Daniel Van Hoomissen, Aparajeo Chattopadhyay, James B. Burkholder
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引用次数: 0
摘要
气相Cl原子与六甲基二硅氧烷((CH3)3SiOSi(CH3)3, L2) k1反应的速率系数k(T)；八甲基三硅氧烷([(CH3)3SiO]2Si(CH3)2, L3) k2；十甲基四硅氧烷((CH3)3SiO[Si(CH3)2O]2Si(CH3)3, L4, k3；十二甲基五硅氧烷((CH3)3SiO[Si(CH3)2O]3Si(CH3)3, L5, k4；六甲基环三硅氧烷（[- si (CH3)2O-]3, D3）， k5；八甲基环四硅氧烷（[- si (CH3)2O-]4, D4）， k6；采用脉冲激光光解(PLP) -共振荧光（RF）技术在273-363 K温度范围内测量了十甲基环五硅氧烷（[- si (CH3)2O-]5, D5, k7）和十二甲基环六硅氧烷（[- si (CH3)2O-]6, D6, k8）。得到的k（296 k）和Arrhenius表达式具有2σ不确定性，包括估计的系统误差为（以10−10 cm3分子−1 s−1为单位）：环过甲基硅氧烷（cyclic permethyl siloxane, cyclic PMS）的反应性低于具有相同CH3-基团数量的类似的线性过甲基硅氧烷（linear PMS）。线性和环状化合物的速率系数与分子中CH3-基团的数目呈线性关系。提出了一种结构-活性关系（SAR），在所有温度下将实验数据再现到~ 10%以内。对于[Cl]≈104原子cm−3，一个近似的自由对流层丰度，由于Cl原子反应造成的PMS损失导致L2、L3、L4、L5、D3、D4、D5和D6的估计寿命相对较短，分别为7、6、5、4、20、10、7和5天。因此，本研究中纳入的PMSs被归类为大气非常短寿命的物质，Cl原子反应代表了一个重要的损失过程。
Rate Coefficients for the Cl Atom Gas-Phase Reaction With Permethylsiloxanes (PMS): L2, L3, L4, L5, D3, D4, D5, and D6
Rate coefficients, k(T), for the gas-phase Cl atom reaction with hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, L2), k1; octamethyltrisiloxane ([(CH3)3SiO]2Si(CH3)2, L3), k2; decamethyltetrasiloxane ((CH3)3SiO[Si(CH3)2O]2Si(CH3)3, L4, k3; dodecamethylpentasiloxane ((CH3)3SiO[Si(CH3)2O]3Si(CH3)3, L5, k4; hexamethylcyclotrisiloxane ([-Si(CH3)2O-]3, D3), k5; octamethylcyclotetrasiloxane ([-Si(CH3)2O-]4, D4), k6; decamethylcyclopentasiloxane ([-Si(CH3)2O-]5, D5, k7), and dodecamethylcyclohexasiloxane ([-Si(CH3)2O-]6, D6, k8) were measured over a range of temperature (273–363 K) using a pulsed laser photolysis (PLP) – resonance fluorescence (RF) technique. The obtained k(296 K) and Arrhenius expressions with 2σ uncertainties including estimated systematic errors are (in units of 10−10 cm3 molecule−1 s−1):
The cyclic permethyl siloxanes (cyclic PMS) were found to be less reactive than the analogous linear permethyl siloxane (linear PMS) with an equal number of CH3- groups. Both linear and cyclic compounds show a linear relationship between the measured rate coefficient and the number of CH3- groups in the molecule. A structure–activity relationship (SAR) is presented that reproduces the experimental data to within ∼10% at all temperatures. For [Cl] ≈ 104 atom cm−3, an approximate free troposphere abundance, the PMS loss due to Cl atom reaction leads to relatively short estimated lifetimes of 7, 6, 5, 4, 20, 10, 7, and 5 days for L2, L3, L4, L5, D3, D4, D5, and D6, respectively. Therefore, the PMSs included in this study are classified as atmospherically very short-lived substances and Cl atom reaction represents a significant loss process.
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.
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