled by an avoided crossing which is accessible after a barrier of a ca. 2000 cm~(-1), in agreement with experimental observations. Subsequently the A~2A'-X~2A" radiationless transition can occur very efficiently through easily accessible conical intersections. A one-dimensional coupled adiabatic state model of the process is developed. The radiationless decay rates of the vibrational levels obtained from this model serve to validate the proposed mechanism.