Dissociation dynamics of carbon dioxide cation (CO ) in the CΣ state via [1+1] two-photon excitation.

The dissociation dynamics of CO in the CΣ state has been studied in the 8.14-8.68 eV region by [1+1] two-photon excitation via vibronically selected intermediate AΠ and BΣ states using a cryogenic ion trap velocity map imaging spectrometer. The cryogenic ion trap produces an internally cold mass selected ion sample of CO . Total translational energy release (TER) and two-dimensional recoiling velocity distributions of fragmented CO ions are measured by time-sliced velocity map imaging. High resolution TER spectra allow us to identify and assign three dissociation channels of CO (CΣ ) in the studied energy region: (1) production of CO(XΣ) + O(P) by predissociation via spin-orbit coupling with the repulsive 1Π state; (2) production of CO(XΣ) + O(D) by predissociation via bending and/or anti-symmetric stretching mediated conical intersection crossing with AΠ or BΣ , where the CΣ /AΠ crossing is considered to be more likely; (3) direct dissociation to CO(AΠ) + O(P) on the CΣ state surface, which exhibits a competitive intensity above its dissociation limit (8.20 eV). For the first dissociation channel, the fragmented CO(XΣ) ions are found to have widely spread populations of both rotational and vibrational levels, indicating that bending of the parent CO over a broad range is involved upon dissociation, while for the latter two channels, the produced CO(XΣ) and CO(AΠ) ions have relatively narrow rotational populations. The anisotropy parameters β are also measured for all three channels and are found to be nearly independent of the vibronically selected intermediate states, likely due to complicated intramolecular interactions in the studied energy region.