Observation of Δn=1 dielectronic recombination resonances of boronlike argon

We report here an observation ofn=1 dielectronic recombination resonances of boron-like argon in the energy region 140–195 eV. With the cooler's electron beam as a target, a resolution of approximately 0.6 eV FWHM was obtained in the observed energy range. The energies of the doubly excited states were estimated with a Hartree-Fock calculation, which indicates that the observed resonances are from Ar¹³⁺(1s²2s²2p) to Ar¹²⁺(1s²2s²3l3l) and Ar¹²⁺(1s²2s2p3l3l) transitions.     

Calculation of ion energy distributions of argon excimer ions generated in helicon plasma

A program is developed to calculate the ion energy distributions （IEDs） of Ar2^＋ making use of a simplified kinetic model with a combination of Monte Carlo method. Several coefficients are used to realize good match between the calculated and measured results. Some important assumptions are confirmed： argon excimer ions have short lifetime, hence they are formed in a short range before the collecting electrode. The excimer ions that encounter collisions will be discarded because they turn to other ion species after they collide with argon atoms. From the calculated results some plasma parameters such as the cross section or neutral density in discharge could be evaluated.     

Quasi-isentropic compression of liquid argon at pressure ≈ 1000 GPa

The measurement of the density of liquid argon at a pressure of about 1000 GPa in a cylindrical setup transforming shock compression to quasi-isentropic compression gives a value of about 9 g/cm³. The experimental data are compared with calculations. The results bring out clearly that no anomaly is observed in the behavior of isentropically compressed liquid argon at pressures up to about 1000 GPa.     

Effect of an axial magnetic field on a DC argon arc

In this paper a commercial CFD （computational fluid dynamics） code FLUENT has been used and modified for the axisymmetric swirl and time-dependent simulation of an atmospheric pressure argon arc in an external axial magnetic field （AMF）. The computational domain includes the arc itself and the anodic region. Numerical results demonstrate that the AMF substantially increases the tangential component of the plasma velocity. The resulting centrifugal force for the plasma rotation impels it to travel to the arc mantel and as a result, a low-pressure region appears at the arc core. With the AMF, the arc presents a hollow bell shape and correspondingly, the maximal values of the temperature, pressure and current density on the anode surface are departing from the arc centreline.     

Ab initio pair potential energy curve for the argon atom pair and thermophysical properties of the dilute argon gas. I. Argon–argon interatomic potential and rovibrational spectra

An argon–argon interatomic potential energy curve was derived from quantum-mechanical ab initio calculations using basis sets of up to d-aug-cc-pV(6+d)Z quality supplemented with bond functions and ab initio methods up to CCSDT(Q). In addition, corrections for relativistic effects were determined. An analytical potential function was fitted to the ab initio values and utilised to compute the rovibrational spectrum. The quality of the interatomic potential function was tested by comparison of the calculated spectrum with experimental ones and those derived from other potentials of the literature. In a following paper the new interatomic potential is used to determine selected thermophysical properties of argon by means of quantum-statistical mechanics and the corresponding kinetic theory considering two-body and three-body interactions.     

Molecular dynamics simulation of the vapour → liquid transition of argon and the reaction coordinate of condensation

We have investigated the n-dependences of the rate constants of absorption and emission of monomers that are attached to and detached from the cluster of n monomers, and have determined n*, the number of monomers that form the critical nucleus of the homogeneous condensation of the Lennard-Jones?Ar vapour. The dynamics was clearly separated into two regions at the critical nucleus; n* did not, however, give the unique dividing point. The observed strong dependences of both the nucleus size and the barrier height of the nucleation on the induction time of the condensation suggest that a slowly changing variable instead of the cluster size is necessary as the reaction coordinate of the nucleation. Although the slow variable is not well characterised at the present stage of the investigation, it seems to be related to the local density of the gas atoms around the liquid-like clusters. Both the slow evolution of the radial distribution function of the gas atoms around the liquid-like atoms, and the correlation between n* and the onset of the condensation indicate that Gibbs energy curves represented in n-space change significantly with the activation of the slow variable.     

