The definition of reaction coordinates for reaction-path dynamics
- Computer Sciences Corporation, Seabrook, Maryland 20706 (USA)
- Molecular Science Research Center, Pacific Northwest Laboratory, Richland, Washington 99352 (USA)
- Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431 (USA)
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{sub 3}+{ital YZ}{r arrow}CX{sub 3} {ital Y}+{ital Z} with reaction paths having {ital C}{sub 3{ital v}} 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{sub 2}{r arrow}H{sub 2}+H, O+H{sub 2}{r arrow}OH+H, and CH{sub 3}+H{sub 2}{r arrow}CH{sub 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{sub 3}+H{sub 2} that should allow for more accurate calculations than the Cartesian system used for previous reaction-path calculations on this and other polyatomic systems.
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 5556575
- Journal Information:
- Journal of Chemical Physics; (USA), Journal Name: Journal of Chemical Physics; (USA) Vol. 94:12; ISSN JCPSA; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKYL RADICALS
CHEMICAL REACTION KINETICS
COORDINATES
ELEMENTS
ENERGY LEVELS
EXCITED STATES
HYDROGEN
KINETICS
METHYL RADICALS
NONMETALS
NORMAL-MODE ANALYSIS
OXYGEN
RADICALS
REACTION KINETICS
VIBRATIONAL STATES