Biology
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.2710i&link_type=abstract
American Astronomical Society, DPS meeting #38, #27.10; Bulletin of the American Astronomical Society, Vol. 38, p.529
Biology
Scientific paper
Recent detection of benzene by Cassini's INMS at 1200 km altitude of Titan's atmosphere (Wait et al., 2005) suggests that complex organic chemistry may occur in the upper atmosphere of Titan. Few experimental simulations, however, have been conducted to investigate the complex organic chemistry induced by EUV-VUV irradiation into N2/CH4 gas mixtures. This study attempts to understand the role of EUV-VUV light in the subsequent complex organic chemistry. The occurrences of photoionization and photodissociation of N2 and CH4 depend on the wavelength of irradiated UV light, so that the subsequent organic chemistry from a N2/CH4 gas mixture might strongly depend on the wavelength of irradiated light. In this study, we report the formation of gaseous species from N2/CH4 gas mixtures as a function of EUV-VUV irradiation wavelengths from 50 nm to 150 nm. A N2/CH4 (= 95/5) gas mixture at 0.066 mbar in a 1 m length windowless photocell is irradiated by VUV light using a synchrotron radiation source at the Advanced Light Source. The photon wavelength can be controlled from 50 nm to 150 nm with a 1 nm bandwidth. The gaseous species produced by photochemistry are analyzed using a quadrupole mass spectrometer. The formation of heavy organics up to C8 to C10 by EUV light irradiation is observed, and the gas products depend on the irradiation wavelength. In particular, the efficient formation of benzene and toluene is observed during the irradiation at wavelengths less than 80 nm. This suggests that the photoionization of nitrogen may initiate the formation of benzene via ion-molecule reactions. In the N2 dominant atmosphere of Titan, the extreme ultraviolet radiation may play an important role in activating complex organic chemistry of the upper atmosphere through the photoionization of N2 molecules. We acknowledge the support by the NASA exobiology grant NNG05GO58G.
Imanaka Hiroshi
Smith Matthew A.
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