A quantitative description of the breaking of a bond between two ions is given by the Landau-Zener-Stueckelberg (LZS) model. In this paper, the possible application of this model to the metallic positive emission is discussed. The example of Cu+emission is chosen in order to show that the model alone is unable to describe the whole ionization processes, and that it has to be inserted into a more comprehensive description. The bond breaking could for instance follow the promotion of a bound electron, or it could occur between the emitted cation and a complex anion including oxygen. Both possibilites can take into acccount the “matrix effect” observed in alloy sputtering.