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- Paul, Jan, et al.
(författare)
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Ab initio calculations of electron distributions in heme-CO models
- 1983
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 722:1, s. 209-213
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Tidskriftsartikel (refereegranskat)abstract
- We have, by the use of ab initio calculations, found a back-bonding state of π symmetry close to the Fermi level for CO bound to FeN5C14. We thus find it likely that small shifts of the redox potential ¦EF - Ev¦ will cause relatively large changes of the CO vibrational frequency. The separation of Fe 3d orbitals in our heme model is found to agree with what is predicted by ligand field theory for Oh symmetry. This paper presents nonrelativistic Hartree-Fock-Slater calculations of the 5σ bonding and 2π back-bonding between CO and Fe. The effects of up to 19 additional atoms are discussed for models of heme (COFe to COFeN5C14). The filled back-bonding state is found to be strongly influenced by second nearest neighbor atoms. By use of symmetry orbitals we have resolved the Fe 3d orbitals into the T2g and Eg representations of the Oh point group and find the former states to be occupied whereas the latter are unoccupied. The difference in occupancy is reduced when the CO ligand is removed which also causes an increased density of states at the Fermi level, i.e., the highest occupied and lowest unoccupied orbitals. Possible correlations between our data and experimental results are discussed for heme proteins as well as for metal surfaces.
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- Larsson, C.G., et al.
(författare)
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Diffraction of UV excited photoelectrons by an ordered overlayer
- 1983
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T4, s. 44-46
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved UV photoemission spectra obtained from Cu(111)-(√3 × √3)R30° Xe and Cu(111)-(√3 × √3)R30° CO samples are compared with spectra obtained from the clean substrate. Interest is focussed on the adsorbate induced changes in the Cu3d band range of initial energies. From the similarity between the spectra observed for the ordered Xe and CO overlayers we conclude that the changes are primarily due to diffraction of the photoexcited Cu3d electrons by the adsorbate. This is supported also by calculated photoelectron energy distributions.
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- Lindgren, S.Å., et al.
(författare)
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Low-energy electron diffraction from close-packed Na
- 1982
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Ingår i: Journal of Physics. C, Solid State Physics. - : IOP Publishing. - 0022-3719. ; 15:30, s. 6285-6291
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Tidskriftsartikel (refereegranskat)abstract
- The authors obtain a homogeneously thick film of close-packed Na with close-packed planes parallel to the surface by evaporating Na onto Cu(111) held at LN2 temperature. Comparison between measured LEED intensity spectra, recorded at LN2 temperature, and theoretical ones, calculated under the assumption that the crystal structure of Na is FCC or HCP, favours the HCP structure. The authors UPS results indicate that if Na is evaporated onto Cu(111) held at RT, it will form three-dimensional clusters on top of a Na film only few atomic layers thick.
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- Lindgren, S.Å., et al.
(författare)
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Photoemission of backbonding electrons from CO chemisorbed on Cu(III)
- 1981
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 84:3, s. 487-490
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoclectron energy spectra recorded in the normal direction for a CO-exposed Cu(111) sample show a peak at the Fermi edge for high monolayer coverages. We associate this peak with a filled part of a resonance-broadened CO 2π level.
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- Lindgren, S.Å., et al.
(författare)
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Surface state energy shifts by molecular adsorption : CO on clean and Na covered Cu(111)
- 1982
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 117:1-3, s. 426-433
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved photoelectron energy spectra recorded in the near UV show that the surface state 0.4 eV below EF of Cu(111) shifts to higher energy upon CO adsorption. The surface band related emission intensity is reduced by the adsorption at a rate suggesting that each adsorbed molecule wipes out the surface state over an area corresponding to seven surface layer Cu atoms. The surface state energy shift is not as closely related to the adsorbate induced workfunction change as found theoretically and experimentally for alkali adsorbates. The influence on the shift of the workfunction and initial energy of the surface state is studied by preadsorbing Na on the Cu(111) surface.
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- Paul, Jan, et al.
(författare)
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Surface state energy shifts by molecular adsorption : CO ON Cu(111)
- 1981
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 40:4, s. 395-397
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Tidskriftsartikel (refereegranskat)abstract
- Molecular adsorption induced energy shifts of a surface state is observed for the Cu(111)/CO system. Angle resolved photoelectron energy spectra show that a zone center surface state shifts to higher energy relative to the Cu bulk bands. The effects is discussed in terms of charge transfer, molecular interaction range and absorption site.
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- Paul, Jan, et al.
(författare)
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The reactivity of adsorbed Na atoms probed by coadsorbed CH3OH
- 1984
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 146:1, s. 43-60
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Tidskriftsartikel (refereegranskat)abstract
- The chemical properties of sodium atoms adsorbed on a Cu(111) surface have been probed by coadsorbed methanol. Methoxide, stoichiometrically close to CH3ONa2, is identified as a product by photoemission spectroscopy. Sodium atoms are found to react in the same manner at all submonolayer coverages, i.e. independent of atomic charge. Films of closely packed Na atoms - the first sp-metal substrate probed by methanol - are slightly less reactive. Hartree-Fock-Slater cluster calculations as well as observed energy shifts of a Cu electronic surface state indicate a transfer of charge from the copper substrate to the methoxide group. The desorption temperature for a monolayer of methanol molecules from a Cu(111) surface is enhanced by the presence of low sodium concentrations (1/20 of a monolayer). CH3OH is found to adsorb associatively on the uncovered Cu(111) surface.
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