The energies of an electron above a liquid-helium surface are analyzed in t
erms of an electron-atom polarizability potential with an infinite barrier.
An integration over a layer, and a summation over different layers, leads
to a one-dimensional Coulomb potential with a l/x(2) correction. This poten
tial provides an accurate description of the observed one-dimensional Rydbe
rg energies with a quantum defect.