HCN2+ dication spectroscopy: theoretical and experimental investigations

The present work combines experimental and theoretical investigations of HCN2+ to investigate the spectroscopy and dissociation dynamics of this dication. Its spectrum is a complex blend of overlapping features, consistent with theoretical calculations showing that the low-lying electronic states of HCN2+ exhibit Renner-Teller and vibronic interactions. The double ionisation spectra are dominated by C-N stretching excitations for all the electronic states investigated. Long-lived HCN2+ ions are observed and are believed to be in low vibrational levels of the X 3Σ− and/or 1Δ and/or 1Σ+ electronic states; some have metastable lifetimes of about 25 ns. The formation of H+ + CN+ products is attributed to predissociation by the lowest 3A″ component resulting from a conical intersection between the X 3Σ− and 3Π states. The overall predissociation processes involve vibronic, Renner-Teller and spin-orbit couplings between several electronic states of HCN2+.