Interaction of Low-Energy Positrons with Atoms and Molecules

正电子是反物质的一种形式，是电子的反粒子。虽然我们的世界几乎完全由物质组成，但人们还不知道为什么。然而，正电子(反粒子)可以使用各种技术来创建，它们在许多应用中都很重要。一个例子是在医学和药物设计中，正电子发射断层扫描(PET)被用来研究代谢过程。正电子还被用来研究和开发新材料，形成反氢(稳定的中性反物质)，以及理解各种天体物理过程。这项研究试图建立一个对正电子与普通物质相互作用的基本理解，特别是以分子的形式，这可以用于进一步的这些应用和开发新的应用。该项目也是科技人员的极好培训基地；从实验计划到研究成果的传播，各级学生和博士后研究人员都参与了该项目。本项目主要研究低能正电子与原子和分子的相互作用。令人感兴趣的是振动Feshbach共振的激发，在这个过程中，正电子与分子碰撞，激发振动模式，并被困在分子上。这项研究的一个特别重点是了解观察到的湮灭率增强作为入射正电子能量的函数，并使用这些光谱来确定正电子-分子结合能。这项研究涉及的原子物理学的基本方面包括了解电子-正电子关联、正电子与原子和分子的结合，以及正电子附着引起的正电子湮没中共振的性质。一种新的冷束将允许研究振动模对称性在确定湮没共振强度中的作用。其他研究目标包括定量了解分子内振动能量重新分配(IVR)时分子上正电子的湮灭。这些正电子-IVR研究可能会为分子动力学提供新的见解，补充化学和生物界目前使用光学技术进行的研究。

Positrons, a form of antimatter, are the antiparticles of electrons. While our world is almost solely composed of matter, it is not understood why. Positrons (antiparticles) can be created using a variety of techniques, however, and they are important in a number of applications. One example is in medicine and drug design, where positron emission tomography (PET) is used to study metabolic processes. Positrons are also used to study and develop new materials, to form antihydrogen (stable neutral antimatter), and to understand a variety of astrophysical processes. This research seeks to establish a fundamental understanding of the interaction of positrons with ordinary matter, particularly in the form of molecules, which can be used to further these applications and to develop new ones. The project is also an excellent training ground for scientific and technical personnel; it involves student and post-doctoral researchers at all levels, from the planning of experiments to the dissemination of research results. This project focuses on studies of the interaction of low-energy positrons with atoms and molecules. Of interest is the excitation of vibrational Feshbach resonances, a process in which a positron, in collision with a molecule, excites a vibrational mode and becomes trapped on the molecule. A particular focus of the research is the understanding of the observed enhancements in annihilation rates as a function of incident positron energy and using these spectra to determine positron-molecule binding energies. Fundamental aspects of atomic physics involved in this research include understanding electron-positron correlations, positron binding to atoms and molecules, and the nature of the resonances in positron annihilation resulting from positron attachment. A new cold beam will allow studies of the role of vibrational-mode symmetry in determining the strengths of the annihilation resonances. Other research goals include understanding quantitatively the annihilation of positrons on molecules when intramolecular vibrational energy redistribution (IVR) is operative. These positron-IVR studies could potentially provide new insights into molecular dynamics, complementary to studies now done by the chemistry and biology communities using optical techniques.