Pulse radiolysis of aqueous solutions of tetraphenylphosphonium ions

The reactions of tetraphenylphosphonium ion (Ar₄P⁺) with e_aq⁻, H atoms and OH radicals have been investigated. The absorption spectra of three transient species were obtained. Ar₄P· radicals formed by the reaction: Ar₄P⁺ + e_aq⁻ → Ar₄P· have a maximum absorption at 305 nm [ε₃₀₅ = (9400 ± 300) dm³ mol⁻¹ cm⁻¹] and decays by second-order kinetics with the rate constant 2k = (2·7 ±0·4) × 10⁹ dm³ mol⁻¹ s⁻¹. H atoms and OH radicals form transient adducts to the phenyl groups of the Ar₄P⁺ ion with the rate constants of (1·5 ± 0·3) × 10⁹ dm³ mol⁻¹ s⁻¹ and (3·0±0·3) × 10⁹ dm³ mol⁻¹ s⁻¹, respectively. Both adducts have broad absorption spectra at 300≈380 nm (λ_max = 340 nm) with the molar extinction coefficients ε₃₄₀ = 5400±300 dm³ mol⁻¹ cm⁻¹ for the H adduct and ε₃₄₀ = 3500±200 dm³ mol⁻¹ cm⁻¹ for the OH adduct.