SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
SUNCAT Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, Stanford, California 95305, USA.
Phys Rev Lett. 2015 Apr 17;114(15):156101. doi: 10.1103/PhysRevLett.114.156101. Epub 2015 Apr 16.
We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5σ and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.
我们表明，共吸附的氧原子对 Ru(0001)上 CO 的脱附动力学有显著影响。与 Ru(0001)上的前体介导脱附机制相反，表面氧的存在改变了 Ru 原子的电子结构，使得 CO 脱附主要通过直接途径发生。这一现象在使用软 X 射线自由电子激光的超快泵浦-探测实验中直接观察到，该实验用于监测表面物种价电子结构的动态演化。这得到了从密度泛函理论计算中获得的 CO 脱附路径上的平均力势的支持。电荷密度分布和冻结轨道分析表明，氧诱导的 Pauli 排斥的降低，以及 CO 5σ 和带电 Ru 原子之间的配位相互作用的相应增加，是独特脱附动力学的电子起源。CO 从 Ru(0001)和共吸附氧的 Ru(0001)上脱附的从头算分子动力学模拟提供了对表面键断裂过程的进一步了解。
