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Alexander M. Mebel - One of the best experts on this subject based on the ideXlab platform.
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A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C5H3 radicals via chemically activated C5H4 and C6H6 intermediates
Physical chemistry chemical physics : PCCP, 2018Co-Authors: Aaron M. Thomas, Ralf I. Kaiser, Michael Lucas, Long Zhao, Jerid Liddiard, Alexander M. MebelAbstract:The crossed molecular beams technique was utilized to explore the formation of three isomers of resonantly stabilized (C5H3) radicals along with their d2-substituted counterparts via the bimolecular reactions of singlet/triplet Dicarbon [C2(X1Σ+g/a3Πu)] with methylacetylene [CH3CCH(X1A1)], d3-methylacetylene [CD3CCH(X1A1)], and 1-butyne [C2H5CCH(X1A')] at collision energies up to 26 kJ mol-1via chemically activated singlet/triplet C5H4/C5D3H and C6H6 intermediates. These studies exploit a newly developed supersonic Dicarbon [C2(X1Σ+g/a3Πu)] beam generated via photolysis of tetrachloroethylene [C2Cl4(X1Ag)] by excluding interference from carbon atoms, which represent the dominating (interfering) species in ablation-based Dicarbon sources. We evaluated the performance of the Dicarbon [C2(X1Σ+g/a3Πu)] beam in reactions with methylacetylene [CH3CCH(X1A1)] and d3-methylacetylene [CD3CCH(X1A1)]; the investigations demonstrate that the reaction dynamics match previous studies in our laboratory utilizing ablation-based Dicarbon sources involving the synthesis of 1,4-pentadiynyl-3 [HCCCHCCH(X2B1)] and 2,4-pentadiynyl-1 [H2CCCCCH(X2B1)] radicals via hydrogen (deuterium) atom elimination. Considering the C2(X1Σ+g/a3Πu)-1-butyne [C2H5CCH(X1A')] reaction, the hitherto elusive methyl-loss pathway was detected. This channel forms the previously unknown resonantly stabilized penta-1-yn-3,4-dienyl-1 [H2CCCHCC(X2A)] radical along with the methyl radical [CH3(X2A2'')] and is open exclusively on the triplet surface with an overall reaction energy of -86 ± 10 kJ mol-1. The preferred reaction pathways proceed first by barrierless addition of triplet Dicarbon to the π-electronic system of 1-butyne, either to both acetylenic carbon atoms or to the sterically more accessible carbon atom, to form the methyl-bearing triplet C6H6 intermediates [i41b] and [i81b], respectively, with the latter decomposing via a tight exit transition state to penta-1-yn-3,4-dienyl-1 [(H2CCCHCC(X2A)] plus the methyl radical [CH3(X2A2'')]. The successful unraveling of this methyl-loss channel - through collaborative experimental and computational efforts - underscores the viability of the photolytically generated Dicarbon beam as an unprecedented tool to access reaction dynamics underlying the formation of resonantly stabilized free radicals (RSFR) that are vital to molecular mass growth processes that ultimately lead to polycyclic aromatic hydrocarbons (PAHs).
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Understanding the chemical dynamics of the reactions of Dicarbon with 1-butyne, 2-butyne, and 1,2-butadiene--toward the formation of resonantly stabilized free radicals.
Physical chemistry chemical physics : PCCP, 2014Co-Authors: Dorian S. N. Parker, Ralf I. Kaiser, Surajit Maity, Beni B. Dangi, Alexander Landera, Alexander M. MebelAbstract:The reaction dynamics of the Dicarbon radical C2(a(3)Πu/X(1)Σg(+)) in the singlet and triplet state with C4H6 isomers 2-butyne, 1-butyne and 1,2-butadiene were investigated at collision energies of about 26 kJ mol(-1) using the crossed molecular beam technique and supported by ab initio and RRKM calculations. The reactions are all indirect, forming C6H6 complexes through barrierless additions by Dicarbon on the triplet and singlet surfaces. Isomerization of the C6H6 reaction intermediate leads to product formation by hydrogen loss in a Dicarbon-hydrogen atom exchange mechanism forming acyclic C6H5 reaction products through loose exit transition states in overall exoergic reactions.
