A spectroscopic study of unstable species in the gas phase

Abstract

This thesis contains the results of spectroscopic investigations on several unstable gas phase species. Two techniques were used: photoelectron spectroscopy with a synchrotron photon source, and resonance enhanced raultiphoton ionization (REMPI) spectroscopy. Chapter 1 contains an introduction to the photoelectron and REMPI spectroscopic techniques. In Chapter 2 the experimental apparatus used for the study of short lived molecules with photoelectron spectroscopy using synchrotron radiation is described. Chapter 3 outlines the fundamental principles of photoelectron spectroscopy using both fixed and tunable wavelength radiation such as that found at a synchrotron source. In Chapter 4 photoionization of the OH and OD radicals, produced from the H + NO; and D + NO2 reactions, has been studied in the photon energy region 13.0-17.0 eV. A comparison of vibrationally specific OH and OD CIS spectra, and photoelectron spectra recorded at resonant wavelengths, has allowed a more complete assignment of structure observed in earlier photoionization mass spectrometric measurements. These assignments have been supported by the results of Franck-Condon calculations. Photoelectron spectra recorded for the first bands of OH and OD at resonant photon energies have allowed more extensive vibrational structure to be obtained than has previously been recorded by PES experiments performed with inert gas discharge photon sources. In Chapter 5 the photoionization behaviour of OaCa'Ag) is studied in the photon energy region 12.5-19.0 eV. Suggestions are made for the nature of the highly excited states of O2 associated with the observed structure in the CIS spectra, based on available ionization energies and spectroscopic constants of known ionic states accessible from 02(a^Ag). In Chapter 6 the experimental apparatus used in the REMPI spectroscopic studies of Ar NO, Kr-NO and (CO): is described. Chapter 7 contains the details of the theoretical models used to interpret the (2+1) REMPI spectra of rare gas-NO (Rg NO) complexes. In Chapter 8 the results of REMPI studies on the Ar NO and Kr-NO van der Waals complexes are presented. For both complexes significant deviation from a T-shaped structure is found in their excited states, although it was not possible to determine the absolute position of the rare gas atom within experimental uncertainty. From the REMPI spectra dissociation energies of 582 and 803 cm'^ were derived for the E^E'" states of Ar NO and Kr-NO respectively. Chapter 9 describes the results of preliminary REMPI studies on (CO):. Chapter 10 describes a statistical technique for determining the number of ions contained in an ion trap mass spectrometer In Chapter 11 conclusions are drawn from the work presented in this thesis and suggestions for further work are made.

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