Quantum dynamics of molecules coupled to helium nanodroplets

这个项目的目标是从实验和理论上研究与超冷氦纳米液滴环境耦合的分子的超快动力学。特别是，该项目专注于激光激发的分子和量子流体团簇之间相互作用的细节，诱导分子动力学中依赖液滴的耗散和退相干。因此，不可逆分子动力学可以用来描述和描述纳米尺度上的集体现象(超流、基元激发)。使用飞秒激光结合先进的探测方案(光电子、离子成像)，将探索电子、振动和旋转波包。我们将研究不同的分子体系，它们与氦环境的相互作用强度不同，复杂程度也不同，从碱二聚体、碱土分子、碱卤化物到小的非均相络合物，理论上将利用分子的已知参数和势能面实现与时间相关的分子波包传播。关键的是，将包括由氦滴引起的耗散和退相干，从现象学的方法开始识别相关的不可逆通道。首先，阻尼率和消相干率被认为是与实验结果相一致的合适参数。然后，将针对分子-液滴相互作用的微观建模，以将阻尼和退相干时间尺度和机制与液滴的性质(激发光谱、态密度)联系起来。唯象方法和微观方法都将借助随机薛定谔方程来实现。在微观方法的情况下，我们必须确定浴场关联(“响应”)函数，这些函数是通过依赖于时间的密度泛函计算获得的。最终，氦液滴内部和表面的超流性的直接特征将通过波包动力学来识别。

The goal of this project is to investigate both experimentally and theoretically the ultrafast dynamics of molecules coupled to an environment of ultracold helium nanodroplets. In particular, the project focuses on the details of the interaction between laser-excited molecules and quantum fluid clusters, inducing droplet-dependent dissipation and decoherence of molecular dynamics. Thus, the irreversible molecular dynamics serves as diagnostics for characterizing and describing collective phenomena (superfluidity, elementary excitations) on the nano-scale. Using femtosecond lasers in combination with advanced detection schemes (photoelectron-, ion-imaging), electronic, vibrational and rotational wave packets will be probed. Different molecular systems will be studied that feature different interaction strengths with the helium environment as well as various degrees of complexity, ranging from alkali dimers, alkaline earth molecules, alkali halides, to small heterogeneous complexes.Theoretically, time dependent molecular wave packet propagation will be implemented utilizing known parameters and potential energy surfaces for the molecules. Crucially, dissipation and decoherence induced by the helium droplet will be included, starting from a phenomenological approach to identify the relevant irreversible channels. First, damping and decoherence rates are seen as fit parameters chosen to agree with experimental findings. Then a microscopic modeling of molecule-droplet interaction will be aimed at in order to relate damping and decoherence time scales and mechanisms to properties of the droplets (spectrum of excitations, density of states). Both the phenomenological and microscopic approach will be implemented with the help of stochastic Schr ¨odinger equations. In the case of the microscopic approach we have to determine bath correlation (“response”) functions which are obtained from a time-dependent density functional calculation. Eventually, direct signatures of superfluidity in and on the surface of helium droplets will be identified through wave packet dynamics.