Study Of The Microscopic Dynamics Of Atoms And Molecules On Metal Surfaces

The dynamics of gas-solid surface interaction is arousing more and more interest inthe community of physicists and chemists. Multi-phase catalysis and colloid catalyzedinteractions are relating to the interaction between reactants as well as between reactant andcatalyzer surface. Therefore, the systemic study on the interaction between atom, moleculeand catalyzer surface, especially the interaction with active sites in theory is necessary.The main contents in this paper are as follows:In chapter 1, the elementary theory for calculation in this paper and the low-indexsurface cluster models are given.The adsorption and diffusion for Cl-Ag,Cl-Ni,H-Ag low-index surface systems entirelyare investigated by constructing atom-solid surface interaction potential named fiveparameters Morse potential (5-MP for short) in chapter 2.The analytical potential of gaseous diatom molecule interaction system, i.e. extendedLEPS potential has been constructed. And CO-Pd low-index surfaces and stepped systemsare studied in chapter 3.The main production of this paper:1. The adsorption system of Cl atom on the Ag low-index surfaces. The vibrationalfrequencies are easy to measure in experiments, and are the most important criticalcharacteritics to ascertain the adsorption sites and states. However, the experiments arecarried out under different conditions, and mostly obtain bitty information. Moreover, theproblem on the attribution of frequencies is usually inconsistent. Our theoretical results showthat the Cl atom can only adsorb in the four-fold hollow site on Ag (100). On (111) surface,there exists adsorption state of Cl atom in the three-fold hollow site, which produces verticalvibrational frequency 250 ㎝^-1 considering as special frequency for the three-fold adsorptionstate of Cl-Ag(111) system. Although the quasi-3-fold hollow site and the long-bridge siteare the stable adsorption sites on the Ag(110) surface for the first and second period atoms,the fourfold-hollow site becomes the most stable adsorption site for Cl on the Ag(110) andobtains the vertical vibrational frequency 244 ㎝-1. Calculated results not only reproduced thevibration frequencies but also ascertained adsorption sites and states.This paper has been published on Acta Chimica Sinica, 2005, 63(14),1276～1280.2. The adsorption system of Cl atom on the Ni low-index surfaces. The experimentalstudies and corresponding theoretical researches are scarce. The calculated results show thatchlorine atoms are likely to adsorb on the high symmetry sites. Cl atoms locate on thefour-fold hollow sites of the intact Ni (100) surface, while they tend to occupy three-foldsites on Ni (111) surface. The fourfold-hollow sites become the most stable adsorption sitesfor Cl on the Ni (110) surface. For the Cl-Ni adsorption system, the surface binding energyof a Cl atom is relevant to the coarse degree of the cluster surface, and the binding energieshave an order as (111)<(100)<(110). This order agrees with the results of S-Ni and Cl-Agsystem. So we can draw a conclusion that there is some relation between the surface bindingenergy and the coarse degree of cluster surface for the atoms of the third period. That is tosay, the coarse the surface is, the higher, the surface binding energy.This paper has been accepted by Chem. J. Chin.Univ.3. The theoretical results show that H atom can only adsorb at three-fold site on Ag(111). The quasi-3-fold site and long-bridge site are stable adsorption sites on Ag (110)surface for the H atom. At low coverage hydrogen predominantly occupies the quasi-3-foldsite and the perpendicular vibrational frequency is 117 meV. At high coverage, the H atomalso locates on the LB site and produces a perpendicular vibrational frequency of 90 meV.And this work predicts that the four-fold hollow site is the most stable adsorption state for Hatom on Ag (100). The results of this work are approved by the experimental and theoreticalresults.This paper has been published on Chinese J. Struct. Chem. 2005, 24(10),1217～1223.4. The adsorption and diffusion of CO molecule on Pd low index surfaces is investigatedwith the extended LEPS (constructed by 5-parameter Morse potential for short 5-MP). Bothadsorption and dissociation of CO on Pd low index surfaces and Pd (110) miss-rowreconstruction surface are investigated in detail. We obtain all critical characteristics of thesystems, such as adsorption geometry, binding energy, eigenvalues for vibration, etc. Theresults show that there exist common patterns when CO molecule adsorbed on Pd low indexsurfaces. The steady adsorption site of CO molecule is changed with coverage increasing.On (100) surface there are two adsorption states: bridge sites are preferred at low coverage, acombination of bridge sites and top sites is observed at high coverage. On (110) surface theshort bridge sites, top sites and hollow sites will become the steady adsorption sites in turnwith coverage increasing. CO molecules obtain the eigenvibration of 1963, 2070 and 1892cm-1 respectively. On (111) surface CO molecule occupies the three-fold hollow site. On themissing row Pd (110)-(1x2) structure CO molecules adsorb in five nonequivalent adsorptionstates: H2, H1, B, SB and T sites.The paper has been contributed.5. The adsorption systems of CO on Pd stepped surfaces. We study only one kind ofstepped surfaces. The calculated results about CO/Pd(s)-[n(111)×(100)] systems mainlyincluding CO-Pd(311) and CO-Pd(211) systems. The results show: there exist commoncharacters of CO molecule adsorption on these two surfaces. At low coverage, CO moleculewill perpendicularly adsorb in three-fold hollow site of the (111) terrace and has a tilt anglewith respect to the surface normal. The critical characters inherit the characters of COmolecule adsorbed in three-fold hollow site of (111) original surface. When the coverage isincreasing, two-fold bridge sites of (100) step are occupied. The critical characters inherit thecharacters of CO molecule adsorbed in two-fold bridge sites of (100) original surface.Considering the different length of (111) terrace, there exist some different characteristics of(311) and (211) stepped surfaces. A number of new sites are exposed on the boundaryregions between the two types of surface, for example H4 of (311) and H5 of (211) surface.When the coverage is up, CO will inside in H5 of (211) surface, but the H4 of (311) surfacewill not be a stable adsorption state.The paper has been contributed.