Collision and Radiative Parameters for Cr ii Lines Observed in Stellar and Nebular Spectra

Abstract

Electron excitation collision strengths (Ω) and transition probabilities (A-values) for the iron-peak element Cr ii lines are of high importance for the stellar and nebular abundance studies. Collision and radiative parameters are presented for all possible inelastic transitions between the Cr ii 512 fine-structure levels covering infrared to extreme ultraviolet lines. These parameters should allow a detailed modeling and analysis of the available measured stellar and nebular spectra from different astrophysical objects. Accurate target wave functions have been generated using the multiconfiguration Hartree–Fock method together with term-dependent one-electron orbitals and well-chosen configuration expansions. The wave functions are then used in the calculations of transition probabilities and collision rates. The B-spline Breit–Pauli R-matrix method has been employed for the calculation of electron excitation collision strengths. The semiempirical fine-tuning procedure has been applied to the energies of the local supercluster (LS) terms prior to transformation of the Hamiltonian matrices to intermediate coupling. The Hamiltonian matrices for the calculation of collision rates also include spin–orbit interaction. The 512 fine-structure levels of the Cr ii 3d 5, 3d 44s, , 3d 44p, and 3d 34s4p configurations have been considered in our work. The thermally averaged collision strengths have been determined using a Maxwellian distribution for a wide range of temperatures from 102 to 105 K. The accuracy of our results has been estimated by comparison with other calculated collision rates and available measured radiative rates.

Branching Fractions and Transition Probabilities for UV Transitions in the Spectrum of Cr ii

“…Recent theoretical calculations of transition probabilities include Raassen & Uylings (1996), Kurucz (2016), Bouazza et al (2018a, 2018b), and Tayal & Zatsarinny (2020. The calculations of Bouazza et al (2018a) focus on highly excited 3d 4 5s levels and those of Bouazza et al (2018b) on low-lying 3d 4 4p levels.…”

“…The calculations of Raassen & Uylings (1996), Kurucz (2016), and Tayal & Zatsarinny (2020) are more extensive and cover levels that have no experimental lifetime measurements. We have redone the semiempirical calculations of Raassen & Uylings (1996) with the new and updated energy levels of Sansonetti & Nave (2014), and compare them with the calculations of Kurucz (2016) and Tayal & Zatsarinny (2020) in Section 4.1.…”

“…From this comparison, we assign an uncertainty of 10% to the semiempirical lifetimes, similar to that of the experimental lifetimes. The calculations of Tayal & Zatsarinny (2020) were also examined, but the lifetimes are systematically 14% shorter than the experimental ones.…”

Benchmark PhotoIonization Cross-Sections of Neutral Scandium from the Ground and Excited States

“…The majority of atomic data of increasing accuracy have been produced through theoretical and computational efforts. Recently we have provided improved computational transition probabilities, electron impact excitation collision strengths, and photoionization cross-sections for Fe I and Fe II [1,2], Cr I and Cr II [3,4], and Ti II [5] for a wide array of transitions to fulfill some of the atomic data needs for the modeling of astrophysical plasmas.…”