1s2s 3S Research Articles

Excitation cross section measurements of doubly excited states produced in low energy collisions between multicharged ions and neutrals

5–60% N 5+ (1s2s 3S) metastable beam fraction has been produced. Single-electron capture from this state will give doubly excited 1s2s nl 2,4L states. The quartets are metastable with respect to Coulomb autoionization and transitions between these doubly excited quartet states have been observed by photon spectroscopy. 1s2p nl states are also observed (TE process). Absolute emission and excitation cross sections have been measured.

Density-sensitive allowed and forbidden dielectronic satellite line profiles in laser-produced plasmas

Calculations of the spectral line broadening for (2p2)1D to (1s2p)1P and (2s2p)1P to (1s2s)1S dielectronic satellite transitions have been performed for the aluminium He-like emitter in hot and dense plasmas. These calculations illustrate that the ion microfield causes an oscillator strength mixing which significantly alters the spectral intensity of such transitions. A discussion of the effects is presented, with particular emphasis on the appearance of the electric-dipole forbidden dielectronic satellite lines.

Theoretical energies for the n = 1 and 2 states of the helium isoelectronic sequence up to Z = 100

The unified method described previously for combining high-precision nonrelativistic variational calculations with relativistic and quantum electrodynamic corrections is applied to the 1s2 1S0, 1s2s 1S0, 1s2s 3S1, 1s2p 1P1, and 1s2p 3P0,1,2 staters of helium-like ions. Detailed tabulations are presented for all ions in the range 2 ≤ Z ≤ 100 and are compared with a wide range of experimental data up to 34Kr+. The results for 90U+ significantly alter the recent Lamb shift measurement of Munger and Gould from 70.4 ± 8.3 to 71.0 ± 8.3 eV, in comparison with a revised theoretical value of 74.3 ± 0.4 eV. The improved agreement is due to the inclusion of higher order two-electron corrections in the present work.

X-ray emission spectroscopy of one-electron capture into Li-like radiative N4+(1s21n'1') configurations by metastable N5+(1s2s 3S) ions in collisions with He and H2 at 3.4 keV amu -1

De-excitation of doubly excited N4+(1s2ln'l') ions produced in N5+(1s2s 3S) (3.4 keV amu-1)+He, H2 collisions has been studied in the 1-5 nm wavelength range. It is shown that the spectrum consists of lines mostly due to states produced by core-conserving capture processes except for an intense peak around 2.9 nm that could be due to electron capture with simultaneous 2s-2p core excitation. Moreover, many lines can be identified as originating from doublet states.

High precision variational calculations for the 1s 21S state of H − and the 1s 21s, 1s2s 1s and 1s2s 3s states of helium

High precision variational eigenvalues are presented for the 1s 21S state of H −, and the 1s 2 1S, 1s2s 1S and 1s2s 3S helium, together with relativistic, mass polarization and relativistic recoil corrections. In addition to the nonrelativistic energy, all corrections of order α 2, μ M ( μ M ) 2 and α 2 M are calculated to an accuracy of better than 10 −6 cm −1. Previous results of similar accuracy are available for the 1 sn d 1 D and 3 D states up to n = 8. A comparison with the high precision 1 s2 s 3 S 1−1 sn d 3 D 1 transition frequency measurements of Hlousek et al. indicates that the known quantum electrodynamic (Lamb shift) contribution of − 0.13488 cm −1 to the ionization energy of the 1s2s 3S 1 state is too small in magnitude by 0.00048(6) cm −1. A discrepancy of this size can reasonably be accounted for by as yet uncalculated contributions to the two-electron Lamb shift.

Subshell selective electron capture in collision of Oq+ ( q = 6, 7) with H 2, He at 10 q keV

Absolute cross sections for electron capture into different ( n, l) subshells have been determined for O 6+ + He and O 7+ + He/H 2 collisions. The n = 4 level of O VI are predominantly populated, while the n = 3 and n = 4 of O VII are nearly equally populated. Transitions between doubly excited quartet states of O VI are observed, they are obtained by one electron capture on the 1s2s 3S O 6+ metastable state.

The electronic and vibrational energies of two double-welled 3Σ+u states of He2

The potential energy curves for the 3Σ+u states of He2 which correspond to the interactions of He 1s2 1S with He 1s2s 3S and He 1s2s 3S with He 1s2s 3S are obtained from second-order configuration interaction calculations which themselves are based on a multiconfiguration self-consistent field calculation. The basis set includes functions obtained by optimizing the dipole, quadrupole, and octapole polarizability of the 3S atom and the dipole and quadrupole polarizabilities of the ground 1S atom. For the lowest 3Σ+u state we estimate the dissociation energy to be De =15 740±60 cm−1; we agree to within about 4 cm−1 with the observed vibrational energy level differences, and agree nicely with the position and depth of the short-range minimum deduced from spectra. We also obtain a potential hump at intermediate separations whose main features agree very well with those obtained from scattering experiments. The potential curve exhibits a van der Waals minimum about 3.82 cm−1 deep at about 11.6 a0. The excited 3Σ+u state has a deep metastable well at small internuclear separations as well as a well in the intermediate region which is about 3430 cm−1 deep.

