The process of Photolysis is associated with Oxygen Evolving Complex (OEC) or water splitting complex in pigment system II and is catalysed by the presence of Mn++ and Cl- . When the pigment system II is active it receives light and the water molecule splits into OH- ions and H+ ions. The OH- ions unite to form water molecules again and release O2 and electrons. Photolysis of water is due to strong oxidant which is yet unknown and designated as Z or Yz.
Widely accepted theory proposed by Kok et al., (1970) explaining photo – oxidation of water is water oxidizing clock (or) S’ State Mechanism. It consists of a series of 5 states called as S0 , S1 , S2, S3 and S4 . Each state acquires positive charge by a photon (hv) and after the S4 state it acquires 4 positive charges, four electrons and evolution of oxygen. Two molecules of water go back to the S0. At the end of photolysis 4H+ , 4e- and O2 are evolved from water.
