Electric field-gradient-induced birefringence in N2, C2H6, C3H6, Cl2, N2O and CH3F

Abstract

The optical birefringence induced by an electric field-gradient has been measured in the four non-polar gases nitrogen, ethane, cyclopropane and chlorine, and in the two polar gases nitrous oxide and methyl fluoride. Together with known values of the anisotropy in molecular polarizability, the measurements on the non-polar molecules yield the electric quadrupole moments Θ = -4·90 ± 0·3 × 10^-40 C m² for nitrogen, -3·34 ± 0·13 × 10^-40 C m² for ethane, 5·3 ± 0·7 × 10^-40 C m² for cyclopropane and 10·79 ± 0·54 × 10^-40 C m² for chlorine. In polar molecules the measured birefringence arises not only from the quadrupole moment, but also from the higher polarizabilities describing the electric dipole induced by an electric field-gradient and a time-varying magnetic field. This additional contribution is shown to be small in the case of nitrous oxide, but in methyl fluoride it predominates.