A unimolecular reaction ABC→A+B+C involving three product molecules and a single transition state. Photodissociation of glyoxal

HCOHCO→H 2+CO+CO

Yoshihiro Osamura, Henry F. Schaefer, Michel Dupuis, William A. Lester

Research output: Contribution to journalArticle

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Abstract

Following an earlier proposal [Y. Osamura and H. F. Schaefer, J. Chem. Phys. 74, 4576 (1981)], the unimolecular reaction HCOHCO→H2 + CO + CO has been examined via nonempirical molecular electronic structure theory. Specifically, the constrained symmetric (point group C2v) transition state for this ABC→A + B + C reaction has been located at several levels of self-consistent-field (SCF) theory. Four different basis sets of contracted Gaussian functions were used: an STO-3G minimum basis, the small split valence 3-21G basis, the standard C(9s 5p/4s 2p) double zeta (DZ) set, and a double zeta plus polarization (DZ + P) basis. Vibrational analyses of the four stationary point structures (all of which are geometrically similar) yield a remarkable variety of results. The STO-3G stationary point has three imaginary vibrational frequencies, 3-21G has one imaginary frequency (and thus is a genuine transition state), while the DZ and DZ + P structures yield two imaginary vibrational frequencies. For the latter two cases, one of the two imaginary vibrations is a very small bending frequency, while the larger frequency clearly connects glyoxal with the three products H2 + CO + CO. This suggests the existence of a slightly nonplanar true transition state. To our knowledge such a unimolecular transition state is without precedent. Configuration interaction (CI) suggests that the barrier for this ABC→A + B + C reaction is competitive with that for HCOHCO→H2CO + CO.

Original languageEnglish
Pages (from-to)5828-5836
Number of pages9
JournalJournal of Chemical Physics
Volume75
Issue number12
Publication statusPublished - 1981

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Glyoxal
Photodissociation
Carbon Monoxide
photodissociation
Molecules
products
molecules
Vibrational spectra
Point groups
Molecular electronics
molecular electronics
Molecular structure
configuration interaction
Electronic structure
self consistent fields
proposals
Polarization
electronic structure
valence
vibration

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

A unimolecular reaction ABC→A+B+C involving three product molecules and a single transition state. Photodissociation of glyoxal : HCOHCO→H 2+CO+CO. / Osamura, Yoshihiro; Schaefer, Henry F.; Dupuis, Michel; Lester, William A.

In: Journal of Chemical Physics, Vol. 75, No. 12, 1981, p. 5828-5836.

Research output: Contribution to journalArticle

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