Atomic resonance fluorescence spectrometry for the rate constants of rapid bimolecular reactions. Part 2.—Reactions Cl + BrCl, Cl + Br2, Cl + ICl, Br + IBr, Br + ICl

Abstract

Atomic resonance fluorescence spectrometry has been used to measure directly the rates of rapid bimolecular reactions of halogen atoms (²P) with halogen molecules at 298 K. Low concentrations of atoms (∼10¹¹ atom cm^–3) were generated in a flow system with a discharge-bypass. The following rate constants (cm³ molecule^–1 s^–1) are reported: Cl + BrCl → Cl₂+ Br, k₁=(1.45 ± 0.20)× 10^–11; Cl + Br₂→ BrCl + Br, k₂=(1.20 ± 0.15)× 10^–10; Cl + ICl → Cl₂+ I, k₃=(8.0 ± 1.0)× 10^–12; Br + ICl → BrCl + I, k₄=(3.0 ± 0.8)× 10^–14; Br + IBr → Br₂+ I, k₅=(3.5 ± 0.6)× 10^–11. k₂ is equal to ∼0.5 of the hard sphere bimolecular collision frequency at 298 K.

The values for k₂ and k₄ ae in good agreement with integral reaction cross sections determined in crossed molecular beams.