Photoelectron (He(I), He(II) and X-ray) spectroscopy of γ-pyrone and its related sulphur derivatives: valence and core ionization energies and shake-up satellites

Abstract

The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one ( 1), 4H-thiopyran-4-one ( 2), 4H-pyran-4-thione ( 3) and 4H-thiopyran-4-thione ( 4) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n X (σ), 3 b 1 (π), 1 a 2(π) for 1, 2 and 4; and 3 b 1(π), n X(σ) and 1 a 2(π) for 3. The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3 b 1 (π) → 4 b 1(π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.