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an experimental and theoretical investigation of the formation of c7h7 isomers in the bimolecular reaction of Dicarbon molecules with 1 3 pentadiene
Chemical Physics Letters, 2014Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Dorian S. N. Parker, Daniel Belisariolara, Alexander M. MebelAbstract:Abstract We report on the crossed molecular beam reaction of Dicarbon, C 2 (X 1 Σ g + , a 3 Π u ), with 1,3-pentadiene (C 5 H 8 ; X 1 A′) conducted at a collision energy of 43 kJ mol −1 under single collision conditions and studied by ab initio and statistical calculations. The reactions involve indirect scattering dynamics initiated by the barrierless addition of Dicarbon to the carbon–carbon double bond of 1,3-pentadiene followed by successive rearrangements leading eventually through hydrogen atom elimination to distinct C 7 H 7 radical species. The experimental reaction exoergicity of 412 ± 52 kJ mol −1 is consistent with the formation of cycloheptatrienyl, m-tolyl, and/or benzyl radicals predicted as the major products by theory.
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Gas-Phase Synthesis of the Benzyl Radical (C6H5CH2)†
Angewandte Chemie (International ed. in English), 2014Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Dorian S. N. Parker, Tao Yang, Alexander M. MebelAbstract:Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of Dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of Dicarbon to the carbon–carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product.
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A combined crossed beam and ab initio investigation of the gas phase reaction of Dicarbon molecules (C2; X1Σg(+)/a3Πu) with propene (C3H6; X1A'): identification of the resonantly stabilized free radicals 1- and 3-vinylpropargyl.
The journal of physical chemistry. A, 2013Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Surajit Maity, Alexander M. MebelAbstract:The crossed molecular beam reactions of Dicarbon, C2(X(1)Σg(+), a(3)Πu), with propene (C3H6; X(1)A') and with the partially deuterated D3 counterparts (CD3CHCH2, CH3CDCD2) were conducted at collision energies of about 21 kJ mol(-1) under single collision conditions. The experimental data were combined with ab initio and statistical (RRKM) calculations to reveal the underlying reaction mechanisms. Both on the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the addition of the Dicarbon reactant to the carbon-carbon double bond of propene. These initial addition complexes rearrange via multiple isomerization steps leading ultimately via atomic hydrogen elimination from the former methyl and vinyl groups to the formation of 1-vinylpropargyl and 3-vinylpropargyl. Both triplet and singlet methylbutatriene species were identified as important reaction intermediates. On the singlet surface, the unimolecular decomposition of the reaction intermediates was found to be barrier-less, whereas on the triplet surface, tight exit transition states were involved. In combustion flames, both radicals can undergo a hydrogen-atom assisted isomerization leading ultimately to the thermodynamically most stable cyclopentadienyl isomer. Alternatively, in a third body process, a subsequent reaction of 1-vinylpropargyl or 3-vinylpropargyl radicals with the propargyl radical might yield to the formation of styrene (C6H5C2H3) in an entrance barrier-less reaction under combustion-like conditions. This presents a strong alternative to the formation of styrene via the reaction of phenyl radicals with ethylene, which is affiliated with an entrance barrier of about 10 kJ mol(-1).
Ralf I. Kaiser - One of the best experts on this subject based on the ideXlab platform.
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A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C5H3 radicals via chemically activated C5H4 and C6H6 intermediates
Physical chemistry chemical physics : PCCP, 2018Co-Authors: Aaron M. Thomas, Ralf I. Kaiser, Michael Lucas, Long Zhao, Jerid Liddiard, Alexander M. MebelAbstract:The crossed molecular beams technique was utilized to explore the formation of three isomers of resonantly stabilized (C5H3) radicals along with their d2-substituted counterparts via the bimolecular reactions of singlet/triplet Dicarbon [C2(X1Σ+g/a3Πu)] with methylacetylene [CH3CCH(X1A1)], d3-methylacetylene [CD3CCH(X1A1)], and 1-butyne [C2H5CCH(X1A')] at collision energies up to 26 kJ mol-1via chemically activated singlet/triplet C5H4/C5D3H and C6H6 intermediates. These studies exploit a newly developed supersonic Dicarbon [C2(X1Σ+g/a3Πu)] beam generated via photolysis of tetrachloroethylene [C2Cl4(X1Ag)] by excluding interference from carbon atoms, which represent the dominating (interfering) species in ablation-based Dicarbon sources. We evaluated the performance of the Dicarbon [C2(X1Σ+g/a3Πu)] beam in reactions with methylacetylene [CH3CCH(X1A1)] and d3-methylacetylene [CD3CCH(X1A1)]; the investigations demonstrate that the reaction dynamics match previous studies in our laboratory utilizing ablation-based Dicarbon sources involving the synthesis of 1,4-pentadiynyl-3 [HCCCHCCH(X2B1)] and 2,4-pentadiynyl-1 [H2CCCCCH(X2B1)] radicals via hydrogen (deuterium) atom elimination. Considering the C2(X1Σ+g/a3Πu)-1-butyne [C2H5CCH(X1A')] reaction, the hitherto elusive methyl-loss pathway was detected. This channel forms the previously unknown resonantly stabilized penta-1-yn-3,4-dienyl-1 [H2CCCHCC(X2A)] radical along with the methyl radical [CH3(X2A2'')] and is open exclusively on the triplet surface with an overall reaction energy of -86 ± 10 kJ mol-1. The preferred reaction pathways proceed first by barrierless addition of triplet Dicarbon to the π-electronic system of 1-butyne, either to both acetylenic carbon atoms or to the sterically more accessible carbon atom, to form the methyl-bearing triplet C6H6 intermediates [i41b] and [i81b], respectively, with the latter decomposing via a tight exit transition state to penta-1-yn-3,4-dienyl-1 [(H2CCCHCC(X2A)] plus the methyl radical [CH3(X2A2'')]. The successful unraveling of this methyl-loss channel - through collaborative experimental and computational efforts - underscores the viability of the photolytically generated Dicarbon beam as an unprecedented tool to access reaction dynamics underlying the formation of resonantly stabilized free radicals (RSFR) that are vital to molecular mass growth processes that ultimately lead to polycyclic aromatic hydrocarbons (PAHs).
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Synthesis of the Smallest Member of the Silylketene Family: H3SiC(H)=C=O
Chemphyschem : a European journal of chemical physics and physical chemistry, 2017Co-Authors: György Tarczay, Pavlo Maksyutenko, Marko Förstel, Sándor Góbi, Ralf I. KaiserAbstract:Exploiting photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) combined with electronic structure calculations, it is shown that the hitherto elusive silylketene molecule (H3 SiC(H)=C=O)-the isovalent counterpart of the well-known methylketene molecule-is forming via interaction of energetic electrons with low-temperature silane-carbon monoxide ices. In combination with the infrared spectroscopically detected triplet Dicarbon monoxide reactant, electronic structure calculations suggest that Dicarbon monoxide reacts with silane via a de facto insertion of the terminal carbon atom into a silicon-hydrogen single bond. This is followed by non-adiabatic reaction dynamics triggered by the heavy silicon atom intersystem crossing from the triplet to the singlet manifold, eventually leading to the formation of silylketene. The non-equilibrium nature of the elementary reactions within the exposed ices results in an exciting and novel chemistry which cannot be explored via traditional preparative chemistry. Since the replacement of hydrogen in silane can introduce side groups such as silyl or alkyl, the reaction of triplet Dicarbon monoxide with silane represents the parent system for a previously disregarded reaction class revealing an elegant path to access the largely reactive group of silylketenes.
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Chemical dynamics of the formation of the 1,3butadiynyl radical (C4H(X 2 � + )) and its isotopomers
2015Co-Authors: Ying Guo, Er M. Mebel, Ralf I. KaiserAbstract:The reaction of Dicarbon molecules in their electronic ground, C2(X1“g+), and first excited state, C2(a3ƒu), with acetylene, C2H2(X1“g+), to synthesize the 1,3-butadiynyl radical, C4H(X2“+), plus a hydrogen atom was investigated at six different collision energies between 10.6 and 47.5 kJ mol-1 under single collision conditions. These studies were contemplated by crossed molecular beam experiments of Dicarbon with three acetylene isotopomers C2D2(X1“g+), C2HD (X1“+), and 13C2H2(X1“g+) to elucidate the role of intersystem crossing (ISC) and of the symmetry of the reaction intermediate(s) on the center-of-mass functions. On the singlet surface, Dicarbon was found to react with acetylene through an indirect reaction mechanism involving a diacetylene intermediate. The latter fragmented via a loose exit transition state via an emission of a hydrogen atom to form the 1,3-butadiynyl radical C4H(X2“+). The D∞h symmetry of the decomposing diacetylene intermediate results in collision-energy