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 k4a/k4b 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 k6,M=–[M]–1[CO]–1 d ln[F]/dt and k7,M=–[M]–1[Xe]–1 d ln[F]/dt, with M = Ar and He, are k6,Ar=(5·0± 1·0)× 10–32, k6,He=(3.4 ± 0.5)× 10–32, and k7,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).