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An extensive study of photoionization from neon excited states was performed. The R-matrix approach was applied to calculate a photoionization cross-section from the metastable 2 p 5 (2 P J f) 3 s [ K ] 0 , 2 and dipole-allowed 2 p 5 (2 P J f) 3 s [ K ] 1 states. The resonance structures and Cooper minimum accessible in photoionization from the excited states by the photons with energy below 30 eV were analyzed. The parameters of the lowest autoionizing states (AISs) of even parity were extracted by fitting of the photoionization cross-section. For the dipole-allowed states, calculations are presented for unpolarized, linearly and circularly polarized radiation. [ABSTRACT FROM AUTHOR]

Using the technique of intersecting beams of slow electrons and atoms of zinc, excitation functions of four spectral lines of Zn I principal series corresponding to the 4snp → 4s21S0 transitions for n = 4, 5, 6, and 7 are measured. Their wavelengths are 213.9, 158.9, 145.8, and 140.4 nm, respectively. Within the energy range of 11–18 eV, the effect of postcollision interaction of electrons (slow scattered and fast ejected ones) has been revealed on these functions with the decay of the autoionizing state. At incident electron energies of ∼11–13 and ∼15–18 eV, such interaction leads to an additional population of the initial levels for these lines and, correspondingly, to the formation of maximum on their excitation functions due to the capture of a scattered electron into these excited levels. The terms of atomic autoionizing states responsible for the observed maximums are determined. The combined influence of the decay of these autoionizing states and postcollision interaction is expressed in the energy shift of the maximums on the excitation functions relative to positions of the corresponding autoionizing states. Using a straightforward calculation in the classical approximation, effective widths of the electron decay of the autoionizing states are estimated. The estimates involve an exact formula and approximation formulas. The latter are valid for different relations between the value of the postcollision shift of maximums on the excitation functions and electron bonding energy at the atomic level. They are used for the determination of effective widths when approximating experimental shifts by the least squares method. [ABSTRACT FROM AUTHOR]

The electron impact excitation (and their decay into the same final ionic state) of the autoionizing states of helium ( 2 s 2 ( S 1 ) , 2 s 2 p ( P 3 ) , 2 p 2 ( D 1 ) and 2 s 2 p ( P 1 ) ) have been studied. The interference of these states can occur when the energies of the autoionizing electrons match that of the scattered electrons. The observation of this exchange interference is disturbed by the Fano interference, which occurs at all primary energies. We intend to study it separately in the neighborhood of the critical energy, and then to estimate its measure for the critical energy. The present measurements were made at 88 eV and 97 eV primary energies (where the groups of the ejected and the scattered electron peaks are well separated), at 130°, 90° and 50° scattering angles. The measured spectra were evaluated by a computer code, using the Shore parametrization. We give the obtained peak parameter values in tabulated form. We found an anomaly of the fitted values of Lorentz width of 2 s 2 ( S 1 ) peak. [ABSTRACT FROM AUTHOR]

The resonant ionization laser ion source is an element selective, efficient and versatile ion source to generate radioactive ion beams at on-line mass separator facilities. For some elements with complex atomic structures and incomplete spectroscopic data, laser spectroscopic investigations are required for ionization scheme development. Laser resonance ionization spectroscopy using Ti:Sa lasers has been performed on antimony (Sb) at TRIUMF's off-line laser ion source test stand. Laser light of 230.217 nm (vacuum wavelength) as the first excitation step and light from a frequency-doubled Nd:YVO 4 laser (532 nm) as the nonresonant ionization step allowed to search for suitable second excitation steps by continuous wavelength scans from 720 nm to 920 nm across the wavelength tuning range of a grating-tuned Ti:Sa laser. Upon the identification of efficient SES, the third excitation steps for resonance ionization were investigated by laser scans across Rydberg states, the ionization potential and autoionizing states. One Rydberg state and six AI states were found to be well suitable for efficient resonance ionization. [ABSTRACT FROM AUTHOR]

