Vibrational Interaction between Hydrogen Atoms Adsorbed on Pd(100)

Vibrational energy shifts have been observed for the substitutionally disordered $p(1\mathrm{}\times 1)(\mathrm{H}+\mathrm{D})$ and $c(2\mathrm{}\times 2)(\mathrm{H}+\mathrm{D})$ structures on Pd(100). Between 0 and 1 hydrogen concentration the hydrogen vibrational energy shifts by 3.5 and 0.5 meV for the $p(1\mathrm{}\times 1)$ and $c(2\mathrm{}\times 2)$ structures, respectively. It is argued that the relatively large energy shift of the $p(1\mathrm{}\times 1)$ structure is mainly due to adatom-adatom interaction mediated by the metal electrons.