Spectroscopy of interstellar carbonaceous dust

Abstract

Carbon is the fourth element by order of abundance in the Universe and it is the first of the light elements that is exclusively formed in the interior of stars [1]. The electronic structure of carbon allows the formation of hybridized orbitals which offer multiple bonding possibilities. As a consequence, carbon is the element with the richest chemistry, a chemistry that leads ultimately to the origin of life. Carbonaceous grains are among the most abundant cosmic dust components. These grains, injected into the ISM, can influence the heating rate of gas and provide a site for heterogeneous chemistry, allowing the formation molecules and, specifically of H2. The size and chemical composition of carbonaceous grains changes markedly as they evolve through the ISM. In dense clouds they can reach ¿m size and get covered by ice layers; from there, they can grow to macroscopic sizes in the protoplanetary disk resulting from the cloud collapse leading to star formation. Solids formed by mixtures of carbon and hydrogen can be very complex. The size of the polyaromatic units and the proportion of aromatic to aliphatic structures predominant in dust grains, are presently a matter of debate [5-8].