Observation of the surface vibrational resonances on Pd(110)

Surface vibrational resonances on Pd(110) have been observed by high-resolution electron-energy-loss spectroscopy. The resonance is observed at 17 meV on the Pd(110) clean surface at both 90 and 300 K, which indicates that the surface force constant is somewhat softened. On the (2×{}1)-H surface, the resonance is observed at 19.5 meV, which is nearly equal to the energy (19 meV) estimated assuming that the surface force constant does not change from the bulk value.