Masters Theses

Date of Award

8-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Physics

Major Professor

Dr. Robert N. Compton

Committee Members

Dr. Stuart Elston, Dr. Soren P. Sorensen

Abstract

A Time-of-Fight mass spectrometer (TOF-MS) equipped with both a standard electron gun and a trochoidal electron monochromator was constructed and made operational and used to study ionization processes of the molecule Chlorodifluoromethane (CHF2Cl). The appearance energies of both the parent ion (CHF2Cl+) and the most intense fragment ion (CHF2+) were carefully analyzed and it was observed that the energy for formation of the parent ion, (CHF2Cl+) at 12.50 eV, was at a higher energy than the fragment ion, (CHF2+) at 12.25 eV. This phenomenon has to our knowledge never before been reported in the literature and is of great interest. The trochoidal electron monochromator allowed for the energy distribution of the ionizing electron beam to be within the difference of the appearance energies for the ions, confirming the result. Metastable decay analysis of the parent ion showed two parent ion states present. One state decayed with a lifetime of 2 ms and another parent ion state appeared to be stable. It was also shown that the parent ion readily dissociated into the CHF2+ fragment ion and possible mechanisms for this effect is discussed. The results show the need for future theoretical calculations of the ionic potential energy surfaces for this molecular cation in order to assess the various possibilities for this mechanism. The atmospheric relevance of the instability of the parent ion of CHF2Cl and its short lifetime to dissociation, in which an ozone destroying chlorine atom is released, should be further considered.

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