Collisional dynamics of C60 with noble-gas-atoms studied by molecular dynamics with empirical two- and three-body forces

Abstract

Abstract. The dynamics of C6o-rare gas collisions is studied using molecular dynamics with empirical two-and three-body forces. The carbon potential is chosen to be able to reproduce the experimentally determined bond lengths and cluster radius of C6o as well as the structure of small carbon clusters. The reaction channels observed can be divided into four categories: deep inelastic scattering, fragmentation, capture and inelastic scattering. The temperature dependence of the threshold energy for capture is studied and compared with available experimental data. The calculations predict a maximum in the lowest tail of the kinetic-energy distribution of the projectile with a transition from a single-to a double-humped maximum with increasing collision energy and, in addition, may provide a natural interpretation for the, as yet unexplained, structure in the experimental shapes.

He capture by negatively charged Buckminsterfullerene

“…Molecular dynamics simulations in which the internal energy dependence of the capture process has been investigated [6] predicted a decrease in the threshold energy of 1.4 eV on increasing the internal energy by about 30 eV, in very good agreement with the results shown in Fig. 1.…”

“…It may seem surprising at first sight that the intensities of the capture peak are identical in both sets of results. During the capture process practically the entire available centre of mass collision energy is converted into internal energy of the C6o (mainly deformation and vibrational energy) [6]. In the positive ion case, this additional internal energy can then lead to metastable fragmentation of the C6o cage and/or release of the captured atom on passage through the mass spectrometer.…”

“…The threshold energy for the capture process in collisions between positively charged Coo and neutral He and Ne atoms has been reported by Campbell et al [4]. Molecular dynamics calculations using empirical forces [2,6] give good agreement with the experimentally determined threshold energies as do estimates obtained by using ab initio molecular orbital calculations for the barrier for penetration of a benzene ring by the rare gas atom [7]. Interestingly, very different threshold energies are obtained for the collision systems C + ÷ Ne (9 __ 1 eV [4]) and Ne + ÷ C6o ( > 20 eV [5]).…”

“…The neutral Coo, on the other hand, was produced by heating to 350 °C [5] and thus had an internal energy of about 3.5 eV estimated from the known vibrational frequencies [ 10]. Recent molecular dynamics simulations [6] have shown, however, that the temperature effect can only account for a difference of 1.5 to 2 eV in the threshold energy so that the observations are probably mainly due to the increased polarisation effects expected for the Ne + + Coo case. …”

Photofragmentation of C60

“…The model which we have used for C6o has already been described in detail [25] and was developed by Brenner [26] to describe bond breaking and formation in hydrocarbon systems. The model assumes that the fragmentation is a statistical process dependent only on the internal vibrational excitation of the molecule, which is certainly over simplified considering the discussion of our results in Sect.…”