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扩展的领域，有可能增强我们对低温反应动力学的理解。在这种情况下，预计反应的量子性质将发挥越来越重要的作用。通过研究这一领域，我们可以更好地了解宇宙最冷部分的反应动力学，并回答一些问题，如与星际介质中的丰度相比，宇宙中的氚丰度有所提高(氘的分馏)。它还将允许我们测试许多提出的理论，这些理论是在几十年前提出的，目前仍有待实验检验。这些理论的验证或改进对化学反应动力学领域将是无价的，并将使以前无法实现的全新分析成为可能。具体地说，我将通过尝试使用我们连接到四极速度导向器的缓冲气体装置来创建定向氨(ND3)分子的内部冷源来开始我的研究。过去用这个装置已经成功地产生了冷束，但是一旦束流通过导出区后的零电场区域，绝大多数的分子取向就会丢失。对该区域施加磁场(或重新设计器械的后引导段)将有助于保留更大百分比的该方向。一个线性的保罗离子陷阱连接到引导出口，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。将这两个冷反应物来源连接起来，将使我们能够研究低温和分子取向对反应速度的影响。进一步的研究将通过目前正在开发的一种新的低温离子陷阱来进行。我们的目标是将其连接到塞曼减速器上，这将提供冷自由基的来源。使用塞曼减速器，我们将能够研究自由基中性物质与捕获在低温离子陷阱中的激光和交感冷却离子的反应性。这两种方法使我们能够研究范围广泛的反应物的反应性，并比以前更深入地探索冷状态。该项目属于EPSRC的化学反应动力学和机理研究领域，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的战略目标保持一致，即建立英国在该领域的世界领先地位。这些技术对物理和化学领域都有兴趣，并将与EPSRC的许多其他研究领域建立联系，如“计算和理论化学”和“冷原子和分子”，使这一项目引起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.