Charge states of nonadiabatic O$_2$ dissociation at Al(111)

The low sticking probability of the dissociative adsorption of O$_2$ molecule on Al substrate has been explained by the nonadiabatic dissociation of the molecule; the dissociated and spin- polarized O$_2$ molecule forms the energy barrier [J. Behler \textit{et al}., Phys.\ Rev.\ B \textbf{77}, 115421 (2008).] We investigate the detailed charge variations of the atoms in the molecule and in the substrate during the nonadiabatic dissociation. The variation is a fundamental concept in the two-body interactions between the atoms and has been investigated extensively in physics and chemistry; in a simple case of an approaching C and O atom the electron transfers from the C to the O atom to form a CO molecule. So we have investigated the charge variations of the atoms in the H$_2$/Au(111) system, in which the charge has transferred from the H$_2$ molecule to Au(111), of which direction is determined by the electro-negativity difference between the H and Au atoms [S. Takagi \textit{et al}., J. Phys.\ Soc.\ Jpn. \textbf{77}, 054705 (2008).] We discuss the relation between the instability of the charged and dissociated O$_2$ molecule and the energy barrier of the nonadiabatic O$_2$ dissociation at Al(111).