Atom symmetry break and metastable level coupling in rare gas atom-surface van der Waals interaction

van der Waals interactions between an atom and a planar surface exhibit a quadrupolar component in D-z(2)-D-2/3 (D, atomic dipole; (z) over cap, normal to surface). This coupling is responsible for an atom symmetry break, mixing levels of the same parity such as metastable P-3(0), P-3(2) levels of rare gas atoms. The strongly exoenergic P-3(0)-P-3(2) transition in Ar and Kr is observed by a time-of-flight technique using as a surface the edge of a copper slit. The results confirm the predicted strong peaking of the angular distribution of inelastically scattered atoms and give a good estimate of the transition probability.