Far-infrared absorption in small metal particles

We analyze the effects of an enveloping electron cloud on the absorption by small metal particles. We present the simplified quasiclassical kinetic model that allows us to treat the problem self-consistently and to write down the explicit response functions. If the surrounding medium is vacuum or a dielectric continuum thus obtained far-infrared absorption is orders of magnitude larger than in a classical treatment for a sharp interface. It is shown, however, that the surface absorption is sensitive to the microscopic potential landscape outside the particle and in some cases may be suppressed.