Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH₃)₂COO

Abstract

Abstract:The Criegee intermediate acetone oxide, (CH 3 ) 2 COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O 2 and characterized by synchrotron photoionization mass spectrometry and by cavity ringdown ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO 2 was measured using photoionization mass spectrometry and pseudo-first order methods to be (7.3 ± 0.5) × 10 -11 cm 3 s -1 at 298 K and 4 Torr and (1.5 ± 0.5) × 10 -10 cm 3 s -1 at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of anti-CH 3 CHOO with SO 2 , and in good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 Torr and 100 Torr) in N 2 from cavity ringdown decay of the ultraviolet absorption of (CH 3 ) 2 COO yielded even larger rate coefficients, in the range (1.84  0.12) × 10 -10 to (2.29 ± 0.08) × 10 -10 cm 3 s -1 . Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, k H /k D = (0.53 ± 0.06), for reactions with SO 2 , which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD 3 ) 2 COO with NO 2 has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10 -12 cm 3 s -1 (measured with photoionization mass spectrometry), again similar to the reaction of anti-CH 3 CHOO with NO 2 . Cavity ringdown 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 (CH 3 ) 2 COO 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 (CH 3 ) 2 COO with SO 2 and the small rate coefficient for its reaction with water. Product measurements of the reactions of (CH 3 ) 2 COO with NO 2 and with SO 2 suggest that these reactions may facilitate isomerization to 2-hydroperoxypropene, possibly by subsequent reactions of association products.

Unimolecular decay strongly limits the atmospheric impact of Criegee intermediates

“…Lifetimes of the order of milliseconds are predicted here, in agreement with literature data, 16,41,[45][46][47][48][49][50][51] and allylresonance (reaction (10)) further increases the reaction rate. These reactions form vinyl hydroperoxides (VHP), where for asymmetric CI the E-VHP is by far the most dominant stereospecific product.…”

Measurements of a potential interference with laser-induced fluorescence measurements of ambient OH from the ozonolysis of biogenic alkenes

“…However, these results do not exclude the possibility that SCIs from the ozonolysis of the other BVOCs in these experiments are also thermally decomposing and contributing to OH production in the flow tube. Recent measurements suggest that the unimolecular decomposition of the (CH 3 ) 2 COO Criegee intermediate can be rapid and compete with the reaction of this intermediate with water or SO 2 (Smith et al, 2016;Chhantyal-Pun et al, 2017). A similar rate for the decomposition of SCIs in the experiments reported here could also compete with the reaction of this intermediate with acetic acid.…”

Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

“…[8] In the dipole capture model, [9] thereaction cross section is greater than the physical dimensions of the reactants,a nd the rate coefficient k d-d is: Here m D1 and m D2 are the dipole moments of the two reactants, m is their reduced mass, k B is the Boltzmann constant, and C is ac onstant dependent on the anisotropy of the capture potential. Figure 2s hows ap lot of the temperature dependence of the measured rate coefficients k 1 (T).…”