Physics Commons^™

Measurement Of The Xenon Σ3/2:Σ1/2 Branching Ratio Within The Xe 5s5p66p(1P1) Resonance, Peter C. Kemeny, James A. R. Samson, Anthony F. Starace

Anthony F. Starace Publications

Photoionization of the 5p6 shell in xenon leaves the ion in either the 5p⁵(²P_3/2) or np⁵(²P_1/2) state. Measurements of the ²P_3/2 : ²P_1/2 branching ratio are reported within the Xe 5s5p⁶6p(¹P₁) resonance and fitted to a new theoretical expression. The maximum value of the ratio as determined by a two-parameter fit of theory to experiment is 8.8 ± 0.5 within the resonance, almost six times the nearly constant value of 1.55 found outside any resonance.

The Quantum Defect Theory Approach, Anthony F. Starace

Anthony F. Starace Publications

The Quantum Defect Theory (QDT) is a method of using the analytically known properties of excited electrons moving in a pure Coulomb field to describe atomic photoabsorption and electron-ion scattering processes in terms of a few parameters. These parameters may be determined either from experimental data or from ab initio theoretical calculations. In addition, they are usually nearly independent of energy in the threshold energy region (i.e., within a few eV of the atomic ionization threshold). Thus the determination of these parameters at any single energy suffices to predict the variation with energy of numerous atomic properties in the threshold …

Photoinization Cross Sections For Atomic Chlorine Using An Open-Shell Random-Phase Approximation, Anthony F. Starace, Lloyd Armstrong Jr.

Anthony F. Starace Publications

The use of the random-phase approximation with exchange (RPAE) for calculating partial and total photoionization cross sections and photoelectron angular distributions for open-shell atoms is examined for atomic chlorine. Whereas the RPAE corrections in argon (Z=18) are large, we find those in chlorine (Z=17) to be much smaller due to geometric factors. Hartree-Fock calculations with and without core relaxation are also presented. Sizable deviations from the close-coupling results of Conneely are found.

2P3/2:2P1/2 Partial Photoionization Cross-Section Ratios In The Rare Gases , James A.R. Samson, J.L. Gardner, Anthony F. Starace

Anthony F. Starace Publications

The ²P_3/2:²P_1/2 partial photoionization cross-section ratios have been measured for the rare gases in the ionization continuum and within resonance structure. The wavelength range for this study was from the ²P_1/2 ionization threshold to 304 Å. The ratio of the cross sections was found to be constant over this wavelength range, yielding ratios of 1.54, 1.77, 1.93, and 2.18 for Xe, Kr, Ar, and Ne, respectively. Within resonances, the ratio changed dramatically. Results are illustrated for xenon.

Gauge Invariance And Radiative Transition Probabilities, Ian P. Grant, Anthony F. Starace

Anthony F. Starace Publications

The relationship between recommendations of some recent papers on the choice of formula (length, velocity, or acceleration type) for calculating radiative transition probabilities is clarified.

Effect Of Elliptically Polarized Light On The Angular Distribution Of Photoelectrons, James A. R. Samson, Anthony F. Starace

Anthony F. Starace Publications

The angular distribution of photoelectrons predicted for elliptically polarized light is shown to be the same as that predicted for partially polarized light having incoherent perpendicular electric field components equal to the electric field components along the major and minor axes of the ellipse.

Includes Corrigendum from J. Phys. B: Atom. Molec. Phys. 12:23 (1979), p. 3993.

