Implementation of cryogenic techniques for the investigation of ion-neutral reactions in the cold regime

“冷”化学，即在1K以下进行的化学，是一个令人兴奋和迅速发展的领域，有可能增强我们对低温反应动力学的理解。在这种状态下，反应的量子性质有望发挥越来越重要的作用。通过对这一领域的研究，我们可以更好地理解宇宙中最冷部分的反应动力学，并回答诸如宇宙中氘的丰度比星际介质中氘的丰度增强（氘分馏）等问题。它还将使我们能够测试许多理论，这些理论是在几十年前提出的，目前仍有待实验验证。这些理论的验证或改进将对化学反应动力学领域具有不可估量的价值，并将使以前不可能的全新分析成为可能。具体来说，我将通过尝试使用连接到四极速度指南的缓冲气体装置创建定向氨（ND3）分子的内部冷源来开始我的研究。过去用这种装置已经成功地制造出了冷光束，但是一旦光束穿过导光后的零电场区域，绝大多数分子的取向就会丢失。在该区域施加磁场（或重新设计仪器的后导向部分）将有助于保持该定向的更大百分比。一个线性保罗离子阱连接到引导出口，这为我们提供了一种通过激光或交感冷却产生平移冷离子源的方法。把这两种冷反应物的来源联系起来，将使我们能够研究低温和分子取向对反应速率的影响。进一步的研究将通过目前正在开发的一种新的低温离子阱。我们的目标是把它连接到塞曼减速机上它将提供冷自由基的来源。利用塞曼减速机，我们将能够研究自由基中性物质与被困在低温离子阱中的激光和共感冷却离子的反应性。这两种方法使我们能够研究各种反应物的反应性，并比以前更深入地研究冷态。该项目属于EPSRC“化学反应动力学和机制”研究领域，将为离子-分子反应的研究提供一种新的方法，这将使我们与EPSRC建立英国作为该领域世界领导者的战略目标保持一致。这些技术对物理和化学领域都很感兴趣，并将与EPSRC的许多其他研究领域联系起来，如“计算和理论化学”和“冷原子和分子”，使该项目成为EPSRC和整个物理化学界的广泛兴趣。

'Cold' chemistry, that is, chemistry conducted below 1K, is an exciting and rapidly expanding field with the potential to enhance our understanding of low temperature reaction dynamics. This is a regime where the quantum nature of the reaction is expected to play an increasingly important role. Through studying this domain, we can develop a better understanding of the reaction dynamics in the coldest parts of the universe and answer problems such as the enhanced abundance of cosmic deuterium compared to the abundance in the Interstellar medium (deuterium fractionation). It will also allow us to test many theories proposed to predict patters of reactivity in this cold regime, theories that were proposed many decades ago and remain to be tested experimentally. Validation or improvement of these theories will be invaluable to the field of chemical reaction dynamics and will enable a completely novel analysis that has not been previously possible. Specifically, I will start my studies by trying to create an internally cold source of oriented ammonia (ND3) molecules using our buffer gas apparatus that is connected to a quadrupole velocity guide. A cold beam has successfully been produced with this apparatus in the past, but the vast majority of molecular orientation is lost once the beam passes through a region of zero electric field after the guide exit. Applying a field to this region (or redesigning the post-guide segment of the apparatus) will help to retain a much larger percentage of this orientation. A linear Paul ion trap is connected to the guide exit which provides us with a way of producing a translationally cold source of ions via either laser or sympathetic cooling. Connecting these two sources of cold reactants will allow us to study the effect of low temperature and molecular orientation on the rates of reaction. Further research will be by way of a new, cryogenic ion trap which is currently being developed. The goal is to attach this to the Zeeman decelerator which will provide a source of cold radicals. Using the Zeeman decelerator we will be able investigate the reactivity of radical neutral species with laser and sympathetically cooled ions which are trapped in the cryogenic ion trap. These two methods allow us to investigate the reactivity of a wide range of reactants and probe the cold regime even further than has been possible before. This project falls within the EPSRC 'Chemical Reaction Dynamics and Mechanisms' research area and will provide a novel methodology for the study of ion-molecule reactions which will align us with the EPSRCs strategic goals of establishing the UK as a world leader in this field. The techniques are of interest to both the physics and chemistry fields and will have links to many other EPSRC research areas such as 'Computational and Theoretical Chemistry' and 'Cold Atoms and Molecules', making this project of wide interest to the EPSRC and the physical chemistry community as a whole.