Rates of Decomposition of Light and Deuterated Alkyl Radicals. 2-Hexyl and 2-Hexyl-d12, and 2-Octyl and 2-Octyl-d16

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Abstract
The rates of decomposition of chemically activated 2‐hexyl‐d12 and 2‐octyl‐d16 radicals have been measured relative to their corresponding light radicals by an internal comparison method. The intermolecular secondary isotope effects so determined for these nonequilibrium systems were the high‐pressure values and ranged from 4.6 for 2‐hexyl at 300°K to 12.1 for 2‐octyl at 195°K. Application of the quantum statistical Marcus—Rice theory to appropriate vibrational models leads to theoretical rate constants for the light and heavy species. The resulting calculated isotope effects are in reasonable agreement with those measured. The effect of energy upon the theoretical magnitudes of the isotope effect has been examined by making a comparative study of the alkyl radicals, ethyl through 2‐octyl, by varying the assumed ambient temperature over the range 100° to 1000°K. The accuracy of enumeration of vibrational energy densities for these large molecules was explicitly tested.