Microwave electronic spectra of the Ar2+ and Ne2+ ions: a combined neutral/ion molecular beam technique

We describe a new ion source in which a nozzle beam of neutral molecules is ionised by an electron beam and the resulting molecular ion beam is studied by microwave spectroscopic methods. This ionisation technique results in significant population of the near-dissociation levels of the molecular ion, so that a sensitive state-selective electric field dissociation method can be used to detect the spectra. We have observed the first state-to-state resonant electronic spectra of the Ar2+ and Ne2+ ions.