Photoelectron data for hollow lithium states obtained with unprecedented high spectral resolution and sensitivity are presented. A critical comparison is made with the most recent theoretical results. Partial cross sections are measured providing the first definitive test of advanced ab initio calculations for this highly excited four-body atomic system. [S0031-9007(96)00241-4] PACS numbers: 32.80. Fb, 32.80.Hd 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 1 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 (1s 2 2s 2 S ! 2s 2 2p 2 P), two total ion yield photoion experiments at high [2] and medium [3] spectral resolution measured the autoionization of several hollow states in both the Li 1 and Li 21 decay channels. Photoelectron spectrometry [4] was also used with low resolution to study the decay of the hollow lithium 2s 2 2p state into the different continua of the Li 1 ion. The 0.5 eV spectral bandpass of the latest experiment however limited the critical nature of the comparison with theory.Double K-shell excitations in atomic helium have culminated in recent ultrahigh resolution measurements [5]. The third electron makes the theoretical and experimental study of hollow lithium states an even greater challenge than that of helium. Although triply excited states of lithium were first observed in collision experiments [6][7][8], only photon-excitation experiments provide the selectivity, sensitivity, and resolution required to unravel the many hollow lithium resonances. The dipole selection rules ensure that only 2 P o final states can be photoexcited from the ground state of the lithium atom. Photoelectron spectrometry combines the advantages of photon excitation with the unique capacity to measure separately the many decay channels and to provide insight into decay dynamics. The key role played by hollow atom states in ion-surface interactions has also been recognized [9]. 0031-9007͞96͞76(21)͞3915(4)$10.00

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