Experimental and theoretical studies of unstable species

Bush, Andrew Marcus (1997) Experimental and theoretical studies of unstable species. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The work presented in this thesis is concerned with the study of unstable species using both experimental and theoretical methods. The experimental studies are described in Chapters 2 to 4, and the theoretical ab initio methods are considered in Chapters 5 and 6.

Structured spectra of the Ã and C̃; states of Kr·NO have been obtained using one-colour and two-colour resonance-enhanced multiphoton ionisation spectroscopy. Estimates of the dissociation energies of both complexes are given. The appearance of spectra in both the Kr·NO⁺ and Kr⁺ mass channels was investigated, and mechanisms for the formation of Kr⁺ ions are discussed. Spectra of the Ã state of the Ar·NO complex are also presented. The non-Rydberg behaviour of the Ã states of Ar·NO and Kr·NO is discussed.

Constant ionic state spectra of carbon monosulphide are presented in the photon energy range 11.3 - 20 electron volts using synchrotron radiation. The spectra, recorded using several vibrational components of the ground ionic state of CS have been assigned using quantum defect analysis.

In Chapter 4, results obtained by scattering laser and synchrotron radiation off pulsed free jet expansions of Ar and N₂O are presented. The results are interpreted in terms of Rayleigh scattering from clusters formed within the free jet. Information on the relative size of clusters formed is obtained and compared to literature data. Where synchrotron radiation was used, contributions from non-Rayleigh scattering processes are considered.

ab initio molecular orbital calculations on the NO₂⁺·X (X=H₂O, N₂, CO₂) series of complexes are reported in Chapter 5. Optimised geometries and vibrational frequencies, as well as computed total energies have been used to calculate standard enthalpies, entropies and free energies for the complexing and ligand-switching reactions between the three molecular complexes. The results obtained have been compared to previous experimental and theoretical values where available.

The intermolecular potential energy surface of the Ar·NO⁺ cationic complex has been calculated using ab initio molecular orbital calculations. The effect of level of theory, basis set, NO⁺ bond length and basis set superposition error was investigated. The calculated surfaces were used to obtain intermolecular vibrational frequencies, which were compared to previous calculations and experimental results.

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