The structure of PF3 adsorbed on Cu(111)

The structure of PF, adsorbed on Cu(111) at 110 K has been determined using both near edge X-ray absorption fine structure (NEXAFS) and normal incidence X-ray standing wave (NIXSW) methods. Two X-ray reflection conditions were used, the (111) and (111), to determine the atomic positions of the phosphorus and fluorine atoms by triangulation using NIXSW, whereas NEXAFS was used to determine the alignment of the molecule. PF3 adsorbs at atop sites with the fluorine atoms away from the surface and its C-3 axis aligned along the surface normal. The Cu-P distance is 2.25 +/- 0.04 Angstrom, and the distance between the copper and the fluorine layers along the C-3 axis is 3.05 +/- 0.04 Angstrom. The adsorbed molecule maintains its gas-phase geometry and undergoes either free rotation about the C-3 axis, or is azimuthally orientated such that the projections of the P-F bonds on to the surface point towards the next nearest neighbour copper atoms. The NIXSW analysis for the fluorine photoemission data was carried out using a backward/forward asymmetry parameter to compensate for a breakdown in the dipole approximation for photoemission that occurs for fluorine Is photoemission under the NIXSW conditions used here. (C) 1998 Published by Elsevier Science B.V. AU rights reserved