Study of the Gas Phase Reactions of Several Perfluorocarbons with Positive Ions of Atmospheric Interest

The bimolecular rate coefficients and ion products for the reactions of H3O+, NO+, O2+, H2O+, N2O+, O+, CO2+, CO+, N+, and N2+ with three fluoroalkenes (C2F4, C3F6, and 2-C4F8) and three fully saturated perfluorocarbons (C2F6, C3F8, and n-C4F10) at 300 K are reported. All six perfluorocarbons are found to be unreactive with NO+. C2F6 is also unreactive with O2+, H2O+, and N2O+, and C3F8 and n-C4F10 are also unreactive with O2+. C3F6 is the only perfluorocarbon studied that reacts with H3O+ at a measurable rate. All the other reactions take place at or close to the collisional rate, the exceptions being the reactions of N2O+ with C2F4 and C3F8, and CO2+ with C2F4 and C2F6, for which the experimental rate coefficients show marked departures from the collisional values. It is proposed that most of the reactions proceed through a complex intermediate resulting in electrophilic attack by the ion on the perfluorocarbon. This mechanism generally takes precedent over “long-range” (formal) charge transfer. This work is of possible relevance to atmospheric ion-chemistry and plasma processes and may also be pertinent to the use of chemical ionization mass spectrometers for the trace detection of perflurocarbons in the environment.