Microwave electronic spectrum of the Ne···Ne+ long-range complex

Abstract

We have used an ion beam method to observe 276 transitions in the microwave electronic spectrum of the long-range Ne···Ne⁺ ionic complex, involving levels which lie within 10.2 cm^-1 of the lowest dissociation limit. An electric field dissociation technique has been used to access directly levels with binding energies of up to 6.8 cm^-1 and we have been able to construct an experimental energy level pattern for at least 17 vibration–rotation progressions in this region of the potential. Microwave–microwave double resonance and Zeeman effect measurements have been crucial in establishing this energy level pattern. The levels are populated by the vertical electron impact ionisation of the neutral neon dimer, produced by means of a nozzle beam, with some population of higher rotational levels of the dimer ion probably resulting from larger cluster fragmentation. A case (c) effective Hamiltonian analysis has been successful in describing the levels in six of the progressions but a full theoretical analysis requires a coupled-states calculation. Analysis of Zeeman splittings for the microwave lines identifies the J values of the levels involved. The observed g-factors provide information about the transition from case (c) to case (e) coupling as both the rotational quantum number increases and the energy levels become more weakly bound.