THEORETICAL-STUDY OF THE UNIMOLECULAR DISSOCIATION HO2-]H-2 .1. CALCULATION OF THE BOUND-STATES OF HO2 UP TO THE DISSOCIATION THRESHOLD ANDTHEIR STATISTICAL-ANALYSIS(O)

This is the first of a series of papers in which we investigate the un imolecular dissociation of hydroperoxyl. Using the DMBE IV potential e nergy surface [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)], in th e present study 726 bound states of HO2((X) over tilde) up to-the H+O- 2 dissociation threshold are calculated in an attempt to access the ex tent of the coupling between the modes of the system. The first approa ch involves an analysis of the nodal structure of the wave functions. While the wave functions for the lowest states are regular and; assign able, the degree of mixing and complexity rapidly increases with energ y. The wave functions close to the dissociation threshold are mostly i rregular without any clear cut nodal structure and fill the entire coo rdinate space available. Nevertheless, a small number of regular state s, that are associated with large excitation in the O-2 stretching coo rdinate and no or only little excitation in the other modes, are found even at high energies. The second approach used to study the degree o f intramolecular coupling is an analysis of the energy spectrum. The n earest neighbor level spacing distribution, which probes the short-ran ge correlation, as well as the Sigma(2) and Delta(3) statistics, which are sensitive to the long-range correlations in the spectrum, are inv estigated and compared to the distributions predicted for regular and irregular spectra. Both of these approaches indicate that the system i s almost totally irregular with a Brody parameter of about 92%. In add ition, the sum of states at a particular energy, which is extremely im portant in all statistical models for unimolecular dissociation, is ap proximately calculated from the volume of classical phase space and fo und to be in excellent agreement with the exact quantum mechanical res ult. (C) 1995 American Institute of Physics.