Aspects of the chemistry of SF₆/O₂ plasmas

Abstract

The production ofSOF ₄ initiated by the reaction of F atoms withSOF ₂ 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 ofSOF ₄ has been analyzed in terms of the competing reactionsSOF ₃+F→SOF₄ andSOF ₃+O→SO ₂ F ₂+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 andSOF ₃ 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 ofSOF ₄ andSO ₂ F ₂ which are observed inSF ₆/O ₂ plasmas. This suggests thatSF ₂ is a major precursor in the sequence of reactions following the dissociation ofSF ₆.