The effect of strong electric and magnetic fields on the depolarization ratios of gases

The influence of a strong electric field F on the polarization of light scattered elastically by small gaseous molecules is investigated. Two effects are found:

• (i) The field distorts the molecules, thereby changing their polarizabilities. If they are isotropically polarizable when F = 0, and hence capable of scattering only polarized light from a parallel beam, this distortion may lead to depolarization. For inert gas atoms, this depolarization is proportional to F ⁴, and hence normally very small, but for tetrahedral molecules it is proportional to β ² F ², where β is the first hyperpolarizability of the molecule.

• (ii) F tends to orientate anisotropic molecules, thereby affecting the polarization of the scattered light; this effect is related to the anisotropy in the molecular polarizability, and to the dipole moment, but is not likely to lead to information that is not obtainable by simpler means.

The effect of a strong magnetic field, in place of F, is also discussed.