Knockout driven reactions in complex molecules and their clusters

Abstract

Energetic ions lose some of their kinetic energy when interacting with electrons or nuclei in matter. Here, we discuss combined experimental and theoretical studies on such impulse driven reactions in polycyclic aromatic hydrocarbons (PAHs), fullerenes, and pure or mixed clusters of these molecules. These studies show that the nature of excitation is important for how complex molecular systems respond to ion/atom impact. Rutherford-like nuclear scattering processes may lead to prompt atom knockout and formation of highly reactive fragments, while heating of the molecular electron clouds in general lead to formation of more stable and less reactive fragments. In this topical review, we focus on recent studies of knockout driven reactions, and present new calculations of the angular dependent threshold (displacement) energies for such processes in PAHs. The so-formed fragments may efficiently form covalent bonds with neighboring molecules in clusters. These unique molecular growth processes may be important in astrophysical environments such as low velocity shock waves.

Ion-induced molecular growth in clusters of small hydrocarbon chains

“…We identify molecular growth processes within the molecular clusters that appears to be driven by knockout processes and that could result in the formation of (aromatic) ring structures. These types of reactions are not unique to specific projectile ions and target molecules, but will occur whenever atoms or ions with suitable masses and kinetic energies collide with aggregates of matter, such as carbonaceous grains in the interstellar medium or aerosol nanoparticles in the atmosphere.Recently it has been shown that keV ions colliding with loosely bound clusters of PAHs or fullerenes can induce molecular growth within these clusters [25][26][27][28][29] . This growth is mainly driven by the prompt fragmentation of molecules in cluster when the impacting projectile ion deposits a large amount of energy and momentum to individual atoms through nuclear scattering processes 29 .…”

Stable Au–C bonds to the substrate for fullerene-based nanostructures

“…We consider C 59 molecules, resulting from the removal of a single C atom. While high-energy collisions can result in a wide range of products after removal of a series of fragments [23], it has been shown that sputtering of carbon materials with such low energies as in our case results in predominantly single vacancies [32–34]. C 59 molecules also have the highest energetic stability after C 60 [24–25] and, as described below, result in strong and stable bonds to the Au(111) surface, in particular stronger than those of C 58 .…”

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

“…Recently, these potentials were also utilized to study single and multiple atom knockouts from PAHs, fullerenes and their clusters (see Ref. [31] and references therein).…”

“…Recent advances in the understanding of ion/atom interactions with isolated polycyclic aromatic hydrocarbons (PAHs), fullerenes and their clusters were discussed in a a e-mail: verkhovtsev@iff.csic.es b On leave from A. F. Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia c On leave from A. F. Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia recent review [31]. Apart from well-known statistical fragmentation of carbon systems leading to evaporation of C 2 dimers, specific non-statistical fragmentation channels resulting in a prompt single-atom atom knockout have been observed [32][33][34][35][36][37].…”