Characterization of RbSr molecules: spectral analysis on helium droplets

Abstract

We report an experimental investigation of RbSr molecules attached to helium nanodroplets. The molecules are prepared on the surface of helium droplets by utilizing a sequential pickup scheme. We provide a detailed analysis of the excitation spectrum in the wavelength range 11,600-23,000 cm(-1). The spectrum has been recorded by resonance enhanced multi-photon ionization time-of-flight spectroscopy. The inherent mass sensitivity of the method allows for an unraveling of the RbSr spectrum, which is influenced by Rb and Sr dimer contributions, because of the proximity of their respective isotopologues. In addition, the vibrationally resolved 4(2)Σ(+) band was investigated using laser induced fluorescence spectroscopy. The vibronic transitions exhibit a lambda-shaped peak form, which is characteristic of excitations on helium droplets and indicative of strong coupling of the molecule to the superfluid helium environment. Furthermore, the vibrationally resolved 4(2)Σ(+) state enables the determination of molecular parameters, which are in excellent agreement with previously measured dispersed fluorescence spectra, originating from bare RbSr molecules. The assignment of recorded transitions is based on calculated transition dipole moments and potential energy curves. The theoretical results allow for the identification of transitions from the vibronic X(2)Σ(+) ground state to the 2(2)Π, 3(2)Σ(+), 4(2)Σ(+), 3(2)Π, 4(2)Π and 6(2)Σ(+) states. The detailed investigation of RbSr on helium droplets provides a solid basis for further high resolution gas phase studies of this diatomic molecule that holds promise in the area of cold molecular physics.

The RbSr2Σ+ground state investigatedviaspectroscopy of hot and ultracold molecules

“…Experimental investigation of RbSr has been restricted so far to Helium-nanodroplet-assisted spectroscopy [40,41]. In these experiments a supersonic jet of He droplets is sequentially injected into pickup cells containing Rb or Sr, which can get caught on the droplet surface and reactively collide forming a RbSr molecule.…”

Vibronic transitions in the alkali-metal (Li, Na, K, Rb) – alkaline-earth-metal (Ca, Sr) series: A systematic analysis of de-excitation mechanisms based on the graphical mapping of Frank-Condon integrals

“…for a given potential energy surface. The selection of isotopes ( 7 Li, 23 Na, 39 K, 87 Rb, 40 Ca, and 84 Sr) enters the calculation through the reduced mass μ. The Franck-Condon (FC) factors,…”

“…For this reason we included the corresponding tables here (Table I-III), while data for the remaining combinations can be found in the Supplemental Material [76]. The parameters were determined for the following choice of isotopes: 7 Li, 23 Na, 39 K, 87 Rb, 40 Ca, and 84 Sr. Values for T 0 , i.e., the energies for the 0 ← 0 vibrational transitions between the ground and the electronically exited states, are calculated after the asymptotic correction of the ab initio data according to the NIST atomic level database [71].…”

“…On the experimental side, the simultaneous magnetooptical trapping of both elements and even combined Bose-Einstein condensates could be achieved [33,34]. The properties of alkali-alkaline earth diatomic molecules have also been studied by helium nanodroplet isolation spectroscopy [35,36] in our group [37][38][39]. In a series of combined experimental and computational studies [40,41] we identified several features of resonance enhanced multiphoton ionization (REMPI) spectra and matched them to computed excited electronic states.…”

Electric dipole moments and chemical bonding of diatomic alkali–alkaline earth molecules

“…39,73 The first realization of a combined quantum degenerate mixture of Rb and Sr 74 was followed by a series theoretical and experimental publications. [40][41][42][75][76][77] The excited states of LiSr, 72 RbBa, 78 LiMg, 79 and RbCa 43 were calculated recently.…”