Calculations of V-V transfer rates in H2 and comparison with experiment

Recent observations on VV transfer in H(2) have shown interesting results. For nonresonant processes, comparison of the experimental rate constants with the results of previous semiclassical calculations, quantum oscillators/classical rotors coupled via classical collisions, showed the theoretical rate constants to be too slow by a factor of 3 or more. The semiclassical rate constant of the resonant VV process (v = 1 + v = 0 --> v = 0 + v = 1) was also found to be too slow, by more than an order of magnitude, compared with the experimental rate. Further, the semiclassical model predicted the value of k(1,1-->0,2) to exceed that of k(1,0-->0,1), but the experimental data shows it to be a factor of approximately 2 less. In this work we employ an accurate interaction potential for the H(2)-H(2) system, and treat both rotation and vibration of the diatoms as coupled quantum-mechanical degrees of freedom. These new calculated results are in better overall agreement with the near-resonant experimental values, but the calculated rate constants are a factor of 2 to 3 larger than experiment for the nonresonant processes.