Browsing by Author "Lee, Yuan-Pern"

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A Direct Mapping Approach to Understand Carrier Relaxation Dynamics in Varied Regions of a Polycrystalline Perovskite Film
(1970-01-01)
Fathi, Amir
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Jokar, Efat
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Lee, Yuan-Pern
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Diau, Eric Wei-Guang
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交大名義發表
We developed a direct mapping approach to overlay the image of a polycrystalline perovskite film obtained from the transient absorption microscope (TAM) with that from the scanning electron microscope (SEM). By mapping these imaging data pixel by pixel, we are able to observe the relaxation dynamics of the photo-generated charge carriers on varied regions of the film. The carrier relaxation dynamics contain a dominated single-exponential decay component owing to the recombination of charge carriers. The lifetime distribution of charge recombination shows a bimodal feature, for which the rapid and slow distributions are assigned as free and trapped carriers, respectively. The charge recombination was slower in the grain boundary (GB) region than in the grain interior (GI) region. The small grains have longer lifetimes than the large grains for the crystal size smaller than 500 nm. Therefore, GB with retarded charge recombination might play a positive role in a perovskite solar cell.
A new method for investigating infrared spectra of protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) using para-hydrogen
(2012-04-21)
Bahou, Mohammed
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Wu, Yu-Jong
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Lee, Yuan-Pern
;
應用化學系
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應用化學系分子科學碩博班
We use protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) to demonstrate a new method that has some advantages over other methods currently used. C6H7+ and c-C6H7 were produced on electron bombardment of a mixture of benzene (C6H6) and para-hydrogen during deposition onto a target at 3.2 K. Infrared (IR) absorption lines of C6H7+ decreased in intensity when the matrix was irradiated at 365 nm or maintained in the dark for an extended period, whereas those of c-C6H7 increased in intensity. Observed vibrational wavenumbers, relative IR intensities, and deuterium isotopic shifts agree with those predicted theoretically. This method, providing a wide spectral coverage with narrow lines and accurate relative IR intensities, can be applied to larger protonated polyaromatic hydrocarbons and their neutral species which are difficult to study with other methods. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3703502]
Absorption cross sections of NH3, NH2D, NHD2, and ND3 in the spectral range 140-220 nm and implications for planetary isotopic fractionation
(2006-08-20)
Cheng, Bing-Ming
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Lu, Hsiao-Chi
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Chen, Hong-Kai
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Bahou, Mohammed
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Lee, Yuan-Pern
Cross sections for photoabsorption of NH3, NH2D, NHD2, and ND3 in the spectral region 140-220 nm were determined at similar to 298 K using synchrotron radiation. Absorption spectra of NH2D and NHD2 were deduced from spectra of mixtures of NH3 and ND3, of which the equilibrium concentrations for all four isotopologues obey statistical distributions. Cross sections of NH2D, NHD2, and ND3 are new. Oscillator strengths, an integration of absorption cross sections over the spectral lines, for both A X and B X systems of NH3 agree satisfactorily with previous reports; values for NH2D, NHD2, and ND3 agree with quantum chemical predictions. The photolysis of NH3 provides a major source of reactive hydrogen in the lower stratosphere and upper troposphere of giant planets such as Jupiter. Incorporating the measured photoabsorption cross sections of NH3 and NH2D into the Caltech/JPL photochemical diffusive model for the atmosphere of Jupiter, we find that the photolysis efficiency of NH2D is lower than that of NH3 by as much as 30%. The D/H ratio in NH2D/NH3 for tracing the microphysics in the troposphere of Jupiter is also discussed.
Activation of Molecular Hydrogen by Arylcarbenes
(2018-12-12)
Mendez-Vega, Enrique
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Maehara, Mika
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Raut, Akshay Hemant
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Mieres-Perez, Joel
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Tsuge, Masashi
The hydrogenation reactions of diphenylcarbene 1, fluorenylidene 2, and dibenzocycloheptadienylidene 3 were investigated in solid H-2 and D-2 matrices and in H-2- and D-2-doped argon matrices at cryogenic temperatures. The reactivity of the carbenes towards H-2 increases in the order 1<3<2. Whereas 1 is stable in solid H-2, 2 and 3 react fast under the same conditions via quantum chemical tunneling. In D-2 both 1 and 3 are stable, whereas 2 slowly reacts. The different reactivity of the three carbenes is rationalized in terms of differing carbene stabilization energies.
