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1. Partial Photoionization Cross Sections of Chromium from the Ground and Excited States

   https://doi.org/10.3390/atoms8030051  

   Zatsarinny, Oleg ; Tayal, Swaraj ( September 2020 , Atoms)

   null (Ed.)

   Partial and total photoionization cross sections of iron-peak elements are important for the determination of abundances in late-type stars and nebular objects. We have investigated photoionization of neutral chromium from the ground and excited states in the low energy region from the first ionization threshold at 6.77 eV to 30 eV. Accurate descriptions of the initial bound states of Cr I and the final residual Cr II ionic states have been obtained in the multiconfiguration Hartree-Fock method together with adjustable configuration expansions and term-dependent non-orthogonal orbitals. The B-spline R-matrix method has been used for the calculation of photoionization cross sections. The 194 LS final ionic states of Cr II 3d44s, 3d34s2, 3d5, 3d44p, and 3d34s4p principal configurations have been included in the close-coupling expansion. The inclusion of all terms of these configurations has significant impact on the near-threshold resonance structures as well as on the nonresonant background cross sections. Total photoionization cross sections from the ground 3d54sa7S and excited 3d54sa5S, 3d44s2a5D, 3d54pz5P, and 3d44s4py5P states of Cr I have been compared with other available R-matrix calculation to estimate the likely uncertainties in photoionization cross sections. We analyzed the partial photoionization cross sections for leaving the residual ion in various states to identify the important scattering channels, and noted that 3d electron ionization channel becomes dominant at higher energies. 

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2. Photoionization of neutral iron from the ground and excited states

   Zatsarinny O, Bartschat ( February 2019 , Physical review, A)

   The B-spline R-matrix method is used to investigate the photoionization of neutral iron from the ground and excited states in the energy region from the ionization thresholds to 2 Ry. The multiconfiguration Hartree-Fock method in connection with adjustable configuration expansions and term-dependent orbitals is employed for an accurate representation of the initial states of Fe I and the target wave functions of Fe II. The close-coupling expansion contains 261 LS states of Fe II and includes all levels of the 3d^6 4s, 3d^5 4s^2, 3d^7, 3d^6 4p, and 3d^5 4s4p configurations. Full inclusion of all terms from the principal configurations considerably changes both the lowenergy resonance structure and the energy dependence of the background cross sections. Partial cross sections are analyzed in detail to clarify the most important scattering channels. Comparison with other calculations is used to place uncertainty bounds on our final photoionization cross sections and to assess the likely uncertainties in the existing data sets. 

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3. Effective Collision Strengths and Radiative Parameters for Lines in the Sc ii Spectrum

   https://doi.org/10.3847/1538-4365/ac502e  

   Tayal, S. S. ; Zatsarinny, O. ( March 2022 , The Astrophysical Journal Supplement Series)

   This work reports large-scale calculations of electron excitation effective collision strengths and transition rates for a wide range of Sciispectral lines for astrophysical analysis and modeling. The present results are important for reliable abundance determinations in various astrophysical objects, including metal-poor stars, Hiiregions, and gaseous nebulae. Accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target levels are of primary importance for calculations of collision and radiative parameters. The target wave functions have been determined by a combination of the multiconfiguration Hartree–Fock and B-spline box-based close-coupling methods, together with the nonorthogonal orbitals technique. The calculations of the collision strengths have been performed using the B-spline Breit–Pauli R-matrix method. The close-coupling expansion includes 145 fine-structure levels of Sciibelonging to the terms of the 3p⁶3d², 3p⁶3d4l(l= 0–3), 3p⁶3d5l(l= 0–3), 3p⁶3d6s, 3p⁶4s², 3p⁶4s4l(l= 0–3), 3p⁶4s5l(l= 0–1), and 3p⁶4p²configurations. The effective collision strengths are reported as a function of electron temperature in the range from 10³to 10⁵K. The collision and radiative rates are reported for all of the possible transitions between the 145 fine-structure levels. Striking discrepancies exist with the previous R-matrix calculations of the effective collision strengths for the majority of the transitions, indicating possible systematic errors in these calculations. Thus, there is a need for accurate calculations to reduce the uncertainties in the atomic data. The likely uncertainties in our effective collision strengths and radiative parameters have been assessed by means of comparisons with other collision calculations and available experimental radiative parameters.

