Van der Waals forces between heavy alkali atoms and gold surfaces: Comparison of measured and predicted values

The Van der Waals potentials between heavy alkali-metal atoms (Cs, Rb, K) and gold surfaces have been investigated by the atomic-beam-deflection technique. The result is consistent with a potential of the form V(R)=-kR³. The observed interaction constant k is 7.0 +/- 0.29 D², 6.04 +/- 0.30 D², and 5.10 +/- 0.62 D² for Cs, Rb, and K, respectively. These values are smaller than the predictions based on all available theories. At best there is agreement within 60% for estimates based on the macroscopic continuum theory of Lifshitz. Other models disagree with measurements by factors of three (200% difference) or more.