The desorption dynamics of rubidium dimers (Rb_2) off the surface of heliumnanodroplets induced by laser excitation is studied employing both nanosecondand femtosecond ion imaging spectroscopy. Similarly to alkali metal atoms, wefind that the Rb_2 desorption process resembles the dissociation of a diatomicmolecule. However, both angular and energy distributions of detected Rb_2^+ions appear to be most crucially determined by the Rb_2 intramolecular degreesof freedom rather than by those of the Rb_2He_N complex. The pump-probedynamics of Rb_2^+ is found to be slower than that of Rb^+ pointing at a weakereffective guest-host repulsion for excited molecules than for single atoms.
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