Unusual adsorption site of hydrogen on the unreconstructed Ir(100) surface

The adsorption of hydrogen on the metastable, unreconstructed Ir(100)-(1x1) surface is investigated by density functional theory (DFT), quantitative low-energy diffraction (LEED), and thermal desorption spectrometry (TDS) complemented by scanning tunneling microscopy (STM). The bridge site is unequivocally identified as the adsorption site, rather unusual for metallic fcc(100) surfaces. There is excellent quantitative agreement between calculated and experimentally determined structural parameters both for the clean surface and the adsorbate covered surface. Given the uncertainty of DFT to reproduce absolute energies there is also good agreement with the measured adsorption energy (460 meV/atom). Additionally, theoretical vibrational and electronic properties are provided without, however, related experiments being available.