Electrons In Water-ices At Outer Solar System Temperatures

Details Electrons In Water-ices At Outer Solar System Temperatures Electrons In Water-ices At Outer Solar System Temperatures

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6210g&link_type=abstract

American Astronomical Society, DPS meeting #38, #62.10; Bulletin of the American Astronomical Society, Vol. 38, p.607

Biology

Scientific paper

Solid water-rich ice is an important constituent of our Solar System. The importance of both laboratory and in-situ observational work to make advances in this field cannot be overstated.
Over the past several years, we have been studying VUV-radiation processing of organic impurities such as the extraterrestrially abundant polycyclic aromatic hydrocarbons (PAHs) embedded in water-ices between 20 K and 180 K. During these in-situ studies we discovered several counter-intuitive phenomena (See Gudipati and Allamandola, J. Phys. Chem. A 110, 9020, 2006 and references therein for details):
1) 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.
2) In water ice, PAH ionization energy is lowered by up to 2 eV compared to the gas-phase, in agreement with recent theoretical predictions.
3) PAH cations are stabilized in water ice to temperatures as high as 120 K.
4) Sequential photoionization leading to the formation and stabilization of doubly positively charged organic (PAH) species in water ice has also been found.
Our recent laboratory studies have focused on the fate of electrons that are produced during PAH photoionization in the ice. Careful warm-up experiments suggest that indeed some electrons are stored over several hours in these ices. During warm-up of these ices between 20 K and 70 K, these stored electrons become mobilized and react with positively charged PAH ions in the ice.
Taken together, these laboratory findings strongly suggest that ice rich trans-Saturnian icy objects including moons, comets, and KBOs, as well as some of Saturn's rings, can host ionized organic impurities and free electrons. These species have physical and chemical properties that can fundamentally alter ice properties such as color, strength, structure, energy-budget, reaction networks etc.
Acknowledgments:
Funded by NASA's Exobiology, Astrobiology, LTSA, and PG&G Programs

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