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Zhao L, Kaiser RI, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Tönshoff C, Reicherter F, Bettinger HF, Mebel AM. A Free-Radical Prompted Barrierless Gas-Phase Synthesis of Pentacene. Angew Chem Int Ed Engl 2020; 59:11334-11338. [PMID: 32266773 PMCID: PMC7383502 DOI: 10.1002/anie.202003402] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Indexed: 11/10/2022]
Abstract
A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C22 H14 ) along with its benzo[a]tetracene isomer (C22 H14 ) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C18 H11 . ) with vinylacetylene (C4 H4 ). The pathway to pentacene-a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes-is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe.
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He C, Zhao L, Doddipatla S, Thomas AM, Nikolayev AA, Galimova GR, Azyazov VN, Mebel AM, Kaiser RI. Gas-Phase Synthesis of 3-Vinylcyclopropene via the Crossed Beam Reaction of the Methylidyne Radical (CH; X 2 Π) with 1,3-Butadiene (CH 2 CHCHCH 2 ; X 1 A g ). Chemphyschem 2020; 21:1295-1309. [PMID: 32291897 DOI: 10.1002/cphc.202000183] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 04/12/2020] [Indexed: 12/18/2022]
Abstract
The crossed molecular beam reactions of the methylidyne radical (CH; X2 Π) with 1,3-butadiene (CH2 CHCHCH2 ; X1 Ag ) along with their (partially) deuterated counterparts were performed at collision energies of 20.8 kJ mol-1 under single collision conditions. Combining our laboratory data with ab initio calculations, we reveal that the methylidyne radical may add barrierlessly to the terminal carbon atom and/or carbon-carbon double bond of 1,3-butadiene, leading to doublet C5 H7 intermediates with life times longer than the rotation periods. These collision complexes undergo non-statistical unimolecular decomposition through hydrogen atom emission yielding the cyclic cis- and trans-3-vinyl-cyclopropene products with reaction exoergicities of 119±42 kJ mol-1 . Since this reaction is barrierless, exoergic, and all transition states are located below the energy of the separated reactants, these cyclic C5 H6 products are predicted to be accessed even in low-temperature environments, such as in hydrocarbon-rich atmospheres of planets and cold molecular clouds such as TMC-1.
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Zhao L, Kaiser RI, Xu B, Ablikim U, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Mebel AM. A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201913037] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Zhao L, Kaiser RI, Xu B, Ablikim U, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Mebel AM. A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase. Angew Chem Int Ed Engl 2020; 59:4051-4058. [DOI: 10.1002/anie.201913037] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Indexed: 11/10/2022]
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Zhao L, Kaiser RI, Lu W, Kostko O, Ahmed M, Evseev MM, Bashkirov EK, Oleinikov AD, Azyazov VN, Mebel AM, Howlader AH, Wnuk SF. Gas phase formation of cyclopentanaphthalene (benzindene) isomers via reactions of 5- and 6-indenyl radicals with vinylacetylene. Phys Chem Chem Phys 2020; 22:22493-22500. [DOI: 10.1039/d0cp03846f] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The reaction of indenyl radicals with vinylacetylene leads to cyclopentanaphthalene at low temperature.
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Zhao L, Kaiser RI, Lu W, Ahmed M, Oleinikov AD, Azyazov VN, Mebel AM, Howlader AH, Wnuk SF. Gas phase formation of phenalene via 10π-aromatic, resonantly stabilized free radical intermediates. Phys Chem Chem Phys 2020; 22:15381-15388. [DOI: 10.1039/d0cp02216k] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
1H-Phenalene can be synthesized via the reaction of the 1-naphthyl radical with methylacetylene and allene under high temperature conditions prevalent in carbon-rich circumstellar environments and combustion systems.
