Coverage- and temperature-dependent site occupancy of carbon monoxide on Rh(111) studied by high-resolution core-level photoemission

Beutler, Andreas S.; Lundgren, Edvin; Nyholm, R.; Andersen, Jesper N; Setlik, B.; Heskett, David R.

doi:10.1016/s0039-6028(97)00664-x

Cited by 83 publications

(100 citation statements)

References 24 publications

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“…Note that the strongest increase in threefold CO is observed between 0.51 and 0.6 ML. The observed site occupation is in agreement with the coverage and temperature dependent HRCLS study of Beutler et al 25 These authors reported an increase of the fractional coverage of CO on threefold hollow sites from 0.02 to 0.21 ML in the total coverage range from 0.50 to 0.56 ML. This is indeed the coverage range where we observe the strongest increase in the threefold CO intensity ͓Fig.…”

Section: B Tds Experimentssupporting

confidence: 91%

“…The HREELS peaks shift to 470 cm Ϫ1 ͑58.3 meV͒ and 2041 cm Ϫ1 ͑253.1 meV͒. These values are still characteristic of linear CO, in agreement with HRCLS 21,25 and tensor-LEED; 22 the resulting structure model is depicted in Fig. 1.…”

Section: A Leed Experiments and Site Assignmentsupporting

confidence: 77%

“…However, Beutler et al reported the existence of the p͑2ϫ2͒ structure, albeit at temperatures below 120 K. 25 We also could not reproduce the ͑4ϫ4͒ structure that these authors reported. 25 It remains unclear whether this is because we could not realize the delicate conditions required for these structures or perhaps because our LEED-CCD camera has insufficient sensitivity.…”

Section: A Leed Experiments and Site Assignmentcontrasting

confidence: 66%

“…Both frequencies clearly indicate that CO occupies the on-top site at low coverage, in agreement with a coverage-dependent HRCLS study. 25 The LEED pattern hardly changes at such a low coverage. CO adsorbs on top without forming any ordered structures as visualized in the structure model beside the LEED pattern.…”

Section: A Leed Experiments and Site Assignmentmentioning

confidence: 97%

“…We also tried to reproduce other reported CO-induced superstructures. 25,28 Above 0.5 ML the so-called ''split ͑2ϫ2͒'' structure was observed which develops into the ͑2ϫ2͒-3CO structure at exposure of about 4 L. Annealing the ͑2ϫ2͒-3CO structure to 240 K ͑still below the desorption temperature of CO͒, converted it irreversibly into a diffuse split ͑2ϫ2͒ LEED pattern. For this reason the sample temperature was always kept below 200 K for the HREELS experiments after the surface had been exposed to CO.…”

Section: A Leed Experiments and Site Assignmentmentioning

confidence: 99%

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CO/Rh(111): Vibrational frequency shifts and lateral interactions in adsorbate layers

Linke

Curulla

Hopstaken

et al. 2001

The Journal of Chemical Physics

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High resolution electron energy loss spectroscopy ͑HREELS͒, low-energy electron diffraction ͑LEED͒, and thermal desorption spectroscopy ͑TDS͒ were used to study lateral interactions in the adsorbate layer of the CO/Rh͑111͒ system. The vibrational spectra show that CO adsorbs exclusively on top at low coverage. At about half a monolayer a second adsorption site, the threefold hollow site, becomes occupied as well. A steady shift to higher frequencies of the internal C-O vibrations is observed over the whole coverage range. The frequency of the metal CO ͑M-CO͒ vibration in the on-top mode hardly shifts at low coverage. However, upon the emergence of the second adsorption site the M-CO vibrations experience a shift to lower frequencies. The population of the second site is also accompanied by the development of a low temperature shoulder in the TD spectra, indicating an increasingly repulsive interaction in the adsorbed CO layer. Vibrational spectra of isotopic mixtures of 12 CO and 13 CO were used to assess the origin of the observed frequency shifts. They confirm that frequency shifts of the C-O stretching vibration at total CO coverage of 0.33 ML in the (ͱ3ϫͱ3)R30°structure arise purely from dipole-dipole coupling. Dilution of an isotopic species effectively suppresses frequency shifts arising from dipole-dipole coupling. Therefore, experiments with a small amount of 13 CO as a tracer to monitor the frequency shifts in the 12 CO adlayer were carried out over the entire coverage range of 12 CO. The results demonstrate that dipole-dipole coupling causes the frequency shifts at low coverage ͑Ͻ0.5 ML͒, whereas chemical effects set in at higher coverage ͑0.5-0.75 ML͒, connected with the population of the threefold sites. The results illustrate that HREELS in combination with isotopic dilution is a powerful tool in the assessment of lateral interactions between adsorbed molecules.

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Section: B Tds Experimentssupporting

confidence: 91%

Section: A Leed Experiments and Site Assignmentsupporting

confidence: 77%