High resolution measurements of partial photoionization cross sections in hollow lithium: A critical comparison with advanced many-body calculations.

In this Letter, we present photoelectron data for hollow lithium states obtained with unprecedented spectral resolution (0.019 eV) and sensitivity which allows a critical comparison with the most advanced recent theoretical calculations. The partial cross sections are measured and resonance profile parameters are determined. In addition, we have used the R-matrix approximation to calculate ab initio the partial photoionization cross sections into all continuum channels of the Li ion over a wide photon energy range. The experimental results provide the first definitive test of such advanced calculations for this highly excited atomic system. The photoexcitation and decay dynamics of hollow lithium atoms, in which all three electrons are in excited states, have become the subject of intense recent experimental and theoretical interest. The single-photon threeelectron excitations depend entirely on electron-electron correlation interactions and so hollow lithium atoms constitute an ideal four-body Coulomb system for testing the most advanced atomic theories. Following the first photon-excited observation [1] of the lowest hollow atom resonance (1s22s 2S ! 2s22p 2P), two total ion yield photoion experiments at high [2] and medium [3] spectral