Alexander M. Mebel’s research while affiliated with Florida International University and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (396)


Computational Study of the Gas-Phase Thermal Degradation and the Reaction Rate Coefficients of Perfluoroalkyl Ether Carboxylic Acids
  • Article

February 2025

·

3 Reads

The Journal of Physical Chemistry A

Claude-Bernard Paultre

·

Alexander M Mebel

·

Kevin E O'Shea



Potential energy diagram of the reaction of acepyrene with coronene radical. Relative energies are in kcal/mol. The shallow well in the entrance channel denotes non-equilibrium physical dimerization.
Blue: histogram of the total energy E produced in NVT MD simulations of the coronene–acepyrene pair of PAHs (189 degrees of freedom) simulations. Red: normal distribution with the mean μ and standard deviation σ as in the energy histogram.
Two-exponential dissociation kinetics of mid-size PAH collisional complexes. Solid lines are exponential fits: red represents pyrene/pyrenyl–acepyrene; blue represents coronene/coronene radical–acepyrene.
(a) and (c) Fast- and (b) and (d)] slow-stage temporal dependences of the (a) and (b) COMS coordinate and (c) and (d) inter-monomer potential energy for the coronene–acepyrene dimer averaged over trajectories with the lifetimes of 2.5, 3, 3.5, 7, 9, and 11 ps.
Monomer size effect in inelastic collisional dynamics of non-equilibrium soot nucleation
  • Article
  • Publisher preview available

December 2024

·

10 Reads

Molecular dynamics (MD) simulations of the collisional dynamics of the coronene–acepyrene and coronene radical–acepyrene pairs have been carried out to investigate the size effect of monomers of polycyclic aromatic hydrocarbons (PAH) on their non-equilibrium dimerization. The results compared to the previous MD simulations of the smaller pyrene–acepyrene and pyrenyl–acepyrene systems corroborate the non-equilibrium hypothesis of crosslinking PAH dimerization enhanced by physical interaction between the monomers. The phenomenon of inelastic collisional dynamics responsible for non-equilibrium van der Waals dimerization, which fosters a covalent bond formation between the monomers, amplifies with increasing PAH size. The increase in the size of the colliding monomers enhances the non-equilibrium effects as the growing pool of low-frequency modes provides a larger sink for the energy of the colliding PAH monomers. Based on the direct count of the crosslinking reaction events observed in the MD simulations, the forward rate constant for the coronene radical–acepyrene association is estimated at ∼10⁻¹¹ cm³ molecule⁻¹ s⁻¹, showing a 15-fold increase with respect to the value from the statistical Rice–Ramsperger–Kassel–Marcus calculations. A comparison with the eightfold increase reported previously for the pyrenyl–acepyrene system shows that the statistical (equilibrium-based) calculations increasingly underestimate the reaction rate with the increasing size of the interacting PAHs from pyrene to coronene. The total increase of the MD-assessed rate constant for the coronene radical–acepyrene dimerization reaction as compared to pyrenyl–acepyrene is a factor of 2.4, with the overall collision efficiency to produce dimerized products growing by 30%.

View access options

Low-temperature gas-phase formation of cyclopentadiene and its role in the formation of aromatics in the interstellar medium

December 2024

·

63 Reads

Proceedings of the National Academy of Sciences

The cyclopentadiene (C 5 H 6 ) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (C 20 H 10 ), nanobowls (C 40 H 10 ), and fullerenes (C 60 ) in deep space. However, the underlying elementary gas-phase processes synthesizing cyclopentadiene from acyclic hydrocarbon precursors have remained elusive. Here, by merging crossed molecular beam experiments with rate coefficient calculations and comprehensive astrochemical modeling, we afford persuasive testimony on an unconventional low-temperature cyclization pathway to cyclopentadiene from acyclic precursors through the reaction of the simplest diatomic organic radical—methylidyne (CH)—with 1,3-butadiene (C 4 H 6 ) representing main route to cyclopentadiene observed in TaurusMolecular Cloud. This facile route provides potential solution for the incorporation of the cyclopentadiene moiety in complex aromatic systems via bottom–up molecular mass growth processes and offers an entry point to the low-temperature chemistry in deep space leading eventually to nonplanar PAHs in our carbonaceous Universe.






