Positronium formation from C$_{\mathrm{60}}$*

Due to the dominant electron capture by positrons from the molecular shell and the spatial dephasing across the shell-width, a powerful diffraction effect universally underlies the positronium (Ps) formation from C$_{\mathrm{60}}$. This results into trains of resonances in the Ps formation cross section as a function of the positron beam energy [1], producing structures in recoil momenta in analogy with classical single-slit diffraction fringes in the configuration space. C$_{\mathrm{60}}$ is modeled by a jellium-based local-density approximation (LDA) method [2] and the Ps formation is treated by the continuum distorted-wave final-state (CDW-FS) approximation [3]. The work may motivate application of the Ps formation spectroscopy to gas-phase nanoparticles and also the access target-level- as well as Ps-level-differential measurements. [1] Hervieux et al (submitted), \underline {arXiv:1610.00335 [physics.atm-clus]}; [2] Choi et al (submitted), \underline {arXiv:1610.00346}\underline {\textbf{~}}\underline {[physics.atm-clus]}; [3] Fojon et al, Phys. Rev. A \textbf{54}, 4923 (1996)