Ultrafast reaction dynamics of the associative hydrogen desorption from Ru(001)
Ultrafast reaction dynamics of the associative hydrogen desorption from Ru(001)
复制标题
Ru(001)缔合氢解吸的超快反应动力学
DOI：
10.1088/0953-8984/20/31/313002
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
C. Frischkorn
中科院分区：
文献类型：
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作者：
C. Frischkorn
为了从微观上理解表面的化学反应，必须获得有关基本过程的详细知识。反应机理、能量流的路径和时间尺度以及反应产物不同自由度之间的能量分配是关键的兴趣。吸附在金属表面上的物质的反应通常通过基底的电子和/或声子激发来介导。由于这些激发之间的热平衡发生在飞秒到皮秒的时间尺度上，超短激光脉冲引发的化学反应提供了研究超出平衡条件的过程的基础。两个氢原子的重组形成一个H2分子，离开表面，代表了人们可以想到的最基本的表面反应之一，因此可以作为飞秒激光诱导表面化学的原型系统。特别地，已经非常详细地研究了Ru（001）表面的Hads+Hads H2气体缔合解吸。小于200 fs的超快能量转移时间以及H2和D2之间的明显同位素效应明确地表明了热衬底电子驱动的反应机制。外部（平移）和内部（振动，旋转）的产品分子的自由度之间的能量分配的测量揭示主要是解吸附氢的平移激发。理论建模的基础上的多维摩擦描述的钌基板和氢层之间的能量转移很好地再现了实验结果。此外，特殊的特性，如阈值样的覆盖度的依赖性的解吸率和促进作用的同位素取代的吸附层已被观察到的实验中，这表明强吸附质-吸附质相互作用的重要性，在H2/D2协会，但仍在等待一个定量的理论处理。
For a microscopic understanding of chemical reactions at surfaces, it is essential to obtain detailed knowledge on the underlying elementary processes. The reaction mechanism, the pathways and timescales of energy flow and the energy partitioning between different degrees of freedom of the reaction products are of key interest. Reactions of species adsorbed on a metal surface are generally mediated through electron and/or phonon excitations of the substrate. Since thermal equilibration between these excitations occurs on a femto- to picosecond timescale, chemical reactions initiated by ultrashort laser pulses provide the base to investigate processes beyond equilibrium conditions. The recombination of two hydrogen atoms forming an H2 molecule, which leaves the surface, represents one of the most basic surface reactions one could think of and thus may serve as a prototype system for femtosecond laser-induced surface chemistry. In particular, the Hads+Hads H2,gas associative desorption from a Ru(001) surface has been studied in great detail. Ultrafast energy transfer times of less than 200 fs in conjunction with a pronounced isotope effect between H2 and D2 unambiguously indicate a hot-substrate electron-driven reaction mechanism. Measurements of the energy partitioning between external (translational) and internal (vibrational, rotational) degrees of freedom of the product molecule reveal predominantly translational excitation of the desorbing hydrogen. Theoretical modelling based on a multidimensional frictional description of energy transfer between the ruthenium substrate and the hydrogen layer excellently reproduces the experimental findings. Furthermore, peculiar characteristics like a threshold-like coverage dependence of the desorption yield and promotion effects in isotopically substituted adlayers have been observed in the experiment which demonstrate the importance of strong adsorbate–adsorbate interactions in the H2/D2 association, yet still awaiting a quantitative theoretical treatment.