The Effect of Particle Size in Second Harmonic Generation from the Surface of Spherical Colloidal Particles. II: The Nonlinear Rayleigh−Gans−Debye Model

The Rayleigh−Gans−Debye model, adapted for nonlinear optical phenomena, is used to describe the second harmonic scattering from the surface of spherical particles in colloids. Specifically, the effect of the size of the particle on the efficiency of second harmonic generation from Malachite Green (MG) molecules adsorbed on polystyrene particles is examined. The model is found to be adequate for describing scattering patterns from smaller particles with diameters ≤200 nm, but less so for larger particles with diameters approaching 1 μm. From the model fit of experimentally measured data (Part I of this series, J. Phys. Chem. A 2009, 113, 4758) it is determined that χ⊥||||S is the dominant susceptibility element. This result suggests that the MG molecules with a dominant βz′′x′′x′′ component adsorb on the surface of the spherical nanoparticles with the C2 axis nearly perpendicular to the surface