The photocombination of hydrogen and chlorine in oxygen-free systems

Abstract

The photosynthesis of hydrogen chloride has been studied under varied conditions of light intensity and of hydrogen, chlorine, hydrogen chloride, nitrogen and argon pressures. The inhibiting actions of chlorine and hydrogen chloride are considered confirmed. With increasing pressure of hydrogen chloride, the quantum efficiency decreased continuously, while with chlorine and also with nitrogen and argon, maxima were observed at intermediate pressures, after which the quantum efficiency fell progressively. With increasing light intensity at the lower pressures, the quantum efficiency was found to decrease to a constant value. Further, the change in intensity exponent with increasing pressure has been investigated, and values approaching 0.5 at high pressures have been observed. In the case of hydrogen chloride indices less than 0.5 were noted at the highest pressures. These results are discussed on the basis of the following scheme: hv Cl 2 ->Cl + Cl, Cl 3 + M ->Cl 2 +Cl+ M , Cl + H 2 ->HCl + H, Cl 3 + Cl 3 -> 3Cl 2 , H + Cl 2 -> HCl + Cl, Cl -> surface, Cl + Cl 2 + M ->Cl 3 + M , Cl 3 -> surface. To account for the abnormally low indices observed at high pressures, other chain ending processes are necessary; it is believed that the reactions Cl + Cl 3 -> 2Cl 2 and Cl + Cl + M -> Cl 2 + M are of importance in this connexion