The adsorption of CO 2 and N 2O on the MgO(001) single crystal surface: a comparative PIRSS and LEED study

Abstract

The adsorption of the isoelectronic molecules CO 2 and, for the first time, N 2O on the MgO(001) surface has been studied at 80 K using high-resolution polarization infrared surface spectroscopy (PIRSS) and low energy electron diffraction (LEED). High-quality surfaces were prepared by cleaving a single crystal in situ under UHV. At 80 K for the monolayer N 2OMgO(001) a (2√2 × √2)R45° superstructure with one glide plane parallel to the long side of the rectangular unit cell was found by LEED. The corresponding infrared spectra of the asymmetric stretching vibration v 3 are characterized by three sharp, polarization dependent absorptions. Two of them are attributed to a correlation field splitting in the ordered layer. Line B at 2217.0 cm −1 is assigned to the antisymmetric collective vibration of the monolayer. Its dynamical dipole moment is oriented parallel to the surface and perpendicular to the projection of the dynamical dipole of line A at 2229.6 cm −1. Therefore the symmetric collective vibration is attributed to line A, its dynamical dipole moment being inclined relative to the surface. The origin of the third absorption (C) at 2216.1 cm −1 is not yet understood. The same superstructure is observed for the monolayer CO 2MgO(001). The polarized infrared spectra in the v 3 spectral range are similar for both adsorbates, two lines being due to a correlation field splitting.