AN HREELS STUDY OF PI-ASTERISK AND SIGMA-ASTERISK NEGATIVE-ION RESONANCES OF C(8X2) BENZOATE ON CU(110)

For the c(8x2) benzoate on Cu(110) system, multiple unoccupied states have been measured through negative ion resonances by high-resolution electron-energy-loss spectroscopy (HREELS). Based on the azimuthal and polar angle dependences, we assign contributions from B-2 and A(1) st ates to a resonant feature in the [001] direction and contributions fr om B-1 and A(1) states in the [110] direction. The B-2 state is observ ed close to 4.7 eV and the B-1 feature is centered at 6.5 eV. The angu lar and azimuthal dependence of the C-H stretch intensity in HREELS at resonance is consistent with their assignment and the results of ab i nitio calculations. Overtone intensity shows an exponential decay as a function of overtone quantum number. From the overtone frequencies, a n anharmonicity of 0.0272 is obtained which leads to a dissociation en ergy of the C-H bond of about 81 kcal/mol. (C) 1998 American Institute of Physics.