Effects Of Anisotropic Electron-Ion Interactions In Atomic Photoelectron Angular Distributions, Dan Dill, Anthony F. Starace, Steven T. Manson

Anthony F. Starace Publications

The photoelectron asymmetry parameter β in LS coupling is obtained as an expansion into contributions from alternative angular-momentum transfers j_t. The physical significance of this expansion of β is shown to be that (i) the electric-dipole interaction transfers to the atom a characteristic single angular momentum j_t=l₀, where l₀ is the photoelectron's initial orbital momentum, whereas (ii) angular-momentum transfers j_t≠l₀ indicate the presence of anisotropic (i.e., term-dependent) interaction of the outgoing photoelectron with the residual ion. For open-shell atoms the photoelectron-ion interaction is generally anisotropic; photoelectron phase shifts …

Photoelectron Angular Distributions, Cross Sections, And Branching Ratios For Atomic Oxygen, Anthony F. Starace, Steven T. Manson, David J. Kennedy

Anthony F. Starace Publications

Theoretical calculations of the angular distribution of photoelectrons ejected from the 2p subshell of atomic oxygen for photoelectron kinetic energies 0≤ε≤30 Ry are presented using both Hartree-Fock (HF) and Herman-Skillman (HS) wave functions. Owing to the weakness of anisotropic electron-ion interactions, as evidenced by small differences between HF photoelectron phase shifts for alternative outgoing channels, the simple HS calculation of the angular-distribution asymmetry parameter is found to agree to within ≲ 0.1 with the HF calculations. Photoionization cross sections and photoelectron branching ratios have also beem computed in both the HF and HS approximation for the 2p subshell …

Photoelectron Angular Distributions As A Probe Of Anisotropic Electron-Ion Interactions, Dan Dill, Steven T. Manson, Anthony F. Starace

Anthony F. Starace Publications

Expressions are given for atomic photoelectron angular distributions in LS coupling in which the role of anisotropic final state electron-ion interactions emerges explicitly. Calculations of photoelectron angular distributions for atomic sulfur are presented in which these anisotropic interactions produce clear deviations from the predictions of the Cooper-Zare model. Such effects are expected to be a general feature of photoelectron angular distributions for most open-shell atoms.

Angular Distribution Of Photoelectrons From Atomic Oxygen, Nitrogen, And Carbon, Steven T. Manson, David J. Kennedy, Anthony F. Starace, Dan Dill

Anthony F. Starace Publications

The angular distributions of photoelectrons from atomic oxygen, nitrogen and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen, and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch angle distribution of photoelectrons is discussed and it is shown that previous approximations of energy independent isotropic or sin² θ distributions are at odds with our results, which vary with energy. This variation with energy is discussed as is the reliability of these calculations.

Effect Of Virtual 4d-Shell Excitations On Rare Earth Spectra, Anthony F. Starace

Anthony F. Starace Publications

Ab initio energies for electric dipole transitions 4d¹⁰ (¹S₀) → 4d⁹4f J = 1 in triply-ionized lanthanum have been calculated by constructing an effective interaction, acting within the configuration 4d⁹4f, that incorporates effects of virtual 4d-shell excitations to all orders of perturbation. Virtual 4d-shell excitations, included within the random phase approximation, and virtual excitations to singly-excited configurations 4d⁹εf are found to reduce the ordinary electrostatic interaction by 38% for the ¹P₁ term of 4d⁹4f, by 6% for the ³D₁ term, and by 3% …

Comment On "Length And Velocity Formulas In Approximate Oscillator-Strength Calculations", Anthony F. Starace

Anthony F. Starace Publications

A previous paper by Starace showed that the length formula for the electric-dipole matrix element is the only consistent one for calculations that solve for the exact eigenfunctions of an approximate Hamiltonian containing a nonlocal potential. It is emphasized here that disagreement between such a length-formula calculation and experiment indicates inadequacy of the approximate Hamiltonian and not that the velocity formula may be preferable.

