Spectroscopy and dissociation of the hydrogen ions

West, Yvonne Deana (1992) Spectroscopy and dissociation of the hydrogen ions. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The spectroscopy of the simplest hydrogen molecular ions, HSD⁺, H₃⁺, H₂D⁺ and D₂H⁺, near their dissociation limits has been studied. Ion beam techniques, infrared laser excitation and detection by rotational predissociation have been employed. Details of the apparatus and the experiment are presented. Vibration-rotation transitions in HD⁺ involving states of high angular momenta (N) have been recorded. The experimental requirements for populating such states are discussed. Transitions are preferentially detected by monitoring protons corresponding to the ground state (1sigma) dissociation limit. In some cases they can also be detected by monitoring deuterons. Transition wavenumbers for ten high N resonances are presented and are in good agreement with theory. These include the fundamental vibrational transition, 1 ← 0, which has im23000cm^-1 of rotational excitation. Linewidths and proton:deuteron branching ratios are given where they can be determined. As the rotational excitation of the dissociating state increases, the branching ratio is shown to tend towards unity. In 1984, Carrington and Kennedy first described the low kinetic energy near-dissociation spectrum of H_3^+. A pseudo low-resolution convolution of the data revealed 4 broad peaks. A detailed systematic study of the peak in the wavenumber range 964.0 to 991.6cm^-1 at various kinetic energy windows (0-100, 500 and 3000cm^-1) is reported. The low kinetic energy low-resolution peak composed of only the strongest lines is shown to be reproducible, and to arise from fragments with kinetic energies ≤50cm^-1. The nature of the spectrum is significantly different from different kinetic energy windows. Kinetic energy studies provide evidence that some state may predissociate through more than one channel. The preferred fragmentation channels, H⁺ or D = n, for H_2D⁺ and D₂H⁺ at different kinetic energies have been investigated. Kinetic energy spectra of the fragment ions from the spontaneous predissociation background have also been recorded. Protons are preferentially formed with low kinetic energy releases and, conversely, deuterons with high kinetic energy releases. The results are in good agreement with theory. Exact Born-Oppenheimer solutions for the electronic Schrodinger equation in the presence of an applied electric field are presented for H₂⁺ and D₂⁺. Previous calculations are discussed. The effects on the vibration-rotation levels are given. Simulated kinetic energy fragment ion spectra arising from state selective electric field dissociation are compared with experimental spectra.