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

In this paper, the molecular dynamics of dissociation and recombinatio n of iodine in argon clusters are reported and compared with the exper imental results of the preceding paper [Wang, J.-K.; et al. J. Phys. C hem. 1995, 99, 11309). The microscopic processes of bond breakage and bond reformation are visualized with the help of simple classical mode ls. The coherent recombination observed experimentally is shown to be closely related to the coherent nature of bond breakage and the homoge neity of local structures in large clusters. Caging, which is found to be efficient in the large clusters, is ultrafast: The caging time sca le ranges from femtoseconds to picoseconds depending on the bond break ing time as well as the size and temperature of the cluster. With the inclusion of the known solute (iodine) femtosecond dynamics and the so lute-solvent Lennard-Jones interaction potentials, the molecular dynam ics simulations reproduce the corresponding experimental results and l ink the microscopic picture to the observables. We examine the effect of the local structure, cluster size and temperature, bond distance, a nd the state excited on the wave packet dynamics of the solute in the solvent. The new mechanism of coherent, concerted caging in the solven t structure is described. From the experimental and theoretical studie s we provide some concepts regarding the molecular basis of the dissoc iation and recombination phenomena.