Energy transfer, stabilization, and dissociation in collisions of helium with highly excited HO2

Charles R. Gallucci, George C Schatz

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

This paper considers application of the classical trajectory method to the determination of cross sections and rate constants for energy transfer, stabilization, and dissociation in collisions of He with highly excited HO2. The resulting rate constants are used to evaluate several models of the termolecular recombination kinetics in He + H + O2, such as the weak and strong collision models of stabilization. An ab initio potential energy surface is used for the HO2 molecule, and the He + HO2 intermolecular potential is approximated as a sum of pairs. Cross sections and rate constants are evaluated for two types of initial HO2* ensembles, one which is microcanonical for the HO2 vibrations but cold for rotation, and one which is microcanonical for both vibration and rotation. For both the rotationally cold and hot ensembles, the stabilization cross sections were found to decrease rapidly with internal energy Eint and increase rapidly with translational energy E0 above the dissociation threshold, with the cross sections always smaller for cold HO2* than for hot. This difference between cold and hot is interpreted in terms of the greater efficiency of R → T energy transfer for rotationally hot HO2*. For both H + O2 and OH + O dissociation, the cross sections increase rapidly with increasing Eint, with the rotationally cold cross sections generally much larger than rotationally hot. The stabilizing influence of centrifugal barriers was found to be important in determining the smaller rotationally hot cross sections. An analysis of stabilization and H + O2 dissociation rate constants indicates that dissociation is faster than stabilization for cold HO2*, but neither rate constant is more than a few percent of the gas kinetic rate constant. For hot HO2*, stabilization is much faster than dissociation, and the stabilization rate constant is 14-18% of gas kinetic. Roughly speaking, hot HO2* is pretty well approximated by the strong collision model (with an appropriate efficiency factor), while cold HO2* is better approximated by using the weak collision approximation. These results emphasize the importance of using accurate stabilization rate constant information in the kinetic modeling of termolecular recombination rates, and the potential importance of collision-induced dissociation in the recombination mechanism.

Original languageEnglish
Pages (from-to)2352-2358
Number of pages7
JournalJournal of Physical Chemistry
Volume86
Issue number13
Publication statusPublished - 1982

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Helium
Energy transfer
Rate constants
Stabilization
stabilization
energy transfer
helium
dissociation
collisions
cross sections
Kinetic theory of gases
kinetics
Potential energy surfaces
Kinetics
vibration
internal energy
gases
Trajectories
potential energy
trajectories

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Energy transfer, stabilization, and dissociation in collisions of helium with highly excited HO2. / Gallucci, Charles R.; Schatz, George C.

In: Journal of Physical Chemistry, Vol. 86, No. 13, 1982, p. 2352-2358.

Research output: Contribution to journalArticle

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abstract = "This paper considers application of the classical trajectory method to the determination of cross sections and rate constants for energy transfer, stabilization, and dissociation in collisions of He with highly excited HO2. The resulting rate constants are used to evaluate several models of the termolecular recombination kinetics in He + H + O2, such as the weak and strong collision models of stabilization. An ab initio potential energy surface is used for the HO2 molecule, and the He + HO2 intermolecular potential is approximated as a sum of pairs. Cross sections and rate constants are evaluated for two types of initial HO2* ensembles, one which is microcanonical for the HO2 vibrations but cold for rotation, and one which is microcanonical for both vibration and rotation. For both the rotationally cold and hot ensembles, the stabilization cross sections were found to decrease rapidly with internal energy Eint and increase rapidly with translational energy E0 above the dissociation threshold, with the cross sections always smaller for cold HO2* than for hot. This difference between cold and hot is interpreted in terms of the greater efficiency of R → T energy transfer for rotationally hot HO2*. For both H + O2 and OH + O dissociation, the cross sections increase rapidly with increasing Eint, with the rotationally cold cross sections generally much larger than rotationally hot. The stabilizing influence of centrifugal barriers was found to be important in determining the smaller rotationally hot cross sections. An analysis of stabilization and H + O2 dissociation rate constants indicates that dissociation is faster than stabilization for cold HO2*, but neither rate constant is more than a few percent of the gas kinetic rate constant. For hot HO2*, stabilization is much faster than dissociation, and the stabilization rate constant is 14-18{\%} of gas kinetic. Roughly speaking, hot HO2* is pretty well approximated by the strong collision model (with an appropriate efficiency factor), while cold HO2* is better approximated by using the weak collision approximation. These results emphasize the importance of using accurate stabilization rate constant information in the kinetic modeling of termolecular recombination rates, and the potential importance of collision-induced dissociation in the recombination mechanism.",
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