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Photoionization cross sections of (Ca XV + hν → Ca XVI + e), with high energy resonant photo-absorption phenomena, of a large number of bound states, 701 in total with n ≤ 10 and l ≤ 9, are reported. They are obtained using the R-matrix method with a close coupling (CC) wavefunction expansion of 29 states of n = 2,3 complexes of the core ion Ca XVI. Characteristic features found in photoionization of the ion are illustrated with examples. The cross section (σPI) of the ground 2s22p2(3P) state is found to be unaffected by the size of the wavefunction expansion except for weak sparse resonances in high energy region. However, effects on excited states are considerable as the core excitations to n = 3 states are manifested in huge resonant absorption in high energy photoionization. They show existence of prominent high peak resonant features and enhancement in the background that were not studied before for Ca XV. In addition photoionization of the excited states with a single valence electron is dominated by Seaton resonant structures formed by the photo-excitation-of-core in the high energy region. These features will impact other quantities, such as the opacity, electron-ion recombination in high temperature plasmas where the ion exists, and hence will play important role in determination of elemental abundances in the astronomical objects.

Photoionization cross section (σPI) of P II, (hν + P II → P III + e), from ground and a large number of excited levels are presented. The study includes the resonant structures and the characteristics of the background in photoionization cross sections. The present calculations were carried out in the Breit–Pauli R-matrix (BPRM) method that includes relativistic effects. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. A singular resonance, formed by the coupling of channels in fine structure but not allowed in LS coupling, is seen at the ionization threshold of photoionization for the ground and many excited levels. The background cross section is seen enhanced compared to smooth decay for the excited levels. Examples are presented to illustrate the enhanced background cross sections at the energies of the core levels, 4P3/2 and 2D3/2, that are allowed for electric dipole transitions by the core ground level 2 P 1 / 2 o . In addition strong Seaton or photo-excitation-of-core (PEC) resonances are found in the photoionization of single valence electron excited levels. Calculations used a close coupling wave function expansion that included 18 fine structure levels of core P III from configurations 3s23p, 3s3p2, 3s23d, 3s24s, 3s24p and 3p3. Photoionization cross sections are presented for all 475 fine structure levels of P II found with n ≤ 10 and l ≤ 9. The present results will provide high precision parameters of various applications involving this less studied ion.

This report presents i) various characteristic features in photoionization cross sections (σPI) of Cl II + hν → Cl III + e for many fine structure levels of Cl II, 392 in total with n ≤ 10 and l ≤ 9, ii) comparison of features with those observed in an experiment carried out at the Advanced Light Source at Lawrence Berkeley National Lab, and iii) partial photoionization cross sections of the ground level for ionization leaving the core ion in to various excited levels for applications in plasma modeling. The features correspond to resonant structures, the shape of the background, and their interference effect in σPI of this near neutral ion Cl II with 16 electrons. σPI for the 5 levels of the ground configuration 3s23p4(3P0,1,2, 1D2, 1S0) of Cl II show regions of narrow Rydberg resonances at and near threshold energies, and resonant structures at higher energies in contrast to typical smooth decrease in the background. Various other features in σPI of levels of excited equivalent electron states and broad Seaton resonances in single valence electron excited levels are illustrated with examples. Comparison of calculated σPI of the 15 lowest levels with the combined features of the measured photoionization spectrum shows excellent agreement by reproducing and thus identifying them to the levels that they belong to. The calculations were carried out in relativistic Breit-Pauli R-matrix (BPRM) method using a close coupling wave function expansion of 45 levels up to 4s of the core ion Cl III. These levels were optimized using a set of 12 configurations going up to orbital 5s, 3s23p3, 3s3p4, 3p5, 3s23p23d, 3s23p24s, 3s23p24p, 3s23p24d, 3s23p24f, 3s23p25s, 3s3p33d, 3s23p3d2, 3p43d producing 283 levels of Cl III. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. The present results will provide high precision parameters for various applications involving this less studied ion.

Detailed photoionization of ground and many excited states with autoionizing resonances of neutral Ti are presented. Ti I with 22 electrons forms a large number of bound states, the present work finds a total of 908 bound states with n ⩽ 10 and l ⩽ 8 . Photoionization cross sections ( σ PI ) for all these bound states have been obtained. Calculations were carried out in the close-coupling R-matrix method using a wave function expansion that included 36 states of core ion Ti II. It is found that the resonances enhance the low energy region of photoionization of the ground and low lying excited states. The resonant features will increase the opacity, as expected of astrophysical observation, and hence play important role in determination of abundances in the elements in the astronomical objects. The excited states also show prominent structures of Seaton or photo-excitation-of-core resonances.

