Formation and reactions of Co+ ions in aqueous solutions: A pulse radiolysis study

The formation of Co+ ions in the reaction of hydrated electrons with Co2+ i ons in aqueous solutions containing an alcohol (methanol, ethanol, isopropa nol, or tert-butanol) or formats ions was studied using a pulse radiolysis technique. The optical spectrum of Co+ exhibits absorption that increases t oward the UV region with lambda(max) less than or equal to 220 nm (epsilon = 5.4 x 10(3) l mol(-1) cm(-1)) in addition to the bands with maximums at 3 15 and 370 nm. The molar absorption coefficients for these bands were found to be 4.4 x 10(3) and 4.8 x 10(3) l mol(-1) cm(-1), respectively. Alcohol radicals and CO2- radical ions oxidize Co+ ions. The rate constants of thes e reactions were found. The reduction potentials for the Co2+/Co-0 and Co+/ Co-0 pairs (Co-0 is the cobalt atom) were calculated to be approximately -2 .3 and -2.9 V, respectively. The reaction mechanisms for the reduction of C o2+, Ag+, Tl+, and Cd2+ ions by CO2- radical ions are discussed.