Double ionization of ﹩{\mathrm{Ar}}^{7+}﹩ forming ﹩{\mathrm{Ar}}^{9+}﹩. The filled circles show the data of Tinschert et al. (1989), the upward-pointing triangles the data of Rachafi et al. (1991), and the downward-pointing triangles the data of Zhang et al. (2002). The solid curve illustrates our fit of the data using Equations (2) and (3).