REORIENTATION CROSS-SECTIONS IN COLLISIONS OF HE(S-1)+H-2(B (1)SIGMA(U)(+)

Reorientation cross sections have been computed for the He(1S) + H-2(B 1SIGMA(u)+) system using a potential energy surface and model previously introduced for rovibrational energy transfer. The model consists of restricting the scattering solely to the excited state potential energy surface and the use of the coupled-channel method. The calculated reorientation cross section is 41.6 angstrom2 for the transition (vjm(j)=0,1,O --> v'j'm(j)'=0,1, +/- 1) at room temperature; the corresponding Boltzmann average is 39.2 angstrom2. The latter result is in very good agreement with a recent measurement by Pibel and Moore of 29.7 +/- 7.4 angstrom2 [j. Chem. Phys. 93,4804 (1990)].