Long range dipole-dipole correlations in nitrobenzene-benzene solutions.

Hyper-Rayleigh scattering (HRS) from liquid nitrobenzene-benzene solutions with nitrobenzene mole fraction in the range 0.001 < x(NB) < 1 was measured for several combinations of linear polarized incident and scattered light, for scattering angles near 90°. Polar collective modes are identified by their distinctive HRS polarization dependence. At all concentrations the nitrobenzene HRS intensity is dominated by the transverse polar collective mode contribution and the longitudinal collective mode contribution is near zero. The transverse polar mode HRS is due to long range dipole-dipole orientation correlations between the nitrobenzene molecules, such that the molecular dipoles are oriented transverse to the wave vector for each spatial Fourier component of the orientation distribution.