Formation and Stability of C6H3+ Isomers

Fingerprinting fragments of fragile interstellar molecules: dissociation chemistry of pyridine and benzonitrile revealed by infrared spectroscopy and theory

The cationic fragmentation products in the dissociative ionization of pyridine and benzonitrile have been studied by infrared action spectroscopy in a cryogenic ion trap instrument at the Free-Electron Lasers for Infrared eXperiments (FELIX) Laboratory. A comparison of the experimental vibrational fingerprints of the dominant cationic fragments with those from quantum chemical calculations revealed a diversity of molecular fragment structures. The loss of HCN/HNC is shown to be the major fragmentation channel for both pyridine and benzonitrile. Using the determined structures of the cationic fragments, potential energy surfaces have been calculated to elucidate the nature of the neutral fragment partner. In the fragmentation chemistry of pyridine, multiple non-cyclic structures are formed, whereas the fragmentation of benzonitrile dominantly leads to the formation of cyclic structures. Among the fragments are linear cyano-(di)acetylene˙+, methylene-cyclopropene˙+ and o- and m-benzyne˙+ structures, the latter possible building blocks in interstellar polycyclic aromatic hydrocarbon (PAH) formation chemistry. Molecular dynamics simulations using density functional based tight binding (MD/DFTB) were performed and used to benchmark and elucidate the different fragmentation pathways based on the experimentally determined structures. The implications of the difference in fragments observed for pyridine and benzonitrile are discussed in an astrochemical context.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

Synchrotron radiation provides insight into spectroscopy and dynamics in clusters and nanoparticles.

Searching for double σ- and π-aromaticity in borazine derivatives

Inspired by the double-aromatic (σ and π) C₆H₃⁺, C₆I₆²⁺, and C₆(SePh)₆²⁺ ring-shaped compounds, herein we theoretically study their borazine derivative analogues. The systems studied are the cation and dications with formulas B₃N₃H₃⁺, B₃N₃Br₆²⁺, B₃N₃I₆²⁺, B₃N₃(SeH)₆²⁺, and B₃N₃(TeH)₆²⁺. Our DFT calculations indicate that the ring-shaped planar structures of B₃N₃H₃⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ are more stable in the singlet state, while those of B₃N₃Br₆²⁺ and B₃N₃(SeH)₆²⁺ prefer the triplet state. Besides, exploration of the potential energy surface shows that the ring-shaped structure is the putative global minimum only for B₃N₃I₆²⁺. According to chemical bonding analysis, B₃N₃H₃⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ have σ and π delocalized bonds. The number of delocalized σ/π electrons is 2/6 for the first, and 10/6 for the second and third, similar to what their carbon analogs exhibit. Finally, the analysis of the magnetically induced current density allows B₃N₃H₃⁺, B₃N₃I₆²⁺, and B₃N₃(TeH)₆²⁺ to be classified as strongly σ aromatic, and poorly π aromatic compounds.

Evolutionary algorithms, Born–Oppenheimer molecular dynamics and the magnetic criteria of aromaticity have been used to evaluate the stability and σ–π aromaticity of borazine derivatives in order to expand the family of double aromatics systems.

Ion-induced molecular growth in clusters of small hydrocarbon chains

We report on studies of collisions between 3 keV Ar⁺ projectile ions and neutral targets of isolated 1,3-butadiene (C₄H₆) molecules and cold, loosely bound clusters of these molecules. 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.

Hydrocarbon growth via ion-molecule reactions: computational studies of the isomers of C4H2+, C6H2+ and C6H4+ and their formation paths from acetylene and its fragments

Structures, vibrational and electronic spectra, and AIMD trajectories of formation paths for C₄H₂⁺, C₆H₂⁺ and C₆H₄⁺ from acetylene ion and its fragments are reported in this article.