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(2)(z)-D(2)/3 (D, atomic dipole; ź, normal to surface). This coupling is responsible for an atom symmetry break, mixing levels of the same parity such as metastable 3P0, 3P2 levels of rare gas atoms. The strongly exoenergic 3P0-3P2 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.