Transitions In Argon Research Articles

Measurement of Plasma Characteristics of the Hollow Cathode Discharge

The argon temperature and the emission intensity in the hollow cathode discharge were measured. We measured the line profiles of the 1s 5 –2p 8 transition in argon, using a single-frequency diode laser. Low power diode lasers have been used to investigate the line profiles of argon transitions in hollow cathode discharges. It turns out that the argon temperature is 640–783 K in the discharge current range of 7.00–10.0 mA. The emission intensity is uniform in the negative glow at the current range over 5.00 mA under the pressure of 3.00 Torr.

UVES Observations of QSO 0000−2620: Argon and Phosphorus Abundances in the Dust‐free Damped Lyα System atzabs = 3.3901

The UV resonance transitions of neutral argon, Ar I j1066, and of singly ionized phosphorus, P II j963, originated in the damped Lya system (DLA) at toward QSO 0000[2620, have been z abs 3.3901 detected by means of the Ultraviolet-Visual Echelle Spectrograph (UVES) spectrograph at the 8.2 m ESO KUEYEN telescope. So far, this is the —rst measurement of Ar I and the second of P II ever performed in damped galaxies and in high-redshift objects. This DLA is well known for having one of the lowest metal abundances and dust content and the lowest fractional abundance of molecular hydrogen The measured Ar abundance is [Ar/H] \[ 1.91 ^ 0.09, which is equal to the abundances of the H 2 . other a-chain elements (O, S, and Si). The similarity of the Ar abundance with the other a-chain elements implies the absence of signi—cant photoionization by either UV background or stellar sources along the sight line throughout the damped Lya system. Both log (Ar/O) and log (Ar/S) ratios are found close to those measured in the extragalactic H II regions and in blue compact galaxies where O is more abundant by at least 1 order of magnitude. This strengthens the universality of the Ar/O and Ar/S ratios and lends support to the existence of a universal IMF. The abundance of the nonrefractory element phosphorus [P/H] \[ 2.31 ^ 0.10 con—rms the low amount of chemical evolution in the DLA. This is the measurement of P in the most metal-poor material and shows a subsolar [P/Fe] \[ 0.27 value. The measured ratios [P/Si] \[ 0.40 ^ 0.13 and [P/S] \[ 0.40 ^ 0.13 provide evidence for a mild odd-even eUect. Finally, a stringent upper limit to the population of the level in the ground state of O I is 3P 1 derived, which provides a lower limit to the physical dimensions of the system of L [ 7p c. z abs 3.3901

Measurement method for electric fields based on stark spectroscopy of argon atoms

We report the development of a method for the measurement of electric fields in glow discharge plasmas, based on Stark spectroscopy of argon atoms. The method is based on laser excitation of transitions in atomic argon. The key feature of the method is that the electric field is determined by matching experimentally obtained absorption spectra to theoretically calculated spectra. The dependence of the positions of energy levels of argon atoms on the strength of the electric field was calculated by solving the Schrodinger equation for the argon atom. Measurements of Stark spectra were made in the sheath region of a glow discharge using laser optogalvanic spectroscopy. The wavelength of the laser radiation was tuned to the transitions 4s-->nf (n=7,8,ellipsis,14) of the argon atom. For n=11, the lower limit for electric field measurements was estimated to be 14 V/mm.

The role of bond orientational order and the nature of the melting transition in an incommensurate physisorbed monolayer: argon on graphite at completion

A constant-temperature, constant density molecular-dynamics (MD) method is utilized to study the behavior of bond-orientational, translational and thermodynamic parameters in the solid, melting transition and fluid regimes of argon physisorbed onto graphite (Ar/gr) at complete coverage. For Ar/gr, completion occurs near ρ=1.26 in units of 0.0636atoms/Å2, where ρ=1 corresponds to the complete 3×3 R30° commensurate adlayer. Several bond-orientational and newly introduced pair-distribution order parameters and effective densities prove especially useful in helping evaluate the temperature behavior of the system's structural order. A broad melting transition accompanied by vacancy formation through large vertical fluctuations in the adsorbate atoms is observed at Tm=135±5K, spanning a temperature range of roughly 40K. The melting transition accompanies a rapid formation of a low-density second layer. Substantial bond-orientational order persists into the high-temperature fluid (T≈300K), which is not hexatic in nature and which exhibits infrequent desorption from the first layer. The behavior and interaction of the neighbor shells are compared and contrasted to those observed in Kr/gr.

Frequency stabilized distributed feedback laser diode system at 1.323 μm using the modulated Zeeman effect

We present the design of a highly stable, compact system that achieves the frequency stabilization of a distributed feedback laser diode to an excited-state argon transition at 1.323 μm. The argon atomic reference is generated in a miniature hollow cathode lamp. A small a/c magnetic field is used to Zeeman split the transition and both right- and left-circularly polarized light are used to generate the error discriminant signal and cancel laser relative intensity noise. The output does not contain any frequency modulated components and has been measured to have long-term frequency stability of better than 8×10−11 (20 kHz) with the Allan Variance technique.

