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Application of unimolecular reaction rate theory for highly flexible transition states to the dissociation of CH2CO into CH2 and CO. II. Photofragment excitation spectra for vibrationally-excited fragments

Klippenstein, Stephen J. and Marcus, R. A. (1990) Application of unimolecular reaction rate theory for highly flexible transition states to the dissociation of CH2CO into CH2 and CO. II. Photofragment excitation spectra for vibrationally-excited fragments. Journal of Chemical Physics, 93 (4). pp. 2418-2424. ISSN 0021-9606. http://resolver.caltech.edu/CaltechAUTHORS:KLIjcp90

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Abstract

Results on vibrationally-excited ketene photofragment excitation (PHOFEX) spectra of Moore and co-workers are interpreted in terms of a previously described variational implementation of Rice–Ramsberger–Kassel–Marcus (RRKM) theory. At subvibrational excitations, the predictions of this theory reduce to those of phase space theory (PST). However, for excess energies just above the threshold of excitation of a particular vibrational mode of the products, the present theory predicts a significantly greater probability for vibrational excitation, compared with PST, in closer agreement with the experimental results, and predicts an energy dependence of the PHOFEX spectrum that is closer to the observed one. A key feature, to which the present calculations lead, is a two-transition state (TS) description for each vibrational excitation of the products, the PST TS region dominating at the threshold for that excitation and an inner TS region dominating at somewhat higher (~200 cm^−1) energies. The behavior contrasts partly with that of the unimolecular dissociation rate constant kEJ (except at the threshold for kEJ), because of the different focus of the two types of measurements. The theory provides a consistent interpretation of both properties.


Item Type:Article
Additional Information:Copyright © 1990 American Institute of Physics. Received 27 December 1989; accepted 7 May 1990. It is a pleasure to acknowledge the support of this research by the National Science Foundation. The authors would also like to thank W.H. Green, Jr., A.J. Mahoney, C.-k. Cheng, and C.B. Moore, for making the results of their photofragment excitation spectra available to us prior to publication, and for their collaboration in the comparison of the experimental and theoretical photofragment excitation spectra. Arthur Amos Noyes Laboratory of Chemical Physics, Contribution No. 8095.
Subject Keywords:CHEMICAL REACTION KINETICS, MOLECULAR FRAGMENTS, INTERNAL ENERGY, VIBRATIONAL STATES, EXCITATION, DISSOCIATION, KETENES, METHYLENE RADICALS, CARBON MONOXIDE, CHEMICAL REACTION YIELD, ENERGY−LEVEL DENSITY
Record Number:CaltechAUTHORS:KLIjcp90
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:KLIjcp90
Alternative URL:http://dx.doi.org/10.1063/1.459023
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10290
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:22 Apr 2008
Last Modified:26 Dec 2012 09:58

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