H2O Maser Pumping: The Effect of Quasi-Resonance Energy Transfer in Collisions between H2 and H2O Molecules

The effect of quasi-resonance energy transfer in collisions between H2 and H2O molecules in H2O maser sources is investigated. New data on the state-to-state rate coefficients for collisional transitions for H2O and H2 molecules are used in the calculations. The results of ortho-H2O level population inversion calculations for the 22.2-, 380-, 439-, and 621-GHz transitions are presented. The ortho-H2O level population inversion is shown to depend significantly on the population distribution of the para-H2 J = 0 and 2 rotational levels. The possibility of quasi-resonance energy transfer in collisions between H2 molecules at highly excited rotational-vibrational levels and H2O molecules is considered. The quasi-resonance energy transfer effect can play a significant role in pumping H2O masers in the central regions of active galactic nuclei and in star-forming regions