Deuterium fractionation in ultracold collisions using trapped molecular ions

使用捕获分子离子进行超冷碰撞中的氘分馏

基本信息

批准号：
EP/I029230/1
负责人：
Matthias Keller
金额：
$ 71.92万
依托单位：
University of Sussex
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI029230%2F1
关键词：
Deuterium fractionation ultracold collisions using

项目摘要

One of the key elements of the quantum theory developed in the early 20th century is the concept of wave-particle duality. Thus particles, such as electrons, can be diffracted in a manner similar to X-rays, and conversely light can be considered to be composed of particle-like energy packets known as photons .In this project we aim to explore chemical processes at temperatures very close to absolute zero where these concepts of wave-particle duality become very important. When matter is cooled, the constituent atoms and molecules have less kinetic energy and move more slowly, hence their momentum is decreased. In the quantum theory this implies that their wavelength increases and their wave-like characteristics are enhanced. The conventional 'particle-view' of chemical processes describes these as occurring through collisions of molecules with one another, breaking and making new chemical bonds. At very low temperatures, however, the fundamental physical description of a chemical transformation changes; the picture of classical collisions needs to be replaced with a description in terms of wave motion, with the implied effects of superposition and interference. The specific goal of this interdisciplinary project is the precise measurement of ultracold reactions of ammonia cations and methyl cations in the gas phase with neutral species such as H2O and NH3. We intend to explore how the intrinsic wave properties of the reaction like tunneling, barrier reflection and interference become important in determining the rate of the reaction as a function of temperature. Ion-neutral reactions tend to have very low energy barriers and hence can be very fast even at the lowest temperatures. The low kinetic energy makes the behaviour of the reaction highly sensitive to the long-range forces between the molecules. Ultracold collisions offer the possibility of new forms of control using electromagnetic fields. This is therefore a very unusual regime for investigating chemical dynamics, but also one well suited for testing quantum theories of chemical reactivity. At temperatures near 10 K the studies become relevant to understand the rich and diverse chemistry of interstellar gas. We will study reactions in which one or two of the hydrogen atoms in the neutral molecule have been replaced with a deuterium atom. Reactions of this type are very important in the context of the interstellar medium because they determine the concentrations of deuterated molecules in space and these can be related back to fundamental theories of the formation of the universe.Experimentally we employ novel devices for controlling the temperature and motion of the reacting species. The ions are trapped in a highly localized region of a vacuum chamber using radiofrequency fields and are maintained at very low temperatures using the technique of laser cooling. The ions interact with a beam of neutral molecules provided by a Stark decelerator , a device which can decelerate polar molecules. Combining this with an ion trap provides us with a unique and internationally leading set-up to measure ultracold reactive collisions with unparalleled control. In order to measure the rates of reactions, novel techniques will be developed to measure the change in the numbers and species of the ions over time. This can be done by applying additional electric fields which shake the trapped ions. The resultant motion of the ions is characteristic of the number of reactant and product ions present and their masses. New laser-based techniques will also be used to control and monitor the internal motions of the molecule. The techniques which will be developed in the scope of this project are novel and timely and will undoubtedly have high impact in one of the most rapidly developing fields of chemical physics. The reaction rate measurements will also have potential impact in Astrophysics as well as computational chemistry.

在20世纪初期开发的量子理论的关键要素之一是波颗粒对偶性的概念。因此，可以以类似于X射线的方式将颗粒（例如电子）衍射，相反的光可以被认为是由称为光子的粒子样能量包组成的。在该项目中，我们旨在在非常接近绝对零的温度下探索这些波 - 颗粒偶性概念的化学过程非常重要。当物质冷却时，成分原子和分子的动能较小，移动较慢，因此动量降低。在量子理论中，这意味着它们的波长增加，并且它们的波动特性得到了增强。化学过程的常规“粒子视图”将它们描述为通过彼此的分子碰撞，破坏并产生新的化学键。但是，在非常低的温度下，化学转化的基本物理描述发生了变化。经典碰撞的图片需要用波动的描述代替，并暗示了叠加和干扰的效果。这个跨学科项目的具体目标是与中性物种（如H2O和NH3）在气相中精确测量氨阳离子和甲基阳离子的超低反应。我们打算探讨反应的固有波特性如何在隧道，屏障反射和干扰中如何在确定反应速率作为温度的函数中变得重要。离子中性反应往往具有非常低的能屏障，因此即使在最低温度下也可能非常快。低动能使反应的行为对分子之间的远距离力高度敏感。 Ultracold碰撞提供了使用电磁场进行新的控制形式的可能性。因此，这是研究化学动力学的一个非常不寻常的制度，但也非常适合测试化学反应性的量子理论。在接近10 K的温度下，研究与了解星际气体的丰富而多样化的化学反应有关。我们将研究反应，其中中性分子中的一个或两个氢原子已被氘原子代替。在星际介质的背景下，这种类型的反应非常重要，因为它们确定了空间中氘化分子的浓度，并且这些分子的浓度可能与宇宙形成的基本理论有关。经常我们采用新颖的设备来控制反应物种的温度和运动。使用射频场将离子捕获在真空室的高度局部区域中，并使用激光冷却技术保持在非常低的温度。离子与Stark减速器提供的中性分子束相互作用，该分子可以减速极性分子。将其与离子陷阱相结合为我们提供了独特的国际领先设置，以测量没有比较的控制的超低反应性碰撞。为了衡量反应速率，将开发新技术来测量离子数量和物种随时间的变化。这可以通过应用摇动被困离子的其他电场来完成。离子的最终运动是反应物和产物离子数量及其质量的特征。新的基于激光的技术也将用于控制和监视分子的内部运动。该项目范围内将开发的技术是新颖的，及时的，无疑将在化学物理学最快发展的领域之一中产生很大的影响。反应速率测量还将对天体物理学以及计算化学产生潜在的影响。