Mathematics – Logic
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.502m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 502
Mathematics
Logic
3
Carbon Isotopes, Graphite, Interstellar Matter, Murchison Meteorite, Polycyclic Aromatic Hydrocarbons, Chemical Composition, Geomorphology, Ion Probes, Mass Spectroscopy, Molecular Spectra
Scientific paper
We present measurements of polycyclic aromatic hydrocarbons (PAHs) associated with individual graphite grains whose C isotopic compositions indicate an interstellar origin. There is evidence from the molecular spectra that PAHs in one of the grains are substantially depleted in C-13, consistent with ion microprobe measurements of the bulk grain that also show a substantial C-13 depletion. This correlation suggests that in at least one case the observed PAHs are indigenous to the graphite grain and are themselves interstellar. Thirty C-rich candidate grains were transferred with a dry W needle from Murchison acid residue (MKE2). The grains were selected on the basis of morphological features that are characteristic of Murchison interstellar graphite. A two-step laser mass spectrometer was used to measure the PAHs present in each of the individual candidate grains and both groups. Five grains and one of the groups produced strong PAH spectra. Seven of the individual grains are demonstrably interstellar on the basis of large C isotopic anomalies. All grouped grains were also highly anomalous in C. Four of the five individual grains that gave strong PAH signals are interstellar. The detection of PAHs in these graphite grains does not prove that the molecules are interstellar since the PAHs may have been introduced to the grains during processing. A correlation of the C isotopic patterns in the molecules with those measured independently in the graphite would constitute strong evidence that the molecules were indigenous to the graphite. Analysis of the PAH spectra for grain 2.8 shows that the dominant mass peaks at 128 amu and 178 amu are not accompanied by their corresponding isotope peaks at 129 amu and 179 amu. The molecular data are thus in qualitative agreement with the factor of 2 depletion in C-13 measured in the ion probe.
Clemett Simon J.
Gao XingHui
Maechling Claude R.
Messenger Scott
O'D. Alexander Conel M.
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