Photolysis of periodate and periodic acid in aqueous solution

The photochemistry of periodate and periodic acid in aqueous solution was studied (i) by quantum yield measurements at low light intensity (ii) by flash photolysis, and (iii) by photolysis of glassy samples at 77 K. The photochemical studies were supplemented with pulse radiolysis studies of aqueous periodate solutions and with kinetic studies using stopped-flow technique. In strongly alkaline solution the photodecomposition of periodate proceeds via formation of O- and Isup(VI). At pH < 12 an additional primary process is the formation of Isup(V) and H2O2. In neutral solution O3P is formed in a small yield. The energetics of the reaction of O1D with H2O with formation of H2O2 is discussed. It is suggested that oxygen atoms are formed only from IO4- and not from other Isup(VII) species. Mechanisms for the secondary processes involving Isup(VIII) and Isup(VI) are given. Isup(VIII) and its relatively stable complex with Isup(VII) both form Isup(V), Isup(VII) and O2. Depending on pH and concentration, Isup(VI) either disproportionates to Isup(V) and Isup(VII), reacts with Isup(VII) with formation of Isup(V) and Isup(VIII) or dissociates into O-(OH) and Isup(V). (author)