Measurements of aromatic hydrocarbons in interstellar graphite grains. 2: Molecular measurements

Details Measurements of aromatic hydrocarbons in interstellar graphite grains. 2: Molecular measurements Measurements of aromatic hydrocarbons in interstellar graphite grains. 2: Molecular measurements

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.457c&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 457-458

Computer Science

Graphite, Interstellar Matter, Murchison Meteorite, Polycyclic Aromatic Hydrocarbons, Abundance, Desorption, Ionization, Mass Spectra, Mass Spectroscopy

Scientific paper

Microprobe two-step laser desorption/laser ionization mass spectrometry was used to analyze the C-rich grains from the Murchison meteorite described. The presence of polycyclic aromatic hydrocarbons (PAHs) was observed on five of the crushed grains and one of the clusters of smaller grains; however, appreciable signal was detected on only the three grains with crushed areas larger than 75 sq. microns: grain 2.8 (87 sq. microns), grain 2.20 (131 sq. microns), and grain 2.18 (173 sq. microns). Mass spectra for these grains are presented. The mass spectra for the three particles are most intense in the low-mass range and indicate the presence of naphthalene (128 amu), acenaphthene (154 amu), and phenanthrene (178 amu). The chemical digestion process used to prepare acid residues increases the abundance of low-mass PAHs relative to that of the bulk meteorite; a similar altered distribution of PAHs appears on these grains. The mass spectrum of grain 2.8 is unlike any we have observed before owing to the notable absence of peaks at 129 and 179 amu, the M+1 peaks of naphthalene and phenanthrene. The absence of peaks in mass spectra of very small signals should be interpreted with caution because too few ions are detected to estimate with confidence the distribution of isotopic components. Dramatic C-13 enrichments and depletions are commonly believed to be indicators of an interstellar origin, and the absence of the C-13 isotopomers of naphthalene and phenanthrene suggest that we may have detected interstellar PAHs. Concerns remain that kerogen contamination may contribute to the signal observed for these three grains. More work is required to elucidate the nature and origin of organic molecules in interstellar graphite grains.

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