Long-Range Forces between Molecules and Metals

Isotherms of oxygen, argon, neopentane, tetramethylsilane, and diethyl ether on optically flat gold surfaces have been determined over the range 0-70 Brunauer-Emmett-Teller) (BET) monolayers, corresponding to 0-220 Å. The results are found to imply a potential energy of interaction $U\left(Z\right)\mathrm{}$ of the form $U\left(Z\right)=\alpha 1.74\times {10}^{-4\mathrm{}}{Z}^{-2\mathrm{}}$ erg/molecule, where $\alpha$ is the molecular polarizability and $Z$ the distance from the surface. The possible source of the disagreement between the experimental results and the theoretical predictions of Margenau, Bardeen, and Lennard-Jones is briefly discussed.