A further study of highly excited resonances in He-

Abstract

High-resolution electron impact excitation studies of helium in the energy region just below the first ionisation threshold provide further evidence for the existence of a Rydberg series of doubly excited resonances. These measurements extended the work of Buckman et al (1983) to states in which both excited electrons have values of the principal quantum number n>or=8. The energies of these states show good agreement with the values predicted by a number of semi-empirical double-Rydberg formulae and with a recent quantum mechanical calculation.