  Here, we report the observation of electron transfer mediated decay (ETMD)
involving Mg clusters embedded in helium nanodroplets which is initiated by the
ionization of helium followed by removal of two electrons from the Mg clusters
of which one is transferred to the He environment neutralizing it while the
other electron is emitted into the continuum. The process is shown to be the
dominant ionization mechanism for embedded clusters for photon energies above
the ionization potential of He. The photoelectron spectrum reveals a low energy
ETMD peak. For Mg clusters larger than 5 atoms we observe stable doubly-ionized
clusters. We argue that ETMD provides a new pathway to the formation of
doubly-ionized cold species.