Viscosity of argon to 5 GPa and 673 K

A rolling-sphere technique has been used to measure shear viscosities of (supercritical) fluid argon in the diamond-anvil cell between the temperatures of 294 and 673 K, up to a maximum pressure of 5 GPa. At these pressures, the viscosities can be fit to a modified free-volume expression. A single correlation between reduced viscosity and reduced residual entropy is shown to give a good account of the current high pressure data, data at lower pressures and those for the sub-critical liquid.     

Intermolecular interaction potentials of methane－argon complex calculated using LDA approaches

The intermolecular interaction potential for methane－argon complex is calculated by local density approximation (LDA) approaches. The calculated potential has a minimum when the intermolecular distance of methane－argon complex is 6.75 a.u.; the corresponding depth of the potential is 0.0163eV which has good agreement with experimental data. We also have made a nonlinear fitting of our results for the Lennard-Jones (12-6) potential function and obtain that V(R)=143794365.332/R^{12}-3032.093 / R^6 (R in a.u. and V(R) in eV).     

Multiple ionization of argon accompanied by electron loss and capture of 0.22-6.35 MeV C^q＋ ions

In this paper a projectile ions recoil ions coincidence technique is employed to investigate the target ionization and projectile charge state changing processes in the collision of 0.22-6.35 MeV Cq^＋ （q = 1 - 4） ions with argon atoms. The partial cross section ratios of the double, triple, quadruplicate ionization to the single ionization （or the single capture） of argon associated with single electron loss （or single electron capture） by the projectile are measured and compared with the previous experimental results. In the present experiment, it is observed that the ratios of ionization cross sections R associated with single loss and single capture depend strongly on the projectile charge state and vary significantly with different reaction channels as impact energy increases. In addition, this paper gets empirical scaling laws for the ionization cross section ratios R corresponding to the projectile single loss and finds that the ratios of the double ionization to the single ionization associated with single electron capture remain constant in the present energy range.     

Investigations of the inductively coupled argon plasma sputtering of Pb1 ? x Sn x Te ternary solid solution

Investigations of the sputtering of films of the Pb_{1 ? x} Sn _x Te ternary solid solution with 0 ?? x ?? 1 in RF high-density low-pressure inductively coupled argon plasma have been performed. The effect of a constant sputtering rate with variation in the composition of the semiconductor solid solution for (111)-oriented films with x < 0.6 and of a sputtering rate decrease with the appearance of (100)-oriented crystallites at x > 0.6 is found. The results are analyzed in the context of a model of ternary alloy sputtering based on the Sigmund solid sputtering theory when taking into account the sublimation energies of binary compounds that constitute a solid solution.     

The study of a homogeneous column of argon plasma at a pressure of 0.5 torr,generated by means of the Beenakker’s cavity

A homogeneous column of argon plasma at a pressure of 0.5 torr, generated by means of the Beenakker cavity, has been investigated by methods of emission spectroscopy, photography and self-consistent 3D modeling in a nonlocal approximation. It is shown that the plasma column, which spreads beyond the resonator, is spatially uniform and it represents the afterglow of the microwave discharge produced inside the cavity. The simulation data of the spatial distributions of the electron energy density and concentrations of electrons, ions and argon atoms in metastable and radiating states are presented. The results of calculations are in agreement with experimental data.     

Theoretical calculation of triple differential cross sections of 3s orbital of argon in coplanar symmetric （e, 2e） reaction

The triple differential cross section for the low-energy electron impact ionization of inner-valence 3s orbital of argon has been calculated using the modified distorted wave Born approximation in coplanar symmetric energy-sharing geometry. Satisfactory agreement between theory and experiraent is achieved when the polarization and post-collisional interaction (PCI) are included in the calculations. It is shown that the polarization and PCI effects play a very important role in the case of argon at low incident energies.     

