Study on decay characteristics of OH radical density in pulsed discharge in Ar/H2O

We measured the time-resolved two-dimensional distribution of OH radicals generated in a pulsed discharge by means of laser-induced fluorescence. The pulsed discharges were generated between point-plane electrodes in Ar/H2O(9%) at a medium pressure of 26.7 kPa. The decay process of OH density in Ar/H2O discharge was investigated by rate equations considering OH, H, O, O-2, H-2, HO2 and H2O2. By fitting the calculated OH decay profile to the experimental one, the OH density was estimated to be 3 x 10(15) cm(-3) under the present gas discharge conditions. At the same time, the densities of other important oxidizing radicals, H2O2 and HO2, were evaluated. The major OH decay process was confirmed to be OH + OH + M --> H2O2 + M, OH + OH --> H2O + O and OH + H + M --> H2O + M, under the present discharge conditions.