Polarizabilities of interacting polar molecules

Collision-induced polarizability in the electro-optical Kerr effect is shown to be the dominant contributor to the second Kerr virial coefficient B_K of dipolar gases. It gives a positive B_K and may be orders of magnitude larger than the contribution due to the intrinsic anisotropy in the polarizability of the free molecules, thus resolving a long-standing discrepancy between experiment and theory. The collision-induced contribution provides a reasonable fit to the observed B_K for the fluoromethanes if a simple Stockmayer-type potential is used.