Dielectronic recombination of Zn and Cd ions involving electron excitation of the ion ns core with simultaneous resonance capture of an incident electron into the doubly-excited intermediate autoionizing npS0-state followed by its radiative stabilization np → nsnp + hν was observed and investigated using an ultrahigh-vacuum apparatus with crossed electron and ion beams. The effective cross sections of dielectronic recombination at the maximum were 0.9·10 cm for Zn and 1.6·10 cm for Cd, which were comparable with those for electron excitation of the resonance lines of the studied ions. The high probability of radiative decay of the autoionizing npS0-state was due to relativistic and correlation effects. [ABSTRACT FROM AUTHOR]

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm-1 and 46943.6 cm-1 are systematically investigated by a three-color multi-step resonant excitation scheme with three different excitation paths. The three intermediate states, 4f 66s7s 7F3, 4f 66s7s 7F4, and 4f 66s7s 9F5 are employed for the three paths, respectively. Based on precise calibration of wavelength, the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions. The possible influence of configuration interaction on the line shape of autoionizing state is also discussed. In addition, a unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths. [ABSTRACT FROM AUTHOR]

Abstract: We discuss three aspects of the analysis of the quasi-bound-state (QBS) or resonance-state effects on multichannel continuum wavefunctions for few-body atomic systems. is devoted to a brief introductory account of the basic concept necessary for understanding the later sections. General properties of the scattering matrix S and a related time-delay matrix Q are discussed in . Both isolated and overlapping resonances are treated, starting from single-channel problems and extending the theory for multichannel cases. Useful relations are derived in detail on the basis of linear algebra. The concept of the resonance channel and nonresonance channel spaces, separated from each other, is introduced via the Q-matrix diagonalization. Outstanding examples of resonance analysis by the inspection of the eigenvalues of the Q matrix are presented. They include the extraction of resonances from a monotonically decreasing phase shift due to a strong background, the detection of a weak resonance, seemingly a nearly constant background behind a strong resonance, and the decomposition of several overlapping resonances into the individual components, some of which are difficult to identify by the conventional methods. examines effective potentials for understanding QBSs. First, the information obtainable from the asymptotic long-range potentials is summarized. This includes the analysis of infinite series of QBSs supported by an attractive Coulomb or dipole potential, the latter appearing in charged-particle collisions with hydrogen-like atoms. The infinite series of dipole-supported QBSs is terminated to only a few resonances, sometimes to one or two, by correcting for relativistic and quantum electrodynamic effects. The dipole potential can also cause the background phase shift to diverge as the energy tends to a channel threshold from above, complicating a resonance structure. The hyperspherical coordinate approach is then briefly discussed. Accurate numerical calculations for three-body systems are possible by solving coupled-channel equations in terms of these coordinates. The resultant resonance structures can be visually and qualitatively interpreted by inspecting the adiabatic potentials with the hyperradius adopted as the adiabatic parameter. Sometimes the adiabatic correction or diabatic connection, or both are necessary for proper resonance analysis. By combining with the knowledge of the long-range potentials, resonances can often be ascribed to particular adiabatic or diabatic hyperspherical potentials out of an intertwined set of potential curves. In particular, when two or more adiabatic potentials exhibit strongly avoided crossings, some resonances appear as if they were associated with no hyperspherical potentials, even though a careful diabatic interpretation can clearly explain them. A shift in hyperspherical potentials with a continuous change in some parameter(s) in the system can result in a sudden change from a bound state to QBS or from a Feshbach to shape resonance without any essential change in the main part of the wavefunction. analyzes the energy dependence of the cross sections near the threshold for the formation of a QBS. The Wigner threshold law breaks down close to the threshold since the threshold itself has an uncertainty due to the finite lifetime of the QBS. The modifications, due to Baz', for a blurred threshold are explained. Positron–atom collisions are discussed as a prototype, where a bound electron–positron pair (positronium, Ps) can be formed. It is a QBS since it annihilates eventually. Pair annihilation, or positron absorption, can also occur during the collision. The conventional theory leads to a divergent positron absorption cross section at the Ps formation threshold E th, and to a Ps formation cross section starting from zero and rapidly increasing above E th. Both of these processes have a common final channel of pair annihilation and should be treated collectively. This is possible by phenomenologically modeling pair annihilation as particle loss due to an imaginary potential in the Schrödinger equation. This approach proves the continuous and smooth transition from positron absorption to Ps formation across E th, following the Baz' threshold law. Thus, the two processes are indistinguishable in the energy region of this transition. [Copyright &y& Elsevier]

