Desorption Dynamics of Rb₂ Molecules Off the Surface of Helium Nanodroplets

The desorption dynamics of rubidium dimers (Rb₂) off the surface of helium nanodroplets induced by laser excitation is studied by employing both nanosecond and femtosecond ion imaging spectroscopy. Similarly to alkali metal atoms, we find that the Rb₂ desorption process resembles the dissociation of a diatomic molecule. However, both angular and energy distributions of detected Rb₂⁺ ions appear to be most crucially determined by the Rb₂ intramolecular degrees of freedom rather than by those of the Rb₂He_N complex. The pump-probe dynamics of Rb₂⁺ is found to be slower than that of Rb⁺, pointing at a weaker effective guest-host repulsion for excited molecules than for single atoms.