Microscopic reaction rates in ion/molecule reactions: Effects of uncoupled modes

Smith, S.C., McEwan, M.J. and Gilbert, R.G. (1989) Microscopic reaction rates in ion/molecule reactions: Effects of uncoupled modes. Journal of Physical Chemistry, 93 25: 8142-8148. doi:10.1021/j100362a005

Author Smith, S.C.
McEwan, M.J.
Gilbert, R.G.
Title Microscopic reaction rates in ion/molecule reactions: Effects of uncoupled modes
Journal name Journal of Physical Chemistry   Check publisher's open access policy
ISSN 0022-3654
Publication date 1989-12
Sub-type Article (original research)
DOI 10.1021/j100362a005
Volume 93
Issue 25
Start page 8142
End page 8148
Total pages 7
Place of publication Washington, DC, United States
Publisher American Chemical Society
Language eng
Abstract A new expression for microscopic rate coefficients is deduced for reactions with a simple-fission transition state wherein certain modes become uncoupled from the reaction coordinate at long range. The new expression, which involves a modification to the standard RRKM result, takes account of this uncoupling, thereby incorporating features inherent in capture models. Application to the case of ion/dipole reactions is considered, where only the hindered dipole rotation is coupled with the reaction coordinate at large separations. When implemented variationally, the new expression is shown analytically to produce in the high-pressure limit a capture-rate expression equivalent to that of Chesnavich, Su, and Bowers. This provides an important conceptual connection between the RRKM approach to ion/dipole reactions, which includes all degrees of freedom and may be applied at any pressure, and that of capture theories (which apply only in the high-pressure limit) in which only those degrees of freedom that are coupled with the reaction coordinate at long range are included. Neglect of uncoupling in conventional RRKM theory can lead to an overestimate (typically by ca. 50%) of ion/molecule rate coefficients at high pressures; the error is however negligible at low pressures.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemistry and Molecular Biosciences
Centre for Nutrition and Food Sciences Publications
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Created: Mon, 07 Mar 2011, 15:57:41 EST