C60–C+60 collisions: Semiempirical molecular dynamics simulations

Semiempirical molecular dynamics is used to study the collision of C60 and C+60. Particles are propagated classically using forces calculated from the modified neglect of differential overlap (MNDO) Hamiltonian. By assigning different collision energies (Ec) and impact parameters (b) to the Buckminster fullerenes (buckyballs), we simulated six collision events: four head on collisions with impact parameter b=0 and collisions energies of 100, 150, 200, and 400 eV, and two collisions with b=1.5 Rb (Rb=buckyball radius) and Ec=100 and 400 eV. The head on collisions show that at 100 eV the two buckyballs scatter off one another and at 200 and 400 eV they fuse, while at 150 eV they either scatter or form a metastable dimer depending on how the simulation is prepared. This barrier is consistent with recent experiments. In addition, we observe tetrahedral bonding in the C+120 structure formed in the 200 eV, b=0 collision, while at 400 eV, b=0 we see large rings and chains of carbon atoms. The off center collisions also display interesting structural features. In the 100 eV b=1.5 Rb collision, the buckyballs graze one another, distorting their cage structure and scattering at an angle relative to their incident velocities. The buckyballs in the 400 eV, b=1.5 Rb collision also scatter, but in contrast to the 100 eV, b=1.5 Rb collision, the individual buckyballs are severely distorted, forming what we refer to as an ‘‘open mouth’’ structure.