Advances in Use of p-H(2) as a Novel Host for Matrix IR Spectroscopy
(2010-08-01)
Bahou, Mohammed
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Huang, Chiung-Wei
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Huang, Ya-Ling
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Glatthaar, Joerg
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Lee, Yuan-Pern
A review of recent advances in IR spectroscopy using p-H(2) as a matrix host in our laboratory is presented. The softness of this novel p-H, matrix host not only makes high-resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C(2)H(4), internal rotation (torsion) of CH(3)OH, and rotation of CH(3)F about a single axis are characterized in this p-H, matrix. In contrast, no evidence for rotation of CH(3)I and CH(3) was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH(3) produced from photolysis of CH(3)I and CH(3)S produced from photolysis of CH(3)SCH(3) and CH(3)SSCH(3). The reaction of Cl with CS(2) in solid p-H(2) yields ClSCS instead of ClCS(2). The reaction of Cl with HCOOH in solid p-H(2) yields only a complex, Cl center dot HCOOH, not HCl and HOCO. The presence of o-H(2) in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p-H(2). Experimental techniques to minimize the amount of o-H(2) and to characterize its relative concentration with spectra of H(2)O center dot o-H(2) are discussed.
Advances in Use of p-H-2 as a Novel Host for Matrix IR Spectroscopy
(2010-08-01)
Bahou, Mohammed
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Huang, Chiung-Wei
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Huang, Ya-Ling
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Glatthaar, Joerg
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Lee, Yuan-Pern
A review of recent advances in IR spectroscopy using p-H-2 as a matrix host in our laboratory is presented. The softness of this novel p-H, matrix host not only makes high-resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C2H4, internal rotation (torsion) of CH3OH, and rotation of CH3F about a single axis are characterized in this p-H, matrix. In contrast, no evidence for rotation of CH3I and CH3 was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH3 produced from photolysis of CH3I and CH3S produced from photolysis of CH3SCH3 and CH3SSCH3. The reaction of Cl with CS2 in solid p-H-2 yields ClSCS instead of ClCS2. The reaction of Cl with HCOOH in solid p-H-2 yields only a complex, Cl center dot HCOOH, not HCl and HOCO. The presence of o-H-2 in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p-H-2. Experimental techniques to minimize the amount of o-H-2 and to characterize its relative concentration with spectra of H2O center dot o-H-2 are discussed.
Alcohol dimers - how much diagonal OH anharmonicity?
(2014)
Kollipost, Franz
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Papendorf, Kim
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Lee, Yu-Fang
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Lee, Yuan-Pern
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Suhm, Martin A.
The OH bond of methanol, ethanol and t-butyl alcohol becomes more anharmonic upon hydrogen bonding and the infrared intensity ratio between the overtone and the fundamental transition of the bridging OH stretching mode decreases drastically. FTIR spectroscopy of supersonic slit jet expansions allows to quantify these effects for isolated alcohol dimers, enabling a direct comparison to anharmonic vibrational predictions. The diagonal anharmonicity increase amounts to 15-18%, growing with increasing alkyl substitution. The overtone/fundamental IR intensity ratio, which is on the order of 0.1 or more for isolated alcohols, drops to 0.004-0.001 in the hydrogen-bonded OH group, making overtone detection very challenging. Again, alkyl substitution enhances the intensity suppression. Vibrational second order perturbation theory appears to capture these effects in a semiquantitative way. Harmonic quantum chemistry predictions for the hydrogen bond-induced OH stretching frequency shift (the widely used infrared signature of hydrogen bonding) are insufficient, and diagonal anharmonicity corrections from experiment make the agreement between theory and experiment worse. Inclusion of anharmonic cross terms between hydrogen bond modes and the OH stretching mode is thus essential, as is a high level electronic structure theory. The isolated molecule results are compared to matrix isolation data, complementing earlier studies in N-2 and Ar by the more weakly interacting Ne and p-H-2 matrices. Matrix effects on the hydrogen bond donor vibration are quantified.
