Influence of the He-resonances in the post-collision interaction process

Abstract

The negative ion resonances involved in electron collisions with helium in the 57-60 eV autoionisation region are studied with recent data obtained from electron scattering measurements. The decay processes into the available channels are discussed in relation to the 'post-collision interaction' (PCI). By means of systematic measurements of differential excitation functions of the n=2 to 8 bound states, new data are obtained on the strengths of the decay into these channels. Least-squares fits carried out with these data show that a good account is given for the direct decay of the 57.19 eV 2P resonance into the single-excitation channels by the empirical relation S(n)=S0ekn2/, where S is the strength, n the quantum number and S0 and k are parameters. Assuming that such a law should hold for the 58.29 eV 2D resonance also, arguments are presented to show that for the features in n=4 channels, the PCI mechanism should proceed via negative-ion formation.