Complex structures in the calculated photoionization spectrum of CO in the 17–17.5 eV energy region

Abstract

Complicated spectral features appear in the CO photoionization spectra between 17 and 17.5 eV photon energy. In order to interpret these processes, we refine in the present paper our previous model [B. Leyh and G. Raşeev, Phys. Rev. A 34, 2920 (1986)] by introducing all the vibrational levels of the first three electronic states of CO+. This more accurate treatment leads to two major results. The resonances at 17.1 and 17.3 eV are complex resonances resulting from the interaction between the Rydberg series converging to the A 2Π and B 2Σ+ ionic states: they can no more be assigned simply to Rydberg states converging to CO+B 2Σ+. The intermediate experimental feature at 17.2 eV, missing in our previous calculation, is now present in the theoretical spectrum. Mainly, this feature, which we have called composite resonance, is a broadened (by the experimental resolution) superposition of Rydberg states converging to the A 2Π ν+=4 state. In this paper, we present and analyze the vibrationally resolved cross sections and asymmetry parameter for the X 2Σ+ν+=0–3 and A 2Π ν+=0–4 states. These theoretical results are compared to recent experimental data by Leyh et al. [Chem. Phys. 115, 243 (1987)] and by Hardis and co-workers (the preceeding paper).