AN INVESTIGATION ON THE OPTICAL PROPERTIES OF CARBON BLACK, FULLERITE, AND OTHER CARBONACEOUS MATERIALS IN RELATION TO THE SPECTRUM OF INTERSTELLAR EXTINCTION OF LIGHT

In this work, the optical properties in the UV-VIS of three carbon blacks having specific surface area from 145 to 7 m²/g and produced with furnace or thermal processes have been studied. The results have been compared to the optical properties (in the same spectral range) of C₆₀ fullerene photopolymer, to fullerite i.e., the carbon soot containing fullerenes and to a sample of carbonaceous matter containing carbyne. The scope of the work was to verify if any of the carbonaceous matter studied was able to match the interstellar extinction spectrum which shows a “bump” at 217.5 nm and which was originally attributed to interstellar graphitic particles. None of the materials studied has shown a peak at 217.5 nm. All the carbonaceous materials studied show maxima of absorption from 252 to 267 nm with the exclusion of C₆₀ photopolymer which has a completely peculiar and different spectrum from all other materials with three maxima at 271, 389 and 510 nm. All the carbon materials studied do not match the 217 nm peak, hence, cannot be considered the carrier of the interstellar “bump” but may be present in some circumstellar shells of late type stars, where the peaks at 240-250 nm have been recorded and attributed to a more ordered and partially graphitized carbonaceous matter. In the discussion, the matrix effect, the particle size, and the clumping of the material studied have been considered as cause of the shift of the peak to longer wavelength.

The carbon black samples have also been extracted with pentane or ethanol and the polycyclic aromatic hydrocarbons (PAH) identified have been discussed in the frame of recent works and in relation to the role that they play in the interstellar medium as potential carriers of the diffuse interstellar bands (DIBS).