EXCITATION OF AUTOIONIZING STATES OF HELIUM BY 100 KEV PROTON IMPACT - THEORY AND EXPERIMENT

A joint theoretical and experimental study of the excitation of the au toionizing (2s(2))S-1, (2p(2))D-1 and (2s2p)P-1 states of helium by 10 0 keV proton impact is presented for the first time. The role of the t hree-body Coulomb interaction in the final state between the ejected e lectron, the scattered proton and the recoil helium ion is emphasized. Calculations have been carried out with inclusion of the three-body C oulomb interaction and within an expansion of a two-electron excitatio n amplitude in powers of projectile-target interaction up to the secon d order. A new parametrization is proposed to describe resonance profi les distorted by the Coulomb interaction in the final state (CIFS). Ne w high-resolution (up to 68 meV) measurements of electron emission spe ctra made it possible to resolve the near-lying (2p(2))D-1 and (2s2p)P -1 resonances and reveal an evident distortion of the resonance profil es by CIFS for forward electron ejection angles below 40 degrees. Proc essing of the experimental spectra has been done both with the new par ametrization, with allowance for CIFS, and with the Shore formula. Con sidering the complexity of the problem, reasonable agreement is achiev ed between experiment and theory.