Do single-bounce nuclear spin flips happen, and can they be measured?

原子，以及随后的分子，都拥有一种称为核自旋的基本性质。简而言之，核自旋可以被认为是一个与每个原子相关的微观磁铁。核自旋在许多非常不同的领域发挥着作用，从磁共振成像等医学应用到高效安全地储存液氢火箭燃料。在基本上所有使用核自旋的应用中，一个重要的过程是当核自旋相互作用并与其环境相互作用时，一个自旋态转换到另一个自旋态。使用上面提到的磁铁的简单类比，这可以被认为是微观磁铁反转其方向。在这个项目中，我们将尝试研究这个领域的一个基本问题，即分子的核自旋态是否会因为与表面的一次碰撞而改变，如果是这样的话，什么类型的表面和碰撞性质会影响这种自旋改变的概率。传统的实验技术不具备跟踪此类事件所需的灵敏度，目前的理论水平也无法提供确凿的答案。我们将使用一种最新开发的仪器，这种仪器应该能够在一次碰撞中感应到自旋的变化。该仪器使用各种磁操作创建了一束处于明确核自旋状态的分子束，将它们对准固体表面，然后检测和分析碰撞中出现的分子的自旋状态。这项研究的结果有望有助于我们对核自旋态的基本理解，作为现有理论计算的基准，并最终帮助开发更先进的理论模型，这些模型将能够可靠地模拟复杂系统，例如在许多涉及核自旋的科学和工业应用中遇到的系统。

Atoms, and consequently molecules, possess a fundamental property called nuclear spin. In simple terms, nuclear spin can be thought of as a microscopic magnet associated with each atom. Nuclear spins play a role in many very different fields, ranging from medical applications such as magnetic resonance imaging to efficient and safe storage of liquid hydrogen rocket fuel. An important process in essentially all the applications which use nuclear spins, is the conversion of one spin state to another when the nuclear spins interact with each other and with their environment. Using the simple analogy to a magnet mentioned above, this can be considered as the microscopic magnet flipping its orientation. In this project, we will attempt to look at a fundamental question in this field, which is whether the nuclear spin state of a molecule can change due to a single collision with a surface, and if it does, which types of surfaces and collision properties affect the probability of such a spin change. Conventional experimental techniques do not have the required sensitivity to follow such an event and the current level of theory cannot provide conclusive answers. We will use a recently developed instrument which should be capable of sensing a spin change in a single collision. The instrument creates a beam of molecules in a well-defined nuclear spin state using various magnetic manipulations, aims them toward a solid surface, and then detects and analyses the spin state of the molecules emerging from the collision. The results of this study are expected to contribute to our fundamental understanding of nuclear spin states, act as a benchmark for existing theoretical calculations, and eventually assist the development of more advanced theoretical models, which will be able to reliably model complex systems such as those encountered in the many scientific and industrial applications involving nuclear spins.