Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions

Highly concentrated potassium carbonate aqueous solutions are studied by picosecond pulse radiolysis with the purpose of exploring the formation processes of carbonate radical CO3 center dot-. The transient absorption band of solvated electron produced by ionizing is markedly shifted from 715 to 600 nm when the solute concentration of K2CO3 is 5 mol L-1. This spectral shift is even more important than that observed for the solvated electron in 10 mol L-1 KOH solutions. The broad absorption band of solvated electron in K2CO3 solutions overlaps with that of carbonate radical CO3 center dot- formed at ultrashort time. Nitrate ion is used to scavenge the solvated electron and to observe the contribution of carbonate radical CO3 center dot-. The analysis of the amplitude and the kinetics of carbonate radical formation in highly concentrated solutions shows that CO3 center dot- is formed within the electron pulse (7 ps) by two parallel mechanisms: a direct effect on the solute and the oxidation of the solute by water radical hole H2O center dot+. These two mechanisms are followed by an additional one, by reaction between the solute and OH center dot radical especially in lower concentration. The radiolytic yield of each process is discussed.