On the Stark broadening of the He I 447.1 nm spectral line

Characteristics of the Stark broadened and overlapping 447.1 nm He I spectral line and its forbidden 447.0 nm components have been measured at electron densities between 4.4×10²² m^-3 and 8.2×10²² m^-3 and electron temperatures between 18 000 K and 33 000 K in plasmas created in five various discharge conditions using the low pressure pulsed arc as an optically thin plasma source operated in helium-nitrogen-oxygen gas mixture. Good agreement was found among our measured line characteristics and their existing calculated values, based on the quasistatic approximation. Possible influence of the singly ionized oxygen impurity atoms (O II) on the intensity values of the dip between allowed and forbidden components was found that can explain the disagreement among some existing experimental and calculated line characteristics data, at higher electron temperatures and densities. On the basis of the observed asymmetry of the 447.1 nm spectral line profile we have obtained the ion contribution parameter at 10²² m^-3 electron density and 8 000 K electron temperature. Received 20 February 2001 and Received in final form 25 April 2001     

Stark broadening of the hydrogen Paschen <Emphasis Type="Bold">γ</Emphasis> transition at electron densities of the order of cm

Stark broadening measurements and calculations of the Paschen γ spectral line of hydrogen ( λ = 1.094[: MU :] m) are reported. Investigations have been performed at plasma electron densities between 1.4×10 ¹⁵ cm ^-3 and 3.7×10 ¹⁵ cm ^-3 . As the light source a wall-stabilized arc operated in a helium-hydrogen gas mixture at atmospheric pressure has been applied. The radiation of the plasma emitted from nearly homogeneous plasma layers in end-on direction, was measured with the use of a grating spectrometer equipped with a charge coupled device (CCD) detector. The radiance calibration was carried out against light outputs originating from a tungsten strip radiation standard. The measured FWHM are compared with results of our calculations based on computer simulation techniques (full computer simulation method -- FCSM). Our broadening data are also compared with results of other theoretical approaches (MM-method, quasi-static approximation) and with experimental data obtained at electron densities about one order of magnitude larger than ours. Received 21 January 2003 Published online 24 April 2003 RID="a" ID="a"e-mail: wujec@uni.opole.pl     

Experimental transition probabilities in N III,N IV and N V spectra

We have obtained transition probabilities (Einstein's A values) of thirteen transitions in doubly (N III), six in triply (N IV) and two in four times (N V) ionized nitrogen spectra belonging to the 3s-3p and 3p-3d transitions using a relative line intensity ratio (RLIR) technique. The linear low-pressure pulsed arc was used as an optically thin plasma source operated at 51 400 K electron temperature and 2.2×10²³ m^-3 electron density in nitrogen plasma. Our A values are compared to recent theoretical and experimental data. Received 18 December 2001 / Received in final form 29 January 2002 Published online 28 June 2002     

Asymmetry of Stark profiles

The theoretical basis is presented that allows to compute the Stark broadened line shapes of atomic ions up to the quadrupole terms in the interaction potential between the radiator and the plasma electric microfields and their gradients. The nature of the corrections due to the plasma polarization effects associated with the electron distribution around ion perturbers are carefully analyzed. The relevant universal plasma functions are evaluated in a cluster expansion or by Monte Carlo simulations, and the line shape is calculated with ion dynamic effects by the Model Microfield Method. The asymmetry of the Lyman line of hydrogenic ions is then studied. Received 21 January 2000 and Received in final form 27 April 2000     

Collisional broadening and shifting of ammonia absorption lines at 790 nm

By using a diode laser spectrometer based on a commercial heterostructure diode laser operating in free-running mode, line shape parameters of some ammonia ro-vibrational overtones at 790 nm have been measured at room temperature. These weak absorption lines have been detected by using the wavelength modulation spectroscopy technique with second-harmonic detection. The broadening and shifting coefficients have been obtained for ten absorption lines by fitting the collected second-harmonic absorption features and varying the pressure of different buffer gases. Received 13 February 2002 / Received in final form 18 September 2002 Published online 17 December 2002 RID="a" ID="a"e-mail: alex@ifam.pi.cnr.it     

Spontaneous relativistic two-photon decay rate mathematical expression in helium-like systems

