Abstract
Surface-induced transitions between Zeeman sub-levels of metastable neon atoms traversing a micro-slit copper grating are investigated. The quadrupolar part of the surface van der Waals interaction suddenly perturbs the evolution of the Zeeman sub-levels in a magnetic field $\bm B$, giving rise to van der Waals - Zeeman transitions. Exothermal inelastic transitions are identified by the related deflection γ. In a diagram (γ, $B^{1/2})$ the location of the inelastic peaks is fitted by straight lines of slopes proportional to $|\Delta m|^{-1/2}$, where $\Delta m$ is the magnetic number change.