Real-time dynamics of clusters. II. I_2X_n (n=1; X=He, Ne, and H_2), picosecond fragmentation

Abstract

In this second paper (II) of a series, we report our picosecond time-resolved studies of the state-to-state rates of vibrational predissociation in iodine–rare gas (van der Waals) clusters. Particular focus is on the simplest system, I2He, which serves as a benchmark for theoretical modeling. Comparisons with I2Ne and I2H2 are also presented. The results from measurements made in real time are compared with those deduced from linewidth measurements, representing a rare example of a system studied by both methods under identical conditions and excited to the same quantum (v^{[script ']}_i) states. The discrepancies are discussed in relation to the origin of the broadening and preparation of the state. The rates as a function of v^{[script ']}_i display a nonlinear behavior which is examined in relation to the energy-gap law. The measured absolute rates and their dependence on v^{[script ']}_i are compared with numerous calculations invoking classical, quantum, and semiclassical theories. In the following paper (III in this series), the cluster size of the same system, I2Xn, is increased (n=2–4) and the dynamics are studied.