Quantum and classical features of the photoionization spectrum of C₆₀

By considering photoionization of the C$_{60}$ fullerene, we elucidate the contributions of various classical and quantum physics phenomena appearing in this process. By comparing the results, based on the {\it ab initio} and model approaches, we map the well-resolved features of the photoabsoprtion spectrum to single-particle and collective excitations which have the different physical nature. It is demonstrated that the peculiarities arising in the photoionization spectrum of C$_{60}$ atop the dominating plasmon excitations have the quantum origin. In particular, we demonstrate that a series of individual peaks can be assigned either to the optically allowed discrete transitions or to ionization of particular molecular orbitals of the system. The analysis performed gives a detailed information on the nature of numerous features in the photoabsorption spectrum of C$_{60}$.