Calculated barriers to abstraction and exchange for CH4+H
10.1063/1.439778
Crossref journal-article
AIP Publishing
The Journal of Chemical Physics (317)
Abstract

Saddle point geometries and barrier heights have been calculated for abstraction and exchange in CH4+H using POL–CI wave functions with basis sets up to triple zeta valence with double zeta polarization on C and single zeta polarization on H. The saddle point for the abstraction reaction is found to have C3v symmetry (abstraction collinear with a CH bond). The calculated saddle point geometry is closer to products (CH3+H2) than to reactants (CH4+H) and has the CH and HH bonds stretched by 0.38 Å (35%) and 0.18 Å (24%), respectively. The CH bond lengths of the remaining three CH bonds change only very slightly (<0.01 Å) during the reaction, while at the saddle point each methyl CH bond is ∼12.4° out of the plane perpendicular to the C–––H–––H axis and containing the C atom (19.47° for CH4 and 0° for CH3). The calculated barrier height is 15.9 kcal/mole (using the largest basis set). Comparison to comparable calculations for H3 indicates an error of ∼2.4 kcal/mole due to the POL–CI approximation leading to 13.5 kcal/mole as the best estimate of the barrier height. The saddle point for the exchange reaction has a trigonal bipyramidal geometry. The calculated saddle point geometry has rCH=1.41 Å (equal CH bond lengths), while the methyl CH bond lengths change only slightly (<0.01 Å) during the reaction. The calculated barrier height is 36.9 kcal/mole (for the largest basis set). Using the same estimate for the error due to the POL–CI approximation as for the abstraction reaction leads to 34.5 kcal/mole as the best estimate of the barrier height for the exchange reaction.

Bibliography

Walch, S. P. (1980). Calculated barriers to abstraction and exchange for CH4+H. The Journal of Chemical Physics, 72(9), 4932–4940.

Authors 1
  1. Stephen P. Walch (first)
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Dates
Type When
Created 22 years, 6 months ago (Feb. 28, 2003, 3 p.m.)
Deposited 1 year, 6 months ago (Feb. 9, 2024, 4:14 p.m.)
Indexed 1 year, 6 months ago (Feb. 11, 2024, 7:26 a.m.)
Issued 45 years, 4 months ago (May 1, 1980)
Published 45 years, 4 months ago (May 1, 1980)
Published Print 45 years, 4 months ago (May 1, 1980)
Funders 0

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@article{Walch_1980, title={Calculated barriers to abstraction and exchange for CH4+H}, volume={72}, ISSN={1089-7690}, url={http://dx.doi.org/10.1063/1.439778}, DOI={10.1063/1.439778}, number={9}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Walch, Stephen P.}, year={1980}, month=may, pages={4932–4940} }