Nf Transitions Research Articles

Extreme ultraviolet spectral characteristic analysis of highly charged ions in laser-produced Cu plasmas

This paper reports the results of spectral measurements and a theoretical analysis of the temporal and spatial evolution of laser-produced Cu plasma in vacuum in the range of 8–14 nm. The time dependence of the extreme ultraviolet band spectrum at different positions near the target surface was obtained and found to be dominated by three broad-band features. The 3p and 3d excitations of Cu5+–Cu9+ ions were calculated using the Hartree–Fock theory with configuration interactions. The characteristics of the spectral line distribution for the 3p–nd and 3d–nf transition arrays were analyzed. Based on the steady-state collisional radiation model and the normalized Boltzmann distribution, the complex spectral structure in the band of 13–14 nm is accurately explained through consistency comparisons and benchmarking between the experimental and theoretical simulation spectra, demonstrating that the structure mainly stems from the overlapping contribution of the 3d–4f and 3p–3d transition arrays for the Cu5+–Cu9+ ions. These results may help in studying the radiation characteristics of isoelectronic series highly-charged ions involving the 3d excitation process.

Precision adiabatic scanning calorimetry of a nematic – ferroelectric nematic phase transition

ABSTRACT In high-resolution adiabatic scanning calorimetry (ASC) experiments, data for the temperature dependence of the specific enthalpy, h(T), and of the specific heat capacity, cp (T), are simultaneously obtained, from which the order of the phase transition and critical behaviour can be evaluated. ASC was applied to study the nematic to ferroelectric nematic phase transition (N–NF) in the liquid crystal molecule 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). The N–NF was found to be very weakly first order with a latent heat Δh = 0.115 ± 0.005 J/g. The pretransitional specific heat capacity behaviour is substantially larger in the high-temperature N phase than in the low-temperature NF phase. In both phases the power-law analysis of cp (T) resulted in a critical exponent α = 0.50 ± 0.05 and amplitude ratio A NF/A N = 0.42 ± 0.03. The very small latent heat and the value of α indicate that the N–NF transition is close to a tricritical point. This is confirmed by a value of the order parameter exponent β ≈ 0.25, recently obtained from electric polarisation measurements. Invoking two-scale-factor universality, it follows from the low value of A NF/A N ratio that the size of the critical fluctuations is much larger in the NF phase than in the N phase.

Forbidden 2P–nP and 2P–nF transitions in the energy spectrum of ultracold Rydberg lithium-7 atoms

Forbidden 2P–nP and 2P–nF transitions in the ranges of the principal quantum number n = 42–114 and n = 38–48 have been detected in the optical spectra of ultracold highly excited lithium-7 atoms. The presence of forbidden transitions is due to induced external electric fields. The quantum defects and ionization energy obtained in various experiments and predicted theoretically have been discussed.

Multiferroic properties and enhanced magnetoelectric coupling in (1 − x)PbTiO3 − xNdFeO3

Multiferroic solid solution of (1 − x)PbTiO3 − xNdFeO3 (PT − NF) compounds are synthesized by a conventional solid state reaction. XRD investigations indicate the phase PT − NF transition from tetragonal to pseudo-cubic and then orthorhombic phase by increasing the dopant NdFeO3. The multiferroic and magnetoelectric (ME) behaviors in (1 − x)PbTiO3 − xNdFeO3 solid solutions are observed in the tetragonal phase (0 ≦ x ≦ 0.3). Further addition of the dopant NdFeO3 results into severe leakage currents and phase transitions. The solid solution compounds achieve strong ferromagnetism with high remnant magnetization (Mr = 0.786 emu/g) at x = 0.8. This work demonstrates a way to tailor the ferroelectric, magnetic properties and ME coupling in multiferroic PT-based compounds.

