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

The reaction rate coefficients and ion products for the gas-phase reactions of O-2(-), O-, OH-, CF3-, and F- with trichloroethene (CCl2=CHCl), 1,1-dic hloroethene (CH2=CCl2), and Z (cis) and E (trans)-1,2-dichloroethene (CHCl= CHCl) are presented. With the exception of CCl2=CHCl, the O-2(-) bimolecula r reaction rate coefficients are substantially below the collisional values . All the other anions react with the molecules with rate coefficients at o r close to (within a factor of two) the corresponding collisional values. T he experimental results are interpreted in terms of pathways initiated by n ucleophilic attack on carbon or by proton abstraction. Proton abstraction i s an exothermic channel for the reactions of O-, OH-, CF3-, and F- with eac h of the three isomers of dichloroethene, but C2HCl2- was only directly obs erved for E-CHCl=CHCl. Orbital overlap arguments provide the explanation of this observation.