SOLVATION ULTRAFAST DYNAMICS OF REACTIONS .10. MOLECULAR-DYNAMICS STUDIES OF DISSOCIATION, RECOMBINATION, AND COHERENCE

In this paper, the molecular dynamics of dissociation and recombination of iodine in argon clusters are reported and compared with the experimental results of the preceding paper [Wang, J.-K.; et al. J. Phys. Chem. 1995, 99, 11309). The microscopic processes of bond breakage and bond reformation are visualized with the help of simple classical models. The coherent recombination observed experimentally is shown to be closely related to the coherent nature of bond breakage and the homogeneity of local structures in large clusters. Caging, which is found to be efficient in the large clusters, is ultrafast: The caging time scale ranges from femtoseconds to picoseconds depending on the bond breaking time as well as the size and temperature of the cluster. With the inclusion of the known solute (iodine) femtosecond dynamics and the solute-solvent Lennard-Jones interaction potentials, the molecular dynamics simulations reproduce the corresponding experimental results and link the microscopic picture to the observables. We examine the effect of the local structure, cluster size and temperature, bond distance, and the state excited on the wave packet dynamics of the solute in the solvent. The new mechanism of coherent, concerted caging in the solvent structure is described. From the experimental and theoretical studies we provide some concepts regarding the molecular basis of the dissociation and recombination phenomena.