Low-energy electron irradiation studies of acetonitrile and acetonitrile/acetylene ices relevant to Titan's atmospheric and surface chemistry

Details Low-energy electron irradiation studies of acetonitrile and acetonitrile/acetylene ices relevant to Titan's atmospheric and surface chemistry Low-energy electron irradiation studies of acetonitrile and acetonitrile/acetylene ices relevant to Titan's atmospheric and surface chemistry

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33e1804d&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P33E-1804

Physics

[5422] Planetary Sciences: Solid Surface Planets / Ices, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites, [6281] Planetary Sciences: Solar System Objects / Titan

Scientific paper

The observation of organic-rich rivers and lakes on Titan has generated much interest concerning possible prebiotic reactions occurring at the surface and in the atmosphere. Acetonitrile (CH3CN) has been detected in the upper atmosphere and stratosphere by the international 30 meter radio telescope in the Spanish Sierra Nevada (operated by IRAM) and on the surface in dark terrain regions by Cassini's Visual and Infrared Mapping Spectrometer (VIMS) [1]. In addition, acetylene (C2H2) has been detected in the atmosphere by the Composite Infrared Spectrometer (CIRS) and the Ion and Neutral Mass Spectrometer (INMS) aboard the Cassini spacecraft [1]. Low-energy electrons are also known to be present at low altitudes and in the near surface regions. At altitudes of 1200 km, the electron flux has been estimated to be 102-105 cm-2s-1eV-1 with energies in the range of 0.1-1 KeV [2], and at lower altitudes appreciable electron densities were measured by the Huygens Probe [3]. In order to examine the reactions induced by low-energy electron irradiation of acetonitrile and acetylene ices, studies have been performed on pure CH3CN ices and CH3CN/C2D2 ice mixtures. These ices were exposed to irradiation by 80-1000 eV electrons and reaction products were detected using temperature programmed desorption (TPD) and reflection/absorption infrared spectroscopy (RAIRS). After irradiation of pure CH3CN ices, desorption of CH4 and HCN was observed with TPD. With CH3CN/C2D2 mixed ices, desorption of neutral H2 was observed, indicating increased availability of hydrogen in the ices. Thermal desorption of C2D2 and CH3CN peak at 90 and 147 K, respectively, in pure ices. However, an additional desorption peak was observed at 110 K in the ice mixture. This suggests desorption of a weakly bound CH3CN-C2D2 complex. Exploring the reactions of these hydrocarbon ices is crucial to determining Titan's role as a prebiotic chemical system in the outer solar system.