Interstellar Carbon Dust

Abstract

In the ranking of cosmic abundance of the elements, carbon is the second element, after oxygen, able to form multiple bonds propagating the formation of a network, thus playing an essential role in the formation of nanometer- to micrometer-sized interstellar dust grains. Astrophysical spectroscopic observations give us remote access to the composition of carbonaceous and organic interstellar grains. Their presence and abundances from spectroscopic observations and the phases of importance for the Galactic carbon budget are considered in this article.

Interstellar Formation of Biorelevant Pyruvic Acid (CH3COCOOH)

“…Here, we demonstrate the first abiotic synthesis of 1 under conditions mimicking extraterrestrial environments via the barrierless radical-radical reaction of the hydroxycarbonyl (HOCO,, 9) and acetyl (CH 3 CO,, 10) radicals (Scheme 1) by exposing low-temperature model ices to ionizing radiation with high-energy electrons simulating secondary electrons formed in the path of galactic cosmic ray (GCR) particles penetrating ices on interstellar grains in molecular clouds. 31,32 Cold molecular clouds encompass the raw material of stars and planetary systems with nanometer-sized grain particles consisting of amorphous and polyaromatic carbon 33 and olivine-type silicates 34 (''interstellar dust'') accumulating icy layers of mainly water (H 2 O), methanol (CH 3 OH), carbon dioxide (CO 2 ), and carbon monoxide (CO) at temperatures as low as 10 K. [35][36][37] These ices are chemically processed by the internal ultraviolet (UV) field 38 and by energetic GCRs, leading to the synthesis of an array of organic molecules, such as the simplest sugar-related compound-glycolaldehyde, 39 other aldehydes 40 (e.g., Abelson, 8 Bennett et al, 31,32 ), ketones (e.g., acetone), and carboxylic acids 41,42 (e.g., formic acid 43 and acetic acid 44 ). 35 When a molecular cloud transits into a star-forming region, matter is incorporated into circumstellar disks, which, in turn, contain the material out of which planets, planetoids, and comets may form.…”

Hydrogenation of C24 Carbon Clusters: Structural Diversity and Energetic Properties

“…Among cosmic elements, carbon is the second most abundant one (after oxygen) among those able to form bonds of various natures and thus to participate in cosmic molecular complexity through top-down 1 (destruction) and bottom-up 2 (growth) processes Given its rich allotropy, a diversity of interstellar carbonaceous molecules and dust grains were shown to contain a large fraction of the carbon budget in the galaxy. We can cite nano-diamonds, fullerenes, polyaromatic structures or (hydrogenated)-amorphous carbon structures 3 . These species were identifed thanks to the interplay between spectroscopic observations, experimental and theoretical studies.…”

Electronic excited states of benzene in interaction with water clusters: influence of structure and size

“…In space, carbon is the fourth most abundant element and it is mainly present under the form of large carbonaceous molecules. [2] Among them, those possessing an aromatic character, Polycyclic Aromatic Hydrocarbons (PAHs), have received considerable interest since they were proposed, in the mid-eighties, as the carriers of the Aromatic Infrared Bands (AIBs), a set of mid-IR emission bands observed in many regions of the interstellar medium [3,4]. This 'Astro-PAH' population would constitute about 10 to 20 percent of the total elemental carbon in the interstellar medium (ISM) [5,6] although no specific PAH molecule has been identified yet [7].…”