Collisional quenching and excitation of water molecules in astrophysical environments is studied computationally, using the mixed quantum/classical theory (MQCT). In this simplified approach the translational motion of collision partners is treated classically, while the rotational motion of each molecule is treated quantum mechanically. Calculations of rotationally inelastic cross sections are carried out within this framework, and the results are compared against exact full-quantum calculations for several real systems, such as H2O + He and H2O + H2. Various combinations of ortho-H2O and para-H2O with ortho-H2 and para-H2 are considered. Collisions of H2O + H2O, important in cometary comas, are also studied. The effect of isotopic substitutions, such as in HD, D2, HOD and DOD, can also be determined. MQCT method remains affordable and reasonably accurate, in particular at high collision energies, where it can probably replace the standard full-quantum approach.

MQCT studies of collisional excitation and quenching of water molecules

Macromolecular Chemistry: The Second Century

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