Doubly charged valence states of formaldehyde, acetaldehyde, acetone, and formamide studied by means of photon excited Auger electron spectroscopy and ab initio calculations

The doubly ionized states in formaldehyde, acetaldehyde, acetone, and formamide have been studied by means of x-ray excited core (C1s, N1s, O1s)-valence-valence Auger electron spectroscopy. Assignments of the spectra have been made using ab initio Hartree-Fock, Green's function, and configuration interaction (CI) calculations. A molecular orbital analysis has been carried out for the high kinetic energy part of the spectra. The breakdown of the single particle picture is found to be important over a large energy interval in the spectra. The results obtained illustrate the usefulness of Auger electron spectroscopy in characterizing the doubly ionized states even in the case of large molecular systems. The first double ionization energies for the four molecules presented have been determined to be 33.8, 30.3, 28.0, and 30 eV, respectively.