Fragmentation dynamics of fullerenes upon extreme electronic excitation near the giant resonance with XUV free-electron laser pulses*

Fullerenes serve as an ideal model system to investigate the complex dynamics in large molecules, which often exhibit a complex interplay of single- and many-body phenomena. The strong coupling between dense electronic states and phonon modes in fullerenes leads to complex energy absorption and dissipation pathways. We explore these processes by leveraging the collective resonance of C₆₀ to deposit a large amount of energy through intense XUV radiation from the FLASH free-electron laser over ultrashort timescales. Using a single-color pump-probe scheme, we measured the kinetic-energy spectra of both light and heavy ionic fragments as a function of the pump-probe delay. Our theoretical modeling revealed the formation of a transient nanoplasma, which explains the distinctive delay dependence of the doubly-charged carbon yield. Furthermore, this model is consistent with the Wigner threshold behavior observed in the kinetic-energy distributions of monomer and dimer ions.