Fusion and rainbow scattering of ${\mathrm{C}}_{60}^{+}$ on crystalline fullerite films

Impact of ${\mathrm{C}}_{60}^{+}$ ions onto an epitaxially grown crystalline fullerite target is studied at a primary kinetic energy of 275 eV as a function of the angle of incidence. Scattered ions are investigated by velocity selective time-of-flight mass spectrometry at a fixed scattering angle of 140°. In addition to scattering of intact ${\mathrm{C}}_{60}^{+}$ ions we also see desorbed ${\mathrm{C}}_{70}^{+}$ as well as larger ions ${\mathrm{C}}_{100}^{+}$ to ${\mathrm{C}}_{130}^{+}$ arising from reactive processes (fusion, coalescence). The velocity distribution of the receding ${\mathrm{C}}_{60}^{+}$ ions reveals a range of processes from nearly elastic to fully inelastic. The angular dependence exhibits rich structure. This may be attributed to rainbow scattering, as confirmed by a simple classical trajectory calculation.