6533b872fe1ef96bd12d2d42

RESEARCH PRODUCT

Theoretical study of electronically excited cis- and trans-glyoxal

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Abstract The equation-of-motion coupled cluster method for excitation energies in the singles and doubles approximation (EOMEE-CCSD) is applied to an investigation of the structure and harmonic frequencies of planar conformers of glyoxal in their first excited singlet states. For the trans-isomer, agreement between calculated harmonic frequencies and observed fundamentals is generally satisfactory, although the theoretical values are slightly more than 10% too high for the carbonyl stretching modes. Parallel calculations of the corresponding ground state properties allow for an empirical prediction of the excited state frequencies in which calculated differences in normal-mode frequencies are simply added to the ground state fundamentals. Estimates made by this procedure are within 20 cm−1 of the actual positions for all modes except the carbonyl stretches and the in-phase CH stretch, for which the experimental assignment is uncertain. For the cis isomer, the results presented here should be useful in analysis of future experiments. Significantly, the experimentally inferred dipole moment of 4.8 Debye for this isomer appears to be in error.