Temperature dependence of reactions involving electron transfer in K(np)/C2Cl4 collisions

Electron transfer in K(np)-C2Cl4 collisions, which leads to formation of both Cl- and C2Cl4- anions, is investigated as a function of target temperature over the range of 300-650 K. Measurements at high n (n similar to 30) show that the likelihood of Cl- production increases rapidly with temperature indicating the presence of a dissociation barrier. The data yield an activation energy of similar to 0.1 eV. A broad distribution of product C2Cl4- lifetimes is observed that extends from microseconds to milliseconds, this distribution moving toward shorter lifetimes as the target temperature is increased. The measured lifetimes are consistent with the predictions of quasiequilibrium theory. Studies at low n (n similar to 14) show a substantial fraction of the product K+-Cl- and K+-C2Cl4- ion pairs is electrostatically bound leading to creation of heavy-Rydberg ion-pair states. Variations in target temperature lead to changes in kinetic energy of relative motion of the reactants that can result in marked changes in the fraction of ion pairs that is bound, especially at low Rydberg atom velocities. In the case of bound K+-C2Cl4- ion pairs a few percent subsequently dissociate by the conversion of internal energy in the anion into translational energy of the ion pair. Analysis of the data points to a mean energy conversion of similar to 60-90 meV, much less than the available excess energy of reaction, similar to 0.7 eV.