Comment on "Energy-loss-spectroscopy studies on the adsorption of hydrogen on cleaved Si(111)-(2×1) surfaces"

In recent energy-loss-spectroscopy studies by Froitzheim, Lammering, and Günter, a new vibrational mode of hydrogen adsorbed on Si(111) surfaces has been found at $\hslash \omega =100\mathrm{}$ meV. This new mode was interpreted as a vibration of the hydrogen atom being bonded in a wide bridgelike configuration between two silicon step edge atoms. We suggest that this new vibrational mode could also be the frequency of motion of a hydrogen atom adsorbed at the open site of Si(111). Further, adsorption at this site could be an intermediate step in silane production, erosive action, and formation of $\mathrm{Si}{\mathrm{H}}_x$ surface complexes. These suggestions are based on the results of our earlier cluster-model study of H/Si(111).