Photoionization of fine structure levels of Ne IV

Study of characteristic features in photoionization of a large number of excited levels of Ne IV, (hν + Ne IV → Ne V + e), using ab initio Breit-Pauli R-matrix (BPRM) method, is presented. This is the second large atomic system, after Fe XVII, for which BPRM method has been used for a full scale computation of photoionization cross sections for a large number of bound levels (N⩽10). The study include features, such as, of Seaton resonances due to photo-excitation-of-core and new near threshold resonant features. Coupling of fine structure channels due to relativistic effects is found to introduce low energy resonances near threshold, not allowed in LS coupling approximation. These resonances play crucial role for low temperature recombination rates. Photoionization cross sections (σPI) for the largest set of levels of Ne IV, a total of 868, with n⩽10 and l⩽9 are presented. A wave function expansion optimized with 24 configurations with orbitals going up to 4p of core Ne V was used. Resonances due to Rydberg series of autoionizing states belonging to various core excited core levels are resolved with fine energy mesh. Details of resonant structures and enhanced background due to Seaton resonances are elaborated in this first study of the ion with relativistic effects.