Potential crossing position in electron transfer of a doubly charged ion and an alkali metal target measured using thermometer molecule W(CO)6

摘要

Doubly charged tungsten hexacarbonyl W(CO)(6)(2+) ions were made to collide with K and Cs targets to give singly and doubly charged positive ions by collision-induced dissociation (CID). The internal energy depositions resulting from the electron transfer were evaluated from the relative abundances of the singly charged fragment W(CO)(n)(+) ions. The internal energy deposition resulting from the electron transfer with the Cs target was very narrow and centered at a particular energy, 8.2 eV above the energy level of the charge reduced W(CO)(6)(+) ion, which was higher than 7.2 eV with the K target. These internal energies correspond to energy differences of 2.9 and 3.5 eV between the entrance channel of W(CO)(6)(2+) + Cs (or K) and the exit channel of W(CO)(6)(+)* + CS+ (or K+), respectively. The potential energy between W(CO)(6)(2+) ions and the alkali metal atoms was found to decrease markedly in the entrance channel of the electron transfer as a result of the large polarizability of the alkali metal targets. The internuclear separation of the Landau-Zener potential crossing of the electron transfer between a W(CO)(6)(2+) ion and the Cs target was evaluated as 6.8 x 10(-8) cm, which was larger than the value for the K target (5.9 x 10(-8) cm). Large cross sections for the electron transfer of the order of 10(-14) cm(2), estimated from the internuclear distances, indicate that the electron capture of the doubly charged ion on collisions with an alkali metal targets is a very effective process for producing charge-reduced ions. The difference in the cross sections between K and Cs target indicates that a target having lower ionization energy is more effective for electron transfer. (C) 2007 Elsevier B.V. All rights reserved.