New laboratory spectra of isolated β-SiC nanoparticles:: Comparison with spectra taken by the Infrared Space Observatory

We present new laboratory infrared spectra of matrix-isolated beta-SiC nanoparticles, which perfectly match the band pro. le of the 11+mum feature observed in carbon stars. The new laboratory spectra differ in the shape of the band pro. le from former measurements of SiC nanoparticles thanks to the matrix-isolation technique which allows to obtain spectra of nonagglomerated particles. The final spectra are corrected for the influence of the surrounding medium (argon-matrix) by a computational technique proposed by Papoular et al. ( 1998). Furthermore, we study the influence of nitrogen incorporation into the SiC lattice, which introduces a strong near-infrared absorption owing to surface-plasmon excitation (Mutschke et al. 1999). Our laboratory spectra are compared with Infrared Space Observatory observations of several carbon stars showing an 11 mum feature either in emission or in absorption. We discuss the implications of the new laboratory results for the interpretation of the spectra of carbon stars.