Figure 1. Pathways to pyridine and (iso)quinoline. A chain of reactions initiated through the formation of methylene amidogen radical (H2CN • ) and cyanomethyl radical (H2CCN • ) lead to the simplest representative of mono and bicyclic aromatic molecules carrying nitrogen. The reactions of atomic carbon and dicarbon with ammonia leading to methylene amidogen radical (5) and cyanomethyl radical (4) are investigated via our crossed molecular beam machine; our calculations also predict the formation of pyridine (1) and pyridinyl radicals (9-11) through the reactions of methylene amidogen with i/n-C4H3 and of cyanomethyl with propargyl. The reactions of pyridinyl radicals (9-11) with vinylacetylene (C4H4) forming (iso)quinoline are depicted in Ref. 29.
Figure 2. Laboratory data of the C-ND3 and C2-NH3 reactions. Laboratory angular distributions (A, C), and time-of-flights (B, D) for the carbon -D3-ammonia (A, B) and dicarbon -ammonia (C, D) reactions. The solid circles with their error bars represent the normalized experimental distribution; the open circles indicate the experimental data. The red lines represent the best fits obtained. Atoms are color coded as follows: carbon, gray; nitrogen, blue; deuterium, light blue; and hydrogen, white.
Figure 3. CM functions of the C-ND3 and C2-NH3 reactions. Center-of-mass translational energy distributions (P(ET); A, D), angular flux distributions (T(θ); B, E), and the corresponding flux contour map (C, F) for the carbon -D3-ammonia (A, B, C) and dicarbonammonia (D, E, F) reactions. The red lines represent the best-fit; shaded areas depict the error limits of the best fits.
Figure S5. Compilation of key bimolecular reactions and photodissociation processes newly introduced into the astrochemical model for TMC-1 leading to pyridine, pyridinyl, and (iso)quinoline.
Low temperature formation of pyridine and (iso)quinoline via neutral neutral reactions

June 2024

·

118 Reads

Aromatic molecules represent fundamental building blocks in prebiotic chemistry and are contemplated as vital precursors to DNA and RNA nitrogen bases. However, despite the identification of some 300 molecules in extraterrestrial environments, the pathways to pyridine (C5H5N), pyridinyl (C5H4N), and (iso)quinoline (C9H7N) the simplest representative of mono and bicyclic aromatic molecule carrying nitrogen are elusive. Here, we afford compelling evidence on the gas phase formation of methylene amidogen (H2CN) and cyanomethyl (H2CCN) radicals via molecular beam studies and electronic structure calculations. The modeling of the chemistries of Taurus Molecular Cloud (TMC 1) and Titans atmosphere contemplates a complex chain of reactions synthesizing pyridine, pyridinyl, and (iso)quinoline from H2CN and H2CCN at levels of up to 75%. This study affords unique entry points to precursors of DNA and RNA nitrogen bases in hydrocarbon rich extraterrestrial environments thus changing the way we think about the origin of prebiotic molecules in our Galaxy.


Citations (58)


... Since the HAVA mechanism generally involves only submerged barriers, it can operate at low temperatures like those in dense molecular clouds. Recently, the reaction between the phenylethynyl radical (C 6 H 5 CC • ) and benzene has been proposed as another viable bottom-up mechanism to form phenanthrene at low temperature 40 . However, vinylacetylene addition to the 4-phenanthrenyl radical is not expected to form pyrene 41 . ...

Reference:

Detections of interstellar aromatic nitriles 2-cyanopyrene and 4-cyanopyrene in TMC-1
Exploring the chemical dynamics of phenanthrene (C14H10) formation via the bimolecular gas-phase reaction of the phenylethynyl radical (C6H5CC) with benzene (C6H6)
  • Citing Article
  • May 2024

Faraday Discussions

... A previous study revealed that the potency of fentanyl analogues varies based on molecular variations at para, ortho, and meta positions. 23 These results confirm this concept reflected in the data presented as specific levels of BChE inhibition occurred when exposed to different fentanyl analogues, which is highlighted in the inhibitory patterns represented in Figure 8. ...

Differentiating Structurally Similar Fentanyl Analogs by Comparing Density Functional Theory (DFT) Calculations and Surface-Enhanced Raman Spectroscopy (SERS) Results
  • Citing Article
  • April 2024

Applied Spectroscopy

... The same applies when Hg 0 (aq) is removed from the solution, e.g., by a gas stream. Hg 2 2+ can be a major speciation component in heavily polluted waters (Fang et al., 2024), but is insignificant in the atmosphere. ...

