Low temperature (1-250 K) chemistry and collision dynamics of radicals and ions

亚利桑那大学的马克·史密斯得到了实验物理化学项目的资助，该项目研究从300K到1Kelvin温度下的气相反应的机理和动力学。这些测量将在自由喷射和超音速拉瓦尔喷管膨胀冷却流动反应堆中对选定的反应物进行激光诱导荧光、共振增强多光子电离和质谱学探测。将确定一系列离子-分子(氢卤离子的猝灭和反应)、自由基-分子(氢和碳原子、氰化物和羟基与各种碳氢化合物和其他小分子的反应)和分子-分子(一氧化氮自猝灭)反应的绝对反应速率常数和产物分支比，其中许多反应具有天体化学应用。将与理论计算和高温实验测量结果进行比较。小离子的电子预解离光谱将作为一种以量子特有的方式跟踪反应的手段。这些研究将使人们更好地理解离子和分子在极低温度下的反应，并提供关于反应机理的基本信息。它们将显示反应有多快，产生哪些产物，以及这些产物如何依赖于可用能量。这些反应在行星大气中很重要，包括地球大气和星际空间。

Mark Smith of the University of Arizona is supported by a grant from the Experimental Physical Chemistry Program to study the mechanisms and dynamics of gas phase reactions from 300K down to temperatures of 1 Kelvin. These measurements will be performed on state selected reactants in free jet and supersonic Laval nozzle expansion cooled flow reactors with laser induced fluorescence, resonance enhanced multi-photon ionization and mass spectrometric probing. Absolute reaction rate constants and product branching ratios will be determined for a series of ion-molecule (quenching and reaction of hydrogen halide ions), radical-molecule (hydrogen and carbon atom, cyanide and hydroxyl reactions with various hydrocarbons and other small molecules) and molecule-molecule (nitric oxide self quenching) reactions, many with astrochemical applications. Comparisons will be made with theoretical calculations and higher temperature experimental measurements. Electronic predissociation spectroscopy of small ions will be explored as a means of following the reactions in a quantum specific fashion.These studies will lead to a greater understanding of how ions and molecules react at very low temperatures and provide fundamental information on the mechanisms of the reactions. They will show how fast the reactions are, what products are generated and how these depend on the available energy. These reactions are important in planetary atmospheres, including that of the Earth, and in interstellar space.