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Mikheyev PA, Chernyshov AK, Svistun MI, Ufimtsev NI, Kartamysheva OS, Heaven MC, Azyazov VN. Transversely optically pumped Ar:He laser with a pulsed-periodic discharge. OPTICS EXPRESS 2019; 27:38759-38767. [PMID: 31878637 DOI: 10.1364/oe.383276] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Accepted: 12/12/2019] [Indexed: 06/10/2023]
Abstract
Optically pumped rare gas lasers have the potential for scaling to high-power cw systems with good beam quality. Metastable atoms of heavier rare gases that are the lasing species are produced in an electric discharge at near atmospheric pressure. The key problem for this class of lasers at present is the development of a suitable discharge system. In this paper, we present the results of optimization of a pulsed discharge system with the goal of minimizing cathode sputtering and peak discharge current. The first demonstration of a transversely pumped system and measurements of the optical pumping threshold for the Ar:He laser are also presented.
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Pershin AA, Ghildina AR, Mebel AM, Azyazov VN, Mikheyev PA, Heaven MC. Computational investigation of energy transfer and line broadening for Ar * + He collisions. J Chem Phys 2019; 151:224306. [PMID: 31837673 DOI: 10.1063/1.5133043] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Potential energy curves for all states arising from the interaction of He with the 3p6, 3p54s, and 3p54p configurations of Ar have been determined using high-level electronic structure calculations. The results have been used to examine collisional energy transfer probabilities and spectral line shape parameters (shifting and broadening rate coefficients). The main focus has been on states and transitions that are of relevance to optically pumped He/Ar* laser systems. The line shape predictions were found to be in good agreement with experimental data, while there is notable disagreement for the energy transfer probabilities. The experimental data are found to be at variance with the predictions of standard two-state curve crossing models for energy transfer.
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Zhao L, Prendergast MB, Kaiser RI, Xu B, Lu W, Ablikim U, Ahmed M, Oleinikov AD, Azyazov VN, Mebel AM, Howlader AH, Wnuk SF. Reactivity of the Indenyl Radical (C 9 H 7 ) with Acetylene (C 2 H 2 ) and Vinylacetylene (C 4 H 4 ). Chemphyschem 2019; 20:1437-1447. [PMID: 30938059 DOI: 10.1002/cphc.201900052] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 02/28/2019] [Indexed: 11/09/2022]
Abstract
The reactions of the indenyl radicals with acetylene (C2 H2 ) and vinylacetylene (C4 H4 ) is studied in a hot chemical reactor coupled to synchrotron based vacuum ultraviolet ionization mass spectrometry. These experimental results are combined with theory to reveal that the resonantly stabilized and thermodynamically most stable 1-indenyl radical (C9 H7 . ) is always formed in the pyrolysis of 1-, 2-, 6-, and 7-bromoindenes at 1500 K. The 1-indenyl radical reacts with acetylene yielding 1-ethynylindene plus atomic hydrogen, rather than adding a second acetylene molecule and leading to ring closure and formation of fluorene as observed in other reaction mechanisms such as the hydrogen abstraction acetylene addition or hydrogen abstraction vinylacetylene addition pathways. While this reaction mechanism is analogous to the bimolecular reaction between the phenyl radical (C6 H5 . ) and acetylene forming phenylacetylene (C6 H5 CCH), the 1-indenyl+acetylene→1-ethynylindene+hydrogen reaction is highly endoergic (114 kJ mol-1 ) and slow, contrary to the exoergic (-38 kJ mol-1 ) and faster phenyl+acetylene→phenylacetylene+hydrogen reaction. In a similar manner, no ring closure leading to fluorene formation was observed in the reaction of 1-indenyl radical with vinylacetylene. These experimental results are explained through rate constant calculations based on theoretically derived potential energy surfaces.
