An overview of laboratory studies on the energetic processes in water-rich ices containing organic impurities at outer Solar System temperatures.

Details An overview of laboratory studies on the energetic processes in water-rich ices containing organic impurities at outer Solar System temperatures. An overview of laboratory studies on the energetic processes in water-rich ices containing organic impurities at outer Solar System temperatures.

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p23e0115g&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P23E-0115

Physics

5422 Ices, 6020 Ices, 6040 Origin And Evolution, 6045 Physics And Chemistry Of Materials, 6055 Surfaces

Scientific paper

Solid water-rich ice is an important constituent in our Solar System. Planets such as Earth and Mars, Moons such as Europa and Enceladus, Comets, rings of Saturn, and KBOs are covered with solid water ices. Thus, understanding the intricate physics and chemistry of these ices is a non-trivial and non-negligible task that needs both laboratory and in-situ observational work to make advances in this field. Over the past several years, we have been systematically studying VUV-radiation processing of organic impurities embedded in water-ices in the temperature range between 20 K and 180 K. Since PAHs are abundant extraterrestrial species and their optical strong absorption occurs in the UV-VIS-NIR region (0.2 -- 0.9 μ m) where water-ice is transparent, we have focused on water rich ices containing PAHs. During these in-situ studies we discovered several counter-intuitive phenomena (see for example: Gudipati {&} Allamandola, 2006, Astrophys. J. 638, 286 {&} J. Phys. Chem. A 110, 9020 and references therein): \begin{itemize}
PAHs embedded in cryogenic water-ice are easily and efficiently ionized (>80{%}, i.e., near quantitative ion yields) to the cation form by VUV photons.
In water ice, PAH ionization energy is lowered by up to 2 eV compared to the gas-phase, in agreement with recent theoretical predictions.
PAH cations are stabilized in water ice to temperatures as high as 120 K.
Sequential photoionization leading to the formation and stabilization of doubly positively charged organic (PAH) species in water ice has also been found.
Electrons are stored in these energy processed water-ices doped with organic impurities. These findings have a range of applications to understanding the geology, chemistry, and physics of icy bodies in the outer Solar System such as coloration, energy budget, outbursts and atmospheres. These and other applications to outer Solar System will be discussed. Acknowledgments: This work was supported by grants from NASA's Exobiology, Astrobiology, and Long Term Space Astrophysics Programs (Grants: 344-58-12, 344-53-92, and 399-20-40 respectively), NASA's Planetary Geology and Geophysics Program (Grant: NNG05GI01G) and a NASA - University of Maryland cooperative agreement (NCC 2-1303).

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