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

Reorientation cross sections have been computed for the He(1S) + H-2(B 1SIGMA(u)+) system using a potential energy surface and model previou sly introduced for rovibrational energy transfer. The model consists o f restricting the scattering solely to the excited state potential ene rgy 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 correspond ing 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)].