Abstract: The investigation of the samarium (Sm) atom autoionizing states, belonging to the 4f 6 6pnl and 4f 5 5d6snl (l=0, 2) configurations, has been carried out by using a three-step isolated-core-excitation (ICE) scheme. Fifty-seven new autoionizing states of the Sm atom have been observed in the energy region between 60,700 and 66,500cm−1. These autoionizing states are classified into five autoionization series in the light of different ionization limits. In most cases, the transition profiles of these autoionizing states are nearly symmetric, from which the peak positions and widths can be easily obtained by Lorentzian-profile-fitting procedure. Some autoionizing states have multi-peak profiles whose spectroscopic properties are analyzed in order to understand the complicated structures. [Copyright &y& Elsevier]

Abstract: In this work, 4f 66pnl and 4f 55d6snl (l=0,2) autoionizing states of the samarium (Sm) atom, especially those with lower principal quantum number, have been studied, using the isolated-core excitation scheme with three dye lasers. In the energy region between 57990 and 61030cm−1, there are 74 autoionizing states of the Sm atom observed. These states can be classified into the autoionization series converging to four different ionization limits. In most cases, the line shapes of these autoionizing states are nearly symmetric, from which the level energies and widths can be easily obtained by fitting the experimental spectra to the Lorentzian profiles. In addition, several spectroscopic properties of these autoionizing states, such as configuration interaction, are also discussed. [Copyright &y& Elsevier]

Laser resonance ionization spectroscopy of atomic thulium (Tm) has been performed at TRIUMF's off-line laser ion source test stand with a system of pulsed titanium sapphire (Ti:Sa) lasers. Automated continuous laser frequency scans across Rydberg states and autoionizing (AI) states were carried out using a pulsed, frequency doubled grating-tuned Ti:Sa laser. A combined analysis of the convergence limits resulting from odd-parity Rydberg series and AI Rydberg series improved the value for the ionization potential to 49,880.57(6) stat (4) sys cm−1, one order of magnitude more precise than the currently accepted value of 49,879.8(5) cm−1. An efficient resonance ionization scheme has been deduced from the photoionization spectra, and applied to online radioactive Tm isotope beam delivery at ISAC-TRIUMF. The ionization scheme will be useful for the extraction of Tm isotopes for nuclear medicine. The production yields of 153–165Tm were measured by evaluating the characteristic γ lines of the Tm isotopes at the ISAC yield station. [Display omitted] • Resonant ionization spectroscopy of Tm using Ti:Sa lasers. • First study of the odd-parity Rydberg states and autoionizing Rydberg states. • An improved IP(Tm) = 49,880.52(1) stat (4) sys cm−1. • An efficient laser ionization scheme. • The radioactive isotope yields 153-163Tm using a hot cavity RILIS. [ABSTRACT FROM AUTHOR]

Abstract: Some recent measurements of excitation of ions by electrons studied in beam–beam experiments are highlighted. The emphasis is on the study of the regularities of electron–ion scattering dynamics related to the excitation and decay of atomic autoionizing states both in electron and radiative channels. Some results are presented in comparison with the data obtained by other scientific groups and with existing theoretic calculations. The significant role of relativistic and correlation effects on dynamics of excitation process has been established. [Copyright &y& Elsevier]

