NOVEL DEVIATIONS FROM THE 'MIXTURE LAW' IN THE RADIOLYSIS OF HYDROCARBON MIXTURES

Abstract

The 'mixture law' states that, if the radiolysis of material A gives a product M with yield GM, then, in a mixture where the mole fraction of A is XA, the yield of M is GMXA.In the radiolysis of dilute mixtures of cyclohexane-d12 or of methylcyclohexane-d14 with other aliphatic hydrocarbons D2 is formed in a process which is first order with respect to the deutero compound. As a consequence these mixtures provide a sensitive method of detecting deviations from the mixture law.Experimentally the yield of D2 and the yield of HD vary widely from one solvent to another amongst the C5 to C10 hydrocarbons selected. The yields of D2 and HD are, approximately, linearly related. The solvents have similar quantitative effects on the yields for both deuterated hydrocarbons.These deviations from the mixture law cannot be explained in terms of kinetic effects (variations in rate constants caused by differing bond strengths), because the D2 yield measures a process without free radical intermediates. Mechanisms involving excitation transfer, ion–molecule reactions, and subexcitation electrons are discussed.