Equilibration of vibrationally excited OH in atomic and diatomic bath gases

McCaffery, Anthony J, Pritchard, Marisian, Turner, John F C and Marsh, Richard J (2011) Equilibration of vibrationally excited OH in atomic and diatomic bath gases. Journal of Physical Chemistry A, 115 (17). pp. 4169-4178. ISSN 1089-5639

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Abstract

In this work, a computational model of state-to-state energy flow in gas ensembles is used to investigate collisional relaxation of excited OH, present as a minor species in various bath gases. Rovibrational quantum state populations are computed for each component species in ensembles consisting of 8000 molecules undergoing cycles of binary collisions. Results are presented as quantum state populations and as (approximate) modal temperatures for each species after each collision cycle. Equilibration of OH is slow with Ar as the partner but much faster when N2 and/or O2 forms the bath gas. This accelerated thermalization is shown to be the result of near-resonant vibration−vibration transfer, with vibrational de-excitation in OH matched in energy by excitation in bath molecules. Successive near-resonant events result in an energy cascade. Such processes are highly dependent on molecule pair and on initial OH vibrational state. OH rotational temperatures initially increase, but at equilibration, they are lower than those of other modes. Possible reasons for this observation in molecules such as OH are suggested. There are indications of an order of precedent in the equilibration process, with vibrations taking priority over rotations, and potential explanations for this phenomenon are discussed.

Item Type: Article
Additional Information: Anthony J. McCaffery Marisian Pritchard and Richard J. Marsh
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science
Depositing User: Anthony McCaffery
Date Deposited: 06 Feb 2012 21:24
Last Modified: 02 Jul 2013 13:27
URI: http://sro.sussex.ac.uk/id/eprint/31094
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