Electric and magnetic deflection of fully field-oriented molecules within superfluid nanodroplets: A probe of simple and complex cold polar molecules

在这项由化学系化学结构、动力学和机制(CSDM-A)计划资助的项目中，南加州大学的Vitaly Kresh教授的团队正在使用极冷的纳米级超流氦液滴作为工具来探测单个分子的电磁性质。“超流体”是一种可以在没有液体内耗或粘度的情况下流动的流体。超流氦的低温(高于绝对零度零下几度，为-273.15摄氏度)和无粘性条件使其有可能利用液滴外部的电场或磁场来控制液滴内部分子的取向。这反过来又使得测量这些分子的基本性质(例如，分子的电极和磁极)成为可能。这也使得理解分子如何聚集成簇成为可能。该研究小组正在考虑研究各种重要的分子及其凝聚体，包括生物物种和“分子磁铁”。该项目的更广泛的科学影响源于这样一个事实，即生物分子-磁体系统的电磁特性与从蛋白质合成到量子计算等领域相关。研究生、本科生和博士后研究人员在一个高度跨学科的研究领域接受指导，并参与外展计划和科学博览会。本科生在南加州大学一年一度的本科生学术和创造性工作研讨会上展示他们的工作，从而获得了发表科学报告的经验。克瑞斯特教授还参与了全国物理学会学生的“领养物理学家”计划，该计划将高中班级与专业科学家联系起来，就职业、科学、学校、工作和生活平衡问题进行对话和提问。氦纳米液滴是由冷氦气体的超音速膨胀产生的。这些液滴通过拾取单元获得客体分子，然后穿过一个强烈的不均匀电场或磁场，这既定向了极性杂质，又施加了强烈的偏转力。这种力是通过绘制光束轮廓来测量的--以这种方式产生单个超冷分子或分子复合体的偶极矩大小的实验读数。这项技术被应用于氨基酸和小肽、水合酸络合物、分子磁体，以及其反应路径可以通过外场定制预先排列的分子组件。冷极性分子相互作用、组装和反应的研究和控制因其与量子计算、新型凝聚相、分子干涉计量学和基本对称性研究的相关性而引起跨学科的极大兴趣。

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program of the Division of Chemistry, Professor Vitaly Kresin's group from the University of Southern California is using a jet of extremely cold nanoscale droplets of superfluid helium as a tool to probe the electric magnetic properties of individual molecules. A "superfluid" is a fluid that can flow without the internal friction or viscosity of liquids. The cold temperature (a fraction of a degree above absolute zero, which is -273.15 degrees Celsius) and viscosity free condition of superfluid helium makes it possible to use electric or magnetic fields outside the droplet to control the orientation of molecules inside the helium droplet. This in turn makes it possible to measure fundamental properties of these molecules (for example the electric and magnetic "poles" of the molecules). It also makes it possible to understand how molecules aggregate into clusters. The research group is considering the study of a variety of important molecules and their agglomerates, including biological species and "molecular magnets." The broader scientific impacts of the project stem from the fact that electric and magnetic characteristics of biological, molecular-magnet systems are relevant to fields ranging from protein synthesis to quantum computing. Graduate and undergraduate students and postdoctoral researchers are mentored in a highly interdisciplinary area of research and are involved in outreach programs and in science fairs. Undergraduate students gain experience in giving scientific presentations, as they present their work at USC's annual Undergraduate Symposium for Scholarly and Creative Work. Professor Kresin is also involved in the national Society of Physics Students' "Adopt-a-Physicist" program which connects high school classes with professional scientists for conversations and questions about careers, science, school, work, and life balance.Helium nanodroplets are produced by the supersonic expansion of cold helium gas. These droplets pick up guest molecules by passing through pick-up cells and then traverse a strong inhomogeneous electric or magnetic field which both orients the polar impurity and exerts an intense deflecting force. This force is measured by mapping out the beam profile - in this way yielding an experimental readout of the magnitude of the dipole moment of a single ultracold molecule or molecular complex. This technique is applied to amino acids and small peptides, to hydrated acid complexes, to molecular magnets, and to molecular assemblies whose reaction pathways can be custom pre-aligned by the external field. The study and control of cold polar molecule interactions, assemblies, and reactions is attracting considerable interdisciplinary interest in view of their relevance to quantum computing, novel condensate phases, molecular interferometry, and investigations of fundamental symmetries.