  Due to the dominant electron capture by positrons from the molecular wall and
the spatial dephasing across the wall-width, a powerful diffraction effect
universally underlies the positronium (Ps) formation from fullerenes. This
results into trains of resonances in the Ps formation cross section as a
function of the positron beam energy, producing uniform structures in recoil
momenta in analogy with classical single-slit diffraction fringes in the
configuration space. The prediction opens a hitherto unknown avenue of Ps
spectroscopy with nanomaterials.
