SPECTRAL STUDIES OF THE REACTION OF THE CRIEGEE INTERMEDIATE CH₃CHOO WITH HCL USING A STEP-SCAN FOURIER-TRANSFORM INFRARED ABSORPTION SPECTROMETER

Lee, Yuan-Pern

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Description

Title

SPECTRAL STUDIES OF THE REACTION OF THE CRIEGEE INTERMEDIATE CH₃CHOO WITH HCL USING A STEP-SCAN FOURIER-TRANSFORM INFRARED ABSORPTION SPECTROMETER

Author(s)

Lee, Yuan-Pern

Contributor(s)

Su, Zih-Syuan

Issue Date

2023-06-20

Keyword(s)

Radicals

Abstract

Reactions between Criegee intermediates and hydrogen halides are important in atmospheric chemistry, because of their large rate coefficients. Employing a Fourier-transform absorption spectrometer in a step-scan mode or a continuous- scan mode, we recorded infrared spectra of transient species and end products in a flowing mixture of CH₃CHI₂/HCl/N₂/O₂ irradiated at 308 nm. Eight bands near 1383.7, 1357.9, 1323.8, 1271.8, 1146.2, 1098.2, 1017.5 and 931.5 cm−¹ were experimentally observed and assigned to bands ν₈ to ν₁₅ of the anti-conformer of chloroethyl hydroperoxide (CEHP, CH₃CHClOOH), according to comparison of vibrational wavenumbers and IR intensities predicted with the B3LYP/aug- cc-pVTZ method. We derived a rate coefficient of anti-CH₃CHOO + HCl to be kHCl = (3.1 ± 0.2)x10−¹⁰ cm³ molecule−¹s−¹ from the formation of anti-CEHP. At a later reaction period, absorption bands of H₂O and acetyl chloride, CH₃C(O)Cl, at 1819.1 cm−¹were observed; these species were produced from the decomposition of anti-CEHP or the secondary reactions of CH₃CHClO + O₂ → CH₃C(O)Cl + HO₂ and OH + HCl → H₂O + Cl according to temporal profiles of CEHP, H₂O, and CH₃C(O)Cl; both O₂ and HCl are major species in the system to participate in the secondary reactions. By adding methanol to deplete anti-CH₃CHOO, we observed only anti-CEHP, indicating that the interconversion from syn- CEHP to anti-CEHP is rapid. The branching ratio of the formation of CH₃C(O)Cl + H₂O to that of CH₃CHClO + OH was estimated to be 0.5 : 0.5. This observation serves as an excellent example that secondary reactions might interfere with the observation of the original products.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122357

DOI

https://doi.org/10.15278/isms.2023.6904

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