Bottlenecks to intramolecular energy transfer and the calculation of relaxation rates

A recently developed theory of MacKay, Meiss, and Percival [Physica D 13, 55 (1984)] and Bensimon and Kadanoff [Physica D 13, 82 (1984)] is applied to the intramolecular relaxation of highly excited, collinear OCS. This theory, which was originally developed to understand the long time relaxation of mappings, possesses many of the features of statistical theories of reactions. Bottlenecks, dividing surfaces, and transition states are all part of the theory, which we employ here to describe the relaxation dynamics of collinear OCS. In particular, the theory is used to find a bottleneck to intramolecular energy transfer, generate a dividing surface, derive the flux across this dividing surface, and then calculate the rate across it. A simple kinetic model then employs this rate to accurately predict the rate of relaxation for collinear OCS. At present the theory is purely classical mechanical, has only been applied to systems of two degrees of freedom, and has only been used to describe the dynamics of bound systems. We discuss extensions of the theory in these three areas.