The Assembly and Spectroscopic Interrogation of Hydrogen Clusters in Helium Droplets

南加州大学的Andrey Vilesov得到了实验物理化学项目的支持，继续他对纯和掺杂氦和氢量子团簇的实验研究。实验方法包括氦液滴分子和分子团簇的红外脉冲激光耗尽光谱和纯氢团簇的CARS光谱。这项研究的最终目标是揭示超流体的性质是如何在将一个系统的尺寸从体积减小到小液滴的过程中演变的，小液滴可能包含几千到几十个氦原子或氢分子。光谱学研究将解决一个问题，即分子附近液氦的超流体和非超流体部分的宏观概念在分子及其氦溶剂化壳的量子力学相互作用方面意味着什么。此外，关于氦和氢团簇的结构和量子态及其与分子的相互作用的新知识有可能对分子光谱学做出有价值的贡献，目前对流态团簇来说是一个相当大的挑战。超流体能够无摩擦地无限流动。由于氢团簇是由分子组成的，所以可以检测其超流动性，而不需要像检测原子流体氦滴那样用其他分子掺杂。该项目旨在解决一些长期存在且有趣的问题，例如学习检测微观液滴中的超流动性，发现簇表现出超流体行为意味着什么，以及确定流体需要多少原子/分子才能成为超流体。

Andrey Vilesov of the University of Southern California is supported by the Experimental Physical Chemistry Program to continue his experimental studies of neat and doped helium and hydrogen quantum clusters. Experimental methods involve infrared pulsed laser depletion spectroscopy of molecules and molecular clusters in helium droplets, and CARS spectroscopy of neat hydrogen clusters. The ultimate goal of this research is to uncover how the properties of a superfluid evolve upon reducing the dimension of a system from bulk to small droplets, which may contain from several thousand to a few tens of helium atoms or hydrogen molecules. Spectroscopic studies will address the question of what the macroscopic concept of superfluid and non-superfluid fractions of liquid helium in the vicinity of a molecule means in terms of the quantum mechanical interaction of the molecule and its helium solvation shell. As well, new knowledge of the structure and quantum states of helium and hydrogen clusters and their interaction with molecules have the potential to make a valuable contribution to molecular spectroscopy, for which fluxional clusters present a considerable challenge at present.Superfluids are able to flow endlessly without friction. Hydrogen clusters, because they are made up of molecules, can be examined for superfluidity without the need for doping by other molecules as is required for atomic fluid helium droplets. This project aims to address a number of long-standing and intriguing issues, such as learning to detect superfluidity in microscopic droplets, discovering what it means for a cluster to exhibit superfluid behavior, and determining how many atoms/molecules are needed for a fluid to become superfluid.