Double differential electron emission cross sections for double excitation and single ionization of helium by fast e-, H+, He+ and He2+ projectiles at zero degree observation in the vicinity of the (2s2)1S, (2pnp)1D and (2snp) 1P0 states for n ≥ 3

The observation of double excitation of He by positively and negatively charged particles is a multielectron effect. Although multiple excitation is easier to understand than multiple ionization, only very little data is available for doubly excitation. In this work we report high resolution data for double excitation of He**, mainly (2s2)1S and (2pnp) 1D and (2snp)1P0 states which decay predominantly by autoionization. The autoionization electrons have been detected in the direction of the incoming beam. Second order scattering amplitudes in Zp, the projectile charge are considered to be important for the (2s2)1S and (2pnp)1D states. The resonance profiles embedded in the continuum background have been parametrized and double differential electron emission cross sections are given as a function of the velocity and projectile charge Zp