FIRST DOUBLE-EXCITATION CROSS-SECTIONS OF HELIUM MEASURED FOR 100-KEVPROTON IMPACT

Excitation cross sections of the (2s(2))S-1, (2p(2))D-1, and (2s2p)P-1 autoionizing states of helium, produced in collisions with 100-keV pr otons, have been measured for the first time. Using a high resolution electron spectroscopy together with a recently proposed parametrizatio n of autoionizing resonances distorted by Coulomb interaction in the f inal state makes it possible to extract from electron spectra total cr oss sections as well as magnetic sublevel populations. These new exper imental data are briefly compared with out theoretical calculations. [ S0031-9007(97)04892-8].