Negatively charged xenon atoms and clusters

Experimental evidence is presented, for the first time, that ${\mathrm{Xe}}_{\mathrm{N}}^{\mathrm{-}}$, N≥1, atoms and clusters have a lifetime of about ${10}^{\mathrm{-}4}$ s or longer. It is discussed whether the negatively charged xenon atoms and small clusters are in the ground or in an electronically excited, metastable state. Ground-state ${\mathrm{Xe}}_{\mathrm{N}}^{\mathrm{-}}$ clusters are stable if N≥6 and probably down to N=2. Structure in the mass spectra correlates well with calculated binding energies.