A mixed quantum/classical theory (MQCT) is developed to describe inelastic scattering of molecules in a broad range of collision energies. In this simplified approach the translational motion of collision partners is treated classically, while the internal degrees of freedom – rotational and/or vibrational motion – are treated quantum mechanically. Calculations of rotationally inelastic cross sections were carried out within this framework, and results were compared against the exact full quantum calculations for several real systems, starting with the simplest diatomic + atom collisions, such as H2 + He, and going up to such complicated examples as rotational excitation of methyl formate HCOOCH3 + He (astrophysically important small organic molecule), or the fundamentally important case of collision between two general asymmetric-top rotor molecules such H2O + H2O (important in cometary comas). The mixed quantum/classical method remains affordable and reasonably accurate, in particular at high collision energies, where it can probably replace the standard full-quantum approach.

Mixed quantum/classical theory of molecular collisions: Applications to rotational-vibrational Inelastic scattering in astrophysical environmens

255th National Meeting (2018)

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