Laser-Induced Fluorescence and Photoelectron-Photon Coincidence Studies of 3,5-Octadiyne Cation

3,5-Octadiyne cation in its lowest excited state has been studied in the gas phase by laser-induced fluorescence and photoelectron-photon coincidence techniques. The excitation spectrum of the ò″←²A″ transition has been obtained and yields vibrational frequencies of some of the fundamentals for the excited cationic state. The fluorescence quantum yields and lifetimes at selected energies within the òA″ state have been determined from the coincidence measurements. This provides quantitative data for the discussion of the relaxation behaviour of such an excited open-shell cation.