Bimolecular reaction of CH3 + CO in solid p-H-2: Infrared absorption of acetyl radical (CH3CO) and CH3-CO complex
(2014-06-28)
Das, Prasanta
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
We have recorded infrared spectra of acetyl radical (CH3CO) and CH3-CO complex in solid para-hydrogen (p-H-2). Upon irradiation at 248 nm of CH3C(O)Cl/p-H-2 matrices, CH3CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (v(9)), 2989.1 (v(1)), 2915.6 (v(2)), 1880.5 (v(3)), 1419.9 (v(10)), 1323.2 (v(5)), 836.6 (v(7)), and 468.1 (v(8)) cm (1) were observed. When CD3C(O)Cl was used, lines of CD3CO at 2246.2 (v(9)), 2244.0 (v(1)), 1866.1 (v(3)), 1046.7 (v(5)), 1029.7 (v(4)), 1027.5 (v(10)), 889.1 (v(6)), and 723.8 (v(7)) cm (1) appeared. Previous studies characterized only three vibrational modes of CH3CO and one mode of CD3CO in solid Ar. In contrast, upon photolysis of a CH3I/CO/p-H-2 matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH3-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm(-1). The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH3CO can be readily produced from photolysis of CH3C(O)Cl because of the diminished cage effect in solid p-H-2 but not from the reaction of CH3 + CO because of the reaction barrier. Even though CH3 has nascent kinetic energy greater than 87 kJ mol(-1) and internal energy similar to 42 kJ mol(-1) upon photodissociation of CH3I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of similar to 27 kJ mol(-1) for the formation of CH3CO from the CH3 + CO reaction; a barrierless channel for formation of a CH3-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H-2. (C) 2014 AIP Publishing LLC.
Bimolecular reaction of CH3 + CO in solid p-H-2: Infrared absorption of acetyl radical (CH3CO) and CH3-CO complex
(2014-06-28)
Das, Prasanta
;
Lee, Yuan-Pern
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
We have recorded infrared spectra of acetyl radical (CH3CO) and CH3-CO complex in solid para-hydrogen (p-H-2). Upon irradiation at 248 nm of CH3C(O)Cl/p-H-2 matrices, CH3CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (v(9)), 2989.1 (v(1)), 2915.6 (v(2)), 1880.5 (v(3)), 1419.9 (v(10)), 1323.2 (v(5)), 836.6 (v(7)), and 468.1 (v(8)) cm (1) were observed. When CD3C(O)Cl was used, lines of CD3CO at 2246.2 (v(9)), 2244.0 (v(1)), 1866.1 (v(3)), 1046.7 (v(5)), 1029.7 (v(4)), 1027.5 (v(10)), 889.1 (v(6)), and 723.8 (v(7)) cm (1) appeared. Previous studies characterized only three vibrational modes of CH3CO and one mode of CD3CO in solid Ar. In contrast, upon photolysis of a CH3I/CO/p-H-2 matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH3-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm(-1). The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predicted with quantum-chemical calculations. This work clearly indicates that CH3CO can be readily produced from photolysis of CH3C(O)Cl because of the diminished cage effect in solid p-H-2 but not from the reaction of CH3 + CO because of the reaction barrier. Even though CH3 has nascent kinetic energy greater than 87 kJ mol(-1) and internal energy similar to 42 kJ mol(-1) upon photodissociation of CH3I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of similar to 27 kJ mol(-1) for the formation of CH3CO from the CH3 + CO reaction; a barrierless channel for formation of a CH3-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H-2. (C) 2014 AIP Publishing LLC.
Blue/near UV light emission from hybrid InN/TiO(2) nanoparticle films
(2011-01-01)
Wu, Chih-Wei
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Lu, Chih-Wei
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Lee, Yuan-Pern
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Wu, Yu-Jong
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Cheng, Bing-Ming
We report on the enhancement of photoluminescence (PL) from anatase TiO(2) thin films covered by InN nanoparticles prepared using plasma enhanced chemical vapor deposition (PECVD). The SEM images and X-ray diffraction spectra illustrate the strong interaction between the InN particles and the TiO(2) films. UV-Vis absorption spectra indicate that the InN particles have an increased absorption in the visible light region and may sensitize the TiO(2) films. The strong PL band observed in the anatase TiO(2) thin films with the addition of InN may have been due to an increased localization of impurities and/or defect-trapped excitons.
