Chemistry at molecular junctions: Rotation and dissociation of O2 on the Ag(110) surface induced by a scanning tunneling microscope.
Chemistry at molecular junctions: Rotation and dissociation of O2 on the Ag(110) surface induced by a scanning tunneling microscope.
复制标题
分子连接处的化学：扫描隧道显微镜诱导 Ag(110) 表面上 O2 的旋转和离解。
DOI：
10.1063/1.4818163
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
M. Ratner
中科院分区：
文献类型：
--
作者：
Sharani Roy;V. Mujica;M. Ratner
扫描隧道显微镜(STM)是一种迷人的工具，用于在单分子水平上执行化学过程，包括键形成、键断裂，甚至化学反应。访问数/每百万人：Reach for[J.太棒了。123,214702(2005年)]利用扫描隧道显微镜在精确的偏置电压下控制了单个O2分子在Ag(110)表面化学吸附的旋转和解离。这些阈值电压取决于偏置电压的方向和化学吸附分子的初始取向。他们还观察到了一种有趣的电压方向和取向依赖的路径选择性，这表明分子结处的模式选择化学，这样在一种情况下，分子经历了直接解离，而在另一种情况下，它经历了旋转介导的解离。我们提出了一个详细的，基于第一性原理的理论研究来研究隧道效应引起的氧气动力学机制，包括观察到的阈值电压的来源，与路径的依赖关系，以及氧气的解离速率。结果表明，观察到的一个过程的阈值电压和该过程的激活能之间存在着直接的对应关系。路径选择性源于电压调节的旋转和解离势垒高度与隧穿电子与被吸附分子的转动和振动模式的耦合强度之间的竞争。最后，我们探讨了非弹性电子隧穿的“偶极”和“共振”机制，以阐明隧穿电子与化学吸附O2之间的能量传递。
The scanning tunneling microscope (STM) is a fascinating tool used to perform chemical processes at the single-molecule level, including bond formation, bond breaking, and even chemical reactions. Hahn and Ho [J. Chem. Phys. 123, 214702 (2005)] performed controlled rotations and dissociations of single O2 molecules chemisorbed on the Ag(110) surface at precise bias voltages using STM. These threshold voltages were dependent on the direction of the bias voltage and the initial orientation of the chemisorbed molecule. They also observed an interesting voltage-direction-dependent and orientation-dependent pathway selectivity suggestive of mode-selective chemistry at molecular junctions, such that in one case the molecule underwent direct dissociation, whereas in the other case it underwent rotation-mediated dissociation. We present a detailed, first-principles-based theoretical study to investigate the mechanism of the tunneling-induced O2 dynamics, including the origin of the observed threshold voltages, the pathway dependence, and the rate of O2 dissociation. Results show a direct correspondence between the observed threshold voltage for a process and the activation energy for that process. The pathway selectivity arises from a competition between the voltage-modified barrier heights for rotation and dissociation, and the coupling strength of the tunneling electrons to the rotational and vibrational modes of the adsorbed molecule. Finally, we explore the "dipole" and "resonance" mechanisms of inelastic electron tunneling to elucidate the energy transfer between the tunneling electrons and chemisorbed O2.