Collisional excitation rates of H2O with H2 II. Rotational excitation with ortho-H2 at very low temperature and application to cold molecular clouds

We present the results of close coupling calculations of pure rotational excitation rate coefficients of H2O by ortho-H2, performed between 5 K and 20 K. At 20 K there is a good agreement with those results obtained previously by Phillips et al. (1996). Fits of our de -excitation collisional rate coefficients are provided. These new rate coefficients are used in the modelling of cold interstellar clouds to determine the influence of the precision of the rate coefficients on predicted line intensities.