Reaction pathways in the gas phase negative ion chemistry of chlorinated ethenes

Abstract

The reaction rate coefficients and ion products for the gas-phase reactions of O₂⁻, O⁻, OH⁻, CF₃⁻, and F⁻ with trichloroethene (CCl₂CHCl), 1,1-dichloroethene (CH₂CCl₂), and Z (cis) and E (trans)-1,2-dichloroethene (CHClCHCl) are presented. With the exception of CCl₂CHCl, the O₂⁻ bimolecular reaction rate coefficients are substantially below the collisional values. All the other anions react with the molecules with rate coefficients at or close to (within a factor of two) the corresponding collisional values. The experimental results are interpreted in terms of pathways initiated by nucleophilic attack on carbon or by proton abstraction. Proton abstraction is an exothermic channel for the reactions of O⁻, OH⁻, CF₃⁻, and F⁻ with each of the three isomers of dichloroethene, but C₂HCl₂⁻ was only directly observed for E-CHClCHCl. Orbital overlap arguments provide the explanation of this observation.