Structures of chlorine on palladium (111)

C1K edge SEXAFS of the Pd(1 1 1)-(root 3 x root 3) R30 degrees-Cl surface r eveals a Pd-Cl bond length 2.39 Angstrom. Two previously unreported structu res of chlorine on Pd(lll) are identified, the (4 x 4) and a highly complic ated surface with chlorine coverages of theta = 0.57 and theta less than or equal to 0.24, respectively, if the (root 3 x root 3) R30 degrees surface is assumed to be theta = 0.33. The (4 x 4) structure is discussed in terms of a close packed hexagonal overlayer of chlorine on an unreconstructed met al surface and as a surface compound of palladium and chlorine. The highly complicated structure appears to comprise crystallites or islands of a pall adium/chlorine compound and once formed is stable over a wide range of nomi nal chlorine coverages. (C) 2000 Elsevier Science B.V. All rights reserved.