We show that the measurement at high resolution of the kinetic energy gain spectrum of a highly charged ion (HCI) scattered and partly neutralized by a molecule, a nanocluster or a surface can reveal the excitation spectrum of the target. As a first application of the analysis, we demonstrate that the periodic oscillations in the measured energy gain spectra of energetic Arq+ ions flying by C60 molecules arise from the multiple excitations of C60 plasmons.