Reactive Scattering Dynamics at the Gas-Liquid Interface: Bridging the Gap between the Gas-Phase and Solution

在气相和液态相遇的任何地方，化学作用都发生在界面上。自然界中的例子包括：生物体的呼吸作用；大气中的气溶胶颗粒；地球上的海洋表面；土星的卫星土卫六大气中的碳氢化合物颗粒。这些界面的化学成分在人造环境中也是至关重要的：液体燃料的燃烧；多相催化、气体隔离和蒸馏等工业过程。然而，尽管它们很重要，但与气相或溶液中的化学反应相比，人们对气液界面反应的了解要少得多。这个项目旨在通过前沿实验和理论的结合来加深我们对液体表面反应的基本理解。考虑气体分子靠近液体表面的情形。它与表面的第一次相遇将是一个孤立的事件；气相分子将与液体表面的单个分子碰撞。在这一点上，相遇基本上与两个孤立分子之间的气相碰撞相同。在气相中，分子会反弹，相遇就会结束。在某些情况下，液体表面的碰撞也会导致气相分子反弹回到气相中。然而，它可能会继续与更多的液体表面分子碰撞，甚至可能穿过液体表面进入溶液，最终返回气相。因此，气液界面上的反应具有气相和溶液相的共同特征，通过研究反应的动力学，我们可以弥合它们之间的差距。这是对这些迄今基本上分开的领域正在进行的密集努力的补充，提供了分子散射动力学的统一图景。我们将根据我们以前在气液界面散射方面的经验，开发一种新的实验装置，并将其与以前用于研究气相动力学的高分辨率激光光谱学相结合。我们将利用这一点来研究CN自由基与液态碳氢化合物的反应，生成HCN。这一基准反应过程的动力学以前已经在气相和溶液相中进行了研究。由于CN自由基是地外大气(如泰坦大气层)和液态碳氢化合物燃烧中的重要活性物种，因此该反应不仅具有根本意义。在实验的同时，我们将发展新的原子间作用力的理论模型，并在计算中使用这些模型来模拟实验条件下的反应动力学。我们将对实验和理论的结果进行比较和结合，以提供有史以来最详细的气液界面反应动力学描述。这项工作提供了对气液界面动力学的基本见解，这将有助于我们理解和模拟对我们社会至关重要的广泛环境中的气液界面过程，例如大气气溶胶、液体燃料燃烧。

Anywhere the gas and liquid phases meet, chemistry occurs at the interface. Examples in the natural world include: respiration in living organisms; atmospheric aerosol particles; the surface of the sea on Earth; hydrocarbon particles in the atmosphere of Saturn's moon Titan. The chemistry of these interfaces is also vital in man-made environments as well: combustion of liquid fuels; industrial processes such as multiphase catalysis, gas sequestration and distillation. However, despite their importance, in comparison to the chemistry of reactions in the gas-phase or in solution, reactions at the gas-liquid interface are much less well understood. This project aims to deepen our fundamental understanding of reactions at liquid surfaces through a combination of cutting-edge experiment and theory. Consider a gas molecule approaching a liquid surface. The first encounter it makes with the surface will be an isolated event; the gas phase molecule will collide with a single molecule of the liquid surface. At this point the encounter is essentially the same as a gas phase collision between two isolated molecules. In the gas-phase, the molecules will then recoil and the encounter will be over. In some cases, collisions at the liquid surface will also result in the gas-phase molecule rebounding back into the gas-phase. However, it may instead go on to collide with further liquid surface molecules, and may even pass through the surface of the liquid and into solution, before eventually returning to the gas-phase. Reactions at the gas-liquid interface thus share characteristics of both the gas and solution phases, and by studying the dynamics of the reactions we can bridge the gap between them. This complements the intensive on-going effort in these hitherto largely separate areas, providing a unifying picture of molecular scattering dynamics. We will develop a new apparatus for our experiments, based on our previous experience in gas-liquid interfacial scattering, and combine it with high-resolution laser spectroscopy previously applied to study gas-phase dynamics. We will use this to study the reaction of CN radicals with liquid hydrocarbons, which forms HCN. The dynamics of this benchmark reaction process have been previously studied in the gas and solution phases. This reaction is not only of fundamental interest, as the CN radical is an important reactive species in extra-terrestrial atmospheres (e.g. atmosphere of Titan), and liquid hydrocarbon combustion. Simultaneously with the experiments, we will develop new theoretical models of the forces between the atoms present, and use those in calculations to simulate the dynamics of the reactions under experimental conditions. We will compare and combine the results of the experiments and theory to provide the most-detailed ever description of gas-liquid interfacial reaction dynamics. The fundamental insights into dynamics at the gas-liquid interface provided by this work will inform our understanding and modelling of the processes at gas-liquid interfaces in a wide range of environments vital to our society, e.g. atmospheric aerosols, liquid fuel combustion.