The technique of laser induced predissociation and laser induced fluorescence is applied to study spectra of gas-phase molecular ions. The main feature of the experiment is a beam of mass selected molecular ions illuminated by a pulsed dye laser. Over an extended range of excitation energies spectroscopic information can be obtained about positive and negative ions including transient species.As a first result we present predissociation spectra of 03, b 4Z~ -a4//, A v = 3 and A v = 2 which can well be simulated by calculated spectra assuming a rotational ion temperature of 300 ~