He-Ag{001}-c(2×2)Clattractive potential from resonance scattering

We present an analysis of the resonance scattering of He from the Ag{001}-$c(2\mathrm{}\times 2)\mathrm{Cl}$ surface. Five resonance energies are assigned: -13.7, -6.9, -3.6, -1.8, and -0.4 meV. We confirm that there is no deeper level than -13.7 meV by studying the momentum-transfer dependence of the Debye-Waller factor, which depends on the attractive well depth. Different forms of one-dimensional potentials are examined based on the premise that the experimental resonance levels are close to those of the one-dimensional laterally averaged potential. A general prescription is proposed for a potential which includes these energy levels as bound states and extends to positive energies by matching the repulsive potential which is independently available.