A STUDY OF AUTOIONIZING DECAY ROUTES OF DOUBLY-EXCITED STATES IN HELIUM USING 2-DIMENSIONAL PHOTOELECTRON-SPECTROSCOPY

The autoionizing decay routes of doubly excited, P-1(o), Rydberg state s in helium have been investigated using two-dimensional photoelectron spectroscopy. Constant ionic state spectra for the He+ (N = 4, 5 and 6) states have been extracted from two-dimensional photoelectron spect ra obtained in the photon energy region 75.5-79 eV. A preference was o bserved for autoionizing decays in which the change in the principal q uantum number, N, of the electron which remains bound was minimized. T his is in accordance with propensity rules determined from theoretical studies. The energies of the lower members of the most prominent Rydb erg series (N, N - 2(n)) converging on each of the He+ (N = 5) and He (N = 6) thresholds have been determined.