Streamlined eigenchannel treatment of open-shell spectra

1994

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We present a general nonperturbative calculation of the photoionization cross section for highly asymmetrical two-electron systems. The calculations were performed using the eigenchannel Rmatrix procedure together with multichannel quantum-defect theory (MQDT), including the effects of long-range multipole interactions. The isolated-core approximation is extended to treat two-photon absorption. The calculations permit a detailed interpretation of recent experimental measurements in atomic strontium and barium.PACS number(s): 32.80.Fb, 31.20.Di, 32.80.Dz

Section: A Calculation Of the R Matrixmentioning

confidence: 99%

Asymmetric two-electron excitations in atomic strontium and barium

Wood

1994

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“…The techniques are "nearly" ab initio; effects of the 18 core electrons are described using a screened Coulomb potential [5] with a dipole polarizability that gives the correct energies of the one-electron-like ion Sc III. We solve for the three-electron valence wave function with the streamlined version [6] of the eigenchannel B-matrix technology in an A-matrix volume rq, r2, r3 ( 21 a.u. We match these solutions onto Coulomb functions at the surface of this volurne to obtain the scattering parameters [7].…”

Section: Introductionmentioning

confidence: 99%

Photoionization of the scandium atom. II. Classifications

Robicheaux

1993

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In this paper we use the calculated photoabsorption cross section and scattering parameters to classify most of the autoionizing lines reported by Garton et al. [Proc. R. Soc. London Ser. A 333, 1 (1973)]. This study proves the capability of eigenchannel R-matrix calculations to provide spectroscopically useful information on the complicated spectra of transition-metal atoms. We present cross sections for the six optically allowed combinations 4s 3d Dsy2 sI2~1 /2, 3 /2, 5 /2, 7 /2 from near the (4s3d) D thresholds to the (3d ) F thresholds.PACS number(s): 32.80.Fb, 31.20.Di, 32.80.Dz I. IN TROD U CTIONThe preceding paper describes general aspects of Sc photoionization dynamics in the low-energy autoionizing region [1]; the transition-metal atoms have rarely been studied in this region of their spectrum. The theoretical description of the spectra is complicated by the large number of closely spaced thresholds; the Rydberg series interact with each other producing a complicated spectrum. The calculated scattering parameters need to be very accurate to place the perturbers in the correct positions; the theoretical spectrum can appear very different even if the perturber has only a small error in its quantum defect (because the error in the position of the perturber is [Aw (a.u. )] = Ap/vs, where the efFective quantum number v is comparatively small in the perturbing channel). The lessons learned in the theoretical treatment of Sc may apply to the other transition metals since the valence shell for all of these elements is composed of s and d orbitals.The focus of this paper is on the detailed classification of the autoionizing lines reported by Garton et al.[2] (GRTE). We present theoretical spectra for photoionization from the D3y2 5/2 ground electronic states along with the positions of some experimental lines marked by vertical lines; this comparison can indicate the level of agreement between theory and experiment. The results reported here are complementary to those reported earlier [1]; a better understanding of Sc can be obtained by studying both the fine-scale details and the large-scale dynamics. The following paper predicts the photoionization of an even-parity Sc excited state and compares to experimental cross sections from threshold to the E thresholds; comparison of the cross sections for photoabsorption from two different initial states adds insight into the dynamics.The results presented in this paper show that the eigenchannel R-matrix technique achieves the accuracy needed for the theoretical description of the complex spectra of transition-metal elements. This method has already produced many spectroscopically useful results for complex spectra of the alkaline earths and for several atoms with open p subshells. However, the density (in energy) of thresholds for the transition-metal atoms near the ionization threshold is an order of magnitude larger than for any of the other elements that have been attempted; the spectra are extremely complicated by perturbers, even near the lowest thresholds...

“…The major physical approximation concerns the Hamiltonian H, which does not refer to the full [7,8]. The eff'ect of the Z -4…”

Section: Theoretical Techniquesmentioning

confidence: 99%

“…II B. We use the eigenchannel R-matrix approach [8) for the brute force part of the calculation and MQDT [9] to extend the wave functions to distances larger than the R-matrix box radius. The R-matrix calculation determines completely nonrelativistic LS-coupled short-range wave functions with the spin-orbit interaction incorporated in the MQDT part of the calculation by applying the LS to jj frame transformation [10].…”

Section: Introductionmentioning

confidence: 99%

Valence-shell photoabsorption spectra of C, Si, Ge, and Sn

Robicheaux

1993

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We present the results of R-matrix calculations for the bound-state properties of the atoms in the carbon group for states with odd parity and J =0-3. The calculations were performed in LS coupling with the fine-structure interaction incorporated through an LS-jj frame transformation. We also present the photoionization cross section of the ns'np Po ground state for each of the atoms for final-state energies between the two ns'np'PJ spin-orbit split thresholds. We discuss some of the limitations of our C method.PACS number(s): 32.30.r, 31.50.+w, 31.20.Di, 32.80.Fb