invariant, isotropic (flat) center-of-mass angular distributions of this microchannel. Isotopic substitution experiments suggested that at least at a collision energy of 29 kJ mol-1, the diacetylene isotopomers are long-lived with respect to their rotational periods. On the triplet surface, the reaction involved three feasible addition complexes located in shallower potential energy wells as compared to singlet diacetylene. The involvement of the triplet surface accounted for the asymmetry of the center-of-mass angular distributions. The detection of the 1,3-butadiynyl radical, C4H(X2“+), in the crossed beam reaction of Dicarbon molecules with acetylene presents compelling evidence that the 1,3-butadiynyl radical can be formed via bimolecular reactions involving carbon clusters in extreme environments such as circumstellar envelopes of dying carbon stars and combustion flames. 1
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Formation of the 2,4-pentadiynyl-1 radical (H2CCCCCH, X 2 B1) in the crossed beams reaction of Dicarbon molecules with methylacetylene
2014Co-Authors: Ying Guo, Nadia Balucani, Ralf I. KaiserAbstract:The chemical dynamics to synthesize the 2,4-pentadiynyl-1 radical, HCCCCCH2(X 2 B1), via the neutralneutral reaction of Dicarbon with methylacetylene, was examined in a crossed molecular beams experiment at a collision energy of 37.6 kJ mol-1. The laboratory angular distribution and time-of-flight spectra of the 2,4-pentadiynyl-1 radical and its fragmentation patterns were recorded at m/z) 63-60 and m/z) 51-48. Our findings suggest that the reaction dynamics are indirect and dictated by an initial attack of the Dicarbon molecule to the π electron density of the methylacetylene molecule to form cyclic collision complexes. The latter ultimately rearranged via ring opening to methyldiacetylene, CH3-CtC-CtC-H. This structure decomposed via atomic hydrogen emission to the 2,4-pentadiynyl-1 radical; here, the hydrogen atom was found to be emitted almost parallel to the total angular momentum as suggested by the experimentally observed sideways scattering. The overall reaction was strongly exoergic by 182 ( 10 kJ mol-1. The identification of the resonance-stabilized free 2,4-pentadiynyl-1 radical represents a solid background for the title reaction to be included into more refined reaction networks modeling the chemistry of circumstellar envelopes and also of sooting combustion flames. 1
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Understanding the chemical dynamics of the reactions of Dicarbon with 1-butyne, 2-butyne, and 1,2-butadiene--toward the formation of resonantly stabilized free radicals.
Physical chemistry chemical physics : PCCP, 2014Co-Authors: Dorian S. N. Parker, Ralf I. Kaiser, Surajit Maity, Beni B. Dangi, Alexander Landera, Alexander M. MebelAbstract:The reaction dynamics of the Dicarbon radical C2(a(3)Πu/X(1)Σg(+)) in the singlet and triplet state with C4H6 isomers 2-butyne, 1-butyne and 1,2-butadiene were investigated at collision energies of about 26 kJ mol(-1) using the crossed molecular beam technique and supported by ab initio and RRKM calculations. The reactions are all indirect, forming C6H6 complexes through barrierless additions by Dicarbon on the triplet and singlet surfaces. Isomerization of the C6H6 reaction intermediate leads to product formation by hydrogen loss in a Dicarbon-hydrogen atom exchange mechanism forming acyclic C6H5 reaction products through loose exit transition states in overall exoergic reactions.
Beni B. Dangi - One of the best experts on this subject based on the ideXlab platform.
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Understanding the chemical dynamics of the reactions of Dicarbon with 1-butyne, 2-butyne, and 1,2-butadiene--toward the formation of resonantly stabilized free radicals.
Physical chemistry chemical physics : PCCP, 2014Co-Authors: Dorian S. N. Parker, Ralf I. Kaiser, Surajit Maity, Beni B. Dangi, Alexander Landera, Alexander M. MebelAbstract:The reaction dynamics of the Dicarbon radical C2(a(3)Πu/X(1)Σg(+)) in the singlet and triplet state with C4H6 isomers 2-butyne, 1-butyne and 1,2-butadiene were investigated at collision energies of about 26 kJ mol(-1) using the crossed molecular beam technique and supported by ab initio and RRKM calculations. The reactions are all indirect, forming C6H6 complexes through barrierless additions by Dicarbon on the triplet and singlet surfaces. Isomerization of the C6H6 reaction intermediate leads to product formation by hydrogen loss in a Dicarbon-hydrogen atom exchange mechanism forming acyclic C6H5 reaction products through loose exit transition states in overall exoergic reactions.
