Assembly and spectroscopic interrogation of large atomic and molecular clusters in helium droplets

在这个由化学部化学结构动力学和机制（CSDM-A）项目资助的项目中，南加州大学的Andrey Vilesov教授询问了接近绝对零度（-460 °F）的化学反应。在如此低的温度下，分子的内部运动大大减慢，使它们更容易研究。 为了在如此低的温度下研究化学反应，原子或分子必须被放置在一个使它们保持低温的环境中，但也允许它们相互作用。由于大多数普通液体在如此低的温度下冻结，溶解在其中的原子和分子被阻止相互碰撞和相互作用。PI通过使用氦滴克服了这些挑战，氦滴在绝对零度下仍然是液体，作为他研究中的试管。在他以前的研究中，Vilesov教授做了一个额外的有趣观察，即氦液滴中存在的微小漩涡（类似于漩涡池）有助于形成只有几个原子的线状粒子。利用激光和低温技术系统地研究了由不同材料制成的这种颗粒的性质和稳定性。本项目主要研究0.4K超低温下原子和分子的聚集机理。直径可达1微米的自由超流氦液滴掺杂有原子或分子，然后在液滴内形成团簇。通过激光光谱、透射电子显微镜和X射线散射技术对团簇的结构、稳定性和能级进行了研究。超流液滴中存在的量子涡旋吸引嵌入的粒子作为低温聚集的模板。由此产生的纳米薄，轨道形状的集群的属性是该项目的重点。此外，该提案还包括开发一种实验技术，利用红外光谱法探索低温离子分子反应，并监测小碳阳离子和质子化水分子团簇的溶剂化效应。这项工作的更广泛影响包括探索制造有用纳米材料的非常规途径的潜在社会效益。该项目通过开发尖端物理实验和编写随后的出版物，为STEM领域的本科生和研究生提供培训机会。

In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Andrey Vilesov of The University of Southern California, interrogates chemical reactions at temperatures close to absolute zero (-460 °F). At such low temperatures, the internal motions of molecules are greatly slowed, making them easier to study. In order to study chemical reactions at such low temperatures, the atoms or molecules must be placed in an environment that keeps them cold, but also allows them to interact with each other. Since most common liquids freeze at such low temperatures, the atoms and molecules dissolved in them are prevented from colliding and interacting with each other. The PI overcomes these challenges by using helium droplets, which are still liquid at absolute zero, as test tubes in his studies. In his previous studies, Professor Vilesov made an additional interesting observation, namely that tiny vortices (similar to whirlpools) present in the helium droplets help form wire-shaped particles just a few atoms across. The properties and stability of such particles made of different materials are systematically studied with state of the art laser and cryogenic techniques. This project focuses on the mechanisms of aggregation of atoms and molecules at an ultra low temperature of 0.4 K. Free superfluid helium droplets up to 1 micrometer in diameter are doped with atoms or molecules, which then form clusters inside the droplet. The structure, stability and energy levels of the clusters are interrogated by laser spectroscopy, transmission electron microscopy and x-ray scattering techniques. Quantum vortices present in the superfluid droplets attract the imbedded particles serving as a template for low temperature aggregation. The properties of the resulting nanometer-thin, track-shaped clusters are in the focus of this project. In addition, this proposal includes the development of an experimental technique for the exploration of low temperature ion-molecule reactions using infrared spectroscopy and monitoring of the solvation effects in small carbocations and protonated water clusters. The broader impacts of this work include potential societal benefits from exploring unconventional paths for making useful nanomaterials. This project provides opportunities for training of undergraduate and graduate students in STEM field by developing of the cutting edge physical experiments and preparation of the ensuing publications.