Coverage-Induced Orientation Change: CO on Ir(111) Monitored by Polarization-Dependent Sum Frequency Generation Spectroscopy and Density Functional Theory

Xia Li, Verena Pramhaas, Christoph Rameshan, Peter Blaha, Günther Rupprechter

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

5 Zitate (Scopus)

Abstract

Polarization-dependent sum frequency generation (SFG) spectroscopy was applied to study the adsorption of carbon monoxide (CO) on the well-ordered (annealed) Ir(111) single-crystal surface at various CO coverages. Coverage was adjusted by varying the substrate temperature (300-575 K) and/or gas pressure (10-7 to 1.0 mbar). Under all conditions investigated, only a single absorption band at 2038-2094 cm-1 was observed, characteristic of linearly bonded (on-top) CO. Using different polarizations, PPP and SSP spectra were acquired with a high signal-to-noise ratio, whereby tilt angles of CO on Ir(111) could be determined for the first time by SFG. It was found that not only the vibrational frequency of on-top CO but also the tilt angle was strongly coverage-dependent. The higher the coverage was, the larger the vibrational frequency and the tilt angle were. At about 0.7 ML coverage, a CO tilt angle of at least 20° was observed, which is in good agreement with density functional theory (DFT) calculations. In addition, the molecular hyperpolarizability ratio (R) of CO (at 0.13 ML in UHV) was determined to be 0.08. Based on the combined SFG/DFT results, it may change to 0.29 at 0.77 ML coverage.
OriginalspracheEnglisch
Seiten (von - bis)18102-18111
Seitenumfang10
FachzeitschriftJournal of Physical Chemistry C
Jahrgang124.2020
Ausgabenummer33
DOIs
PublikationsstatusVeröffentlicht - 30 Juli 2020
Extern publiziertJa

Bibliographische Notiz

Funding Information:
This work was supported by the Austrian Science Fund (FWF) via project M 2787-N (Lise Meitner Fellowship of X.L.). GR acknowledges FWF funding via projects W1243 (DK + Solids4Fun) and I1041-N28 (ComCat). We thank T. Haunold for technical assistance.

Publisher Copyright:
Copyright © 2020 American Chemical Society.

Dieses zitieren