Classical trajectory calculations for collisions between vibrationally hot pyrazine (E ) 40332 cm -1 ) and room-temperature CO are compared with recent diode laser experiments. Ab initio calculations were carried out to determine parameters for the pairwise Lennard-Jones intermolecular potential. The trajectory results appear to show good qualitative agreement with preliminary experimental results. The highest ∆E collisions occur when the CO happens to lie above the pyrazine plane just as the underlying CH wag executes an unusually high amplitude motion. Artificially doubling the length of the CO produces results for the angular momentum transfer to the CO molecule that look quite similar to those for angular momentum transfer to CO 2 in analogous pyrazine-CO 2 experiments. † Part of the special issue "William H. Miller Festschrift".

Vibrational energy transfer from hot pyrazine (E′ ) 40 322 cm -1 ) to cold CO is modeled using classical trajectories. Collisional energy transfer properties are studied as a function of the initial rotational state J′ of the CO, the length of the CO, the energy E′ in pyrazine, the relative kinetic energy, the temperature, isotopic substitution on pyrazine, and the intermolecular potential. The energy transfer probability function P(E,E′) exhibits distinct deviation from single exponential behavior. Collisions that transfer particularly large energy are associated with large amplitude out-of-plane motion of a C-H bond, imparting a kick to the departing CO. Slower collisions are particularly effective in relaxing pyrazine; faster collisions can add energy as often as they remove it. Energy transfer properties also depend on the initial rotational state of the CO. Temperature effects on 〈E -E′〉 are weak in the 200-500 K range; this results from an increase in the magnitudes of both 〈∆E〉 down and 〈∆E〉 up . The fraction of pyrazine energy partitioned to translation increases with temperature. Decreasing the rotational temperature of pyrazine (at fixed translational temperature) decreases -〈E -E′〉 significantly. Decreasing translational temperature (at fixed pyrazine rotational temperature) increases -〈E -E′〉. This is in contrast to the conventional expectation, based on Landau-Teller theory. Effects of making modest changes of the intermolecular potential are also discussed. † Part of the special issue "Richard Bersohn Memorial Issue".