Centrifugal barrier effects in the high Rydberg states and autoionising resonances of neon

The photoabsorption spectrum of neon in the range 500-700 AA has been investigated at high resolution using synchrotron radiation and a 3 m normal incidence vacuum spectrograph equipped with holographic gratings. All of the five Rydberg series 2p 5 ( 2 P 3 2/)ns(3/2) 1 0 , nd(1/2) 1 0 and 2p 5 ( 1 P 1 2/)ns(1/2) 1 0 , nd(3/2) 1 0 have been extended to high principal quantum numbers yielding accurate values for the ionisation potentials ( 2 P 3 2/=173 929.6+or-0.2 cm -1 and 2 P 1 2/=174 709.8+or-0.2 cm -1 ). In contrast with the corresponding features of heavier rare gases, the ns-nd interchannel interactions and autoionisation broadening are shown to be weak. The behaviour is discussed with reference to multichannel quantum defect and Hartree-Fock theory, and is shown to result from centrifugal barrier effects in the nd channels.