Vacuum-ultraviolet emission detection of organometallic multiphoton ionization and discharge processes in bulk gases

We have measured the multiphoton ionization spectrum of benzene chromium tricarbonyl by monitoring nondispersed vacuum-UV emission at 90° to the incoming laser beam. The spectrum recorded was identical to the total ion current spectrum simultaneously measured with parallel plate electrodes. The dependence of the vacuum-UV signal on the pressure of added buffer gas and collection field strength differs significantly from that of the ion signal. The majority of differences can be interpreted in terms of basic electron impact processes and subsequent interatomic/molecular reactions. A possible application of these laser-induced discharge processes is suggested. However, in some cases the ion signal exhibits an increase, which is not observed in the vacuum-UV signal, that may be positive evidence of an intermolecular effect, an "incipient cage effect", on the time scale of the laser pulse.