Laboratory analogs of carbonaceous matter: Soot and its precursors and by-products

Abstract

Abstract. Carbonaceous materials have been prepared in the laboratory by laser-induced pyrolysis of a mixture of hydrocarbons under different conditions and laser ablation of graphite in reactive gas atmospheres. We have investigated the soluble and insoluble parts of the condensed carbon powders with several spectroscopic and chromatographic methods in order to obtain information on the composition of the condensate. The results of these experiments have demonstrated that, at temperatures lower than 1700 K, the pyrolysis by-products are mainly PAHs, whereas at higher temperatures fullerenes and polyyne-based compounds are formed. The experimental findings point to different soot formation mechanisms with variable intermediates and end products. It has been found that soot extracts can contain more than 65 different polycyclic aromatic hydrocarbons (PAHs). Eventually, the study of the condensation pathways of soot particles and their precursors and by-products will permit the prediction of the spectral properties of carbonaceous matter in space.

Crossed Molecular Beam Study on the Formation of Phenylacetylene and Its Relevance to Titan’s Atmosphere

“…[13][14][15][16][17][18][19][20][21] But how are PAHs formed in these extreme environments? Multiple experimental studies have been completed in the last decades, where PAHs and nanosized soot particles were observed ranging from the hydrocarbon rich flame chemistry studies [22][23][24] to the shock wave experiment of Mimura 25 and the laser ablation experiment of graphite under different quenching atmospheres by Jäger et al 26 Chemical reaction networks that model the formation of PAHs in combustion flames [27][28][29] and in the interstellar medium 30 stress the importance of the phenylacetylene molecule (C 6 H 5 CCH) in the growth of PAHs starting from an initial hydrogen abstraction/acetylene addition sequence via the phenyl radical. Here, PAHs are suggested to be formed via "polymerization" of acetylene via the HACA mechanism (hydrogen abstraction acetylene addition) starting with the addition of a phenyl radical to acetylene 27 followed by acetylene additions eventually closing the secondary ring.…”

First results of the ORGANIC experiment on EXPOSE-R on the ISS

“…Circumstellar regions of carbon stars support chemical reactions that lead to the formation of complex carbon compounds, the nature and structure of which are strongly influenced by physical and chemical parameters such as temperature, density and composition (Pascoli & Polleux 2000; Cherchneff 2011; Contreras & Salama 2013). At condensation temperatures higher than 3500 K and when hydrogen is absent, polyynes cross-link to form fullerenes (Cataldo 2004; Jäger et al 2008, 2009).…”