Rotational quenching of monodeuterated water by hydrogen molecules

Abstract

Cross sections and rate coefficients for low lying rotational transitions in HDO induced by para and ortho-H₂ collisions are presented for the first time. Calculations have been performed at the close-coupling and coupled-states levels with the deuterated variant of the H₂O–H₂ interaction potential of Valironet al. [J. Chem. Phys., 2008, 129, 134306]. Rate coefficients are presented for temperatures between 5 and 100 K and are compared to the corresponding rates for H₂O and D₂O. Significant differences caused by the isotopic substitution, in particular the C_2v symmetry breaking, are observed. Finally, our rates are found to be significantly larger (by up to three orders of magnitude at 50 K) than the corresponding HDO–He rates and should lead to a thorough re-estimation of the abundance of interstellar HDO.