Study of characteristic features in photoionization of a large number of excited levels of Ne IV, (h ν + 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 ( σ PI ) 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.

Characteristic features of the resonances and background cross sections for photoionization (σPI) of oxygen-like iron ion, Fe XIX + hν → Fe XX + e, are demonstrated. The features are introduced by excitations of the core ion to states of n = 2,3,4 complexes in σPI of the ground, equivalent electron, and single valence electron excited states. Study from a large number of states is important to establish the general properties of photoionization for complex ions. This is the first detailed study of the ion with a complete set of σPI for 900 bound states with n ≤ 10 and l ≤ 9. The ion itself is of great interest for being detected in the x-ray to UV spectra of various astronomical objects. It is found that i) the ground and equivalent electron states have high peak narrow Rydberg resonances in the low energy region corresponding to n = 2 excitations only, ii) for other excited states the resonant features are stronger for core ion excitations to n = 3 complex compared to those for n = 2,4, iii) Seaton resonances due to photo-excitation of the core (PEC) are found most distinct in the energy region for dipole allowed excitation from n = 2 to n = 3 states, and iv) resonances with lower peaks in the energy region between n = 3 and n = 4 excitation indicate convergence. Computations were carried out in the R-matrix method using a large close coupling wavefunction expansion up to orbital 4f and 16 configurations. The present results should provide the data for precise modeling and applications.

Results are reported for Fe XIV energy levels and transitions obtained from the ab initio relativistic Breit–Pauli R-matrix (BPRM) method. BPRM method developed under the Iron Project is capable of calculating very large number of fine structure energy levels and corresponding transitions. However, unlike in the atomic structure calculations, where levels are identified spectroscopically based on the leading percentage contributions of configurations, BPRM is incapable of such identification of the levels and hence the transitions. The main reason for it is that the percentage contributions can not be determined exactly from the large number of channels in the R-matrix space. The present report describes an identification method that uses considerations of quantum defects of channels, contributions of channel from outer regions, Hund’s rule, and angular momenta algebra for addition and completeness of fine structure components. The present calculations are carried out using a close coupling wave function expansion that included 26 core excitations from configurations 2 s 2 2 p 6 3 s 2 , 2 s 2 2 p 6 3 s 3 p , 2 s 2 2 p 6 3 p 2 , 2 s 2 2 p 6 3 s 3 d , and 2 s 2 2 p 6 3 p 3 d . A total of 1002 fine structure levels with n ⩽ 10, l ⩽ 9, and 0.5 ⩽ J ⩽ 9.5 with even and odd parities and the corresponding 130,520 electric dipole allowed (E1) fine structure transitions, a most complete set for astrophysical modelings of spectral analysis and opacities, is presented. Large number of new energy levels are found and identified. The energies agree very well, mostly in less than 1% with the highest being 1.9%, with the 68 observed fine structure levels. While the high lying levels may have some uncertainty, an overall accuracy of energy levels should be within 10%. BPRM transitions have been benchmarked with the existing most accurate calculated transition probabilities with very good agreement for most cases. Based on the accuracy of the method and comparisons, most of the transitions can be rated with A ( ⩽ 10 % ) to C ( ⩽ 30 % ).

Using the unified method, the inverse processes of photoionization and electron–ion recombination are studied in detail for neutral chromium, ( Cr I + h ν ↔ Cr II + e ), for the ground and excited states. The unified method based on close-coupling approximation and R-matrix method (i) subsumes both the radiative recombination (RR) and dielectronic recombination (DR) for the total rate and (ii) provides self-consistent sets of photoionization cross sections σ PI and recombination rates α RC . The present results show in total photoionization of the ground and excited states an enhancement in the background at the first excited threshold, 3 d 4 4 s 5 D state of the core. One prominent phot-excitation-of-core (PEC) resonance due to one dipole allowed transition ( 6 S - 6 P o ) in the core is found in the photoionization cross sections of most of the valence electron excited states. Structures in the total and partial photoionization, for ionization into various excited core states and ground state only, respectively, are demonstrated. Results are presented for the septet and quintet states with n ≤ 10 and l ≤ 9 of Cr I. These states couple to the core ground state 6 S and contribute to the recombination rates. State-specific recombination rates are also presented for these states and their features are illustrated. The total recombination rate shows two DR peaks, one at a relatively low temperature, at 630 K, and the other around 40,000 K. This can explain existence of neutral Cr in interstellar medium. Calculations were carried out in LS coupling using a close-coupling wave function expansion of 40 core states. The results illustrate the features in the radiative processes of Cr I and provide photoionization cross sections and recombination rates with good approximation for this astrophysically important ion.