Electron-produced shift and width of 2l2l' dielectronic satellite lines

An analysis, based on the quantum mechanical impact theory, is made of the electron-produced width and shift of the 2l2l' dielectronic satellite lines. In particular, the screening effects of the spectator electron on the dielectronic lineshift are investigated and discussed in connection with the parent lineshift. Numerical calculation has been carried out for the line parameters of the two helium-like transitions (2p2)1D to (1s2p)1P and (2s2p)1P to (1s2s)1S in laser plasmas. It is shown that the perturbation effects in the upper and lower levels of these transitions are of equal importance and also that the inelastic cross section contribution in line broadening completely masks the elastic one.

Coulomb autoionisation of Li I quartet states above the Li+(1s2s)3S threshold

Four distinct structures are observed in the zero-degree projectile electron energy spectra of 300 keV lithium ions excited in C foils. The lowest single narrow peak has a centre of mass energy 140 meV and is attributed to Coulomb autoionisation of the Li I ((1s2p)3Po3p)4D initial state, e.g. ((1s2p)3Po3p)4D to ((1s2s)3S in d)4D. A second rather sharp peak has a centre of mass energy of 360 meV and originates from Coulomb autoionisation of the Li I((1s2p)3Po3p)4S state decaying into the ((1s2s)3S in s)4S continuum. Finally, a third broader peak, centred at 610 meV, results from the ((1s2p)3Po3d)4Fo to ((1s3s)3S in f)4Fo rapidly autoionising transition. Theoretically the (1s2p nl) quartet levels of lithium are calculated within the framework of the saddle point technique and the complex-rotation method.

Mechanisms of configuration interaction in relativistic autoionisation: threshold phenomena and the Li4PJlevels

The authors have calculated the relativistic autoionisation of the low-lying 4P/sub /J levels of Li using the state-specific theory with the Breit-Pauli Hamiltonian. The results provide a definitive explanation of the shorter lifetimes of metastable Li quartets above the Li+ 1s2s 3S threshold compared with the theoretical predictions from the radiative transition probabilities. This discrepancy between previous theory and experiment is explained in terms of the indirect mechanism of relativistic autoionisation, which is suddenly enhanced-as a result of symmetry, electron correlation and non-orthonormality effects-as the 1s2s 3S channel opens up. The explanation of the threshold effect is thus based on a configuration interaction mechanism and not on a low-energy electron emission effect recently proposed by Mannervik and Cederquist (1986).

The time-dependent Hartree-Fock method within a Gauss-lobe basis and application to proton-He collisions

For the description of ion-atom collisions in the semiclassical approximation, the time-dependent Hartree-Fock (TDHF) method is used. The TDHF equations are solved by expanding the electron wavefunctions within a basic set of Gauss-lobe functions. In this basis the matrix elements of the TDHF Hamiltonian can be obtained analytically, even if translational factors are included. As an application, the authors calculate the excitation cross sections of the (1s2s)1S and (1s2p) 1P states of He in proton-He collisions.

Wavelength predictions for the 1s 22s-1s2s3p satellite transitions

The experimentally known energies of the 1s22s → 1s2s(1S, 3S)3p transitions are considered for lithium to calcium. Their differences from the corresponding He-like resonances are fitted to the atomic number by means of a polynomial function and, through interpolation, the wavelengths for nitrogen to sodium are calculated.

Relativistic energy contributions to the N = 2 triplet levels in helium-like ions

The 1s2s 3S−1s2p 3P J ( J = 0, 1, 2) transitions in helium-like ions can be used to test QED, but only if the other contributions to the transition energy, and especially the relativistic contributions are known to high accuracy. This work tests the relativistic calculations by comparing the theoretical 3P J splittings (which are nearly ndependent of QED) with each other and with experiment. An estimate of the largest uncalculated relativistic term, of relative order α 4 Z 4, is also made. It is found that the calculations of Hata and Grant are not very accurate, and that the small discrepancy between Drake and experiment vanishes if the α 4 Z 4 relativistic term is included.

