Internal Energy of Molecules Ejected Due to Energetic C₆₀ Bombardment

Abstract

The early stages of C 60 bombardment of octane and octatetraene crystals are modeled using molecular dynamics simulations with incident energies of 5-20 keV. Using the AIREBO potential, which allows for chemical reactions in hydrocarbon molecules, we are able to investigate how the projectile energy is partitioned into changes in potential and kinetic energy as well as how much energy flows into reacted molecules and internal energy. Several animations have been included to illustrate the bombardment process. The results show that the material near the edge of the crater can be ejected with low internal energies and that ejected molecules maintain their internal energies in the plume, in contrast to a collisional cooling mechanism previously proposed. In addition, a single C 60 bombardment was able to create many free and reacted H atoms which may aid in the ionization of molecules upon subsequent bombardment events.

Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

“…Precise measurements of these ion yields are difficult to obtain but estimates range from one parent ion per every 100 to 100 000 impacts. Recent measurements of useful yields for Ar + and SF 5 + bombardment [1] are consistent with this estimate. These yields seem incredibly small given that simulations of C 60 bombardment on molecular targets show that all the energy (10-120 keV) is deposited in the top 2-3 nm of the substrate in a time of 50-100 fs.…”

“…[5] These molecules fragment (larger gray spheres in the figure) and react in the next ∼0.5 ps. Subsequently, the intact molecules flow from the edge of the conical region as shown in Fig.…”

“…[5] As with the simulation on water with the dissociative potential, the reactions are confined to a cylinder under the impact point with a radius of ∼2 nm. The intact molecules initiate their motion off the surface by a fluid flow-type process.…”

Dynamics of large Ar cluster bombardment of organic solids

“…This observation is different from the data reported for ion emission and predictions of computer simulations performed at normal incidence on coarse-grained organic systems, where a strong dependence on the projectile size is observed. [10][11][12][13] In this study, we investigate the effect of a projectile size, its kinetic energy and the impact angle on ejection of intact molecules and fragments from an atomistic benzene crystal bombarded by large noble gas cluster projectiles. The results are utilized to explain why simulations performed at normal incidence may not always represent the data obtained with off-normal impact angles.…”

Simulation of Fragmentation of Polyethylene Glycol by Quantum Molecular Dynamics for TOF-SIMS Spectral Analysis

“…Fragmentation process was almost completed within 500 fs. In sputtering MD simulations for organic utmost surface layer [12], fragmentation of molecule after ion bombardment was also finished within 500 fs. Fig.3 shows experimental TOF-SIMS spectrum of PEG by using 20keV Au + .…”