Wave - function collapse with increasing ionization : 4 d photoabsorption of Cs through Cs 4 ¿

The 4d relative photoabsorption cross section of cesium has been observed to change dramatically in appearance along the isonuclear sequence Cs through Cs. In each case, discrete structure is observed below threshold and for Cs through Cs, a giant dipole 4d→« f resonance is also present above threshold. Between Cs and Cs, there is a striking change, with much of the oscillator strength available in the 4d→ f channel being abruptly transferred to the discrete spectrum. Despite the complexity of the transitions involved, the oscillator strength envelope for the discrete transitions yields relatively few features and remains essentially static in energy regardless of the parent terms. Hartree-Fock with configuration interaction and time-dependent local-density-approximation calculations successfully account for this behavior and permit identification of the discrete features.