Gas phase ion chemistry of titanium–oxofullerene with ligated solvents

Gas phase fragmentation events of fullerene-like titanium oxo-cluster anions were investigated in detail. The fragmentation channel of the ions was comparable to the fragmentation of C60 ions with systematic C2 losses which is a consequence of topological similarity.

Photoinduced polycyclic aromatic hydrocarbon dehydrogenation The competition between H- and H2-loss

Polycyclic aromatic hydrocarbons (PAHs) constitute a major component of the interstellar medium carbon budget, locking up to 10–20% of the elemental carbon. Sequential fragmentation induced by energetic photons leads to the formation of new species, including fullerenes. However, the exact chemical routes involved in this process remain largely unexplored. In this work, we focus on the first photofragmentation steps, which involve the dehydrogenation of these molecules. For this, we consider a multidisciplinary approach, taking into account the results from experiments, density functional theory (DFT) calculations, and modeling using dedicated Monte-Carlo simulations. By considering the simplest isomerization pathways — i.e., hydrogen roaming along the edges of the molecule — we are able to characterize the most likely photodissociation pathways for the molecules studied here. These comprise nine PAHs with clearly different structural properties. The formation of aliphatic-like side groups is found to be critical in the first fragmentation step and, furthermore, sets the balance of the competition between H- and H2-loss. We show that the presence of trio hydrogens, especially in combination with bay regions in small PAHs plays an important part in the experimentally established variations in the odd-to-even H-atom loss ratios. In addition, we find that, as PAH size increases, H2 formation becomes dominant, and sequential hydrogen loss only plays a marginal role. We also find disagreements between experiments and calculations for large, solo containing PAHs, which need to be accounted for. In order to match theoretical and experimental results, we have modified the energy barriers and restricted the H-hopping to tertiary atoms. The formation of H2 in large PAHs upon irradiation appears to be the dominant fragmentation channel, suggesting an efficient formation path for molecular hydrogen in photodissociation regions (PDRs).

XUV-induced reactions in benzene on sub-10 fs timescale: nonadiabatic relaxation and proton migration

Short XUV pulses produce excited cationic states of benzene. Their dynamics are probed by few-cycle VIS/NIR pulses. Very fast τ ≈ 20 fs nonadiabatic processes dominate the relaxation. In the CH3+ fragmentation channel a non-trivial transient behaviour is observed.

STABILITIES AND FRAGMENTATION BEHAVIORS OF Agn CLUSTERS (n = 2–34)

A global search on the lowest-energy structures of the medium-sized silver clusters Ag n(n = 21–34) was performed by using a genetic algorithm (GA) coupled with a tight-binding (TB) method. Structures, binding energies per atom, second differences in energies, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO), and fragmentation behaviors of Ag n(n = 21–34) are investigated by using DFT method. The calculated results show that the neutral silver clusters prefer to decay by evaporation of a monomer except a small sized silver cluster ( Ag 4), which favors a dimmer evaporation. For the collision induced dissociation of cationic silver clusters, decaying a silver atom is found to be the dominant fragmentation channel. But for some small sized cationic silver clusters, a neutral dimmer evaporation is found to be energetically favorable. Our calculated results are consistent with previous studies.

Fragmentation and Gas Phase Aggregation Processes in the Laser Desorption/Ionization of Chlorodiaminotriazines

Fragmentation and supramolecular aggregation induced during the laser desorption/ionization (LDI) of four chlorodiaminotriazines (simazine, atrazine, terbutylazine and propazine) have been investigated. The laser wavelength employed (266 nm) lies within the first absorption band of the four triazines. The main fragmentation channel observed involves the prompt cleavage of the Cl atom, followed by partial or total fragmentation of the side alkyl chains. Breakage of the triazinic ring becomes efficient at moderate laser powers; however, the deamination of the triazine is not observed to take place. In addition, the formation of both covalent and non-covalent triazinic aggregates in the desorption plume is found to be particularly efficient. Aggregates as large as heptamers are neatly detected, with the observation that those with the most intense signal involve the dechlorinated triazinic fragment. Both aggregation and fragmentation are largely suppressed upon dilution of the triazine under matrix-assisted laser desorption/ionization conditions.