Light-atom location in adsorbed benzene by experiment and theory.

Locations of light atoms in C6D6 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(square root of [7] x square root of [7])-R19 degrees phase, we find alternating outward bowing of the C-D bonds of 24 degrees and 9 degrees via LEED, and 22 degrees and 14 degrees 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.