Optical extinction by spherical carbonaceous particles

We set up a simple model for the optical properties of carbon particles in which the particles are considered to be a mixture of two materials-a graph itic and an amorphous material. Several models for the geometrical arrangem ent of these materials are discussed. Based on these models, the optical ex tinction cross-sections of small spherical carbon particles of different in ternal structures are calculated in the framework of classical electromagne tic theory. For ordered structures such as onion-shaped particles, analytic al formulas are used, while for disordered structures effective-medium form alisms are applied which take into account the anisotropy of graphite and w hich have become available only recently. We find that the shape and positi on of the UV feature in the optical extinction at ca. 220 nm depends on the internal structure of the particle. (C) 1999 Elsevier Science Ltd. All rig hts reserved.