Vibronic structure and photoelectron angular distribution in the photoelectron spectrum of ICN.

The valence shell photoelectron spectrum of ICN has been simulated using the equation-of-motion coupled-cluster method to calculate the ionization energies and the norms of the Dyson orbitals to describe the intensity of the photoelectron bands. The simulated spectrum not only reproduces the position and intensity of the four main bands observed in the experimental photoelectron spectrum, but the vibronic structure present in the individual photoelectron bands is also reproduced to a reasonable extent. The agreement between the experimental and simulated vibronic structures at higher energies corresponding to the à and B ̃ states is particularly noteworthy. Additionally, the photoionization cross section and asymmetry parameter have been calculated for the ionization of four outermost valence molecular orbitals in the photon energy range of 0-50 eV. The computed asymmetry parameters are found to provide a qualitative description of the corresponding experimental measurements. The shape-resonance seen in the experimental asymmetry parameters and the trends seen in the calculated cross section for the four ionization channels have been explained by the partial wave analysis of the contribution of the individual angular momentum channels to the photoelectron.