同步辐射光电离质谱/Laval 喷嘴超声冷却技术用于低温气相自由基反应动力学研究

Gas-phase free radical reactions at low temperature are playing crucial role in setting the stage for the emergence of life to occur and studying chemical processes in the atmosphere, especially in the regions of the interstellar medium and atmospheric troposphere. Laval nozzle supersonic expansion, refered to as a “wall-less flow tube reactor”, has found a unique application as a major experimental method for low-temperature reaction kinetics studies. The radical reactions are intiated by laser photolysis of the precursor in the cold and uniform supersonic molecule beam, which is created by Laval nozzle. Utilizing photoionization from synchrotron radiation (SR) with high brightness and high resolution and reflectron time-of-flight mass spectrometer (RTOF MS) for detection of products, the approach is capable of further research on low-temperature kinetics studies of important free radicals in the interstellar chemistry and atmospheric chemistry, such as Criegee intermediate CH2OO and cyano radical CN. The experiments enable the measurement of rate coef?cients as a function of temperature, detection of reaction products and distinguishing of different structural isomers. Combining with the reaction intermediates, transition states and potential energy surfaces from theoretical calculations, the low-temperature reaction mechanisms will be unravelled comprehensively, and reliable thermochemical data will be provided for accurate simulation of reaction progresses in the interstellar chemistry and atmospheric chemistry. The build-up experiment apparatus will open to users and perform function as extention of national large-scale scientific research facilities and application fields of synchrotron radiation.

星际云层和大气对流层的气相自由基反应大多是在低温条件下进行的，在探索生命起源的不同阶段和研究大气化学的变化过程中起着关键作用。Laval 喷嘴超声冷却产生稳定流气相分子束，被称为“无壁的流动管反应器”，已成为低温气相反应动力学的主要实验技术。利用Laval 喷嘴产生浓度和温度相对稳定的分子束流和激光光解产生自由基作为起始反应，使用高亮度、高分辨的同步辐射单光子电离，用飞行时间质谱仪探测反应产物，可用于星际化学和大气化学中一些重要自由基(如Criegee双自由基、CN自由基等)低温反应动力学研究。实验测量不同低温条件下自由基反应速率常数、反应产物并区分其异构体；结合量化计算获得反应中间体、过渡态和势能面等，掌握低温气相自由基反应机理，为准确模拟星际化学和大气化学反应过程提供可靠的热力学数据。建立的实验技术方法，将对用户开放服务，充分发挥国家大科学装置的作用，同时拓展同步辐射应用领域。