Ion–molecule reactions of SF6: Determination of I.P.(SF5), A.P.(SF5+/SF6), and <i>D</i>(SF5–F)

Abstract

SF6 reacts with CF3+ to produce SF5+ and CF4. Under conditions of large amounts of CF4, an equilibrium is established. From flowing afterglow data, not only is a forward rate constant kf = (2.5±0.2)×10−10 cm3 molecule−1 s−1 determined, but also an equilibrium constant of 5.9×103 (±50%) is deduced. Using this equilibrium constant and standard entropies for the various species, ΔH°298 = −0.17±0.02 eV is calculated. A thermochemical cycle then yields a value of A.P.(SF5+/SF6) = 14.62±0.09 eV. An examination of charge exchange reactions of SF5+ leads to establishment of the ionization potential of SF5 at 10.5±0.1 eV. Combining this with A.P.(SF5+/SF6) allows a calculation of the bond dissociation energy D°298(SF5–F) = 4.1±0.13 eV. In addition to these new values of A.P.(SF5+/SF6), I.P.(SF5), and D°298(SF5–F), the fragmentation pattern of SF6 reacting with He+ as well as rates of reaction of SF6 with several positive ions are reported.