Using a laser-induced fluorescence method a detailed analysis of profiles of the ¹¹⁴Cd 326.1 nm line perturbed by argon was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for different interaction potentials. Received 19 July 2000     

Laser-induced fluorescence study of the influence of N <Emphasis Type="Bold">2</Emphasis> and CH <Emphasis Type="Bold">4</Emphasis> on the <Emphasis Type="Bold">114</Emphasis>Cd intercombination line

Using a laser-induced fluorescence method a detailed analysis of profiles of the ¹¹⁴Cd 326.1 nm line perturbed by N₂ and CH₄ was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated for van der Waals interaction potential. Received 29 November 2001 / Received in final form 12 July 2002 Published online 4 February 2003     

Determination of the deuterium temperature profile in magnetic fusion plasmas

Summary A new experimental method for determining the radial deuterium temperature profileT _D(R) in axisymmetrical toroidal fusion plasmas is presented. The method is based on a generalized Abel inversion of neutron brightness data providing the radial neutron emissivity profile of the plasma. This profile, combined with information on the deuterium density profile, is used to determineT _D(R) under the assumption that the ion velocity distribution is Maxwellian. Results are presented here from the analysis of JET data. It is found that, for typical JET plasma conditions, the dominant source of uncertainty arises from the high plasma impurity level and the fact that it is poorly known; these problems can be expected to be remedied and neutron brightness measurements would be expected to be very effective (especially in high-density plasmas) as aT _D(R) diagnostics.     

Coupling and ionization effects on hydrogen spectral line shapes in dense plasmas

A study of hydrogen lines emitted in dense and low temperature plasmas is presented. Coupling and ionization effects in a transition from impact to quasi-static broadening for electrons are analyzed with the help of the Frequency Fluctuation Model (FFM). Electron broadening of Balmer series lines is studied for different densities and temperatures spanning a wide domain from impact to quasi-static limit. It is shown that electronic broadening makes a transition from impact to quasi-static limit depending on plasma conditions and principal quantum number. Even for the Balmer alpha line, at a density equals 10¹⁸ cm^-3 and a temperature equals 1 eV, this transition occurs both in the wings and the core of the line.     

The light σ-meson

In the framework of the dispersion relation N/D-approach, we restore the low-energy (IJ ^PC = 00^{+ +})-wave amplitude sewing it with the previously obtained K-matrix solution for the region 450-1900 MeV. The restored N/D-amplitude has a pole on the second sheet of the complex-s plane near the threshold, that is the light -meson. Received: 21 February 2000 / Accepted: 20 June 2000     

Measurements of electron density and Stark width of neutral helium lines in a helium arc plasma

Electron densities in an atmospheric helium arc plasma have been measured with the Stark broadening parameters of helium spectral lines. The spatially distributed radiation intensities are converted to plasma emission coefficients at every wavelength by means of Abel inversion. From the inverted profiles of He I lines of 4713 ?, 5016 ?, and 6678 ? electron density has been calculated, which ranges from 0.5 ×10¹⁶ to 4 ×10¹⁶ cm^-3 for a helium arc with current 200 A. Stark widths of He I lines of 3889 ? and 7065 ? are determined based on the measurements and compared with existing data.     

Two-color pump-probe experiments in helium using high-order harmonics

A pump-probe technique has been applied for measuring the lifetimes and absolute photoionization cross-sections of excited He states. The 1s2p ¹P and 1s3p ¹P states of He are excited by using the 13th and the 14th harmonic, respectively, of a tunable 70 ps dye laser generated in a Kr gas jet. The states are ionized after a varying time delay, by absorption of probe photons with energies between 1.6 and 4.5 eV. Lifetimes of τ(1s2p) = 0.57 ns and τ(1s3p) = 1.76 ns are determined with a precision of about 15%. A significant enhancement of the number of ions present in the lifetime curves at zero time delay for pressures above 6×10^-5 mbar is attributed to direct two-photon ionization of He in combination with AC Stark broadening of the excited state and absorption of the XUV light in the medium. Absolute photoionization cross-sections from the He 1s2p ¹P and He 1s3p ¹P states in the threshold region are determined by measuring the saturation of the ionization process with a precision of ∼ 25%. In addition, the variation of the relative orientation between the polarization vectors of the pump and probe beams enables the determination of partial photoionization cross-sections. Received 3 June 2002 / Received in final form 14 August 2002 Published online 22 October 2002 RID="a" ID="a"Present address: Department of Biophysics, Leiden University, 2333 CA Leiden, The Netherlands. RID="b" ID="b"Present address: Continuum Electro-Optics Inc., 3150 Central Expressway, Santa Clara, CA 95051, USA. RID="c" ID="c"Present address: CEA/DRECAM/SPAM, CEN Saclay, 91105 Gif-sur-Yvette, France. RID="d" ID="d"Present address: Department of Physics, National University of Rwanda, Butare, Rwanda. RID="e" ID="e"Present address: CELIA, Université Bordeaux 1, 33405 Talence, France. RID="f" ID="f"Present address: MAX-Lab, Lund University, Box 118, 221 00 Lund, Sweden. RID="g" ID="g"e-mail: anne.lhuillier@fysik.lth.se     

