First Double Excitation Cross Sections of Helium Measured for 100-keV Proton Impact

Excitation cross sections of the (2s²)¹S,  (2p²)¹D, and (2s2p)¹P autoionizing states of helium, produced in collisions with 100-keV protons, have been measured for the first time. Using a high resolution electron spectroscopy together with a recently proposed parametrization of autoionizing resonances distorted by Coulomb interaction in the final state makes it possible to extract from electron spectra total cross sections as well as magnetic sublevel populations. These new experimental data are briefly compared with out theoretical calculations.