Stark Parameters Research Articles

Experimental and Theoretical Electron Collision Broadening Parameters for Several Ti II Spectral Lines of Industrial and Astrophysical Interest

A Q-switched Nd:YAG laser was focused on the Pb–Ti alloy samples in several laser-induced breakdown experiments in order to measure the Stark parameters of several spectral lines (58) of singly ionized titanium, including the 3504.89 Å and 3510.83 Å lines (where we achieved new experimental and theoretical values). The diagnostics of the laser-induced plasmas (electron density and electron temperature) were performed using Balmer’s H alpha line (6562.7 Å). The temperatures were obtained by the Boltzmann plot technique with spectral lines of Pb I (after correction for its evident self-absorption). Subsequently, the calculations by the Griem approach of the Stark broadening parameters for several spectral lines were performed using the Gaunt factors proposed by van Regemorter and those proposed by Douglas H. Sampson. In the latter case, the values obtained were very close to the experimental values. This enables us to assume that the calculations performed for the spectral lines of Ti II, without experimental information, are more accurate using the Gaunt factors proposed by Sampson.

Asymmetric profiles of Ca I lines belonging to the transitions n1F°3 → 31D2 observed in long laser spark

This study aimed to determine the Stark broadening parameters of asymmetric profiles for Ca I lines within the singlet transitions [4,5f] 1F°3 → [3d4s] 1D2. To improve the signal-to-noise ratio of the measurements, a long laser plasma, also known as “long spark”, was utilized as a plasma source. Compared to common spherical plasma, long plasma is more homogeneous and illuminates a larger area in the focal plane of the spectrograph, resulting in a 5–7 fold increase in the vertical dimension of the plasma image on the detector. Therefore, the use of long laser plasma is more appropriate for determining the Stark parameters. The electronic density was determined using Mg I lines with known electron-impact shift and width, while the plasma temperature was determined using Fe I lines within the 368–375 nm range. The temperature and electron density were varied within the range of 3500–10,000 K and (1–16) × 1016 cm−3. The profile distortion caused by Doppler, resonance, and van der Waals broadening mechanisms were considered and found to have no significant influence on the studied lines. The determined electron-impact parameters are precise within 25%, and the ion parameter's contribution for the 435 nm line is substantially higher than that for the 487 nm line.

Ethical Challenges and Implications of Deactivating Mechanical Circulatory Support for Patients With Preserved Cognitive Function.

Ethical Challenges and Implications of Deactivating Mechanical Circulatory Support for Patients With Preserved Cognitive Function.

Study by Optical Spectroscopy of Bismuth Emission in a Nanosecond-Pulsed Discharge Created in Liquid Nitrogen.

Time-resolved optical emission spectroscopy of nanosecond-pulsed discharges ignited in liquid nitrogen between two bismuth electrodes is used to determine the main discharge parameters (electron temperature, electron density and optical thickness). Nineteen lines belonging to the Bi I system and seven to the Bi II system could be recorded by directly plunging the optical fibre into the liquid in close vicinity to the discharge. The lack of data for the Stark parameters to evaluate the broadening of the Bi I lines was solved by taking advantage of the time-resolved information supported by each line to determine them. The electron density was found to decrease exponentially from 6.5 ± 1.5 × 1016 cm−3 200 ns after ignition to 1.0 ± 0.5 × 1016 cm−3 after 1050 ns. The electron temperature was found to be 0.35 eV, close to the value given by Saha’s equation.

Determination of Stark Shifts and Widths Using Time Resolved Laser-Induced Breakdown Spectroscopy (LIBS) Measurements.

Stark broadening parameters have been estimated for resonant lines of Al(I) using time resolved measurements. The relation between the various emission line characteristics at different phases of opacity have been utilized to obtain the value of plasma temperature and Stark width parameters from the experimental data. The observed value of the center line intensity and Lorentzian component of the line width are compared against a simulated value of these parameters for optically thin case. The plasma temperature and Stark broadening parameters are obtained for the best fit condition by matching the experimentally observed and the simulated values of intensity and line widths. The time resolved measurements result in much better estimates for Stark parameters by allowing multiple points for fitting keeping the number of variables limited. The Stark shift parameters are also obtained from the slope of the plot of observed central wavelength shifts versus observed electron number density which is measured as a function of time. Hence, a method utilizing multiple-time observation data to obtain the Stark broadening parameters for lines showing self-absorption has been demonstrated.

