2π levels of CO and NO adsorbed at Pd(100) surfaces

Rogozik, J.; Küppers, J.; Dose, V.

doi:10.1016/0039-6028(84)90571-5

Cited by 91 publications

(9 citation statements)

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“…The 2 Ã orbital is strongly hybridized with the surface, giving rise to the shift far away from the Fermi level. It was observed to split at $2 eV below and above the Fermi level on Ni and Pd surfaces by (inverse) photoemission spectroscopies [3][4][5]. Thus, we found that there exist two adsorbed states of NO on Cu(110): One is a weakly bound upright species with the 2 Ã molecular resonance located at the Fermi level, and the other is a more stable bent species which no longer retains the molecular character due to significant hybridization with the substrate.…”

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confidence: 71%

“…Nitric oxide (NO) has an unpaired electron in its 2 Ã orbital, and this could give rise to a covalent interaction between two NO molecules on the surface to form a dimer as in a gas phase [1] and in a matrix [2]. Upon adsorption on metal surfaces, however, the 2 Ã orbital of NO is usually hybridized with surface electronic states [3][4][5] so that the unpaired electron is delocalized in the metal, resulting in the loss of the paramagnetism [6]. On the other hand, the 2 Ã orbital was suggested to be mostly retained on Cu and Ag surfaces [7,8], where the surface d bands are located far below the Fermi level and thus the interaction is weak enough for NO to retain its molecular character.…”

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confidence: 99%

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

et al. 2011

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Using a scanning tunneling microscope, we found metastable upright NO on Cu(110) with the 2π* molecular resonance at the Fermi level. Upon heating above 40 K, it converts to a bent structure with the loss of molecular resonance. By manipulating the distance between two upright NO, we controlled the overlap between 2π* orbitals and observed its splitting below and above the Fermi level, thus visualizing the covalent interaction between them.

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confidence: 71%

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

et al. 2011

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“…5 UPS spectra exhibit typical features at about -8 eV (5u + 11T CO levels) and -11 eV (40" CO level) with respect to the Fermi leve1. I • 6 Inverse photoemission 7 shows a peak at about 5 eV above the Fermi level which has been attributed to the 21T* levels of CO. The large amount of experimental data has stimulated several theoretical studies based on different approaches.…”

Section: Introductionmentioning

confidence: 99%

Cluster calculations of CO chemisorbed on the bridge site of Pd(100)

Pacchioni

Bagus

1990

The Journal of Chemical Physics

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Articles you may be interested inThe transition of chemisorbed hydrogen into subsurface sites on Pd (311) The interaction of CO chemisorbed on the bridge site of the Pd ( 1(0) surface has been investigated by means of ab initio relativistic and nonrelativistic Hartree-Fock and MCSCF calculations. Pd 2 and Pd g clusters were used to determine the Pd/CO chemisorption properties. The interaction energy has been decomposed into different contributions arising from intraunit polarization and interunit effects including charge transfer and covalent bonding. Besides the classical1T back bonding found for other transition metal surfaces, the CO u donation to the partially occupied 4du-5sp metal hybrid orbitals significantly contributes to the chemisorption energy. By increasing the cluster size from Pd 2 to Pd s , the average Pd atomic configuration becomes more d 9 s l -like, with consequent increase ofthe u repulsion between the metal 5sp and the CO 5u charge distributions. However, this increased repulsion is largely compensated by the increased metal polarization resulting in a strong surface bond.

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“…In the adsorbed state one expects therefore the 2re manifold to straddle the Fermi level. IPE spectra of adsorbed NO have been reported by Rogozik et al [34] for Pd(100), by Johnson and Hulbert [14] for Ni(100) and Pd(111), and by Reimer et al [35] for Ni(100) and Ni(111). In all these cases the 2n* derived IPE structure appears 1.5-1.8 eV above E F with its tail Nevertheless the interpretation of the IPE spectra -as well as the UPS spectra -of adsorbed NO remains controversial [2,14,36].…”

Section: Strong Chemisorption: Diatomic Moleculesmentioning

confidence: 85%

Unoccupied electronic states in adsorbate systems

Bertel

1991

Appl. Phys. A

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Abstract. Experimental work on unoccupied electronic states in adsorbate systems on metallic substrates is reviewed with emphasis on recent developments. The first part is devoted to molecular adsorbates. Weakly chemisorbed hydrocarbons are briefly discussed. An exhaustive inverse photoemission (IPE) study of the CO bond to the transition metals Ni, Pd, and Pt is presented. Adsorbed NO is taken as an example to demonstrate the persisting discrepancies in the interpretation of IPE spectra. Atomic adsorbates are discussed in the second part. The quantum well state model is applied to interpret the surface states in reconstructing and non-reconstructing adsorption systems of alkali metals and hydrogen. A recent controversy on the unoccupied electronic states of the Cu(110)/O p(2 × i) surface is critically reviewed. The quantum well state model is then compared to tight binding and local-density-functional calculations of the unoccupied bands and the deficiencies of the various approaches are pointed out. Finally, the relation between the surface state model and more chemically oriented models of surface bonding is briefly discussed.PACS: 73.20.Hb, 79.60.-i A knowledge of unoccupied electronic states in adsorbate systems is crucial to the understanding of the surface chemical bond. The unoccupied levels determine the reactivity of surfaces and surface species just as much as the occupied levels do. One example out of many is provided by the hydrogen dissociation on Ni, where the empty Ni d-levels as hole reservoirs and are indispensable for the reaction to proceed [-1]. Another motivation for the study of unoccupied states derives from the fact that widely used techniques, such as scanning tunneling microscopy (STM) or second harmonic generation (SHG) on surfaces are based on processes involving empty levels. A thorough understanding of these processes therefore requires a knowledge of the unoccupied electronic level structure. There are, however, only a limited number of techniques available for providing independent information on the empty states. Ultraviolet photoelectron spectroscopy (UPS), where the unoccupied levels are probed as final states in k-conserving dipole transitions, and secondary electron spectroscopy, which may also yield information on the kll resolved unoccupied density of states, only access empty states above the vacuum level. This is a serious restriction if one considers the fact that the chemical bond involves primarily the "frontier orbitals", i.e. the highest occupied and the lowest unoccupied adsorbate orbitals and substrate Bloch states, which in an adsorbate system are usually aUtogether located below the vacuum level. Similarly, the position of the empty states involved in STM and SHG is in general restricted to a narrow range extending a few eV above the Fermi level. Spectroscopy of the near-edge X-ray absorption fine structure (NEXAFS) is a valuable tool for probing final states just above the Fermi level, but the presence of a core hole in the final state commonly results in large ...

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2π levels of CO and NO adsorbed at Pd(100) surfaces

Cited by 91 publications

References 11 publications

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

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

Cluster calculations of CO chemisorbed on the bridge site of Pd(100)

Unoccupied electronic states in adsorbate systems

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