Stark broadening in the Sb III spectrum

The shapes of nine doubly ionized antimony (Sb III) spectral lines have been obtained in the laboratory helium plasma at 17 500 K electron temperature and electron density of . Measured line profiles are of a Voigt type. At the mentioned plasma conditions the Stark broadening has been found as the dominant mechanism in the Sb III line shapes formation. Using a deconvolution procedure the Lorentz (Stark) FWHM (Full-Width at Half of the Maximal intensity, W) have been obtained. Our measured Sb III Stark widths are the first data in the literature. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in helium with antimony atoms, as impurities. They were evaporated from the thin antimony layer, deposited on the silver cylindrical plates, located in the homogenous part of the discharge. This plasma source ensures good conditions for the generation of the doubly ionized antimony atoms in the helium plasma due to atomic processes concerning helium metastables.     

High resolution polarization spectroscopy and laser induced fluorescence of CO<Subscript>2</Subscript> around 2μm

High resolution Infrared Polarisation Spectroscopy (IRPS) and Infrared Laser Induced Fluorescence (IRLIF) techniques were used to probe CO₂/N₂ binary gas mixture at atmospheric pressure and ambient temperature. The probed CO₂ molecules were prepared by laser excitation to an overtone and combination ro-vibrational state (12⁰1, J=15) of CO₂, centred at 4988.6612 cm^-1. IRPS and IRLIF line profiles were recorded for several CO₂/N₂ binary mixtures. The observed IRLIF line shapes have the expected Lorentzian form while the observed IRPS line shapes are narrower by a factor of two than those recorded with the IRLIF and appear to have a Lorentzian-cubed profile. The recorded line profiles provide measurements of the pressure-broadening coefficient directly at atmospheric pressure. The Full-Width-Half-Maxima (FWHM) pressure broadening coefficients are measured, based on IRLIF, to be 0.2174±0.0092 cm^-1atm^-1 and 0.1327 ±0.0077 cm^-1atm^-1 for self- and N₂ collision broadening, respectively. The broadening coefficients obtained based on IRPS were measured to be ~8% larger than those obtained with IRLIF.     

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.     

Gamow-Teller transitions from 58Ni to discrete states of 58Cu

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T _z = ±1 nuclei to the common excited states of the T _z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T _z = 1 with those from the β-decay of the T _z = - 1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from ⁵⁸Ni (T _z = 1) to ⁵⁸Cu (T _z = 0) by using the zero-degree (³ He, t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., near to the Q window limitation ( Q _EC = 9.37 MeV) of the β-decay from ⁵⁸Zn (T _z = - 1) to ⁵⁸Cu. The strength distribution is compared with that from shell-model calculations. Received: 24 November 2001 / Accepted: 30 January 2002     

Stark broadening of isolated lines: calculation of the diagonal multiplet factor for complex configurations (n1l1 n n2l2 m n3l3 p)

