Inner shell and double excitation spectrum of ytterbium involving the 4f and 6s subshells

The absorption spectrum of ytterbium in the wavelength range 1200-2000 AA has been recorded in the first order of a 3 m spectrograph equipped with a 6000 line mm -1 holographic grating, using synchrotron radiation as the background source of continuum. More than 200 new levels of Yb I are reported which are interpreted as the inner shell transitions, 4f 14 6s 2 to 4f 13 ( 2 F 712,512 )nd,ng and the doubly excited transitions, 4f 14 6s 2 to 4f 14 5d( 2 D 312,512 )np,nf and 4f 14 6s 2 to 4f 14 6p( 2 P 112,312 )ns,nd. All the observed levels lie above the first ionization threshold and can be ordered into Rydberg series converging onto six limits. The interchannel interactions between the overlapped series have been parametrized using multichannel quantum defect theory.