Quantum dynamics of overtone relaxation in benzene. III. Spectra and dynamics for relaxation from CH(v=3)

Abstract

This series is concerned with the quantum dynamics of overtone relaxation in benzene and in reduced mode benzene fragments. In part III of this series, emphasis is placed on the CH(v=3) overtone spectrum and the survival probability for both 16 mode (five CH stretch modes are forced to remain inactive out of 21 planar modes) and 21 mode planar benzene models. Through use of the wave operator contraction algorithm, primitive vibrational basis sets containing up to 9×109 states are contracted to active spaces containing 2000–7000 states. The exact dynamics within the active space is developed with the recursive residue generation method (RRGM). Specific results reported in this study include the following: (a) a comparison is made between dipole spectra and residue spectra, the former explicitly involving the CH dipole function; (b) for the 16 mode model, the following quantities are displayed: overtone spectrum, survival probability of the initial state, complex-valued autocorrelation function, number of phase space cells explored as a function of time, and the rate of exploring phase space cells; (c) sensitivity of the overtone spectrum to the size and composition of the active space built with the wave operator contraction algorithm; (d) for 21 mode benzene, we consider the sensitivity of the overtone spectrum to ‘‘softening’’ the anharmonic potential; (e) comparisons are made with recent jet cooled beam experimental overtone spectra.