The ndπ 1Π and ndδ 1Δ Rydberg states of CO and their interactions with 1Π valence states

Extensive vacuum-ultraviolet Fourier-transform photoabsorption spectra of isotopic CO, recorded at the SOLEIL synchrotron, have been reanalyzed. In particular, a number of weak bands in the 100 000-109 000-cm-1 region are shown to represent transitions to the previously undocumented 3, 4dδ1Δ(v = 0, 1) and 4, 5dπ1Π(v = 0, 1) levels of Rydberg states converging on the X2Σ+ state of the CO+ ion. The analysis of their local perturbations, together with the observation of further weak transitions, leads to the spectroscopic characterization of a significant number of previously unknown 1Π valence-state levels and determination of the associated Rydberg-valence level-interaction parameters. These results will inform the optimization of future coupled-channels Schrödinger-equation models of CO 1Π-manifold spectroscopy and predissociation.