Observation of a barrier and a double-potential curve in the<i>C</i>state of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">CO</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>molecule

The C state of ${\mathrm{CO}}^{+}$ has been studied using uv photoelectron spectroscopy. The spectrum was excited by a monochromatized He i${\mathrm{i}}_{\mathrm{\ensuremath{\alpha}}}$ 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 \AA{}. Moreover, the progression extends 0.09 eV above the dissociation limit and therefore a potential barrier must exist with a maximum around 2.3 \AA{}.