STUDIES OF WATER VAPOR DISSOCIATED BY MICROWAVE DISCHARGES AT LOW FLOW RATES .I. EFFECT OF RESIDENCE TIME IN TRAVERSED VOLUME ON PRODUCT YIELDS AT LIQUID AIR TEMPERATURE

Yields of hydrogen peroxide and evolved oxygen from the products trapped at liquid air temperature from water vapor dissociated by a low pressure microwave discharge at low flow rates were determined as functions of the time elapsing between the dissociation of the vapor and trapping of the dissociated products, using different traversed volumes and inlet pressures. For very small traversed volumes the yields of both H2O2 and evolved O2 were negligible at all discharge powers studied, suggesting that either OH was not present in the gases passing out of the discharge or that, at least when H is present, OH radicals do not dimerize in a liquid air-cooled trap to form H2O2, but react with H to form H2O. Both yields increased to a maximum and decreased thereafter with increasing traversed volume (at constant pressure) and increasing discharge pressure (at constant traversed volume), but were not affected markedly by increasing the discharge power. In any case, the maxima did not coincide and the evolved oxygen to peroxide ratio varied with traversed volume and pressure. However, the ratio was independent of the discharge power at all traversed volumes, thus indicating that the oxygen evolution is not due to decomposition of H2O2 by impurities carried over from the discharge. Finally, material balances showed that O2 passed through the cold trap only at pressures and traversed volumes higher than those at which the peroxide yield was a maximum, suggesting that O2 is one of the precursors involved in the formation of H2O2 and evolved O2.