Microwave spectroscopy of near-dissociation molecular ions

Gammie, David Ian (1999) Microwave spectroscopy of near-dissociation molecular ions. University of Southampton, Doctoral Thesis.

Abstract

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.

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