EVIDENCE FOR A PARTIAL BREAKDOWN OF THE MOLECULAR-ORBITAL PICTURE IN THE IONIZATION SPECTRA OF LARGE SATURATED-HYDROCARBONS

The x-ray photoionization spectra of large saturated hydrocarbons have been investigated by means of one-particle Green's function calculati ons. These spectra saturate overall rather quickly to their asymptotic form with increasing system size. The results obtained indicate a sev ere breakdown of the molecular orbital picture of ionization above a b inding energy threshold of about 23 eV, for n-alkane chains ranging fr om n-propane to n-nonane, or cycloalkane compounds such as cyclobutane , cyclopentane, and cyclohexane. in spite of the fast multiplication o f satellite solutions, shake-up lines remain confined above that thres hold, as a result of the delocalization properties of one-electron can onical states. The ring closure is shown to emphasize the dispersion o f photoionization intensity into satellites. Conformational changes, o n the other hand, have only marginal effects on the convoluted correla tion bands. (C) 1996 American Institute of Physics.