Breakdown of adsorbate site assignment from vibrational frequencies. NO on Ni(111) re-visited by tensor LEED

Interadsorbate interactions in the c(4×2) NO/Ni(111) system

“…These frequencies may be a better guide to the local adsorption geometry of adsorbates than their intramolecular stretch frequencies, which have recently been shown to be much harder to interpret than previously appreciated. 1,14,19 We also report the dispersion of the dipole active NO internal stretch mode on this surface, and fit this dispersion with a model of which assumes dipole-dipole coupling between adsorbates. We report experimentally de-termined polarizabilities, and show that dispersion measurements are a convenient method for determining singleton frequencies, the frequency of an adsorbate in the static chemical environment of the coverage in question, but without the contribution to the frequency shift caused by dynamic dipole coupling.…”

“…The ordered NO overlayers were prepared by dosing at a surface temperature of 120 K, by either dosing the clean surface with the molecular beam or by backfilling of the chamber, followed by annealing at 270 K for 2 min. 11,14 The experiments were carried out at two coverages, one near 0.4 ML, and one corresponding to the 0.5 ML c͑4ϫ2͒ overlayer shown in Fig. 1.…”

“…Formerly, these two bands were assigned to NO adsorbed at bridge sites in a bent geometry at low coverages, and to an upright geometry at high coverages. Recently, photoelectron diffraction ͑PED͒, 12 surface extended x-ray absorption fine structure ͑SEXAFS͒, 13 and LEED I-V analysis 1,14 have been used to show that the local adsorption site of the NO molecule is a threefold hollow site, contradicting the earlier assignments based on vibrational frequencies alone. Using symmetry arguments in addition to dynamical LEED analysis, Mapledoram et al 14 have shown that the NO molecule is adsorbed in both fcc and hcp threefold hollow sites on Ni͑111͒ at all coverages, and Materer et al 1 have suggested that the two distinct stretching frequencies observed in the HREELS and IRAS spectra are in fact due to dipole-dipole coupling between NO molecules with and without nearest neighbors in the 0.5 ML structure ͑Fig.…”

“…The frequencies of the frustrated translations parallel to the surface thus may serve as a more reliable indication of local adsorption geometry than the frequencies of intramolecular stretching vibrations, which have recently been shown to result in inaccurate assignments for both CO/Ni͑111͒ 19 and NO/Ni͑111͒. 1,14…”

Surface enhanced Raman spectroscopic studies on the adsorption behaviour of nitric oxide on a Ru covered Au nanoparticle film

“…25 Low energy electron diffraction (LEED) and photoelectron diffraction studies demonstrated that assignment of the adsorption conguration of NO was ambiguous based on the frequencies of the NO stretching vibrational mode. [26][27][28] However, to solve these problems, SERS as a "ngerprinting" information tool provides a direct and viable method for studying molecular adsorption at metal surfaces.…”