Transfer of F− in the reaction of SF 6 − with SOF4: Implications for SOF4 production in corona discharges

The temperature (T) and electric field-to-gas pressure (E/P) dependences of the rate coefficientk for the reaction SF ₆ ^– +SOF₄SOF ₅ ^– +SF₅ have been measured. ForT<270 K,k approaches a constant of 2.1×10^–9 cm³/s, and for 433>T>270 K,k decreases withT according tok (cm³/s)=0.124 exp –3.3 lnT(K)]. ForE/Pk has a constant value of about 2.5×10^–10 cm³/s, and for 130 V/cm·torr>E/P>60 V/cm·torr, the rate is approximately given byk (cm³/s)7.0×10^–10 exp (–0.022E/P). The measured rate coefficient is used to estimate the influence of this reaction on SOF₄ production from negative, point-plane, glow-type corona discharges in gas mixtures containing SF₆ and at least trace amounts of O₂ and H₂O. A chemical kinetics model of the ion-drift region in the discharge gap is used to fit experimental data on SOF₄ yields assuming that the SF ₆ ^– +SOF₄ reaction is the predominant SOF₄ loss mechanism. It is found that the contribution of this reaction to SOF₄ destruction falls considerably below the estimated maximum effect assuming that SF ₆ ^– is the predominant charge carrier which reacts only with SOF₄. The results of this analysis suggest that SF ₆ ^– is efficiently deactivated by other reactions, and the influence of SF ₆ ^– +SOF₄ on SOF₄ production is not necessarily more significant than that of other slower secondary processes such as gas-phase hydrolysis.