Owing to the increasing sensitivity of detectors, accurate line profiles are needed for accurate stellar atmospheres modelling and for laboratory and technological plasmas as well. So, Stark broadening parameters of isolated lines of complex atoms and ions within the impact and quasistatic approximation are needed, even if the atomic abundance of the considered element is low. Angular factors of the diagonal line strength entering the quadrupole term appearing in the semi-classical expression of the width of line broadened by electron or ion perturbers, are needed. The aim of this paper is to extend the previous calculations of this diagonal multiplet factor which were obtained for configurations of the type lⁿ and l₁ ⁿl₂ ^m to more complex configurations in LS coupling. To study the Stark broadening of isolated lines in the impact and quasistatic approximation, we use the semi-classical-perturbation treatment, including both dipole and quadrupole contribution in the expansion of the electrostatic interaction between the optical electron and the perturber. We also use the Fano-Racah algebra. Angular factors of the diagonal line strength entering the quadrupole term appearing in the semi-classical expression of the width of line broadened by electron or ion perturbers, are calculated. New diagonal multiplet factor formulae for more complicated configurations such as (n₁l₁ ⁿ(L_nS_n)n₂l₂ ^m(L_mS_m)n₃l₃ ^p(L_pS_p)) are provided. These formulae can enter the computer Stark semi-classical perturbation codes.     

Phase separation of polymer blends in solution near adsorbing surface

In this paper, we consider a mixture of two polymers A and B of different chemical nature, dissolved in a common good solvent, in contact with an interacting surface. We start from a mixture of two incompatible homopolymers A and B in the molten state, and assume that the surface adsorbs strongly one or both polymer species at high temperature. It is assumed that this is a strong adsorption, so that chains cannot desorb once they are linked to the surface. This constrains the system to a quenched composition on the surface. Once the adsorption process is finished, a quantity of a good solvent is added to get a semi-dilute solution. We assume that demixing transition in the presence of solvent occurs at lower temperature. The purpose is to discuss the influence of the quenched surface fluctuations on the critical properties of the mixture. Within the framework of the so-called blob model, we determine the exact shape of the composition profile as a function of the distance z to the surface, for any value of the relevant parameters, namely, the temperature T, the molecular weight M, the monomer concentration c and the surface composition x₀. Our analysis reveals a universal character of the composition profile for , where the characteristic size D is some known length depending on the relevant parameters of the problem, and not on temperature, and is the thermal correlation length. Near surface, for (a is the monomer size), the profile is no longer universal, and in particular, it is sensitive to the boundary condition. Far from the surface, that is , the profile tends exponentially to its bulk value. We show that the length Dapproaches its lowest value as the surface composition reaches its saturated value l. In this limit, we find that the profile shape is a characteristic of critical adsorption in simple binary fluid mixtures. Finally, this work must be regarded as a natural extension of a previous one, which was concerned with the same problem, but in the absence of solvent. Received 24 June 1999 and Received in final form 5 November 1999     

Electron capture in the ion-cluster collision: effect of the electronic interaction

We investigate the electron capture occurring in the collision between an ion A⁺ and a cluster A_n (n = 5). The process has been modelled within the Hubbard Hamiltonian,which takes into account the intrasite U electron correlation. An exact procedure has been numerically applied which involves all the excited states to examine the time evolution of the system during the collision. We have applied the model to the sodium case. We have investigated the time evolution of the electron population during the collision on the projectile versus the kinetic energy of the projectile. It displays some oscillations which means that the electron exchanges between the ion and the cluster occurs alternatively in one direction and the other. We also vary U and examine its influence on the dynamics of the oscillation of the average population. Finally the cross section is derived versus the energy and U. Received 29 November 2000     

Separable-entangled frontier in a bipartite harmonic system

We consider a statistical mixture based on that of two identical harmonic oscillators which is characterized by four parameters, namely, the concentrations (x and y) of diagonal and nondiagonal bipartite states, and their associated thermal-like noises (T/α and T, respectively). The fully random mixture of two spins 1/2 as well as the Einstein-Podolsky-Rosen (EPR) state are recovered as particular instances. By using the conditional nonextensive entropy as introduced by Abe and Rajagopal, we calculate a bound for the separable-entangled frontier. Although this procedure is known to provide a necessary but in general not sufficient condition for separability, it does recover, in the particular case x = T = 0 ( ∀α), the 1/3 exact result known as Peres' criterion. The x = 0 frontier remarkably resembles to the critical line associated with standard diluted ferromagnetism where the entangled region corresponds to the ordered one and the separable region to the paramagnetic one. The entangled region generically shrinks for increasing T or increasing α. Received 18 April 2002 / Received in final form 11 July 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: celia@cbpf.br