High-resolution study of dipole-active vibrations at the Ag(110) ( n × 1)O surface

Atomic chemisorption of oxygen on Ag(110) at room temperature has been studied by high resolution electron energy loss spectroscopy (HREELS). It is well known that upon increasing exposure the LEED pattern sequentially changes as ( n × 1), with n = 7, 6, ⋯ 2. We present the first dear evidence that the oxygen vibration frequency changes from ( ω⊥ = 38.5 meV ( n = 7) to 40.9 meV ( n = 2). Simultaneously the surface phonon observed on Ag(110) at 13.2 meV shifts to 17.0 meV (at n = 2) and a second phonon appears at lower energies (8.7 meV at n = 2). We discuss implications of our data for the formation of the ( n × 1) added row structure.