Theoretical and experimental studies of the valence photoemission spectrum of propionitrile

The valence photoemission spectrum of propionitrile for all outer and inner valence levels up to the ionization energy of 23 eV is calculated by ab initio third-order algebraic diagrammatic construction (ADC(3)) Green's function method. The spectrum is also measured by high resolution He I photoelectron spectroscopy to resolve additional spectral features mainly due to the vibronic excitations. The present (ADC(3)) calculation provides a fairly good description of the vertical-electronic ionization spectral features of the valence PES spectrum of propionitrile. From the ionization threshold up to and including the 8a' ionization, the ionization phenomena appear essentially as one-particle processes. For 11a' and 10a' ionization, the hole mixing occurs between this pair of ionization of the same symmetry, although the hole mixing is not so significant as ill molecules containing several CN groups. For the innermost 7a' band, the breakdown of the one-electron picture occurs.