Adsorption and Reactivity of NO and N₂O on Cu{110}:  Combined RAIRS and Molecular Beam Studies

Abstract

The interaction of NO with Cu{110} is complex and is strongly dependent on both coverage and temperature. When Cu{110} is exposed to NO in the temperature range 40-85 K, initial adsorption leads to the presence of molecular NO on the surface. With further exposure this is replaced by the dimeric (NO) 2 species and N 2 O. Below 60 K, subsequent adsorption leads to the formation of multilayers of (NO) 2 . A detailed molecular beam study shows that adsorption is accompanied by the appearance of a range of gaseous reaction products. At 85 K, beaming of NO at a Cu{110} surface results in a large uptake of NO, which leads to gaseous N 2 and N 2 O production followed by a sudden saturation of the surface. The observed gaseous products are derived from adsorbed N 2 O formed on the surface upon exposure to NO, which dissociates to give the observed gaseous N 2 and O ad . This was confirmed in independent experiments with N 2 O beams, demonstrating gaseous N 2 production at 85 K. Saturation of the surface with O ad results in a sudden fall in NO uptake. At higher temperatures N ad , which associatively desorbs as N 2 at ∼800 K, is also produced on the surface by dissociation of incident NO. The NO dissociative sticking probability passes through a maximum at 200 K, with an anomalously sharp fall between 220 and 300 K.

Imaging Covalent Bonding between Two NO Molecules on Cu(110)

“…1 direction and thus is assigned to bent NO with the axis tilted along [001], that was previously observed by vibrational spectroscopies [10,18]. The dark image reflects that the 2 Ã molecular resonance is no longer retained for the bent species, as confirmed by its disappearance in the STS recorded over the depression [dashed curve in Fig.…”

“…On these surfaces, covalent interaction could contribute between NO molecules via the overlap of the ''active'' 2 Ã molecular orbitals. Actually, dimerization of NO has been observed in the submonolayer regime on Cu [9,10] and Ag [11,12]. Nevertheless, it remains yet to be clarified if the 2 Ã molecular state is indeed present for an isolated NO monomer and then how it evolves as NO forms a dimer.…”

Direct Molecular Imaging of NO Monomers and Dimers and a Surface Reaction on Ag{111}

“…Similar observations have been made by Jorgensen et al for coadsorbed hydroxyl and oxygen on Ag-{110}, for which it was found that atomic O stabilizes the hydroxyl groups via attractive lateral interactions that can extend for up to twice the lattice distance. 20 The production of oxide rings, Ag 12 15 Spontaneous ring formation results from the heating of the (NO) 2 adlayer to 130 K, but the low temperature does not allow sufficient diffusion, for the formation of an equilibrated surface with p(4×4)-O islands and atomic subsurface O c . 15 At higher temperatures (>400 K), these rings would become unstable and break up into a two-phase system composed of islands of p(4×4)-oxide and subsurface atomic O c .…”

The influence of steps on the dissociation of NO on Pt surfaces: Temperature-programmed desorption studies of NO adsorption on Pt{211}

“…The N 2 O is formed from the reaction of N atoms with NO, most likely at the step edges. Most of the N 2 O that is formed then immediately dissociates to form gas 33 Due to the presence of the step sites, it might be expected that an even larger proportion of the N 2 O might dissociate on Pt͕211͖. The O atoms which would result from the decomposition of N 2 O would bind strongly to the step sites on Pt͕211͖ as shown previously.…”