SELECTIVE EXCITATION OF PARABOLIC STARK STATES OF HE-I BY PROTON IMPACT

Resonancelike intensity variations of the impact radiation were observ ed at electric-field anticrossings of 1snl 1L and 3L Stark sublevels ( n = 5,6,7; l greater-than-or-equal-to 2), when investigating excitatio n of helium atoms by 12.5 keV proton impact. The measured signal ampli tudes provide strong evidence that the collision process excites the e lectron selectively to the (n1, n2, m) hydrogenic Stark states (0, n-1 ,0) and (0, n-2, +/-1), indicating that the electron is promoted along in-saddle sequences of H-2+-like molecular orbitals during the final phase of the collision.