Blue/near UV light emission from hybrid InN/TiO2 nanoparticle films
(2011-01-01)
Wu, Chih-Wei
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Lu, Chih-Wei
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Lee, Yuan-Pern
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Wu, Yu-Jong
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Cheng, Bing-Ming
We report on the enhancement of photoluminescence (PL) from anatase TiO2 thin films covered by InN nanoparticles prepared using plasma enhanced chemical vapor deposition (PECVD). The SEM images and X-ray diffraction spectra illustrate the strong interaction between the InN particles and the TiO2 films. UV-Vis absorption spectra indicate that the InN particles have an increased absorption in the visible light region and may sensitize the TiO2 films. The strong PL band observed in the anatase TiO2 thin films with the addition of InN may have been due to an increased localization of impurities and/or defect-trapped excitons.
Comparison of Geometric, Electronic, and Vibrational Properties for All Pentagon/Hexagon-Bearing Isomers of Fullerenes C(38), C(40), and C(42)
(2009-08-05)
Malolepsza, Edyta
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Lee, Yuan-Pern
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Witek, Henryk A.
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Irle, Stephan
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Lin, Chun-Fu
The self-consistent-charge density-functional tight-binding (SCC-DFTB) method is employed for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all pentagon/hexagon-bearing isomers of C(38), C(40), and C(42) as the second part of a larger effort to catalogue the CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C(20)-C(180) [analogous data for C(20)-C(36) were published previously in Malolepsza et al., J Phys Chem A, 2007, 111, 6649]. Common features among the fullerenes are identified and properties characteristic for each specific fullerene cage size are discussed. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1999-2011, 2009
Comparison of Geometric, Electronic, and Vibrational Properties for All Pentagon/Hexagon-Bearing Isomers of Fullerenes C-38, C-40, and C-42
(2009-08-05)
Malolepsza, Edyta
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Lee, Yuan-Pern
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Witek, Henryk A.
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Irle, Stephan
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Lin, Chun-Fu
The self-consistent-charge density-functional tight-binding (SCC-DFTB) method is employed for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all pentagon/hexagon-bearing isomers of C-38, C-40, and C-42 as the second part of a larger effort to catalogue the CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C-20-C-180 [analogous data for C-20-C-36 were published previously in Malolepsza et al., J Phys Chem A, 2007, 111, 6649]. Common features among the fullerenes are identified and properties characteristic for each specific fullerene cage size are discussed. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1999-2011, 2009
Computational Chemical Kinetics for the Reaction of Criegee Intermediate CH2OO with HNO3 and Its Catalytic Conversion to OH and HCO
(2017-05-25)
Raghunath, P.
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Lee, Yuan-Pern
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
The kinetics and mechanisms for the reaction of the Criegee intermediate CH2OO with HNO3 and the unimolecular decomposition of its reaction product CH2(O)NO3 are important in atmospheric chemistry. The potential-energy profile of the reactions predicted with the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ method shows that the initial association yields a prereaction complex that isomerizes by H migration to yield excited intermediate nitrooxymethyl hydroperoxide NO3CH2OOH* with internal energy similar to 44 kcal mol(-1). A fragmentation of this excited intermediate produces CH2(O)NO3 + OH with its transition state located 5.0 kcal mor(-1) below that of the reactants. Further decomposition of CH2(O)NO3 produces HCO + HNO3, forming a catalytic cycle for destruction of CH2OO by HNO3. The rate coefficients and product-branching ratios were calculated in the temperature range 250-700 K at pressure 20-760 Torr (N-2) using the variational-transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate coefficient for reaction CH2OO + HNO3 at 295 K, 5.1 x 10(-10) cm(3) molecule(-1) s(-1), agrees satisfactorily with the experimental value, (5.4 +/- 1.0) X 10(-10) cm(3) molecule(-1) s(-1). The predicted branching ratios at 295 K are 0.21 for the formation of NO3CH2OOH and 0.79 for CH2(O)NO3 + OH at a pressure of 40 Torr (N-2), and 0.79 for the formation of NO3CH2OOH and 0.21 for CH2(O)NO3 + OH at 760 Torr (N-2). This new catalytic conversion of CH2OO to HCO + OH by HNO3 might have significant impact on atmospheric chemistry.
