36th DPS Meeting, 8-12 November 2004
Session 16 Jovian System
Poster I, Tuesday, November 9, 2004, 4:00-7:00pm, Exhibition Hall 1A

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[16.08] Silicon Tetrafluoride on Io

B. Fegley, Jr., L. Schaefer (Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Washington University)

Silicon tetrafluoride (SiF4) is observed in volcanic gases on the Earth. The SiF4 is detected by observing its 9.7 \mu m band with infrared (IR) absorption spectroscopy, which is also used to measure SO2/SiF4 molar ratios. The SO2/SiF4 ratios vary from 71 to over 3000 at different terrestrial volcanoes. On Earth, SiF4 is formed by reaction of HF with silica:

4 HF (g) + SiO2 (silica) = SiF4 (g) + 2 H2O (g)

While Io is bone-dry and we therefore do not expect HF gas to be present, alkali fluoride gases may react with pure silica to give SiF4 via reactions analogous to the one above. We therefore performed equilibrium calculations modeling the reaction of pure silica with volcanic gases containing O, S, Na, K, Li, Rb, Cs, Cl, F, Br, and I (Schaefer and Fegley, Icarus, 2004, in review). These calculations covered a range of temperatures from 500 - 2000 K and pressures from 10-8 to 10+2 bars. We found that SiF4 is only important at low temperatures. For a nominal pressure of 0.01 bars, SiF4 is the most abundant fluorine compound at temperatures below ~ 800 K. This work is supported by the NASA Planetary Atmospheres program.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.