A theoretical study of the X-ray photoelectron ionization energies of related carbonyl compounds: Formaldehyde, acetaldehyde, and acetone

Abstract

The C1s and O1s ionization energies are calculated for formaldehyde, acetaldehyde, and acetone, and the calculated results are compared to the experimental X-ray photoelectron spectra. The theoretical techniques employed involve the ΔSCF method followed by a perturbative CI treatment to capture electron correlation effects. The calculated C1s and O1s ionization energies including electron correlation are within ∼0.5 eV of the experimental values. Both Mulliken atomic populations and electron density difference plots indicate a shift in electron density from neighboring atoms toward the ionized atom which demonstrates a symbiotic role in the screening process. The effects of π-donor substituents, e.g., methyl groups, on the O1s ionization energy for the C=O group are discussed and found to agree with the experimental trend of producing a decrease in ionization energy with increasing methyl substitution. Finally, the fragmentation processes of acetone for excitations involving C1s, O1s → valence, and O1s → Rydberg transitions are discussed. The excitation energies for these types of transitions are found to agree reasonably well with the corresponding experimental values, and the fragmentation patterns can be rationalized in terms of changes in overlap populations for the C1s(C=O) → π* and O1s → 3s excitations. © 1992 American Chemical Society.