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Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH3)2COO
journal contribution
posted on 2016-10-18, 00:00 authored by Rabi Chhantyal-Pun, Oliver Welz, John D. Savee, Arkke J. Eskola, Edmond
P. F. Lee, Lucy Blacker, Henry R. Hill, Matilda Ashcroft, M. Anwar H. Khan, Guy C. Lloyd-Jones, Louise Evans, Brandon Rotavera, Haifeng Huang, David
L. Osborn, Daniel K. W. Mok, John M. Dyke, Dudley E. Shallcross, Carl J. Percival, Andrew J. Orr-Ewing, Craig A. TaatjesThe
Criegee intermediate acetone oxide, (CH3)2COO,
is formed by laser photolysis of 2,2-diiodopropane in the presence
of O2 and characterized by synchrotron photoionization
mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy.
The rate coefficient of the reaction of the Criegee intermediate with
SO2 was measured using photoionization mass spectrometry
and pseudo-first-order methods to be (7.3 ± 0.5) × 10–11 cm3 s–1 at 298 K and
4 Torr and (1.5 ± 0.5) × 10–10 cm3 s–1 at 298 K and 10 Torr (He buffer). These
values are similar to directly measured rate coefficients of anti-CH3CHOO with SO2, and in good
agreement with recent UV absorption measurements. The measurement
of this reaction at 293 K and slightly higher pressures (between 10
and 100 Torr) in N2 from cavity ring-down decay of the
ultraviolet absorption of (CH3)2COO yielded
even larger rate coefficients, in the range (1.84 ± 0.12) ×
10–10 to (2.29 ± 0.08) × 10–10 cm3 s–1. Photoionization mass spectrometry
measurements with deuterated acetone oxide at 4 Torr show an inverse
deuterium kinetic isotope effect, kH/kD = (0.53 ± 0.06), for reactions with SO2, which may be consistent with recent suggestions that the
formation of an association complex affects the rate coefficient.
The reaction of (CD3)2COO with NO2 has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) ×
10–12 cm3 s–1 (measured
with photoionization mass spectrometry), again similar to rate for
the reaction of anti-CH3CHOO with NO2. Cavity ring-down measurements of the acetone oxide removal
without added reagents display a combination of first- and second-order
decay kinetics, which can be deconvolved to derive values for both
the self-reaction of (CH3)2COO and its unimolecular
thermal decay. The inferred unimolecular decay rate coefficient at
293 K, (305 ± 70) s–1, is similar to determinations
from ozonolysis. The present measurements confirm the large rate coefficient
for reaction of (CH3)2COO with SO2 and the small rate coefficient for its reaction with water. Product
measurements of the reactions of (CH3)2COO with
NO2 and with SO2 suggest that these reactions
may facilitate isomerization to 2-hydroperoxypropene, possibly by
subsequent reactions of association products.
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cavity ring-down decayacetone oxide removalunimolecular decay rate coefficientrate coefficientsCH 3Cavity ring-down measurements2 COOCH 3 CHOOphotoionization mass spectrometrycmUV absorption measurementsBimolecular Reaction Kinetics4 Torr4 Torr show293 Krate coefficientacetone oxide298 KPhotoionization mass spectrometry measurementssynchrotron photoionization mass spectrometry
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