Chemical applications of second harmonic light scattering from solution

When light of wavelength l falls on molecules in solution, a part of it is scattered by the molecules.This is known as Rayleigh scattering. A small part of light in interaction with molecules is scattered at half the incident wavelength (l/2) or twice the frequency. This incoherent second harmonic (SH) or hyper-Rayleigh scattering (HRS) light intensity is directly proportional to the square of the molecular second order polarizability (b) which is an intrinsic property of a molecule and is zero if the molecule or the medium in which the molecules are confined has a center of symmetry. Exploiting the relationship between molecular nonlinearity with the density of the molecular scatterers, symmetry at the microscopic as well as macroscopic sources of SH light scattering and anisotropy of the second order polarization tensor, we have demonstrated many new chemical applications of this SHLS technique.

As a demonstration of the powerfulness of this technique, several examples of chemical applications will be shown. In particular, how the geometry of a weak charge transfer complex in solution is determined by this technique will be presented.