He-diffraction investigation of the (1 × 1) CO phase on NaCl(100): a fully quantum study

Abstract

We investigate numerically the ability of helium atom scattering (HAS) to characterize the correct CO orientation in the (1 × 1) commensurate monolayer adsorbed on a single crystal NaCl(100) surface. The fully quantum description is based on two potentials recently proposed which exhibit a significant discrepancy in whether the CO axis is normal to the surface or inclined by about 40°. Both pictures can be used to interpret reasonably experimental observations made with polarization Fourier transform infrared spectroscopy (PIRS). We therefore suggest HAS studies which, when coupled with the companion technique of PIRS, can provide information on the ambiguity remaining on the CO equilibrium geometry. To this end we report both the bound-state energies which are the discriminating quantities in specular beam studies probing selective adsorption, and diffraction spectra for typical HAS experiments. We show that an accurate analysis of the He diffraction spectrum should be successful provided that an exact treatment of the collisional process between the helium probe and the adsorbate-substrate system can be performed.