Energy distributions of He+ and He2+ ions formed in ultracold He(23S1)+He(23P2) collisions

Energy distributions of He + and He 2 + ions produced in ultracold He(2 3 S 1 ) + He(2 3 P 2 ) collisions are presented. These helium metastable atoms are trapped and cooled in a magneto-optical trap, and have a temperatureof 1.1′0.2 mK. Initial kinetic energies of the product He + and He 2 + ions are analyzed in energy, using a weak electrostatic extraction field in combination with a time-of-flight technique. A pronounced structure is observed in the He + ion distribution, which can be well explained by a theoretical model that considers the avoided crossings between only three metastable 3 Σ + g states of the transient He 2 molecule. The measured He 2 + distribution has a width that is consistent with the maximum recoil energy of 1.1 meV.