Fine-structure energy levels,oscillator strengths and lifetimes in Mg-like chromium

Excitation energies from ground state for 86 fine-structure levels as well as oscillator strengths and radiative decay rates for all fine-structure transitions among the levels of the terms (1s²2s²2p⁶)3s²(¹S), 3s3p(^1,3P^o), 3s3d(^1,3D), 3s4s(^1,3S), 3s4p(^1,3P^o), 3s4d(^1,3D), 3s4f(^1,3F^o), 3p²(¹S, ³P, ¹D), 3p3d(^1,3P^o, ^1,3D^o, ^1,3F^o), 3p4s(^1,3P^o), 3p4p(^1,3S, ^1,3P, ^1,3D), 3p4d(^1,3P^o, ^1,3D^o, ^1,3F^o), 3p4f(^1,3D, ^1,3F, ^1,3G) and 3d²(¹S, ³P, ¹D, ³F,¹G) of Cr XIII are calculated using extensive configuration-interaction (CI) wave functions obtained with the CIV3 computer code of Hibbert. The important relativistic effects in intermediate coupling are included through the Breit-Pauli approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. Small adjustments to the diagonal elements of the Hamiltonian matrices have been made. The mixing among several fine-structure levels is found to be very strong. Our excitation energies, including their ordering, are in excellent agreement (better than 0.5%) with the available experimental results. From our transition probabilities, we have also calculated radiative lifetimes of some fine-structure levels. Our calculated lifetime for the longer-lived level 3s3p(³P₁) is found to be in excellent agreement with the experimental result of Curtis compared to other theoretical calculations.     

Photoionization cross section and oscillator strength distribution in the near-threshold region of strontium

We present experimentally measured absolute values of the photoionization cross sections from the 5s5p ¹P₁ and 5s5p ³P₁ excited states of strontium at the first ionization threshold as 11.4±1.8 Mb and 10.7±1.7 Mb respectively using saturated absorption technique along with a thermionic diode ion detector in conjunction with a Nd:YAG pumped dye laser system. These threshold photoionization cross sections values have been utilized to determine the oscillator strengths of the 5s5p ¹P₁↦5snd ¹D₂ and 5s5p ³P₁↦5snd ³D₂ Rydberg transitions. The oscillator strength densities in the continuum corresponding to the 5s5p ³P₁ excited state have also been determined by measuring the photoionization cross sections at five ionizing wavelengths above the first ionization threshold. Smooth merging of the discrete f-values into the oscillator strength densities has been observed for the 5s5p ³P₁↦5snd ³D₂ series across the ionization threshold.     

Oscillator strength measurements of the 3p ↦ nd Rydberg transitions of sodium

We report new measurements of the oscillator strengths of the 3p ²P_3/2 ↦nd ²D_{5/2, 3/2} and 3p ²P_1/2 ↦ nd ²D_3/2 Rydberg transitions of sodium using a thermionic diode ion detector in conjunction with the Nd:YAG pumped dye lasers. The ns ²S_1/2 and nd ²D_5/2,3/2 Rydberg series have been recorded via two-step excitation, from the 3p ²P_3/2 and 3p ²P_1/2 intermediate states. Employing the saturation technique, the photoionization cross sections from the 3p ²P_3/2 and 3p ²P_1/2 intermediate states at the first ionization threshold are determined as 7.9(1.3) Mb and 6.7(1.1) Mb respectively. The f-values of the Rydberg transitions are calibrated with the photoionization cross section measured at the first ionization threshold and compared with the earlier data.     

Relativistic R-matrix close-coupling calculations for photoionization of Ne-like Al IV

We present relativistic close-coupling photoionization calculations of Al IV using the Breit-Pauli R-matrix method to obtain photoionization cross-section of Al IV from the ground state and the lowest two J=0 (even) excited states. A multi-configuration eigenfunctions expansion of the core Al V is employed with spectroscopic configurations 2s²2p⁵, 2s2p⁶, 2s²2p⁴3s, 2s²2p⁴3p, 2s²2p⁴3d and 2s²2p⁴4s. We have included, for the first time, the lowest 68 level target states of Al V in the photoionization calculations of Al IV. Extensive configuration interaction wavefunctions are used to describe both the initial Al IV states and the final Al V states. Cross-sections are compared from three level calculations including only 2s² 2p^{5 2}P^o _3/2, _1/2 and 2s 2p^{6 2}S_1/2 levels of Al V. The present calculation using the lowest 68 target levels of Al V are presented for the first time and should provide reasonably complete database for practical application for photoionization cross-section for Al IV, where high-energy cross-sections along with near-threshold photoionization cross-section is required.     

