Polycyclic aromatic hydrocarbon formation chemistry in a plasma jet revealed by IR-UV action spectroscopy

Abstract

Large polycyclic aromatic hydrocarbons (PAHs) are the most abundant complex molecules in the interstellar medium; however, their possible formation pathways from small molecular species are still elusive. In the present work, we follow and characterize the formation of PAHs in an electrical discharge, specifically the PAH naphthalene in a molecular beam of argon. The fragments, products and reaction intermediates are unambiguously structurally identified by mass-selective IR-UV spectroscopy combined with quantum chemical calculations. This experiment provides evidence of the formation of larger PAHs containing up to four cyclic rings in the gas phase originating from a non-radical PAH molecule as a precursor. In addition to PAH formation, key resonance stabilized radical intermediates and intermediates containing di-acetylenic side groups are unambiguously identified in our experiment. We thereby not only reveal competing formation pathways to larger PAHs, but also identify intermediate species to PAH formation that are candidates for detection in radio-astronomy.

High-resolution infrared spectroscopy of naphthalene and acenaphthene dimers

“…The interactions governing cluster formation of small PAH molecules are receiving significant interest from both theoreticians and experimentalists [1][2][3][4][5][6][7]. The π-π stacking and/or CH-π interactions that may be present in these archetypal complexes can have important contributions to the structure of molecules or molecular complexes of interest in astrochemistry [8][9][10][11][12][13], biochemistry soot formation, and to the astrochemistry community because they form a link between isolated molecules and carbonaceous grains [8][9][10][11][12][13].…”

Physically inspired deep learning of molecular excitations and photoemission spectra

“…79,80 Polycyclic aromatic hydrocarbons are oen considered for the design of new organic lightemitting diode materials, eld-effect transistors or photovoltaics. 3,7,81 Their electronic properties make these molecules not only relevant for optoelectronic applications, but also for other research areas such as astrochemistry 82 and atmospherical chemistry. 83 The excitation spectra are predicted with the ML model trained on PBE0 orbital energies of the OE62 data set (denoted as ML(PBE0)) and the D-ML model trained on the difference of the ML(PBE0) model and the G0W0@PBE0 values of 4k datapoints of the GW5000 data set.…”

Analytical chemistry, formation, mitigation, and risk assessment of polycyclic aromatic hydrocarbons: From food processing to in vivo metabolic transformation

“…The HACA mechanism produces mostly cyclopenta‐fused PAHs (Kislov et al., 2013). Another study provided alternatives to the HACA mechanism by identifying intermediates containing acetylene and diacetylene side chains in the formation of larger PAHs with up to four rings (Lemmens, Rap, Thunnissen, Willemsen, & Rijs, 2020). The experimental results indicated that growth of one of the smallest PAHs, NAP, would result in the formation of phenanthrene (Phe) and pyrene (Pyr).…”