Rate coefficients for the gas-phase reaction of OH radicals with the L4, L5, D5, and D6 permethylsiloxanes

IF 1.5 4区化学 Q4 CHEMISTRY, PHYSICAL

International Journal of Chemical Kinetics Pub Date : 2024-11-20 DOI:10.1002/kin.21769

François Bernard, James B. Burkholder

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Abstract

Rate coefficients, k(T), for the gas-phase OH radical reaction with decamethyltetrasiloxane ((CH₃)₃SiO[Si(CH₃)₂O]₂Si(CH₃)₃, L₄, k₁), dodecamethylpentasiloxane ((CH₃)₃SiO[Si(CH₃)₂O]₃Si(CH₃)₃, L₅, k₂), and decamethylcyclopentasiloxane ([–Si(CH₃)₂O–]₅, D₅, k₃), and dodecamethylcyclohexasiloxane ([–Si(CH₃)₂O–]₆, D₆, k₄) were measured using a pulsed laser photolysis—laser induced fluorescence absolute method over the temperature range 270–370 K. The obtained room temperature rate coefficients, with quoted 2σ absolute uncertainties, and fitted temperature dependence are (cm⁻³ molecule⁻¹ s⁻¹):

The 2σ absolute rate coefficient uncertainty, for all compounds included in this study, is conservatively estimated to be ∼10% over the entire temperature range. The cyclic permethylsiloxanes were found to be less reactive than the analogous linear compound, while both linear and cyclic compounds show increasing reactivity with increasing number of CH₃- groups. A structure activity relationship (SAR) parameterization for the permethylsiloxanes is presented. The estimated atmospheric lifetimes due to OH reaction for L₄, L₅, D₅, and D₆ are 5.2, 4.4, 6.8, and 5.2 days, respectively.

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OH自由基与L4、L5、D5、D6过甲基硅氧烷气相反应的速率系数

采用脉冲激光光解-激光诱导荧光绝对法，在270 ~ 370 k温度范围内测量了十甲基四硅氧烷((CH3)3SiO[Si（CH3)2O]2Si(CH3)3, L4, k1）、十二甲基五硅氧烷((CH3)3SiO[Si（CH3)2O]3Si(CH3)3, L5, k2）、十甲基环五硅氧烷（[- Si(CH3)2O -]5, D5, k3）和十二甲基环六硅氧烷（[- Si(CH3)2O -]6, D6, k4）气相OH自由基反应的速率系数k(T)。得到的室温速率系数，引用的2σ绝对不确定度，以及拟合的温度依赖性为（cm−3分子−1 s−1）：本研究中所有化合物的2σ绝对速率系数不确定度在整个温度范围内保守估计为~ 10%。环型过甲基硅氧烷的反应性比类似的线性化合物低，而线性和环型化合物的反应性随CH3-基团数目的增加而增加。提出了过甲基硅氧烷的构效关系参数化方法。L4、L5、D5和D6因OH反应而产生的大气寿命估计分别为5.2、4.4、6.8和5.2天。

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来源期刊

International Journal of Chemical Kinetics 化学-物理化学

CiteScore

3.30

自引率

6.70%

发文量

审稿时长

3 months

期刊介绍： As the leading archival journal devoted exclusively to chemical kinetics, the International Journal of Chemical Kinetics publishes original research in gas phase, condensed phase, and polymer reaction kinetics, as well as biochemical and surface kinetics. The Journal seeks to be the primary archive for careful experimental measurements of reaction kinetics, in both simple and complex systems. The Journal also presents new developments in applied theoretical kinetics and publishes large kinetic models, and the algorithms and estimates used in these models. These include methods for handling the large reaction networks important in biochemistry, catalysis, and free radical chemistry. In addition, the Journal explores such topics as the quantitative relationships between molecular structure and chemical reactivity, organic/inorganic chemistry and reaction mechanisms, and the reactive chemistry at interfaces.