Impact broadening and shift rates for the 6p2 3PJ′ → 7s 3P J o transitions of lead induced by collisions with argon and helium

The collisional broadening and shift rate coefficients of the 283.39 nm (6p ^{2 3}P₀ → 7s ³P₁ ^o ), 364.06 nm (6p ^{2 3}P₁ → 7s ³P₁ ^o ), 368.45 nm (6p ^{2 3}P₁ → 7s ³P₀ ^o ) and 405.90 nm (6p ^{2 3}P₂ → 7s ³P₁ ^o ) Pb lines by He and Ar have been measured by fitting the experimental absorption line shapes to theoretical Voigt profiles. The absorption measurements were performed in a resistively heated, Pb loaded oven with an integrated dc noble gas discharge to produce also Pb atoms in the 6p ^{2 3}P¹ and 6p ^{2 3}P² metastable states. The diffusion of the metastable atoms out of the discharge zone into the neutral noble-gas atmosphere enabled the line-shape and shift measurement of the lines involving the metastable states without the influence of the discharge plasma.     

Photoionization cross-section measurements from the 2p, 3d and 3s excited states of lithium

The photoionization cross-sections from the 2p²P_{1/2, 3/2}, 3d²D_{3/2, 5/2} and 3s²S_1/2 excited states of lithium have been measured at different ionizing laser wavelengths, above the first ionization threshold. The experiments are performed by using a thermionic diode working in the space charge limited mode and the cross-sections are measured by employing the saturation technique. By changing the ionization photon energy, a smooth frequency dependence of the cross-sections has been observed for the 2p and 3d states. The cross-section from the 3s excited state has been measured at a single photon energy. The measured values of the photoionization cross are compared with the available data.     

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In⁺ 5s^{2 1}S₀ (F = 9/2)–5s5p ³P₁ (F = 11/2) transition near 230.6 nm. The laser-induced fluorescence from a single In⁺ in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes ¹¹⁵In⁺ and ¹¹³In⁺ are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.     

Laser-induced fluorescence study of a xenon Hall thruster

2 ⁰→6p[3/2]₂(³P₂-¹D₂) transition at 823.2 nm and the xenon-ion 5d[3]_7/2→6p[2]_5/2 ⁰(⁴D_7/2-⁴P_5/2) transition is used to measure plasma parameters in the plume of a laboratory-model xenon Hall thruster. The Hall discharge operates nominally at 62 V, 4.2 A, and 3.2 mg s^-1 xenon flow, with an overall thruster power of 320 W. A tunable semiconductor diode laser and an Ar⁺-pumped dye laser are used to probe the respective excited-state transitions. Axial velocity measurements are made at a number of axial and radial locations up to 4.5 cm downstream of the thruster-exit plane and under a variety of thruster operating conditions. Neutral velocities from 100 m s^-1 to 400 m s^-1 and ion velocities as high as 12 km s^-1 are calculated from measured Doppler shifts. The charge-exchange phenomenon evidently does not significantly affect the xenon neutrals. The spectral-line shapes of the ion indicate a spread in ion energies through a non-Maxwellian distribution of axial velocities. Neutral kinetic temperatures of 500 (±200) K are observed under standard operating conditions. Zeeman and Stark effects on the spectral-line shapes, from the thruster’s magnetic and electric fields, are not substantial. The measured line center of the ion transition is 16521.23 (±0.02) cm^-1. Received: 20 January 1997/Revised version: 12 May 1997     

Determination of the calcium ground state scattering length by photoassociation spectroscopy at large detunings

Photoassociation spectroscopy was used to determine the s-wave scattering length of ⁴⁰Ca atoms in their electronic ground state. Vibrational levels were observed in an extended range of up to 182 GHz below the dissociation limit 4s^{2 1}S₀–4s4p ¹P₁. Thus, the frequency interval was nearly tripled, in which photoassociation was observed compared to previous measurements. The spectra were analyzed by means of quantum mechanical simulations. With the new data it was possible to resolve the discrepancy concerning the ground state scattering length presented in earlier publications [Phys. Rev. A 67, 043408 (2003); Eur. Phys. J. D 26, 155 (2003)]. An improved dipole-dipole coupling constant C₃ ^Σ = 0.52306(20) ×10³ cm^-1 nm³ is obtained.     

