NEGATIVE-ION CHEMISTRY OF SF4

A selected ion flow tube was used to conduct an extensive study of negative ion-molecule reactions of SF4 and SF4-. Rate constants and product ion branching fractions were measured for 56 reactions. The reactions bracket both the electron affinity of SF4 (1.5±0.2 eV or 34.6 ±4.6 kcal mol -1 ) and the fluoride affinity of SF3 (1.84±0.16 eV or 42.4±3.2 kcal mol-1). These results may be combined to give the neutral bond energy D(SF3-F)=3.74±0.34 eV or 86.2±7.8 kcal mol -1, independent of other thermochemical data except for the accurately known electron affinity of F. The heat of formation of SF 4- is derived from the electron affinity of SF 4:Δ fH(SF4-)=- 9.2 ±0.3 eV or -212.9±7.5 kcal mol-1. Lower limits to EA(SF 2) and EA(SF3) are deduced from observation of SF 2-(35%) and SF3-(65%) ion products of the reaction S-+SF4. Rapid fluoride transfer from both SF2- and SF3- to SF4 places upper limits on the electron affinities of SF2 and SF 3. The combined results are 0.2 eV≤EA(SF2)≤1.6 eV and 2.0 eV≤EA(SF3)≤3.0 eV. We review the status of measurements of EA(SFn), n = 1-7. © 1995 American Institute of Physics.