Start the clock: a new direct method to study collisions of electronically excited molecules

启动时钟：研究电子激发分子碰撞的新直接方法

基本信息

批准号：
EP/J017973/1
负责人：
Matthew Costen
金额：
$ 68.9万
依托单位：
Heriot-Watt University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ017973%2F1
关键词：
Start clock new direct method

项目摘要

Understanding the chemistry of the atmosphere, combustion systems and technological plasmas is of great importance in the modern world. A very significant process in these gas-phase environments is the transfer of energy between molecules during collisions. The total amount of internal energy that a molecule possesses is important, but equally if not more important is what form that energy takes. It may be in the form of translational, rotational or vibrational motion of the molecule, or even in the arrangement of the electrons. A large amount of energy may be stored in a rearrangement of the electronic structure of a molecule, producing an electronically excited state. Such excited states occur in energetic environments such as combustion or plasmas, and their decay is what is responsible for the typically observed light emission. The excited states are often also created when molecules are probed in experiments using optical methods. The electronic energy may be re-radiated, but generally not before the molecule has undergone collisions with other gas-phase molecules. This may result in translational, rotational or vibrational energy transfer within the excited electronic state. Significantly, it may also involve either a reaction that removes the excited molecule altogether, or a quenching collision in which the electronic energy is lost to the collision partner.Despite their importance, surprisingly little is known about the fundamental forces involved in collisions of electronically excited molecules. The best way to determine the detailed dynamics of the collisions of such molecules is using a technique called crossed molecular beam (CMB) scattering. In this method, defined beams of different molecules are collided in a vacuum chamber, and the details of their directions of travel and internal energies are observed in some fashion. We will extend this technique previously used for electronic ground state molecules to the collisions of electronically excited molecules, specifically NO, which is an important molecule in the atmosphere and combustion. We will build a new state-of-the-art CMB scattering apparatus, and by using a combination of laser pulses of different wavelengths will prepare NO molecules in their excited state. After these have collided with the target molecules we will probe the scattered molecules with a laser-based detection technique called velocity map ion-imaging, which is capable of accurately measuring their velocities. The laser pulse that prepares the excited NO defines a zero-time for the experiment, and so 'starts the clock' ticking. This will give us much better definition of the experiment than is usual in CMB experiments, and hence higher sensitivity to the scattering dynamics. We will use this sensitivity to study the collisions of NO with simple molecules relevant to combustion and the atmosphere, namely N2, O2 and CO. These are known to show very different quenching and reactive behaviours with excited NO, but little or nothing is known about the forces involved in these interactions. The results from our experiments will be used to deepen our understanding of what is important is directing energy transfer in electronically excited molecules, and will help to drive the development of better theoretical models and calculations, as well as providing information of direct relevance to scientist working in the combustion and atmospheric probing of NO.

在现代世界中了解大气，燃烧系统和技术等离子体的化学反应至关重要。在这些气相环境中，一个非常重要的过程是碰撞过程中分子之间的能量转移。分子拥有的内部能量总数很重要，但同样重要的是能量采取的形式。它可能是分子的平移，旋转或振动运动的形式，甚至是电子的排列形式。可以将大量能量存储在分子的电子结构的重排中，从而产生电子激发态。这种激发态发生在燃烧或等离子体等能量环境中，它们的衰变是造成通常观察到的光发射的原因。当使用光学方法在实验中探测分子时，通常还会产生激发态。电子能可以重新辐射，但通常不会在分子与其他气相分子发生碰撞之前。这可能会导致激发电子状态内的平移，旋转或振动能传递。值得注意的是，它也可能涉及一种完全去除激发分子的反应，或者是对碰撞伴侣丢失电子能量的淬灭碰撞。尽管如此，但令人惊讶的是，对于参与电子激发分子碰撞的基本力而言，知之甚少。确定此类分子碰撞的详细动力学的最佳方法是使用一种称为交叉分子束（CMB）散射的技术。在这种方法中，在真空室中碰撞了不同分子的定义光束，并且以某种方式观察到它们的旅行方向和内部能量的细节。我们将将以前用于电子基态分子的技术扩展到电子激发分子的碰撞，特别是NO，这是大气和燃烧中的重要分子。我们将构建一个新的最先进的CMB散射设备，并结合使用不同波长的激光脉冲，将在其激发态下制备任何分子。这些与靶分子相撞后，我们将使用称为速度图离子成像的基于激光的检测技术探测散射的分子，该技术能够准确测量其速度。准备兴奋的激光脉冲没有定义实验的零时间，因此“开始时钟”的滴答作响。这将使我们对实验的定义要比CMB实验的平常更好，从而使我们对散射动力学的敏感性更高。我们将使用这种敏感性来研究与燃烧和大气相关的简单分子的碰撞，即N2，O2和CO。这些众所周知，这些表现出非常不同的淬火和反应性行为，具有激动的NO，但对这些相互作用所涉及的力量几乎一无所知。我们的实验的结果将被用来加深我们对重要的事情的理解，这是指导电子激发分子中的能量转移，并将有助于推动更好的理论模型和计算的发展，并向从事燃烧和大气探测的科学家提供直接相关性的信息。