Atmospheric Chemistry of 1,1,1,2-Tetrachloroethane (CCl 3 CH 2 Cl): Spectrokinetic Investigation of the CCl 3 CClHO 2 Radical, Its Reactions with NO and NO 2 , and Atmospheric Fate of the CCl 3 CClHO Radical Trine E. Møgelberg, Merete Bilde, and Jens Sehested* Section for Chemical ReactiVity, EnVironmental Science and Technology Department, Risø National Laboratory, DK-4000 Roskilde, Denmark Timothy J. Wallington* Ford Research Laboratory, Mail Drop SRL-3083, Ford Motor Company, P.O. Box 2053, Dearborn, Michigan 48121-2053 Ole J. Nielsen* Ford Forschungszentrum Aachen, Dennewartstrasse 25, D-52068 Aachen, Germany ReceiVed: May 22, 1996; In Final Form: September 25, 1996 X A pulse radiolysis technique was used to study the ultraviolet absorption spectra of CCl 3 CClH and CCl 3 - CClHO 2 radicals, the kinetics of the self-reaction of CCl 3 CClHO 2 radicals, and the kinetics of the reactions of CCl 3 CClHO 2 with NO and NO 2 in the gas phase at 296 K. At 240 nm, σ(CCl 3 CClH) ) (303 ( 35) × 10 -20 , and at 250 nm, σ(CCl 3 CClHO 2 ) ) (288 ( 48) × 10 -20 cm 2 molecule -1 . The observed rate constant for the self-reaction of CCl 3 CClHO 2 radicals was (5.0 ( 1.2) × 10 -12 cm 3 molecule -1 s -1 . The rate constants for reactions of CCl 3 CClHO 2 radicals with NO and NO 2 were k 3 > 9.0 × 10 -12 and k 4 ) (8.9 ( 2.6) × 10 -12 cm 3 molecule -1 s -1 , respectively. A long path length Fourier transform infrared technique was used to show that at 295 K in 700 Torr total pressure of air 76 ( 3% of CCl 3 CClHO radicals decompose via C-C bond scission and 24 ( 3% undergo three-center intramolecular HCl elimination. As part of this work rate constants for the reaction of F and Cl atoms with CCl 3 CH 2 Cl were determined to be (6.4 ( 1.2) × 10 -12 and (5.7 ( 1.0) × 10 -14 cm 3 molecule -1 s -1 , respectively. The results are discussed with respect to the atmospheric chemistry of tetrachloroethane. 1. Introduction The adverse impact of chlorine released from chlorofluoro- carbons (CFCs) on stratospheric ozone has led to a ban on their production beginning in 1996. At this time a variety of compounds are being considered as CFC replacements. Hy- drofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are two important classes of CFC replacements. The choice of HFCs and HCFCs is motivated by a number of considerations, not least of which is that, unlike CFCs, the HFCs and HCFCs contain at least one C-H bond which makes them susceptible to attack by OH radicals and, hence, to degradation in the lower atmosphere. The probable future large-scale use of HFCs and HCFCs has generated considerable interest in their environ- mental acceptability and thus their atmospheric chemistry. As part of a collaborative study of the atmospheric chemistry of HFCs and HCFCs we have undertaken a study of CCl 3 CH 2 Cl. While CCl 3 CH 2 Cl is not expected to assume any major industrial importance in the near future, it possesses structural similarity to CF 3 CH 2 F (HFC-134a), which is the most important CFC substitute. Hence, information concerning CCl 3 CH 2 Cl provides insight into the atmospheric chemistry of other more important compounds. Following release into the atmosphere CCl 3 CH 2 Cl will react with OH radicals: By analogy to other peroxy radicals, 1 CCl 3 CClHO 2 radicals will react with NO, NO 2 , HO 2 , and other peroxy radicals in the atmosphere: A pulse radiolysis technique combined with time-resolved UV- visible spectroscopy was used to determine the UV absorption spectra of CCl 3 CClH and CCl 3 CClHO 2 radicals and to study the kinetics of reactions 3, 4, and 6. In the case of reaction 6 we studied the self-reaction of the peroxy radical (R′ ) CCl 3 - CClHO 2 ). The fate of the CCl 3 CClHO radical produced in reaction 3a was determined using a FTIR spectrometer coupled to a smog chamber. The results are reported herein. 2. Experimental Section Two different experimental systems were used. Both have been described in detail in previous publications 2,3 and will only be discussed briefly here. X Abstract published in AdVance ACS Abstracts, November 1, 1996. CCl 3 CH 2 Cl + OH f CCl 3 CClH + H 2 O (1) CCl 3 CClH + O 2 + M f CCl 3 CClHO 2 + M (2) CCl 3 CClHO 2 + NO f CCl 3 CClHO + NO 2 (3a) CCl 3 CClHO 2 + NO + M f CCl 3 CClHONO 2 + M (3b) CCl 3 CClHO 2 + NO 2 + M f CCl 3 CClHO 2 NO 2 + M (4) CCl 3 CClHO 2 + HO 2 f products (5) CCl 3 CClHO 2 + R′O 2 f products (6) 18399 J. Phys. Chem. 1996, 100, 18399-18407 S0022-3654(96)01489-X CCC: $12.00 © 1996 American Chemical Society