Lehrstuhl Thermodynamik/Thermische Verfahrenstechnik, BrandenburgischeTechnische-Universität, Siemens-Halske-Ring 8, Cottbus D-03046, Germany.
Molecules. 2013 Nov 4;18(11):13608-22. doi: 10.3390/molecules181113608.
Photochemically driven reactions involving unsaturated radicals produce a thick global layer of organic haze on Titan, Saturn's largest moon. The allyl radical self-reaction is an example for this type of chemistry and was examined at room temperature from an experimental and kinetic modelling perspective. The experiments were performed in a static reactor with a volume of 5 L under wall free conditions. The allyl radicals were produced from laser flash photolysis of three different precursors allyl bromide (C3H5Br), allyl chloride (C3H5Cl), and 1,5-hexadiene (CH2CH(CH2)2CHCH2) at 193 nm. Stable products were identified by their characteristic vibrational modes and quantified using FTIR spectroscopy. In addition to the (re-) combination pathway C3H5+C3H5 → C6H10 we found at low pressures around 1 mbar the highest final product yields for allene and propene for the precursor C3H5Br. A kinetic analysis indicates that the end product formation is influenced by specific reaction kinetics of photochemically activated allyl radicals. Above 10 mbar the (re-) combination pathway becomes dominant. These findings exemplify the specificities of reaction kinetics involving chemically activated species, which for certain conditions cannot be simply deduced from combustion kinetics or atmospheric chemistry on Earth.
光化学驱动的不饱和自由基反应在泰坦（土星最大的卫星）上产生了一层厚厚的全球有机霾。烯丙基自由基自反应就是这种类型的化学反应的一个例子，从实验和动力学建模的角度对其进行了研究。实验在一个 5 升的静态反应器中进行，在无壁条件下，在室温下进行。烯丙基自由基是通过 193nm 的三种不同前体烯丙基溴（C3H5Br）、烯丙基氯（C3H5Cl）和 1,5-己二烯（CH2CH（CH2）2CHCH2）的激光闪光光解产生的。通过其特征振动模式鉴定稳定产物，并使用 FTIR 光谱进行定量。除了在低压力（约 1mbar）下，我们发现（再）组合途径 C3H5+C3H5→C6H10，对于前体 C3H5Br，所有烯和丙烯的最终产物产率最高。动力学分析表明，最终产物的形成受到光化学激活的烯丙基自由基的特定反应动力学的影响。在 10mbar 以上，（再）组合途径变得占主导地位。这些发现说明了涉及化学激活物质的反应动力学的特殊性，对于某些条件，这些特殊性不能简单地从燃烧动力学或地球上的大气化学中推断出来。
