Microwave spectroscopy of molecular ions near dissociation

Taylor, Susan Mary (1997) Microwave spectroscopy of molecular ions near dissociation. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Microwave transitions involving vibration-rotation levels lying within 10 cm^-1 of the dissociation limit have been recorded for the D₂⁺, HeKR⁺, Ne₂⁺ and HeH₂⁺ molecular ions. The analyses of these spectra have challenged the current ab initio theories, and furthered the understanding of long-range intermolecular forces. Electric field dissociation has been used as a sensitive indirect detection method, where the fragment ions produced by a strong electric field were monitored for any changes in intensity induced by a spectroscopic transition.

Eight new resonances have been observed in D₂⁺, and their frequencies are found to be in excellent agreement with theoretical calculations. Hyperfine splitting has again been observed in one of the transitions, and interpreted in terms of electronic g/u symmetry breaking by the Fermi contact interaction.

In the study of HeKr⁺, 25 resonances have been recorded for the He⁸⁴Kr⁺ isotopomer and 11 for the He⁸⁶Kr⁺ isotopomer, and the isotope shift has been found to be opposite to that expected for low-lying rotational levels. Close-coupled calculations have been used in the analysis of this spectrum, which accurately predicted the well depth from a single rotational manifold 3 cm^-1 below dissociation, and this molecule is identified as Hund's case (e), the first time this case has been observed experimentally.

145 transitions have been recorded in Ne₂⁺, which represent the first spectroscopic observations for this system. 29 energy levels have been assigned experimentally through Zeeman and double-resonance experiments. The theoretical analysis of this spectrum is at an early stage, but close-coupled calculations, similar to those used for HeKr⁺, are fully expected to provide an accurate description of the long-range part of the potential.

10 resonances have been observed in HeH₂⁺, again the first spectroscopic investigation for this system, which confirms the applicability of our methods to systems other than diatomics. Hyperfine effects are recorded for some of these transitions, but none have been uniquely assigned at present.

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