Raman spectroscopic investigation of two grains from comet 81P/Wild 2: Information that can be obtained beyond the presence of sp2-bonded carbon

Raman analyses were performed of individual micrometer-sized fragments of material returned to Earth by the NASA Stardust mission to comet 81P/Wild 2. The studied fragments originated from grains (C2054,0,35,91,0 and C2092,6,80,51,0) of two different penetration tracks that occurred in two different silica aerogel collector cells. All fragments of both particles have Raman spectra characteristic of amorphous sp2-bonded carbon that are in general agreement with the results published in previous Stardust particle studies. The present study, however, does not focus on the discussion of specific details of the D and G band parameters, but rather reports on additional information that can be obtained from returned Stardust samples via Raman spectroscopy. Most notably, the Raman spectra show that all analyzed fragments of the particles were contaminated with the capture medium (i.e., aerogel). The silica aerogel is laced with organic aliphatic and aromatic hydrocarbon impurities that resulted in strong bands in the similar to 2900 ?cm-1 spectral range (C-H stretching modes). Aerogel bands are also found in the 10001600 ?cm-1 spectral range, where they overlap with the bands of the amorphous sp2-bonded carbon. The peaks associated with the aerogel contamination differ between the two grains that originated from two different aerogel cells. In addition to the bands due to aerogel contamination and the always present sp2-bonded carbon bands, fragments of particle C2092,6,80,51,0 also show Raman peaks for pyrrhotite and Fa30Fo70 olivine. Complete (up to 4000 ?cm-1) raw and baseline-corrected Raman spectra of the Stardust particles are shown and discussed in detail.