We report the first observation of Young-type interference effects in a two-electron transfer process. These effects change strongly as the projectile velocity changes in fast (1.2 and 2.0 MeV) ${\mathrm{He}}^{2+}+{\mathrm{H}}_2$ collisions as manifested in strong variations of the double-electron capture rates with the ${\mathrm{H}}_2$ orientation. This is consistent with fully quantum mechanical calculations, which ignore sequential electron transfer, and a simple projectile de Broglie wave picture assuming that two-electron transfer probabilities are higher in collisions where the projectile passes close to either one of the ${\mathrm{H}}_2$ nuclei.

• Received 24 October 2008

DOI:https://doi.org/10.1103/PhysRevLett.102.153201