Depolarization in H₂O–He collisions

Abstract

Elastic tensor and elastic depolarization cross-sections for collisions of specified rotational levels of H₂O with helium are determined using an accurate ab initio potential energy surface computed by Patkowski et al. The elastic depolarization cross-sections display large maxima at low collision energies due to shape resonances and generally decrease smoothly with increasing collision energy, with superimposed sharp peaks due to resonances with quasibound van der Waals levels associated with higher rotational asymptotes. The cross-sections show a striking dependence upon the k-projection quantum numbers of the rotational levels, as well as a general decrease in magnitude with increasing values of the total rotational angular momentum j.

Keywords:

• molecular collisions
• tensor cross-sections
• elastic depolarization cross-sections

Acknowledgements

The authors gratefully thank the US National Science Foundation for partial support under Grant No. CHE-0848110. They also thank Phillip Stancil and Benhui Yang for providing H₂O–He state-to-state integral cross-sections computed with MOLSCAT.