SPECTROSCOPY OF LiCa AND RbSr MOLECULES ON HELIUM NANODROPLETS
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Date
2013
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Ohio State University
Abstract
We report on the investigation of mixed alkali metal (Ak) - alkaline earth metal (Ake) molecules on the surface of helium nanodroplets (He$_{N}$). These molecules have recently attracted considerable attention as candidates for the formation of ultracold molecules with a magnetic and an electronic dipole moment. In our experiments, LiCa and RbSr molecules are formed in a sequential pick-up process in their X$^{2}\Sigma^{+}$ ground state and cool down rapidly to the droplet temperature of 0.38\,K. Excitation spectra of LiCa and RbSr were recorded by using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy. On the helium droplet, vibronic transitions in Ak-Ake molecules are broadened and show a characteristic asymmetric peak form, which is caused by the interaction between the molecule and the superfluid He$_{N}$ environment. For the lower electronic transitions in LiCa and RbSr progressions of vibrational bands excited from the X$^{2}\Sigma^{+}$ ($\nu'' = 0$) state are observed. The LiCa spectra can be compared to molecular beam experiments, which enables the assignment of three band systems near 15260\,cm$^{-1}$, 19300\,cm$^{-1}$ and 22120\,cm$^{-1}$ as $^{2}\Sigma^{+}$, $^{2}\Pi_{\Omega}$ and $^{2}\Pi$ band, respectively. In the RbSr excitation spectrum we observe a vibrationally resolved band system near 14020\,cm$^{-1}$. \\ Upon electronic excitation, a fraction of the molecules desorb from the droplet surface and dispersed fluorescence spectra allow to study the X$^{2}\Sigma^{+}$ ground state and excited states of free Ak-Ake molecules.
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Author Institution: Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria