Quantum scattering calculations for H2S-He between 1-600 K in comparison with pressure broadening, shift, and time resolved double resonance experiments

We have performed quantum scattering calculations to predict pressure broad ening, pressure shift, and inelastic depopulation cross-sections for the ro tational transitions 1(1,0)<-- 1(0,1) and 2(2,0)<-- 2(1,1) of the H2S molec ule in collision with helium atoms over a temperature range from 1 to 600 K . The calculated cross-sections are compared with experimental values obtai ned by millimeter wave spectroscopic techniques and the collisional cooling method. We observe good agreement between theory and experiment over the t emperature region from 20 to 600 K, but increasing differences below 20 K. Possible reasons for the deviations at lower temperatures are discussed. Th e calculations also illustrate the contribution of elastic collisions to th e pressure broadening cross-sections. (C) 1999 American Institute of Physic s. [S0021-9606(99)01143-5].