An absolute measurement of the rate constant for ethyl radical combination

Abstract

Abstract An absolute value of k r of ethyl radicals at 860 ± 17°K of 4.5 × 10 9 M −1 ·sec −1 was determined under VLPP conditions, where the value of k r / k r ∞ should be about 1/2. Thus k r ∞ ( M −1 ·sec −1 ) ∼ 10 10 at 860°K. An error of as much as a factor of 2 in k r would be surprising, but possible. The value of 10 10 M −1 ·sec −1 seems to be a factor of from 2 to 5 too high to be compatible with extensive data on the reverse reaction and the accepted thermochemistry. Changes in the heat of formation and entropy of the ethyl radical can change the situation somewhat, but even these changes when applied to the work of Hiatt and Benson [3] indicate that ethyl combination should be ∼ 10 9.3 M −1 ·sec −1 . More work is necessary if a better value is desired.