Rate Constants For F- Transfer from SF6- to Fluorinated Gases and SO2. Temperature Dependence and Implications or Electrical Discharges in SF6

Article abstract of DOI:10.1021/j100314a025

The reactivity of SF6^- toward SO2, SOF2, SO2F2, SOF4, SF4, and SiF4 has been investigated by using the technique of pulsed electron beam high-pressure mass spectrometry.These studies were initiated in order to probe the complex anionic chemistry occuring during electrical discharge in SF6.Although no reaction of any type was observed with SOF2 and SO2F2, efficient F^- transfer of the type SF6^- + A --> AF^- + SF5 was found in all of the other systems including the SO2F^- + SOF4 pair, which was studied separately.With the exception of the SF6^- + SiF4 reaction, all of the pairs exhibited a negative temperature coefficient in that the rate constants for F^- transfer decreased substantially with increasing temperature.The reaction SF6^- + SiF4 --> SiF5^- + SF5 was found to proceed with a rate constant of (5.6 +/-0.8)E-10 cm³/(molecule*s) throughout the temperature range studied (298-510 K), which corresponds to a collision efficiency of unity.The other reactions were found to approach unit collision efficiency only at reduced temperatures (<300 K).The reactions studied were used to provide additional information concerning the gas-phase F^- affinity scale, and the F^- affinity of SiF4 was defined as 2.2 +/-0.4 kcal/mol higher than SOF4 via equilibria measurements.The placement of SF5 within the F^- affinity scale indicates that SF6^- is reactive toward several of the major stable byproducts generated during electrical breakdown in SF6.This behavior was verified by direct observation of the temporal growth and decay profiles of the various anions produced after pulsed ionization of an SF6 sample which had been subjected to prior partial decomposition in a negative corona discharge.Some comments are also included concerning the stability of the SF6^-*SF6 dimer ion, and the implications of all of the present data with respect to mobility measurements in SF6 are also discussed.