Fullerene-fullerene Collisions Research Articles

Classical molecular dynamics simulations of fusion and fragmentation in fullerene-fullerene collisions

We present the results of classical molecular dynamics simulations of collision-induced fusion and fragmentation of C60 fullerenes, performed by means of the MBN Explorer software package. The simulations provide information on structural differences of the fused compound depending on kinematics of the collision process. The analysis of fragmentation dynamics at different initial conditions shows that the size distributions of produced molecular fragments are peaked for dimers, which is in agreement with a well-established mechanism of C60 fragmentation via preferential C2 emission.Atomic trajectories of the colliding particles are analyzed and different fragmentation patterns are observed and discussed. On the basis of the performed simulations, characteristic time of C2 emission is estimated as a function of collision energy.The results are compared with experimental time-of-flight distributions of molecular fragments and with earlier theoretical studies. Considering the widely explored case study of C60–C60 collisions, we demonstrate broad capabilities of the MBN Explorer software, which can be utilized for studying collisions of a broad variety of nanoscale and biomolecular systems by means of classical molecular dynamics.

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 C60 + C60 collisions reveals that the dominant excitation of an exceptionally “giant” oblate-prolate 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.

Calculation of the cross section for charge transfer in C 70 + + C60 collisions

Expressions for the charge transfer cross section in C60/70 fullerene-fullerene collisions are derived by using an instanton approximation for the tunnel splitting of energy levels. The resulting formulas are valid in the adiabatic approximation and provide an accurate description of available experimental data.

Calculation of the cross section for charge transfer in fullerene-fullerene collisions

An expression for the charge transfer cross section in fullerene-fullerene collisions is derived by using an instanton approximation for the tunnel splitting of energy levels. The expression is valid in the adiabatic approximation and provides an accurate description of available experimental data.

Thermal conductivity of carbon nanotube peapods

Thermal conductivity of a $(10,10)$ carbon nanotube filled with ${\mathrm{C}}_{60}$ fullerenes (or a peapod) is computed using direct molecular-dynamics simulations with the Tersoff-Brenner potential for $\mathrm{C}\text{\ensuremath{-}}\mathrm{C}$ bonding interactions and the van der Waals potential for nonbonding interactions. The temperature-dependent thermal conductivity of the peapod, while showing qualitatively similar behavior to that of an unfilled carbon nanotube, is found to be higher than the nanotube at all temperatures. This is in agreement with recent experimental observations. The increase in thermal conductivity in the peapod is explained through (a) an energy transfer between fullerenes and nanotube due to low-frequency radial vibration coupling between fullerenes and nanotube, and (b) energy transfer along the peapod axis due to fullerene-fullerene collisions.

Inelastic, quasi-elastic and charge transfer scattering in C 60++C 60 collisions

Differential cross-section data is presented for quasi-elastically scattered fullerene projectile ions in fullerene-fullerene collisions. The degree of inelasticity is reported as a function of collision energy and scattering angle. In addition, differential cross-section data are reported for resonant charge transfer. The data are used to correct previously reported total cross-section measurements for charge transfer that underestimated the loss of signal due to scattering.

Angular-resolved studies of fragmentation in fullerene-fullerene collisions

Fragmentation channels in collisions between fullerenes were studied as a function of collision energy (115--1400 eV center of mass) and scattering angle using a rotatable reflectron time-of-flight mass spectrometer. The products from fusion reactions and those from inelastically scattered (but not fused) projectile ions represent the two fragmentation channels in the collisions studied. The fragment size dependence is discussed as a function of collision energy and scattering angle. The results are in good qualitative agreement with theoretical models. A change in fragmentation behavior due to the onset of a finite-system analog of a phase transition in the reaction products can be seen in the mass and angular distributions of the fragment ions.

Fullerene-fullerene collisions

The results of experimental studies of fullerene-fullerene collisions are presented and compared with molecular dynamics simulations and statistical models. The similarities with and differences to nuclear heavy ion collisions are discussed.