Photoabsorption of the 4d electrons in xenon and barium: a comparison

The 4d absorption spectra of xenon and barium show very different behavior. In xenon the cross section was measured for two series of resonances converging to the 4d9(2D/sub 5/2,3/2/) limit. By a parameterization technique, the amplitudes and widths of these resonances were obtained. The widths of the resonances are essentially constant, but the widths of the resonances converging to the 4d9(2D/sub 5/2/) limit (N/sub V/ edge) are somewhat narrower than those converging to the 4d9(2D/sub 3/2/) limit (N/sub IV/ edge). The oscillator strength in these 4d9(2D/sub 5/2,3/2/)np series is small (0.06) compared to the total continuum oscillator strength integrated over open p and f channels. The barium spectrum is very different from the xenon spectrum because the 4f orbital contracts in excited barium and overlaps the 4d orbit. This contraction produces two terms, 3P and 3D, of the 4d9f configuration below the 4d ionization limits, while the strong electrostatic exchange interaction drives the 1P term of this configuration some 10 eV above the limit. Furthermore, extensive mixing of the 4d96s26p configuration with 4d95d26p and 4d95d6s6p produces many weak resonances near the 4d10 → 4d9(2D/sub 5/2/)6s26p(2P/sub 3/2/) resonance. A suggested classification of these features is given with the aid of known features of the La I spectrum. Finally, from the known x-ray splitting of the N/sub IV,V/ threshold and the energy interval between the 6s26p(2P) and 6s2(1S) levels in La I and La II, the ionization thresholds of the 4d electron were determined to be 814,800(1000)cm-1 and 792,500(1000)cm-1