AB-INITIO CI INVESTIGATION OF VALENCE PHOTOELECTRON-SPECTRA OF CONJUGATED HYDROCARBONS

The valence photoelectron spectra of unsaturated hydrocarbons of increasing complexity, ethylene and all-trans butadiene, hexatriene, octatetraene and pentadecaene, have been calculated at the ab initio CI level. The analysis of the influence of the many-body effects on the spectral features and their evolution along the series can be the basis upon which to anticipate the spectral behaviour of longer chain molecules with alternating double bonds. The capability of the 2h-1p CI and 2h-1v CI schemes to give a qualitative description both of the outer and the inner valence structures has been proved, pointing out the usefulness of the simpler scheme, i.e. 2h-1v CI, for investigating the whole valence spectrum of all molecules considered.