SIMULATION OF EFFECTIVE VIBRATIONAL-TRANSLATIONAL ENERGY-EXCHANGE IN COLLISIONS OF VIBRATIONALLY EXCITED OH WITH O-2 ON THE MODEL POTENTIAL-ENERGY SURFACE - CAN THE RELAXATION OF OH(V) BE ONE-QUANTUM FOR LOW-VAND MULTIQUANTUM FOR HIGH-V

The collision of OH with the oxygen molecule is studied by the traject ory simulation technique on the model; potential energy surface of OH + O-2 --> O-3 + H chemical reaction. Although the reaction channel is closed, we aim to demonstrate that the L-shape of the OH + O-2 valley leads to the effective coupling of OH(upsilon) vibration with the rela tive motion of collisional partners and therefore explains the high va lue of the vibrational relaxation rate constant observed experimentall y, The characteristic feature of the mechanism considered is the predo minance of one-quantum relaxation for low and multiquantum transitions for high OH vibrational levels. To estimate state-to-state vibrationa l relaxation rate constants, the method of dynamical corrections of tr ansition state theory is used. The expression for the rate constant co nsists of a transition state term and a correction factor, determined in two-dimensional classical trajectory calculations. We also demonstr ate the instability of motion on the potential energy surface with the L-shape valley, resulting from the scattering of the trajectory on th e ''corner'' of the potential energy surface and the presence of regul ar and chaotic motions.