MULTIPLE SITE COINCIDENCES AND THEIR RESOLUTION IN PHOTOELECTRON DIFFRACTION - PF3 ADSORBED ON NI(111)

Using scanned energy mode photoelectron diffraction from the P2p emission of PF3 on Ni(Ill) the adsorption structure has been determined; PF3 occupies an atop site with a P-Ni nearest neighbour distance of 2.07 +/- 0.03 angstrom. Using the normal emission data alone, comparison of theory and experiment with reliability factors shows a succession of minima as a function of the P-Ni distance. These multiple ''site'' coincidences are very similar to those seen in LEED analyses. The ambiguity is removed not only by the depth of these minima, but more importantly by using selected off-normal emission data sensitive to other scattering path-lengths which also show successive minima, but with a different spatial periodicity