Fusion mechanism in fullerene-fullerene collisions -- The deciding role of giant oblate-prolate motion

We provide answers to long-lasting questions in the puzzling behavior of fullerene-fullerene fusion: Why are the fusion barriers so exceptionally high and the fusion cross sections so extremely small? An ab initio nonadiabatic quantum molecular dynamics (NA-QMD) analysis of C$_{60}$+C$_{60}$ collisions reveals that the dominant excitation of an exceptionally giant oblate-prolate H$_g(1)$ mode plays the key role in answering both questions. From these microscopic calculations, a macroscopic collision model is derived, which reproduces the NA-QMD results. Moreover, it predicts analytically fusion barriers for different fullerene-fullerene combinations in excellent agreement with experiments.