Temperature‐dependent a factor in thermal unimolecular reactions II. Exponential dependence

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Abstract
It is assumed that A∞ in the limiting high‐pressure unimolecular rate constant expression k∞ = A∞ exp(−Ea∞/kT) is given by A∞ = A″∞eBkT. The test case is the decomposition butane → 2 ethyl, where a negative B reproduces the temperature dependence of A∞ about as well as the previously considered power law A∞ = A′∞(kT)n. It is shown that the term eBkT modifies significantly the high‐temperature falloff of the general‐pressure rate constant kuni and its various derivatives, and admits of a fairly simple interpretation in terms of Benson's restricted rotor theory. On physical grounds, the exponential law appears more reasonable than the power law.