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Zhao L, Prendergast MB, Kaiser RI, Xu B, Lu W, Ablikim U, Ahmed M, Oleinikov AD, Azyazov VN, Mebel AM, Howlader AH, Wnuk SF. Cover Feature: Reactivity of the Indenyl Radical (C9
H7
) with Acetylene (C2
H2
) and Vinylacetylene (C4
H4
) (ChemPhysChem 11/2019). Chemphyschem 2019. [DOI: 10.1002/cphc.201900486] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Zhao L, Kaiser RI, Xu B, Ablikim U, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Zagidullin MV, Morozov AN, Howlader AH, Wnuk SF, Mebel AM, Joshi D, Veber G, Fischer FR. Gas phase synthesis of [4]-helicene. Nat Commun 2019; 10:1510. [PMID: 30944302 PMCID: PMC6447558 DOI: 10.1038/s41467-019-09224-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 02/27/2019] [Indexed: 11/29/2022] Open
Abstract
A synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry involving elementary reactions with aryl radicals is presented. In contrast to traditional synthetic routes involving solution chemistry and ionic reaction intermediates, the gas phase synthesis involves a targeted ring annulation involving free radical intermediates. Exploiting the simplest helicene as a benchmark, we show that the gas phase reaction of the 4-phenanthrenyl radical ([C14H9]•) with vinylacetylene (C4H4) yields [4]-helicene (C18H12) along with atomic hydrogen via a low-barrier mechanism through a resonance-stabilized free radical intermediate (C18H13). This pathway may represent a versatile mechanism to build up even more complex polycyclic aromatic hydrocarbons such as [5]- and [6]-helicene via stepwise ring annulation through bimolecular gas phase reactions in circumstellar envelopes of carbon-rich stars, whereas secondary reactions involving hydrogen atom assisted isomerization of thermodynamically less stable isomers of [4]-helicene might be important in combustion flames as well. Helicenes represent key building blocks leading eventually to carbonaceous nanostructures. Here, exploiting [4]-helicene as a benchmark, the authors present a synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry with aryl radicals involving ring annulation.
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Zhao L, Xu B, Ablikim U, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Howlader AH, Wnuk SF, Mebel AM, Kaiser RI. Gas‐Phase Synthesis of Triphenylene (C
18
H
12
). Chemphyschem 2019. [DOI: 10.1002/cphc.201900200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Zhao L, Xu B, Ablikim U, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Howlader AH, Wnuk SF, Mebel AM, Kaiser RI. Front Cover: Gas‐Phase Synthesis of Triphenylene (C
18
H
12
) (ChemPhysChem 6/2019). Chemphyschem 2019. [DOI: 10.1002/cphc.201900201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Zhao L, Xu B, Ablikim U, Lu W, Ahmed M, Evseev MM, Bashkirov EK, Azyazov VN, Howlader AH, Wnuk SF, Mebel AM, Kaiser RI. Gas‐Phase Synthesis of Triphenylene (C
18
H
12
). Chemphyschem 2019; 20:791-797. [DOI: 10.1002/cphc.201801154] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 01/30/2019] [Indexed: 11/09/2022]
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Zhao L, Prendergast M, Kaiser RI, Xu B, Ablikim U, Lu W, Ahmed M, Oleinikov AD, Azyazov VN, Howlader AH, Wnuk SF, Mebel AM. How to add a five-membered ring to polycyclic aromatic hydrocarbons (PAHs) – molecular mass growth of the 2-naphthyl radical (C10H7) to benzindenes (C13H10) as a case study. Phys Chem Chem Phys 2019; 21:16737-16750. [DOI: 10.1039/c9cp02930c] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The reaction of aryl radicals with allene/methylacetylene leads to five-membered ring addition in PAH growth processes.
