Velocity dependent electron transfer during emission of ion-beam sputtered Cu atoms

We report on our investigations on the electronic processes during keV sputtering of metals. The population partition and the state-selective velocity distributions of Cu atoms sputtered in the ground and metastable states are obtained by resonant laser ionization. The qualitative trends in the observations are successfully interpreted assuming a resonant transfer of electrons between the bulk metal and the escaping particle to be the dominant mechanism to populate atomic states. We show that the velocity dependence of the population probabilities is in good agreement with the outcome of a rate-equation description of the resonant electron transfer process.