C2 formation in vibrationally excited CO

The formation of C2 has been observed following the vibrational excitation of CO. Emission from four different electronic states has been observed: Swan bands (d3Πg → a3Πu); Deslandres-dʹAzambuja bands (C1Πg → A1Πu); Fox-Herzberg bands (e3Πg → a3Πu) and a Mulliken band (D 1Σu+ → X 1Σg+). The vibrational populations in the electronic states have been determined from low-resolution emission spectra. The time-resolved behaviour of the emissions indicates that the upper states close to the dissociation limit are populated first, while the lower electronic states are populated following a time delay. Formation mechanisms are discussed.