Volume 2 I 3, number 5,6 CHEMICAL PHYSICS LETTERS I5 October 1993 Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas phase at 295 K Jens Sehested, Ole John Nielsen zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC Chemical Reactivity Section, EnvironmentalScience and TechnologyDepartment,Rise National Laboratory, DK-4000Roskilde, Denmark and Timothy J. Wallington Research Stafl SRLE3083, Ford Motor Company,P.O. Box 2053, Dearborn,MI 48121-2053,USA Received 2 1 June 1993 The rate constants for the reaction of NO with a series of peroxy radicals: CHa02, C2H102, (CH&XH201, (CH,)3CC(CHS)2CHZ02, CH2FOI, CH$lO~, CH2Br02, CHFz02, CF#Zl02, CHF&F,Oz, CF$F202, CFCl,CHz02 and CF2ClCH202 were measured at 298 K and a total pressure of 1 atm. The rate constants were obtained using the absolute technique of pulse radiolysis combined with time-resolved UV-VIS spectroscopy. The results are discussed in terms of reactivity trends and the atmospheric chemistry of peroxy radicals. 1. Introduction Peroxy radicals, ROz, are important imterme- diates in the atmospheric degradation of organic compounds emitted to the atmosphere. The alkyl radical, R, can be produced from emitted organic compounds in several ways, e.g., by reactions with OH, or N03, radicals, or by photolysis. Alkyl radi- cals will react rapidly with atmospheric O2 to form peroxy radicals, ROz, R+Oz+M+ROz+M, (1) where M is a third body, N2 and 02, in the atmo- sphere. The fate of ROz radicals in the atmosphere is determined by reaction with NO, NOz, HOz, or other R02 radicals, ROz +NO-+products , ROz +N02 +M-+R02N0, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA +M , ROz + HOz -+ products , RO1 + R’Oz + products . (21, (3) (4) (5) The relative importance of reactions (2)-( 5 ) de- pends on the NO, NO*, HO2 and R02 concentra- tions and the values of the respective rate constants. In remote areas NO, concentrations as low as 1 ppt have been measured [ 11, decreasing the importance of reactions (2) and (3). However, in urban areas with higher NO, concentrations reaction (2) and (3) will be the major sink for ROz radicals. The reaction of ROz radicals with NO proceeds through two channels, RO,+NO+RO+NO,, @a) R02+NO+M+RON02+M. (2b) In this work we have used the pulse radiolysis tech- nique to investigate reaction (2) for a number of al- kyl peroxy and halogenated alkyl peroxy radicals: C&O,, CZHSOZ, (CH,),CCH,O,, (C&)&C- ( CH3)&H202, CH2F02, CH2C102, CH2Br02, CHF202, CF2C102, CHF2CF,02, CF3CFz02, CFC12CH202, and CF,ClCH,O,. 0009-2614/93/$ 06.00 0 1993 Elsevier Science Publishers B.V. All rights reserved. 457