Browsing by Author "Lin, Jim Jr-Min"

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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
;
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.
Direct kinetic measurement of the reaction of the simplest Criegee intermediate with water vapor
(2015-02-13)
Chao, Wen
;
Hsieh, Jun-Ting
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Chang, Chun-Hung
;
Lin, Jim Jr-Min
;
應用化學系
Carbonyl oxides, or Criegee intermediates, are important transient species formed in the reactions of unsaturated hydrocarbons with ozone. Although direct detection of Criegee intermediates has recently been realized, the main atmospheric sink of Criegee intermediates remains unclear. We report ultraviolet absorption spectroscopic measurements of the lifetime of the simplest Criegee intermediate, CH2OO, at various relative humidity levels up to 85% at 298 kelvin. An extremely fast decay rate of CH2OO was observed at high humidity. The observed quadratic dependence of the decay rate on water concentration implied a predominant reaction with water dimer. On the basis of the water dimer equilibrium constant, the effective rate coefficient of the CH2OO + (H2O)(2) reaction was determined to be 6.5 (+/-0.8) x 10(-12) cubic centimeters per second. This work would help modelers to better constrain the atmospheric concentrations of CH2OO.
Does Ozone-Water Complex Produce Additional OH Radicals in the Atmosphere?
(2012-12-13)
Jin, Bing
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Su, Man-Nung
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Lin, Jim Jr-Min
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應用化學系
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Department of Applied Chemistry
Ozone-water complex has been thought to play a role in producing atmospheric OH radicals through its photolysis. Here, we re-examined the absorption cross-section of the ozone-water complex with a new method to tell whether the above speculation is valid. With argon solvation and photoionization by tunable vacuum ultraviolet light, we were able to selectively probe the ozone-water 1:1 complex. The measured cross-section of the complex is only similar to the sum of the cross-sections of ozone and water monomers at 157.6, 248.4, and 308.4 nm. In addition, we did not observe any absorption of the complex at 351.8 nm. The results indicate that the OH production through the photolysis of the ozone-water complex is much slower than previously thought.
Electronic quenching of O(D-1) by Xe: Oscillations in the product angular distribution and their dependence on collision energy
(2015-08-07)
Garofalo, Lauren A.
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Smith, Mica C.
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Dagdigian, Paul J.
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Klos, Jacek
;
Alexander, Millard H.
The dynamics of the O(D-1) + Xe electronic quenching reaction was investigated in a crossed beam experiment at four collision energies. Marked large-scale oscillations in the differential cross sections were observed for the inelastic scattering products, O(P-3) and Xe. The shape and relative phases of the oscillatory structure depend strongly on collision energy. Comparison of the experimental results with time-independent scattering calculations shows qualitatively that this behavior is caused by Stueckelberg interferences, for which the quantum phases of the multiple reaction pathways accessible during electronic quenching constructively and destructively interfere. (C) 2015 AIP Publishing LLC.
Energy dependent oscillations in the angular distribution of O(D-1) + Xe inelastic scattering
(2014-08-10)
Garofalo, Lauren A.
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Smith, Mica C.
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Boering, Kristie A.
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Lin, Jim Jr-Min
;
應用化學系
Kinetics and absolute UV absorption spectrum of a methyl substituted Criegee intermediate CH3CHOO
(2014-08-10)
Smith, Mica
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Ting, Wei-Lun
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Chang, Chun-Hung
;
Boering, Kristie
;
Lin, Jim Jr-Min
Note: A transient absorption spectrometer using an ultra bright laser-driven light source
(2013-08-01)
Su, Man-Nung
;
Lin, Jim Jr-Min
;
應用化學系
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Department of Applied Chemistry
An apparatus to measure transient absorption spectra for short-lived species in the gas phase was built. This was achieved by coupling a laser-driven plasma light source to a time-gated intensified-CCD spectrometer. Although the laser-driven light source features high brightness, ultra broad bandwidth and long lifetime, we found it possesses a plasma oscillation at a frequency of similar to 200 kHz with a peak-to-peak amplitude of similar to 7%. This oscillation caused significant variation of the baseline of the transient absorption spectra even after averaging. To reduce this problem, we synchronized the detector gate time with the phase of the plasma oscillation. This arrangement results in much greater stability of the spectral baseline. We have tested the performance of the whole system with the time-resolved absorption spectra of excited NO3 radicals produced by pulsed laser photolysis of N2O5. (C) 2013 AIP Publishing LLC.
Photodissociation dynamics of ClOOCl at 248.4 and 308.4 nm
(2011)
Huang, Wen-Tsung
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Chen, Andrew F.
