Three-dimensional quantum close-coupling calculations are presented for the vibrational predissociation of He–ICl B state complexes containing two quanta of ICl vibrational excitation. The dynamics are evaluated for the lowest quasibound van der Waals levels of He–ICl with total angular momentum J=0 and 1. The vibrational predissociation lifetime and final ICl B(v=1, j ) rotational distribution are calculated using the golden rule approximation. The calculated ICl product rotational distributions are broadly bimodal with maxima at j=7 and 15, as experimentally observed. The computed rotational distributions exhibit pronounced oscillations, which are expected to be suppressed when averaged over the initial angular momentum distribution sampled in the experiment. The theoretical analysis points to the dominant role of final-state interactions in determining the rotational distribution of the ICl fragments. The zero-point bending motion of the He–ICl complex and the coupling between the initial and final vibrational states make only small contributions to the final ICl rotational-state distributions. The extensive rotational excitation of the ICl product is primarily due to the anisotropic intermolecular interaction between the separating ICl and He fragments.

We examine the classical, semiclassical, and quantum mechanics of the Hamiltonian H= 1/2 (p2x+p2y+x2y2). The dynamics of this system are globally chaotic. However, the classical and quantum mechanical problems can be solved analytically by assuming an adiabatic separation of the x and y motion. We construct the canonical transformation to adiabatic action–angle variables and investigate the connection between this integrable approximation and the exact dynamics. In addition, we present a simple semiclassical formula that predicts energy levels in excellent agreement with the exact energy spectrum. The quantum adiabatic potential curves of this system have a very unusual structure—infinitely many curves cross at one point.

We compare the classical and quantum mechanics of a system whose classical dynamics are dominated by chaos. We observe a quantum "scars" of short periodic orbits. By examining the states on a quantum surface of section, we find that the stable and unstable manifolds of the periodic orbits have a clear effect on the eigenstates, in addition to the orbits themselves. A local density operator, constructed from a band of energy eigenstates, is strongly scarred by short periodic orbits. We also demonstrate a relation between the quantum eigenvalue spectrum and the actions of the periodic orbits.

Strongly peaked ICl fragment rotational distributions are observed following vibrational predissociation of ICl–He B state complexes containing two or three quanta of ICl vibrational excitation. The nascent rotational distributions of the ICl product exhibit two distinct maxima, occurring at j=7 and j=16. A theoretical analysis demonstrates that the two maxima are due to rotational rainbows, arising from the He atom scattering off of the I and Cl ends of the ICl molecule. The vibrational predissociation of ICl–He B(vB=2) is simulated with a semiclassical scattering theory which is analogous to that developed by Schinke [J. Chem. Phys. 85, 5049 (1986)] for direct photodissociation. Vibrational predissociation is modeled as a rotationally inelastic ‘‘half-collision,’’ following deactivation of the ICl vibration. The final rotational angular momentum of the ICl fragments is determined from exact classical trajectories and in a sudden limit on a model potential energy surface. The calculated ICl product rotational distribution, like the experimentally observed distributions, is bimodal.