Polarized Electron Physics

这个项目涉及研究极化电子（具有优先指向一个方向的平均自旋）与手性或“手性”分子以及锌原子之间的碰撞。以前的实验解决了关于电子-分子散射动力学的物理问题，特别是关于电子自旋在与具有手性立体化学结构的分子碰撞中所起的作用。它们还将提供有关生物同手性起源的重要线索——所有自然产生的DNA都以相同的方向螺旋。锌的实验是为了验证最近一个澳大利亚小组所做的实验的结果，在这个实验中，锌被极化电子激发的状态显示出相对于碰撞中入射光束方向倾斜的线性极化。这个结果被所有已知的原子碰撞理论所禁止；如果澳大利亚的结果被重现，我们关于电子如何与原子和分子碰撞的许多基本理论知识将被证明是错误的。改进的极化电子源和分析仪正在开发中。我们正在测试越来越紧凑的电子自旋探测器设计。我们也在研究块状材料的多光子电离，比如半导体砷化镓，看看极化电子是否可以从这种材料中发光，即使表面没有准备好给它一个负电子亲和度——这是生产高效光电发射器的常规方法。后一项工作有望为生物和材料研究以及工业提供新的分析工具。这些实验的影响将超出原子、分子和光学科学的直接领域。除了其更广泛的科学意义，这项工作将有一个重要的教育组成部分。参与这些项目的本科生将首次体验科学研究。为了扩大原子、分子和光学物理学的人才库，这些职位将特别招聘女性和代表性不足的少数族裔。手性分子实验及其与天体生物学问题的联系，将成为定期向高中和民间团体进行讲座的绝佳话题，并有助于向广大外行观众展示基础物理学的美妙之处。

This project involves the study of collisions between polarized electrons (having an average spin that points preferentially in one direction) and chiral, or "handed" molecules as well as zinc atoms. The former experiments address physics questions about the dynamics of electron-molecule scattering, particularly with regard to the role played by electron spin in collisions with molecules that have a handed stereochemical structure. They will also provide important clues about the origins of biological homochirality -- the fact that all naturally-occurring DNA spirals in the same direction. The zinc experiments are being done to check the results of an experiment done recently by an Australian group in which states of zinc excited by polarized electrons exhibited linear polarization that was tilted relative to the incident beam direction in the collision. This result is forbidden by all known theories of atomic collisions; if the Australian result is reproduced, much of our basic theoretical knowledge of how electrons collide with atoms and molecules will be shown to be in error. Improved sources and analyzers of polarized electrons are being developed. We are testing increasingly compact designs of electron spin detectors. We also are studying multiphoton ionization of bulk materials such as the semiconductor GaAs to see if polarized electrons can be photoemitted from such material even when the surface has not been prepared to give it a negative electron affinity -- the normal method used to produce efficient photoemitters. This latter work holds the promise of providing new analytical tools for biological and materials research, and for industry. These experiments will have an impact beyond the immediate community of atomic, molecular, and optical science. In addition to its broader scientific implications, this work will have a significant educational component. Undergraduates working on these projects will have their first experience in scientific research. In an effort to expand the talent pool for atomic, molecular, and optical physics, women and underrepresented minorities will be especially recruited for these positions. The experiments with chiral molecules and their connection to astrobiological questions make an excellent topic for talks that will be given regularly to high school and civic groups, and that serve to illustrate the beauty of basic physics to a large lay audience.