## Abstract

Statistical theory is used to calculate the F^{-} + CH_{3}Cl → FCH_{3}+ Cl^{-} rate constant versus relative translational energy E(re1) and CH_{3}Cl temperature. The calculations are performed on a potential energy surface derived from MP2 and QCISD(T) ab initio calculations with the 6-311++G(2df,2pd) basis set. At best, statistical theory only qualitatively reproduces the dependence of the experimental rate constant on translational energy and temperature. Using the height of the central barrier with respect to the pre-reaction complex as an adjustable parameter, the experimental rate constant at E(re1) = 0.9 kcat/mol and T = 296 K may be fit by statistical theory with a central barrier 3 kcal/mol higher than that determined from the QCISD(T) calculation. The calculation of the S(N)2 rate constant is insensitive to whether the unified statistical model or standard RRKM branching ratio expression is used. Also, including an harmonicity for the F^{-} - - -CH_{3}Cl complex does not affect the calculated rate constant. A comparison of statistical rate constants with parametrized trajectory capture rate constants suggests that, during the entrance channel capture dynamics, the F^{-} + CH_{3}Cl relative translation and CH_{3}Cl rotation motions are strongly and weakly coupled at low and high E(re1), respectively.

Original language | English |
---|---|

Pages (from-to) | 3093-3102 |

Number of pages | 10 |

Journal | Journal of the American Chemical Society |

Volume | 119 |

Issue number | 13 |

DOIs | |

State | Published - Apr 2 1997 |