We previously predicted [P. A. Hervieux et al., Phys. Rev. A 95, 020701(R) (2017)] that, owing to predominant electron capture by incoming positrons from the molecular shell, ${\mathrm{C}}_{60}$ acts like a spherical diffractor inducing resonances in the positronium (Ps) formation as a function of the positron impact energy. By extending the study for a larger ${\mathrm{C}}_{240}$ fullerene target, we now demonstrate that the diffraction resonances compactify in energy in analogy to the shrinking fringe separation for larger slit size in classical single-slit experiment. The result provides further impetus for conducting Ps spectroscopic experiments with fullerene targets, including target- and/or captured-level differential measurements. The ground states of the fullerenes are modeled in a spherical jellium frame of the local-density approximation method with the exchange-correlation functional based on the van Leeuwen-Baerends model potential [R. van Leeuwen and E. J. Baerends, Phys. Rev. A 49, 2421 (1994)], while the positron impact and Ps formation are treated in the continuum distorted-wave final-state approximation.

• Received 1 July 2019
• Revised 5 September 2019

DOI:https://doi.org/10.1103/PhysRevA.100.042701