Production of singly charged Sn ions by charge exchange in H₂ gas

The evolution of charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn as a function of the density of the H₂ buffer gas surrounding the LPP is investigated. Without a H₂ buffer gas, energetic 1 - 5 keV Sn ions in charge states of 4+ up to 8+ are detected. In this keV regime, lower Sn charge states, i.e., below 4+ are absent. When H₂ is introduced into the system, low-charged energetic Sn ions can be produced by a series of consecutive electron capture processes. However, as electron capture by Sn²⁺ ions from H₂ is endothermic, no significant population of singly charged Sn ions is expected in the keV regime. At H₂ pressures of 6x10⁻⁴ mbar and higher, however, we only detect Sn²⁺ and Sn⁺ ions.