Unimolecular Decomposition of Chemically Activated Ethyl-d2 Radicals

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Abstract
Addition of H atoms to trans‐ethylene‐d2 produces chemically activated ethyl‐d2 radicals. This choice of the reactant ethylene permits all subsequent secondary processes of the hot ethyl radicals to be counted. The system has been studied between —78° and 160°C, and in most detail at room temperature, as a function of ethylene pressure. Experimental details are similar to those given in previous work on butyl. The relative energy spread of the formed ethyl radicals is here effectively greater than that observed for butyl radical since the thermal spread is not superimposed upon a minimum excess above the critical energy, as was the case for butyl. Nevertheless, relative to high‐temperature thermal decompositions, the product ethyl radicals are comparatively monoenergetic, especially at the lowest temperature. The observed rate constant for decomposition ka was evaluated from the amounts of stabilization vs decomposition by C–H rupture. The decomposition rate is compared with theoretical expressions. An isotope effect appears to exist for transfer of H and D in the disproportionation of ethyl‐d2 radicals at 25°.