Measurement of the electric quadrupole moments of CO2, CO, N2, Cl2 and BF3

Abstract

The electric quadrupole moments of a number of molecules have been determined from measurement of the birefringence induced in a gas by an electric field gradient. The values obtained are: carbon dioxide (− 14·27 ± 0·61)x 10⁻⁴⁰ C m², carbon monoxide (− 9·47 ± 0·15)x 10⁻⁴⁰ C m², nitrogen (− 4·65±0·08)x 10⁻⁴⁰ C m² and boron trifluoride (12·6±0·7)x 10⁻⁴⁰ C m². In the calculation of the moments for carbon monoxide and boron trifluoride the small hyperpolarizability contribution was neglected in the absence of known values. By means of the Jones calculus a detailed analysis was made of the effects of strain birefringence in the cell windows and imperfect orientation of polarizing components in the light path. This analysis led to a measurement procedure which yielded results significantly different from previously reported ones obtained with essentially the same apparatus. The probable error in the earlier procedure is identified.