Accurate relativistic coupled-cluster calculations show that the triply charged species ${\mathrm{HeY}}^{3+}$ is a stable molecule and represents the lightest diatomic trication that does not undergo a Coulomb fragmentation into charged fragments. The diatomic potential-energy curve is approximated by an extended Morse potential, and vibrational-rotational constants for ${\mathrm{HeY}}^{3+}$ are predicted ${(R}_e=224.3\mathrm{}\mathrm{pm},$ $D_0=0.394\mathrm{}\mathrm{eV},$ ${\omega }_e=437\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ ${\omega }_e{x}_e=15.8\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ $B_e=0.877\mathrm{}{\mathrm{cm}}^{\mathrm{-}1}).\mathrm{}$ It is further shown that the ${\mathrm{He}\mathrm{—}\mathrm{Y}}^{3+}$ bond can basically be described as a charge-induced dipole interaction.

• Received 19 July 1999

DOI:https://doi.org/10.1103/PhysRevA.60.R3347