SEMICLASSICAL TREATMENT OF TUNNELING EFFECTS IN HONO CIS-TRANS ISOMERIZATION

The classical-plus-tunneling method of Waite and Miller [J. Chem. Phys . 73, 3713 (1980)] has been used to study tunneling effects in the cis -trans isomerization of HONO. The, calculated classical-plus-tunneling rate coefficients are two and three times larger than the correspondi ng purely classical values for trans-->cis and cis-->trans isomerizati ons, respectively. The tunneling rate is governed by the rate of energ y flow into the tunneling coordinate, the effective mass, and the tunn eling frequency. An approximation to the actual torsional potential us ed in the classical dynamics calculations was developed to give an ana lytical solution for the Jeffreys-Wentzel-Kramers-Brillouin (JWKB) bar rier-penetration integral. The approximation yields accurate results ( compared to those obtained by solving the JWKB integral numerically us ing the true torsional potential) and a considerable reduction in comp utational expense.