New Laboratory Spectra of Isolated β-SiC Nanoparticles: Comparison with Spectra Taken by the Infrared Space Observatory

Abstract

We present new laboratory infrared spectra of matrix-isolated β-SiC nanoparticles, which perfectly match the band profile of the 11+ μm feature observed in carbon stars. The new laboratory spectra differ in the shape of the band profile 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 μm 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.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the UK) and with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.