Neutralized ion-beam studies of the rare gas hydrides: Observation of unique metastability for NeH

The rare gas hydride radicals have been produced by charge exchange of the corresponding ion in a mass selected, high velocity beam with K, Na, Mg, Zn, or Hg target metals. NeH shows unique behavior, being produced in both dissociative and long-lived ( > 5.0 μs) metastable states. Arguments based on energetic considerations are presented that the observed metastability should be associated with the ground state of the NeH radical, requiring that it have a shallow well and dissociation barrier analogous to those previously determined for the ground states of the isoelectronic NH₄, H₃O, and H₂F radicals. The existence of a structured radiative transition near 6.1 eV is predicted for the NeH radical. The other rare gas hydrides exhibit only dissociation of the radical with the kinetic energy released explainable in terms of production of known electronic states of the radicals by near resonant electron transfer. For HeH and ArH the first excited electronic state (A ²Σ⁺) is observed to efficiently predissociate into the repulsive ground state, whereas for KrH and XeH, lower limits of 4.5 and 3.9 eV, respectively, are determined for the energies of the corresponding excited states with respect to the separated ground state atoms.