Biology
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p11a1198m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P11A-1198
Biology
[3924] Mineral Physics / High-Pressure Behavior, [5205] Planetary Sciences: Astrobiology / Formation Of Stars And Planets, [5215] Planetary Sciences: Astrobiology / Origin Of Life, [6240] Planetary Sciences: Solar System Objects / Meteorites And Tektites
Scientific paper
The carbonaceous content of meteorites has been increasingly quantified in the past two decades, as have the conditions meteorites undergo during planetary assembly. Models suggest that pressures of up to 10 GPa can be induced by near-miss collisions, and the shock pressures of collison range even higher. Polyaromatic hydrocarbons (PAHs) are known to graphitize or carbonize at high pressures and temperatures; however, the exact P-T conditions are known for only a few specific molecules. Consequently, it is unclear if primordial PAHs can survive planetary accretion processes. To understand the mechanism of PAH breakdown and the possible stability of PAHs during planetary accretion, we have measured the high-pressure IR spectra of three common PAHs: chrysene, coronene and acridine. Calculations of vibrational frequencies in gas phase molecules using density functional theory helps clarify band assignments; however, large discrepancies between gas phase C-H vibrational frequencies and those observed in the condensed phase suggest strong intermolecular interactions. (Results of periodic density functional calculations on solid phases, and the ability of exchange correlation functionals to describe the intermolecular interactions, will be discussed.) In chyrsene, we find that vibrational modes shift to higher frequencies and a new vibrational feature is appears at ~775 cm-1 when pressure >9 GPa. Coronene shows no change with pressure (up to 10 GPa) and temperature (up to 350°C) suggesting it is stable during accretion processes. For acridine, we see a strong splitting of the C-H stretch and some of the C-C stretch modes. These changes, however, are reversible with decompression and appear to result simply from intermolecular interactions in the condensed phase. In summary, we hypothesize that polyaromatic compounds may survive planetary accretion processes and may have been a source of reduced carbon in the crust of the early Earth.
Jennings Elise
Lerch Ph.
Montgomery William
Sherman David
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