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By use of the resonant metastability-exchange process, a metastable-atom beam possessing all genuine qualities of a “ natural ” ground-state atom nozzle beam is prepared. Owing to the angular narrowness (0.35 mrad) and smallness of the effective source diameter (15 μm) of this beam, the scattering of metastable atoms by a silicon-nitride nano-slit grating is investigated in detail, in a partially coherent regime. The elastic scattering exhibits high-order diffraction peaks combined with a standard van der Waals deflection effect. When a static magnetic field is present, surface-induced exo-energetic transitions among Zeeman sub-levels are observed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The symmetry of atomic wave functions is broken by the quadrupolar component of the van der Waals interaction between the atom and a planar surface. This results into a coupling able to mix levels of same parity such as ³P[sub 0] and ³P[sub 2] metastable levels of heavy rare gas atoms. The ³P[sub 0]-³P[sub 2] transition in Ar and Kr has been evidenced in a time-of-flight experiment using as a surface the edge of a copper slit. [ABSTRACT FROM AUTHOR]