Measurement of the ultrashort bond length inHe2++

Coulomb explosion experiments have been carried out on both the dihelium cation ${\mathrm{He}}_2^{+}$ and the corresponding doubly charged molecule ${\mathrm{He}}_2^{++}$ yielding bond-length distributions for each species. These measurements provide the first experimental evidence for the bond length of ${\mathrm{He}}_2^{++}$. The most probable value of the measured bond-length distribution is 0.75±0.2 Å. We also determine the lifetime to be longer than 5 μsec. This demonstrates the suitability of the Coulomb explosion method to the study of structures of short-lived, highly reactive, rare, or otherwise exotic molecules.