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an experimental and theoretical investigation of the formation of c7h7 isomers in the bimolecular reaction of Dicarbon molecules with 1 3 pentadiene
Chemical Physics Letters, 2014Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Dorian S. N. Parker, Daniel Belisariolara, Alexander M. MebelAbstract:Abstract We report on the crossed molecular beam reaction of Dicarbon, C 2 (X 1 Σ g + , a 3 Π u ), with 1,3-pentadiene (C 5 H 8 ; X 1 A′) conducted at a collision energy of 43 kJ mol −1 under single collision conditions and studied by ab initio and statistical calculations. The reactions involve indirect scattering dynamics initiated by the barrierless addition of Dicarbon to the carbon–carbon double bond of 1,3-pentadiene followed by successive rearrangements leading eventually through hydrogen atom elimination to distinct C 7 H 7 radical species. The experimental reaction exoergicity of 412 ± 52 kJ mol −1 is consistent with the formation of cycloheptatrienyl, m-tolyl, and/or benzyl radicals predicted as the major products by theory.
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Gas-Phase Synthesis of the Benzyl Radical (C6H5CH2)†
Angewandte Chemie (International ed. in English), 2014Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Dorian S. N. Parker, Tao Yang, Alexander M. MebelAbstract:Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of Dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of Dicarbon to the carbon–carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product.
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A combined crossed beam and ab initio investigation of the gas phase reaction of Dicarbon molecules (C2; X1Σg(+)/a3Πu) with propene (C3H6; X1A'): identification of the resonantly stabilized free radicals 1- and 3-vinylpropargyl.
The journal of physical chemistry. A, 2013Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Surajit Maity, Alexander M. MebelAbstract:The crossed molecular beam reactions of Dicarbon, C2(X(1)Σg(+), a(3)Πu), with propene (C3H6; X(1)A') and with the partially deuterated D3 counterparts (CD3CHCH2, CH3CDCD2) were conducted at collision energies of about 21 kJ mol(-1) under single collision conditions. The experimental data were combined with ab initio and statistical (RRKM) calculations to reveal the underlying reaction mechanisms. Both on the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the addition of the Dicarbon reactant to the carbon-carbon double bond of propene. These initial addition complexes rearrange via multiple isomerization steps leading ultimately via atomic hydrogen elimination from the former methyl and vinyl groups to the formation of 1-vinylpropargyl and 3-vinylpropargyl. Both triplet and singlet methylbutatriene species were identified as important reaction intermediates. On the singlet surface, the unimolecular decomposition of the reaction intermediates was found to be barrier-less, whereas on the triplet surface, tight exit transition states were involved. In combustion flames, both radicals can undergo a hydrogen-atom assisted isomerization leading ultimately to the thermodynamically most stable cyclopentadienyl isomer. Alternatively, in a third body process, a subsequent reaction of 1-vinylpropargyl or 3-vinylpropargyl radicals with the propargyl radical might yield to the formation of styrene (C6H5C2H3) in an entrance barrier-less reaction under combustion-like conditions. This presents a strong alternative to the formation of styrene via the reaction of phenyl radicals with ethylene, which is affiliated with an entrance barrier of about 10 kJ mol(-1).
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a combined crossed beam and ab initio investigation of the gas phase reaction of Dicarbon molecules c2 x1σg a3πu with propene c3h6 x1a identification of the resonantly stabilized free radicals 1 and 3 vinylpropargyl
Journal of Physical Chemistry A, 2013Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Surajit Maity, Alexander M. MebelAbstract:The crossed molecular beam reactions of Dicarbon, C2(X(1)Σg(+), a(3)Πu), with propene (C3H6; X(1)A') and with the partially deuterated D3 counterparts (CD3CHCH2, CH3CDCD2) were conducted at collision energies of about 21 kJ mol(-1) under single collision conditions. The experimental data were combined with ab initio and statistical (RRKM) calculations to reveal the underlying reaction mechanisms. Both on the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the addition of the Dicarbon reactant to the carbon-carbon double bond of propene. These initial addition complexes rearrange via multiple isomerization steps leading ultimately via atomic hydrogen elimination from the former methyl and vinyl groups to the formation of 1-vinylpropargyl and 3-vinylpropargyl. Both triplet and singlet methylbutatriene species were identified as important reaction intermediates. On the singlet surface, the unimolecular decomposition of the reaction intermediates was found to be barrier-less, whereas on the triplet surface, tight exit transition states were involved. In combustion flames, both radicals can undergo a hydrogen-atom assisted isomerization leading ultimately to the thermodynamically most stable cyclopentadienyl isomer. Alternatively, in a third body process, a subsequent reaction of 1-vinylpropargyl or 3-vinylpropargyl radicals with the propargyl radical might yield to the formation of styrene (C6H5C2H3) in an entrance barrier-less reaction under combustion-like conditions. This presents a strong alternative to the formation of styrene via the reaction of phenyl radicals with ethylene, which is affiliated with an entrance barrier of about 10 kJ mol(-1).
