Dynamics of the fragmentation and ionization of free metal clusters by mild femtosesond laser pulses

简单金属团簇具有类自由电子的电子结构，是研究少数到多个粒子动力学的理想模型系统。在这样的系统中，集体电子共振可能有一个巨大的电偶极子；对于具有合适频率的光场，它就像一个天线，产生强烈的局部电场强度放大。另一方面，关闭共振，靠近团簇的外场被显著屏蔽。移动电子云对电磁近场的强烈修正将对发射电子或光碎片的动能和角分布产生决定性的影响。在一项联合的实验和理论研究中，我们将详细研究这些效应。在实验上，测量了飞秒激光激发自由、冷、大小选择的碱金属和贵金属团簇后光电子和光碎片的角分辨动能分布。在理论方面，我们将用含时密度泛函理论(TD-DFT)和含时紧束缚理论(TDTB)结合分子动力学计算来模拟这些非线性电离和碎裂过程。特别是，新开发的TDTB-MD将允许在与碎片相关的长时间尺度上进行详细的模拟。

Simple metal clusters with their free-electron-like electronic structure are ideal model systems to study few to many particle dynamcis. The collective electron resonance possible in such systems has a huge electric dipole; for light fields with the right frequency it acts as an antenna producing a strong local amplification of the electric field strength. Off resonance, on the other hand, close to the cluster external fields are significantly screened. This strong modification of the electromagnetic near field by the mobile electron cloud will have a decisive influence on the kinetic energy and angular distribution of emitted electrons or photofragments. In a joint experimental and theoretical study these effects will be examined in detail. Experimentally, the angular resolved kinetic energy distributions of photoelectrons and photofragments after femtosecond laser excitation of free, cold, size selected alkali and noble metal clusters will be measured. On the theory side, time-dependent density functional theory (TD-DFT) and time-dependent tight-binding (TDTB) combined with molecular dynamics calculations will be used to model these nonlinear ionization and fragmentation processes. Especially the newly developed TDTB-MD will allow detailed simulations on the long time scales relevant for fragmentation.