Dipped adcluster model for chemisorptions and catalytic reactions on a metal surface

We propose a model for chemisorptions and surface reactions in which ‘‘adcluster’’ (admolecule+cluster) is dipped onto the electron ‘‘bath’’ of a solid metal and an equilibrium is established for the electron and/or spin transfer between them. The equilibrium condition is described with the use of the chemical potentials of the adcluster and the solid surface. Since the adcluster is a partial system, the number of the transferred electrons n is not necessarily an integer. Some typical behaviors of the energy E(n) of the adcluster are explained. A molecular orbital model is proposed to calculate the energy E(n) and the electronic structure of the adcluster. The electrostatic energy due to a charge polarization is also important though it is insensitive to the chemical structure of the adcluster. Sample application is given for the Pd–O2 system.