Chart summarizing the availability of double-ionization data for various ions. The elements are given in rows, and each column represents the initial charge state for the reaction, e.g., ﹩{\mathrm{He}}^{0+}﹩ is represented by the top-left corner of the table. The astrophysically abundant elements, He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni, are highlighted in bold. An “X” in the corresponding box indicates that experimental double-ionization data exist for the reaction. Note that isoelectronic sequences fall on the diagonals. The references for these experimental data can be found in Table 1.