Effects of relaxation and hyperconjugation on shake-up transitions in X-ray excited photoelectron spectra of some small carbonyl compounds

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 π-type orbitals on the CH 3 groups of acetaldehyde and acetone is responsible for the large differences found in the core shake-up spectra between these molecules and formaldehyde. Owing to the redistribution of charge upon O1s ionization, the energy ordering of the CO and the CH 3 π-type orbitals in acetaldehyde is reversed, compared with the neutral molecule. The ionization from the 6a 1 σ(CO) orbital in acetone gives rise to a clearly observable vibrational progression whereas the corresponding orbital in formaldehyde is structureless. This indicates a substantial stabilization of the bonds due to the methyl substitution.