Structure of interstellar carbonaceous dusts and their surface.

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Quenched Carbonaceous Composite (QCC) is a carbonaceous material condensed from an ejecta of hydrocarbon plasma. A.Sakata and his colleagues have shown that QCC has a 220 nm absorption feature, a set of infrared absorption bands that correspond to the infrared emission features in reflection nebulae, HIT regions, and planetary nebulae, and exhibits visible fluorescence matching the extended red emission seen in reflection nebulae. These properties make Q CC a strong candidate material as a laboratory analog to the carbonaceous material in the interstellar medium.High-resolution transmission electron micrographs (HRTEM) revealed that the dark-QCC is a coagulation of carbonaceous onion-like particles. Each particle consists of multiple shells, and many of the particles have a void at the center. The HRTEM images implied that the particles have many defected sites in their structure.By exposuring of the QCC with hydrogen gas, the defected sites in the dark-QCC particles were reacted with hydrogen molecules easily. As a result, peak intensities of infrared absorption bands at 3.42, 3.51, 6.9, 7.3, 12.5mum were increased, However, the 220 nm absorbance peak of the dark-QCC was stable. On the other hands, the filmy-QCC did not react with hydrogen both under irradiation of uv (222nm) and under dark condition.In order to clarify molecular cloud chemistry, we need more studies about the surface of the candidate materials.