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 (3)Sigma(-) and/or (1)Delta and/or (1)Sigma(+) electronic states; some have metastable lifetimes of about 25 ns. The formation of H+ + CN+ products is attributed to predissociation by the lowest (3)A" component resulting from a conical intersection between the X(3)Sigma(-) and (3)Pi States. The overall predissociation processes involve vibronic, Renner-Teller and spin-orbit couplings between several electronic states of HCN2+ (C) 2004 Elsevier B.V. All rights reserved.