Rotational excitation of highly excited H2O by H2

Water is a key molecule for interstellar chemistry. Observations with Herschel telescope show significant population of very high rotational transitions (j greater than or similar to 8) in young stellar objects, indicating significant amounts of water in hot (T greater than or similar to 1500 K) and dense (n greater than or similar to 10(6) cm(-3)) gas. Non-local thermodynamic equilibrium (LTE) modelling of these observations requires the knowledge of the collisional and radiative properties of highly excited water at high temperature. The aim of this work is to calculate a new set of excitation rate coefficients for both para- and ortho-H2O induced by collisions with H-2 for energy levels up to j = 17. Quantum scattering calculations were performed using a reduced dimensional approach and the coupled states approximation. Rate coefficients were obtained for 97 pure rotational energy levels of both para- and ortho-H2O and for temperatures up to 2000 K. With the forthcoming launch of the James Webb Space Telescope, these new collisional data will allow us to gain more insight into the physical conditions in star- and planet-forming regions.