DIFFUSION-KINETIC MODELING OF THE GAMMA-RADIOLYSIS OF LIQUID CYCLOALKANES

A deterministic diffusion-kinetic model has been successfully applied to the radiation chemistry occurring in a typical spur produced in the gamma-radiolysis of liquid cyclopentane, cyclohexane, and cyclooctane . The predictions of the yields of the cycloalkenes, bicycloalkyls, an d the cycloalkyl iodides in solutions of iodine are in excellent agree ment with experimental data. The major adjustable parameters in the mo del are the characteristic radii of the initial Gaussian spatial distr ibutions of the reactive species. Values for these radii were found to be 0.5, 1.1, and 0.55 nm in cyclopentane, cyclohexane, and cyclooctan e, respectively. The results suggest that the spurs of cyclopentane an d cyclooctane are very small, ca. one molecular diameter, with resulti ng large local concentrations of reactants. With cyclohexane, the spur size is twice as large and the initial local concentrations are an or der of magnitude smaller. The experimentally observed temporal invaria nce of the cyclohexyl radical can be explained by competing effects in the spur evolution. Details and implications of the spur model are di scussed.