Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl₄

Abstract

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.