A classic case of Jahn-Teller effect theory revisited: Ab initio simulation of hyperfine coupling and pseudorotational tunneling in the 12E′ state of Na3

The predictive capabilities of current ab initio approaches are tested in a benchmark study on the well known case of the Na-3 ground state. This molecule is small enough to be treated with computationally demanding methods, but also shows an interesting interplay between Jahn-Teller-, spin-orbit-, rovibrational- and hyperfine-interactions. The necessary parameters for the effective Hamiltonian are derived from the potential energy surface of the 1(2)E' ground state and from spin density evaluations at selected geometries, without any fitting adjustments to experimental data. We compare our results to highly resolved microwave spectra, with the aim to improve previous assignment attempts, where some parameters had to be estimated from fits to measured spectra. (C) 2015 The Authors. Published by Elsevier B.V.