Multiphoton processes of CO at 230 nm

High resolution kinetic energy release spectra were obtained for C+ and O+ from CO multiphoton ionization followed by dissociation of CO+. The excitation was through the CO (B (1)Sigma(+)) state via resonant two-photon excitation around 230 nm. A total of 5 and 6 photons are found to contribute to the production of carbon and oxygen cations. DC slice and Megapixel ion imaging techniques were used to acquire high quality images. Major features in both O+ and C+ spectra are assigned to the dissociation of some specific vibrational levels of CO+(X (2)Sigma(+)). The angular distributions of C+ and O+ are very distinct and those of various features of C+ are also different. A dramatic change of the angular distribution of C+ from dissociation of CO+(X (2)Sigma(+), v(+) = 1) is attributed to an accidental one-photon resonance between CO+(X (2)Sigma(+), v(+) = 1) and CO+(B (2)Sigma(+), v(+) = 0) and explained well by a theoretical model. Both kinetic energy release and angular distributions were used to reveal the underlying dynamics.