    

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4. Quantum electronic control on chemical activation of methane by collision with spin–orbit state selected vanadium cation

   https://doi.org/10.1039/D0CP04333H  

   Ng, Cheuk-Yiu ; Xu, Yuntao ; Chang, Yih-Chung ; Wannenmacher, Anna ; Parziale, Matthew ; Armentrout, P. B. ( January 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   By coupling a newly developed quantum-electronic-state-selected supersonically cooled vanadium cation (V + ) beam source with a double quadrupole-double octopole (DQDO) ion–molecule reaction apparatus, we have investigated detailed absolute integral cross sections ( σ 's) for the reactions, V + [a 5 D J ( J = 0, 2), a 5 F J ( J = 1, 2), and a 3 F J ( J = 2, 3)] + CH 4 , covering the center-of-mass collision energy range of E cm = 0.1–10.0 eV. Three product channels, VH + + CH 3 , VCH 2 + + H 2 , and VCH 3 + + H, are unambiguously identified based on E cm -threshold measurements. No J -dependences for the σ curves ( σ versus E cm plots) of individual electronic states are discernible, which may indicate that the spin–orbit coupling is weak and has little effect on chemical reactivity. For all three product channels, the maximum σ values for the triplet a 3 F J state [ σ (a 3 F J )] are found to be more than ten times larger than those for the quintet σ (a 5 D J ) and σ (a 5 F J ) states, showing that a reaction mechanism favoring the conservation of total electron spin. Without performing a detailed theoretical study, we have tentatively interpreted that a weak quintet-to-triplet spin crossing is operative for the activation reaction. The σ (a 5 D 0 , a 5 F 1 , and a 3 F 2) measurements for the VH + , VCH 2 + , and VCH 3 + product ion channels along with accounting of the kinetic energy distribution due to the thermal broadening effect for CH 4 have allowed the determination of the 0 K bond dissociation energies: D 0 (V + –H) = 2.02 (0.05) eV, D 0 (V + –CH 2 ) = 3.40 (0.07) eV, and D 0 (V + –CH 3 ) = 2.07 (0.09) eV. Detailed branching ratios of product ion channels for the titled reaction have also been reported. Excellent simulations of the σ curves obtained previously for V + generated by surface ionization at 1800–2200 K can be achieved by the linear combination of the σ (a 5 D J , a 5 F J , and a 3 F J ) curves weighted by the corresponding Boltzmann populations of the electronic states. In addition to serving as a strong validation of the thermal equilibrium assumption for the populations of the V + electronic states in the hot filament ionization source, the agreement between these results also confirmed that the V + (a 5 D J , a 5 F J , and a 3 F J ) states prepared in this experiment are in single spin–orbit states with 100% purity. 

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5. Electron scattering on molecular nitrogen: common gas, uncommon cross sections

   https://doi.org/10.1140/epjd/s10053-023-00687-5  

   Song, Mi-Young ; Cho, Hyuck ; Karwasz, Grzegorz P. ; Kokoouline, Viatcheslav ; Tennyson, Jonathan ( June 2023 , The European Physical Journal D)

   Abstract We discuss peculiar features of electron scattering on the N 2 molecule and the N 2 + ion, that are important for modeling plasmas, Earth’s and other planets’ atmospheres. These features are, among others: the resonant enhancement of the vibrational excitation in the region of the shape resonance around 2.4 eV, the resonant character of some of electronic excitation channels (and high values of these cross sections, both for triplet and singlet states), high cross section for the dissociation into neutrals, high cross sections for elastic scattering (and electronic transitions) on metastable states. For the N 2 + ion we discuss both dissociation and the dissociative ionization, leading to the formation of atoms in excited states, and dissociative recombination which depends strongly on the initial vibrational state of the ion. We conclude that the theory became an indispensable completion of experiments, predicting many of partial cross sections and their physical features. We hope that the data presented will serve to improve models of nitrogen plasmas and atmospheres. Graphical abstract 

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