Couling, Vincent William.Moodley, Verlan.2020-03-282020-03-2820192019https://researchspace.ukzn.ac.za/handle/10413/17129Master of Science in physics in the School of Chemistry and Physics,University of KwaZulu-Natal .Pietermaritzburg campus,2019.A molecular-tensor theory of the second electric-field-gradient-induced birefringence (EFGIB) virial coeffcient BQ, which describes the effects of molecular pair interactions on the molar Buckingham constant mQ, is developed for non-dipolar molecules with axial and higher symmetry. The resulting expressions for contributions to BQ are evaluated numerically for the molecules CO2, C2H4 and C2H6. These molecules were chosen since previously developed molecular-tensor theories of the second light-scattering virial coeffcient Bp and the second Kerr-effect virial coeffcient BK have yielded calculated values for these species which are in close agreement with the available measured data. The BQ values calculated for CO2, C2H4 and C2H6 reveal that, for the uids behaving as gases, the pair-interaction contributions to mQ are generally at or below the threshold of resolution of the EFGIB apparatus, so that the measured mQ values reported in the literature have not been contaminated by pair-interaction effects. In addition, it is seen that if the precision of measured mQ data can be increased by around an order of magnitude, it should in principle become possible to resolve BQ contributions, particularly for higher gas densities.enBuckingham-effect,Virial coeffcients,non-dipolar molecules,molecular-tensor theory,Thesis