Effects of relaxation and hyperconjugation on shake-up transitions in X-ray excited photoelectron spectra of some small carbonyl compounds.
M.P. Keane, S. Lunell, A.Naves de Brito, M. Carlsson Göthe, S. Svensson, B. Wannberg and L. Karlsson.
Abstract: The C1s and O1s core shake-up and HeII excited valence photoelectron spectra of formaldehyde, acetaldehyde and acetone have been studied experimentally and by INDO-CI calculations. It is found that the presence of the π type orbitals on the CH3 groups of acetaldehyde and acetone is responsible for the large differences found in the core shake-up spectra between these molecules and formaldehyde. Due to the redistribution of charge in the oxygen acetaldehyde and acetone core ionised systems, tire energy ordering between the C=O π orbital and the CH3 1b1 π type orbital is reversed compared to the neutral molecules. The ionization from the 6a1 σ(C-O) orbital in acetone gives rise to a clearly observable vibrational progression whereas the corresponding orbital on formaldehyde is structureless. This indicates a substantial stabilization of the bonds due to the methyl substitution.
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