Angular momentum coherences of helium atoms excited by proton impact

Using electric-field anticrossing techniques, we investigated the coherent excitation of n=5-8 He I states with different orbital angular momenta by proton impact. These measurements give strong evidence that saddle dynamics of H2+-like systems are well suited for describing the final phase of 12.5 keV H+-He collisions. We conclude that, besides electron promotion via the 2pσ orbital, the collision system undergoes diabatic 1sσ-3dσ transitions during the close encounter and present an explanation of the electric dipole moments measured for excitation of H(n=2) states by H+-He and H-He collisions. (orig.)