title: Direct Measurements of Unimolecular and Bimolecular Reaction Kinetics of the Criegee Intermediate (CH3)2COO.
abstract: The Criegee intermediate acetone oxide, (CH3)2COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O2and 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 SO2was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10-11cm3s-1at 298 K and 4 Torr and (1.5 ± 0.5) × 10-10cm3s-1at 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 N2from cavity ring-down decay of the ultraviolet absorption of (CH3)2COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10-10to (2.29 ± 0.08) × 10-10cm3s-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 NO2has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10-12cm3s-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 SO2and the small rate coefficient for its reaction with water. Product measurements of the reactions of (CH3)2COO with NO2and with SO2suggest that these reactions may facilitate isomerization to 2-hydroperoxypropene, possibly by subsequent reactions of association products.
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Rabi
authors.initials: R
authors.lastname: Chhantyal-Pun
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: Oliver
authors.initials: O
authors.lastname: Welz
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: John D
authors.initials: JD
authors.lastname: Savee
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: Arkke J
authors.initials: AJ
authors.lastname: Eskola
authors.affiliation: School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, U.K.|Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University , Hung Hom, Hong Kong.
authors.forename: Edmond P F
authors.initials: EP
authors.lastname: Lee
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Lucy
authors.initials: L
authors.lastname: Blacker
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Henry R
authors.initials: HR
authors.lastname: Hill
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Matilda
authors.initials: M
authors.lastname: Ashcroft
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: M Anwar H
authors.initials: MA
authors.lastname: Khan
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Guy C
authors.initials: GC
authors.lastname: Lloyd-Jones
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Louise
authors.initials: L
authors.lastname: Evans
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: Brandon
authors.initials: B
authors.lastname: Rotavera
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Huang
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
authors.affiliation: The Centre for Atmospheric Science, The School of Earth, Atmospheric and Environmental Science, The University of Manchester , Simon Building, Brunswick Street, Manchester M13 9PL, U.K.
authors.forename: Daniel K W
authors.initials: DK
authors.lastname: Mok
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University , Hung Hom, Hong Kong.
authors.forename: John M
authors.initials: JM
authors.lastname: Dyke
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Dudley E
authors.initials: DE
authors.lastname: Shallcross
authors.affiliation: The Centre for Atmospheric Science, The School of Earth, Atmospheric and Environmental Science, The University of Manchester , Simon Building, Brunswick Street, Manchester M13 9PL, U.K.
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Percival
authors.affiliation: School of Chemistry, The University of Bristol , Cantock's Close BS8 1TS, U.K.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Orr-Ewing
authors.affiliation: Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories , Livermore, California 94551-0969, United States.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Taatjes