OPTICAL-PROPERTIES OF CARBONACEOUS DUST ANALOGS

Structurally different carbon materials with an increasing sp(2)/sp(3) ratio were synthesized by pyrolizing cellulose materials at 400, 600, 800 and 1000 degrees C. The hybridization ratios and the internal str uctures in these samples were determined by using High Resolution Tran smission 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 sur face was grinded and polished. The reflectance of the samples could be measured in the range between 200 nm and 500 mu m, covering most of t he spectral range relevant for radiative transfer calculations. Using the Lorentz-oszillator fit method we were able to determine the optica l constants n and k. A big change in the optical behaviour could be se en between 600 and 800 degrees C, which is caused by the presence of f ree charge carriers in the samples pyrolized at 800 and 1000 degrees 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 l imit and a continous distribution of ellipsoids (CDE) were calculated. The spectral index beta in the FIR region (lambda greater than or equ al to 100 mu m) increases from 1.2 for the very disordered still aliph atic-dominated carbon material pyrolized at 400 degrees C to 2.2 for t he more ordered graphitic sample carbonized at 1000 degrees C in case of spherical particles. In the more graphitic samples pyrolized at 800 and 1000 degrees C, the spectral index beta is strongly dependent on the shape of the particles.