MASS EXTINCTION COEFFICIENTS OF VARIOUS SUBMICRON AMORPHOUS-CARBON GRAINS - TABULATED VALUES FROM 40 NM TO 2 MM

Amorphous carbon grains are considered among the main components of cosmic dust. The characterization in the laboratory of their physico-chemical properties may represent a substantial contribution to the interpretation of astronomical observations. In the frame of the experimental activity developed in our laboratory on cosmic grain ''analogues'', we have performed a systematic analysis in order to provide a quantitative determination of the extinction properties of various amorphous carbon samples in a wide spectral range, from the vacuum UV to the mm regions. Particular care has been placed to eliminate possible systematic errors introduced by dust-matrix interaction. The extinction signatures of both hydrogenated and dehydrogenated carbon grains have been analysed, also on the ground of other experimental results obtained by means of complementary analytical techniques. The measured general spectral trend, as well as UV and IR typical features, are interpreted taking into account the intrinsic properties of our samples. The results are compared with previous experimental data and with the output of theoretical models which make use of carbon optical constants. The present quantitative data offer the opportunity to interpret in a more complete way the characteristics of carbonaceous analogues and can be helpful to infer information about cosmic dust. On the other hand, the wide spectral range covered by our measurements provides a set of self-consistent data which can be applied to determine the optical constants of small amorphous carbon grains.