#### Document Type

Article

#### Publication Date

2014

#### Source Publication

Journal of Chemical Physics

#### Source ISSN

0021-9606

#### Abstract

The mixed quantum/classical theory (MQCT) for inelastic molecule-atom scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys.139, 174108 (2013)] is extended to treat a general case of an asymmetric-top-rotor molecule in the body-fixed reference frame. This complements a similar theory formulated in the space-fixed reference-frame [M. Ivanov, M.-L. Dubernet, and D. Babikov, J. Chem. Phys.140, 134301 (2014)]. Here, the goal was to develop an approximate computationally affordable treatment of the rotationally inelastic scattering and apply it to H_{2}O + He. We found that MQCT is somewhat less accurate at lower scattering energies. For example, below *E* = 1000 cm^{−1} the typical errors in the values of inelastic scattering cross sections are on the order of 10%. However, at higher scattering energies MQCT method appears to be rather accurate. Thus, at scattering energies above 2000 cm^{−1} the errors are consistently in the range of 1%–2%, which is basically our convergence criterion with respect to the number of trajectories. At these conditions our MQCT method remains computationally affordable. We found that computational cost of the fully-coupled MQCT calculations scales as *n* ^{2}, where *n* is the number of channels. This is more favorable than the full-quantum inelastic scattering calculations that scale as *n* ^{3}. Our conclusion is that for complex systems (heavy collision partners with many internal states) and at higher scattering energies MQCT may offer significant computational advantages.

## Comments

Published version.

Journal of Chemical Physics, Vol. 141, No. 11 (2014): 114304. DOI. © American Institute of Physics 2014. Used with permission.