CHEMISTRY OF CFN+ (N = 1-3) IONS WITH HALOCARBONS

The gas-phase reactions of CF+, CF2+, and CF3+ with the halocarbons CF3Cl, CF3Br, CF3I, CF4, and C2F6 have been studied using a variable-temperature-selected ion flow tube (VT-SIFT) instrument at 300 and 496 K. The ion CF+ reacts rapidly with CF3X (X = Cl, Br, I) producing the ions CF2X+. In the reaction of CF+ with CF3Cl, CF3+ is also produced as a minor product. Curvature was observed in the pseudo-first-order kinetics plots for the reactions of CF+ with CF4 and C2F6. In both cases the curvature is attributed to the presence of two or more CF+ states (probably vibrational) of differing reactivities toward the perfluorocarbon of interest. This conclusion is supported by our observation of charge transfer from CF+ to NO, a reaction which is endothermic by 15 kJ/mol for the ground state of CF+. CF+ is unreactive with O2, N2, and Xe. The reactions of CF2+ with CF3X yield CF3+ and CF2X+ for X = Cl and Br; for X = I, CF2I+ and CF3I+ are produced. The overall reactions proceed at approximately the collision rate at 300 and 496 K, and the branching ratios are not strongly dependent on temperature. The reactions of CF2+ with CF4 and C2F6 produce CF3+ and C2F5+, respectively. The rate constants decrease significantly with increasing temperature. CF2+ reacts rapidly by charge transfer with NO. The reaction of CF2+ with O2, producing CF2O+, is inefficient. CF2+ is unreactive with N2. CF3+ reacts with CF3X (X = Cl, Br, I) at rates below the collision values, producing a single ionic product, CF2X+. While the rate constants for the reactions of CF3+ with CF3X increase in the series with increasing CF3X mass, the rate constants for reaction with each CF3X decrease sharply with increasing temperature. A mechanism is proposed in which the reaction proceeds on a double-well potential energy surface. No reaction was observed for the CF3+/CF4 system. CF3+ appeared to react very slowly with C2F6 and NO, producing C2F5+ and NO+, respectively, but reactions with impurities in the neutral reagents cannot be ruled out as the source of these ions. CF3+ is unreactive with O2 and N2.