A theoretical photoelectron spectrum of cyanogen by a Green-function method

A Green-function method is used to calculate a photoelectron spectrum of C₂N₂ including the vibrational structure. The calculated spectrum and the experimental spectrum are in good agreement. It is found that the second band is due to ionization of the 5a_g electron. In addition predictions are made concerning the ionization potentials and vibrational structure of low lying bands which have not yet been measured. The ionization potentials obtained in the different orders of the perturbation expansion of the self-energy part are discussed as well as the influence of many-body effects on the vibrational coupling constants.