Unimolecular dissociation of the CH 3OCO radical : An intermediate in the CH 3O + CO reaction

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Laura R. McCunn
  • Maria J. Krisch
  • Laurie J. Butler
  • Jieh-Wen Tsung
  • Jim J. Lin

Detail(s)

Original languageEnglish
Pages (from-to)1625-1634
Journal / PublicationJournal of Physical Chemistry A
Volume110
Issue number4
Publication statusPublished - 2 Feb 2006
Externally publishedYes

Abstract

This work investigates the unimolecular dissociation of the methoxycarbonyl, CH 3OCO, radical. Photolysis of methyl chloroformate at 193 nm produces nascent CH 3OCO radicals with a distribution of internal energies, determined by the velocities of the momentum-matched Cl atoms, that spans the theoretically predicted barriers to the CH 3O + CO and CH 3 + CO 2 product channels. Both electronic ground- and excited-state radicals undergo competitive dissociation to both product channels. The experimental product branching to CH 3 + CO 2 from the ground-state radical, about 70%, is orders of magnitude larger than Rice-Ramsperger-Kassel-Marcus (RRKM)-predicted branching, suggesting that previously calculated barriers to the CH 3OCO → CH 3 + CO 2 reaction are dramatically in error. Our electronic structure calculations reveal that the cis conformer of the transition state leading to the CH 3 + CO 2 product channel has a much lower barrier than the trans transition state. RRKM calculations using this cis transition state give product branching in agreement with the experimental branching. The data also suggest that our experiments produce a low-lying excited state of the CH 3OCO radical and give an upper limit to its adiabatic excitation energy of 55 kcal/mol. © 2006 American Chemical Society.

Citation Format(s)

Unimolecular dissociation of the CH 3OCO radical : An intermediate in the CH 3O + CO reaction. / McCunn, Laura R.; Lau, Kai-Chung; Krisch, Maria J. et al.

In: Journal of Physical Chemistry A, Vol. 110, No. 4, 02.02.2006, p. 1625-1634.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review