Silicon tetrafluoride on Io

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.05.020 Byline: Laura Schaefer, Bruce Fegley Keywords: Io; Volcanic gases; Silicon; Fluorine; Silicon tetrafluoride; Condensates; Geochemistry; Atmospheric chemistry Abstract: Silicon tetrafluoride (SiF.sub.4) is observed in terrestrial volcanic gases and is predicted to be the major F-bearing species in low-temperature volcanic gases on Io [Schaefer, L., Fegley Jr., B., 2005b. Alkali and halogen chemistry in volcanic gases on Io. Icarus 173, 454-468]. SiF.sub.4 gas is also a potential indicator of silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial basalts, and gas/lava enrichment factors for F and S measured at terrestrial volcanoes to calculate equilibrium SiF.sub.4/SO.sub.2 ratios in volcanic gases on Io. We conclude that SiF.sub.4 can be produced at levels comparable to the observed NaCl/SO.sub.2 gas ratio. We also considered potential loss processes for SiF.sub.4 in volcanic plumes and in Io's atmosphere including ion-molecule reactions, electron chemistry, photochemistry, reactions with the major atmospheric constituents, and condensation. Photochemical destruction (t.sub.chem [approximately equal to]266 days) and/or condensation as Na.sub.2SiF.sub.6 (s) appear to be the major sinks for SiF.sub.4. We recommend searching for SiF.sub.4 with infrared spectroscopy using its 9.7 [mu]m band as done on Earth. Author Affiliation: Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Campus Box 1169, Washington University, One Brookings Dr., St. Louis, MO 63130-4899, USA Article History: Received 7 February 2005; Revised 17 May 2005