Electronic and optical properties of polyanionic metal clusters

有限系统的物理和化学性质通常以简单的方式与颗粒大小成比例，并表现出特征趋势。相比之下，当改变原子的数量时，非常小的簇显示出明显的量子大小效应。最近在数字射频陷阱中产生大量选择的聚阴离子金属团簇的实验方法，为研究尚未接近的潜在表面上的（金属）纳米系统提供了机会。一个令人兴奋的方面是形成一个排斥性库仑势作为一个特征，其中一个势垒是由电荷排斥力和电子-电子相关性之间的相互作用形成的。高于真空水平的结合能允许电子穿过势垒使复合物松弛。与分子和富勒烯相比，具有离域电子的多阴离子体系的光致动力学迄今尚未得到实验和理论的详细研究。除了库仑势垒的电子结构和可能的各向异性外，该项目还重点研究了聚阴离子金属团簇的光学活性，重点是集体激发。目前，纳米粒子中等离子体模式的衰减和单电子能级的耦合仍在讨论中。我们将使用可调谐激光脉冲进行实验，以及泵浦探针技术，以研究聚阴离子金属团簇的物理性质，使用角分辨光谱作为现有电子飞行时间诊断的延伸。我们的目的是表征电子能级结构，光学响应和超快动力学。隧穿和内部弛豫是光发射过程中必须考虑的相关衰变途径。在实验中，我们将重点放在铜、银和金簇上，因为它们的等电子结构代表了模型系统。由于其等离子体特性，贵金属团簇在技术应用方面也很有趣。

The physical and chemical properties of finite systems often scale in a simple way with the particle size and show characteristic trends. In contrast, very small clusters show distinct quantum-size effects when changing the number of atoms. Recently developed experimental methods for generating mass-selected, polyanionic metal clusters in digital radio frequency traps have opened up opportunities to study (metallic) nanosystems on not yet accessible potential surfaces. An exciting aspect is the formation of a repulsive Coulomb potential as a characteristic feature, whereby a barrier is formed by the interplay between charge repulsion and electron-electron correlations. Binding energies above the vacuum level allows for a relaxation of the complex by electron tunneling through the barrier. In contrast to molecules and fullerenes, the photo-induced dynamics of polyanionic systems with delocalized electrons has not been studied in detail by experiment and theory so far. In addition to the electronic structure and possible anisotropies of the Coulomb barrier, the project focuses on the optical activity of polyanionic metal clusters with emphasis on thecollective excitations. Currently, the decay of the plasmon mode and the coupling to single-electron levels in nanoparticles is still under discussion. We will conduct experiments using tunable laser pulses, as well as the pump-probe technique in order to study the physical properties of polyanionic metal clusters, using angular-resolved spectroscopy as an extension of the already existing electrontime-of-flight diagnostics. We aim to characterize the electronic level structure, the optical response and the ultrafast dynamics. Tunneling and internal relaxation are relevant decay pathways, which have to be considered in the photoemission process. In the experiments we concentrate on copper, silver and gold clusters as they represent model systems due to their isoelectronic structure. Due to their plasmonic properties, the noble metal clusters are also interesting for technical applications.