  Fullerene complexes may play a key role in the design of future molecular
electronics and nanostructured devices with potential applications in light
harvesting using organic solar cells. Charge and energy flow in these systems
is mediated by many-body effects. We studied the structure and dynamics of
laser-induced multi-electron excitations in isolated C$_{60}$ by two-photon
photoionization as a function of excitation wavelength using a tunable fs UV
laser and developed a corresponding theoretical framework on the basis of
\emph{ab initio} calculations. The measured resonance line width gives direct
information on the excited state lifetime. From the spectral deconvolution we
derive a lower limit for purely electronic relaxation on the order of
$\tau_\mathrm{el}=10^{+5}_{-3}$ fs. Energy dissipation towards nuclear degrees
of freedom is studied in time-resolved techniques. The evaluation of the
non-linear autocorrelation trace gives a characteristic time constant of
$\tau_\mathrm{vib}=400\pm100$ fs for the exponential decay. In line with the
experiment, the observed transient dynamics is explained theoretically by
nonadiabatic (vibronic) couplings involving the correlated electronic, the
nuclear degrees of freedom (accounting for the Herzberg-Teller coupling), and
their interplay.
