Locations of light atoms in $C_6{D}_6$ on Ru{0001} have been determined by low energy electron diffraction (LEED) and density functional theory (DFT). For the favored site/orientation in the $p(\sqrt{7}\times \sqrt{7})-R19\mathrm{}°$ phase, we find alternating outward bowing of the C-D bonds of 24° and 9° via LEED, and 22° and 14° via DFT. This remarkable agreement gives important cross confirmation of the validity of these techniques in describing the subtle contributions of light atoms to adsorbate scattering and energetics. The buckling is explained as a consequence of decreased aromaticity induced by the bonding to the substrate.

• Received 31 May 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.216102