Vibrational excitation in C 1s and O 1s photoionization of CO

The C 1s and O 1s photoelectron spectra of the CO molecule have been measured with high resolution. The vibrational spacing of the state (226 +/- 7 meV) is significantly lower than in the state and in the molecular ground state. Compared to the ground-state equilibrium C - O distance of 1.128 Å, we extract from the analysis of the Franck - Condon factors bond lengths of 1.079(2) Å and 1.167(4) Å for the C 1s and O 1s core-ionized states, respectively.