| There are two parts in this dissertation. In part one, theoretical calculations and systematical studies on effect of isotopic substitution for rotational excitation in He,Ne,Ar,Kr,Xe—HD,HT,DT collisions are presented; In part two, The Scanning-tunnelling-microscopy(STM)images of inertia gas atoms adsorbed on a manslayer graphite sheet are calculated using the first-principle total-energy clectronic structure calculations.Rotationally excitational scattering of an atom by a diatomic molecule is of both theoretical and practical importance. It plays a very important role in practical processes such as the cooling of interstellar matter, predicating of laser action, resonance fluorescence and gas phase relaxation ets..Moreover, it can serve as a prototype for general molecular collisions. Collisions between inertia atoms and a hydrogen molecule is one of the simplest molecular scattering systems and have received much attention. Since hydrogen has three isotopes. Effect of isotopic substitution must be considered in practical problems. However, little has been reported in this field few data are available. In the paper, theoretical calculations and systematical studies of the cross sections for rotational excitation in He-H2,D2,T2,HD,HT,DT collisions are presented. In calculation, we employ the Murrell-Sorbie potential to calculate the intermolecular potential of hydrogen molecule and isotopic substitution systems. Moreover and calculate the vibration and rotational energy. For inertia atoin and hydrogen molecular scattering system. We employ Tang-Toennies model potential. Within the Born-Oppenheimer approximation, isotopic substitution does not change the intermolecular potential However it may cause the c.m. of the diatom to shift a distance δ. For systems of symmetric isotopic substitution, the c.m. of hydrogen molecule remains unshifted, and so the symmetric isotopic substitution does not change the intermolecular potential. For asymmetric isotopic substitution systems, the potential surface is till the same as that of He-H2, however, the c.m. of the hydrogen molecule shifts a distance ofδ, and since it is more convenient to treat this kind of scattering problem in a c.m. coordinate system, the potential must be reconstructed in the new coordinate. Furthermore, the differential cross sections(DCS), the partial wave cross sections(PCS)and the rotational excitation cross sections(RECS)for the collision of inertia gas atoms He,Ne,Ar,Kr,Xe with asymmetric isotopic substitution molecule HD,HT,DT have been calculated by using the close- coupling approximation method at incidence energy of 0.05eVto0.25eV,respectively. By analyzing the differentiae of the total cross sections(TCS), the differential cross sections(DCS), the partial wave cross sections(PCS), the change patterns of the cross sections and the influence on the cross sections(PCS), the change patterns of the cross sections and the influence on the cross sections because of the variations in the mass of systems and the relative kinetic energy of incoming atoms for symmetric isotopically substituted systems He,Ne,Ar,Kr,Xe—HD,HT,DT have been obtained.In part two of this paper, the scanning-tunnelling-microscopy (STM)images of inertia atoms adsorbed on a monolayer graphite sheet are calculated using the first-principle calculations.Scanning tunneling microscopes(STM) have become a powerful tool in atomic and molecular physics, surface science et al to imaging of various adsorbate atoms and molecules on atomically flast surfaces since the invention(1981). In the constant tunneling current mode, the STM image is given by recording the dip-to-surfact distance changes. In the current-imaging mode, however, an STM image is given by recording the tunnelling current as the tip rapidly scans the surface at a constant distance. In most cases, STM images can be associated with the topography of the electronic states of materials, such as Si(111)-7×7. In some cases, STM images show the electronic structure efforts and form different patterns...
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