129Xe on Ir(111): NMR study of xenon on a metal single crystal surface

doi:10.1073/pnas.0405426101

¹²⁹Xe on Ir(111): NMR study of xenon on a metal single crystal surface

Department of Physics and Center for Materials Science, Philipps Universität Marburg, 35032 Marburg, Germany

Communicated by Alexander Pines, University of California, Berkeley, CA, July 27, 2004 (received for review January 9, 2004)

Abstract

NMR experiments of ¹²⁹Xe adsorbed on an iridium single crystal surface are reported. Very high nuclear polarization (P_z ≈ 0.7) makes the experiment possible. A coverage of less then one monolayer is investigated on the Ir(111) surface with an area of 0.8 cm². The observed resonance line shifts are very large and highly anisotropic. We find σ_iso = 1,032 ± 11 ppm and σ_an = 291 ± 33 ppm, which are far above the typical range of physisorption. The highly ordered substrate leads to homogeneous conditions for the xenon atoms, as seen in the narrow linewidth of 20 ppm. Chemical shifts under physisorption conditions are not large enough to totally explain the results. Knight shift can clearly be identified as the cause of the findings. This shift shows the presence of conduction electrons of the metallic substrate at the xenon nucleus and thus the mixing of metallic and atomic states at the Fermi level. Such mixing is in accordance with recent Hartree–Fock and density functional calculations of similar van der Waals adsorption systems. Quantitative comparisons, however, fail completely. The size and ratio of σ_an and σ_iso are pure ground-state properties in a structurally simple system. They are accessible to theory and provide detailed local information that can serve as a benchmark for theory.

Footnotes

↵ * To whom correspondence should be addressed. E-mail: heinz.jaensch{at}physik.unimarburg.de.
Abbreviations: DFT, density functional theory; vdW, van der Waals; ML, monolayer.
Data deposition: The NMR chemical shifts have been deposited in the Physics and Astronomy Classification Scheme database, www.aip.org/pacs (accession nos. 33.25.+k, 68.43.–h, and 76.60.Cq).