Tensor LEED analysis for the Rh(110)-(3x2)-S surface structure

A tensor LEED analysis for the Rh(110)-(3 x 2)-S surface supports an arrangement of chemisorbed S atoms at 2/3 monolayer coverage on a basically unreconstructed metallic structure. Alternating [1(1) over bar0$] channels in the metal surface are occupied differently, although each has two S atoms per unit mesh. In one set, the S atoms occupy long-bridge and centre sites with a constant separation along the channel of 4.03 Angstrom. In the other set of channels, all S atoms occupy equivalent positions, displaced from regular centre sites by 0.39 Angstrom, to give successive S to S separations of 3.47 and 4.60 Angstrom. The long-bridge site bonding is a novel feature which is facilitated by the neighbouring topmost Rh atoms relaxing laterally by about 0.27 Angstrom perpendicular to the [1(1) over bar0$] row. Bucklings of 0.20 and 0.10 Angstrom are indicated to occur in the first and second Rh layers respectively; the latter value essentially equals that (0.11 Angstrom) reported earlier for the corresponding half monolayer c(2 x 2) surface. For S atoms at or near centre sites in the (3 x 2) structure, the average S-Rh bond distances are 2.42 and 2.29 Angstrom to the first and second layer Rh atoms respectively; the corresponding values at the long-bridge sites are 2.20 and 2.27 Angstrom.