Field shift analysis of visible and near-infrared argon transitions

We report a systematic study of the isotope shift of an argon atom for s–p and p–d transitions in the visible and the near-infrared regions. The isotope shifts were determined by saturation spectroscopy, and the measurements were effected by use of a standard error of approximately 1 MHz. Combining our spectroscopic measurements with the nuclear charge radii available from muonic transitions, we were able to extract the specific mass and the volume contributions to the isotope shift. In all the investigated transitions we observed a field shift contribution that is surprising for a light element like argon. Moreover, for p–d transitions we also found a field shift larger than for s–p ones, in spite of the fact that s orbitals experience more of the electron density at the nucleus.

Calculation of the vacuum-UV radiation gains in transitions of Ne-like argon in capillary discharges

A collisional — radiative kinetic model is proposed for calculation of the gain occurring in transitions of Ne-like argon ions in a capillary discharge plasma. New efficient laser transitions are predicted on the basis of the calculations. The calculated dependences of the gain on the electron temperature and density and on the capillary diameter are used to estimate the plasma parameters in capillary discharges from measurements of the spontaneous emission gain.

Interstellar Medium Absorption Profile Spectrograph Observations of Interstellar Neutral Argon and the Implications for Partially Ionized Gas

We use the absorption features from the resonance transitions of neutral argon at 1048 and 1066 Å to determine interstellar argon abundances or their lower limits toward nine early-type stars. These features were observed with the interstellar medium absorption profile spectrograph (IMAPS) along sight lines with low reddening and low fractional abundances of molecular hydrogen. Four of the sight lines in our sample have reliably measured interstellar Ar abundances, of which three also have good determinations of N(H I). We find that the interstellar Ar is below its solar and B-star abundance with respect to hydrogen toward ζ Pup, γ2 Vel, and β Cen A with (logarithmic) reduction factors D = -0.37 ± 0.09 dex, D = -0.18 ± 0.10 dex, and D = -0.61 ± 0.12 dex, respectively.

Relativistic many-body calculations for the oscillator strengths of the resonance lines of neon, argon, krypton, and xenon

The $f$ values for the ${\mathrm{np}}^{6}\ensuremath{\rightarrow}{\mathrm{np}}^{5}(n+1)s$ dipole transitions of neon, argon, krypton, and xenon are studied using relativistic many-body perturbation theory. The contributions from the correlation corrections of single and pair excitations are calculated to all orders. It is hoped that the present work may help to distinguish among the considerable variety of experimental and theoretical values presently available.

Coupled cluster response calculations of two-photon transition probability rate constants for helium, neon and argon

The implementation of two-photon transition moments is described for the hierachy of coupled cluster models CCS, CC2 and CCSD and applications are reported for the two-photon transition probability rate constants for transitions from the ground state to the first excited Se1 state in helium and to the lowest De1 and Se1 states in neon and argon. At the CCSD level the rate constant for the Se1 transition in argon is in good agreement with the experimental rate constant and also with a recent MCSCF calculation.

A method to measure electric field strengths in an argon glow discharge plasma using laser spectroscopy

A method for electric field measurement based on laser spectroscopy of argon atoms has been developed and calibrated. Measurements were made using both laser optogalvanic spectroscopy and laser-induced fluorescence spectroscopy. Measurements using several different transitions in argon were carried out, and it was found that the 4s/spl rarr/7f and 4s/spl rarr/8f transitions were the most suitable for measurements in the sheath region of glow discharges. The lower limit for electric field measurements was estimated to be 500 V/cm. A minimal pressure of about 100 mtorr was required to detect optogalvanic signals and about 1 torr was required for the fluorescence signals to be detectable. These detection limits make this method applicable for measurement of sheath electric fields for a wide range of discharge conditions.

Laser spectroscopy of the 1s 2 2s2p 3 P 2 - 3 P 1 transition in beryllium-like argon using the Oxford EBIT

A study of the 1s22s2p 3P2-3P1 fine-structure transition in beryllium-like argon is planned on the Oxford electron beam ion trap (EBIT), using laser-induced resonance. This transition wavelength was measured previously as 594.373(4) nm, which is accessible using a dye laser. The ions are produced and excited in the EBIT and are confined during laser irradiation using the magnetic trapping mode. The 3P2 level population is depleted by the laser and by subsequently monitoring the emitted fluorescence a laser resonance signal can be obtained.

