Fragmentation of the helium dimer by the impact of relativistic highly charged ions.*

We study the fragmentation of He₂ dimers into He⁺ ions by relativistic highly charged projectiles. We demonstrate that the interaction between an ultrafast projectile with an extremely extended object—the helium dimer—possesses interesting features that are absent in collisions with “normal” molecules. We also show that such projectiles, due to their enormous interaction range, can accurately probe the ground state of the dimer and even be used for a determination of its binding energy.