The photoionization of lithium to energies between the Li 1 1s2s 3 S and 1s2p 1 P thresholds is studied with accurate ground and target state wave functions. Saddle-point full-core plus correlation wave functions are used for the closed channel. The result agrees with recent photoion measurements. Thirty nine resonances are found in the observed spectra and the predicted sharp peaks agree with experiment to meV levels. The predicted line profile agrees closely with experiment. Several earlier identifications are reassigned. Strong mixing of different resonance series is also found in a few instances. [S0031-9007(97)02417-4] PACS numbers: 31.15. Ar, 32.30.Rj, 32.80.Fb Lithium exhibits many-electron atomic properties that are not found in smaller systems. In a two-electron system, the thresholds are one-electron states with exact degeneracy in the nonrelativistic approximation. For a three-electron system, this degeneracy is no longer present. However, the two-electron thresholds could be close in energy and the Feshbach resonances associated with different thresholds may lie in the same energy region. Depending on the energy positions and the angular coupling strength of the resonances, they may or may not mix strongly. Consequently, the resulting spectra could be very complex and irregular. The lithium spectrum between the Li 1 1s2s 3 S and 1s2p 3 P thresholds is a classic example. It is unusual in that it has extended regions of strong absorption and a highly irregular resonance pattern. Ederer, Lucatorto, and Madden [1] pointed out that, "detailed theoretical calculations will be required for positive identification of the structure in this region." This mystery has remained for over a quarter of a century.The first high-resolution absorption spectrum of singly core-excited lithium is reported by Ederer et al.[1] using synchrotron radiation. In this reference, the energy positions of the ͑1s2s͒ 3 S, np 2 P 0 , ͑1s2p͒ 1 P, ns 2 P 0 , and ͑1s2p͒ 1 P, nd 2 P 0 states are measured to an accuracy of a few meV. This precision experiment has stimulated much experimental and theoretical interest [2][3][4][5][6][7]. The absolute photoabsorption cross section of lithium is measured by Mehlmam et al. [4] A comprehensive review of earlier works on lithium is given by Sonntag and Zimmermann [8].Recently, great advances have been made in the synchrotron-related experiments. In particular, Kiernan et al.[9] reinvestigated the photoabsorption of singly 1s-excited lithium using photoion measurement techniques. Impressive well-resolved spectra were obtained. Although R-matrix calculations are carried out in Kiernan et al. [9], their spectra are mainly analyzed and identified using a quantum defect method. In the energy region of interest, there should be five resonance series, ͑1s2s͒ 1 S, np, ͑1s2p͒ 3 P, ns, ͑1s2p͒ 3 P, nd, ͑1s2p͒ 1 P, ns, and ͑1s2p͒ 1 P, nd. Kiernan et al. have identified four with only two members in the ͑1s2p͒ 3 P, ns series; the ͑1s2p͒ 3 P, nd resonance series is missing. Since lithium is one of the sim...