Comparison of the Kinetics of O(3P) Reactions with the Four Butenes over Wide Temperature Ranges

Abstract

Rate coefficients for reactions of ground-state oxygen atoms with isobutene, trans-2-butene, and cis-2-butene have been measured using the high-temperature photochemistry (HTP) technique. The oxygen atoms were generated by flash photolysis of either O[sub 2] or CO[sub 2] and the relative atom concentrations were monitored by resonance fluorescence. We find, in cm[sup 3] molecule[sup [minus]1] s[sup [minus]1] units, for isobutene, k(284-1015 K) = 2.0 x 10[sup [minus]15](T/K)[sup 1.28] exp(543 K/T); trans-2-butene, k(292-1022 K) = 3.9 x 10[sup [minus]17](T/K)[sup 1.87] exp(743 K/T); and cis-2-butene, k(292-1086 K) = 2.4 x 10[sup [minus]17](T/K)[sup 1.94] exp(716 K/T). The 2[sigma] precision limits are around [+-]10%, and the corresponding 2[sigma] accuracy limits are estimated to be about [+-]25%. Conventional transition-state-theory calculations for the electrophilic O-addition to the double bond yield at high temperatures rate coefficients smaller than observed. A method is developed for estimating rate coefficients for H abstraction. When the results are added to those of the addition, good agreement with experiments is attained. The differences between the k(T) expressions for the present three reactions and the corresponding 1-butene reaction are discussed. Based on these observations, a method is presented for estimating rate coefficients for O-atom reactions with higher olefins over wide temperature ranges. 38 refs.,more » 8 figs., 4 tabs.« less