Transition energy and dipole oscillator strength of 1s23d-1s2 nf transitions for Sc18+ ion

The transition energies of the 1s23d-1s2nf (4⩽n⩽9) transitions and fine structure splittings of 1s2nf (n⩽9) states for Sc18+ ion are calculated with the full-core plus correlation method. The quantum defect of 1s2nf series is determined by the single-channel quantum defect theory. The energies of any highly excited states with n⩾10 for this series can be reliably predicted using the quantum defect as function of energy. Three alternative forms of the dipole oscillator strengths for the 1s23d-1s2nf (n⩽9) transitions of Sc18+ ion are calculated with the transition energies and wave functions obtained above. Combining the quantum defect theory with the discrete oscillator strengths, the discrete oscillator strengths for 1s23d-1s2nf (n > 9) transitions and the oscillator strengths densities corresponding to the bound-free transitions are obtained.

The evolution of 4d photoabsorption in Sb with increasing ionization

The photoabsorption spectra of Sb+, Sb2+, Sb3+ and Sb4+ have been obtained in the XUV spectral region with the dual laser-produced plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 30-100 eV energy region. In Sb+, for photon energies between 30 and 50 eV, discrete structure corresponding to 4d np, n1f (n5,n14) transitions is obtained, while above 50 eV the spectrum is dominated by an intense 4df resonance. Apart from the 4d5p transitions the features are very weak. The 4df resonance is still observed in Sb2+ as the dominant feature in the spectrum, but in Sb3+ and Sb4+ there is significant transfer of oscillator strength from the continuum to the discrete spectra, in particular to the 4d nf transitions. This behaviour mirrors the effects of contraction of the 4f wavefunction, which is seen to be more gradual here than in elements with Z>54. Multiconfiguration Hartree-Fock and time-dependent local density approximation calculations successfully reproduce this behaviour.

Trends in 4d-subshell photoabsorption along the iodine isonuclear sequence: I, I+, and I2+

The 4d absorption spectra of I, ${\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ have been observed in the 45--300-eV region using the dual laser-produced plasma technique. At lower energies each spectrum is dominated by intense 4d\ensuremath{\rightarrow}5p transitions, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared, where possible, with experiment. In the case of neutral iodine 4d\ensuremath{\rightarrow}6p transitions are also observed in the region close to the $^{2}$${\mathit{D}}_{5/2}$ threshold. The dominant feature in each spectrum, however, arises from 4d-f excitation, which evolves from a 4d-\ensuremath{\varepsilon}f shape resonance in neutral iodine to a feature containing discrete 4d\ensuremath{\rightarrow}nf transitions in ${\mathrm{I}}^{2+}$. \textcopyright{} 1996 The American Physical Society.

Analysis of X-ray spectra from laser-irradiated high- Z targets

The X-ray spectra of highly ionized hafnium, tantalum, tungsten and rhenium have been observed in laser-produced plasmas. Isolated peaks were found in the 3.6 to 5 Å region. A detailed analysis of these peaks has been performed by using the spin-orbit-split array model of Bauche-Arnoult et al. Besides the resonance lines in the Ni-like ions, the 3d- nf transition bands in Cu-like through Ge-like ions were identified.

3d absorption spectra of Sr I through Sr IV.

The extreme ultraviolet photoabsorption spectra of neutral to three-times-ionized strontium have been recorded in a comprehensive series of experiments with the dual laser-produced plasma technique. Striking differences were found in the spectra, which can be attributed to the transfer of oscillator strength from 3d\ensuremath{\rightarrow}np to 3d\ensuremath{\rightarrow}nf transitions at ${\mathrm{Sr}}^{2+}$ due to nf wave-function contraction. In Sr and ${\mathrm{Sr}}^{+}$, 3d\ensuremath{\rightarrow}5p transitions dominate; in ${\mathrm{Sr}}^{2+}$, 3d\ensuremath{\rightarrow}nf transitions are most intense, while in ${\mathrm{Sr}}^{3+}$ the 4p subshell opens and 3d\ensuremath{\rightarrow}4p transitions are the strongest features. Partial cross sections for 3d\ensuremath{\rightarrow}\ensuremath{\varepsilon}f and 3d\ensuremath{\rightarrow}\ensuremath{\varepsilon}p photoionization were calculated and compared with experiment.

