Knowledge Bank

The potential of the interaction between an atom (H, He...) and an alkali halide surface has been calculated from the spectrum of the discrete atom-surface states detected in atomic beam scattering studies of physical adsorption. The long-range part of the potential is of the form U(r) = -A$/r3$ in which the parameter A has been calculated from complex atomic polarizabilities and dielectric function of the surface, A hybrid potential has been constructed using this long-range potential for large atom-surface distances r $\ge rp$ and a shifted Morse potential $U(r)=D(x2-2x-\delta$) with x $ = exp(-a(r-r_{e}$)) for shorter distances 0 $ \leq r \leq r_{p}$. The parameters D, a, and the shift $\delta$ have been determined from a fit to the observed energy levels for H and D on a LiF surface. By matching the value and the slope of the long-range potential to the Morse potential one obtains the coordinate of the contact point $rp$ and the equilibrium distance $re$ of the atom-surface complex. This hybrid potential reproduces the known data extremely well. Another, model-independent, calculation of the atom-surface potential has been performed by the RKR method. The widths of the potential well, $rMax-rMin$, thus determined are in excellent agreement with those obtained from the hybrid potential.