Aspects of the chemistry of SF6/O2 plasmas

The production ofSOF₄ initiated by the reaction of F atoms withSOF₂ has been studied in a gas-flow reactor at 295 K for helium bath gas number densities in the range (3.0–27.0)×10¹⁶ cm^-3. The effect of O atoms on the formation ofSOF₄ has been analyzed in terms of the competing reactionsSOF₃+F?SOF₄ andSOF₃+O?SO₂F₂+F. This analysis leads to the conclusion that the rate coefficients for these two processes are equal within an uncertainty of about 50%. Furthermore, both experiment and calculations indicate that the rate coefficient for reactions between F atoms andSOF₃ is close to its high-pressure limit under the conditions employed. The experiments set a lower limit on this rate coefficient of 5×10^-11 cm³ s^-1, while calculations based on unimolecular rate theory suggest that it may be greater than 1×10^-10 cm³ s^-1. These results make it clear that the two reactions shown above cannot explain the relative abundances ofSOF₄ andSO₂F₂ which are observed inSF₆/O₂ plasmas. This suggests thatSF₂ is a major precursor in the sequence of reactions following the dissociation ofSF₆.