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Chen, I-Cheng
;
Tsai, Chen-Hsun
;
Lin, Jim Jr-Min
The dynamics of ClOOCl photodissociation at 248.4 and 308.4 nm was studied with photofragment translational spectroscopy. At 248.4 nm photoexcitation, the observed products are Cl, O(2), ClO and O. Product translational energy distributions P(E) and anisotropy parameters beta were deduced from the measured time-of-flight spectra of the Cl, O(2), and ClO photoproducts. The photodissociation mechanisms have been discussed and compared with available theoretical results. Synchronous and fast sequential breaking of the two Cl-O bonds may both contribute to the dissociation. The relative product yields for [ClO] : [Cl] was measured to be 0.15 +/- 0.04 : 1. The relative amounts of [O] : [O(2)] products were estimated to be 0.12 : 1. The branching ratios among the Cl + O(2) + Cl : ClO + ClO : ClO + Cl + O product channels were estimated to be 0.82 : 0.08 : 0.10. At 308.4 nm excitation, time-of-flight spectra of the O(2) and ClO photoproducts were recorded while there was interference from Cl(2) impurity in detecting the Cl product. Nonetheless, the observed ClO yield relative to the O(2) yield at 308.4 nm is 1.5 times that at 248.4 nm. The branching ratio between the Cl + O(2) + Cl : ClO + ClO product channels was estimated to be 0.81 : 0.19 at 308.4 nm. This result suggests that the ClO product may contribute a noticeable yield in the photolysis of ClOOCl at the atmospherically important wavelengths above 300 nm.
The bending vibrational levels of the acetylene cation: A case study of the Renner-Teller effect in a molecule with two degenerate bending vibrations
(2006-10-07)
Tang, Sheunn-Jiun
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Chou, Yung-Ching
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Lin, Jim Jr-Min
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Hsuc, Yen-Chu
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應用化學系
Forty three vibronic levels of C2H2+, X (2)Pi(u), with upsilon(4)=0-6, upsilon(5)=0-3, and K=0-4, lying at energies of 0-3520 cm(-1) above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+1(') two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the A (1)A(u), 4 nu(3) (K=1-2), 5 nu(3) (K=1), nu(2)+4 nu(3) (K=0), and 47 206 cm(-1) (K=1) levels of C2H2. Seven of the trans-bending levels of C2H2+ (upsilon(4)=0-3, K=0-2) had been reported previously by Pratt [J. Chem. Phys. 99, 6233 (1993)]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with upsilon(4)+upsilon(5)<= 2, except for the unobserved upper (2)Pi(u) component of the 2 nu(4) overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm(-1). The vibronic coupling parameter epsilon(5) (about whose magnitude there has been controversy) was determined to be -0.0273(7). For the higher vibronic levels, an additional parameter, r(45), was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the upsilon(4)+upsilon(5)=3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with upsilon(4)+upsilon(5)<= 5, an rms deviation of 0.34 cm(-1) was obtained using 20 parameters. An interesting finding is that Hund's spin-coupling cases (a) and (b) both occur in the Sigma(u) components of the nu(4)+2 nu(5) combination level. The ionization potential of C2H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91 953.77 +/- 0.09 cm(-1) (3 sigma). (c) 2006 American Institute of Physics.
The UV absorption spectrum of the simplest Criegee intermediate CH2OO
(2014)
Ting, Wei-Lun
;
Chen, Ying-Hsuan
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Chao, Wen
;
Smith, Mica C.
;
Lin, Jim Jr-Min
SO2 scavenging and self-reaction of CH2OO were utilized for the decay of CH2OO to extract the absorption spectrum of CH2OO under bulk conditions. Absolute absorption cross sections of CH2OO at 308.4 and 351.8 nm were obtained from laser-depletion measurements in a jet-cooled molecular beam. The peak cross section is (1.23 +/- 0.18) x 10(-17) cm(2) at 340 nm.
UV absorption spectrum of the C2 Criegee intermediate CH3CHOO
(2014-08-21)
Smith, Mica C.
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Ting, Wei-Lun
;
Chang, Chun-Hung
;
Takahashi, Kaito
;
Boering, Kristie A.
The UV spectrum of CH3CHOO was measured by transient absorption in a flow cell at 295 K. The absolute absorption cross sections of CH3CHOO were measured by laser depletion in a molecular beam to be (1.06 +/- 0.09) x 10(-17) cm(2) molecule-1 at 308 nm and (9.7 +/- 0.6) x 10(-18) cm(2) molecule-1 at 352 nm. After scaling the UV spectrum of CH3CHOO to the absolute cross section at 308 nm, the peak UV cross section is (1.27 +/- 0.11) x 10(-)1(7) cm(2) molecule-1 at 328 nm. Compared to the simplest Criegee intermediate CH2OO, the UV absorption band of CH3CHOO is similar in intensity but blue shifted by 14 nm, resulting in a 20% slower photolysis rate estimated for CH3CHOO in the atmosphere. (C) 2014 AIP Publishing LLC.