Study Of The Ch2i + O2 Reaction With A Step-scan Fourier-transform Infrared Absorption Spectrometer: Spectra Of The Criegee Intermediate Ch2oo And Dioxirane(?)

Huang, Yu-Hsuan

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https://hdl.handle.net/2142/51225 Copy

Description

Title

Study Of The Ch2i + O2 Reaction With A Step-scan Fourier-transform Infrared Absorption Spectrometer: Spectra Of The Criegee Intermediate Ch2oo And Dioxirane(?)

Author(s)

Huang, Yu-Hsuan

Contributor(s)

Lee, Yuan-Pern

Issue Date

2014-06-16

Keyword(s)

Radicals

Abstract

The Criegee intermediates are carbonyl oxides that play key roles in ozonolysis of unsaturated organic compounds. This mechanism was first proposed by Criegee in 1949, but the first direct observation of the simplest Criegee intermediate CH$_{2}$OO in the gaseous phase has been reported only recently using photoionization mass spectrometry.\footnote{O. Welz, J. D. Savee, D. L. Osborn, S. S.Vasu, C. J. Percival, D. E. Shallcross, and C. A. Taatjes, Science {\bf 335}, 204 (2012).} Our group has reported the low-resolution IR spectra of CH$_{2}$OO, produced from the reaction of CH$_{2}$I + O$_{2}$, with a second-generation step-scan Fourier-transfom IR absorption spectrometer.\footnote{Y.-T. Su, Y.-H. Huang, H. A.Witek, and Y.-P. Lee, Science {\bf 340}, 174 (2013).} The spectral assignments were based on comparison of observed vibrational wavenumbers and rotational contours with theoretical predictions. Here, we report the IR absorption spectra of CH$_{2}$OO at a resolution of 0.32 \wn, showing partially rotationally-resolved structures. The origins of the \nub{3}, \nub{4}, \nub{6}, and \nub{8} vibrational modes of CH$_{2}$OO are determined to be 1434.1, 1285.7, 909.2, and 847.3 \wn, respectively. With the analysis of the vibration-rotational spectra, we provide a definitive assignment of these bands to CH$_{2}$OO. The observed vibrational wavenumbers indicate a zwitterionic contribution to this singlet biradical showing a strengthened C-O bond and a weakened O-O bond. This zwitterionic character results to an extremely rapid self reaction via a cyclic dimer to form 2H$_{2}$CO + O$_{2}$ ($^{1}$$\Delta$$_{g}$). Another group of weak transient IR bands centered at 1231.5, 1213.3, and 899.8 \wn are also observed. These bands might be contributed from dioxirane, which was postulated to be another important intermediate that might be isomerized from the Criegee intermediate in the reaction of O$_{3}$ with 1-alkenes.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/51225

DOI

https://doi.org/10.15278/isms.2014.MI04

Copyright and License Information

Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/

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