STUDY OF DISSOCIATIVE ELECTRONIC STATES OF THE HYDROGEN HALIDE MOLECULES AND MOLECULAR IONS YIELDING HYDROGEN ION THROUGH TIME-OF-FLIGHT SPECTROSCOPY (PREDISSOCIATION, NEGATIVE ION).

摘要

This dissertation describes the results of time-of-flight spectroscopic examination of H⁺ ions resulting from electron bombardment of the hydrogen halide molecules HF, HCl, HBr, and HI. The time-of-flight spectra of the H⁺ fragments and their corresponding H⁺ fragment kinetic energy spectra are used to study the dissociative processes that yield H⁺ fragments for electron bombardment energies in the 15 eV to 51 eV range. The H⁺ fragments are produced in an interaction region defined by a pulsed electron beam colliding with the target gas. By keeping the gas pressure sufficiently low to guarantee that the fragment path length to the ion detector is much less than the mean-free path length in the gas, the fragments' velocities can be considered a sample of fragment velocities produced by the electron beam and hydrogen halide gas in the interaction region. The geometry of the interaction region primarily detected fragments produced at 90° to the electron beam axis. The electron gun used was designed to allow computer control of the electron bombardment energy. The computer also controlled a programmable multichannel analyzer that allowed the data to be acquired in a fashion that permitted normalization of the H⁺ TOF spectra taken at different electron bombardment energies. This normalization procedure allowed the use of ionization efficiency curves in detection of the thresholds of H⁺ production channels for HCl and HBr. For HF and HI the thresholds of H⁺ production channels had to be determined by visual examination of the TOF spectra. The electronic structure of the hydrogen halide molecules has been a popular topic of study over the years. Since this work represents the first TOF study of electronic excitation processes that lead to dissociation resulting in H⁺ fragments from the hydrogen halides, it should prove to be a significant contribution toward an understanding of the highly excited electronic states of these molecules and their molecular ions. The interpretation of the results obtained indicated that both configuration interactions between adiabatic electronic states that lead to predissociation-type processes and inner valence shell excitations were probably the primary contributors to the H⁺ fragment production.