The objective of this research project was to study applications of statistical unimolecular reaction theories to a simple model chemical process. Such studies are needed to test the existing theories and provide direction for their further development. T-shaped Ar3, a simple chaotic two degree of freedom system, is an excellent candidate for such study, since statistical behavior is generally associated with chaotic dynamics.
Chemical kinetics predicts fully statistical decay curves of microcanonical population associated with one of the two equivalent arrangements of T-shaped Ar3. However numerical computations, presented here, reveal nonstatistical characteristics of microcanonical T-shaped Ar3 inversion at energies associated with strongly chaotic dynamics. Nonstatisticality is most pronounced at higher energies where internal relaxation time scales are comparable to the inversion time. At such energies, population decay curves exhibit damped oscillations about the equilibrium population. At energies just above the inversion threshold, where inversion is very slow, near statistical nonoscillatory behavior is observed. The "absorbing barrier method" of J.E. Straub and B.J. Berne [J. Chem. Phys. 83, 1138 (1985)] is shown to provide a reasonable model for observed population decays. Characteristics of corresponding gap distributions are described in terms of an adapted "delayed lifetime gap model". Analysis of the model which combines the absorbing barrier method and the adapted delayed lifetime gap model provides insight into the observation of both oscillatory and nonoscillatory population decays. Specifically, the analysis describes the observations in terms of an "underdamped" or "overdamped" harmonic oscillator, respectively.