Fangtong Zhang - One of the best experts on this subject based on the ideXlab platform.
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A crossed molecular beams and ab initio study on the formation of C6H3 radicals. an interface between resonantly stabilized and aromatic radicals.
The journal of physical chemistry. A, 2011Co-Authors: Ralf I. Kaiser, Fangtong Zhang, Alexander Landera, Pavlo Maksyutenko, Mausumi Goswami, Y. S. Kim, Alexander M. MebelAbstract:The crossed molecular beams reaction of Dicarbon molecules, C(2)(X(1)Σ(g)(+)/a(3)Π(u)) with vinylacetylene was studied under single collision conditions at a collision energy of 31.0 kJ mol(-1) and combined with electronic structure calculations on the singlet and triplet C(6)H(4) potential energy surfaces. The investigations indicate that both reactions on the triplet and singlet surfaces are dictated by a barrierless addition of the Dicarbon unit to the vinylacetylene molecule and hence indirect scattering dynamics via long-lived C(6)H(4) complexes. On the singlet surface, ethynylbutatriene and vinyldiacetylene were found to decompose via atomic hydrogen loss involving loose exit transition states to form exclusively the resonantly stabilized 1-hexene-3,4-diynyl-2 radical (C(6)H(3); H(2)CCCCCCH; C(2v)). On the triplet surface, ethynylbutatriene emitted a hydrogen atom through a tight exit transition state located about 20 kJ mol(-1) above the separated stabilized 1-hexene-3,4-diynyl-2 radical plus atomic hydrogen product; to a minor amount (
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Formation of the Phenyl Radical [C6H5(X2A1)] under Single Collision Conditions: A Crossed Molecular Beam and ab Initio Study
Journal of the American Chemical Society, 2010Co-Authors: Fangtong Zhang, Ralf I. Kaiser, Pavlo Maksyutenko, Brant M. Jones, Christine Chin, Vadim V. Kislov, Alexander M. MebelAbstract:Reactions of Dicarbon molecules (C(2)) with C(4)H(6) isomers such as 1,3-butadiene represent a potential, but hitherto unnoticed, route to synthesize the first aromatic C(6) ring in hydrocarbon flames and in the interstellar medium where concentrations of Dicarbon transient species are significant. Here, crossed molecular beams experiments of Dicarbon molecules in their X(1)Sigma(g)(+) electronic ground state and in the first electronically excited a(3)Pi(u) state have been conducted with 1,3-butadiene and two partially deuterated counterparts (1,1,4,4-D4-1,3-butadiene and 2,3-D2-1,3-butadiene) at two collision energies of 12.7 and 33.7 kJ mol(-1). Combining these scattering experiments with electronic structure and RRKM calculations on the singlet and triplet C(6)H(6) surfaces, our investigation reveals that the aromatic phenyl radical is formed predominantly on the triplet surface via indirect scattering dynamics through a long-lived reaction intermediate. Initiated by a barrierless addition of triplet Dicarbon to one of the terminal carbon atoms of 1,3-butadiene, the collision complex undergoes trans-cis isomerization followed by ring closure and hydrogen migration prior to hydrogen atom elimination, ultimately forming the phenyl radical. The latter step emits the hydrogen atom almost perpendicularly to the rotational plane of the decomposing intermediate and almost parallel to the total angular momentum vector. On the singlet surface, smaller contributions of phenyl radical could not be excluded; experiments with partially deuterated 1,3-butadiene indicate the formation of the thermodynamically less stable acyclic H(2)CCHCCCCH(2) isomer. This study presents the very first experimental evidence, contemplated by theoretical studies, that under single collision conditions an aromatic hydrocarbon molecule can be formed in a bimolecular gas-phase reaction via reaction of two acyclic molecules involving cyclization processes at collision energies highly relevant to combustion flames.
