H Atom Reactions in the Sonolysis of Aqueous Solutions

Article abstract of DOI:10.1021/j100311a026

Aqueous solutions of the spin trap 5,5-dimethylpyrroline N-oxide (DMPO) and or Br2, I2, MnO4^-, AuCl4^-, and Ag⁺ were irradiated with 1-MHz ultrasound under argon-hydrogen mixtures of various compositions.DMPO was found to trap only very small amounts of hydrogen atoms while substantially greater amounts could be scavenged by the other solutes.The yield of H atoms as measured by the ESR signal of the DMPO adduct decreased with increasing H2 concetration in the gas mixture.The yields of the reduction products of the other solutes passed through a maximum at about 20 vol percent H2.The efficiency of scavenging did not correlate to the rate constant of reaction with H in homogeneous solution.It seems that the ability of a solute to be accumulated at the liquid-gas interface cavitation bubbles strongly influences the scavenging efficiency.Thallium ions are reduced in solutions of high pH.This reduction is attributed to hydrated electrons which are formed in the reaction of the H atoms with OH^- anions.It is concluded that the local concetration of H atoms in the interfacial region of the cavitation spots is about 10^-3 M and that hydrated electrons are not primary products of sonolysis.