H$_{2}$O Maser Pumping: The Effect of Quasi-Resonance Energy Transfer in
  Collisions between H$_2$ and H$_2$O Molecules
  The effect of quasi-resonance energy transfer in collisions between H$_2$ and
H$_2$O molecules in H$_2$O maser sources is investigated. New data on the
state-to-state rate coefficients for collisional transitions for H$_2$O and
H$_2$ molecules are used in the calculations. The results of ortho-H$_2$O level
population inversion calculations for the 22.2-, 380-, 439-, and 621-GHz
transitions are presented. The ortho-H$_2$O level population inversion is shown
to depend significantly on the population distribution of the para-H$_2$ $J =
0$ and $2$ rotational levels. The possibility of quasi-resonance energy
transfer in collisions between H$_2$ molecules at highly excited
rotational-vibrational levels and H$_2$O molecules is considered. The
quasi-resonance energy transfer effect can play a significant role in pumping
H$_2$O masers in the central regions of active galactic nuclei and in
star-forming regions.