Line shape parameters study of the 6p7p (<Superscript>1</Superscript>P<Subscript>1</Subscript>, <Superscript>3</Superscript>D<Subscript>1</Subscript> and <Superscript>3</Superscript>P<Subscript>1</Subscript>): Autoionizing resonances in barium

We report a systematic line shape analysis study of the 6p7p configuration based ¹P₁, ³D₁ and ³P₁ autoionizing resonances in barium using a Nd:YAG pumped dye laser system in conjunction with a thermionic diode ion detector. The even parity isolated autoionizing resonances have been approached via four intermediate states 6 snp ¹P₁ (6 ≤n ≤8) and 5d6p ¹P₁. A comparison of the Fano parameters of the resonance profiles reveals that the width of an autoionizing resonance is independent of the excitation path while the line profile parameter changes with the selection of different intermediate states.     

Charge radius change in the heavy tin isotopes until A = 132 from laser spectroscopy

Laser spectroscopy measurements have been carried out on the very neutron-rich tin isotopes with the COMPLIS experimental setup. Using the 5s ²5p ²³ P ₀ → 5s ²5p6s ³ P ₁ optical transition, hyperfine spectra of ^126-132Sn and ^{125m, 127m, 129m-131m}Sn where recorded for the first time. The variation of the mean-square charge radius ( δ〈r ²〉) between these nuclei and nuclear moments of the isomers and the odd isotopes were thus measured. An odd-even staggering which inverts at A = 130 is clearly observed. This indicates a small appearance of a plateau on the δ〈r ²〉 which has to be confirmed by measuring the isotope shift beyond A = 132. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: leblanc@ipno.in2p3.fr     

High-resolution isotope shift measurement of the MgI 1 S 0 - 3 P 1 intercombination transition

We measured the isotope shift of the MgI intercombination line 3s3p ³ P ₁-3s ^{2 1} S ₀ (=457 nm) for the three stable isotopes ²⁴Mg, ²⁵Mg and ²⁶Mg. The measurement was performed by optical Ramsey spectroscopy (respectively saturation spectroscopy for ²⁵Mg) on a magnesium atomic beam. The rf precision of the measurement was achieved by using optical sideband techniques for the stabilization and tuning of a dye laser relative to an ultrastable cavity.     

Photolysis of NO2 at multiple wavelengths in the spectral region 200–205 nm

A study of the photodissociation dynamics of NO₂ in the 200–205 nm region using resonance enhanced multiphoton ionization (REMPI) in conjunction with the velocity map imaging technique is presented. We chose this region because it allowed the use of a single laser to photodissociate the NO₂ molecule and probe both the O(¹D₂) fragment using (2+1) REMPI via the 3p'¹P₁ state at 2 ×205.47 nm and the 3p'¹F₃ state at 2 ×203.5 nm, and the O(³P_J) fragments using (2+1) REMPI via the P_J states around 2 ×∼200 nm. Translational energy and angular distributions are extracted from the O(¹D) and O(³P) product images. A growth in the population of highly excited vibrational levels of the NO X(²Π) co-fragment is found as the dissociation wavelength decreases. These are compared with similar trends observed previously for other triatomic O-atom containing molecules. Detailed information on the electronic angular momentum alignment of the ¹D₂ state is obtained from analysis of the polarization sensitivity of the O(¹D) images using the two resonant intermediate states. The angular dependence of the potential energy in the exit channels is examined using long-range quadrupole-dipole and quadrupole-quadrupole interaction terms, from which molecular-frame multipole moments of the total angular momentum of the recoiling O atoms have been calculated. Comparison with the experimentally derived multipole moments is used to help provide insight into the dissociation mechanism.     

Large-scale collisional energy transfer in laser-pumped metastable Ca atoms: Excitation of resonance states of Ca II

We report the first experimental observation of the excitation of the 4p ² P _{3/2, 1/2} resonance states of Ca II (located at 74 720.4 and 74 497.5 cm^–1 above the ground state of Ca I) following pulsed-laser pumping of the 4s ^{2 1} S _O–4s4p ³P₁ intercombination transition of Ca I (E _ex = 15 210 cm^–1). Large scale collisional transfer of energy between the laser-excited atoms is believed to be responsible for this. This is possibly because sufficient time is available (_rad of the 4s4p ³ P ₁ state is approximately 350 µs) for collisions to build such a high level of excitation. Some interesting additional features of the fluorescence spectra of the laser-pumped Ca vapor, such as temperature dependence of the fluorescence intensities and evolution in time of some selected states, are also presented.     

