Spectroscopyof Cold LiCa Molecules Formed on HeliumNanodroplets

摘要

We report on the formation of mixed alkali–alkaline earth molecules (LiCa) on helium nanodroplets and present a comprehensive experimental and theoretical study of the ground and excited states of LiCa. Resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy were used for the experimental investigation of LiCa from 15000 to 25500 cm^–1. The 4²Σ⁺ and 3²Π states show a vibrational structure accompanied by distinct phonon wings, which allows us to determine molecular parameters as well as to study the interaction of the molecule with the helium droplet. Higher excited states (4²Π, 5²Σ⁺, 5²Π, and 6²Σ⁺) are not vibrationally resolved and vibronic transitions start to overlap. The experimental spectrum is well reproduced by high-level ab initio calculations. By using a multireference configuration interaction (MRCI) approach, we calculated the 19 lowest lying potential energy curves (PECs) of the LiCa molecule. On the basis of these calculations, we could identify previously unobserved transitions. Our results demonstrate that the helium droplet isolation approach is a powerful method forthe characterization of tailor-made alkali–alkaline earth molecules.In this way, important contributions can be made to the search foroptimal pathways toward the creation of ultracold alkali–alkalineearth ground state molecules from the corresponding atomic species.Furthermore, a test for PECs calculated by ab initio methods is provided.