Details

Autor(en) / Beteiligte

• Ivanov, Mikhail
• Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881
• Dubernet, Marie-Lise
• Babikov, Dmitri

Titel

Rotational quenching of H{sub 2}O by He: Mixed quantum/classical theory and comparison with quantum results

Ist Teil von

• The Journal of chemical physics, 2014-04, Vol.140 (13)

Ort / Verlag

United States

Erscheinungsjahr

2014

Link zum Volltext

Quelle

AIP Journals (American Institute of Physics)

Beschreibungen/Notizen

• The mixed quantum/classical theory (MQCT) formulated in the space-fixed reference frame is used to compute quenching cross sections of several rotationally excited states of water molecule by impact of He atom in a broad range of collision energies, and is tested against the full-quantum calculations on the same potential energy surface. In current implementation of MQCT method, there are two major sources of errors: one affects results at energies below 10 cm{sup −1}, while the other shows up at energies above 500 cm{sup −1}. Namely, when the collision energy E is below the state-to-state transition energy ΔE the MQCT method becomes less accurate due to its intrinsic classical approximation, although employment of the average-velocity principle (scaling of collision energy in order to satisfy microscopic reversibility) helps dramatically. At higher energies, MQCT is expected to be accurate but in current implementation, in order to make calculations computationally affordable, we had to cut off the basis set size. This can be avoided by using a more efficient body-fixed formulation of MQCT. Overall, the errors of MQCT method are within 20% of the full-quantum results almost everywhere through four-orders-of-magnitude range of collision energies, except near resonances, where the errors are somewhat larger.