Hypermetallic dilithium fluoride, Li 2F, and its cation and anion: a combined dissociation and charge permutation study

Abstract

Dilithium fluoride, Li–F–Li, has been produced in the gas phase by neutralization of the Li 2F + cation, generated by fast atom bombardment ionization of lithium trifluoroacetate. Subsequent reionization after ∼0.2 μs conclusively shows that the hypermetallic fluoride Li 2F has survived intact and, thus, exists as a bound species. Charge reversal of Li 2F + reveals that the anion Li 2F − is stable also. These results are in agreement with previous results of ab initio calculations which predict considerable binding energies (≥129 kJ mol −1) for radical Li 2F and anion Li 2F −, both of which violate the octet rule. Collisionally excited Li 2F + cations dissociate to Li +, LiF +·, Li 2 +·, and F + fragments. The yield of F + strongly depends on the collision gas used, maximizing with He and Ne targets whose ionization energies lie above that of the fluorine atom.