Charge-exchange and fragmentation cross-section measurements on ${\mathrm{Au}}_2^{2+}$, ${\mathrm{Au}}_3^{2+}$, ${\mathrm{Au}}_4^{2+}$ and ${\mathrm{Au}}_4^{3+}$ are presented. Limits on the cluster electron affinities are obtained in terms of the ionization energies of Ar, ${\mathrm{N}}_2$, Kr, CO, Xe, and ${\mathrm{O}}_2$. Fragmentation cross sections, largely independent of the gas species, are comparable to those for charge exchange. The metastability of ${\mathrm{Au}}_2^{2+}$ is shown to be implied by the lower bound on its electron affinity.

• Received 5 October 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.1037