Threshold photoelectron spectroscopy of benzene up to 26.5 eV

The threshold photoelectron spectrum of benzene has been recorded up to 26.5 eV photon energy under high-resolution conditions using synchrotron radiation and employing the penetrating-field threshold electron collection method. By means of a direct comparative study with a recent HeI photoelectron spectrum of benzene of equally high resolution, numerous autoionization effects are observed in the formation of the ionic band systems of benzene in the outer valence ionization region in the threshold photoelectron spectrum. The Rydberg states responsible for these effects are identified. Autoionization does not appear to play a role in the formation of the two lowest-energy, inner-valence bands of C6H6+.Key words: threshold photoelectron spectroscopy, photoelectron spectroscopy, benzene, ionization, autoionization, Rydberg states.