| Abstract
| - Infrared spectra were measured at 80 K for dimethyl ether (CH3OCH3, DME) and dimethyl ether-d6 (CD3OCD3, DME-d6) with increasing amounts of exposures to metal substrates, Ag(110), Cu(110), and their atomicoxygen-reconstructed surfaces, p(2 × 1)O−Ag(110) and p(2 × 1)O−Cu(110). At relatively lower surfacecoverages, the IR spectra of DME on Ag(110) and Cu(110) in the 1500−800 cm-1 region give rise to IRbands mainly ascribable to A1 species, including symmetric COC stretching (νs(COC)) bands at 903 cm-1 onAg(110) and 895 cm-1 on Cu(110), while at nearly saturation coverages, the adsorbate gives IR bands ascribableto B1 and/or B2 species in addition to the A1 bands with the νs(COC) band discretely sifted to 915 cm-1 onAg(110) and to 901 cm-1 on Cu(110). Similar distinct spectral changes were observed also for DME andDME-d6 on the reconstructed surfaces. The stepwise spectral changes were interpreted in terms of a conversionfrom a state of DME with the C2 axis almost perpendicular to the surfaces to a state with the C2 axis tiltedaway from the perpendicular orientation. Fermi resonance effects cause stepwise but complicated spectralchanges in the CH3 stretching vibration region of DME during the conversion. The changes strongly dependon the kind of the substrates, in contrast to the spectral changes in the 1500−800 cm-1 region, suggestingthat the analyses of Fermi resonances can delineate subtle differences in the DME/substrate interaction modesamong the substrates. Density functional theory (DFT) molecular orbital calculations were carried out on thecluster models of DME/Cu(110), where the oxygen atom of DME is coordinated to two copper atoms in thesurface of metal clusters consisting of 12 copper atoms in the first layer and six copper atoms in the secondlayer. The results of calculations reproduce the observed frequencies appreciably well, substantiating thecoordination interaction model.
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