Quattrucci Joseph G, Jackson Bret
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Chem Phys. 2005 Feb 15;122(7):074705. doi: 10.1063/1.1851498.
Using quasiclassical methods and a potential energy surface based on total energy calculations, we have found that H atoms react with Cl atoms adsorbed onto a Au(111) surface to produce HCl via Eley-Rideal (ER), hot atom (HA), and Langmuir-Hinschelwood (LH) pathways. We observe two ER mechanisms. At small normal incidence energies reaction results from a more or less direct collision with Cl, leading to a large amount of product vibration (nu=8), and relatively cold rotation and translation. In the second mechanism, more dominant at near-normal incidence and/or large incident energies, the H atom passes near Cl, recoils from the metal, and is pulled into orbit about Cl. This leads to broader product state distributions, and a more even distribution of the 3.0 eV of available energy among the product degrees of freedom, similar to products formed via the HA pathway. Overall, ER processes tend to contribute less than 10% to the reactivity, and most of the HCl is formed via HA processes. There is an increase in HCl formation with surface temperature for both the ER and HA mechanisms, but this increase is relatively weak. We observe typically about 12% H atom sticking, which would lead to HCl formation via a LH process in the experiments, above 140 K. We observe a weak forward scattering due to the direct ER component, as in the experiments. However, unlike the experiments, we observe a dip in our product angular distributions about thetaf=0 degrees, which we ascribe to our quasiclassical approximation. While we tend to see more energy in the hot products than in the experiments, our product translational, rotational, and vibrational distributions are in relatively reasonable agreement with those measured. One major disagreement with experiment is that there is apparently a significant sticking of the H atom at low temperatures, leading to a large LH component. In addition, the ER and HA components increase much more strongly with temperature than in the calculations. It is possible that electon-hole pair excitations in the metal strongly relax both the H atom and the excited HCl molecules formed.
使用准经典方法以及基于总能量计算的势能面，我们发现氢原子与吸附在金（111）表面的氯原子发生反应，通过伊莱-里德（ER）、热原子（HA）和朗缪尔-欣谢尔伍德（LH）途径生成氯化氢。我们观察到两种ER机制。在小的垂直入射能量下，反应源于与氯原子或多或少的直接碰撞，导致大量产物振动（ν = 8），以及相对较低的转动和平动温度。在第二种机制中，在接近垂直入射和/或大的入射能量时更占主导，氢原子经过氯原子附近，从金属上反弹，并被拉进围绕氯原子的轨道。这导致更宽的产物态分布，并且在产物自由度之间更均匀地分配3.0电子伏特的可用能量，类似于通过HA途径形成的产物。总体而言，ER过程对反应性的贡献往往小于10%，并且大多数氯化氢是通过HA过程形成的。对于ER和HA机制，随着表面温度升高，氯化氢的形成都有所增加，但这种增加相对较弱。我们观察到通常约12%的氢原子发生吸附，在实验中，高于140 K时这将通过LH过程导致氯化氢的形成。我们观察到由于直接的ER成分导致的微弱前向散射，如同在实验中一样。然而，与实验不同的是，我们观察到在产物角分布中在θf = 0度附近有一个凹陷，我们将其归因于我们的准经典近似。虽然我们倾向于在热产物中比在实验中看到更多能量，但我们的产物平动、转动和振动分布与测量结果相对合理地一致。与实验的一个主要分歧在于，在低温下显然有大量氢原子发生吸附，导致较大的LH成分。此外，ER和HA成分随温度的增加比计算中要强得多。金属中的电子-空穴对激发很可能强烈地弛豫了氢原子以及所形成的激发态氯化氢分子。