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Untangling the chemical evolution of Titan's atmosphere and surface–from homogeneous to heterogeneous chemistry
Faraday discussions, 2010Co-Authors: Ralf I. Kaiser, Fangtong Zhang, Alexander M. Mebel, Pavlo Maksyutenko, Courtney Ennis, Sergey P. Krishtal, Oleg Kostko, Musahid AhmedAbstract:In this article, we first explored the chemical dynamics of simple diatomic radicals (Dicarbon, methylidyne) utilizing the crossed molecular beams method. This versatile experimental technique can be applied to study reactions relevant to the atmospheres of planets and their moons as long as intense and stable supersonic beam sources of the reactant species exist. By focusing on reactions of Dicarbon with hydrogen cyanide, we untangled the contribution of Dicarbon in its singlet ground and first excited triplet states. These results were applied to understand and re-analyze the data of crossed beam reactions of the isoelectronic Dicarbon plus acetylene reaction. Further, we investigated the interaction of ionizing radiation in form of energetic electrons with organic molecules ethane and propane sequestered on Titan’s surface. These experiments presented compelling evidence that even at irradiation exposures equivalent to about 44 years on Titan’s surface, aliphatic like organic residues can be produced on Titan’s surface with thicknesses up to 1.5 m. Finally, we investigated how Titan’s nascent chemical inventory can be altered by an external influx of matter as supplied by (micro)meteorites and possibly comets. For this, we simulated the ablation process in Titan’s atmosphere, which can lead to ground and electronically excited atoms of, for instance, the principal constituents of silicates like iron, silicon, and magnesium, in laboratory experiments. By ablating silicon species and seeding the ablated species in acetylene carrier gas, which also acts as a reactant, we produced organo silicon species, which were then photoionized utilizing tunable VUV radiation from the Advanced Light Source. In combination with electronic structure calculations, the structures and ionization energies of distinct organo-silicon species were elucidated.
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formation of the 1 3 5 hexatriynyl radical c6h x2π via the crossed beams reaction of Dicarbon c2 x1σg a3πu with diacetylene c4h2 x1σg
Journal of Physical Chemistry A, 2009Co-Authors: Fangtong Zhang, Ralf I. Kaiser, Seol Kim, Alexander M. MebelAbstract:Crossed molecular beams experiments were conducted to investigate the chemical dynamics of the reaction of Dicarbon molecules, C2(X1Σg+/a3Πu), with diacetylene, C4H2(X1Σg+) at two collision energies of 12.1 and 32.8 kJmol−1. The dynamics were found to be indirect, involved C6H2 intermediates, and were dictated by an initial addition of the Dicarbon molecule to the carbon−carbon triple bond of diacetylene. The initial collision complexes could isomerize. On the singlet surface, the resulting linear triacetylene molecule (C6H2(X1Σg+)) decomposed without an exit barrier to form the linear 1,3,5-hexatriynyl radical (C6H(X2Π)). On the triplet surface, the dynamics suggested at least a tight exit transition state involved in the fragmentation of a triplet C6H2 intermediate to yield the 1,3,5-hexatriynyl radical (C6H(X2Π)) plus atomic hydrogen. On the basis of the experimental data, we recommend an experimentally determined enthalpy of formation of the 1,3,5-hexatriynyl radical of 1014 ± 27 kJmol−1 at 0 K. Our e...
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Formation of the 1,3,5-Hexatriynyl Radical (C6H(X2Π)) via the Crossed Beams Reaction of Dicarbon (C2(X1Σg+/a3Πu)), with Diacetylene (C4H2(X1Σg+))
The journal of physical chemistry. A, 2009Co-Authors: Fangtong Zhang, Ralf I. Kaiser, Seol Kim, Alexander M. MebelAbstract:Crossed molecular beams experiments were conducted to investigate the chemical dynamics of the reaction of Dicarbon molecules, C(2)(X(1)Sigma(g)(+)/a(3)Pi(u)), with diacetylene, C(4)H(2)(X(1)Sigma(g)(+)) at two collision energies of 12.1 and 32.8 kJ mol(-1). The dynamics were found to be indirect, involved C(6)H(2) intermediates, and were dictated by an initial addition of the Dicarbon molecule to the carbon-carbon triple bond of diacetylene. The initial collision complexes could isomerize. On the singlet surface, the resulting linear triacetylene molecule (C(6)H(2)(X(1)Sigma(g)(+))) decomposed without an exit barrier to form the linear 1,3,5-hexatriynyl radical (C(6)H(X(2)Pi)). On the triplet surface, the dynamics suggested at least a tight exit transition state involved in the fragmentation of a triplet C(6)H(2) intermediate to yield the 1,3,5-hexatriynyl radical (C(6)H(X(2)Pi)) plus atomic hydrogen. On the basis of the experimental data, we recommend an experimentally determined enthalpy of formation of the 1,3,5-hexatriynyl radical of 1014 +/- 27 kJ mol(-1) at 0 K. Our experimental results and the derived reaction mechanisms gain full support from electronic structure calculations on the singlet and triplet C(6)H(2) potential-energy surfaces. The identification of the 1,3,5-hexatriynyl radical under single collision conditions implies that the neutral-neutral reaction of Dicarbon with diacetylene can lead to the formation of 1,3,5-hexatriynyl radicals in the interstellar medium and possibly in the hydrocarbon-rich atmospheres of planets and their moons such as Saturn's satellite Titan.
