Slow ${\mathrm{F}}^{+}$ ions $(v<\mathrm{}0.1\mathrm{}\mathrm{a}.\mathrm{u}.\mathrm{})$ scattered from a clean and flat LiF(001) surface under a grazing angle of incidence exhibit a high probability for forming ${\mathrm{F}}^{-}$ ions in the reflected beam, whereas no negative ions are found for neutral ${\mathrm{F}}^0$ projectiles. From detailed studies of projectile energy loss and charge transfer, we find evidence for a correlated double-electron capture process in the formation of the ${\mathrm{F}}^{-}$ ions.

• Received 8 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.89.043201