Oxidation of bromide ions by hydroxyl radicals: spectral characterization of the intermediate BrOH•-.

The reaction of (•)OH with Br(-) has been reinvestigated by picosecond pulse radiolysis combined with streak camera absorption detection and the obtained spectro-kinetics data have been globally analyzed using Bayesian data analysis. For the first time, the absorption spectrum of the intermediate species BrOH(•-) has been determined. This species absorbs in the same spectral domain as Br(2)(•-): the band maximum is roughly at the same wavelength (λ(max) = 352 nm instead of 354 nm) but the extinction coefficient is smaller (ε(max) = 7800 ± 400 dm(3) mol(-1) cm(-1) compared with 9600 ± 300 dm(3) mol(-1) cm(-1)) and the band is broader (88 nm versus 76 nm). Quantum chemical calculations have also been performed and corroborate the experimental results. In contrast to Br(2)(•-), the existence of several water-BrOH(•-) configurations leading to different transition energies may account for the broadening of the absorption spectrum in addition to the higher number of degrees of freedom.