Abstract We review several representative experimental results of action spectroscopy (AS) of single molecules on metal surfaces using a scanning tunneling microscope (STM) by M. Kawai’s group over last decade. The experimental procedures to observe STM-AS are described. A brief description of a low-temperature STM and experimental setup are followed by key experimental techniques of how to determine an onset bias voltage of a reaction and how to measure a current change associated with reactions and finally how to observe AS for single molecule reactions. The experimental results are presented for vibrationally mediated chemical transformation of trans-2-butene to 1.3-butadiene molecule and rotational motion of a single cis-2-butene molecule among four equivalent orientations on Pd(1 1 0). The AS obtained from the motion clearly detects more vibrational modes than inelastic electron tunneling spectroscopy with an STM. AS is demonstrated as a useful and novel single molecule vibrational spectroscopy. The AS for a lateral hopping of water dimer on Pt(1 1 1) is presented as an example of novelty. Several distinct vibrational modes are detected as the thresholds in the AS. The assignment of the vibrational modes determined from the analysis of the AS is made from a view of the adsorption geometry of hydrogen-bond donor or acceptor molecules in water dimer. A generic theory of STM-AS, i.e., a reaction rate or yield as a function of bias voltage, is presented using a single adsorbate resonance model for single molecule reactions induced by the inelastic tunneling current. Formulas for the reaction rate R ( V ) and Y ( V ) , i.e., reaction yield per electron Y ( V ) = eR ( V ) / I are derived. It provides a versatile framework to analyze any vibrationally mediated reactions of single adsorbates on metal surfaces. Numerical examples are presented to demonstrate generic features of the vibrational generation rate and Y ( V ) at different levels of approximations and to show how the effective broadening of the vibrational density of states (as described by Gaussian or Lorentzian functions) manifest themselves in Y ( V ) near the threshold bias voltage corresponding to a vibrational excitation responsible for reactions. A prefactor of Y ( V ) is explicitly derived for various types of elementary processes. Our generic formula of Y ( V ) also underlines the need to observe Y ( V ) at both bias voltage polarities, which can provide additional insight into the adsorbate projected density of states near the Fermi level within a span of the vibrational energy. The theory is applied to analysis of some highlights of the experimental results: Xe transfer, hopping of a single CO molecule on Pd(1 1 0), a dissociation of a single dimethyl disulfide (CH3S)2 and a hopping of a dissociated product, i.e., single methyl thiolate CH3S on Cu(1 1 1). It underlines that an observation of Y ( V ) at both bias polarities permits us to certain insight into the molecular alignment with respect to the Fermi level.

中文翻译：

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单分子反应的作用光谱——实验和理论

摘要 我们回顾了 M. Kawai 小组在过去十年中使用扫描隧道显微镜 (STM) 对金属表面单分子的作用光谱 (AS) 的几个代表性实验结果。描述了观察 STM-AS 的实验程序。低温 STM 和实验装置的简要描述之后是如何确定反应的起始偏置电压和如何测量与反应相关的电流变化以及最后如何观察单分子反应的 AS 的关键实验技术。实验结果展示了振动介导的反式 2-丁烯向 1.3-丁二烯分子的化学转化和单个顺式 2-丁烯分子在 Pd(1 1 0) 上四个等效取向之间的旋转运动。从运动中获得的 AS 比使用 STM 的非弹性电子隧道光谱清楚地检测到更多的振动模式。AS被证明是一种有用且新颖的单分子振动光谱。用于在 Pt(1 1 1) 上横向跳跃水二聚体的 AS 作为新颖性示例提出。检测到几种不同的振动模式作为 AS 中的阈值。从 AS 分析确定的振动模式的分配是从氢键供体或受体分子在水二聚体中的吸附几何学的角度进行的。STM-AS 的一般理论，即作为偏置电压函数的反应速率或产率，使用用于由非弹性隧道电流引起的单分子反应的单个吸附质共振模型来呈现。反应速率 R ( V ) 和 Y ( V ) 的公式，即，推导出每个电子的反应产率 Y ( V ) = eR ( V ) / I。它提供了一个通用框架来分析金属表面上单个吸附物的任何振动介导的反应。数值例子展示了振动发生率和 Y ( V ) 在不同近似水平下的一般特征，并展示了状态振动密度的有效展宽（如高斯或洛伦兹函数所描述的）在 Y ( V ) 接近阈值偏置电压，对应于负责反应的振动激发。Y ( V ) 的前因数是为各种类型的基本过程明确导出的。我们的 Y ( V ) 通用公式也强调需要在两个偏置电压极性下观察 Y ( V )，这可以提供对振动能量跨度内接近费米能级的吸附质投影态密度的进一步了解。该理论用于分析实验结果的一些亮点：Xe 转移、单个 CO 分子在 Pd(1 1 0) 上的跳跃、单个二甲基二硫 (CH3S)2 的解离和解离产物的跳跃，即，Cu(1 1 1) 上的单甲基硫醇盐 CH3S。它强调了在两个偏置极性下对 Y ( V ) 的观察允许我们对费米能级的分子排列有一定的了解。单个二甲基二硫醚 (CH3S)2 的解离和一个解离产物的跳跃，即单个硫醇甲酯 CH3S 在 Cu(1 1 1) 上。它强调了在两个偏置极性下对 Y ( V ) 的观察允许我们对费米能级的分子排列有一定的了解。单个二甲基二硫醚 (CH3S)2 的解离和一个解离产物的跳跃，即单个硫醇甲酯 CH3S 在 Cu(1 1 1) 上。它强调了在两个偏置极性下对 Y ( V ) 的观察允许我们对费米能级的分子排列有一定的了解。