Cross sections and rate constants for rotational and vibrational excitation of H2 and D2 colliding with 4He

Cross sections and rate constants for vibrational deexcitation of H2 and D2 colliding with 4He are calculated using the semiclassical coupled states (SCS) method. A 23-parameter potential hyper-surface is used to describe the molecular interaction. Good agreement with experimental data for vibrational relaxation is obtained if a vibrating rotator model is used for the H2 and D2 molecules. It is found that n-D2 relaxes about fifteen times slower than n-H2 at 50 K. (Auth.)