Absorption measurements on a low-pressure, inductively coupled, argon - mercury discharge for lighting purposes: 1. The gas temperature and argon metastable states density

The gas temperature and the absolute density of the argon level in an 80 W inductively coupled low-pressure argon - mercury plasma are determined for three different argon filling pressures. This is done by measuring the line profile of the transition in argon, using a tuneable laser diode. Since the width of this argon line is found to depend on the kinetic heavy particle temperature only, radial profiles of the gas temperature can be obtained. It turns out that the maximum gas temperature in this discharge (550 - 810 K depending on the filling pressure) is significantly higher than that in a common tubular fluorescent lamp. From the radial distribution of the argon 4s density it can be concluded that the maxima of the electron density and of the electron temperature are situated close to the coil. It is also found that the position of these maxima depends on the argon filling pressure.

Interference and PCI in argon Auger (e, 2e) spectra

Angle-dependent interference is observed in electron-impact ionization (e, 2e) coincidence experiments on the argon and Auger transitions. Recapture of the slow ejected electron from the Auger process leads to interference with the satellite-state ionization processes. The post-collision interaction (PCI) and interference effects are quantified for a large range of excess energies.

Atomistic Simulation of Shock Wave-Induced Melting in Argon

A three-dimensional molecular dynamics simulation of shock wave loading was undertaken to investigate the Hugoniot equation of state at the transition of argon from solid to liquid. The simulated data agree with shock wave and static high-pressure experimental data. The melting transition in this simulation occurs without overshooting the argon melting temperature. There are two discontinuities that may bracket a mixed-phase region of solid and liquid along the simulated argon Hugoniot. This is an intrinsic feature of the Hugoniot crossing the argon melting curve and does not require the addition of any solid-solid phase transition.

Studies of magnetic dipole transitions in highly charged argon and barium using an electron beam ion trap

Using the Oxford electron beam ion trap (EBIT), we have studied a number of magnetic-dipole fine-structure transitions in highly charged argon and barium, which lie in the visible and near-UV region of the spectrum. Our wavelength measurements, with uncertainties of between 7 and 20 ppm, are the most accurate yet reported using an EBIT as a spectroscopic source of ions, and provide a useful test of atomic structure calculations for many-electron systems. The argon transitions studied are also of astrophysical interest. Finally, we present the first studies of the polarization of a visible transition from a highly charged ion trapped in an EBIT.

Amplified spontaneous emission on the J = 2 → 1, 3p-3s transition of neonlike argon in a capillary discharge

We report the observation of amplified spontaneous emission on the J = 2 → 1, 3p-3s transition (C-line) of neonlike argon at 69.78 nm in capillaries of 6-mm bore. The simple discharge is driven by a small capacitor bank having a capacitance of 0.1 μF. Gain coefficients between G = 0.17 cm −1 and G = 0.25 cm −1 are derived.

Absolute generalized oscillator strengths of 4s, 4s', 4p+4p' excitations of argon determined by the angle-resolved electron-energy-loss spectrometer.

The absolute differential cross sections and generalized oscillator strengths of resolved 3p 61 S 0 ! 3 p 5 ( 2 P 1/2)4s ,3 p 5 ( 2 P 3/2)4s8 transitions in argon were determined by angle-resolved electronenergy-loss spectrometer at an incident electron energy of 1500 eV and scattering angles from 2° to 11.5°. Corrections of the experimental results for the angular factor and pressure effect have been made. These results are compared with other experimental and theoretical results. The absolute differential cross sections and generalized oscillator strengths of unresolved nondipole excitations 3 p 6 !3p 5 4p14p8 are reported. The profile of the generalized oscillator strength curve is similar to that of neon atoms. @S1050-2947~96!09809-5#

A diode laser absorption study on a 100 MHz argon ICP

Diode laser absorption on the - argon transition is used to measure heavy particle temperatures in a 100 MHz argon inductively coupled plasma. Radial profiles of this temperature are obtained from the Gaussian part of the absorption profile with an accuracy of about 500 K, for four different input powers and at two different heights. The integrated profile is used to calculate the 4s level density and to trace the ionizing and recombining plasma parts. The measurements also show that the method of attributing the Lorentzian width only to Stark broadening for calculating electron densities is not correct for this argon transition in atmospheric plasmas. A second broadening process with Lorentzian shape, Van der Waals broadening, has to be taken into account. Under the measured conditions at the hottest positions in the plasma about 50% of the Lorentz component is due to Van der Waals broadening and this increases to almost 100% at the edges of the plasma.

Radiative transition probabilities for Ne-like ions. Consistent quantum mechanical calculations

It is shown that the calculation of atomic constants by some versions of the multi-configurational method, or its relativistic generalizations, violates the principles of a consistent theory based upon the quantum electrodynamic (QED) approach. The consequences of this violation for the radiative transition probabilities are under investigation. We obtained the probabilities of innershell radiative transitions in Ne-like argon and iron in the lowest approximation of a consistent theory. These results are compared with the corresponding data from some recent publications.