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Pershin AA, Torbin AP, Zagidullin MV, Mebel AM, Mikheyev PA, Azyazov VN. Rate constants for collision-induced emission of O 2(a 1Δ g) with He, Ne, Ar, Kr, N 2, CO 2 and SF 6 as collisional partners. Phys Chem Chem Phys 2018; 20:29677-29683. [PMID: 30474096 DOI: 10.1039/c8cp06231e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Rate constants for singlet oxygen collision induced emission of the a1Δg-X3Σ-g transition at 1.27 μm were measured for CO2, N2, SF6, and rare gases as collisional partners. Photolysis of ozone by 266 nm laser radiation produced singlet oxygen. We performed direct measurements of pressure dependences of the 1.27 μm emission intensity for partner gases. The measured rate constants kMa-X in the units of 10-24 cm3 s-1 are as follows: CO2 - 10 ± 2; N2 - 3.2 ± 0.6; SF6 - 7 ± 1; He - 1.1 ± 0.3; Ne - 1.3 ± 0.3; Ar - 2.8 ± 0.6; Kr - 6 ± 1. The measured values of kMa-X are close to the values calculated from absorption measurements. Considering the known rate constants kMb-a for the b1Σg+-a1Δg transition in the gas phase we found that the ratio kMa-X/kMb-a was constant and independent of a collisional partner according to the "spin-orbit based" mechanism of intensity borrowing proposed by Minaev (THEOCHEM, 1989, 183, 207). However, this ratio amounted to (1.3 ± 0.2) × 10-4, which is considerably lower than the theoretically predicted value of (3-6) × 10-4.
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Zagidullin MV, Kaiser RI, Porfiriev DP, Zavershinskiy IP, Ahmed M, Azyazov VN, Mebel AM. Functional Relationships between Kinetic, Flow, and Geometrical Parameters in a High-Temperature Chemical Microreactor. J Phys Chem A 2018; 122:8819-8827. [PMID: 30345750 DOI: 10.1021/acs.jpca.8b06837] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Computational fluid dynamics (CFD) simulations and isothermal approximation were applied for the interpretation of experimental measurements of the C10H7Br pyrolysis efficiency in the high-temperature microreactor and of the pressure drop in the flow tube of the reactor. Applying isothermal approximation allows the derivation of analytical relationships between the kinetic, gas flow, and geometrical parameters of the microreactor, which, along with CFD simulations, accurately predict the experimental observations. On the basis of the obtained analytical relationships, a clear strategy for measuring rate coefficients of (pseudo) first-order bimolecular and unimolecular reactions using the microreactor was proposed. The pressure- and temperature-dependent rate coefficients for the C10H7Br pyrolysis calculated using variable reaction coordinate transition state theory were invoked to interpret the experimental data on the pyrolysis efficiency.
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Zhao L, Kaiser RI, Xu B, Ablikim U, Ahmed M, Zagidullin MV, Azyazov VN, Howlader AH, Wnuk SF, Mebel AM. VUV Photoionization Study of the Formation of the Simplest Polycyclic Aromatic Hydrocarbon: Naphthalene (C 10H 8). J Phys Chem Lett 2018; 9:2620-2626. [PMID: 29717871 DOI: 10.1021/acs.jpclett.8b01020] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The formation of the simplest polycyclic aromatic hydrocarbon (PAH), naphthalene (C10H8), was explored in a high-temperature chemical reactor under combustion-like conditions in the phenyl (C6H5)-vinylacetylene (C4H4) system. The products were probed utilizing tunable vacuum ultraviolet light by scanning the photoionization efficiency (PIE) curve at a mass-to-charge m/ z = 128 (C10H8+) of molecules entrained in a molecular beam. The data fitting with PIE reference curves of naphthalene, 4-phenylvinylacetylene (C6H5CCC2H3), and trans-1-phenylvinylacetylene (C6H5CHCHCCH) indicates that the isomers were generated with branching ratios of 43.5±9.0 : 6.5±1.0 : 50.0±10.0%. Kinetics simulations agree nicely with the experimental findings with naphthalene synthesized via the hydrogen abstraction-vinylacetylene addition (HAVA) pathway and through hydrogen-assisted isomerization of phenylvinylacetylenes. The HAVA route to naphthalene at elevated temperatures represents an alternative pathway to the hydrogen abstraction-acetylene addition (HACA) forming naphthalene in flames and circumstellar envelopes, whereas in cold molecular clouds, HAVA synthesizes naphthalene via a barrierless bimolecular route.
