LOW-ENERGY DISSOCIATIVE ELECTRON-ATTACHMENT TO CFCL3, CF2BR2, AND 1,1,1-C2CL3F3 AND 1,1,2-C2CL3F3 - INTERMEDIATE LIFETIMES AND DECAY ENERGETICS

Dissociative electron attachment to CFCl3, CF2Br2 and 1,1,1- and 1,1,2 -C2Cl3F3 is studied by measuring the velocity and angular distribution s of negative ions produced through electron transfer in collisions wi th velocity-selected K(np) Rydberg atoms. The data are analyzed with t he aid of a Monte Carlo collision code that models the detailed kinema tics of the reactions. Measurements with CFCl3 and CF2Br2, show that t he mean lifetimes of the CFCl3- and CF2Br2-* intermediates initially 3 formed by Rydberg electron capture are similar to 3.5 and 4.5 ps, re spectively, and that, upon dissociation, only a small fraction of the excess energy of reaction appears as translational energy of the fragm ents. The data for 1,1,1-C2Cl3F3 indicate that reaction proceeds by tw o channels: in the first, essentially all the excess energy appears in translation, suggesting that the electron is captured directly into a n antibonding orbital; in the second, limited conversion of the excess energy to internal motions occurs, pointing to an intermediate lifeti me of similar to 0.1 to 1 ps. The data for the 1,1,2 isomer suggest th at again only limited energy transfer to internal motions occurs, but the particular reaction channel(s) operative could not be identified. Possible reaction channels for the C2Cl3F3 isomers are discussed with the aid of ab initio calculations. (C) 1997 American Institute of Phys ics.