2001 journal article
Electric-field effects on He ground-state photoionization
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 34(7), 1245–1259.
A saddle-point complex-rotation method is used to study the photoionization of helium in the presence of a dc electric field. A four-angular-symmetry calculation (i.e. Lmax = 3) is carried out to study two locally isolated resonance groups, one consisting of He (2, 5c) 1Po, (2, 5b) 1Se, (2, 6b) 1Po and (2, 6a) 1Se states, and the other consisting of He (2, 6c) 1Po, (2, 6b) 1Se, (2, 7b) 1Po and (2, 7a) 1Se states. The variations of the structure of cross section profiles and resonance strengths for the ML = 0 components of these two resonance groups are examined in detail. A general Ntot-state sum rule for the total resonance strength Stot is shown, which suggests that the sum of the total resonance strength of a locally isolated resonance group is not affected by the presence of a weak static field. We have also performed a five-symmetry (i.e. Lmax = 4) multichannel calculation for the doubly excited spectra converging to the n = 3 threshold of He+. Overlapping resonances are found and resolved.