2012MNRAS.420..699F

Rate coefficients for rotational transitions in HDO and D₂ O induced by H₂ collisions below 300 K are presented. Calculations have been performed at the close-coupling and coupled-states levels with the deuterated variants of the H₂O-H₂ interaction potential of Valiron et al. The HDO-H₂ and D₂O-H₂ rate coefficients are compared to the corresponding rate coefficients for HDO-He and H₂O-H₂, respectively. Significant differences are observed. In particular the new HDO rate coefficients are found to be significantly larger (by up to three orders of magnitude) than the corresponding HDO-He rate coefficients. The impact of the new HDO rate coefficients is examined with the help of non-LTE radiative transfer calculations. A number of potential HDO maser lines are finally identified, in particular the 80.6 GHz (1_1.0 - -1_1.1) transition.