We present an overview of experimental findings on the inelastic photoemission process through the excitation of surface vibrations. The tunable laser system is used as the excitation light source. The photon energy is tuned slight above the work function of the sample to emit the very low energy photoelectron, which passes through the surface layer in an enough long time to produce the large inelastic cross section for the vibrational excitation. The sample is CO covered Cu(001) surface. The energy loss structures appear as a step at 254 meV and 34.6 meV below the Fermi edge. The steps originate from the vibrational excitation of C-O internal stretching mode and frustrated rotation mode by the photoelectron, respectively.