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 t his six-dimensional wave function is computed using diffusion quantum Monte Carlo (DQMC). The photodissociation dynamics are simulated by cl assical trajectories in which the molecule undergoes vertical excitati on to an electronic state that is repulsive along one of the HCI stret ch coordinates. The initial conditions for these trajectories are samp led 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' m olecule to form HCI'. Of the remaining collisions, most are nonreactiv e, but a small number lead to H-2 formation. The trajectories in which an exchange reaction occurs result typically in formation of HCI' mol ecules that are rotationally and vibrationally hotter and in H atoms w ith lower kinetic energies than are found in the nonreactive trajector ies. Resonances, in which the H atom undergoes multiple collisions wit h 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 ph otoinduced chemical reactivity in hydrogen-bonded clusters.