The structure of N2 adsorbed on the rumpled NaCl(100) surface--a combined LEED and DFT-D study.

The structure of N(2) physisorbed on the NaCl(100) single crystal surface is investigated by means of quantitative low-energy electron diffraction (LEED) in combination with dispersion corrected density functional theory (DFT-D). In the temperature range between 20 K and 45 K, a p(1 × 1) structure is observed in the LEED experiment. According to the structure analysis based on the measured diffraction spot intensity profiles, the N(2) molecules are adsorbed over the topmost Na(+) ions. The experimental distance of the lower nitrogen to the Na(+) ion underneath is (2.55 ± 0.07) Å; the corresponding DFT-D value is 2.65 Å. The axes of the molecules are tilted (26 ± 3)° with respect to the surface normal, while in the zero Kelvin optimum structure from DFT-D, the molecules have a perpendicular orientation. The experimental monolayer heat of adsorption, deduced from a Fowler-Guggenheim kinetic model of adsorption is -(13.6 ± 1.6) kJ mol(-1), including a lateral molecule-molecule interaction energy of -(2.0 ± 0.4) kJ mol(-1). The zero Kelvin adsorption energy from DFT-D, including zero point energy correction, is -15.6 kJ mol(-1); the molecule-molecule interaction is -2.4 kJ mol(-1). While the rumpling of the NaCl(100) surface is unchanged upon adsorption of nitrogen, the best-fit root mean square thermal displacements of the ions in the topmost substrate layer are significantly reduced.