Two-electron Lamb shifts and 1s2s3S1-1s2p3PJtransition frequencies in helium-like ions

The leading terms in the 1/Z expansion of the two-electron Bethe logarithm are calculated for the states 1s2 1S0, 1s2s 1S1, 1s2s 3S1, 1s2p 1P1 and 1s2p 3PJ by the use of a novel finite basis set method. The resulting QED terms are combined with other relativistic and mass polarisation corrections to obtain total transition frequencies. The results are compared with recent measurements in helium-like ions from Li+ to Fe24+.

Singlet-triplet mixing in ns(n=12-14) Rydberg states of3He

The hyperfine structure of the n3S (n=12-14) Rydberg levels in 3He have been studied by ultraviolet-infrared double-resonance laser spectroscopy. Using the frequency-doubled output of a CW ring dye laser the authors have populated the 1s5p 3P state of 3He by excitation from the metastable 1s2s 3S state at 294.5 nm. In a second step, an infrared single-mode colour-centre laser is used to excite s Rydberg levels. The experimental results for the hyperfine splittings can only be explained with calculations which include singlet-triplet mixing.

Soft x-ray pumping of metastable levels of Li+

Soft x rays from a plasma generated by a neodymium: yttrium aluminum garnet laser beam (1.06 μm) are used to photoionize neutral Li vapor to produce Li+ metastables. Maximum metastable densities of Li+ (1s2s) 1S=6×1014 ions/cm3 and Li+ (1s2s) 3S=3×1015 ions/cm3 are obtained. The effective lifetimes of these levels are measured to be approximately 5 ns. At 50 mJ of incident laser energy the inferred conversion efficiency from 1.06-μm radiation to soft x rays is ∼14%.

Self‐consistent calculation of 1s2s1S state wave function of helium

AbstractA simple self consistent variation perturbation method in the coupled Hartree–Fock scheme has been proposed to calculate 1s2s 1S state of the He atom. The present paper deals with an 1s2s 1S wave function in which all the relevant orthogonality conditions are imposed in successive stages. The resulting wave functions together with some interesting features are discussed.

Electron densities in a solar flare derived from X-ray spectra

view Abstract Citations (59) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron densities in a solar flare derived from X-ray spectra McKenzie, D. L. ; Broussard, R. M. ; Landecker, P. B. ; Rugge, H. R. ; Young, R. M. ; Doschek, G. A. ; Feldman, U. Abstract A major solar flare was observed with the rubidium acid phthalate crystal of the satellite-borne SOLEX B spectrometer and high-resolution solar X-ray spectra were obtained during the rising phase of the flare. Measurements of the density-sensitive line ratio of the O VII 1s2 1S(0) - 1s2s 3S(1) (22.10 A) flux to the O VII 1s2 1S(0) - 1s2p 3P(1) (21.80 A) flux indicate that the density of the plasma at around 2,000,000 K exceeded 10 to the 11th per cu cm near the peak of the flare. This corresponds to an electron pressure of about 30 dynes per sq cm. Publication: The Astrophysical Journal Pub Date: May 1980 DOI: 10.1086/183254 Bibcode: 1980ApJ...238L..43M Keywords: Electron Density (Concentration); Satellite Observation; Solar Electrons; Solar Flares; Solar Physics; X Ray Spectra; Electron Pressure; Satellite-Borne Instruments; Solar Spectrometers; Solar Physics full text sources ADS |

Measurement of the lifetime of the3 P 2 and4 P 5/2 states in Ar16+ and Ar15+

Promptly decaying levels in Li- and Be-like Ar could be identified in the delayed x-ray and electron spectrum in addition to the four known metastable (1s2s)1S0, (1s2s)3S1, (1s2p)3P2, and (1s2s2p)4P5/2 states in He- and Li-like systems. The states having lifetimes of about 10−14s still contribute to the spectrum observed 10−9s after the ions have passed a foil. This observation is explained by cascading processes from states of high principal quantum numbern≧14. The measured lifetime of the4P5/2 state subtracting the contribution of cascades is (0.594±0.016) ns and slightly larger than the theoretically predicted value of 0.563 ns. The3P2 state is depopulated at short distances behind the foil by cascading processes. Its measured lifetime of (1.44±0.08) ns compares to a theoretical value of 1.48 ns.

Inner-shell photoionization of Be. Fluorescence yield of Be

The coupled equations were solved for the collision of an electron with Be+. The Be+ levels included were 1s22s and 1s22p in solving for the 1s22s2 ground state and 1s2s2 2S, 1s2s(1S)2p 2P, 1s2s(3S)2p 2P and 1s2p2 2D, 2P, 2S for the Be+ (inner shell)+continuum states. The solutions were used to calculate the photoionization cross section. The fluorescence yield of Be was calculated with the assumption that the photon radiation created the inner-shell vacancy. Comparisons with experiments were made for both the inner-shell photoionization and the fluorescence yield.