Excited states and Jahn–Teller interactions in the sodium trimer

We present a complete assignment from first principles of the excited state spectrum for gas phase Na3 in the region below 2.7 eV. We find that the spectrum is complicated by the presence of numerous Jahn–Teller split states derived from both symmetry and accidental degeneracy. Our results indicate that the absorption bands observed experimentally at about 2 eV the B and B′ bands Ref.(1) correspond to a complicated mixing between an E′ doublet and an A′1 state, in which coupling between the A1 state and the E′ state dominates the usual coupling between E′ components. Another set of bands due to a similar mixing of E′ and A′1 states is predicted to lie at lower energy, outside the energy region explored in previous experiments. We are able to assign all four experimentally observed bands, and find a total of four new electronic states below 1.5 eV, which should result in two additional bands in the optical spectrum. All orbitals for Na3 ground and excited states can be characterized in terms of the electron droplet or shell model.