Point-charge model for vibronic coupling constants of metal atom trimers

A simple point charge model is proposed for estimating the relative size of Jahn-Teller (JT) and pseudo Jahn-Teller (PJT) coupling constants in metal trimers with a single ‘active’ valence electron. Applied to the B-system of the two-photon ionization spectrum of Na₃ it correctly reproduces the unexpected relative smallness of the linear JT coupling in the final electronic state. General implications for the nuclear dynamics in metal trimers and possible extensions of the approach are discussed.