Theoretical Study of the Low-Energy Photoionization of Large Molecules: Benzene

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Abstract
In this paper we use a linear combination of phase‐shifted atomic continuum factions to represent the unbound orbitals of large molecules. These functions take into account the interference arising from phase coherence between atomic centers with finite internuclear separations, an important effect at low energies. The effect of vibrations and configuration interaction on oscillator strengths calculated from these wavefunctions is discussed. A significant rounding (in energy) of the ionization threshold is seen to be caused by vibrational effects, and it is suggested that configuration interaction in large molecules may result in radiationless decay without ionization even when the molecules are excited to a continuum state. The results of sample calculations pertaining to benzene are presented in the form of differential oscillator strength curves in which interference effects are either included or neglected. Existing experiments give some support to the results of these calculations, but there are important discrepancies between calculation and some of the observations.