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Introduction

Chloroethenes are produced in large amounts and are widely used in industrial activities as solvents, dry cleaning, degreasing agents and in the PVC production. As highly volatile organic compounds, significant fractions enter the atmosphere. In the troposphere the reaction with OH radicals is the dominant primary oxidation step and also the reaction with the chlorine atom should be considered since the rate constant for this process is larger than for the reaction with OH. The possibility of Br-atom reaction occurring in the troposphere has been suggested [1]. The reaction with O(³P) atoms is generally not competitive with the other paths because of the low concentration of O(³P) atoms although it is a prototype system for the addition reactions to the C=C bond. The NO₃ radical has strong oxidizing capacity and although it generally much less reactive than OH, its peak tropospheric concentration is higher during the night, making its reaction with the halocarbons comparable to that with OH radicals [2].

The total atmospheric burden of a halocarbon is determined both by the rate of its release and by the atmospheric lifetime (itself directly related to the rates of loss processes). Photolysis in the stratosphere (and in the upper troposphere) constitutes are important sink for the halocarbons. The atmospheric lifetime against photolysis is shorter for molecules that contain relatively more chlorine than fluorine and is even shorter if bromine is substituted for chlorine. Molecules that contain hydrogen in place of halogens are susceptible to attack by OH in the troposphere, as are molecules possessing double bonds.

The reactions of CH₂=CHCl, CH₂=CCl2, Z-CHCl=CHCl, E-CHCl=CHCl, CHCl=CCl₂ and CCl₂=CCl₂ with O(³P), Cl(²P) and Br(²P) atoms and with OH and NO₃ radicals were studied in this work using semiempirical and ab-initio calculations.