Diffusion−Kinetic Modeling of the γ-Radiolysis of Liquid Cycloalkanes

Abstract

A deterministic diffusion−kinetic model has been successfully applied to the radiation chemistry occurring in a typical spur produced in the γ-radiolysis of liquid cyclopentane, cyclohexane, and cyclooctane. The predictions of the yields of the cycloalkenes, bicycloalkyls, and the cycloalkyl iodides in solutions of iodine are in excellent agreement with experimental data. The major adjustable parameters in the model are the characteristic radii of the initial Gaussian spatial distributions of the reactive species. Values for these radii were found to be 0.5, 1.1, and 0.55 nm in cyclopentane, cyclohexane, and cyclooctane, respectively. The results suggest that the spurs of cyclopentane and cyclooctane are very small, ca. one molecular diameter, with resulting large local concentrations of reactants. With cyclohexane, the spur size is twice as large and the initial local concentrations are an order of magnitude smaller. The experimentally observed temporal invariance of the cyclohexyl radical can be explained by competing effects in the spur evolution. Details and implications of the spur model are discussed.

Radical yields in the radiolysis of cyclic compounds

“…Previous radiation chemistry studies on the decomposition of cyclopentane, cyclohexane, and cyclooctane focused on the similarities in the types of products to extract information on the underlying mechanism (LaVerne et al, 1997;Wojnarovits and LaVerne, 1998). Although the absolute yields vary slightly, these studies suggest that a common scheme can explain the observed products in a wide variety of organic liquids.…”

Radiation chemistry of organic liquids: Saturated hydrocarbons

“…For example, in radiolysis of cyclohexane, the yield of the S 1 states is only 1.45±0.15 per 100 eV [104] (other estimates are 1.5±0.4 [105], 1.4-1.7 [100], and 1.75 per 100 eV [89]) while the T 1 states are generated at 3.4 per 100 eV [89], as estimated from the solvent luminescence yield and the product analysis, respectively. If these S 1 states were mainly produced in recombination of electron-hole pairs (as follows from studies of the effect of electron scavengers on the yield of solvent luminescence), the radiolytic yields would seemingly be equal to the G-value of ionization times the singlet recombination probability, f s .…”

“…Radiolytic yields of solvent excited states in decalins (3 MeV electrons) [108] and cyclohexane ( 60 Co ©-radiolysis) [89] estimated from product analysis.…”

Radiation Chemistry of Organic Liquids: Saturated Hydrocarbons

“…Modeling of light -particle spurs. Many simulations of the spur kinetics in hydrocarbons have been reported over the last decade [84][85][86][87][88][89] (see reference [84] for a review). As may be anticipated, none of these simulations attained the level of complexity needed to obtain a selfconsistent picture of the early radiolytic events in hydrocarbons.…”

“…Due to the limited state of knowledge, the present-day simulations should be viewed as exploratory. While some researchers focus on the general aspects of spur dynamics using stochastic Monte Carlo simulations [84][85][86][87][88], others focus on the chemical kinetic aspects assuming simple (inhomogeneous) dynamics [23,24,89]. There are also models intended to integrate the chemical kinetics and the charge recombination dynamics [25,65].…”