Characteristic Features In Low Energy Photoionization of O~II

The low-energy resonant features due to fine structure in photoionization of the ground state $2p^3~^4S^o_{3/2}$ of O~II are found for the first time. These resonances appear in the small energy difference between the fine structure levels of the ground state of the residual ion O~III ($2p^2~^3P^o_{0,1,2}$), and are expected to play an important role in low-temperature dielectronic recombination and the formation of O~II recombination lines. The recombination rates should be able to explain the current discrepancy of O~II abundance in astrophysical plasmas. The calculations have been carried out in the relativistic Breit-Pauli R-matrix (BPRM) method. The BPRM codes have been advanced further in accuracy recently by including the two-body magenetic terms of Breit interaction not existed before. We will present level-specific and partial state-resolved photoionization cross sections of O~II to illustrate the new features. We will also present individual and combined theoretical results for photoionization of several excied states that are found to be in agreement with two experimental measurements, thereby identifying the excited O~II levels present in the ion beams.