Reactivity of Negative Ions with Trifluoromethyl Halides

Abstract

The kinetics of reactions of selected anions (A-) with the trifluoromethyl halides CF3X (X = F, Cl, Br, I) in the gas phase were measured at 300 K. Reaction rate constants and product branching fractions were determined using a selected ion flow tube (SIFT) instrument. The chosen anions were C5F5N-, o-, m-, and p-CF3C6H4CN-, C6F5Br-, C6F5Cl-, C6F5CF3 -, C6F5COCH3 -, Fe-, FeCO-, SF6 -, SO-, SO2 -, NO-, NO2 -, and NO3 -. The reactivity of these systems varies from unreactive to collisional, and a variety of reaction types was found. The results of our present and previous measurements on A- + CF3X reactions show that, in cases where nondissociative electron transfer (NDET) is energetically allowed, the total reactivity tends to be high, approaching collisional. This suggests that reactivity in these cases is initiated and controlled by electron transfer from the anion. In addition, association reactions tend to be preempted when NDET is energetically allowed. A few exceptions to these tendencies were found and are discussed.

Reactivity of gas-phase anions with fully halogenated alkanes

“…For the negative ions A-tabulated here, the electron detachment energies (DEs) (or the EAs of the corresponding neutrals A) are not known for most of the transition metal complex anions but are available for most of the small anions (Miller 1995). As we have reported previously (Morris et al 1995c(Morris et al , 1996, when the EA of CF,X exceeds the DE of A-, i.e. when nondissociative electron transfer (NDET) is exothermic, the reaction is usually fast (except for SF; where a large geometry change is required, as discussed below).…”

“…The 0; reactions form X-for all X and, for CF,Br and CF,I, also generate the product of nondissociative electron transfer, CF,X-. Actual CF,Xproduction has been reported for these cases and for the reaction of SO-with CFJ (Morris et al 1995c(Morris et al , 1996. The direct observation of CF,X-lends support to the initial electron transfer mechanism.…”

“…Branching (Morris et al 1995c(Morris et al , 1996 (Fehsenfeld 1971) exothermic pathways for some of the unreactive systems, e.g. 0-+ CF, + F-+ CF,O, but the strong C-F bond represents a likely barrier to reaction.…”

“…CF,X adduct, which influences the association reaction rate (Bates 1979, Herbst 1980. Examples of this trend include the reactions of NO; and NO, with CF,X (Morris et al 1996).…”

Low Pressure Gas-phase Reactions of the Atomic Oxygen Radical Anion with Halomethanes Studied Using Fourier Transform Ion Cyclotron Resonance

“…This reaction is known to yield free electrons and also relatively abundant NO -ions, 21,22 which may react further with the halomethanes. 23,24 A second series of experiments was performed with a higher pressure of nitrous oxide in order to examine the influence of the pressure of this neutral species on the product ion distributions. In these experiments, the ratio between the partial pressures of nitrous oxide and a halomethane was 1:1, the total pressure being Ϸ 5 × 10 -5 Pa.…”