US-Federal Republic of Germany Cooperative Research: Experimental Studies of Helium Microclusters

该奖项支持罗德岛大学的Jan A. Northby教授与西德哥廷根马克斯普朗克流动研究所的J. Peter Toennies教授在研究方面的合作。他们正在合作研究在低温自由射流膨胀中形成的微观氦团簇的性质。他们的方法包括在美国实验室生产和研究氦簇离子，在德国实验室生产和研究中性氦簇，然后比较结果。他们研究的主要目的是研究宏观现象的演变，特别是随着原子数量的增加而产生的超流动性。他们目前的努力集中在开发生产和表征氦团束的技术上，这些束覆盖了可以预期偏离宏观行为的尺寸范围。德国实验室有两台专门用于氦团实验的分子束机，非常适合拟议的合作研究；然而，他们最近才开始研究冷凝氦。Northby教授对最初以离子形式形成的稀有气团有着丰富的经验，并受益于Toennies博士在分子束工作方面的专业知识。调查人员的互补专业知识和设施创造了一个非常强大的合作安排。原子团簇构成了原子性质和整体性质之间的桥梁。在过去的十年里，人们对各种材料簇中与尺寸相关的性质的研究兴趣急剧增长。从实验方面来看，这是由自由射流膨胀技术的发展所推动的。从理论方面来看，计算机能力的巨大增长推动了增长，现在可以对相当大的有限系统的性质进行详细的从头计算。提出的研究将导致对超流动性和物质从原子到体态转变的基本新认识。这可能会对电影发展和其他领域产生实际的影响。

This award supports Professor Jan A. Northby of the University of Rhode Island for collaboration in research with Professor J. Peter Toennies of the Max Planck Institute for Flow Research in Gottingen, West Germany. They are collaborating in the study of the properties of microscopic helium clusters which are formed in cryogenic free jet expansions. Their approach involves producing and studying helium cluster ions at the U.S. lab and neutral helium clusters at the German lab, then comparing results. The broad objective of their research is to examine the evolution of macroscopic phenomena, in particular of superfluidity, as the number of atoms increases. Their current efforts are concentrated in developing the technology for producing and characterizing helium cluster beams covering the size range where departures from macroscopic behavior can be expected. The German laboratory has two molecular beam machines dedicated to helium cluster experiments and uniquely suited to the proposed collaborative research; however, they have only recently begun working with condensed helium. Professor Northby has had considerable experience with rare gas clusters initially formed as ions and has benefited from Dr. Toennies expertise in molecular beam work. The complementary expertise and facilities of the investigators create a very strong collaborative arrangement. Clusters of atoms form the bridge between atomic properties and the properties of the bulk. Interest in the study of size-dependent properties in clusters of all kinds of materials has grown dramatically in the past decade. From the experimental side, this has been driven by the development of free jet expansion techniques for the production of cluster beams. From the theoretical side, growth has been driven by the tremendous expansion in computer power which now permits detailed ab initio calculations of the properties of quite large finite systems. The proposed research should lead to fundamental new understanding of superfluidity and the transition of matter from the atomic to the bulk state. This could have a practical spin-off for film growth and other areas.