Transformation of Mercurous [Hg(I)] Species during Laboratory Standard Preparation and Analysis: Implication for Environmental Analysis
  • Citing Article
  • April 2024

Environmental Science and Technology

... One of the main stages of the synthesis and destruction of PAHs is the sequential addition of acetylene molecules, atomic or molecular hydrogen or various hydrocarbon radicals to PAH molecules, usually consisting of several five-and six-member ring fragments [5][6][7][8][9][10][11][12][13][14]. Fusion reactions of two or more hydrocarbon fragments into a single complex are also one of possible growth mechanism of soot particles [15][16][17]. ...

Phenalenyl growth reactions and implications to prenucleation chemistry of aromatics in flames
  • Citing Article
  • April 2024

Physical Chemistry Chemical Physics

... Besides the intensively investigated reactions discussed above, a diverse range of other plasmon-driven bondcleaving reactions, including but not limited to N-H bond cleavage in mercaptopyridine [177] and hypoxanthine [178], C-B bond cleavage in mercaptophenylboronic acid [179], C-N bond cleavage in para-nitrothiophenol [180], azo bond cleavage in 4,4 ′ -dimercaptoazobenzene [181], O-O bond cleavage in hydrogen peroxide [182], [183], C-I bond cleavage in diaryliodonium salts [184], [185], C-H bond cleavage in aromatic methyl groups [186], and C-O bond cleavage in 1-phenoxy-2-phenylethane [187], allyl phenyl ether [188], and alkoxyamines [189], have also been reported in the literature. The experimental observations reported so far suggest that these reactions are primarily driven by either injection of hot carriers into the molecular adsorbates or plasmon-enhanced intramolecular electronic excitations. ...

Plasmon-mediated dehydrogenation of the aromatic methyl group and benzyl radical formation

... This radiosensitization enhancement is believed to be attributed to the generation of nitrogen centered radicals (NCRs) such as the oxidizing neutral, π-type aminyl radical (RNH•) [25][26][27][28] and their subsequent reactions [29][30][31] known to play an important role in peptide cellular signaling [32][33][34] and conjugation [35]. Employing a combination of electron spin resonance (ESR) spectroscopy at low temperature, pulse radiolysis at ambient temperature and theoretical calculations, we previously showed that azidosubstituted nucleosides and sugars form NCRs specifically at the site of the azide group via dissociative electron attachment (DEA) [25][26][27][28][36][37][38]. Thus, addition of an electron to the azido group in 5-AmdU forms the highly unstable azide anion radical (RN 3 •‾) which following facile N 2 loss forms the highly basic nitrene anion radical (RN•‾). ...

6-azido and 6-azidomethyl uracil nucleosides
  • Citing Article
  • October 2023

Nucleosides Nucleotides & Nucleic Acids

... Finally, the T(θ) function exhibits a forwardbackward symmetry with sideway scattering and hence a distribution maximum at 90 o . These results propose indirect scattering dynamics via the formation of long-lived C2NH3 intermediates 33 . ...

Gas-phase formation of the resonantly stabilized 1-indenyl (C9H7•) radical in the interstellar medium

Science Advances

... The experiments were conducted at the VUV beamline (BL03U) at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China [9]. Details of the experimental setup are documented in previous publications [10]. Briefly, the reactor consists of a 40 mm long silicon carbide (SiC) tube located in a high vacuum chamber (~10 -6 Torr). ...

Gas-phase preparation of azulene (C10H8) and naphthalene (C10H8) via the reaction of the resonantly stabilized fulvenallenyl and propargyl radicals

... Pyrazole, as an aromatic heterocycle with π-electron excess, displays distinct reactivity patterns in organic chemistry. Nucleophilic attacks are favored at positions 3 and 5, while electrophilic substitution reactions preferentially take place at position 4 [10] ( Figure 2). Unsubstituted pyrazole can be represented in three distinct tautomeric forms, as illustrated in Figure 3. ...

Completion of Crystallographic Data for the Series of 4-Halogenated-1H-pyrazoles: Crystal Structure Determination of 4-Iodo-1H-pyrazole and Spectroscopic Comparison

Crystals