Charge-state distributions of nitrogen ions resulting from the foil-induced dissociation of 4.2-MeVN2+ions

We have studied the dependence of the charge-state distributions of heavy-ion fragments resulting from the foil-induced dissociation of 4.2-MeV ${\mathrm{N}}_2$ ${\mathrm{}}^{+}$ ions on the thickness of the carbon target foil. The results are compared to those distributions measured for impact of 2.1-MeV ${\mathrm{N}}^{+}$ projectiles. Whereas the mean charge state for atomic-ion impact is already equilibrated in moderately thin targets (2 μg/${\mathrm{cm}}^2$), those measured for molecular-ion impact are strongly dependent on the target thickness, even for the thickest targets (20 μg/${\mathrm{cm}}^2$). The distributions for molecular-ion impact show a marked shift towards lower charge states, evidencing an enhanced electron-capture probability over the case of monatomic-ion impact. A quantitative model is described which explains this phenomenon by reducing the two-center potential of the cluster fragments to a separation-dependent one-center potential.