Luminescence, laser flash photolysis and continuous photolysis studies of equilibrated solutions of CuBr2- and CuBr32- were carried out in the UV region. Excitation of the absorption band at 279 nm in CuBr32- results in emission centered at 475 nm, with a lifetime of 710 ns in neutral solution, and quenched by hydronium ions with a rate constant of 6.2 × 108 M-1 s-1. Neutral solutions of the complexes produce hydrated electrons when they absorb 15 ns pulses of laser light at 266 nm. The electrons are scavenged by the copper(I) species itself with a second-order rate constant of 7.5 × 109 M-1 s-1, and by hydronium ions with a second-order rate constant of 1.3 × 1010 M-1 s-1 at 0.5 M ionic strength. Individual quantum yields of electron production, determined at 1 M ionic strength, are 0.67 for CuBr2- and 0.34 for CuBr32-. Continuous photolysis of acidic solutions of the complexes reveals a dependnece on hydronium ion concentration which is different from that for the scavenging of electrons, a dependence on Br- concentration and an action spectrum consistent with the 279 nm absorption band as the photoactive state. These plus other observations and arguments support a mechanism for dihydrogen evolution, involvin the formation of a steady state hydride intermediate which reacts with H+ to form dihydrogen.
|Number of pages||13|
|Journal||Journal of Photochemistry and Photobiology, A: Chemistry|
|Publication status||Published - Aug 30 1991|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Physics and Astronomy(all)