Optical extinction by spherical carbonaceous particles Original Research Article

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 graphitic and an amorphous material. Several models for the geometrical arrangement of these materials are discussed. Based on these models, the optical extinction cross-sections of small spherical carbon particles of different internal structures are calculated in the framework of classical electromagnetic theory. For ordered structures such as onion-shaped particles, analytical formulas are used, while for disordered structures effective-medium formalisms are applied which take into account the anisotropy of graphite and which have become available only recently. We find that the shape and position of the UV feature in the optical extinction at ca. 220 nm depends on the internal structure of the particle.