The transient optical absorption bands (λ_max= 315 and 345 nm) formed on reaction of ˙OH radicals with 1-chloro-3-iodopropane in N₂O-saturated neutral aqueous solutions have been assigned to an OH-adduct formed between iodine atom and ˙OH radicals (t_½= 1.5 µs, ε₃₅₀= 2.46 × 10³ dm³ mol^–1 cm^–1). In acidic solutions, iodine-centred radical cations (λ_max= 345 nm, t_½= 4.0 µs, ε₃₄₅= 2.41 × 10³ dm³ mol^–1 cm^–1) are formed at low solute concentrations and dimer radical cations (λ_max= 430 nm, t_½= 16.0µs, ε₄₃₀= 6.7 × 10³ dm³ mol^–1 cm^–1) at high solute concentrations. In chloroiodomethane, the ˙OH radicals do not seem to form OH-adducts in neutral aqueous solutions. In acidic solutions, intramolecular radical cation (λ_max= 430 nm, t_½= 8.0 µs, ε₄₃₀= 2.63 × 10³ dm³ mol^–1 cm^–1) with oxidized iodine and chlorine is observed. The intermolecular dimer radical cations are formed at high solute concentration (λ_max= 500 nm).