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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L02204, doi:10.1029/2006GL028317, 2007

Role of photoionization in the formation of complex organic molecules in Titan's upper atmosphere

Hiroshi Imanaka

Department of Chemistry, University of Arizona, Tucson, Arizona, USA
SETI Institute, Mountain View, California, USA


Mark A. Smith

Department of Chemistry, University of Arizona, Tucson, Arizona, USA


Abstract

Recent observations by the Cassini Orbiter suggest that complex organic chemistry occurs in the upper atmosphere of Titan. To understand the role of EUV-VUV light in the complex organic chemistry of Titan's upper atmosphere, we investigate the formation of gaseous species from a N2/CH4 gas mixture as a function of irradiation wavelengths from 50 nm to 150 nm. A N2/CH4 gas mixture (= 95/5) at 0.066 mbar in a windowless photocell is irradiated using a narrowband synchrotron radiation source. The analysis of gaseous products by quadrupole mass spectrometry reveals the formation of heavy organics up to C7 to C8 by EUV light irradiation. In particular, the efficient formation of benzene and toluene is observed at wavelengths less than 80 nm, which is well correlated to photoionization of N2. In Titan's upper atmosphere, EUV radiation may play an important role in the formation of complex organic molecules through photoionization of N2.

Received 28 September 2006; accepted 13 December 2006; published 23 January 2007.

Keywords: atmospheric chemistry; photoionization; Titan.

Index Terms: 6281 Planetary Sciences: Solar System Objects: Titan; 6005 Planetary Sciences: Comets and Small Bodies: Atmospheres (1060); 6026 Planetary Sciences: Comets and Small Bodies: Ionospheres (2459); 5210 Planetary Sciences: Astrobiology: Planetary atmospheres, clouds, and hazes (0343).

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Citation: Imanaka, H., and M. A. Smith (2007), Role of photoionization in the formation of complex organic molecules in Titan's upper atmosphere, Geophys. Res. Lett., 34, L02204, doi:10.1029/2006GL028317.