Rotational structure of the B-X system of Na₃ from high-resolution resonant two-photon ionization spectroscopy

First investigations of the B²A^′ ₁-X²B₂ system of Na₃ at rotational resolution are reported. Using resonant two-photon ionization and optical-optical double resonance spectroscopy, two vibronic bands were assigned and rotationally analyzed. In the B state, the three sodium nuclei perform a nearly free pseudorotational motion in the moat of a pseudo-Jahn-Teller potential that is characterized by a vibronic angular momentum quantum number;'. In states with; > 0, each rotational level is split by Coriolis interaction. Rotational and Coriolis coupling parameters were determined and are discussed in terms of the dynamics of the vibronic coupling in this floppy molecule.