Browsing by Author "Chung, Chen-An"

Now showing 1 - 3 of 3

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
;
Su, Jou Wei
;
Lee, Yuan-Pern
;
交大名義發表
;
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.
Detection of a Criegee Intermediate with an Unsaturated Hydrocarbon Substituent: Fourier-Transform Microwave Spectroscopy of Methyl Vinyl Ketone Oxide
(2020-07-30)
Endo, Yasuki
;
Witek, Henryk A.
;
Chung, Chen-An
;
Lee, Yuan-Pern
;
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.
Rate coefficient of the reaction CH2OO + NO2 probed with a quantum-cascade laser near 11 mu m
(2019-08-28)
Luo, Pei-Ling
;
Chung, Chen-An
;
Lee, Yuan-Pern
;
交大名義發表
;
應用化學系
The reaction of the simplest Criegee intermediate CH2OO with NO2 is considered to be important in atmospheric chemistry because of its prospective contribution to the decay of CH2OO and the additional source of NO3, hence its effects on the NOx and HOx cycles. The reported rate coefficients of this reaction varied by a factor of 5. Employing a cw quantum-cascade laser with wavelength near 11 mu m coupled with Herriott mirrors to probe CH2OO sensitively, we investigated in detail the reaction CH2OO + NO2 under total pressure 5.9-9.7 Torr at 298 K and reported a rate coefficient k(NO2) = (1.0 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1), about one-seventh the value determined with direct measurements of CH2OO by Weltz et al. This smaller rate coefficient implies that the title reaction contributes to the atmospheric source of NO3 and the decay of CH2OO much less than previously conceived.