Dynamics of Gas-Liquid Reactions; The Pseudo-Surface Approach

化学反应需要两种化学物种之间的碰撞，并已被合成化学家广泛开发和利用，以制造各种产品，如塑料和药物。物理化学家更详细地研究化学相互作用，他们经常与气体合作，以分离单个分子碰撞进行定量研究。然而，人们对双相(气-液)相互作用的基本动力学知之甚少，到目前为止，只得到了有限的关注。气液相互作用对于各种各样的物理过程特别重要，从生物体的呼吸(依赖于从空气中吸收氧气进入血液)到蒸馏、气相色谱和气溶胶颗粒(例如空气中的水滴可以吸收硫酸以产生酸雨)和地球海洋表面的大气化学。这项研究的目的是通过采用一种新的实验策略来提高对气-液表面相互作用的基本理解；使用一个大的但易挥发的柔性分子作为液体表面(拟表面)的简化代理。这将使发生在气液界面上的化学反应能够利用基于高分辨率激光的技术和成像方法进行前所未有的详细研究。这种成像可以拍摄化学反应产物的命运照片，这将使我们能够深入了解所涉及的机制。该项目将专注于建造和使用一种独特的、紧凑的成像实验，这将是英国首个此类实验。利用这个实验，我们可以测量任何反应产物的飞行方向和速度。这将使我们能够深入了解分子与伪表面碰撞的不同可能的反应机制。最简单的途径是单一的碰撞反应，称为直接机制。然而，一些相互碰撞的原子或分子被捕获在表面上，在反应之前经历多次碰撞(所谓的捕获-解吸机制)，在极端情况下，伪表面吸附另一种试剂。足球和苹果树的类比在这里很有帮助：想象一下，如果你把一个足球踢到苹果树上，它可能会立刻出来，从树枝上弹跳，带着一个苹果(直接机械)，或者它可能会暂时在树枝之间弹跳，然后带着苹果离开(陷阱-解吸)，或者它可能会卡在树枝之间。这里提出的工作将详细研究足球和苹果树问题，并将其作为模型来研究足球和果园问题(真正的液体，其中许多相同的分子(苹果树)组成表面)。这个类比可以扩展到使用橄榄球和其他形状的球来表示我们打算研究的不同的入射原子/分子/自由基。这项研究将对表面相互作用的理解产生深远的影响，并将对化学、物理、工程以及最终对气液界面感兴趣的广泛的生命科学研究人员有所裨益。

Chemical reactions require a collision between two chemical species, and have been widely developed and exploited in solution by synthetic chemists to make a variety of products such as plastics and drugs. Chemical interactions are studied in greater detail by physical chemists, who often work with gases in order to isolate individual molecular collisions for quantitative study. However the fundamental dynamics of dual-phase (gas-liquid) interactions are poorly understood and, to date, have received only limited attention. Gas-liquid interactions are of particular importance to a wide variety of physical processes, ranging from respiration in living organisms (which relies on uptake of oxygen from air, into the blood) to distillation, gas chromatography, and atmospheric chemistry at the surfaces of aerosol particles (where for example water droplets in air can absorb sulfuric acid to from acid rain) and the Earth's oceans. The aim of the proposed research is to improve the fundamental understanding of gas-liquid surface interactions by employing a novel experimental strategy; using a large, but volatile, flexible molecule as a simplified proxy for a liquid surface (a pseudo-surface). This will allow chemical reactions that occur at the gas-liquid interface to be studied in unprecedented detail using high resolution laser based techniques coupled with imaging methods. The imaging allows pictures to be taken of the fate of products of a chemical reaction, which will allow us to develop in-depth understanding of the mechanisms involved. This project will focus on the construction and use of a unique, compact imaging experiment that will be the first of its kind in the UK. Using the experiment we can measure the direction and speed with which any products of reactions fly. This will allow us to gain in-depth knowledge of the different possible reaction mechanisms of collisions of molecules with pseudo-surfaces. The simplest pathway is a single collision reaction, called a direct mechanism. Some colliding atoms or molecules are trapped on the surface, however, undergoing multiple collisions before reacting (a so called trapping-desorption mechanism), and in extreme cases the pseudo-surface adsorbs the other reagent. The football / apple tree analogy is helpful here: imagine if you kick a football into an apple tree, it could come out straight away, bouncing off a branch, bringing an apple with it (direct mechanism), or it could get temporarily caught bouncing from branch to branch before leaving with an apple (trapping-desorption), or it could become wedged between the branches. The work proposed here will study the football and apple tree problem in detail and use it as a model to investigate the football and orchard problem (the real liquid, where lots of identical molecules (apple trees) make up the surface). This analogy can be extended to use rugby and other shaped balls to represent different incoming atoms/molecules/radicals that we intend to study. The research will have a profound impact on the understanding of surface interactions, and will be of benefit to a broad community of researchers in Chemistry, Physics, Engineering, and ultimately Life Sciences, with interest in gas-liquid interfaces.