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 language | English |
|---|---|
| Pages (from-to) | 5828-5836 |
| Number of pages | 9 |
| Journal | Journal of Chemical Physics |
| Volume | 75 |
| Issue number | 12 |
| Publication status | Published - 1981 |
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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 journal › Article
}
TY - JOUR
T1 - A unimolecular reaction ABC→A+B+C involving three product molecules and a single transition state. Photodissociation of glyoxal
T2 - HCOHCO→H 2+CO+CO
AU - Osamura, Yoshihiro
AU - Schaefer, Henry F.
AU - Dupuis, Michel
AU - Lester, William A.
PY - 1981
Y1 - 1981
N2 - 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.
AB - 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.
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M3 - Article
VL - 75
SP - 5828
EP - 5836
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 12
ER -