Chemical shifts and coupling interactions for the bonding vibrational modes for CO/Cu(111) and (100) surfaces

Journal Article · Wed Nov 15 04:00:00 EST 1995 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.52.14177· OSTI ID:130717

Hirschmugl, C J; Williams, G P ^[1]

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1. National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)

Low-frequency infrared reflection absorption spectra have been measured for isotopic mixtures of CO and {sup 13}C {sup 18}O on Cu(100) and (111) surfaces. Although the integrated intensities are only 1/100 of those for the intramolecular modes, both the carbon-metal and the dipole-forbidden hindered rotational modes can clearly be seen in the spectral range 250--350 cm{sup {minus}1} for both isotopes in the admixtures. The data thus allow chemical shifts to be distinguished from coupling effects for these two bonding modes. For the two surfaces, the normalized chemical frequency shifts for the C-O stretch are very similar. However, dramatic differences are observed for the modes directly related to the bonding, i.e., the C-metal stretch and the hindered rotation. The dominant coupling mechanism for the perpendicular modes is shown to be dipole-dipole coupling as confirmed by a comparison to coherent potential approximation calculations. For the parallel modes the data cannot be explained in terms of dipole-dipole coupling, and we postulate that the surface state present on the (111) surface is largely responsible for the observed behavior. When the data are interpreted using a model assuming point dipoles, then the vibrational polarizability can be determined for these modes. A more stringent test of the theory is also provided through estimates of the polarizability obtained from intensities of the carbon-metal stretch mode.

• Research Organization: Brookhaven National Laboratory
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 130717
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 19 Vol. 52; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
66 PHYSICS
ABSORPTION SPECTRA
CARBON 13
CARBON MONOXIDE
CHEMICAL SHIFT
CHEMISORPTION
COPPER
EPITAXY
INFRARED SPECTRA
ISOTOPE EFFECTS
OSCILLATION MODES
SORPTIVE PROPERTIES
SPECTRAL REFLECTANCE
STEREOCHEMISTRY
SYNCHROTRON RADIATION