Classical dynamics of H2O vibrational self-relaxation.

Abstract

The vibrational self-relaxation rate constants of the (001), (100), (020), and (010) states of H2O from 295 to 2500 K are calculated, using ∼1.6 × 10(6) classical trajectories with Gaussian binning for determining product vibrational quantum numbers. The calculations use a new H2O-H2O potential surface obtained by fitting 1.25 × 10(5) ab initio geometry points at the CCSD(T)//cc-pvtz level of theory. The resulting vibrational self-relaxation rate constants are generally within a factor of 2 of the measured data, which are large in magnitude and tend to increase with decreasing temperature. At lower temperatures, the calculations show long-lived (20 ps and longer) H2O-H2O collision complexes which accompany vibrational relaxation. Product rotational and translational energy distributions are investigated, and joint vibrational state and molecule-specific relaxation rate constants are presented.