The classical mechanics of vibrational predissociation: A model based study of phase space structure and its influence on fragmentation rates

The classical dynamics pertinent to van der Waals molecule vibrational predissociation of a T-shaped model for HeI2(B) is examined. An interesting phase space structure involving nonlinear resonances and stochastic motion is found. For low initial vibrational excitations of the I2 partner of the vdW complex the relevant part of phase space is dominated by quasiperiodic motion indicating a purely quantal mode of decay (‘‘dynamical tunneling’’), but for higher initial vibrational excitations van der Waals molecule predissociation is a classically allowed process. Classically determined rates of decay agree to within a factor of 3 with the rates calculated from quantum mechanics.