Browsing by Author "Su, Yu-Te"

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Extremely rapid self-reaction of the simplest Criegee intermediate CH2OO and its implications in atmospheric chemistry
(2014-06-01)
Su, Yu-Te
;
Lin, Hui-Yu
;
Putikam, Raghunath
;
Matsui, Hiroyuki
;
Lin, M. C.
Criegee intermediates, which are carbonyl oxides produced when ozone reacts with unsaturated hydrocarbons, play an important role in the formation of OH and organic acids in the atmosphere, but they have eluded direct detection until recently. Reactions that involve Criegee intermediates are not understood fully because data based on their direct observation are limited. We used transient infrared absorption spectroscopy to probe directly the decay kinetics of formaldehyde oxide (CH2OO) and found that it reacts with itself extremely rapidly. This fast self-reaction is a result of its zwitterionic character. According to our quantum-chemical calculations, a cyclic dimeric intermediate that has the terminal O atom of one CH2OO bonded to the C atom of the other CH2OO is formed with large exothermicity before further decomposition to 2H(2)CO + O-2 ((1)Delta(g)). We suggest that the inclusion of this previously overlooked rapid reaction in models may affect the interpretation of previous laboratory experiments that involve Criegee intermediates.
Infrared Absorption Spectrum of the Simplest Criegee Intermediate CH2OO
(2013-04-12)
Su, Yu-Te
;
Huang, Yu-Hsuan
;
Witek, Henryk A.
;
Lee, Yuan-Pern
;
應用化學系
The Criegee intermediates are carbonyl oxides postulated to play key roles in the reactions of ozone with unsaturated hydrocarbons; these reactions constitute an important mechanism for the removal of unsaturated hydrocarbons and for the production of OH in the atmosphere. Here, we report the transient infrared (IR) absorption spectrum of the simplest Criegee intermediate CH2OO, produced from CH2I + O-2 in a flow reactor, using a step-scan Fourier-transform spectrometer. The five observed bands provide definitive identification of this intermediate. The observed vibrational frequencies are more consistent with a zwitterion rather than a diradical structure of CH2OO. The direct IR detection of CH2OO should prove useful for kinetic and mechanistic investigations of the Criegee mechanism.