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本文用EHMO法对Pt(100)面上CO的吸附进行了处理。先计算了Pt-Pt,Pt-H,Pt-C 等二元体系的平衡间距及离解能,与实测值进行比较以确定计算中所用的基轨道及其轨道参数(如电离电位及轨道指数)以及非对角哈密顿矩阵元的近似方式。然后假设了三种吸附模型,分别进行计算。结果能很好地解释CO在Pt表面上的吸附型式以及 C-O键吸附后减弱的情况,并与红外光谱的实验结果一致。由计算得到的吸附能与由热脱附测得的脱附活化能颇相近。从紫外光电子能谱得到CO分子中σ_(2ρ)轨道的能级吸附后产生位移和π_(2ρ)轨道的能峰重迭。计算的结果表明,CO中的σ_(2ρ)轨道吸附后的稳定化程度确较π_(2ρ)轨道大,因而谱线向π_(2ρ)方向移动。又根据“表面分子”的对称性,对CO和Pt之间的轨道相互作用以及CO在Pt上的解离进行了讨论。
In this paper, the adsorption of CO on Pt (100) surface has been treated by EHMO method. The equilibrium spacing and dissociation energies of binary systems such as Pt-Pt, Pt-H and Pt-C are calculated and compared with the measured values to determine the base orbital and orbital parameters (such as ionization potential and orbital index) As well as the approximation of non-diagonal Hamiltonian elements. Then assume three adsorption models, which are calculated separately. The results can well explain the adsorption pattern of CO on the Pt surface and the weakening of the C-O bond adsorption, consistent with the experimental results of infrared spectroscopy. The calculated adsorption energy is quite similar to the desorption activation energy measured by thermal desorption. The energy levels of σ 2 (2ρ) orbitals in the CO molecule are obtained by UV photoelectron spectroscopy, and the displacement of the π 2 (2ρ) orbit is overlapped. The calculated results show that the stability of σ_ (2ρ) orbitals in CO is indeed larger than that of π_ (2ρ) orbitals, and the line shifts toward π_ (2ρ). According to the symmetry of “surface molecule”, the orbital interaction between CO and Pt and the dissociation of CO on Pt are also discussed.