Simple Parametrization Scheme for Electric Dipole Intensities

A simple phenomenological model for the electric dipole intensities of nf →nf transitions is proposed. The model is derived by adopting of the common angular overlap mode1 to the generalized Judd-Ofelt theory of the static coupling mechanism. It leads to reduction of a number of the effective intensity parameters to six, three of which correspond to the f → d excitations and the remaining to the f →g ones. Calculations performed for some lanthanide complexes show that the model, despite its inborn crudeness, provides satisfactory results and may be a convenient tool for a preliminary estimation of intensities. Regularity of the obtained parameters indicates a possibility of further reduction of their number. PACS numbers: 78.20.Bh, 78.20.Dj

Stark-broadening measurements of 3d-->nf transitions in lithiumlike and heliumlike ions.

We report here on high-resolution spectral measurements of Stark-broadened 3d-5f lines from lithiumlike ions and 3d-4f lines from heliumlike ions. The spectra were emitted from high-density laser-produced plasmas. Plasmas were produced by irradiating thin- and thick-foil targets made of magnesium, aluminum, phosphorus, and chlorine with the OMEGA laser in a line-focus geometry. Line profiles were compared to a Stark-broadening calculation that uses the static-ion approximation and an impact approximation for the electrons. The dependence of Stark broadening on atomic number is discussed. For the aluminum plasmas \ensuremath{\sim}10% narrowing was observed in the width of the 3d-5f line as the length of the plasma was increased from 3 to 6 mm.

High resolution absorption spectrum of CO2between 10 and 14 eV

The gas-phase absorption spectra of 12CO2 and 13CO2 between 880 and 2000 A, at a resolution limit of 0·008 A, were recently photographed dy Cossart-Magos et al. Rotational structure observed at 1106 A was then assigned to absorption to the … 1π3 g 3pπ u 3Σ- u Rydberg state. The whole region between 898 and 1145 A is now analysed. Ab initio calculations are carried out to estimate the energy of the lower Rydberg states of the s, p, d and f series converging to [Xtilde] 2Π g CO+ 2. nf transition bands are characterized by sharp features in their rotational contours and assigned from n = 4 to n = 28 and 32, respectively for the limits Ωc = 3/2 and 1/2 in the [Xtilde] 2Π g state of the ion core. A new value of the first ionization potential of CO2 results: 111 201 ± 2 cm-1 (average of the two limits). np transition bands, with the exception of the 1106 A band referred to above, are diffuse, and were assigned by a method based on comparison of experimental and calculated quantum defects plotted against the red...

Radiative lifetimes of metastable states of free radicals. II. PF b 1Σ + and CO a 3Π

Metastable CO a 3Π and PF b 1Σ + radicals were generated by a pulsed Tesla discharge technique in dilute mixtures of CO 2 and of PF 3 in Ar. For CO a 3Π, ν′ = 0 the averaged radiative lifetime τ rad for the a-X transition. was determined to be (7.9 ± 1.5) ms, and the quenching rate coefficients ( k M cm 3 s −1) obtained were k CO 2 < 3 × 10 −11 and k Ar = (2.3 ± 0.5) × 10 −16, in good agreement with previous determinations by other techniques. For PF b 1Σ +, ν′ = 0 the measurements yielded τ rad = (6.2 ± 0.7) ms, k PF 3 < 5 × 10 −13 and k Ar < 1 × 10 −17. From this value for τ rad a magnitude of (2.2 ± 0.2) × 10 −4 D 2 is calculated for the square of the transition moment, | R e| 2, for PF b 1Σ +-X 3Σ. The transition moment is an order of magnitude larger than that for the corresponding NF transition; reasons for this difference are discussed. The analogous transitions of O 2 and NCl also are considered.

The ionization limits of NI

The ionization limits of N I have been calculated using the 3d- nf transitions, and found to be 117356.58 cm −1, 117274.25 cm −1 and 117225.35 cm −1 for the 3P 2, 3P 1 and 3P 0 ground levels of N II respectively.