The C state of ${\mathrm{CO}}^{+}$ has been studied using uv photoelectron spectroscopy. The spectrum was excited by a monochromatized He i${\mathrm{i}}_{\mathrm{\alpha }}$ electron cyclotron resonance source. The vibrational progression in the C state has earlier been obesrved up to v=6, and an anomalous anharmonicity has been inferred. In the present spectrum the progression has been followed up to v=11, and the progression can be described as originating from two nearly harmonic potentials. A perturbation is thus found for the C state at an internuclear distance of about 1.4 Å. Moreover, the progression extends 0.09 eV above the dissociation limit and therefore a potential barrier must exist with a maximum around 2.3 Å.

• Received 26 November 1990

DOI:https://doi.org/10.1103/PhysRevA.44.R17