Critical interpretation of CH- and OH- stretching regions for infrared spectra of methanol clusters (CH3OH)(n) (n=2-5) using self-consistent-charge density functional tight-binding molecular dynamics simulations
(2014-09-07)
Nishimura, Yoshifumi
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Lee, Yuan-Pern
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Irle, Stephan
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Witek, Henryk A.
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交大名義發表
Vibrational infrared (IR) spectra of gas-phase O-H center dot center dot center dot O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that nu(3), nu(9), and nu(2) C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum. (C) 2014 AIP Publishing LLC.
Design and Characterization of Heteroleptic Ruthenium Complexes Containing Benzimidazole Ligands for Dye-Sensitized Solar Cells: The Effect of Fluorine Substituents on Photovoltaic Performance
(1970-01-01)
Huang, Wei-Kai
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Wu, Hui-Ping
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Lin, Pi-Lun
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Lee, Yuan-Pern
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Diau, Eric Wei-Guang
"We designed heteroleptic ruthenium complexes (RD12-RD15) containing fluoro-substituted benzimidazole ligands for dye-sensitized solar cells (DSSCs). These dyes were synthesized according to a typical one-pot procedure with the corresponding ancillary ligands produced in two simple steps; they were prepared into DSSC devices according to the same conditions of fabrication. The eventual devices show a systematic trend of increasing V-OC and decreasing J(SC) with fluorine atoms of increasing number substituted on the ligand. The charge extraction results show that upward shifts of the TiO2 potential occurred when the fluoro-substituted dyes were sensitized on TiO2 with a systematic trend of shift N719 > RD15 (with 5 F) > RD12 (with 2 F) > RD5 (no F); the intensity modulated photovoltage spectra indicate that those fluoro substituents retard charge recombination with the electron lifetimes (tau(R)) in the order RD15 > RD12 > RD5 > N719, consistent with the variation of V-OC for the systems."
Detailed mechanism and kinetics of the reaction of Criegee intermediate CH2OO with HCOOH investigated via infrared identification of conformers of hydroperoxymethyl formate and formic acid anhydride
(2019-10-14)
Chung, Chen-An
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Su, Jou Wei
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Lee, Yuan-Pern
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交大名義發表
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應用化學系
The reaction of Criegee intermediate CH2OO with HCOOH is important in atmospheric chemistry, but its mechanism and kinetics are little investigated. We recorded time-resolved infrared absorption spectra of transient species produced upon irradiation at 308 nm of a flowing mixture of CH2I2/O-2/N-2/HCOOH at 298 K. Bands of CH2OO were observed initially upon irradiation; their decrease was accompanied with the appearance of several bands near 887, 925, 1052, 1115, 1170, 1342, 1391, and 1760 cm(-1), assigned to the absorption of hydroperoxymethyl formate [HC(O)OCH2OOH, HPMF], that decreased in intensity at a later period with the appearance of absorption bands of the anti-conformer of formic acid anhydride [anti-(HCO)(2)O, FAN] near 998, 1101, 1767, and 1821 cm(-1). The main contributions of the infrared absorption of HPMF are from an open-form conformer, but small contributions from the intramolecular hydrogen-bonded conformer that absorbs near 1070, 1170, and 1732 cm(-1) were identified. Observed infrared spectra of both conformers of HPMF and anti-FAN agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/aug-cc-pVTZ method. We derived a rate coefficient for CH2OO + HCOOH to be k = (1.4 +/- 0.3) x 10(-10) cm(3) molecule(-1) s(-1) from formation of HPMF. We found also that anti-FAN was produced mainly from the open-form conformer with rate coefficient k = (1460 +/- 30) s(-1); the intramolecular hydrogen-bonded conformer of HPMF is stable.
