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160 results on '"Thomas, Aaron M."'

1. Bimolecular Reaction Dynamics in the Phenyl–Silane System: Exploring the Prototype of a Radical Substitution Mechanism

Author

Lucas, Michael, Thomas, Aaron M, Yang, Tao, Kaiser, Ralf I, Mebel, Alexander M, Hait, Diptarka, and Head-Gordon, Martin

Subjects
Physical Sciences, Chemical Sciences, Atomic, Molecular and Optical Physics, Physical Chemistry, Chemical sciences, Physical sciences
Abstract

We present a combined experimental and theoretical investigation of the bimolecular gas-phase reaction of the phenyl radical (C6H5) with silane (SiH4) under single collision conditions to investigate the chemical dynamics of forming phenylsilane (C6H5SiH3) via a bimolecular radical substitution mechanism at a tetracoordinated silicon atom. Verified by electronic structure and quasiclassical trajectory calculations, the replacement of a single carbon atom in methane by silicon lowers the barrier to substitution, thus defying conventional wisdom that tetracoordinated hydrides undergo preferentially hydrogen abstraction. This reaction mechanism provides fundamental insights into the hitherto unexplored gas-phase chemical dynamics of radical substitution reactions of mononuclear main group hydrides under single collision conditions and highlights the distinct reactivity of silicon compared to its isovalent carbon. This mechanism might be also involved in the synthesis of cyanosilane (SiH3CN) and methylsilane (CH3SiH3) probed in the circumstellar envelope of the carbon star IRC+10216.

Published
2018

6. Photodissociation Dynamics of Astrophysically Relevant Propyl Derivatives (C3H7X; X = CN, OH, HCO) at 157 nm Exploiting an Ultracompact Velocity Map Imaging Spectrometer: The (Iso)Propyl Channel

Author

Paul, Dababrata, Yang, Zhenghai, Goettl, Shane J., Thomas, Aaron M., He, Chao, Suits, A.G, Parker, David H., Kaiser, Ralf I., Paul, Dababrata, Yang, Zhenghai, Goettl, Shane J., Thomas, Aaron M., He, Chao, Suits, A.G, Parker, David H., and Kaiser, Ralf I.

Abstract

Contains fulltext : 282389.pdf (Publisher’s version ) (Closed access)

Published
2022

10. Directed gas phase preparation of ethynylallene (H2CCCHCCH; X1A′) via the crossed molecular beam reaction of the methylidyne radical (CH; X2Π) with vinylacetylene (H2CCHCCH; X1A′).

Author

He, Chao, Yang, Zhenghai, Doddipatla, Srinivas, Thomas, Aaron M., Kaiser, Ralf I., Galimova, Galiya R., Mebel, Alexander M., Fujioka, Kazuumi, and Sun, Rui

Abstract

The gas-phase bimolecular reaction of the methylidyne (CH; X2Π) radical with vinylacetylene (H2CCHCCH; X1A′) was conducted at a collision energy of 20.3 kJ mol−1 under single collision conditions exploiting the crossed molecular beam experimental results merged with ab initio electronic structure calculations and ab initio molecular dynamics (AIMD) simulations. The laboratory data reveal that the bimolecular reaction proceeds barrierlessly via indirect scattering dynamics through long-lived C5H5 reaction intermediate(s) ultimately dissociating to C5H4 isomers along with atomic hydrogen with the latter predominantly originating from the vinylacetylene reactant as confirmed by the isotopic substitution experiments in the D1-methylidyne–vinylacetylene reaction. Combined with ab initio calculations of the potential energy surface (PES) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) calculations, the experimental determined reaction energy of −146 ± 26 kJ mol−1 along with the distribution minimum of T() at 90° and isotopic substitution experiments suggest ethynylallene (p1; ΔrG = −230 ± 4 kJ mol−1) as the dominant product. The ethynylallene (p1) may be formed with extensive rovibrational excitation, which would result in a lower maximum translational energy. Further, AIMD simulations reveal that the reaction dynamics leads to p1 (ethynylallene, 75%) plus atomic hydrogen with the dominant initial complex being i1 formed by methylidyne radical addition to the double C＝C bond in vinylacetylene. Overall, combining the crossed molecular beam experimental results with ab initio electronic structure calculations and ab initio molecular dynamics (AIMD) simulations, ethynylallene (p1) is expected to represent the dominant product in the reaction of the methylidyne (CH; X2Π) radical with vinylacetylene (H2CCHCCH; X1A′). [ABSTRACT FROM AUTHOR]

Published
2022
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19. Cheerleaders, the Anthem and the VFW

Author

Thomas, Aaron M.

Subjects
Social media, School districts, Misinformation, Education, Social sciences
Abstract

FOR MANY OF us in school leadership, social media has become a vital tool for connecting with colleagues and professional growth and an important vehicle for communicating with our various [...]

Published
2020

46. Combined Experimental and Computational Investigation of the Elementary Reaction of Ground State Atomic Carbon (C; 3Pj) with Pyridine (C5H5N; X1A1) via Ring Expansion and Ring Degradation Pathways

Author

Lucas, Michael, Thomas, Aaron M., Kaiser, Ralf I., Bashkirov, Eugene K., Azyazov, Valeriy N., and Mebel, Alexander M.

Abstract

We explored the elementary reaction of atomic carbon (C; 3Pj) with pyridine (C5H5N; X1A1) at a collision energy of 34 ± 4 kJ mol–1utilizing the crossed molecular beams technique. Forward-convolution fitting of the data was combined with high-level electronic structure calculations and statistical (RRKM) calculations on the triplet C6H5N potential energy surface (PES). These investigations reveal that the reaction dynamics are indirect and dominated by large range reactive impact parameters leading via barrier-less addition to the nitrogen atom and to two chemically nonequivalent “aromatic” carbon–carbon bonds forming three distinct collision complexes. At least two reaction pathways through atomic hydrogen loss were identified on the triplet surface. These channels involve multiple isomerization steps of the initial collision complexes via ring-openingand ring expansionforming an acyclic 1-ethynyl-3-isocyanoallyl radical (P1; 2A″) and a hitherto unreported seven-membered 1-aza-2-dehydrocyclohepta-2,4,6-trien-4-yl radical isomer (P3; 2A), respectively. For RRKM calculations at zero collision energy, representing conditions in cold molecular clouds, the ring expansion product P3is formed nearly exclusively for the atomic hydrogen loss channel, but based on these computations, the molecular fragmentation channel forming acetylene (C2H2) plus 3-cyano-2-propen-1-ylidene (P6; 3A″) accounts for nearly all of the degradation products of the reaction of atomic carbon with pyridine, proposing a destruction pathway of interstellar pyridine, which may account for the absence in the detection of pyridine in the interstellar medium. These results are also discussed in light of the isoelectronic carbon–benzene (C6H6; X1A1) system with important implications to the rapid degradation of nitrogen-bearing polycyclic aromatic hydrocarbons (NPAHs) in the interstellar medium compared to mass growth processes of PAH counterparts through ring expansion.

Published
2024
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