A theoretical analysis of the CH{sub 3} + H reaction [electronic resource] : isotope effects, the high pressure limit, and transition state recrossing

Published: Washington, D.C. : United States. Dept. of Energy, 2001.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description: vp : digital, PDF file
Additional Creators: Argonne National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary

The reaction of methyl radicals with hydrogen atoms is studied with a combination of ab initio quantum chemistry, variational transition state theory, and classical trajectory simulations. The interaction between the two radicals, including the umbrella mode of the methyl radical, is examined at the CAS+1+2 level using an augmented correlation consistent polarized valence triple zeta basis set. The implementation of an analytic representation of the ab initio data within variable reaction coordinate transition state theory yields predictions for the zero-pressure limit isotopic exchange rate constants that are about 15% greater than the available experimental data. Trajectory simulations indicate that the transition state recrossing factor for the capture process is 0.90, essentially independent of temperature and isotope. The dynamically corrected theoretical prediction for the CH₃ + H high pressure rate coefficient is well reproduced by the expression 1.32 x 10⁻¹°T{sup 0.153}exp(-15.1/RT) cm³molecule⁻¹s⁻¹, where R = 1.987 cal mole⁻¹ K⁻¹, for temperatures between 200 and 2400 K. This prediction is in good agreement with the converted experimental data for all but the one measurement at 200 K. Calculations for the triplet abstraction channel suggest that it is unimportant. Methyl umbrella mode variations have surprisingly little effect on the predicted rate coefficients.

Report Numbers

E 1.99:anl/chm/cp-106499
anl/chm/cp-106499

Subject(s)

Hydrogen

Other Subject(s)

Note

Published through SciTech Connect.
12/20/2001.
"anl/chm/cp-106499"
29th International Symposium on Combustion, Sapporo (JP), 07/21/2002--07/26/2002.
Harding, L.; Klippenstein, S. J.; Georgievskii, Y.

Funding Information

W-31-109-ENG-38

View MARC record | catkey: 14391084