High resolution measurement and MQDT analysis of the 5d<Superscript>9</Superscript> 6s<Superscript>2</Superscript> np,nf (J = 1) autoionizing resonances of mercury

We report new high resolution photoabsorption measurements of the 5d-subshell excitation spectra of mercury using a 3-meter normal incidence spectrograph equipped with a 6000 line/mm holographic grating and synchrotron radiation emitted by the Bonn 2.5 GeV electron accelerator as the background source of continuum. The observed spectra reveal autoionizing resonances attached to the 5d⁹(²D_5/2)6s² and 5d⁹(²D_3/2)6s² parent ion levels of mercury. We have analysed the line shapes of the lower members of the 5d⁹6s² np and nf J = 1 autoionizing resonances using the phase shifted formulation of the MQDT and extracted the interaction parameters.     

Breit-Pauli energy levels and radiative lifetimes in neutral chlorine

Breit-Pauli Energy levels, oscillator strengths and transition probabilities for all the transitions in Cl I between the fine structure levels of 3s² 3p⁵, 3s² 3p⁴3d, 3s² 3p⁴4s and 3s²3p⁴4p states are calculated using extensive configuration interaction (CI) wave functions. We have also determined the lifetimes of 3s² 3p⁴3d, 3s² 3p⁴4s and 3s² 3p⁴4p levels. The relativistic effects are included through Breit-Pauli approximation via spin-orbit, Darwin and mass correction terms. Prior to the calculations of the oscillator strengths and transition probabilities, we fine-tune the CI coefficient using experimental energies. Our results are compared with experimental and other available theoretical data. The calculated energy levels are in close agreement with most of the NIST compiled data. We predict new lifetime data for several levels where no other theoretical and/or experimental results are available, which will form the basis for the future experimental work. Electronic supplementary material Online Material     

Relativistic multireference configuration interaction calculations of lifetime of 2s22p 2P3/2 level along boron isoelectronic sequence

Lifetime of 2s²2p ²P_3/2 level along with fine structure separations for the lowest ²P doublet of boron-like ions, from Z=14 to Z=30 have been calculated using multireference relativistic configuration interaction (MR RCI) method based on the no-pair Dirac-Coulomb-Breit (DCB) Hamiltonian. Analytic basis sets of Gaussian-type functions are employed to expand the upper and lower components of the Dirac four-spinors in the matrix Dirac-Fock self-consistent field (DF SCF) and relativistic MR CI procedures. Error with respect to variation of basis set parameters was estimated. QED corrections were estimated by evaluation of electron self-energy and vacuum polarisation.     

Decay of metastable autoionization state in a highly charged lithium-type ion

Relativistic wave functions have been used to calculate the probabilities for (1s2s2p)⁴P_5/2-(1s²Kf)²F₅/₂ autoionization and (ls2s2p)⁴P₅/₂-(1s²2s)² S_1/2 magnetic quadrupole transition, together with the lifetimes of the (1s2s2p)⁴P_5/2 states, for lithium-type ions with Z from 10 to 60; the results are compared with measurements and with calculations from literature sources.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 13–18, December, 1977.I am indebted to A. D. Gurchumeliya and L. N. Ivanov for valuable discussions.     

Appearance of anisotropic non s-wave superconductivity above the critical pressure of antiferromagnetic CeRhIn5

We have carried out ¹¹⁵In nuclear quadrupole resonance (NQR) measurements in CeRhIn₅. At ambient pressure, CeRhIn₅ undergoes an antiferromagnetic AF phase transition at K. The ¹¹⁵In NQR spectrum has shown the appearance of a small internal field in the direction perpendicular to the tetragonal c-axis. With application of a hydrostatic pressure, the AF state is suppressed and the superconductivity appears just above the critical pressure (P = 17 kbar). The nuclear spin lattice relaxation rate 1/T₁ of ¹¹⁵In measured at P = 27 kbar indicates the occurrence of the superconductivity in the nearly AF region. In the superconducting state, 1/T₁ has no Hebel-Slichter coherence peak just below of 2 K and has a power law T-dependence (T³) down to 300 mK. This is consistent with anisotropic superconductivity, with line nodes in the superconducting energy gap: non-s-wave superconductivity occurs in CeRhIn₅. Received 5 July 2000     

g factor of the [(1s)2(2s)22p]2P3/2 state of middle-Z boronlike ions

Theoretical g-factor calculations for the first excited ²P_3/2 state of boronlike ions in the range Z=10–20 are presented and compared with the previously published values. The first-order interelectronic-interaction contribution is evaluated within the rigorous quantum electrodynamics (QED) approach in the effective screening potential. The second-order contribution is considered within the Breit approximation. The QED and nuclear recoil corrections are also taken into account.