Since the advent of third generation synchrotron light sources optimized for providing soft X-rays up to 2 keV, X-ray photoelectron spectroscopy (XPS) has been developed to be an outstanding tool to study surface properties and surface reactions at an unprecedented level. The high resolution allows identifying various surface species, and for small molecules even the vibrational fine structure can be resolved in the XP spectra. The high photon flux reduces the required measuring time per spectrum to the domain of a few seconds or even less, which enables to follow surface processes in situ. Moreover, it also provides access to very small coverages down to below 0.1% of a monolayer, enabling the investigation of minority species or processes at defect sites. The photon energy can be adjusted according to the requirement of a particular experiment, i.e., to maximize or minimize the surface sensitivity or the photoionization cross-section of the substrate or the adsorbate. For a few instruments worldwide, a next step forward was taken by combining in situ high-resolution spectrometers with supersonic molecular beams. These beams allow to control and vary the kinetic and internal energies of the incident molecules and provide a local pressure of up to ~10⁻⁵ mbar, which can be switched on and off in a controllable way, thus offering a well-defined time structure to study adsorption or reaction processes.

Herein, we will review some specific scientific aspects which can be addressed by in situ XPS in order to demonstrate the power and potential of the method: In particular, the following topics will be addressed: (1) The sensitivity of the binding energy to adsorption sites will be analyzed, using CO on metals as example. From measurements at different temperatures, the binding energy difference between different sites can be derived, and exchange processes between different adsorbate species at step edges can be followed. (2) The vibrational fine structure of adsorbed small hydrocarbon species on metal surfaces will be analyzed in detail. We will first introduce the linear coupling model, then discuss the properties of adsorbed methyl and of a number of other small hydrocarbons, and show that the vibrational signature can be used as fingerprint for identifying surface species. (3) It is demonstrated that the binding energy of equivalent atoms in a molecule can be differentially changed by adsorption to a substrate; this sensitivity to the local environment will be discussed for adsorbed ethylene, benzene and graphene. (4) By temperature programmed XPS, the thermal evolution of adsorbed species can be followed in great detail, allowing for the identification of reaction intermediates and the determination of their stabilities. (5) The investigation of reaction kinetics by isothermal XPS measurements will be discussed; here results for the oxidation of sulfur and of CO will be presented and the corresponding activation energies of the rate limiting steps will be determined.

自第三代同步加速器光源问世以来，它已被优化以提供高达2 keV的软X射线，因此X射线光电子能谱（XPS）已发展成为研究表面性质和表面反应的前所未有的出色工具。高分辨率可以识别各种表面物质，对于小分子，甚至可以在XP光谱中解析出振动的精细结构。高光子通量可将每个光谱所需的测量时间减少到几秒或更短的范围，从而可以就地跟踪表面过程。此外，它还可以访问非常小的覆盖层，覆盖率低至单层的0.1％以下，从而可以调查缺陷部位的少数物种或过程。可以根据特定实验的要求调整光子能量，即，最大化或最小化基底或被吸附物的表面敏感性或光电离截面。对于世界范围内的一些仪器，将原位高分辨率光谱仪与超音速分子束结合起来，迈出了下一步。这些光束可以控制和改变入射分子的动能和内能，并提供高达〜10的局部压力⁻⁵  mbar，可以以可控制的方式打开和关闭，因此提供了明确的时间结构来研究吸附或反应过程。

在这里，我们将回顾一些可以通过原位XPS解决的特定科学方面，以证明该方法的功能和潜力：特别是，将解决以下主题：（1）结合能对吸附的敏感性以金属上的一氧化碳为例，对这些位点进行分析。通过在不同温度下的测量，可以得出不同位点之间的结合能差，并且可以遵循台阶边缘处不同吸附物之间的交换过程。（2）将详细分析金属表面吸附的小烃类的振动精细结构。我们将首先介绍线性耦合模型，然后讨论吸附的甲基和许多其他小烃的性质，并表明振动信号可以用作识别表面物种的指纹。（3）证明了分子中等效原子的结合能可以通过吸附到基质上而有区别地改变。对于吸附的乙烯，苯和石墨烯，将讨论对当地环境的敏感性。（4）通过程序升温XPS，可以非常详细地跟踪被吸附物质的热演化，从而可以识别反应中间体并确定其稳定性。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。（3）证明了分子中等效原子的结合能可以通过吸附到基质上而有区别地改变。对于吸附的乙烯，苯和石墨烯，将讨论对当地环境的敏感性。（4）通过程序升温XPS，可以非常详细地跟踪被吸附物质的热演化，从而可以识别反应中间体并确定其稳定性。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。（3）证明了分子中等效原子的结合能可以通过吸附到基质上而有区别地改变。对于吸附的乙烯，苯和石墨烯，将讨论对当地环境的敏感性。（4）通过程序升温XPS，可以非常详细地跟踪被吸附物质的热演化，从而可以识别反应中间体并确定其稳定性。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。对于吸附的乙烯，苯和石墨烯，将讨论对当地环境的敏感性。（4）通过程序升温XPS，可以非常详细地跟踪被吸附物质的热演化，从而可以识别反应中间体并确定其稳定性。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。对于吸附的乙烯，苯和石墨烯，将讨论对当地环境的敏感性。（4）通过程序升温XPS，可以非常详细地跟踪被吸附物质的热演化，从而可以识别反应中间体并确定其稳定性。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。（5）将讨论通过等温XPS测量研究反应动力学；在此将给出硫和CO氧化的结果，并确定限速步骤的相应活化能。