Absolute fragmentation cross sections in atom-molecule collisions: Scaling laws for non-statistical fragmentation of polycyclic aromatic hydrocarbon molecules

Abstract

We present scaling laws for absolute cross sections for non-statistical fragmentation in collisions between Polycyclic Aromatic Hydrocarbons (PAH/PAH(+)) and hydrogen or helium atoms with kinetic energies ranging from 50 eV to 10 keV. Further, we calculate the total fragmentation cross sections (including statistical fragmentation) for 110 eV PAH/PAH(+) + He collisions, and show that they compare well with experimental results. We demonstrate that non-statistical fragmentation becomes dominant for large PAHs and that it yields highly reactive fragments forming strong covalent bonds with atoms (H and N) and molecules (C6H5). Thus nonstatistical fragmentation may be an effective initial step in the formation of, e.g., Polycyclic Aromatic Nitrogen Heterocycles (PANHs). This relates to recent discussions on the evolution of PAHNs in space and the reactivities of defect graphene structures.

Formation of H2 from internally heated polycyclic aromatic hydrocarbons: Excitation energy dependence

“…We will argue that it is likely that H 2 may form directly from pristine PAHs for sufficiently high internal energies which are not reached by absorption of single photons with energies below the Lyman limit. We will discuss the present experimental results on 11.25 keV He + + C 14 H 10 /C 16 H 10 /C 24 H 12 collisions and earlier experimental results 22,28 in view of the present detailed molecular structure calculations of PAH stabilities and a simple model 35 for estimates of electronic energy transfers in ion-PAH collisions. …”

“…Internal energies and temperatures of the molecules after collisions with He are calculated using a simple electronic stopping model. 35 In this model, the energy transfer to the PAH electron clouds is calculated assuming that the He atoms scatter inelastically on a free electron gas with a density distribution calculated for unperturbed PAHs by means of DFT. Energy differential cross sections are then calculated from 200 000 random He trajectories through the PAH electron clouds.…”

“…The latter is relevant for the present experimental study and the one by Champeaux et al 22 as strong interactions with the PAH electron clouds dominate the energy transfer for ion collision energies of a few keV and above. 35 As we will see below, this may lead to internal PAH excitation energies much larger than UV photo-absorption below 13.6 eV.…”

High-energy collisions of protonated enantiopure amino acids with a chiral target gas

“…From these studies, it was concluded that the nature of the collision gas has little influence on the product fragment intensity ratios [16,17]. Though, in recent studies with other molecules, the nature of the collision gas was observed to influence the fragmentation [18][19][20]. Chiral projectile ions, however, were not studied in high-energy collision experiments with chiral target gases.…”

Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces

“…However, advances in experimental and theoretical methods have revealed the existence of non-statistical/non-equilibrium effects in a number of chemical reactions [14][15][16][17][18][19][20][21][22]. These effects cannot be taken into account by TST (or related theories), and although they sometimes may be neglected in the calculation of highly averaged macroscopic coefficients, as thermal rate constants, they are of key importance in the analysis of the reaction from a microscopic point of view.…”