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isolable Dicarbon stabilized by a single phosphine ligand
Nature Chemistry, 2021Co-Authors: Tsz-fai Leung, Tao Yang, Dandan Jiang, Dengmengfei Xiao, Wei-min Ching, Glenn P. A. Yap, Lili Zhao, Tiow-gan OngAbstract:In contrast to naturally occurring F2, O2 and N2, diatomic C2 is an intriguing species that has only been observed indirectly in the gas phase, and because of its high reactivity has eluded isolation in the condensed phase. It has previously been stabilized in L→C2←L compounds but the bonding situation of the central C2 in this motif differs remarkably from that of free C2. Here we have prepared and structurally characterized diatomic C2 as a monoligated complex L→C2 using a bulky phosphine ligand bearing two imidazolidin-2-iminato groups (L is (NHCR=N)2(CH3)P, where NHCR is an N-heterocyclic carbene). The compound is stable in solution at ambient temperature and has also been isolated in the solid state. Reactivity studies, in combination with quantum chemical analysis, suggest that the two carbon atoms of the L→C2 complex both have carbene character. The complex underwent intermolecular C–H bond activation upon thermolysis and exhibited hydroalkoxylation-like reactivity with methanol. Diatomic C2 is an elusive species that has only been indirectly observed in the gas phase. It had previously been stabilized in the condensed phase using two ligands, but now a monoligated L→C2 complex has been prepared with a bulky phosphine ligand (L) bearing two imidazolidin-2-iminato groups. Reactivity studies and theoretical quantum chemical analysis point to the C2 moiety having a dicarbene character.
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Isolable Dicarbon stabilized by a single phosphine ligand.
Nature chemistry, 2020Co-Authors: Tsz-fai Leung, Tao Yang, Dandan Jiang, Dengmengfei Xiao, Wei-min Ching, Glenn P. A. Yap, Lili Zhao, Tiow-gan Ong, Gernot FrenkingAbstract:In contrast to naturally occurring F2, O2 and N2, diatomic C2 is an intriguing species that has only been observed indirectly in the gas phase, and because of its high reactivity has eluded isolation in the condensed phase. It has previously been stabilized in L→C2←L compounds but the bonding situation of the central C2 in this motif differs remarkably from that of free C2. Here we have prepared and structurally characterized diatomic C2 as a monoligated complex L→C2 using a bulky phosphine ligand bearing two imidazolidin-2-iminato groups (L is (NHCR=N)2(CH3)P, where NHCR is an N-heterocyclic carbene). The compound is stable in solution at ambient temperature and has also been isolated in the solid state. Reactivity studies, in combination with quantum chemical analysis, suggest that the two carbon atoms of the L→C2 complex both have carbene character. The complex underwent intermolecular C-H bond activation upon thermolysis and exhibited hydroalkoxylation-like reactivity with methanol.
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Gas-Phase Synthesis of the Benzyl Radical (C6H5CH2)†
Angewandte Chemie (International ed. in English), 2014Co-Authors: Beni B. Dangi, Ralf I. Kaiser, Dorian S. N. Parker, Tao Yang, Alexander M. MebelAbstract:Dicarbon (C2), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas-phase synthesis is presented of the benzyl radical (C6H5CH2) by the crossed molecular beam reaction of Dicarbon, C2(X1Σg+, a3Πu), with 2-methyl-1,3-butadiene (isoprene; C5H8; X1A′) accessing the triplet and singlet C7H8 potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of Dicarbon to the carbon–carbon double bond of the 2-methyl-1,3-butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C7H7 radical species through atomic hydrogen elimination. The benzyl radical (C6H5CH2), the thermodynamically most stable C7H7 isomer, is determined as the major product.