Detailed mechanism of the CH2I + O-2 reaction: Yield and self-reaction of the simplest Criegee intermediate CH2OO
(2014-09-14)
Ting, Wei-Lun
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Chang, Chun-Hung
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Lee, Yu-Fang
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Matsui, Hiroyuki
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Lee, Yuan-Pern
The application of a new reaction scheme using CH2I + O-2 to generate the simplest Criegee intermediate, CH2OO, has stimulated lively research; the Criegee intermediates are extremely important in atmospheric chemistry. The detailed mechanism of CH2I + O-2 is hence important in understanding kinetics involving CH2OO. We employed ultraviolet absorption to probe simultaneously CH2I2, CH2OO, CH2I, and IO in the reaction system of CH2I + O-2 upon photolysis at 248 nm of a flowing mixture of CH2I2, O-2, and N-2 (or SF6) in the pressure range 7.6-779 Torr to investigate the reaction kinetics. With a detailed mechanism to model the observed temporal profiles of CH2I, CH2OO, and IO, we found that various channels of the reaction CH2I + O-2 and CH2OO + I play important roles; an additional decomposition channel of CH2I + O-2 to form products other than CH2OO or ICH2OO becomes important at pressure less than 60 Torr. The pressure dependence of the derived rate coefficients of various channels of reactions of CH2I + O-2 and CH2OO + I has been determined. We derived a rate coefficient also for the self-reaction of CH2OO as k = (8 +/- 4) x 10(-11) cm(3) molecule(-1) s(-1) at 295 K. The yield of CH2OO from CH2I + O-2 was found to have a pressure dependence on N-2 and O-2 smaller than in previous reports; for air under 1 atm, the yield of similar to 30% is about twice of previous estimates. (C) 2014 AIP Publishing LLC.
Detection of a Criegee Intermediate with an Unsaturated Hydrocarbon Substituent: Fourier-Transform Microwave Spectroscopy of Methyl Vinyl Ketone Oxide
(2020-07-30)
Endo, Yasuki
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Witek, Henryk A.
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Chung, Chen-An
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Lee, Yuan-Pern
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交大名義發表
Pure rotational transitions of methyl vinyl ketone oxide, or the so called methyl-vinyl Criegee intermediate, were observed by Fourier-transform microwave spectroscopy. Among the four possible conformers of this species, predicted by theory within an energy window of 3 kcal/mol, only the lowest-energy conformer, the syn-trans form, was detected in a discharged jet of a 1,3-diiode-but-2-ene (either in Z- or E-conformation) and O-2 mixture diluted in Ar. Thirty pure rotational transitions with internal rotation splitting of the methyl top were observed. The observed frequencies were analyzed by the XIAM program, yielding an internal rotation barrier of 702.8(28) cm(-1), which reasonably agrees with a theoretical value of 680 cm(-1) determined with CCSD(T)/cc-pVTZ.
Detection of transient infrared absorption of SO3 and 1,3,2-dioxathietane-2,2-dioxide [cyc-(CH2)O(SO2)O] in the reaction CH2OO+SO2
(2018-02-14)
Wang, Yi-Ying
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Dash, Manas Ranjan
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Chung, Chao-Yu
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Lee, Yuan-Pern
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應用化學系
We recorded time-resolved infrared absorption spectra of transient species produced on irradiation at 308 nm of a flowing mixture of CH2I2/O-2/N-2/SO2 at 298 K. Bands of CH2OO were observed initially upon irradiation; their decrease in intensity was accompanied by the appearance of an intense band at 1391.5 cm(-1) that is associated with the degenerate SO-stretching mode of SO3, two major bands of HCHO at 1502 and 1745 cm(-1), and five new bands near > 1340, 1225, 1100, 940, and 880 cm(-1). The band near 1340 cm(-1) was interfered by absorption of SO2 and SO3, so its band maximum might be greater than 1340 cm(-1). SO3 in its internally excited states was produced initially and became thermalized at a later period. The rotational contour of the band of thermalized SO3 agrees satisfactorily with the reported spectrum of SO3. These five new bands are tentatively assigned to an intermediate 1,3,2-dioxathietane-2,2-dioxide [cyc-(CH2)O(SO2)O] according to comparison with anharmonic vibrational wavenumbers and relative IR intensities predicted for this intermediate. Observation of a small amount of cyc-(CH2)O(SO2)O is consistent with the expected reaction according to the potential energy scheme predicted previously. SO3+HCHO are the major products of the title reaction. The other predicted product channel HCOOH+SO2 was unobserved and its branching ratio was estimated to be < 5%. Published by AIP Publishing.