E. Charon

Nanostructuration of carbonaceous dust as seen through the positions of the 6.2 and 7.7 μm AIBs

Context. Carbonaceous cosmic dust is observed through infrared spectroscopy either in absorption or in emission. The details of the spectral features are believed to shed some light on its structure and finally enable the study of its life cycle. Aims. The goal is to combine several analytical tools in order to decipher the intimate nanostructure of some soot samples. Such materials provide interesting laboratory analogues of cosmic dust. In particular, spectroscopic and structural characteristics that help to describe the polyaromatic units embedded into the soot, including their size, morphology, and organisation are explored. Methods. Laboratory analogues of the carbonaceous interstellar and circumstellar dust were produced in fuel-rich low-pressure, premixed and flat flames. The soot particles were investigated by infrared absorption spectroscopy in the 2−15 μm spectral region. Raman spectroscopic measurements and high-resolution transmission electron microscopy were performed, which offered complementary information to better delineate the intimate structure of the analogues. Results. These laboratory analogues appeared to be mainly composed of sp 2 carbon, with a low sp 3 carbon content. A cross relation between the positions of the aromatic C=C bands at about 6.2 micron and the band at about 8 micron is shown to trace differences in shapes and structures of the polyaromatic units in the soot. Such effects are due to the defects of the polyaromatic structures in the form of non-hexagonal rings and/or aliphatic bridges. The role of these defects is thus observed through the 6.2 and 7.7 μm aromatic infrared band positions, and a distinction between carriers composed of curved aromatic sheets and more planar ones can be inferred. Based on these nanostructural differences, a scenario of nanograin growth and evolution is proposed.

On a reliable structural characterization of polished carbons in meteorites by Raman microspectroscopy

ABSTRACT Polished section of Acapulco meteorite was used for the structural examination of graphitic matter by Raman microspectroscopy. The polishing process was shown to be necessary for the samples, where carbon matter is embedded in metallic phases. However, this process is known to drastically change the Raman spectrum, inducing unacceptable errors in the intrinsic structural characterization of these carbon materials. The deconvolution of spectra shows that the G-band width, related to the only bond stretching of sp2 atoms, gives real structural information, even on polished carbon, whereas the common intensity ratio ID/IG, which is too sensitive to polishing process, has to be avoided.

Dome C ultracarbonaceous Antarctic micrometeorites: Infrared and Raman fingerprints⋆

UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) represent a small fraction of interplanetary dust particles reaching the Earths surface and contain large amounts of an organic component not found elsewhere. They are most probably sampling a contribution from the outer regions of the solar system to the local interplanetary dust particle flux. We characterize UCAMMs composition focusing on the organic matter, and compare the results to the insoluble organic matter (IOM) from primitive meteorites, IDPs, and the Earth.We acquired synchrotron infrared microspectroscopy and micro-Raman spectra of eight UCAMMs from the Concordia/CSNSM collection, as well as N/C atomic ratios determined with an electron microprobe. The spectra are dominated by an organic component with a low aliphatic CH versus aromatic C=C ratio, and a higher nitrogen fraction and lower oxygen fraction compared to carbonaceous chondrites and IDPs. The UCAMMs carbonyl absorption band is in agreement with a ketone or aldehyde functional group. Some of the IR and Raman spectra show a C

Graphitization at low temperatures (600–1200 °C) in the presence of iron implications in planetology

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Raman spectroscopic properties and Raman identification of CaS-MgS-MnS-FeS-Cr2FeS4 sulfides in meteorites and reduced sulfur-rich systems

N band corresponding to a nitrile. The absorption band profile from 1400 to 1100 cm-1 is compatible with the presence of C-N bondings in the carbonaceous network, and is spectrally different from that reported in meteorite IOM. We confirm that the silicate-to-carbon content in UCAMMs is well below that reported in IDPs and meteorites. Together with the high nitrogen abundance relative to carbon building the organic matter matrix, the most likely scenario for the formation of UCAMMs occurs via physicochemical mechanisms taking place in a cold nitrogen rich environment, like the surface of icy parent bodies in the outer solar system. The composition of UCAMMs provides an additional hint of the presence of a heliocentric positive gradient in the C/Si and N/C abundance ratios in the solar system protoplanetary disc evolution.