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State-to-state, multi-collision, energy transfer in H–H2 gas ensembles

journal contribution
posted on 2023-06-09, 09:07 authored by Anthony J McCaffery, Richard J Marsh
We use our recently developed computational model of energy flow in gas ensembles to study translation-to-internal energy conversion in an ensemble consisting of H2(0; 0) in a bath of H atoms. This mixture is found in plasmas of industrial importance and also in interstellar clouds. The storage of energy of relative motion as rovibrational energy of H2 represents a potential mechanism for cooling translation. This may have relevance in astrophysical contexts such as the post-recombination epoch of the early universe when hydrogenic species dominated and cooling was a precondition for the formation of structured objects. We find that conversion of translational motion to H2 vibration and rotation is fast and, in our closed system, is complete within around 100 cycles of ensemble collisions. Large amounts of energy become stored as H2 vibration and a tentative mechanism for this unequal energy distribution is suggested. The “structured dis-equilibrium” we observe is found to persist through many collision cycles. In contrast to the rapidity of excitation, the relaxation of H2(6; 10) in H is very slow and not complete after 105 collision cycles. The quasi-equilibrium modal temperatures of translation, rotation, and vibration are found to scale linearly with collision energy but at different rates. This may be useful in estimating the partitioning of energy within a given H + H2 ensemble.

History

Publication status

  • Published

Journal

Journal of Chemical Physics

ISSN

0021-9606

Publisher

American Institute of Physics

Issue

23

Volume

139

Page range

234310

Department affiliated with

  • Chemistry Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2017-12-01

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