Stability of multiply positively charged homonuclear clusters

Singly and multiply charged clusters of the elements Ag, Au, Bi, and Pb—prepared by the gas-aggregation technique and ionized by electron impact—are detected by a single-focusing magnetic mass spectrometer. Stable doubly and triply charged clusters $X_n^{m+}$ (m=2,3) are observed for values of n which are well below both of the previously reported ones and the theoretical values predicted in the open literature. The various critical values we obtain are as follows: ${\mathrm{Pb}}_{\mathrm{n}}^{2+}$ ($n_c$=3); ${\mathrm{Bi}}_{\mathrm{n}}^{2+}$ ($n_c$=5); ${\mathrm{Ag}}_{\mathrm{n}}^{2+}$, ${\mathrm{Au}}_{\mathrm{n}}^{2+}$ ($n_c$=9), and ${\mathrm{Au}}_{\mathrm{n}}^{3+}$ ($n_c$=22); ${\mathrm{Ag}}_{\mathrm{n}}^{3+}$ ($n_c$=22); ${\mathrm{Bi}}_{\mathrm{n}}^{3+}$ ($n_c$=38); ${\mathrm{Pb}}_{\mathrm{n}}^{3+}$ ($n_c$=43). A strong dependence of the obtained values on the experimental formation conditions of the neutral clusters is observed.