Theoretical transition probabilities, radiative lifetimes and Stark broadening parameters of singly ionized magnesium

ABSTRACTThe presence of spectral lines of singly ionized magnesium (Mg ii) in stellar atmospheres has been reported in different stars. Recently, the low-resolution spectrum obtained from Supernova 2014 J in M82, in which Mg ii absorption lines centred on 4400 Å as well as 7600 Å stand out, has been analysed. This is the motive for the atomic data calculations in this work, which are of much interest in the astrophysical area. In this article, ab initio relativistic Hartree–Fock calculations in an intermediate coupling formalism using Cowan’s code allowed us to obtain the required transition probabilities to calculate the theoretical radiative lifetimes for excited nS−, nP−, nD− and nF− states of singly ionized magnesium. An asymptotic dependence of lifetime (τnl) on the effective principal quantum number (n*) has been determined. Also, the Griem semi-empirical approach was used to obtain the theoretical Stark parameters (width and shift) of spectral lines; these data are displayed for an electron density of 1017 cm−3 and temperatures T = 10–100 (×103 K). We have compared the results of lifetimes for 16 levels and Stark parameters for seven spectral lines with previously reported experiments available in the literature. Finally, we discuss the behaviour of the Stark parameters versus temperature for three relevant spectral lines (2802.70, 2797.99 and 7868.04 Å).

Stark Broadening of Neutral Boron Lines

Stark broadening parameters, width and shift, of lines within B I 2s22p–2s2ns spectral series have been calculated. Semi-classical theory in impact approximation has been applied. Temperature dependence of Stark parameters has been studied. The presented results could be applied for plasma diagnostics.

The effect of hyperfine splitting on Stark broadening for three blue-green Cu i lines in laser-induced plasma

ABSTRACT Stark effect is observed in many natural and artificial plasmas and is of great importance for diagnostic purposes. Since this effect alters profiles of spectral lines, it should be taken into account when assessing chemical composition of radiation sources, including stars. Copper is one of the elements which studies of stellar atmospheres deal with. To this end, UV and visible Cu lines are used. However, there is a lack of agreement between existing data on their Stark parameters. It is therefore of interest to obtain new experimental data on these lines and to compare them to previous results. In this work, we have estimated Stark widths and shifts for three blue-green lines at 5105.54, 5153.24, and 5218.20 Å (corresponding transitions are [3d104p] 2P° → [3d94s2] 2D and [3d104d] 2D → [3d104p] 2P°) observed in a ‘long-spark’ laser-induced plasma. For the first time, we have accurately estimated an impact of hyperfine splitting on the profile shapes of the studied lines taking also into account the isotope shifts. We have shown that both effects considerably influence shift and width of Cu i line at 5105.54 Å, and shifts of Cu i lines at 5153.24 and 5218.20 Å.

Molecular emissions in sonoluminescence spectra of water sonicated under Ar-based gas mixtures.

Sonoluminescence (SL) spectroscopy is one of the very few ways to study the plasma formed in solutions submitted to ultrasound. Unfortunately, up to now only very limited emission bands were reported in SL spectra of aqueous solutions, moreover broad and badly resolved. It is shown here that by adding some N2 and/or CO2 in Ar, new molecular emissions (CN, N2 and CO) can be observed and that for some of them rovibronic temperatures can be derived. The paramount importance of Stark broadening in these emissions is underlined, together with the need for data on Stark parameters for molecular emissions.

Stationary model of laser-induced plasma: Critical evaluation and applications

We present an algorithm for both laser-induced plasma emission spectra simulation and rapid peak-identification suitable for selection of analytical lines (free of spectral interferences, minimally self-absorbed, most intense lines). Calculations of plasma composition and radiation transport are based on the model of a uniform plasma under local thermodynamic equilibrium (LTE) requiring 3 + (K − 1) parameters – temperature T, electron density ne, plasma mass m and array of K mass fractions of chemical elements {c}. A simple cost function based on Pearson's r with a sole maximum in T–ne space is proposed to achieve the best convergence between the experimental and model spectra. We have found the best fitted T, ne, m for spatially integrated experimental spectra of standard samples of high- and low-alloy steels at delays of 1–10 μs (gate 0.4 μs) after a laser pulse within three spectral ranges (255.1–276.4, 392.6–412.2, 529.3–547.0 nm) by a brute force technique. The instrumental function of the Czerny–Turner spectrometer equipped with an intensified charge coupled device (ICCD) detector has been accurately accounted for which has been notably improved the model and experimental spectra similarity. Several optimizations including a fast Fourier transform (FFT) convolution and a polynomial approximation of Voigt profile allowed acceleration of computing to several milliseconds per spectrum.We observed a discrepancy between the best-fitted values of T obtained in the ultraviolet (UV) and visible ranges, while the ne values were close to each other in these ranges. The UV range is dominated by the ionic Fe II lines but most of the lines in the visible range are atomic Fe I lines. Thus, a possible explanation of the T difference is an inhomogeneity of the plasma (different temperatures for the “hot” plasma core and the “cold” periphery). As a spectacular example for line identification, we demonstrate that 275 emission lines are ascribed to 106 peaks within the UV range out of a total of ~12,000 lines found in spectral databases. Selection of analytical lines to determine chromium in cast iron and carbon in steels is discussed. Applicability of the algorithm to reveal analytical lines for silver, lanthanum and yttrium determination in soils and ores is mentioned. The developed algorithms are useful for choice of the best analytical line under certain plasma and spectrometer parameters in terms of: (i) spectral interferences, (ii) transmittance and (iii) intensity, for estimation of detection limits of trace elements in a known sample matrix, for detection of erroneous entries in databases, including transition probabilities and Stark parameters.

