Exploring the weakest bond: Structure and ionization of the Helium Dimer, Trimer and the search for the Efimov State

只有两个氦原子(二聚体，He2)和三个原子(三聚体，HE3)组成的分子是极其脆弱、松软和弥漫的量子对象。氦二聚体是迄今为止观察到的最长、最弱的键。它的传播范围超过原子直径的100倍。对于三聚体，预测了一种激发晕态，即所谓的Efimov态，但尚未在实验中发现。二聚体和三聚体迷人的量子本质导致了大量经常存在争议的理论工作。在实验上，到目前为止，只能确定二聚体和基态三聚体的存在以及核间距的平均值。目前的项目提出了一种研究这些天体的全新方法：我们将用同步辐射、短激光脉冲和自由电子激光对它们进行电离，以探索它们的电离动力学，通过库仑爆炸成像来成像它们的结构，并寻找难以捉摸的Efimov态。通过将二聚体和三聚体放入COLTRIMS反应显微镜中，这些独特的研究将成为可能，COLTRIMS反应显微镜是一种多粒子成像系统，申请人对此做出了重大贡献。我们将获得基态的几何结构和核间距离的直接图像，使我们能够解决理论上的争议，并为寻找Efimov态提供最敏感和最无背景的信号。

Molecules made of only two Helium atoms (Dimers, He2) and three atoms (Trimers, He3) are extremely fragile, floppy and diffuse quantum objects. The Helium dimer has the by far longest and weakest bond ever observed. It spreads over 100 times the atomic diameter. For the trimer an excited halo state, a so called Efimov state, is predicted but not yet found experimentally. The fascinating quantum nature of the dimer and trimer resulted in a large body of often controversial theoretical work. Experimentally so far only the existence of the dimer and ground state trimer and the mean value of the internuclear distance could be established. The current project suggests a completely new approach to study these objects: we will ionize them with synchrotron radiation, short laser pulses and free electron laser beams to explore their ionization dynamics, image their structure via Coulomb explosion imaging and search for the elusive Efimov state. These unique studies will become possible by putting the dimer and trimer in a COLTRIMS reaction microscope, a multiparticle imaging system, to which the applicant has made major contributions. We will obtain a direct image of the geometrical structure and internuclear distances of the ground state, allowing us to settle the theoretical controversies and providing the most sensitive and background free signal for a search for the Efimov state.