Interaction of Low-Energy Positrons with Atoms and Molecules

正电子是反物质的一种，是电子的反粒子。虽然我们的世界几乎完全是由物质组成的，但我们不知道为什么。然而，正电子（反粒子）可以使用各种技术产生，并且它们在许多应用中很重要。一个例子是在医学和药物设计中，正电子发射断层扫描（PET）用于研究代谢过程。正电子也被用来研究和开发新材料，形成反氢（稳定的中性反物质），并了解各种天体物理过程。 这项研究旨在建立对正电子与普通物质，特别是分子形式的物质相互作用的基本理解，这可用于促进这些应用并开发新的应用。该项目也是科学和技术人员的一个极好的培训基地;它涉及各级学生和博士后研究人员，从实验规划到研究成果的传播。 该项目的重点是研究低能正电子与原子和分子的相互作用。感兴趣的是振动Feshbach共振的激发，在该过程中，正电子与分子碰撞，激发振动模式并被捕获在分子上。研究的一个特别重点是了解所观察到的增强湮没率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。本研究涉及的原子物理学的基本方面包括理解电子-正电子相关性，正电子与原子和分子的结合，以及正电子附着导致的正电子湮灭中的共振性质。 一种新的冷束将允许振动模式对称性的作用，在确定湮灭共振的强度的研究。其他研究目标包括定量地了解分子内振动能量再分配（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，补充化学和生物学社区现在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.