The rotational excitation of the water isotopologues by molecular hydrogen

We present cross-sections and rate coefficients for rotational transitions in the water isotopologues D2O, (H2O)-O-18, and HDO induced by collisions with para-H-2(j(2) = 0) and ortho-H-2(j(2) = 1). Quantum scattering calculations are performed at the full close-coupling level with the isotopic variants of an accurate full-dimensional H2O-H-2 interaction potential. The D2O, (H2O)-O-18, and HDO cross-sections are compared to the corresponding cross-sections for H2O. Large isotopic effects are observed in the case of D2O and HDO, in particular for collisions with p-H-2(j(2) = 0), while the O-18 isotopic substitution is found to be negligible. Rate coefficients are provided for rotational transitions among all para-D2O, ortho-D2O, and HDO levels with internal energy below 300 cm(-1) and for kinetic temperatures in the range 5-300 K. Non-LTE radiative transfer calculations show that the HDO 225.9 GHz and (H2O)-O-18 203.4 GHz transitions recently detected with ALMA in the young proto-planetary disc V883 Ori should be inverted (weak masers) in a large fraction of the disc.