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Astron. Astrophys. 332, 291-299 (1998)

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Optical properties of carbonaceous dust analogues

C. Jäger , H. Mutschke and Th. Henning

Friedrich-Schiller-Universität Jena, Astrophysikalisches Institut und Universitäts-Sternwarte, Schillergässchen 3, D-07745 Jena, Germany

Received 18 September 1997 / Accepted 27 November 1997

Abstract

Structurally different carbon materials with an increasing sp2 /sp3 ratio were synthesized by pyrolizing cellulose materials at 400, 600, 800 and [FORMULA] C. The hybridization ratios and the internal structures in these samples were determined by using High Resolution Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, Raman spectroscopy, IR spectroscopy and elemental combustion analysis. The pyrolized carbon samples were embedded in an epoxide resin and the surface was grinded and polished. The reflectance of the samples could be measured in the range between 200 nm and 500 µm, covering most of the spectral range relevant for radiative transfer calculations. Using the Lorentz-oszillator fit method we were able to determine the optical constants n and k. A big change in the optical behaviour could be seen between 600 and [FORMULA] C, which is caused by the presence of free charge carriers in the samples pyrolized at 800 and [FORMULA] C. In these samples the graphitic areas have been grown to about 1.5 nm in size. The absorption behaviours of small spheres in the Rayleigh limit and a continous distribution of ellipsoids (CDE) were calculated. The spectral index [FORMULA] in the FIR region ([FORMULA] [FORMULA] 100 µm) increases from 1.2 for the very disordered still aliphatic-dominated carbon material pyrolized at [FORMULA] C to 2.2 for the more ordered graphitic sample carbonized at [FORMULA] C in case of spherical particles. In the more graphitic samples pyrolized at 800 and [FORMULA] C, the spectral index [FORMULA] is strongly dependent on the shape of the particles.

Key words: circumstellar matter – dust, extinction – infrared: ISM: lines and bands

Send offprint requests to: C. Jäger

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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