Terasaki Akira
Cluster Research Laboratory, Toyota Technological Institute, in East Tokyo Laboratory, Genesis Research Institute, Inc., 717-86 Futamata, Ichikawa, Chiba 272-0001, Japan.
J Phys Chem A. 2007 Aug 16;111(32):7671-89. doi: 10.1021/jp0700377. Epub 2007 May 25.
Clusters of atoms/molecules show dynamics characteristic of the method of excitation. Two contrasted processes are discussed: (1) electronic excitation via single-photon absorption and (2) impulsive excitation of nuclear motions by surface impact. Process 1 is exemplified by photodissociation dynamics of size-selected metal cluster ions. The electronic energy is converted most likely to vibrational energy of internal modes; dissociation follows via statistical mechanism to produce energetically favored fragments. Exceptionally, a silver cluster ion, Ag4(+), is shown to undergo nonstatistical dissociation along the potential-energy surface of the excited state. Energy partitioning to translational and vibrational modes of fragments is analyzed as well as bond dissociation energies. Furthermore, the spectrum of the photodissociation yield provides electronic and geometrical structures of a cluster with the aid of ab initio calculations; manganese, Mn(N)(+), and chromium, Cr(N)(+), cluster ions are discussed, where the importance of magnetic interactions is manifested. On the other hand, momentum transfer upon surface impact plays a role in process 2. An impulsive mechanical force triggers extraordinary chemical processes distinct from those initiated by atomic collision as well as photoexcitation. Experiments on aluminum, Al(N)(-), silicon, SiN(-), and solvated, I(2)(-)(CO2)(N), cluster anions provide evidence for reactions proceeding under extremely high temperatures, such as pickup of surface atoms, annealing of products, and mechanical splitting of chemical bonds. In addition, a model experiment to visualize and time-resolve the cluster impact process is performed by using a micrometer-sized liquid droplet. Multiphoton absorption initiates superheating of the droplet surface followed by a shock wave and disintegration into a number of small fragments (shattering). These studies further reveal how the nature of chemical bonds influences the dynamics of clusters.
原子/分子簇表现出激发方法的动力学特征。讨论了两个形成对比的过程：（1）通过单光子吸收进行的电子激发和（2）表面撞击对核运动的脉冲激发。过程1以尺寸选择的金属簇离子的光解离动力学为例。电子能量最有可能转化为内部模式的振动能量；随后通过统计机制发生解离，以产生能量上有利的碎片。特别地，银簇离子Ag4(+)被证明沿着激发态的势能面进行非统计解离。分析了碎片的平动和振动模式的能量分配以及键解离能。此外，光解离产率的光谱借助于从头算计算提供了簇的电子和几何结构；讨论了锰Mn(N)(+)和铬Cr(N)(+)簇离子，其中磁相互作用的重要性得以体现。另一方面，表面撞击时的动量传递在过程2中起作用。脉冲机械力引发了与原子碰撞以及光激发引发的过程不同的非凡化学过程。对铝Al(N)(-)、硅SiN(-)以及溶剂化的I(2)(-)(CO2)(N)簇阴离子的实验提供了在极高温度下进行的反应的证据，例如表面原子的拾取、产物的退火以及化学键的机械断裂。此外，通过使用微米级液滴进行了一个可视化并对簇撞击过程进行时间分辨的模型实验。多光子吸收引发液滴表面的过热，随后产生冲击波并分解成许多小碎片（破碎）。这些研究进一步揭示了化学键的性质如何影响簇的动力学。
