  Scattering resonances play a central role in collision processes in physics
and chemistry. They help building an intuitive understanding of the collision
dynamics due to the spatial localization of the scattering wavefunctions. For
resonances that are localized in the reaction region, located at short
separation behind the centrifugal barrier, sharp peaks in the reaction rates
are the characteristic signature, observed recently with state-of-the-art
experiments in low energy collisions. If, however, the localization occurs
outside of the reaction region, mostly the elastic scattering is modified. This
may occur due to above barrier resonances, the quantum analogue of classical
orbiting. By probing both elastic and inelastic scattering of metastable helium
with deuterium molecules in merged beam experiments, we differentiate between
the nature of quantum resonances -- tunneling vs above barrier -- and
corroborate our findings by calculating the corresponding scattering
wavefunctions.
