## Abstract

We present equations for generalized-normal-mode vibrational frequencies in reaction-path calculations based on various sets of coordinates for describing the internal motions of the system in the vicinity of a reaction path. We consider two special cases in detail as examples, in particular three-dimensional atom-diatom collisions with collinear steepest descent paths and reactions of the form CX_{3} + YZ→CX_{3}Y+Z with reaction paths having C_{3v} symmetry. We then present numerical comparisons of the differences in harmonic reaction-path frequencies for various coordinate choices for three such systems, namely, H + H_{2} → H_{2} + H, O + H_{2} → OH + H, and CH_{3} + H _{2} → CH_{4} + H. We test the importance of the differences in the harmonic frequencies for dynamics calculations by using them to compute thermal rate constants using variational transition state theory with semiclassical ground-state tunneling corrections. We present a new coordinate system for the reaction CH_{3} + H_{2} that should allow for more accurate calculations than the Cartesian system used for previous reaction-path calculations on this and other polyatomic systems.

Original language | English (US) |
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Pages (from-to) | 7875-7892 |

Number of pages | 18 |

Journal | The Journal of chemical physics |

Volume | 94 |

Issue number | 12 |

DOIs | |

State | Published - 1991 |