37th DPS Meeting, 4-9 September 2005
Session 67 Laboratory Research
Oral, Friday, September 9, 2005, 2:00-3:30pm, Law LG19

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[67.08] H2O2: A precursor for O2 on icy satellites? Laboratory studies

M.J. Loeffler, R.A. Baragiola (University of Virginia)

Radiation processes affect the surface chemistry in planetary systems and in the ISM, and thus they need to be studied extensively. Recently, we have studied H2O2 production in water ice by 100 keV H+ irradiation at temperatures relevant to Europa and the ISM. Although hydrogen peroxide has only been detected so far in the infrared reflectance of Europa, this molecule is believed to be an important factor for the radiation-induced chemistry that occurs in water ice in other outer solar system objects. In particular, it has been proposed that this molecule may be a precursor for the production of O2 exospheres around icy satellites and Saturn's rings. Previously, we have irradiated crystalline H2O2 and identified the synthesis of H2O and O3. The saturation water concentration appeared to be high, but quantification of initial radiation yields (G values) was not possible because of the large change in the shape of the infrared absorption bands due to the concurrent amorphization. Further measurements could not be made, because we could only grow H2O2 at high temperatures by distillation, and thus growing amorphous H2O2 was not possible. Recently, we developed a method to grow amorphous H2O2 in the solid phase that allowed us to measure H2O2 destruction quantitatively. We have performed radiolysis with 50 keV H+ at 17 K to ensure that most radiolytic products stay in the ice and have detected H2O, O2 and O3 but not HO2; we have measured initial radiation yields for H2O and O2. Annealing the irradiated samples at 0.2 K/min to 200 K we found that most of the O2 produced stays trapped in the ice until ~ 154 K, where it leaves immediately. Infrared absorption shows the production of dangling H bonds, which grow in importance during annealing and can even be observed at ~ 150 K.

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Bulletin of the American Astronomical Society, 37 #3
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