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1. Chemical dynamics study on the gas-phase reaction of the D1-silylidyne radical (SiD; X 2 Π) with deuterium sulfide (D 2 S) and hydrogen sulfide (H 2 S)

   https://doi.org/10.1039/d1cp01629f  

   Goettl, Shane J. ; Doddipatla, Srinivas ; Yang, Zhenghai ; He, Chao ; Kaiser, Ralf I. ; Silva, Mateus X. ; Galvão, Breno R. ; Millar, Tom J. ( June 2021 , Physical Chemistry Chemical Physics)

   The reactions of the D1-silylidyne radical (SiD; X 2 Π) with deuterium sulfide (D 2 S; X 1 A 1 ) and hydrogen sulfide (H 2 S; X 1 A 1 ) were conducted utilizing a crossed molecular beams machine under single collision conditions. The experimental work was carried out in conjunction with electronic structure calculations. The elementary reaction commences with a barrierless addition of the D1-silylidyne radical to one of the non-bonding electron pairs of the sulfur atom of hydrogen (deuterium) sulfide followed by possible bond rotation isomerization and multiple atomic hydrogen (deuterium) migrations. Unimolecular decomposition of the reaction intermediates lead eventually to the D1-thiosilaformyl radical (DSiS) (p1) and D2-silanethione (D 2 SiS) (p3) via molecular and atomic deuterium loss channels (SiD–D 2 S system) along with the D1-thiosilaformyl radical (DSiS) (p1) and D1-silanethione (HDSiS) (p3) through molecular and atomic hydrogen ejection (SiD–H 2 S system) via indirect scattering dynamics in barrierless and overall exoergic reactions. Our study provides a look into the complex dynamics of the silicon and sulfur chemistries involving multiple deuterium/hydrogen shifts and tight exit transition states, as well as insight into silicon- and sulfur-containing molecule formation pathways in deep space. Although neither of the non-deuterated species – the thiosilaformyl radical (HSiS) and silanethione (H 2 SiS) – have been observed in the interstellar medium (ISM) thus far, astrochemical models presented here predict relative abundances in the Orion Kleinmann-Low nebula to be sufficiently high enough for detection. 

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2. Combined Crossed Molecular Beams and Ab Initio Study of the Bimolecular Reaction of Ground State Atomic Silicon (Si; 3 P) with Germane (GeH 4 ; X 1 A 1 )

   https://doi.org/10.1002/cphc.202100235  

   Krasnoukhov, Vladislav S. ; Azyazov, Valeriy N. ; Mebel, Alexander M. ; Doddipatla, Srinivas ; Yang, Zhenghai ; Goettl, Shane ; Kaiser, Ralf I. ( June 2021 , ChemPhysChem)

   The chemical dynamics of the elementary reaction of ground state atomic silicon (Si;³P) with germane (GeH₄; X¹A₁) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol⁻¹exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium‐hydrogen bonds forming a triplet collision complex (HSiGeH₃;³i1). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH₃;¹i1). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H₃SiGeH isomeri5. This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly‐structured isomer¹p1(Si(μ‐H₂)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts toi6andi7, followed by fragmentation of each of these intermediates, could also form¹p1(Si(μ‐H₂)Ge) along with molecular hydrogen. The overall non‐adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist.

    

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3. A chemical dynamics study of the reaction of the methylidyne radical (CH, X 2 Π) with dimethylacetylene (CH 3 CCCH 3 , X 1 A 1g )

   https://doi.org/10.1039/D1CP04443E  

   He, Chao ; Fujioka, Kazuumi ; Nikolayev, Anatoliy A. ; Zhao, Long ; Doddipatla, Srinivas ; Azyazov, Valeriy N. ; Mebel, Alexander M. ; Sun, Rui ; Kaiser, Ralf I. ( December 2021 , Physical Chemistry Chemical Physics)

