Theoretical study of the low-temperature vibrational relaxation of o-H2 in collisions with 4He

Cross sections and rate constants for the vibrational relaxation of H2(γ=1,j=1) in collisions with 4He were determined using the coupled states method with a fully-converged channel basis. The interaction potential was taken to be that of Gordon and Secrest with the elastic matrix elements modified to include the spherically-symmetric component of the semi-empirical Shafer-Gordon potential. First-order forbidden transitions play a significant role in the overall relaxation process. The cross sections for the de-excitation of the γ=1,j=1 level are slightly larger than those for the γ=1,j=0 level. The ratio of the corresponding rate constants for vibrational relaxation varies smoothly from a value of 1.25 at 500 K to 1.63 at 60 K. (Auth.)