ANOMALOUS COVERAGE BEHAVIOR OF THE CS-AG DISTANCE ON CS AG(110)/

The position of Cs on the (1 X 2) missing row reconstructed Ag(110) su rface was determined by X-ray diffraction for two different Cs-coverag es: theta(Cs) = 0.2 and theta(Cs) = 0.3. The Cs was found to be adsorb ed in incommensurate chains in the troughs of the missing row with an average adsorption height of 1.7 Angstrom (theta(Cs) = 0.2) and 1.4 An gstrom (theta(Cs) = 0.3) above the topmost Ag layer. The apparent cont radiction to the classical picture of alkali adsorption, which expects an increase of the Cs adsorption height with coverage, might be partl y resolved by introducing a fraction of commensurately adsorbed Cs at theta(Cs) = 0.2.