Infrared spectrum of (z)-3-iodo-but-2-en-1-yl [•CH2CHC(CH3)I] produced upon photodissociation of (z)-1,3-diiodo-but-2-ene [(CH2I)HC = C(CH3)I] in solid para-hydrogen

Lee, Yuan-Pern

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https://hdl.handle.net/2142/104519 Copy

Description

Title

Infrared spectrum of (z)-3-iodo-but-2-en-1-yl [•CH2CHC(CH3)I] produced upon photodissociation of (z)-1,3-diiodo-but-2-ene [(CH2I)HC = C(CH3)I] in solid para-hydrogen

Author(s)

Lee, Yuan-Pern

Contributor(s)

Haupa, Karolina Anna

Issue Date

2019-06-18

Keyword(s)

Radicals

Abstract

Isoprene is the most abundant volatile organic compound (VOC) in the Earth’s atmosphere after methane. Ozonolysis of isoprene, with the production of the Criegee intermediate methyl vinyl ketone oxide (MVKO), plays an important role in atmospheric chemistry. Recently, Barber \textit{et al.}\footnote{V. P. Barber \textit{et al.} J. Am. Chem. Soc., \textbf{140}, 10866-10880 (2018).} photolyzed 1,3-diiodo-but-2-ene [\chem{(CH_2I)HC=C(CH_3)I}] in the presence of O$_2$ with UV light and identified the Criegee intermediate \textit{syn-trans-}MVKO as the main reaction product. However, the detailed mechanism for the production of MVKO is unexplored. It was assumed that photolysis of \chem{(CH_2I)HC=C(CH_3)I} at 248 nm results in preferential dissociation of the weaker allylic C$_{(1)}$--I bond, rather than the vinylic (sp$^{2}$-hybridized) C$_{(3)}$--I bond. Addition of O$_2$ to the C$_{(3)}$ atom, followed by breaking the C$_{(3)}$--I bond, produces the Criegee intermediate MVKO.\\ In this work we took the advantege of the diminished cage effect of solid \textit{para-}hydrogen (\textit{p-}H$_2$) as a matrix host to study the UV photodissociation of \chem{\textit{(Z)-}(CH_2I)HC=C(CH_3)I}. We report the formation and infrared identification of \textit{(Z)-}3-iodo-but-2-en-1-yl [\chem{\bullet CH_2CHC(CH_3)I}] radical intermediate upon photodissociation of \chem{\textit{(Z)-}(CH_2I)HC=C(CH_3)I} in solid \textit{p-}H$_2$ at 3.3 K with light at 280 nm. Lines at 3115.6, 2025.2, 3001.2, 2933.2, 2880.3, 2835.8, 1474.9, 1409.6, 1406.7, 1375.5, 1265.3, 1061.8, 1018.5, 1008.6, 922.0, 913.7, and 792.5 cm$^{-1}$ are assigned to \chem{\textit{(Z)-}\bullet CH_2CHC(CH_3)I}. The assignments were derived according to behavior on secondary photolysis and comparison of the vibrational wavenumbers and the IR intensities of the observed lines with values predicted with the B2PLYP-D3/cc-pVTZ-pp method. No evidence of breakage of the C$_{(3)}$--I bond to form \chem{\bullet C(CH_3)=C(CH_2I)H} was observed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104519

DOI

https://doi.org/10.15278/isms.2019.TD03

Copyright and License Information

Copyright 2019 Yuan-Pern Lee

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