Sun Lipeng, Peterson Kirk A, Alexeev Yuri, Windus Theresa, Kindt James, Hase William L
Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.
J Chem Phys. 2005 Jan 22;122(4):44704. doi: 10.1063/1.1829993.
In a previous paper [L. Sun, P. de Sainte Claire, O. Meroueh, and W. L Hase, J. Chem. Phys. 114, 535 (2001)], a classical trajectory simulation was reported of CH(4) desorption from Ni{111} by Ar-atom collisions. At an incident angle theta(i) of 60 degrees (with respect to the surface normal), the calculated collision-induced desorption (CID) cross sections are in excellent agreement with experiment. However, for smaller incident angles the calculated cross sections are larger than the experimental values and for normal collisions, theta(i)=0 degrees , the calculated cross sections are approximately a factor of 2 larger. This trajectory study used an analytic function for the Ar+Ni(s) intermolecular potential which gives an Ar-Ni{111} potential energy minimum which is an order of magnitude too deep. In the work reported here, the previous trajectory study is repeated with an Ar+Ni(s) analytic intermolecular potential which gives an accurate Ar-Ni{111} potential energy minimum and also has a different surface corrugation than the previous potential. Though there are significant differences between the two Ar+Ni(s) analytic potentials, they have no important effects on the CID dynamics and the cross sections reported here are nearly identical to the previous values. Zero-point energy motions of the surface and the CH(4)-Ni(s) intermolecular modes are considered in the simulation and they are found to have a negligible effect on the CID cross sections. Calculations of the intermolecular potential between CH(4) and a Ni atom, at various levels of theory, suggest that there are substantial approximations in the ab initio calculation used to develop the CH(4)+Ni{111} potential. The implication is that the differences between the trajectory and experimental CID cross sections may arise from an inaccurate CH(4)+Ni{111} potential used in the trajectory simulation.
在之前的一篇论文[L. 孙、P. 德圣克莱尔、O. 梅罗埃和W. L. 哈泽，《化学物理杂志》114, 535 (2001)]中，报道了通过氩原子碰撞使甲烷从Ni{111}表面解吸的经典轨迹模拟。在相对于表面法线60度的入射角θi下，计算得到的碰撞诱导解吸（CID）截面与实验结果高度吻合。然而，对于较小的入射角，计算得到的截面大于实验值，而对于垂直碰撞（θi = 0度），计算得到的截面大约大两倍。该轨迹研究使用了一个用于Ar + Ni(s)分子间势的解析函数，该函数给出的Ar - Ni{111}势能最小值比实际深一个数量级。在本文报道的工作中，使用了一个给出准确的Ar - Ni{111}势能最小值且表面起伏与之前的势不同的Ar + Ni(s)解析分子间势，重复了之前的轨迹研究。尽管这两个Ar + Ni(s)解析势之间存在显著差异，但它们对CID动力学没有重要影响，本文报道的截面与之前的值几乎相同。模拟中考虑了表面的零点能运动以及CH(4) - Ni(s)分子间模式，发现它们对CID截面的影响可忽略不计。在不同理论水平下对CH(4)与镍原子之间分子间势的计算表明，用于构建CH(4) + Ni{111}势的从头算计算存在大量近似。这意味着轨迹和实验CID截面之间的差异可能源于轨迹模拟中使用的不准确的CH(4) + Ni{111}势。
