ON THE EQUIVALENCE OF EELS AND IRAS - THE CASE OF O-AG(110)

The coverage dependence of electron-energy loss intensity (EELS) and o f the frequency of the O-Ag(110) stretching vibration are re-examined and compared with other EELS and infrared reflection absorption spectr oscopy (IRAS) data. The analysis of the EELS intensity in our experime nt yields a charge transfer q=0.51+/-0.03 e(-), which compares well wi th independent EELS estimates but is at variance with the much smaller IRAS value reported by Peng and Reutt-Robey [Surf. Sci. 336 (1995) L7 55]. Our value can account for most of the observed frequency shift wi th coverage, indicating that no chemical shift occurs; in contrast wit h the recent theory of Schimizu and Tsukada [Surf. Sci. 295 (1993) L10 17], the opposite conclusion would be supported by IRAS. The (surprisi ng) inconsistency of EELS in dipole scattering and IRAS could be indic ative that the physical basis of the two spectroscopies is not unique, as assumed so far.