Microwave spectroscopy of near-dissociation molecular ions

A molecular ion beam technique has been employed to enable the spectroscopic study of near-dissociation energy levels in several molecular ions; transitions are detected indirectly using the technique of electric field dissociation. Such studies of near-dissociation states are fundamental to the understanding of the correlations between atomic and molecular states and to the description of ion/molecule reaction dynamics. The first observations of resonant transitions in Ne+2, HeHe+2 and HeN+ are reported, together with a near-dissociation electronic spectrum of N+2. The analyses of these studies represent a significant challenge for the methods of theoretical chemistry.The experimental study of Ne+2 has located the majority of energy levels (J ≤ 15/2) that lie within 10 cm-1 of the lowest dissociation limit in Ne+2. Experimental g-factors have been obtained for many of these levels and rotational progressions associated with at least 18 vibronic states have been identified. Six vibronic states of u symmetry have been described by an effective Hamiltonian analysis and preliminary coupled-channel calculations have been successful in describing all of the experimental energy levels.Ten transitions have been detected in HeH+2 and a clear distinction is observable between transitions which exhibit hyperfine structure (ortho-HeHe+2 ) and those which do not (para-HeHe+2). Preliminary analyses of the transitions are discussed and a complex Zeeman pattern is analysed. The near-dissociation microwave spectra of HeN+ and N+2 are also reported and discussed.