The Assembly and Spectroscopic Interrogation of Hydrogen Clusters in Helium Droplets

南加州大学的安德烈·维列索夫受到实验物理化学计划的支持，继续他对纯净和掺杂的氦和氢量子团簇的实验研究。实验方法包括氦液滴中分子和分子团簇的红外脉冲激光耗尽光谱，以及整齐氢团簇的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系统的维度从块状减少到小液滴的情况下演变的，液滴可能包含从数千到几十个氦原子或氢分子。光谱研究将解决的问题是，根据分子及其氦溶剂化壳层的量子力学相互作用，分子附近的液氦的超流和非超流部分的宏观概念意味着什么。此外，关于氦和氢团簇的结构和量子态以及它们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，目前流体团簇对分子光谱构成了相当大的挑战。超流体能够在没有摩擦的情况下无休止地流动。由于氢团簇是由分子组成的，因此可以检查其超流性，而不需要像原子流体氦液滴那样进行其他分子的掺杂。该项目旨在解决一些长期存在且耐人寻味的问题，例如学习检测微观液滴中的超流性，发现一个星团表现出超流体行为意味着什么，以及确定一个流体需要多少原子/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.