Equilibrium structure of CO+ from its millimeter wave spectrum. Breakdown of the Born–Oppenheimer approximation

Microwave transitions of CO+ have been observed for several isotopic substitutions, in different vibrational states: 12C 16O+(v=0,1,2,3,4), 12C 18O+(v=0,1), 13C 16O+(v=0,1), and 13C 18O+(v=0). All measured frequencies are fitted together in a one step procedure, leading to a precise determination of molecular constants and equilibrium structure. The vibrational dependence of the 13C hyperfine structure is pointed out, and the ΔC01 and ΔO01 mass scaling coefficients are determined.