Abstract: The spectra of the Ba 6pnk autoionizing Stark states with |M|=0, 1, converging to the 6p1/2 + and 6p3/2 + ionization thresholds, are measured as a function of the electric field strength F. Several 6p j nk Stark manifolds with n =13–15 have been systematically studied in order to explore their characteristics of configuration interaction. Experimental results are analyzed by fitting them to the Lorentzian profile, from which the positions and widths are determined. Different spectroscopic properties between the Ba 6p1/2 nk and 6p3/2 nk autoionizing Stark states are investigated. Comparison between the Ba 6p j nk autoionizing Stark states with |M|=0 and those with |M|=1 are made. [Copyright &y& Elsevier]

We have studied the optical excitation functions (OEFs) for 12 mercury spectral lines emerging from n1S0, n1P1, n1D2, n3S1, n3Pj and n3Dj-levels using the modified hypocycloidal electron monochromator to produce the electron beam with the 10–70 meV energy spread. The OEFs reveal nearly 100 features due to the decay of short-lived negative-ion states. [Copyright &y& Elsevier]

With a combination of the isolated core excitation (ICE) technique and a proper polarization configuration of three lasers, both the 6p1/2nk and 6p3/2nk autoionizing Stark states excited from the 6snk Stark states with M=1 have been measured for the first time. The experimental results are analyzed by fitting them to the Lorentzian profiles, from which the positions and widths are determined at various electric-field strengths. The experimental results indicate that the 6p1/2nk and 6p3/2nk autoionizing Stark states have different spectroscopic properties due to the difference of their cores. [Copyright &y& Elsevier]

With different polarization configurations the spectroscopic properties of Ba 6p1/2ns (J=0) and 6p1/2ns (J=1) autoionizing states have been studied systematically by using an isolated core excitation scheme. Level energies and widths of n members for the J=1 series with n=9–33 and for the J=0 series with n=9–10,12–20 are reported, most of which are observed for the first time. Further information about these two autoionizing series, such as energies of the higher n members and their interseries interactions with 6p3/2nl series, are obtained by means of saturation excitation method. The experimental data on the J=1 series are analyzed with a 13-channel multichannel quantum defect theory, and general agreement between them has been obtained. Several parts of the experimental results are compared with those of previous works, and agree well with them. [Copyright &y& Elsevier]

Using TRIUMF's off-line laser ion source test stand with a system of tunable titanium sapphire lasers, the polarization dependence of laser resonance ionization has been investigated using beryllium. A significant polarization dependence was observed for the excitation path 1S 0 → 1P 1 ∘ → 1S 0 , which are typical transitions for alkaline-earth and alkaline-earth like elements. This polarization dependence was further verified on Be radioactive isotopes at TRIUMF's isotope separator and accelerator facility (ISAC). Laser polarization was proven to be an important parameter in operating resonance ionization laser ion sources (RILIS). The polarization spectroscopy was performed off-line both on the 2p2 1S0 autoionizing (AI) state and high- n Rydberg states of the 2 sns 1 S 0 and 2 snd 1 D 2 series. The energy of the 2p2 1S0 AI state and ionization potential (IP) of beryllium were extracted as 76,167(6) cm−1 and 75,192.59(3) cm−1. Polarization spectroscopy can be used to determine the J values of newly found states in in-source spectroscopy of the complex/radioactive alkaline-earth like elements such as Ra, Sm, Yb, Pu and No. Unlabelled Image • Polarization-dependent laser resonance ionization of Be in hot-cavity ion sources • Polarization spectroscopy on the 2p 2 1 S 0 AI state and 2sns 1 S 0 and 2snd 1 D 2 series • 2p 2 1 S 0 autoionizing state energy measured to be 76,167(6) cm−1 • Ionization potential of Be measured to be 75,192.59(3) cm−1 • Polarization dependence observed for 9–11 Be isotopes in hot-cavity ion sources. [ABSTRACT FROM AUTHOR]