The Efficiency of the Primary Photochemical Process in Solution

Abstract

A study has been made of the effect of an inert solvent on the efficiency of the primary process in the photolysis of oxalyl bromide and nitrosyl chloride. The oxalyl bromide was studied at the wave‐lengths 2650, 3130, 3650, 4047, and 4358A, the nitrosyl chloride at 3650, 4047, 4358, 5461, and 5790A. In order to eliminate the back reaction between nitric oxide and chlorine, oxygen was introduced which converted the nitric oxide into nitrogen dioxide. The solvent used was carbon tetrachloride. Quantum yields for nitrosyl chloride showed only a slight trend ranging from 0.7 at 3650A to 0.5 at 5790A as compared to approximately 2 at all wave‐lengths in the gas phase. Oxalyl bromide gave approximately the same quantum yield in solution as in the gas phase at 2650A, i.e., ∼0.9, and the values in solution decreased to ∼0.3 at 4358A with most of the change occurring between 3130 and 3650A. The results are discussed in terms of the Franck‐Rabinowitch hypothesis and it is pointed out that they are most readily accounted for by assuming a deactivating action of the solvent rather than a high efficiency of recombination. A new quartz capillary arc of high intensity is described. The equilibrium N2O4=2NO2 has been studied in carbon tetrachloride solution and the equilibrium constant at 25°C found to be 6.4×10—5, concentrations expressed in mole fractions.