Stereodynamics of Chemical Reactions on Solid Surfaces Induced by Molecules and Radicals

表面科学的最终目标之一是能够设计出具有特殊催化活性的表面。这就需要在原子水平上理解表面成键和断键的基本原理(基本过程)。进入表面的分子的取向有望在这些基本过程中发挥重要作用。为了研究入射分子在表面化学反应中的初始取向效应，我们一直在研制一台与超高真空兼容的定向分子束线装置。本研究项目的目的是通过控制入射分子的分子取向来详细地探索表面化学反应，特别是在硅表面上的化学反应。我们报道了CH_3CL在Si(100)表面解离吸附中空间效应的入射能量和表面温度依赖性的研究结果。用King-Wells方法测量了CH_3Cl在Si(100)面上的初始粘着几率。数据表明，当入射能量为120 meV时，氯端碰撞的初始粘着几率比甲烷端碰撞的初始粘着几率大。此外，这种空间择优对CH_3Cl的动能、旋转态和表面温度非常敏感。研究表明，非平衡表面陷阱在CH_3CL在Si(100)上分解的初始阶段起着关键作用。我们还介绍了使用另一种新的装置进行的实验，该装置配备了定向分子束线和反应室，用于X射线光电子能谱。在定向NO分子与Si(111)的反应中，我们发现N端碰撞比O端碰撞更有利于解离吸附。此外，我们还用氧分子束解释了铜表面的氧化物形成过程。

One of the ultimate goals of surface science is to be able to design surfaces with particular catalytic reactivity. This entails a need for an atomic-level understanding of the fundamental principles (elementary processes) underlying the bond-making and bond-breaking at surfaces. The orientation of a molecule incoming on the surface is expected to play an important role in such elementary processes. We have been developing a new machine of ultra-high-vacuum (UHV) compatible oriented-molecular beam line, in order to investigate for initial orientation-effect of an incoming molecule in the surface chemical reactions. The purpose of the present research project is to probe the surface-chemical reaction, especially on Si surfaces, in detail by controlling the molecular orientation of impinging molecules. We report results of a study on the incident-energy and the surface-temperature dependence of the steric effects in the dissociative adsorption of CH_3Cl on a Si(100) surface. The initial sticking probability of CH_3Cl on Si(100) was measured by the King-Wells method. Data presented show that the initial sticking probability for the Cl-end collision is larger at an incident energy of 120 meV than that in the CH_3-end collision. Furthermore, this steric preference is quite sensitive to the kinetic energy and the rotational state of CH_3Cl and the surface temperature. This study shows that the non-equilibrium surface trapping plays a key role in the initial step of the decomposition of CH_3Cl on Si(100). We also introduce the on-going experiments using another new apparatus equipped with the oriented-molecular beam line and the reaction chamber for X-ray photo-emission spectroscopy. In the reaction of oriented NO molecules with Si(111), we found that a N-end collision is more effective in the dissociative adsorption than O-end collision. In addition, we also elucidate the oxide-formation processes on Cu surfaces with oxygen molecular beam.