Double excitation of helium by fast electrons, protons, andC(46)+ions

Abstract
The electron emission yield from the doubly excited {(2p1 )2D+(2s2p)1P} states in He excited by impact of fast equivelocity electrons, protons, and carbon ions (charge state 46) has been measured at the reduced energy of 1.84 MeV/amu. The data constitute a challenge to the recently proposed models that incorporate electron-correlation effects in atomic collisions.