Electron-molecule chemistry and charging processes on organic ices and Titan’s icy aerosol surrogates

•DEA studies of N-bearing organic condensates were carried out at 90K and 130K.•Transformation of 2keV-irradiated HCN ice was investigated using XPS and FTIR.•Electron trapping was studied on tholins at 130K. Electron-induced polymerization processes and charging events that can occur within Titan’s...

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Bibliographic Details
Published in:Icarus (New York, N.Y. 1962) N.Y. 1962), 2015-09, Vol.258, p.109-119
Main Authors: Pirim, C., Gann, R.D., McLain, J.L., Orlando, T.M.
Format: Article
Language:English
Subjects:
Aerosols
Atmospheres
Atmospheres, chemistry
Charging
Chemical Physics
Cosmic rays
Desorption
Electron irradiation
Environmental Engineering
Environmental Sciences
Ices
Ocean, Atmosphere
Physics
Saturn satellites
Sciences of the Universe
Titan
Titan, clouds
Titan, surface
Trapping
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Summary:•DEA studies of N-bearing organic condensates were carried out at 90K and 130K.•Transformation of 2keV-irradiated HCN ice was investigated using XPS and FTIR.•Electron trapping was studied on tholins at 130K. Electron-induced polymerization processes and charging events that can occur within Titan’s atmosphere or on its surface were simulated using electron irradiation and dissociative electron attachment (DEA) studies of nitrogen-containing organic condensates. The DEA studies probe the desorption of H− from hydrogen cyanide (HCN), acetonitrile (CH3CN), and aminoacetonitrile (NH2CH2CN) ices, as well as from synthesized tholin materials condensed or deposited onto a graphite substrate maintained at low temperature (90–130K). The peak cross sections for H− desorption during low-energy (3–15eV) electron irradiation were measured and range from 3×10−21 to 2×10−18cm2. Chemical and structural transformations of HCN ice upon 2keV electron irradiation were investigated using X-ray photoelectron and Fourier-transform infrared spectroscopy techniques. The electron-beam processed materials displayed optical properties very similar to tholins produced by conventional discharge methods. Electron and negative ion trapping lead to 1011chargescm−2 on a flat surface which, assuming a radius of 0.05μm for Titan aerosols, is ∼628charges/radius (in μm). The facile charge trapping indicates that electron interactions with nitriles and complex tholin-like molecules could affect the conductivity of Titan’s atmosphere due to the formation of large negative ion complexes. These negatively charged complexes can also precipitate onto Titan’s surface and possibly contribute to surface reactions and the formation of dunes.
ISSN:0019-1035
1090-2643
DOI:10.1016/j.icarus.2015.06.006