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Lucas M, Thomas AM, Kaiser RI, Bashkirov EK, Azyazov VN, Mebel AM. 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. J Phys Chem A 2018. [DOI: 10.1021/acs.jpca.8b00756] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Krasnoukhov VS, Porfiriev DP, Zavershinskiy IP, Azyazov VN, Mebel AM. Kinetics of the CH3 + C5H5 Reaction: A Theoretical Study. J Phys Chem A 2017; 121:9191-9200. [DOI: 10.1021/acs.jpca.7b09873] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Zagidullin MV, Khvatov NA, Medvedkov IA, Tolstov GI, Mebel AM, Heaven MC, Azyazov VN. O 2(b 1Σ g+) Quenching by O 2, CO 2, H 2O, and N 2 at Temperatures of 300-800 K. J Phys Chem A 2017; 121:7343-7348. [PMID: 28892383 DOI: 10.1021/acs.jpca.7b07885] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rate constants for the removal of O2(b1Σg+) by collisions with O2, N2, CO2, and H2O have been determined over the temperature range from 297 to 800 K. O2(b1Σg+) was excited by pulses from a tunable dye laser, and the deactivation kinetics were followed by observing the temporal behavior of the b1Σg+-X3Σg- fluorescence. The removal rate constants for CO2, N2, and H2O were not strongly dependent on temperature and could be represented by the expressions kCO2 = (1.18 ± 0.05) × 10-17 × T1.5 × exp[Formula: see text], kN2 = (8 ± 0.3) × 10-20 × T1.5 × exp[Formula: see text], and kH2O = (1.27 ± 0.08) × 10-16 × T1.5 × exp[Formula: see text] cm3 molecule-1 s-1. Rate constants for O2(b1Σg+) removal by O2(X), being orders of magnitude lower, demonstrated a sharp increase with temperature, represented by the fitted expression kO2 = (7.4 ± 0.8) × 10-17 × T0.5 × exp[Formula: see text] cm3 molecule-1 s-1. All of the rate constants measured at room temperature were found to be in good agreement with previously reported values.
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Yang T, Kaiser RI, Troy TP, Xu B, Kostko O, Ahmed M, Mebel AM, Zagidullin MV, Azyazov VN. HACA's Heritage: A Free‐Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars. Angew Chem Int Ed Engl 2017; 56:4515-4519. [DOI: 10.1002/anie.201701259] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Indexed: 11/10/2022]
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Azyazov VN, Bresler SM, Torbin AP, Mebel AM, Heaven MC. Removal of Rb(6(2)P) by H(2), CH(4), and C(2)H(6). OPTICS LETTERS 2016; 41:669-672. [PMID: 26872159 DOI: 10.1364/ol.41.000669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The saturated hydrocarbons methane and ethane are often used as collisional energy transfer agents in diode-pumped alkali vapor lasers (DPALs). Problems are encountered because the hydrocarbons eventually react with the optically pumped alkali atoms, resulting in the contamination of the gas lasing medium and damage of the gas cell windows. The reactions require excitation of the more highly excited states of the alkali atoms, which can be generated in DPAL systems by energy pooling processes. Knowledge of the production and loss rates for the higher excited states is needed for a quantitative understanding of the photochemistry. In the present study, we have used experimental and theoretical techniques to characterize the removal of Rb(6P2) by hydrogen, methane, and ethane.
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Zagidullin MV, Pershin AA, Azyazov VN, Mebel AM. Luminescence of the (O2(a(1)Δ(g)))2 collisional complex in the temperature range of 90-315 K: Experiment and theory. J Chem Phys 2015; 143:244315. [PMID: 26723679 DOI: 10.1063/1.4938425] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O2(a(1)Δg) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O2(a(1)Δg))2 collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90-315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k2 and k3 are found to be similar, with the k3/k2 ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k2 slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O2)2 dimole, which were utilized to compute rate constants k2 and k3 within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O2 molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1(1)Ag←(1)B3u transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1(1)Ag←2(1)Ag transition induced by the asymmetric O-O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k2 and k3 close to one another.
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