Negative ion–molecule reactions of SF4

Abstract

A study of some negative ion–molecule reactions involving SF4 has been carried out by the flowing afterglow technique at ambient temperature. By examining a series of charge exchange reactions of SF4 and SF4−, the electron affinity of SF4 has been determined to be 2.35±0.1 eV. Rate coefficients for the charge exchange reactions of HS−, S−, OH−, and O− with SF4 and of SF4− with Cl2 and NO2 are reported. In addition, the fluoride transfer reactions of SF4− and SF6− with SF4 to produce SF5− have been examined. That both reactions proceed indicates that the fluoride affinity of SF4 is greater than that of SF3 or SF5. A lower limit of 3.7 eV for the electron affinity of SF5 may also be deduced from the fluoride transfer reactions. The two body addition of halide ions (X−) to SF4 to form the adduct SF4X− proceeds at near the collision limit (k = 9.7×10−10 cm3 molecule−1 s−1) for F−, very slowly (k = 2.6×10−11 cm3 molecule−1 s−1) for Cl−, and not at all within experimental limits (k<2×10−12 cm3 molecule−1 s−1) for Br−.