X-RAY PHOTOELECTRON-SPECTROSCOPY AND ABINITIO CI STUDY OF THE CORE AND VALENCE IONIZATION OF FORMAMIDE

High resolution X-ray photoelectron spectra have been recorded of the core and valence levels of the formamide molecule using monochromatised Al Kalpha radiation for the excitation of the spectra. Ab initio CI calculations of the binding energies and intensities have been carried out in order to interpret the experimental results and to provide additional information on the electronic structure. The core level shake-up spectra are found to be similar to those observed earlier of the CO molecule, acetaldehyde and acetone. In particular, the substitution of a hydrogen atom by methyl or amino groups tends to give rise to an additional shake-up line corresponding to the additional valence orbital of pi symmetry. The valence photoelectron spectrum reveals new structures compared to previous studies. This has enabled an assignment in terms of both single hole states and many-electron states and the study confirms that the orbital ordering in the outermost region should be given as 10a' (n) 2a'' (pi)1a'' (pi)9a' (sigma) in order of increasing binding energy. Ionisation from the 7a' (sigma) orbital at about 18 eV leads to two structures in the spectrum with almost equal intensity. The two strong photoelectron bands in the inner valence region are found to be composed of four- or five-component states, which implies a more or less complete breakdown of the orbital model in this region.