ABSTRACT

Context. Interstellar carbonaceous particles and molecules are subject to intense shocks in astrophysical environments. Shocks induce a rapid raise in temperature and density which strongly affects the chemical and physical properties of both the gas and solid phases of the interstellar matter. Aims. The shock-induced thermal processing of C 60 particles in hydrogen has been investigated in the laboratory under controlled conditions up to 3900 K with the help of a material shock-tube. Methods. The solid residues generated by the exposure of a C 60 /H 2 mixture to a millisecond shock wave were collected and analyzed using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman micro-spectroscopy, and infrared micro-spectroscopy. The gaseous products were analyzed by Gas Chromatography and Cavity Ring Down Spectroscopy. Results. Volatile end-products appear above reflected shock gas temperatures of ∼2540 K and reveal the substantial presence of small molecules with one or two C atoms. These observations confirm the role played by the C 2 radical as a major product of C 60 fragmentation and less expectedly highlight the existence of a single C atom loss channel. Molecules with more than two carbon atoms are not observed in the post-shock gas. The analysis of the solid component shows that C 60 particles are rapidly converted into amorphous carbon with a number of aliphatic bridges. Conclusions. The absence of aromatic CH stretches on the IR spectra indicates that H atoms do not link directly to aromatic cycles. The fast thermal processing of C 60 in H 2 over the 800-3400 K temperature range leads to amorphous carbon. The analysis hints at a collapse of the cage with the formation of a few aliphatic connections. A low amount of hydrogen is incorporated into the carbon material. This work extends the range of applications of shock tubes to studies of astrophysical interest.

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In this work, we discuss the structural and transport properties of iodine intercalated amorphous conducting carbon (a-C: I) films prepared by vapor phase pyrolysis of maleic anhydride and iodine. X-ray photoelectron spectroscopy studies reveal the presence of iodine in the a-C: I samples. Microhardness measurements of the films show a decrease in the value of the hardness with an increase in iodine concentration. Iodine incorporation accounts for a change in electrical conductivity of the a-C samples. Magnetoresistance measurements performed on a-C: I samples show a decrease in the value of magnetoresistance. The thermal stability of a-C: I samples has been studied by thermogravimetric analysis, which is found to depend on the host structure and amount of intercalated iodine.

Maximal activity levels of phosphorylase A and AB at 20.00 h alternate with minimal levels at 08.00 h of the day, while the glycogen content exhibited a reverse trend in the heart of the scorpion, Heterometrus fulvipes.