An ab initio molecular orbital study connected with adsorption experiments was performed to determine the mechanism of physical adsorption and chemical adsorption of C2H4 on metals

and to compare the effects of the two kinds of adsorption.The results indicated that the adsorption styles were determined by whether there were local symmetry-adapted orbitals

whether the energy gap between symmetry-adapted orbitals was small and whether the electron occupancy of the symmetry-adapted orbitals was “occupancy vs. vacancy”.The different valence shells and orbital energies of Ag+ and Na+ resulted in different adsorption styles

chemical adsorption of C2H4 on Ag+ and physical adsorption of C2H4 on Na+ respectively.