Reaction kinetics of ground state fluorine, F 2P, atoms. Part 2.—Reactions forming inorganic fluorides, studied mass spectrometrically

Abstract

Elementary reactions involving F ²P atoms have been studied kinetically in a discharge-flow apparatus at 296–298 K, using mass spectrometric detection with a beam inlet system. Reactions of F with the following molecules have been investigated: Cl₂, Br₂, I₂, ICl, HOF, CO, Xe, Kr, XeF₂, XeF₄ and BrO₃F.

The rates of reaction of F with all three halogen molecules at 298 K are close to the hard-sphere bimolecular collision frequency, and we report the following rate constants (cm³ molecule^–1 s^–1): F + Cl₂ [graphic omitted] ClF + Cl …(1); k₁=(1.6 ± 0.5)× 10^–10;, F + Br₂ [graphic omitted] BrF + Br …(2); k₂=(3.1 ± 0.9)× 10^–10;, F + I₂ [graphic omitted] IF + I …(3); k₃=(4.3 ± 1.1)× 10^–10;. The overall rate constant, k₄, for the F + ICl reaction is (5 ± 2)× 10^–10 cm³ molecule^–1 s^–1; the major reaction channel (4a) forms IF + Cl. This result supports a new determination of the dissociation energy, D^°₀(IF)=(277 ± 2) kJ mol^–1. A minor reaction channel in F + ICl forms ClF + I (reaction 4b) and k_4a/k_4b has been determined to be (3.3 ± 0.7). IF is kinetically unstable, and rapidly forms IF₅ via a heterogeneous reaction mechanism.

F atoms react with CO and Xe via slow reactions considered to be kinetically third order to yield COF₂ and XeF₂, respectively, as final products. The third order rate constants (cm⁶ molecule^–2 s^–1), at 298 K, defined by k_6,M=–[M]^–1[CO]^–1 d ln[F]/dt and k_7,M=–[M]^–1[Xe]^–1 d ln[F]/dt, with M = Ar and He, are k_6,Ar=(5_·0± 1_·0)× 10^–32, k_6,He=(3.4 ± 0.5)× 10^–32, and k_7,Ar≃ 2 × 10^–33. No reaction was observed between F atoms and krypton, and an upper limit of 2 × 10^–34 was set for the analogous third order rate constant for this reaction with M = He.

Abstraction of H from HOF by F was rapid (k 2 × 10^–10 cm³ molecule^–1 s^–1), and FO radicals were detected as a reaction product: F + HOF → HF + FO. On the other hand, no reaction could be observed between F and XeF₂, XeF₄ or BrO₃F (k < 7 × 10^–16 cm³ molecule^–1 s^–1).