SIMPLE-MODEL FOR HYDROGEN-ATOM REACTIONS IN NEOPENTANE-CYCLOHEXANE MIXTURES IRRADIATED AT 4.2-K

In this paper, a simple model is given to explain why hydrogen atoms produced in crystalline neopentane at 77 K have a high probability of reacting with dilute solute molecules, whereas at 4.2 K they abstract hydrogen from neopentane matrix molecules. The model is based on the following assumptions: at 77 K hydrogen atoms which do not undergo short-range hot abstractions migrate until they encounter a solute molecule, and abstract hydrogen from it. At 4.2 K the hydrogen atoms which would be mobile at 77 K are immobilized at their place of birth and eventually abstract only from one of the molecules in the cage wall surrounding each hydrogen atom. The experimental data at 4.2 K are compared with estimates of the solute radical yields for different assumed values of (a) the fraction of hydrogen atoms which undergo short-range hot abstraction; (b) the ratio of the rate constants for the reaction of immobilized hydrogen atoms with a matrix and a solute molecule; and (c) the number of molecules in the cage wall. By this comparison plausible numerical values are obtained for each of these parameters. © 1979 American Chemical Society.