Photolysis of Liquid Water at 1849 Å

Abstract

The photolysis of pure water and of aqueous solutions of alcohols (methanol, ethanol, and isopropanol) at 1849 Å, when the light is absorbed by the water, proceeds according to [Complex chemical formula] The quantum yield for the formation of the geminate pair (H+OH) is φ=0.45 at room temperature. Scavengers compete with the recombination of the geminate pair according to diffusive inhomogeneous kinetics. A value of 3.9×10⁻⁶ sec^½ is obtained for the Noyes parameter a, in agreement with theory. The results exclude direct interaction between scavenger and excited water molecules and also exclude molecular processes in the formation of H₂. Solvated‐electron formation has a quantum yield of ≤0.045. Isotope experiments support the conclusions. In the reaction with the alcohols, that of the OH radicals determines the competition with secondary geminate recombination. From the results a value of k(dim)/k(dis)=6.6 is obtained for the ratio of dimerization to disproportionation of CH₂OH radicals.