Optical spectroscopy of small particles near a surface

Solving the self-consistent volume integral equation, we compute the local susceptibilty, as well as volume-averaged one of a small parallelepipedal particle interacing with a flat substrate. To estimate the measure of nonpointness of a particle, the susceptibility in the particle center is compared with that calculated in the dipole point-like approximation. It is shown that a parameter specifying nonpointness is determined by the difference in the particle and ambient dielectric constant, as well as by measure of deviation of the particle shape from cubic one. Numerical calculations of absorption cross-section carried out for small dielectric particles shw that the substrate effects lead to the low-frequency shift of the spectra and appearance of a low-frequency subsidiary peak.