A NEW COINCIDENCE TECHNIQUE FOR VACUUM ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY OF NEUTRAL CLUSTERS IN A MOLECULAR-BEAM

The magnetic bottle photoelectron spectrometer principle has been employed for the study of neutral clusters in a seeded supersonic molecular beam. Mass selectivity is achieved by correlating each detached photoelectron to the cluster cation that is produced simultaneously. The necessary high detection probabilities for both particles, the photoelectron and the cluster ion, are achieved by time-of-flight spectrometers for both channels. The collection efficiency of the magnetic photoelectron spectrometer is increased to almost-equal-to 80% of 4-pi by combining a permanent ring magnet, which produces an inhomogeneous field to parallelize the electron trajectories, with a 730-mm-long coil that guides the electrons by a weak, homogeneous field through the flight tube towards a scintillation detector. An advanced data acquisition electronics is described that is capable of recording and storing simultaneously photoelectron-photoion coincidence spectra of those neutral clusters that have sufficient intensity in the molecular beam.