Reaction Dynamics At Surfaces, A-Molecule-At-A-Time

这项研究提出利用近年来出现的一个机会，详细了解简单化学反应在表面发生的方式。这一机会源于当代三个研究领域的融合：扫描隧道显微镜（STM）（1986年诺贝尔物理学奖）、实验反应动力学（1986年诺贝尔化学奖）和揭示复杂反应相遇分子动力学的计算机模型的发展（诺贝尔化学奖，2013年）。STM，允许实验者获得表面上单个分子的图像。反应动力学（由申请人和其他许多人开创的领域）是对引起化学反应的分子运动的实验研究。计算机模拟揭示了将试剂转化为产品的复杂原子和分子运动。这三个领域的结合首次提供了在表面上观察单个试剂分子的机会，跟踪它们在热、光或电子的激活，并将它们的初始和最终几何形状联系起来。本周，诺贝尔化学奖评选委员会主席在宣布分子建模化学奖时表示：“理论化学为我们提供了整个戏剧。”在表面反应过程中绘制分子运动图的机会，一次一个分子，是本提案的主题。这个实验室很适合进行这类研究，因为它将实验与计算机理论相结合。具体来说(1)它特别配备了四个超高真空STM，用于研究半导体和金属表面的反应，(2)它最近介绍并演示了（在本授权期发表的五篇论文中）一个从头计算模型（“脉冲两态”，I2S，模型），该模型可作为指导试剂转化的分子运动序列，其表面几何形状由STM观察。变成产品，它们的几何形状是用同样的方法来观察的。这项工作的目的是在分子水平上提供对化学和生命的核心事件的理解，即化学反应将一种物质转化为另一种物质的能力——打破旧的键并形成新的键。反应动力学的基本问题是试剂如何接近，它们如何碰撞，它们如何分离。本文提出的一种实验方法（在本报告期间，我们首先在一个简单的化学反应中证明了STM之后）是在表面定位和排列一对试剂，然后通过激发其中一个分子对来触发“表面排列反应”（SAR）。其他实验方法构成了本提案的一部分，包括通过表面电荷转移来研究低温表面反应，以及通过比较振动和电子激发来研究反应动力学对试剂激发方式的依赖性。这些实验及其相关理论具有明显的实际目的，正如本文所报道的当前研究结果所表明的那样，因为制造纳米结构的进展将取决于我们对表面反应产物的位置和结合的知识和控制能力。这篇论文描述了一种强大的表面模式化方法——“分子尺度印迹”，它适用于半导体，也首次适用于金属。NSERC发现资助通过培养影响深远的基础科学，为随后的变革性应用提供了最好的希望。

This research proposes to exploit an opportunity which has arisen in recent years to obtain detailed understanding of the way in which simple chemical reactions take place at surfaces. The opportunity stems from the confluence of three fields of contemporary research: Scanning Tunneling Microscopy (STM) (Nobel Prize in Physics, 1986) experimental Reaction Dynamics (Nobel Prize in Chemistry, 1986) and the development of Computer Models revealing the molecular dynamics in complex reactive encounters (Nobel Prize in Chemistry, 2013). STM, allows the experimenter to obtain images of single molecules at surfaces. Reaction Dynamics (a field pioneered by the applicant with many others) is the experimental study of the molecular motions that give rise to chemical reaction. Computer modeling reveals the complex atomic and molecular motions that transform reagents into products. A combination of these three fields offers, for the first time, the opportunity to see individual reagent molecules at surfaces, follow their activation by heat, light or electrons, and correlate their initial and final geometries. "Theoretical chemistry provides us with the whole drama," said the Chair of the Chemistry Nobel Selection Committee in announcing the Chemistry award for molecular modeling, this week. The opportunity to map the molecular motions in the course of surface reactions, a-molecule-at-a-time, is the subject of the present proposal. This laboratory is well placed for studies of this type, since it combines experiment with computer-based theory. Specifically (1) it is equipped, exceptionally, with four Ultra-High Vacuum STM's for studies of reactions at the well-characterized surfaces of semi-conductors and metals, and (2) it has recently introduced and demonstrated (in five published papers from the present granting period) an ab initio model (the 'Impulsive Two-State', I2S, model) that serves as a guide to the sequence of molecular motions responsible for converting reagent, whose geometry at the surface is observed by STM, into products, whose geometry is observed by the same means. The purpose of the proposed work is to provide understanding at the molecular level of an event central to chemistry, as also to life, namely the ability of chemical reactions to convert one substance into another--breaking old bonds and forming new. The fundamental question of Reaction Dynamics is how reagents approach, how they collide, and how they separate. One experimental approach proposed here (first demonstrated by us for a simple chemical reaction followed by STM, in the present reporting period) is to position and align a pair of reagents at the surface, and then trigger 'Surface Aligned Reaction' (SAR) by excitation of one of the molecular pair. Other experimental approaches that form a part of this Proposal are studies of Low-Temperature Surface Reaction by charge-transfer from the surface, and Dependence of Reaction Dynamics on Mode of Reagent Excitation by comparing vibrational with electronic excitation. These experiments and their accompanying theories have an evident practical purpose, as demonstrated in results reported here from the current period of research, since progress in fabricating nano-structures will depend on our knowledge of, and ability to control, the location and binding of reaction products at surfaces. A powerful means to pattern surfaces, 'Molecular-Scale Imprinting', shown here to be applicable to semi-conductors and (for the first time) also to metals, is described in this submission. NSERC Discovery Grants by fostering far-reaching basic science offer the best possible hope for subsequent transformative applications.