Angle and velocity variation of electron capture from a Stark state

Total electron capture by K+ or Cs+ from a Na Rydberg n=24 extremal Stark state, aligned with a weak external electric field, has been measured as a function of the angle between the atoms’ electric dipole moment and the projectile beam in the reduced-velocity range ṽ=0.15 to 1.05. A novel “Stark barrel” is described that produces the arbitrarily directed uniform electric field, smoothly switchable in both magnitude and direction in under 2 μs. The results illustrate the importance of spatial effects as opposed to velocity matching for a full understanding of electron capture near ṽ=1.