Overtones of the C–H stretch vibrations on C(0 0 1)(2 ×1 )–H

The overtones of the C–H stretch vibrations on the diamond C(0 0 1)(2 × 1)–H surface are studied by means of electron energy loss spectroscopy (EELS). The dimer structure of the C–H bonds gives rise to the intra-dimer coupling of the C–H stretch vibrations. The fundamental excitations appear at 360 and 362 meV and are assigned to the antisymmetric and symmetric stretch modes, respectively. The overtone excitations are observed at 705 and 1036 meV with two and three quanta on the dimer, respectively. They are analyzed with a model of coupled anharmonic oscillators, and it is shown that the overtone excitations are almost localized on the single C–H bonds.