ANGULAR-MOMENTUM COHERENCES OF HELIUM-ATOMS EXCITED BY PROTON IMPACT

Using electric-field anticrossing techniques we investigated the coher ent excitation of n = 5-8 He I states with different orbital angular m omenta by proton impact. These measurements give strong evidence that saddle dynamics of H-2+ -like systems are well suited for describing t he final phase of 12.5 keV H+-He collisions. We conclude that, besides electron promotion via the 2psigma orbital, the collision system unde rgoes diabatic 1ssigmal-3dsigma transitions during the close encounter and present an explanation of the electric dipole moments measured fo r excitation of H(n=2) states by H+-He and H-He collisions.