### Abstract

Canonical variational transition-state theory (CVTST) is used to compare H + CH_{3} and H + diamond {111} association rate constants calculated from the Brenner empirical potential function and molecular anharmonic potentials written with switching (MAPS) functions. Previous work [J. Am. Chem. Soc. 1987, 109, 2916; J. Chem. Phys. 1994, 101, 2476] has shown that the MAPS functions, derived from ab initio calculations, give rate constants in agreement with experiment. For the 300-2000 K temperature range, the Brenner potential function gives CVTST H + CH_{3} and H + diamond {111} association rate constants which are 159-30 and 49-7 times smaller, respectively, than the values from the MAPS functions. An analysis of the Brenner potential function shows that it inaccurately represents the intermediate and long-range H - C association potential, which controls the structure of the variational transition state and the CVTST rate constant. The MAPS functions give H + CH_{3} and H + diamond {111} variational transition states with similar properties. Angular momentum and external rotation have no effect on the H + diamond {111} association rate constant, which makes it approximately an order-of-magnitude smaller than that for H + CH_{3} association.

Original language | English |
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Pages (from-to) | 1761-1766 |

Number of pages | 6 |

Journal | Journal of physical chemistry |

Volume | 100 |

Issue number | 5 |

DOIs | |

State | Published - Feb 1 1996 |

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## Cite this

*Journal of physical chemistry*,

*100*(5), 1761-1766. https://doi.org/10.1021/jp951693m