The optics of spherically stratified graphite grains

Extinction and scattering efficiencies are calculated for spherically stratified graphite spheres using formulae which are valid in the small particle limit. The resulting extinction curve for this model is shown to peak at an ultraviolet wavelength _-1=4.8–5 _-1 close to that for the case of the less probable plane stratified model of a graphite sphere. The albedo in the present model is higher than that calculated for the plane stratified case by a factor 1.5–2 in the far ultraviolet. Extinction curves are also obtained for the case of a dielectric sphere surrounded by a thin graphite film, and it is shown that there now is an extinction minimum at _-14.6 _-1.