Abstract
Rate coefficients for rotational transitions in HDO and D2O induced by H2 collisions below 300 K are presented. Calculations have been performed at the close-coupling and coupledstates 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 (11,0–11,1) transition.
Highlights
Despite the low cosmic deuterium abundance, D/H ∼ 10−5, a spectacular deuterium enrichment of various interstellar molecules is observed in star-forming regions (Ceccarelli et al 2007, and references therein)
The deuterated isotopologues of water, HDO and D2O are of special importance because they can help to understand the origin of water in the interstellar medium and its possible link with the D/H ratios observed in comets and in the Earth’s oceans (∼10−4) (Hartogh et al 2011)
We have reported rate coefficients for rotational transitions in HDO and D2O induced by H2 collisions below 300 K
Summary
Despite the low cosmic deuterium abundance, D/H ∼ 10−5, a spectacular deuterium enrichment of various interstellar molecules is observed in star-forming regions (Ceccarelli et al 2007, and references therein). Among these molecules, the deuterated isotopologues of water, HDO and D2O are of special importance because they can help to understand the origin of water in the interstellar medium and its possible link with the D/H ratios observed in comets and in the Earth’s oceans (∼10−4) (Hartogh et al 2011). The computation of molecular abundances relies on radiative transfer mod-
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