Low-energy dissociative electron attachment to CFCl3, CF2Br2, and 1,1,1- 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 distributions of negative ions produced through electron transfer in collisions with velocity-selected K(np) Rydberg atoms. The data are analyzed with the aid of a Monte Carlo collision code that models the detailed kinematics of the reactions. Measurements with CFCl3 and CF2Br2, show that the mean lifetimes of the CFCl3-* and CF2Br2-* intermediates initially 3 formed by Rydberg electron capture are similar to 3.5 and 4.5 ps, respectively, and that, upon dissociation, only a small fraction of the excess energy of reaction appears as translational energy of the fragments. The data for 1,1,1-C2Cl3F3 indicate that reaction proceeds by two channels: in the first, essentially all the excess energy appears in translation, suggesting that the electron is captured directly into an antibonding orbital; in the second, limited conversion of the excess energy to internal motions occurs, pointing to an intermediate lifetime of similar to 0.1 to 1 ps. The data for the 1,1,2 isomer suggest that 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 Physics.