High-resolution threshold photoelectron measurements of the Ne+$nbsp$2p4n satellite states

The Ne + 2p 4 n ℓ satellite states lying between the Ne + 2s main line and the Ne 2+ 2p 4 ( 3 P, 1 D, 1 S) doubly charged ion states have been studied. The study combined the high-energy resolution of the threshold photoelectron technique and of the gas phase photoemission beamline at the Elettra synchrotron radiation source. The threshold photoelectron (TPE) measurements show many more states than observed in previous photoemission or optical measurements. The TPE spectrum in the region of the Ne 2+ 2p 4 ( 1 D) ionization potential shows a clear cusp-like shape, the typical signature of threshold photodouble ionization. This feature is found to be well represented by an asymmetric power law as in the He 2+ ( 1 S) case.