Abstract
We have employed the laser flash photolysis–resonance fluorescence technique to investigate the gas‐phase kinetics of elementary steps in the Br‐initiated oxidation of 2,3‐dimethyl‐2‐butene (TME) under atmospheric conditions. At T⩾ 274 K, measured rate coefficients are independent of pressure suggesting hydrogen abstraction as the dominant pathway. The following Arrhenius expression adequately describes all kinetic data at 274 K ⩽T⩽ 420 K: k~1a~(T) = (3.84 ± 0.84) × 10^− 11^ exp[(−169 ± 61)/T] cm^3^ molecule^−1^s^−1^ (uncertainties are 2__σ__, precision only). At 203 K ⩽T⩽ 241 K, kinetic evidence for reversible addition, Br + TME ↔ Br−TME (k~1b~, k~−1b~), is observed. Analysis of the approach to equilibrium data allows evaluation of the rate coefficients k~1b~ and k~−1b~. At atmospheric pressure addition of Br to TME occurs at a near gas kinetic rate. Equilibrium constants are obtained from k~1b~/k~−1b~. Combining the experimental results with electronic structure calculations allows third‐law analyses of the equilibrium data. The following thermochemical parameters for the addition reaction (1b) at 0 and 298 K are obtained (standard state = 1 atm): Δ~r~H~0~= −47.1 ± 3.0 kJ mol^−1^, Δ~r~H~298~=−47.3 ± 3.0 kJ mol^−1^, and Δ~r~S~298~=−101.5 ± 10.0 J mol^−1^ K^−1^. Examination of the effect of added O~2~ on Br atom kinetics under conditions where reversible adduct formation is observed allows determination of the rate coefficient for the Br–TME + O~2~ reaction (k~2~). At 223 K, we find that k~2~ increases from 3.9 to 5.5 × 10^−12^ cm^3^ molecule^−1^s^−1^ as pressure increases from 25 to 200 Torr. Our results suggest that under most atmospheric conditions the Br–TME reaction with O~2~ occurs more rapidly than the Br–TME unimolecular decomposition. Hence, the fast addition reaction appears to control the rate of TME loss by reaction with Br in the atmosphere. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 13–26, 2012