PAH Growth in Flames and Space: Formation of the Phenalenyl Radical

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are intermediates in the formation of soot particles and interstellar grains. However, their formation mechanisms in combustion and interstellar environments are not fully understood. The production of tricyclic PAHs and, in particular, the conversion of a PAH containing a five-membered ring to one with a six-membered ring is of interest to explain PAH abundances in combustion processes. In the present work, resonant ionization mass spectrometry in conjunction with isotopic labelling is used to investigate the formation of the phenalenyl radical from acenaphthylene and methane in an electrical discharge. We show that in this environment, the CH cycloaddition mechanism converts a fivemembered ring to a six-membered ring. This mechanism can occur in tandem with other PAH 1 formation mechanisms such as hydrogen abstraction/ acetylene addition (HACA) to produce larger PAHs in flames and the interstellar medium.

Flipping Kinetics of the Water Trimer on Acenaphthylene: Persistence of a Highly Dipolar ddd Configuration at Interstellar Temperatures

“…As is known in the literature, an isolated water trimer adopts a cyclic, quasiplanar ring structure, whose equilibrium configuration can be conveniently represented by uud (where “ u ” and “ d ” denote a free hydrogen “up” and “down” regarding the O–O–O plane) . In turn, Ace is a tricyclic PAH of astrochemical interest that can favor geometrically the interaction of three O–H···π bonds with the water trimer, resulting in a ddd configuration with respect to the molecular plane. Thus, we have geometrically selected and calculated the molecular properties of four possible minimum structures of Ace···(H 2 O) 3 , and located a transition state (TS) for the ddu ↔ ddd flipping process of one of the water molecule above an Ace molecule.…”

New Carbenes and Cyclic Allenes Energetically Comparable to Experimentally Known 1-Azulenylcarbene

“…Unequivocally, if a molecule is polar (μ ≠ 0), then the laboratory rotational transitions are a pre-requisite for potential confirmation of the same molecules many light-years away. − Thus, a firm experimental and theoretical understanding of carbene and its related chemistry has become necessary for many related fields such as astrochemistry, combustion, and soot formation . Along the same lines, phenyl/naphthyl/azulenyl rings containing carbenes (arylcarbenes) have drawn considerable attention to the astrochemistry community because of their ease of thermal and photochemical transformations. − The recent discovery of four neutral molecules, cyclopentadiene (C 5 H 6 ), two isomers of ethynylcyclopentadiene (C 7 H 6 ), and indene (C 9 H 8 ), along with two of the C 5 H 2 carbenes aforementioned in the Taurus Molecular Cloud-1, ,, reinforces the possibility of polycyclic aromatic hydrocarbon (PAH) formation in space through resonance-stabilized carbene intermediates. − In this endeavor, C 11 H 8 is the next higher homologue potentially suitable for laboratory and radioastronomical studies . Our recent theoretical account on C 11 H 8 isomers established a fact that six low-lying indene isomers (2aH-cyclopenta­[ cd ]­indene, 7-ethynyl-1 H -indene, 4-ethynyl-1 H -indene, 6-ethynyl-1Hindene, 5-ethynyl-1 H -indene, and 7bH-cyclopenta­[cd]-indene) remain elusive till date in the laboratory .…”

Why Are MgC3H Isomers Missing in the Interstellar Medium?

“… 10 − 23 Therefore, logically analyzing astrochemical issues requires a coordinated effort from experts across the scientific community, which includes radioastronomers, astrophysicists, molecular spectroscopists, organic chemists, electrical engineers, and quantum information scientists. 24 − 33 As an example, let us take the case of a linear MgC 2 H radical. The pure rotational spectrum of 1-magnesaprop-2-yn-1-yl (MgC 2 H, 2 Σ + ) was recorded by Ziuyrs and co-workers in 1995.…”

“…Finding molecules many light years away is not only an open challenge to the scientific community but also an essential study that needs to be undertaken for a thorough understanding of star-forming regions, the formation of planets, and astrobiology. − To confirm the molecules in an unambiguous manner in the interstellar medium (ISM) and circumstellar shells, laboratory rest frequencies are an essential prerequisite in most cases. − Therefore, logically analyzing astrochemical issues requires a coordinated effort from experts across the scientific community, which includes radioastronomers, astrophysicists, molecular spectroscopists, organic chemists, electrical engineers, and quantum information scientists. − As an example, let us take the case of a linear MgC 2 H radical. The pure rotational spectrum of 1-magnesaprop-2-yn-1-yl (MgC 2 H, 2 Σ + ) was recorded by Ziuyrs and co-workers in 1995. , It was speculated at that time that MgC 2 H would be present in the ISM because it is isoelectronic with MgNC and MgCN .…”