Cheramangalath Balan Ramya, Rajakumar B
Department of Chemistry , Indian Institute of Technology Madras , Chennai 600036 , India.
J Phys Chem A. 2019 Aug 29;123(34):7361-7373. doi: 10.1021/acs.jpca.9b02225. Epub 2019 Aug 14.
The temperature-dependent reaction kinetics of methyl cyclohexane (MCH) and methyl cyclopentane (MCP) with Cl atoms were experimentally explored via the relative rate technique. Gas chromatography coupled with a flame ionization detector was employed to follow the reactant as well as the reference compound concentrations during the course of reaction. Gas chromatography coupled with mass spectrometry and gas chromatography coupled with infrared spectroscopy were used as the diagnostic tools for the detection and identification of the products in the title reaction. The rate coefficients for the reaction of Cl atoms with methyl cyclohexane and methyl cyclopentane were measured in the temperature range of 283-363 K at 760 Torr using isoprene and propylene as reference compounds. To support the experimental results, computational calculations were performed over the temperature range of 200-400 K using canonical variational transition state theory coupled with small curvature tunneling (CVT/SCT), conventional transition state theory (CTST) coupled with Wigner tunneling corrections, and CVT coupled with Wigner tunneling methods using the MP2 level of theory with 6-31G(d,p) as the basis set. The temperature-dependent rate coefficients were measured for the reaction of methyl cyclohexane and methyl cyclopentane with Cl atoms to be = [(4.48 ± 0.75) × 10]exp[(604 ± 25)/] cm molecule s and = [(5.71 ± 0.66) × 10]exp[(1819 ± 669)/] cm molecule s, respectively. The measured rate coefficients at 298 K for the reactions of Cl atoms with methyl cyclohexane and methyl cyclopentane are = (3.36 ± 0.34) × 10 cm molecule s and = (2.25 ± 0.24) × 10 cm molecule s, respectively. The conceivable atmospheric degradation mechanism for the reaction of methyl cyclohexane as well as methyl cyclopentane with Cl atoms was projected based on the products obtained during the reaction. Atmospheric implications, cumulative atmospheric lifetimes, thermochemistry, ozone formation potentials, and branching ratios of these molecules were also calculated and have been reported in this article.
通过相对速率技术对甲基环己烷（MCH）和甲基环戊烷（MCP）与氯原子的温度依赖反应动力学进行了实验研究。在反应过程中，采用气相色谱联用火焰离子化检测器来跟踪反应物以及参考化合物的浓度。气相色谱联用质谱和气相色谱联用红外光谱被用作检测和鉴定上述反应产物的诊断工具。使用异戊二烯和丙烯作为参考化合物，在760托的压力下，于283 - 363 K的温度范围内测量了氯原子与甲基环己烷和甲基环戊烷反应的速率系数。为了支持实验结果，在200 - 400 K的温度范围内，使用正则变分过渡态理论结合小曲率隧道效应（CVT/SCT）、传统过渡态理论（CTST）结合维格纳隧道效应校正以及使用MP2理论水平并以6 - 31G(d,p)为基组的CVT结合维格纳隧道效应方法进行了计算。测量得到甲基环己烷和甲基环戊烷与氯原子反应的温度依赖速率系数分别为 = [(4.48 ± 0.75) × 10]exp[(604 ± 25)/] cm³ molecule⁻¹ s⁻¹ 和 = [(5.71 ± 0.66) × 10]exp[(1819 ± 669)/] cm³ molecule⁻¹ s⁻¹。在298 K时，氯原子与甲基环己烷和甲基环戊烷反应的测量速率系数分别为 = (3.36 ± 0.34) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ 和 = (2.25 ± 0.24) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹。基于反应过程中获得的产物，推测了甲基环己烷以及甲基环戊烷与氯原子反应可能的大气降解机制。本文还计算并报告了这些分子的大气影响、累积大气寿命、热化学、臭氧形成潜力和分支比。
