Abstract
The kinetics of the binding of Br to Fe(III) were studied as a function of [H+] and [Br] on a high pressure laser temperature jump apparatus up to 2.76 kbar. At constant [H+] the pseudo first order rate constant for formation of FeBr2+ showed little dependence on pressure or on [Br] over the range 0.02 to 1.9 M. The results were interpreted by a mechanism in which Fe3+ and FeOH2+ react with Br to form ion pairs prior to formation of their inner sphere complexes. The kinetic activation volume for the conversion of the Fe3+, Br ion pair to FeBr2+ appears to be quite negative, consistent with an associative interchange (Ia) mechanism.