Inert gas effects in the photosynthesis of hydrogen bromide

Abstract

Recent studies of many chemical gas reactions which involve the production and behaviour of atoms, have shown that the effect of the surface of the reaction vessel on the atom concentration can seldom be regarded as a small disturbing factor to be allowed for by a semi-empirical correction, but must be adequately considered in relation to the other processes determining the velocity of reaction. In this connection, therefore, alteration in the pressure of any one reactant must involve an effect depending on the diffusion coefficient of the atom concerned, with regard to the expected from the mass action principles of the chemical kinetics. Examples of this simple diffusion effect are well known. The results to be expected on these lines are sometimes complicated by the existence of other factors consequent on increase in pressure in the reacting system. In the photosynthesis of hydrogen bromide, where bromine atoms are involved, it has been shown that increase in total pressure, by the introduction of an otherwise inert gas, produces a relative decrease in reaction velocity, where the application of the simple diffusion theory as above would lead one to expect an increase in velocity by prevention of the removal of bromine atoms by the walls. This decrease has been attributed to the stabilization of the bromine “quasi-molecule” by the added gas molecule, the removal of bromine atoms being thus facilitated by what is virtually a triple collision. Similar considerations apply to the photochemical formation of posgene.