DISSOCIATIVE THERMAL ELECTRON ATTACHMENT TO SOME ALIPHATIC CHLORO, BROMO, IODO COMPOUNDS

Thermal electron attachment to several aliphatic fluoro, chloro, and bromo derivatives have been investigated in the range 30°-220°C and activation energies of 0-12 kcal have been determined. The relationship between the energy of activation (E*) and change in internal energy (ΔE) for the dissociative electron attachment reaction is uniquely linear with approximately a unit slope. Both chloro and bromo compounds apparently satisfy the same relationship. This empirical relationship can be used to predict bond dissociation energies for aliphatic chloro, bromo, and iodo compounds from the energy of activation for thermal electron attachment. Bond dissociation energies for 1,3-dichloropropane, 1,2-dibromoethane, and 1,3-dibromopropane have been so determined as 75.6, 69.8, 70.9 kcal/mole, respectively. An expression for a two-dimensional representation of the potential-energy curve for the negative ion is proposed with which the linear relationship between E* and ΔE can be derived. The proposed potential-energy curve is empirical, but contains only a single adjustable parameter characteristic of each compound.