Anomalous behavior of the near-threshold photoionization cross section of the neon isoelectronic sequence: A combined experimental and theoretical study

We present a combined theoretical and experimental investigation of photoio nization along the Ne isoelectronic sequence and show that the near-thresho ld behavior of the cross section for Si4+ differs radically from the nearby ions in the sequence. We demonstrate that the general nature of the underl ying physics implies that dramatic changes in near-threshold behavior may b e expected for many other ions.