The adsorptions and configurations of CO molecules on W (110) and W (100) surface: Molecular orbital theory

Abstract

The adsorption and configuration of CO molecules adsorbed on W (110) and W (100) surfaces have been calculated by the atomic superposition and electron delocalization molecular orbital (ASED-MO) method. Referred to as the ASED-MO method, it has been used in the present study to calculate the geometries, binding energies, vibrational frequencies, orbital energies, reduced overlap population (ROP), and charges. From these results adsorption properties of α-state and β-state were deduced. The calculated binding energies are in good agreement with the experimental result. On the W (110), the calculated average binding energies are 2.56 eV for the end-on configuration and 3.20 eV for the lying-down configuration. Calculated vibrational frequency is 1927 cm-1 at a 1-fold site and 1161 cm-1 at a long-bridge (2) site. These results are in reasonable agreement with experimental values. On the W(100) surface, calculated average binding energies of the end-on and the lying-down are 2.54 eV and 4.02 eV respectively. The differences for binding energy and configuration on the surfaces are explained on the basis of surface-atom coordination and atom-atom spacing. In the favored lying-down CO configuration on the W(110) and W(100) surfaces, 4σ and 1π donation interactions, coupled with the familiar 5σ donation to the surfaces and back-donations to the CO 2π* orbital, are responsible for adsorption to the surface.