NONLINEAR RESONANCE AND CORRELATED BINARY COLLISIONS IN THE VIBRATIONAL PREDISSOCIATION DYNAMICS OF I-2(B,V)-AR-13 CLUSTERS

The vibrational predissociation dynamics of the van der Waals cluster I2(B, upsilon)-Ar13 are studied theoretically from a classical mechanical perspective. The focus is on the ejection of the first Ar atom from the excited cluster. This process is found to occur by two competing mechanisms (1) evaporation of a cluster atom induced by the slow vibrational relaxation of the I2 impurity, and (2) direct ejection of a geometrically favored Ar atom by two or more impulsive collisions with the vibrating I2. In contrast with the picture of independent binary collisions, the multiple argon-iodine interactions leading to successful direct dissociation are correlated in time. The relative propensity of the direct channel is a highly structured function of upsilon, the initial vibrational level of the I2. This behavior results from the energy-dependent frequencies of motion of the diatomic and the localized Ar cluster mode, and is a novel example of a nonlinear resonance between ''system'' and ''bath'' degrees of freedom.