DETERMINATION OF THE LOCAL-STRUCTURE OF GLYCINE ADSORBED ON CU(110)

Scanned-energy mode N ls and O ls photoelectron diffraction has been u sed to determine the local geometry of glycine adsorbed on Cu(110) in an ordered (3x2) phase. The results are consistent with a molecular ge ometry in which the C-C axis lies approximately parallel to the surfac e and the molecule bonds across a pair of [<1(1)over bar>0] Cu surface rows through the two oxygen atoms of the carboxyl group and the N ato m of the amino group. The N atom is displaced by 0.24+/-0.10 Angstrom off an atop site along the [<1(1)over bar>0] rows with a Cu-N nearest- neighbour distance of 2.04+/-0.02 Angstrom. The carboxyl bonds to two Cu atoms in a [<1(1)over bar>0] row, with the O atoms displaced 0.80+/ -0.07 Angstrom from atop in [001] towards the amino group with a Cu-O nearest-neighbour bond length of 2.03+/-0.03 Angstrom and a resulting tilt of the O-Cu bond relative to the surface normal of 23+/-2. A spec ific structural model comprising two molecular moieties per unit mesh which has the space group plgl, consistent with the qualitative LEED o bservations, is proposed on the basis of these data. (C) 1998 Elsevier Science B.V.