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@ARTICLE{Novelli:890512,
author = {Novelli, A. and Cho, C. and Fuchs, H. and Hofzumahaus, A.
and Rohrer, F. and Tillmann, R. and Kiendler-Scharr, A. and
Wahner, A. and Vereecken, L.},
title = {{E}xperimental and theoretical study on the impact of a
nitrate group on the chemistry of alkoxy radicals},
journal = {Physical chemistry, chemical physics},
volume = {23},
issn = {1463-9076},
address = {Cambridge},
publisher = {RSC Publ.},
reportid = {FZJ-2021-01003},
pages = {5474-5495},
year = {2021},
abstract = {The chemistry of nitrated alkoxy radicals, and its impact
on RO2 measurements using the laser induced fluorescence
(LIF) technique, is examined by a combined theoretical and
experimental study. Quantum chemical and theoretical kinetic
calculations show that the decomposition of
β-nitrate-alkoxy radicals is much slower than
β-OH-substituted alkoxy radicals, and that the spontaneous
fragmentation of the α-nitrate-alkyl radical product to a
carbonyl product + NO2 prevents other β-substituents from
efficiently reducing the energy barrier. The systematic
series of calculations is summarized as an update to the
structure–activity relationship (SAR) by Vereecken and
Peeters (2009), and shows increasing decomposition rates
with higher degrees of substitution, as in the series ethene
to 2,3-dimethyl-butene, and dominant H-migration for
sufficiently large alkoxy radicals such as those formed from
1-pentene or longer alkenes. The slow decomposition allows
other reactions to become competitive, including epoxidation
in unsaturated nitrate-alkoxy radicals; the decomposition
SAR is likewise updated for β-epoxy substituents. A set of
experiments investigating the NO3-initiated oxidation of
ethene, propene, cis-2-butene, 2,3-dimethyl-butene,
1-pentene, and trans-2-hexene, were performed in the
atmospheric simulation chamber SAPHIR with measurements of
HO2 and RO2 radicals performed with a LIF instrument.
Comparisons between modelled and measured HO2 radicals in
all experiments, performed in excess of carbon monoxide to
avoid OH radical chemistry, suggest that the reaction of HO2
with β-nitrate alkylperoxy radicals has a channel forming
OH and an alkoxy radical in yields of $15–65\%,$
compatible with earlier literature data on nitrated isoprene
and α-pinene radicals. Model concentrations of RO2 radicals
when including the results of the theoretical calculations
described here, agreed within $10\%$ with the measured RO2
radicals for all species investigated when the alkene
oxidation is dominated by NO3 radicals. The formation of NO2
in the decomposition of β-nitrate alkoxy radicals prevents
detection of the parent RO2 radical in a LIF instrument, as
it relies on formation of HO2. The implications for
measurements of RO2 in ambient and experimental conditions,
such as for the NO3-dominated chemistry during nighttime, is
discussed. The current results appear in disagreement with
an earlier indirect experimental study by Yeh et al. on
pentadecene.},
cin = {IEK-8},
ddc = {540},
cid = {I:(DE-Juel1)IEK-8-20101013},
pnm = {211 - Die Atmosphäre im globalen Wandel (POF4-211)},
pid = {G:(DE-HGF)POF4-211},
typ = {PUB:(DE-HGF)16},
pubmed = {33650597},
UT = {WOS:000627550700036},
doi = {10.1039/D0CP05555G},
url = {https://juser.fz-juelich.de/record/890512},
}