Quasi-Landau Spectrum Of A Hydrogen Like Atom In A High Magnetic Field, Anthony F. Starace

Anthony F. Starace Publications

A two dimensional semiclassical approximation is used to examine the σ polarization spectrum of a hydrogen like atom in a strong magnetic field. Resonances above the zero field ionization limit are found and their energy separations are computed over the region from the ionization limit to 40 ħω_c above, where ω_c is the cyclotron frequency, for magnetic fields of 10, 17, 25, 32, 40 and 47 kG. At the ionization limit the separation between resonances is found to be 1.500 ħω_c, independent of magnetic field strength, which is in agreement with a separation of 1.5 ħω …

Absolute Line Strengths By Analysis Of Lu-Fano Plots With Application To Excited State Transitions In Neon, Anthony F. Starace

Anthony F. Starace Publications

Using energy eigenfunctions obtained by semi-empirical analysis of the Lu-Fano plot of energy level positions and employing the Coulomb approximation of Bates and Damgaard, we calculate absolute line strengths for transitions between the neon two-channel Rydberg series 2p⁵(²P_3/2,1/2)ns J = 1 and 2p⁵ (²P_3/2,1/2)n′ p J = 0 for n, n' = 3,4. Each Rydberg series is analyzed separately to obtain a set of five parameters which completely define the energy eigenfunctions for all values of n and n'. Interactions between the ns J = 1 …

Potential-Barrier Effects In Photoabsorption. I. General Theory, Anthony F. Starace

Anthony F. Starace Publications

This paper combines parts of the theories of spectroscopy, collisions, and autoionization to provide a unified framework for a quantitative theory of experimental data on 4d-shell photoabsorption in rare earths. The calculations by atomic theory are intended for tentative application to solids. The theory should also apply to 3p-shell photoabsorption in the transition metals and to other cases where the effect of a potential barrier is crucial. A prescription is given for the ab initio numerical calculation of total and partial photoabsorption cross sections, as well as of the profiles, energies, and widths of resonances. A …

Potential-Barrier Effects In Photoabsorption. Iii. Application To 4D-Shell Photoabsorption In Lanthanum, J.L. Dehmer, Anthony F. Starace

Anthony F. Starace Publications

An exploratory calculation of the photoabsorption cross section near the 4d ionization threshold of lanthanum metal is carried out. The level structure of the configuration 4d⁹4f is found to be altered by interaction with the continuum configuration 4d⁹εf. The Fano profile of the resonance above threshold is calculated, as are the oscillator strengths of the discrete states below threshold. Our results provide the ground work for more detailed calculations.

Raising Of Discrete Levels Into The Far Continuum, J.L. Dehmer, Anthony F. Starace, U. Fano, J. Sugar, J.W. Cooper

Anthony F. Starace Publications

Broad peaks observed in the photoabsorption spectra of rare earths ∼10-20 eV above the 4d edge are attributed to transitions 4d¹⁰4f^N→4d⁹4f^N+1. Exchange interaction splits the 4d⁹4f^N+1 configuration and raises some multiplets by ∼20 eV. Autoionization to 4d⁹-4f^Nεf broadens the high levels. The interpretation extends to p→d processes observed in the absorption of synchrotron light by transition elements.

Length And Velocity Formulas In Approximate Oscillator-Strength Calculations, Anthony F. Starace

Anthony F. Starace Publications

The matrix element for electric dipole transitions is correctly given by the length formula in the Hartree-Fock, configuration-interaction, and related approximations, which involve the diagonalization of an approximate, but nonlocal, Hamiltonian.

Photoionization Of Argon And Xenon Including Final-State Correlation, Anthony F. Starace

Anthony F. Starace Publications

Effects of final-state correlation on the photoionization cross sections for the 3p shell in argon and the 4d shell in xenon are calculated by the reaction-matrix method, starting from the Herman-Skillman model Hamiltonian, for photoelectron energies 0<~ε<~1.2 a.u. and 0<~ε<~2.52 a.u., respectively. The results for argon complement Hartree-Fock and other final-state correlation calculations; the results for xenon are the first ab initio calculations of this kind. Although length and velocity forms of the transition matrix element agree in the initial local-field approximation, they are shown to diverge necessarily when only the final state is improved.