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1. A chemical dynamics study on the gas phase formation of thioformaldehyde (H 2 CS) and its thiohydroxycarbene isomer (HCSH)

   https://doi.org/10.1073/pnas.2004881117  

   Doddipatla, Srinivas ; He, Chao ; Kaiser, Ralf I. ; Luo, Yuheng ; Sun, Rui ; Galimova, Galiya R. ; Mebel, Alexander M. ; Millar, Tom J. ( September 2020 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   Complex organosulfur molecules are ubiquitous in interstellar molecular clouds, but their fundamental formation mechanisms have remained largely elusive. These processes are of critical importance in initiating a series of elementary chemical reactions, leading eventually to organosulfur molecules—among them potential precursors to iron-sulfide grains and to astrobiologically important molecules, such as the amino acid cysteine. Here, we reveal through laboratory experiments, electronic-structure theory, quasi-classical trajectory studies, and astrochemical modeling that the organosulfur chemistry can be initiated in star-forming regions via the elementary gas-phase reaction of methylidyne radicals with hydrogen sulfide, leading to thioformaldehyde (H 2 CS) and its thiohydroxycarbene isomer (HCSH). The facile route to two of the simplest organosulfur molecules via a single-collision event affords persuasive evidence for a likely source of organosulfur molecules in star-forming regions. These fundamental reaction mechanisms are valuable to facilitate an understanding of the origin and evolution of the molecular universe and, in particular, of sulfur in our Galaxy. 

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2. 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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3. Gas-phase formation of silicon monoxide via non-adiabatic reaction dynamics and its role as a building block of interstellar silicates

   https://doi.org/10.1039/D2CP02188A  

   He, Chao ; Luo, Yuheng ; Doddipatla, Srinivas ; Yang, Zhenghai ; Millar, Tom J. ; Sun, Rui ; Kaiser, Ralf I. ( August 2022 , Physical Chemistry Chemical Physics)

   Silicon monoxide (SiO) is classified as a key precursor and fundamental molecular building block to interstellar silicate nanoparticles, which play an essential role in the synthesis of molecular building blocks connected to the Origins of Life. In the cold interstellar medium, silicon monoxide is of critical importance in initiating a series of elementary chemical reactions leading to larger silicon oxides and eventually to silicates. To date, the fundamental formation mechanisms and chemical dynamics leading to gas phase silicon monoxide have remained largely elusive. Here, through a concerted effort between crossed molecular beam experiments and electronic structure calculations, it is revealed that instead of forming highly-stable silicon dioxide (SiO 2 ), silicon monoxide can be formed via a barrierless, exoergic, single-collision event between ground state molecular oxygen and atomic silicon involving non-adiabatic reaction dynamics through various intersystem crossings. Our research affords persuasive evidence for a likely source of highly rovibrationally excited silicon monoxide in cold molecular clouds thus initiating the complex chain of exoergic reactions leading ultimately to a population of silicates at low temperatures in our Galaxy. 

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4. Gas Phase Preparation of the Elusive Monobridged Ge( μ ‐H)GeH Molecule through Nonadiabatic Reaction Dynamics

   https://doi.org/10.1002/chem.202103999  

   Yang, Zhenghai ; Sun, Bing‐Jian ; He, Chao ; Fatimah, Siti ; Chang, Agnes H. H. ; Kaiser, Ralf I. ( January 2022 , Chemistry – A European Journal)

   The hitherto elusive monobridged Ge(μ‐H)GeH (X¹A′) molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH₄). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium‐hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH₃); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH₃predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ‐H)GeH isomer, which is in equilibrium with the vinylidene‐type (H₂GeGe) and dibridged (Ge(μ‐H₂)Ge) isomers. This reaction leads to the formation of cyclic dinuclear germanium molecules, which do not exist on the isovalent C₂H₂surface, thus deepening our understanding of the role of nonadiabatic reaction dynamics in preparing nonclassical, hydrogen‐bridged isomers carrying main group XIV elements.

    

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5. 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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