Biology
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2002i&link_type=abstract
American Astronomical Society, DPS meeting #40, #20.02; Bulletin of the American Astronomical Society, Vol. 40, p.421
Biology
Scientific paper
The recent Cassini mission revealed the organic haze formation in the ionosphere of Titan, where the ionization of the dominant N2 molecules is the primary process. Previous study of the vacuum UV photolysis of N2/CH4 gas mixtures indicates that photoionization of N2 by EUV radiation plays a major role in initiating the production of complex organic molecules such as benzene and toluene (Imanaka and Smith, 2007). It is not clear, however, how much nitrogen is incorporated in Titan's organic haze. Many aspects of the nitrogen fixation process by EUV-VUV photochemistry have not been fully understood.
We demonstrate the first evidence of nitrogenated organic haze production by EUV-VUV irradiation of a N2/CH4 gas mixture. A N2/CH4 (= 95/5) gas mixture at 0.066 mbar in a 0.7 m length windowless photocell is irradiated by EUV-VUV light using a tunable synchrotron radiation source at the Advanced Light Source. The solid and gaseous species generated at the photon wavelengths of 60 nm and 82.5 nm are investigated in detail. The accumulated solid materials are characterized with Laser Desorption Ionization- Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry. The obtained ultra-high-resolution mass spectra enable the unambiguous CHN formula assignments, and they show the predominance of highly nitrogenated compounds in both solid materials. They consist of the distinct functional groups dominated with highly unsaturated compounds. The solid material produced at 82.5 nm contains more nitrogen than that generated at 60 nm. Although the presence of NH3 is clearly detected in the gas phase products at both photon wavelengths, the gaseous neutral species are dominated by hydrocarbons with less nitrogen incorporation. This implies that dissociated nitrogen favors to be partitioned into the solid phase and that substantial amounts of nitrogen may exist as organic haze in Titan's atmosphere.
We acknowledge support from the NASA Exobiology program (grant NNG05GO58G).
Imanaka Hiroshi
Smith Matthew A.
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