Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl 4
Résumé
Negative ion formation in electron transfer experiments from fast neutral potassium (K) atom collisions with neutral tetrachloromethane (CCl4) molecules has been investigated in the laboratory frame range of 8–1000 eV. Comprehensive calculations on the electronic structure were performed for CCl4 in the presence of a potassium atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K+ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl4. A vertical electron affinity of −0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl4 ground state to the 2T2 state of the temporary negative ion yielding Cl– formation. Other features in the energy loss spectrum were observed for the first time and related to Cl2–, CCl2–, and CCl3– formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl4 ground state into the triply degenerate 2T2 excited state of the negative ion. The combined time-of-flight mass spectrometry together with K+ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl4 electronic states in collision induced dissociation to date.