Strong Correlation and Alignment near the Be 1s Photoionization Threshold

Photoionization in atomic beryllium has been studied in detail near the $1s$ threshold. Multiple excitation to the 1s(2s2p1,3P) states, i.e., conjugate shakeup, is found to be unusually strong, 40% of single excitation. The ³P component rapidly loses strength with increasing photon energy, while the ¹P component persists. The $1s2s2p$ states are highly aligned, as shown by the Auger-electron angular distribution. The A₂ value of -0.65 implies a d-wave contribution of 0.39. Our results indicate that resonances reported for the solid-state photoabsorption are of atomic origin.