Anisotropic molecular polarizabilities from Rayleigh light scattering investigations of gases and vapours

Abstract

This thesis is concerned with the experimental determination of the Rayleigh depolarization ratios and polarizability anisotropies of various gases and vapours. Significant improvements were made to increase the stability, reliability and signal-to-noise ratio of the apparatus. This permitted the analysis of molecules with much lower depolarization ratios. Depolarization ratios are reported for carbon dioxide, carbonyl sulfide and carbon disulfide; boron trifluoride boron trichloride and boron tribromide; benzene, toluene, 'o'-xylene, 'm'-xylene and 'p'-xylene; ethane, fluoroethane and hexafluoroethane; acetylene, methylacetylene, dimethylacetylene and hexafluoro-2-butyne; pyridine, pyridazine, pyrimidine and pyrazine; bromomethane, dibromomethane and tribromomethane; argon; cyclopropane; formaldehyde and acetaldehyde; ammonia; nitrogen; l,4-dioxane; 1,2,3,5-tetrafluorobenzene and 1,2,4,5-tetrafluorobenzene; and trimethylboroxine. The accuracy and precision of recording mean polarizabilities with the light scattering apparatus was also investigated. The project also involved the application of the CADPAC and GAMESS ab initio programs to calculate the properties of interest. These included polarizability components, polarizability anisotropies and mean polarizabilities. Both zero-frequency and optical-frequency values are reported. Relatively small basis sets such as the 6-31G(+sd+sp), 6-31G(+pd+sp) and HUZ-SV(+sd+sp) basis sets were used to accommodate the larger species.