AUTO-IONIZATION STATES OF HELIUM ISOELECTRONIC SEQUENCE BELOW THE N=3 HYDROGENIC THRESHOLDS

The complex rotation method is applied to calculate autoionisation states (1Se, 1Po and 3P o) of the helium isoelectronic sequence (Z=2-10) below the n=3 hydrogenic thresholds. The Hylleraas-type wavefunctions are employed and up to 161 terms for S states and 165 terms for P states are used, so that several lower-lying states are determined. For He and Li+ states, comparisons are made with other calculations and experiments. The width of the lowest 1Po state of helium below the n=3 threshold is determined to be (191+or-7) meV which differs quite significantly from the experimental value of (132+or-14) meV of Dhez and Ederer (1973). Furthermore, it is concluded that the width computed by the complex rotation method would not reduce to the experimental value even if more terms in the wavefunction are used.