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Oxidation of Bromide Ions by Hydroxyl Radicals: Spectral Characterization of the Intermediate BrOH•–

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posted on 07.02.2013 by Isabelle Lampre, Jean-Louis Marignier, Malaknaz Mirdamadi-Esfahani, Pascal Pernot, Pierre Archirel, Mehran Mostafavi
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 Br2•–: the band maximum is roughly at the same wavelength (λmax = 352 nm instead of 354 nm) but the extinction coefficient is smaller (εmax = 7800 ± 400 dm3 mol–1 cm–1 compared with 9600 ± 300 dm3 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 Br2•–, 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.

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