Atomic beam diffraction and resonant scattering studies of clean Rh(311) and the c(1x1)H phase

Diffraction studies on clean Rh(311) have been performed with low and high temperature He beams and with room temperature Ne beams. The corrugation amplitude perpendicular to the close-packed rows as seen with He is similar to 0.30 Angstrom. The asymmetrical out-of-plane rainbow structure observed with He and Ne points to a more pronounced corrugation amplitude along the (100) microfacets and a much more smoothed amplitude along the (111) ones, in agreement with expectation but in contrast with Ni(311), where the reverse situation was reported. Selective adsorption of He on clean Rh(311) and the c(1 x 1)H phase could be measured with low temperature beams, allowing the determination of three and four bound-state levels, respectively. These energies were fitted with a two-parameter Morse potential, showing that the resonance levels as well as the potential depth of similar to 7.7 meV are essentially the same for Rh(311) as for Rh(110). The resonant scattering structure measured for the c(1 x 1)H phase could be wen reproduced by close-coupled channels calculations performed with a Morse potential, supporting the structure in which the lowest coverage ordered hydrogen phase on Rh(311) exhibits a coverage of one monolayer.