The transport cross sections and collision integrals for H-H-2 interac
tions have been calculated from the results of accurate ab initio stru
cture calculations using sudden scattering approximations. The low-tem
perature diffusion and viscosity coefficients agree well with the resu
lts of a close-coupling scattering calculation. The values calculated
from the potential energies deduced from scattering measurements are i
n agreement with the theoretical results. The viscosity coefficients f
or H-H and H-2-H-2 have also been calculated; the H-2-H-2 results are
very close to the measured data for temperatures in the range 200-400
K.