Sprengnether Michele M, Demerjian Kenneth L, Dransfield Timothy J, Clarke James S, Anderson James G, Donahue Neil M
Atmospheric Sciences Research Center, State University of New York, Albany, New York 12203, USA.
J Phys Chem A. 2009 Apr 30;113(17):5030-8. doi: 10.1021/jp810412m.
We report absolute rate-constant measurements for the reactions of nine C(6)-C(9) alkanes with OH in 8-10 torr of nitrogen from 230 to 379 K in the Harvard University High-Pressure Flow System. Hydroxyl concentrations were measured using laser-induced fluorescence, and alkane concentrations were measured using Fourier transform infrared Spectroscopy. Ethane's reactivity was simultaneously measured as a test of experimental performance. Results were fit to a modified Arrhenius equation based on transition state theory (ignoring tunneling), k(T) = Be(-E(a)/T)/(T(1 - e(- 1.44nu(1)/T))(2)(1 - e(- 1.44nu(2)/T)), with nu(1) and nu(2) bending frequencies, set to 280 and 500 cm(-1). Results were as follows for B (10(-9) K cm(3) s(-1)), E(a) (K), and k(298) (10(-12) cm(3) s(-1)): cyclohexane, 3.24 +/- 0.14, 332 +/- 12, 7.13; cyclo-octane, 3.47 +/- 0.30, 149 +/- 26, 14.1; 2-methylhexane, 1.45 +/- 0.08, 110 +/- 15, 6.72; 3-methylhexane, 1.50 +/- 0.08, 128 +/- 16, 6.54; methylcyclopentane, 1.65 +/- 0.07, 109 +/- 13, 7.65; methylcyclohexane, 1.86 +/- 0.09, 83 +/- 14, 9.43; methylcycloheptane, 3.45 +/- 0.45, 142 +/- 36, 14.4; n-propylcyclohexane, 2.83 +/- 0.14, 112 +/- 15, 13.0; isopropylcyclohexane, 1.79 +/- 0.11, -44 +/- 34, 13.9. Uncertainties are one sigma results from linear regression fits and are likely underestimated. Room temperature rate coefficients of reaction are accurate to within 10% at two sigma. A comprehensive fit to 17 separate studies including the present work for cyclohexane gives good agreement with the present results: terms as above, 3.09 +/- 0.12, 326 +/- 12, 6.96. Five of these compounds are routinely measured in urban air within a suite of atmospheric nonmethane hydrocarbons and reach parts per billion levels. The remaining four are C8-C9 cycloalkanes with low anthropogenic emissions. Because of their high, specific reactivity with OH, their concentration decays may be used as an indirect measurement of [OH] in the atmosphere or laboratory. This data set serves to further constrain the reaction barriers for cyclohexane and cyclo-octane, is the first temperature-dependent study for methylcyclopentane and methylcyclohexane, and provides the first measurements for the rate constants of the remaining five hydrocarbons. Reactivity follows general trends observed for other saturated alkanes, increasing with size and extent of substitution. Reaction barriers are heavily influenced by the presence of tertiary hydrogens. The reaction barrier for cyclo-octane is significantly lower than that for cyclohexane, a result that is not predicted from our current understanding of hydrocarbon reactivity.
我们报告了在哈佛大学高压流动系统中，在230至379K、8 - 10托氮气环境下，9种C(6)-C(9)烷烃与OH反应的绝对速率常数测量结果。使用激光诱导荧光测量羟基浓度，使用傅里叶变换红外光谱测量烷烃浓度。同时测量乙烷的反应活性以检验实验性能。结果根据基于过渡态理论的修正阿伦尼乌斯方程进行拟合（忽略隧穿），k(T) = Be(-E(a)/T)/(T(1 - e(- 1.44nu(1)/T))(2)(1 - e(- 1.44nu(2)/T))，其中nu(1)和nu(2)弯曲频率分别设为280和500 cm(-1)。以下是B (10(-9) K cm(3) s(-1))、E(a) (K)和k(298) (10(-12) cm(3) s(-1))的结果：环己烷，3.24 +/- 0.14，332 +/- 12，7.13；环辛烷，3.47 +/- 0.30，149 +/- 26，14.1；2 - 甲基己烷，1.45 +/- 0.08，110 +/- 15，6.72；3 - 甲基己烷，1.50 +/- 0.08，128 +/- 16，6.54；甲基环戊烷，1.65 +/- 0.07，109 +/- 13，7.65；甲基环己烷，1.86 +/- 0.09，83 +/- 14，9.43；甲基环庚烷，3.45 +/- 0.45，142 +/- 36，14.4；正丙基环己烷，2.83 +/- 0.14，112 +/- 15，13.