   The gas-phase reaction of the methylidyne (CH; X 2 Π) radical with dimethylacetylene (CH 3 CCCH 3 ; X 1 A 1g ) was studied at a collision energy of 20.6 kJ mol −1 under single collision conditions with experimental results merged with ab initio calculations of the potential energy surface (PES) and ab initio molecule dynamics (AIMD) simulations. The crossed molecular beam experiment reveals that the reaction proceeds barrierless via indirect scattering dynamics through long-lived C 5 H 7 reaction intermediate(s) ultimately dissociating to C 5 H 6 isomers along with atomic hydrogen with atomic hydrogen predominantly released from the methyl groups as verified by replacing the methylidyne with the D1-methylidyne reactant. AIMD simulations reveal that the reaction dynamics are statistical leading predominantly to p28 (1-methyl-3-methylenecyclopropene, 13%) and p8 (1-penten-3-yne, 81%) plus atomic hydrogen with a significant amount of available energy being channeled into the internal excitation of the polyatomic reaction products. The dynamics are controlled by addition to the carbon–carbon triple bond with the reaction intermediates eventually eliminating a hydrogen atom from the methyl groups of the dimethylacetylene reactant forming 1-methyl-3-methylenecyclopropene (p28). The dominating pathways reveal an unexpected insertion of methylidyne into one of the six carbon–hydrogen single bonds of the methyl groups of dimethylacetylene leading to the acyclic intermediate, which then decomposes to 1-penten-3-yne (p8). Therefore, the methyl groups of dimethylacetylene effectively ‘screen’ the carbon–carbon triple bond from being attacked by addition thus directing the dynamics to an insertion process as seen exclusively in the reaction of methylidyne with ethane (C 2 H 6 ) forming propylene (CH 3 C 2 H 3 ). Therefore, driven by the screening of the triple bond, one propynyl moiety (CH 3 CC) acts in four out of five trajectories as a spectator thus driving an unexpected, but dominating chemistry in analogy to the methylidyne – ethane system. 

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4. Directed Gas Phase Formation of the Elusive Silylgermylidyne Radical (H 3 SiGe, X 2 A′′)

   https://doi.org/10.1002/cphc.202000913  

   Yang, Zhenghai ; Doddipatla, Srinivas ; Kaiser, Ralf I. ; Krasnoukhov, Vladislav S. ; Azyazov, Valeriy N. ; Mebel, Alexander M. ( December 2020 , ChemPhysChem)

   The previously unknown silylgermylidyne radical (H₃SiGe; X²A′′) was prepared via the bimolecular gas phase reaction of ground state silylidyne radicals (SiH; X²Π) with germane (GeH₄; X¹A₁) under single collision conditions in crossed molecular beams experiments. This reaction begins with the formation of a van der Waals complex followed by insertion of silylidyne into a germanium‐hydrogen bond forming the germylsilyl radical (H₃GeSiH₂). A hydrogen migration isomerizes this intermediate to the silylgermyl radical (H₂GeSiH₃), which undergoes a hydrogen shift to an exotic, hydrogen‐bridged germylidynesilane intermediate (H₃Si(μ‐H)GeH); this species emits molecular hydrogen forming the silylgermylidyne radical (H₃SiGe). Our study offers a remarkable glance at the complex reaction dynamics and inherent isomerization processes of the silicon‐germanium system, which are quite distinct from those of the isovalent hydrocarbon system (ethyl radical; C₂H₅) eventually affording detailed insights into an exotic chemistry and intriguing chemical bonding of silicon‐germanium species at the microscopic level exploiting crossed molecular beams.

    

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5. Technical note: Improved synthetic routes to cis - and trans -(2-methyloxirane-2,3-diyl)dimethanol ( cis - and trans - β -isoprene epoxydiol)

   https://doi.org/10.5194/acp-23-7859-2023  

   Frauenheim, Molly ; Surratt, Jason D. ; Zhang, Zhenfa ; Gold, Avram ( July 2023 , Atmospheric Chemistry and Physics)

   Abstract. We report improved synthetic routes to the isomericisoprene-derived β-epoxydiols (β-IEPOX) in high yield(57 %–69 %) from inexpensive, readily available starting compounds. Thesyntheses do not require the protection/deprotection steps or time-consumingpurification of intermediates and can readily be scaled up to yield thetarget IEPOX isomers in gram quantities. Emissions of isoprene(2-methyl-1,3-butadiene, C5H8), primarily from deciduousvegetation, constitute the largest source of nonmethane atmospherichydrocarbons. In the gas phase under low-nitric-oxide (NO) conditions,addition of the atmospheric hydroxyl radical (OH) followed by rapid addition ofO2 yields isoprene-derived hydroxyperoxyl radicals. The major sink(>90 %) for the peroxyl radicals is a sequential reaction withthe hydroperoxyl radical (HO2), OH, and O2, which is then followed bythe elimination of OH to yield a ∼2:1 mixture ofcis- and trans-(2-methyloxirane-2,3-diyl)dimethanol (cis- and trans-β-IEPOX). The IEPOXisomers account for about 80 % of closed-shell hydroxyperoxylproducts and are rapidly taken up into acidic aerosols to form secondaryorganic aerosol (SOA). IEPOX-derived SOA makes a significant masscontribution to fine particulate matter (PM2.5), which is known to be amajor factor in climate forcing as well as adversely affecting respiratory andcardiovascular systems of exposed populations. Prediction of ambientPM2.5 composition and distribution, both in regional- and global-scaleatmospheric chemistry models, crucially depends on the accuracy ofidentification and quantitation of uptake product formation. Accessibilityof authentic cis- and trans-β-IEPOX in high purity and in large quantity forlaboratory studies underpins progress in developing models as well asidentification and quantitation of PM2.5 components.

    

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