Kinetics and thermodynamics of the reaction SF6⇄SF5+F

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Abstract
A reanalysis of most of the existing data bearing on the strength of the S–F bond in SF6 does not support the generally accepted value of BDE(SF5–F)=390.8±15.1 kJ mol−1 at 298 K. Instead, a new value of BDE(SF5–F)=420±10 kJ mol−1 at 298 K is shown to be compatible with all the existing data. This conclusion is based on a critical examination of earlier shock‐tube data on the thermal decomposition of SF6, recent measurements of the rate constant for the reverse reaction, F+SF5, various experiments on ion thermodynamics and photoionization energetics, and studies of the chemiluminescent reactions of Ca and Sr atoms. As a consequence of the present analysis, we find that the rate expressions for SF6 decomposition and the reverse combination rate expressions (at the high pressure limit) are k(SF6→SF5+F)=1.7×1022(1/T)1.9 exp(−50 800/T)s−1, k(SF5+F→SF6)=1×10−11(T/300)−1 cm3 molecule−1 s−1 and the step‐size down for collisions of argon with SF6, in the temperature range 1700–2000 K, is about 400 cm−1. We are also able to derive a new value for the appearance energy of SF+5 from SF6 of 14.0 eV, and a new value for ΔfH(SF4)=−746±12 kJ mol−1.

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