DIRECT INFRARED IDENTIFICATION OF THE CRIEGEE INTERMEDIATES syn- and anti-CH3CHOO AND THEIR DISTINCT CONFORMATION-DEPENDENT REACTIVITY

Lee, Yuan-Pern

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Description

Title

DIRECT INFRARED IDENTIFICATION OF THE CRIEGEE INTERMEDIATES syn- and anti-CH3CHOO AND THEIR DISTINCT CONFORMATION-DEPENDENT REACTIVITY

Author(s)

Lee, Yuan-Pern

Contributor(s)

• Witek, Henry A
• Nishimura, Yoshifumi
• Bowman, Joel
• Wang, Xiaohong
• Huang, Yu-Hsuan
• Lin, Hui-Yu

Issue Date

26-Jun-15

Keyword(s)

Atmospheric science

Abstract

The Criegee intermediates are carbonyl oxides that play critical roles in ozonolysis of alkenes in the atmosphere. Su et al. reported the mid-infrared spectrum of the simplest Criegee intermediate chem{CH_2OO}.footnote { Y.-T. ~Su, Y.-H. ~Huang, H. A. ~Witek, Y.-P. ~Lee, textit{Science} underline{textbf{340}}, 174 (2013).} Methyl substitution of chem{CH_2OO} produces two conformers of chem{CH_3CHOO} and consequently complicates the infrared spectrum. We report the transient infrared spectrum of both $syn$- and $anti$-chem{CH_3CHOO}, produced from chem{CH_3CHI} + chem{O_2} in a flow reactor, using a step-scan Fourier-transform spectrometer. Guided and supported by high-level full-dimensional quantum calculations, rotational contours of the four observed bands are simulated successfully and provide definitive identification of both conformers. Although nearly all observed bands of $anti$-chem{CH_3CHOO} overlapped with $syn$-chem{CH_3CHOO}, the Q-branch of $nu$$_{8}$ near 1090.6 cm$^{-1}$ is contributed solely by $syn$-chem{CH_3CHOO}, and that of $nu$$_{7}$ near 1280.8 cm$^{-1}$ is also dominated by $syn$-chem{CH_3CHOO}. Furthermore, $anti$-chem{CH_3CHOO} shows a reactivity greater than $syn$-chem{CH_3CHOO} toward NO/chem{NO_2}; at the later period of reaction, the spectrum can be simulated with only $syn$-chem{CH_3CHOO}. Without NO/chem{NO_2}, $anti$-chem{CH_3CHOO} also decays much faster than $syn$-chem{CH_3CHOO}. The direct infrared detection of $syn$- and $anti$-chem{CH_3CHOO} should prove useful for field measurements and laboratory investigations of the Criegee mechanism.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

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