Stratified dust grains in the interstellar medium. III: Infrared cross-sections

We construct a model of interstellar dust in which H-rich amorphous carbon is deposited on silicate substrates in the interstellar medium, and is annealed to form H-poor amorphous carbon. The model grains are stratified spheres composed of hollow silicate cores coated with two carbonaceous layers, the inner layer of sp2 carbon and the outer layer of sp3 carbon. Using an accurate method of computing the optical properties of such layered grains, we explore the consequences of varying the core-grain size distribution and the thicknesses of the carbonaceous layers on the resulting infrared extinction. We find a wide dispersion in the curve morphology that reflects the grain size distributions and the chemical composition of dust materials.

Research highlights► Silicate grains with carbon mantles and PAHs can fit the mean ISEC from UV to IR. ► Variations in the grain size ranges produce large variation in the IR extinction. ► Mantle chemical composition affects IR extinction. ► The degree of porosity in the grains modifies the shape of the spectral features. ► IR extinction observations may help to constrain some physical parameters in dust models.