Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part I. Vibronic spectra simulations based on ab initio calculations

Abstract

We compare the 3⁴A₁ and 4⁴B₂ states of homonuclear and heteronuclear alkali trimers formed of potassium and rubidium. The Multireference Rayleigh Schrödinger Perturbation Theory of second order is applied to obtain the corresponding adiabatic potential energy surfaces. In the case of homonuclear trimers these pairs of states correspond to the two branches of the E⊗e Jahn–Teller distorted 2⁴E′ state. For heteronuclear trimers, the vibrational modes Q_x and Q_y are no longer degenerate, but the two electronic states still show a conical intersection at obtuse (KRb₂) or acute (K₂Rb) isosceles geometries. Spectroscopic consequences of this situation are discussed, vibronic spectra are predicted and compared to laser-induced fluorescence spectra obtained in helium droplet isolation spectroscopy experiments of our group.