Local-field effect on linear and nonlinear optical properties of adsorbed molecules

Abstract

A classical point-dipole model is used to calculate the local-field effect on the optical properties of adsorbed molecules on a substrate. The spatially nonvarying component of the local field at the molecules can be described by using a local-field correction factor. Equally important is the spatially varying component of the local field which arises mainly from the molecule-substrate interaction. The rapid variation over the molecular dimension can appreciably modify the transition-matrix elements and break down the electric dipole selection rules. The effect becomes insignificant if the molecules are more than 2.5 \AA{} away from the substrate even in the metal case. Both components of the local field contribute to the effective linear and nonlinear polarizabilities of the adsorbed molecules. Nonlinearity due to molecular response to the harmonic frequency components of the local field discussed by Antoniewicz appears to be less important.