Browsing by Author "Ting, Wei-Lun"

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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
;
Chang, Chun-Hung
;
Lee, Yu-Fang
;
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.
Kinetics and absolute UV absorption spectrum of a methyl substituted Criegee intermediate CH3CHOO
(2014-08-10)
Smith, Mica
;
Ting, Wei-Lun
;
Chang, Chun-Hung
;
Boering, Kristie
;
Lin, Jim Jr-Min
The UV absorption spectrum of the simplest Criegee intermediate CH2OO
(2014)
Ting, Wei-Lun
;
Chen, Ying-Hsuan
;
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.
;
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.