Photoionization of CO Using R-matrix Theory

Abstract

Abstract CO molecules possess three valence orbitals, 5σ, 1π, and 4σ in the ground state X 1Σ+. These orbitals show intense absorptions due to the presence of Rydberg transitions, which exhibit sharp features in the photoionization curve. The autoionization to these orbitals causes a sudden increase in the photoionization cross section. Shape resonances are also detected in valence shell photoionization. Our aim is to resolve the autoionizing Rydberg structures of CO and study their effect on the photoionization cross section, assigning the correct symmetry responsible for the resonances occurring in valence state photoionization. For the present study we have employed the UK R-matrix formalism. In this article, we report a valence state photoionization cross section for 5σ, 1π, and 4σ orbitals of CO, which produces X 2Σ+, A 2Π, and B 2Σ+ ionic states and compared it with existing results, wherever available. The photoionization rate coefficients for these valence states are also calculated and the effect of Rydberg transitions on the rate is discussed. We have observed a major contribution of the Rydberg series coming from the ground state of CO and a shape resonance was found for the B 2Σ+ ionic state. This is the first report of high-resolution valence state photoionization of CO. The near threshold features in the photoionization curve (which are absent in previous studies) are produced with high precision. We have reported a detailed study of the photoionization cross section for three valence orbitals of CO in the vicinity of complex autoionizing Rydberg series transitions.