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Potential energy curves of the ground and excited states for the dissociation of the Rydberg H3O radical into (OH+H2) have been calculated using ab initio Hartree–Fock (HF) and singly and doubly excited configuration interaction (SDCI) methods with a large basis set including Rydberg basis functions. Under C2v symmetry constraint, the ground 2A1 potential curve of (H3O+)(e−)3s adiabatically correlates to [OH(A2Σ+)+H2(X1Σg+)], while the first excited 2E state of (H3O+)(e−)3s correlates to [OH(X2Π)+H2(X1Σg+)]. The avoided curve crossings between the attractive diabatic states emerging from the cation–anion pair of [OH++H2−] and the repulsive diabatic states from antibonding orbitals of [OH*+H2] occurs around ROH≃1.8 A˚. [Copyright &y& Elsevier]