DYNAMICS OF PHOTOINDUCED REACTIONS IN HYDROGEN-BONDED CLUSTERS - CLASSICAL-STUDIES OF THE PHOTODISSOCIATION OF (HCL)2

A theoretical investigation of the photodissociation dynamics of (HCI)2 at 193 nm is presented. Prior to excitation, the cluster is taken to be in its rotation-vibration ground state. A quantal description of this six-dimensional wave function is computed using diffusion quantum Monte Carlo (DQMC). The photodissociation dynamics are simulated by classical trajectories in which the molecule undergoes vertical excitation to an electronic state that is repulsive along one of the HCI stretch coordinates. The initial conditions for these trajectories are sampled according to the Wigner function which was obtained from the DQMC wave function. In a significant fraction of these trajectories, there is a reactive collision in which the H atom interacts with the H'Cl' molecule to form HCI'. Of the remaining collisions, most are nonreactive, but a small number lead to H-2 formation. The trajectories in which an exchange reaction occurs result typically in formation of HCI' molecules that are rotationally and vibrationally hotter and in H atoms with lower kinetic energies than are found in the nonreactive trajectories. Resonances, in which the H atom undergoes multiple collisions with Cl and H'Cl', are observed in all three classes of trajectories. The above results indicate that this is a rich system for the study of photoinduced chemical reactivity in hydrogen-bonded clusters.