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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.

了解大气化学、燃烧系统和等离子体技术在现代世界是非常重要的。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传递。一个分子拥有的内能总量很重要，但同样重要的是能量的形式。它可能以分子的平动、转动或振动运动的形式存在，甚至以电子的排列形式存在。大量的能量可以储存在分子电子结构的重排中，从而产生电子激发态。这种激发态发生在能量环境中，如燃烧或等离子体，它们的衰变是导致典型观察到的光发射的原因。在实验中使用光学方法探测分子时，通常也会产生激发态。电子能量可以再辐射，但通常在分子与其他气相分子发生碰撞之前不会再辐射。这可能导致激发态内的平动、转动或振动能量传递。值得注意的是，它也可能涉及到一个将被激发的分子完全移除的反应，或者一个电子能量丢失给碰撞伙伴的猝灭碰撞。尽管它们很重要，但令人惊讶的是，人们对电子激发分子碰撞所涉及的基本力知之甚少。确定这种分子碰撞的详细动力学的最好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，不同分子的确定光束在真空室中碰撞，并以某种方式观察其行进方向和内能的细节。我们将把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，它是大气和燃烧中的重要分子。我们将建立一个新的最先进的CMB散射装置，并通过不同波长激光脉冲的组合来制备处于激发态的NO分子。在它们与目标分子碰撞后，我们将使用一种称为速度图离子成像的激光探测技术探测分散的分子，这种技术能够精确测量它们的速度。准备激发NO的激光脉冲为实验定义了一个零时间，因此“开始时钟”滴答作响。这将给我们提供比通常的CMB实验更好的实验定义，因此对散射动力学具有更高的灵敏度。我们将利用这种灵敏度来研究NO与与燃烧和大气相关的简单分子（即N2、O2和CO）的碰撞。已知这些分子在激发NO时表现出非常不同的猝灭和反应行为，但对这些相互作用中涉及的力知之甚少或一无所知。我们的实验结果将用于加深我们对电子激发分子中指导能量转移的重要性的理解，并将有助于推动更好的理论模型和计算的发展，以及为从事NO燃烧和大气探测工作的科学家提供直接相关的信息。