Jahn–Teller Effect and Spin-Orbit Coupling in Heavy Alkali Trimers

Triatomic alkali-metal clusters in their high-spin manifolds of electronically excited states provide the chance to investigate the spectroscopic consequences of the combination of Jahn–Teller effect and spin-orbit coupling with powerful methods of quantum chemistry such as open-shell coupled cluster approaches and multireference Rayleigh-Schroedinger perturbation theory. With respect to available experimental data the 2⁴E ^′ ← 1⁴A₂ ^′ transitions are selected to document the quenching of the paradigmatic E ⊗ e Jahn–Teller distortion with increasing spin-orbit coupling. The simulated spectra for potassium, rubidium and cesium trimers are provided together with all relevant parameters such as harmonic frequencies, Jahn–Teller parameters and spin-orbit splittings obtained from the ab initio approach. Beside that, the molecular geometries and formation energies of these van der Waals molecules are also listed in this chapter.