Theoretical Study of Transition Probabilities and Stark Broadening Parameters and of Several Spectral Lines with Astrophysical Interest of Double-ionized Thallium

Abstract Leckrone et al. reported the presence of double-ionized thallium (Tl iii) in the stellar atmosphere of the chemically peculiar star, χ Lupi, in 1999. Two spectral lines at 1332.3 and 1558.6 Å were detected in its stellar spectrum. Here, we claim that there are ions and lines that need further study to make possible the LTE abundance analysis once improved atomic data is available. In this sense, Tl iii is included in the ions list that requires improved atomic data. To contribute to the solution of this problem, an analysis of the atomic parameters of the double-ionized thallium is presented here. In this work, calculations of transition probabilities were made to obtain values of the theoretical radiative lifetimes and theoretical Stark parameters for widths and shifts of 22 spectral lines of Tl iii. Relativistic Hartree–Fock calculations using Cowan’s code allowed us to obtain the required transition probabilities. In our calculations, the core polarization effects were included. Later, the Griem semiempirical approach was used to obtain the Stark parameters. Our lifetimes values for 10 levels were compared with the experimental ones. In this paper, we discuss the behavior of the Stark parameters versus the temperature of three relevant spectral lines. Stark width values of the isoelectronic sequence Tl iii–Pb iv are also displayed.

Stark resonance parameters for the 3a1 orbital of the water molecule

The Stark resonance parameters for the 3a1 molecular orbital of H2O are computed by solving a system of partial differential equations in spherical polar coordinates. The starting point of the calculation is the non-spherical quantum potential derived for this orbital from a single-center expanded Hartree–Fock orbital. The resonance positions and widths are obtained after applying an exterior complex scaling technique to describe the ionization regime for external fields applied along the two distinct directions associated with the symmetry axis. Comparison is made with previous results for the 1b1 and 1b2 orbitals obtained from a spherical potential approximation.

Stark broadening of several Bi iv spectral lines of astrophysical interest

The presence of spectral lines of bismuth in stellar atmospheres has been reported in different stars. The anomalous values of the spectral intensities of Bi II and Bi III, compared to the theoretical Local Termodinamic Equilibrium (LTE) standards of Bi I/Bi II/Bi III, have been reported in the spectra obtained with the High Resolution Spectrograph of the Hubble/Goddard Space Telescope in the chemically peculiar stars HgMn stars χ Lupi and HR 7775. Spectral lines of 1436.8, 1902.3, 2630.9 and 2936.7 A of Bi II and 1423.4 A of Bi III were reported and their relative intensities were measured in these studies Litzen & Wahlgren 2002. These lines are overlapped with spectral lines of 1437.65, 2630.1 and 2937.1 A of Bi IV. A study of the Stark broadening parameters of Bi IV spectral lines can help to study these overlaps. In this paper, using the Griem semi-empirical approach, we report calculated values of the Stark parameters for 64 spectral lines of Bi IV. The matrix elements used in these calculations have been determined from 17 configurations of Bi IV. They were calculated using the COWAN code including core polarization effects. Data are displayed for an electron density of 10¹⁷ cmˉ³ and temperatures T=10 000–160 000 K. Also calculated radiative lifetimes for 12 levels with experimental lifetime are presented, in order to test the goodness of our calculations. Theoretical trends of the Stark width and shift parameters versus the temperature for spectral lines of astrophysical interest are displayed.

Calculation of Stark resonance parameters for valence orbitals of the water molecule

An exterior complex scaling technique is applied to compute Stark resonance parameters for two molecular orbitals ($1b_{1}$ and $1b_{2}$) represented in the field-free limit in a single-center expansion. For electric DC field configurations that guarantee azimuthal symmetry of the solution the calculation is carried out by solving a two-dimensional partial differential equation in spherical polar coordinates using a finite-element method. The resonance positions and widths as a function of electric field strengths are shown for field strengths starting in the tunnelling ionization regime, and extending well into the over-barrier ionization region.

