Dipole coupling and chemical shifts of CO and NO adsorbed on oxides and halides with rock-salt structure

Abstract

The infrared spectra of CO and NO adsorbed at 77 K on sintered alkali-metal halide films (LiF, NaCl, KCl and NaI) and on sintered polycrystalline oxides (MgO and NiO) are reported. The most intense bands have been assigned to monomeric (CO) and dimeric (N₂O₂) species adsorbed on (100) faces. The CO molecules are adsorbed in a localized form on surface cations with orientation perpendicular to the (100) planes and form a regular array of parallel oscillators which interact via dynamic and static effects. The dynamic polarizability (α_v) of CO adsorbed on alkali-metal halides and magnesium oxide is very small (α_v≈ 0.02–0.03), while that of CO on NiO is one order of magnitude larger. The molecules of CO adsorbed on (100) faces also interact through the solid via inductive effects. NO is adsorbed on (100) planes of alkali-metal halides and MgO in the dimeric cis form; on NiO monomeric nitrosylic species predominate.