TRAJECTORY STUDY OF PHOTODISSOCIATION DYNAMICS IN THE NAI(H2O) CLUSTER SYSTEM

The photodissociation dynamics of the NaI(H2O) dimer is studied theore tically. The dynamics are simulated via the ''molecular dynamics with quantum transitions'' trajectory method of Tully and co-workers in ord er to describe nonadiabatic transitions between the excited and ground electronic states. In the calculations, the electronic structure of N aI is determined at every point along trajectories by semiempirical va lence-bond theory, while the water is described by classical potential s. It is found that the clustered water enhances the probability of an excited-to-ground-state nonadiabatic transition compared to the isola ted NaI case. In addition, the clear oscillatory dynamics for the boun d excited state motion for isolated NaI is considerably muted by the p resence of the water. Other characteristic features of the process inc lude a considerable transfer of rotational kinetic energy to the water molecule and a rapid ''evaporation'' of that molecule. These latter c haracteristic features are shown to arise from a reversed polarity of the Franck-Condon excited state NaI compared with the ground state pol arity Na+deltaI-delta.