The definition of reaction coordinates for reaction-path dynamics

Gregory A. Natanson, Bruce C. Garrett, Thanh N. Truong, Tomi Joseph, Donald G. Truhlar

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138 Scopus citations


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 CX3 + YZ→CX3Y+Z with reaction paths having C3v symmetry. We then present numerical comparisons of the differences in harmonic reaction-path frequencies for various coordinate choices for three such systems, namely, H + H2 → H2 + H, O + H2 → OH + H, and CH3 + H 2 → CH4 + 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 CH3 + H2 that should allow for more accurate calculations than the Cartesian system used for previous reaction-path calculations on this and other polyatomic systems.

Original languageEnglish (US)
Pages (from-to)7875-7892
Number of pages18
JournalThe Journal of chemical physics
Issue number12
StatePublished - 1991


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