Is the interaction between Ti atoms and fullerenes the origin of the 21-mum feature?
Y. Kimura, J. A. Nuth III (NASA GSFC), F. T. Ferguson (NASA GSFC & Catholic University of America) A 21-\mum-emission feature has been observed in the shells of carbon-rich post-asymptotic giant branch (AGB) stars. The carrier of the 21-\mum feature remains unidentified, although many candidate materials have been proposed, including nanodiamond, SiS2, a derivative of SiC and nanometer-sized TiC. In particular, TiC grains were extensively discussed after the report by von Helden (2000). Gas-phase TiC clusters less than 1 nm in diameter have been suggested as the source of the 21-\mum dust feature. The spectrum of TiC clusters recorded in the laboratory provides a good fit with the observational data. However, only negative results have been reported for both theoretical and laboratory experimental studies concerning TiC since the discovery by von Helden. Recent measurements of fullerenes and Ti atoms recorded in our laboratory have demonstrated the presence of an infrared feature near
