New Directions in Molecular Scattering: Multiple Pathways and Products

在真空中碰撞分子对已经成为研究分子相互作用和交换能量或化学反应的基本机制的独特而强大的方法。这种类型的散射实验已经达到了高度的复杂性。理论建模也取得了平行的进展，使分子之间的作用力越来越准确地计算出来，并为机制的解释提供了严格的解释。然而，直到最近，这些先进的方法还只能处理小分子系统，通常包含不超过三个原子，往往只有一组化学产物通过一个单一的机制形成。我们的愿景是通过扩大系统的范围，可以研究那些更典型的现实世界中的应用，使一个戏剧性的步骤改变到分子碰撞领域。在基础基准研究的核心基础上，我们将研究具有挑战性的、以前难以解决的问题，这些问题的共同特点是具有多种反应途径和多种不同的结果。现在只能抓住这个机会，因为最近在实验方法和基础理论的概念发展方面取得了技术进步，这些理论利用了可用计算能力的指数增长。研究人员代表了一个独特的团队，具有多样化，互补的实验和理论专业知识，来自英国两个卓越的分子散射中心。我们将在三个平行主题下处理一个雄心勃勃的计划：1）分散到基准基础理论。有一个持续的至关重要的需要，继续推进散射实验的目标是完全控制的量子态，相对取向和速度的传入分子，并测量同样充分的产品的相应属性。这种“终极”实验为最先进的理论预测提供了最严格的测试。我们将进行一系列关于小的、高活性的自由基（NO、OH）与分子伴侣碰撞的实验。计算实际势能面的理论方法的补充进展，将使观测结果与高级散射计算的预测进行比较。2）大气、燃烧和等离子体科学的散射。这些环境中的化学反应由高活性自由基、离子或电子驱动，这些自由基、离子或电子以低浓度存在，但负责使稳定分子相互转化的反应序列。一些最重要的反应发生在气相和液体或固体表面之间的界面处。主要的突出挑战在于理解不同产品通过竞争机制形成的各个步骤。我们将回答几个关键反应系统的问题。这些包括OH与挥发性有机化合物的反应;电子与DNA、其他生物分子和多环芳烃（PAH）的结构单元的碰撞;以及重要的大气氧化剂OH和Cl与代表气溶胶颗粒的液体表面的碰撞。3）散射催化。多相催化在工业和其他地方被广泛应用，以加速否则不切实际的缓慢反应的速率。在大多数情况下，潜在的机制仍然是未知的，所以现实世界的催化过程的优化主要是通过经验试错。我们将帮助克服这种缺乏机制的洞察力，通过研究模型，混合过渡金属簇，模拟固体多相催化剂的活性位点的反应。我们还将开发新的散射方法，基于高能金属原子，以表征离子液体的表面结构，这是它们在多相催化形式中的核心作用。

Colliding pairs of molecules in vacuum has become a uniquely powerful method for investigating the fundamental mechanisms through which molecules interact and either exchange energy or chemically react. Scattering experiments of this type have reached a high level of sophistication. Theoretical modelling has progressed in parallel, allowing the forces that act between the molecules to be calculated increasingly accurately and providing rigour to the interpretation of the mechanisms. However, until recently, these advanced methods have only been able to treat small molecular systems, typically containing no more than three atoms and often with only one set of chemical products formed via a single mechanism.Our vision is to make a dramatic step-change to the field of molecular collisions by extending the range of systems that can be studied to those more typical of real-world applications. Building on a core of fundamental, benchmark studies, we will progress to challenging, previously intractable problems with common features of having multiple reaction pathways and multiple distinct outcomes. This opportunity can only be grasped now because of recent technical advances in experimental methods and conceptual developments in the underlying theory that exploit the exponential growth in available computing power. The Investigators represent a unique team with diverse, complementary experimental and theoretical expertise, drawn from the two centres of excellence for molecular scattering in the UK. We will tackle an ambitious programme under three parallel themes:1) Scattering to benchmark fundamental theory. There is an on-going vital need to continue the advance in scattering experiments towards the goal of controlling fully the quantum states, relative orientation and speed of the incoming molecules, and measuring equally fully the corresponding properties of the products. Such 'ultimate' experiments provide the most stringent tests of state-of the-art theoretical predictions. We will perform a series of experiments on collisions of small, highly reactive free radicals (NO, OH) with molecular partners. Complementary advances in theoretical methodology for the calculation of realistic potential energy surfaces, which encode the forces, will allow the observations to be compared against the predictions of advanced-level scattering calculations.2) Scattering for the atmosphere, combustion and plasma science. The chemistry in these environments is driven by highly reactive radicals, ions, or electrons, present at low concentrations but responsible for sequences of reactions that interconvert stable molecules. Some of the most important reactions take place at the interface between the gas phase and liquid or solid surfaces. The major outstanding challenges lie in understanding individual steps in which different products are formed via competing mechanisms. We will answer such questions for several key reaction systems. These include reactions of OH with volatile organic compounds; collisions of electrons with building blocks of DNA, other biomolecules and polycyclic aromatic hydrocarbons (PAHs); and collisions of OH and Cl, important atmospheric oxidants, with the surfaces of liquids representative of aerosol particles.3) Scattering for catalysis. Heterogeneous catalysis is used widely in industry and elsewhere to accelerate the rates of otherwise impractically slow reactions. The underlying mechanisms have in most cases remained unknown, so that optimisation of real-world catalytic processes has been largely through empirical trial-and-error. We will help to overcome this lack of mechanistic insight by investigating reactions on model, mixed transition-metal clusters that mimic the active sites in solid heterogeneous catalysts. We will also develop new scattering methods, based on energetic metal atoms, to characterise the surface structures of ionic liquids, central to their role in forms of multiphase catalysis.