The ground-state energy curves of HeH - , NeH - and ArH - have been computed at coupled-cluster level using large basis sets. These dimers are weakly bound systems, due to the interaction between the negative ion H - and the (polarised) rare-gas atom. The Schrodinger equation for the nuclei has been solved, and the energy levels have been computed. The effect of replacing the innermost electrons with pseudopotentials has also been investigated on the heaviest system ArH - .