Intermediates in the nanosecond pulse radiolysis of dimethylaniline solutions in cyclohexane

Abstract

The intermediates formed in solutions of dimethylaniline (DMA) in cyclohexane subjected to pulse irradiation have been studied using absorption spectrophotometry on a nanosecond timescale. In deaerated solutions two species with absorption maxima at 370 and 460 nm are observed. The latter is attributed to the triplet state of DMA and the former to the cyclohexadienyl radical derivative formed by hydrogen atom addition to DMA. In oxygen saturated solutions both intermediates decay rapidly (τ_½≲ 20 ns), but a relatively slowly decaying species (τ_½≃ 1 µs) with an absorption maximum at 470 nm remains. The end-of-pulse yield of this species increases by only a factor of ∼2 in going from 10^–4 to 10^–1 mol dm^–3 DMA and is identified as the DMA radical cation, DMA⁺. On addition of the electron scavenger perfluoromethylcyclohexane (C₇F₁₄) to an O₂ saturated solution, the end-of-pulse yield of DMA⁺ is increased. This additional yield induced by the presence of C₇F₁₄ decays very rapidly (τ_½ < 100 ns). The results are discussed in terms of the scavenging of free and geminate solvent positive ions by DMA and the effect of electron scavenging on the yield and decay kinetics of DMA⁺.