DYNAMIC ORIENTATION OF DIATOMIC FRAGMENTS FORMED IN THE DECOMPOSITION OF STATISTICAL TRIATOMIC COMPLEXES .1. SEMICLASSICAL STUDY

The dynamic rotational orientation of a diatomic fragment formed in the decomposition of a triatomic complex is calculated in the framework of the statistical adiabatic channel model (SACM). The orientation is created as a result of the interplay between the adiabatic interaction in the atom-diatom exit channel and the rotationally nonadiabatic coupling in the perturbed rotor region. Numerical calculations for two types of potentials (charge-rotating dipole interaction proportional to R(-4), and anisotropic van der Waals potential proportional to R(-6)) establish the region of applicability of the perturbation treatment and yield the average rotational orientation of a diatom as a function of the initial adiabatic channel quantum number. For a statistical complex, the degree of orientation of a diatom in a given rotational state is directly related to the number of open adiabatic channels converging to this level. This result can be used for counting the number of open channels that become degenerate for free fragments, and therefore for an additional test of the underlying assumption of the statistical adiabatic channel model on a state-to-state level. A simple model estimate indicates a substantial degree of dynamic orientation of the fragments formed close to the appearance threshold.