  We analyzed 2 ultra-carbonaceous interplanetary dust particles and 2 cometary
Wild 2 particles with infrared spectroscopy. We characterized the carrier of
the 3.4 micron band in these samples and compared its profile and the CH2/CH3
ratios to the 3.4 micron band in the diffuse interstellar medium (DISM), in the
insoluble organic matter (IOM) from 3 primitive meteorites, in asteroid 24
Themis and in the coma of comet 103P/Hartley 2. We found that the 3.4 micron
band in both Wild 2 and IDPs is similar, but different from all the other
astrophysical environments that we compared to. The 3.4 micron band in IDPs and
Wild 2 particles is dominated by CH2 groups, the peaks are narrower and
stronger than in the meteorites, asteroid Themis, and the DISM. Also, the
presence of the carbonyl group C=O at 1700 cm-1 (5.8 micron) in most of the
spectra of our samples, indicates that these aliphatic chains have O bonded to
them, which is quite different from astronomical spectra of the DISM. Based on
all these observations we conclude that the origin of the carrier of the 3.4
micron band in IDPs and Wild 2 samples is not interstellar, instead, we suggest
that the origin lies in the outermost parts of the solar nebula.
