A temperature-dependent selected ion flow tube study of anions reacting with SF5CF3

Abstract

Rate constants and product distributions were measured for the reactions of trifluoromethyl sulfurpentafluoride (SF5CF3) with 11 anions using two selected ion flow tube instruments. The reaction of O2− was studied from 240 to 500K and was found to proceed at approximately 30% of the collisional rate, yielding SF5− as the only product ion, presumably via a dissociative electron transfer mechanism. The reaction of OH− proceeds predominantly via nucleophilic attack at the carbon atom, displacing SF5− at approximately 25% of the collisional rate at 298K. The rate constant exhibits a T−1.8 dependence from 240 to 500K, suggesting the reaction occurs through a long-lived collision complex. The F− reaction, which proceeds at 70% the collisional rate at 298K, also occurs via nucleophilic attack at the carbon atom, leading to the SF5− product ion. The O− ion reacts predominately by nucleophilic attack at the carbon atom and also via CF3 radical transfer to O−. The product branching fraction for the O− reaction did not vary with temperature, although the rate constant exhibits a T−1.6 dependence, similar to that of the OH− reaction. The ions SF6−, CF3−, NO2−, CO3−, Cl−, NO3−, and SF5− were found to be unreactive toward SF5CF3, despite the fact that sufficiently exothermic reactive channels exist for many of these ions.