Large Stark tuning of donor electron spin qubits in germanium

Donor electron spins in semiconductors make exceptional quantum bits because of their long coherence times and compatibility with industrial fabrication techniques. Despite many advances in donor-based qubit technology, it remains difficult to selectively manipulate single donor electron spins. Here, we show that by replacing the prevailing semiconductor host material (silicon) with germanium, donor electron spin qubits can be electrically tuned by more than an ensemble linewidth, making them compatible with gate addressable quantum computing architectures. Using X-band pulsed electron spin resonance, we measured the Stark effect for donor electron spins in germanium. We resolved both spin-orbit and hyperfine Stark shifts and found that at 0.4 T, the spin-orbit Stark shift dominates. The spin-orbit Stark shift is highly anisotropic, depending on the electric field orientation relative to the crystal axes and external magnetic field. When the Stark shift is maximized, the spin-orbit Stark parameter is four orders of magnitude larger than in silicon. At select orientations a hyperfine Stark effect was also resolved and is an order of magnitude larger than in silicon. We report the Stark parameters for $^{75}$As and $^{31}$P donor electrons and compare them to the available theory. Our data reveal that $^{31}$P donors in germanium can be tuned by at least four times the ensemble linewidth making germanium an appealing new host material for spin qubits that offers major advantages over silicon.

Corrigendum: Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma.

Scientific Reports 6: Article number: 25609; published online: 12 May 2016; updated: 12 August 2016. In this Article, the Data resources have been omitted from the Methods section. It should read: “All data used in the preparation of this paper are available from the University of Bristol’s researchdata repository, and can be accessed using the DOI 10.

Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma.

We illustrate a Stark broadening analysis of the electron density Ne and temperature Te in a laser-induced plasma (LIP), using a model free of assumptions regarding local thermodynamic equilibrium (LTE). The method relies on Stark parameters determined also without assuming LTE, which are often unknown and unavailable in the literature. Here, we demonstrate that the necessary values can be obtained in situ by cross-calibration between the spectral lines of different charge states, and even different elements, given determinations of Ne and Te based on appropriate parameters for at least one observed transition. This approach enables essentially free choice between species on which to base the analysis, extending the range over which these properties can be measured and giving improved access to low-density plasmas out of LTE. Because of the availability of suitable tabulated values for several charge states of both Si and C, the example of a SiC LIP is taken to illustrate the consistency and accuracy of the procedure. The cross-calibrated Stark parameters are at least as reliable as values obtained by other means, offering a straightforward route to extending the literature in this area.

Stark widths dependence on electron temperature for neutral chromium spectral lines

In this work, Stark widths dependence on electron temperature for neutral chromium spectral lines have been studied. Different fitting methods have been analyzed to have the method that will give the best results. So it can be used with more confidence to interpolate and extrapolate the theoretical Stark parameters with different experimental electron temperature values. The Stark widths for nine neutral chromium spectral lines were analyzed and fitted by the power and the modified power formulas and by the quadratic logarithmic formula. The last analytic expression showed better result even both are three fitting parameters.

Theoretical Stark broadening parameters for spectral lines arising from the 2p5ns, 2p5np and 2p5nd electronic configurations of Mg iii

In the present work we report theoretical Stark widths and shifts calculated using the Griem semi-empirical approach, corresponding to 237 spectral lines of Mg iii. Data are presented for an electron density of 1017 cm−3 and temperatures T = 0.5–10.0 (104K). The matrix elements used in these calculations have been determined from 23 configurations of Mg iii: 2s22p6, 2s22p53p, 2s22p54p, 2s22p54f and 2s22p55f for even parity and 2s22p5ns (n = 3–6), 2s22p5nd (n = 3–9), 2s22p55g and 2s2p6np (n = 3–8) for odd parity. For the intermediate coupling (IC) calculations, we use the standard method of least-squares fitting from experimental energy levels by means of the Cowan computer code. Also, in order to test the matrix elements used in our calculations, we present calculated values of 70 transition probabilities of Mg iii spectral lines and 14 calculated values of radiative lifetimes of Mg iii levels. There is good agreement between our calculations and experimental radiative lifetimes. Spectral lines of Mg iii are relevant in astrophysics and also play an important role in the spectral analysis of laboratory plasma. Theoretical trends of the Stark broadening parameter versus the temperature for relevant lines are presented. No values of Stark parameters can be found in the bibliography.

Observing Charge Dynamics in Surface Reactions by Time-Resolved Stark Effects

Surfaces facilitate chemical reactions occurring in biological and synthetic systems with wide-ranging applications from energy conversion to catalysis and sensing. Microscopic understanding of the structure and dynamics that underpin these reactions is keenly pursued with novel experimental techniques such as sum frequency generation and laser-assisted photoemission spectroscopy. Herein, we demonstrate a method for interpreting the time-resolved observation of the Stark effect to provide an in situ optical probe of the charge dynamics during an interfacial reaction. The analysis holds broad potential for investigating charge migration in surface-bound catalysts and sensors, as well as photocenter and retinal proteins, even when the Stark parameters of the material are unknown. We demonstrate the analysis with respect to the energy conversion reaction in solid-state dye-sensitized solar cells.