Carbon 1s photoelectron spectroscopy of six-membered cyclic hydrocarbons

The carbon 1s photoelectron spectra of cyclohexane, cyclohexene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene have been measured. These have been analyzed in terms of a theoretical model of the vibronic structure that includes the effects of the changes in equilibrium geometry that accompany core ionization as well as those of vibronic coupling in the core-ionized molecule. This theoretical approach gives an excellent description of the vibronic structure and makes it possible to identify the contributions of the inequivalent carbon atoms to the spectra. The carbon 1s ionization energies are reported and used in the analysis of photoelectron spectra of adsorbed molecules.