Rate Coefficients for the Reaction of Iodine Oxide with Methyl Peroxy Radicals

Abstract

Pulsed laser photolysis radical generation is used to study the title reaction IO+CH(3)O(2)→products. Sensitive and selective laser-induced fluorescence detection of IO allows excess CH(3)O(2) conditions to be maintained throughout, ensuring minimal interference from other fast IO reactions. The rate coefficients, k(5)(296 K)=(3.4±1.4)×10(-12) cm(3) molecule(-1) s(-1), are obtained relative to a well-characterised reference value (k(3) for IO+HO(2)). This result agrees well with a previous determination from this laboratory and demonstrates that the above reaction proceeds an order of magnitude slower than suggested in other recent experimental and theoretical studies. Implications for HOx production/O(3) destruction within the marine boundary layer are briefly discussed.

Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance

“…Discussion of the possible importance of BrO/RO 2 in non-polar marine boundary layers has been presented by Sakamoto et al 174 The reactions of IO with organic peroxy radicals are also receiving significant attention due to their potential role in ozone destruction in marine boundary layers, with data now available for three species (CH 3 O 2 , CF 3 O 2 and CH 3 CH 2 O 2 ). However, agreement among the multiple studies of the CH 3 O 2 /IO reaction is poor, as measurements of Dillon et al, 180,181 using a pulsed-photolysis/LIF detection method (k E 3 Â 10 À12 cm 3 molecule À1 s À1 ), differ from other data 182,183 by more than an order of magnitude. Agreement regarding the CF 3 O 2 + IO reaction is better, but the data of Enami et al 183 still exceed other measurements by about 50%.…”

Reactive halogen chemistry in the troposphere

“…The reaction of IO with the methyl dioxy radical 56 can enhance the HO 2 formation rates by up to 10%, therefore producing more OH and ozone loss:…”

Rate constant of the reaction between CH3O2 and OH radicals

“…is run by using the two rate constants found in the literature: the full line represents the model with k 16 = 7×10 -11 cm 3 s -1 such as proposed by Enami et al[28] and Bale et al[29], while the dashed line represents a model using k 16 = 3.4×10 -12 cm 3 s -1 , the most recent value from Dillon et al[30]. Again, the initial CH 3 -and Iconcentrations have been adjusted such that the CH 3 O 2 concentration is best reproduced on longer time scales.…”