Influence of temperature on the ionization coefficient and ignition voltage of the Townsend discharge in an argon–mercury vapor mixture

The kinetics of main types of charged and excited particles present in a low-current discharge in an argon–mercury vapor mixture used in gas-discharge illuminating lamps has been investigated in a wide interval of the reduced electric field strength and temperature. Mechanisms behind the production and loss of ions and metastable atoms have been discovered, and the temperature dependences of their contributions to maintaining their balance have been determined. It has been shown that, when the discharge is initiated in the lamp and the mercury content in the mixture is low, the ionization coefficient exceeds that in pure argon, which is almost exclusively due to the Penning reaction. The influence of this reaction grows with a reduction of the electric field strength in the interelectrode gap. The dependences of the discharge ignition voltage on the interelectrode gap (Paschen curves) for different temperatures of the mixture have been calculated, and the nonmonotonicity of the temperature dependence of the ignition voltage has been explained.     

Measurements and calculations of ethylene line-broadening by argon in the ν7 band at room temperature

Argon broadening coefficients are measured for 32 vibrotational lines in the ν₇ band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3 ≤ J ≤ 19, 0 ≤ K_a ≤ 4, 2 ≤ K_c ≤ 19 in the P, Q and R branches are located in the spectral range 919–1023 cm^?1. The fitting of experimental line shapes with Rautian profile provides collisional widths slightly larger than those derived from the Voigt profile. The independent theoretical estimation of these line widths is performed by the semiclassical approach of Robert-and-Bonamy type with exact isotropic trajectories generalized to asymmetric tops. Even with a rough atom–atom intermolecular potential model the calculated values show good agreement with experimental results.     

Simulation of multiple scattering in argon ion collisions with an aluminum target at grazing angles of 5°–10°

A model for calculating the atom scattering from a polycrystalline surface consisting of randomly oriented single crystals is proposed. In the calculation it is possible to distinguish the contribution of scattering from any surface layer, and it also takes into account inelastic energy losses in primary ion collisions with target atoms. A comparison with the measurements shows that the proposed model well describes the peak positions in the energy spectra of the scattered atoms. A comparison of the calculated and experimental peak-to-background ratios for scattering from polycrystalline and amorphous targets allows a conclusion to be made about the degree of order of surface layers in the material under investigation.     

Sputtering characteristics of fullerene C60 films under bombardment with 0.1–1-keV argon ions and atoms

The sputtering of fullerene C₆₀ films under bombardment with Ar⁺ ions was studied. In thin films, blistering effects related to diffusion of the implanted argon ions along the layer and substrate interface have been found to occur. A threshold behavior was observed for sputtering at ion energies around 0.2 keV, which is much higher than in graphites. It has been shown that dependence of the work function on ion energy can be described in the framework of Zigmund-Falcone’s approximation, which takes into account anisotropic effects in cascade collisions, and with Yudin’s approximation for the sputtering of elemental materials. The obtained surface binding energy for fullerenes is U _s?6.7 eV, which is less than the value for graphites, U _{s graph}=7.7 eV.     

Generation of 2.5 μJ vacuum ultraviolet pulses with sub-50 fs duration by noncollinear four-wave mixing in argon

Generation of sub-50fs vacuum UV pulses with more than 2.5μJ energy at a 1kHz repetition rate is reported. The pulses at 160nm are produced using noncollinear difference-frequency four-wave mixing between the fundamental and third harmonics of an amplified Ti:sapphire laser in argon. While the pulse duration is maintained by increasing the phase-matching pressure, noncollinear interaction improves the conversion efficiency by 1 order of magnitude in comparison with the previous results in collinear geometry.     

Theoretical calculation of the triple differential cross sections of the 2p orbital of argon in a coplanar highly asymmetric（e,2e） reaction

The triple differential cross sections of the 2p electron of argon in a coplanar highly asymmetric geometry have been calculated with the modified distorted wave Born approximation (DWBA) and the target Hartree－Fock approximation methods. The damping polarization of the semi-classical short-range potentials and the M_ee factor are included in the distorting potentials of the modified DWBA. Theoretical results are compared with a recent experiment. The dynamic mechanism of inner shell ionization in a coplanar highly asymmetric geometry (e, 2e) reaction are also discussed.     

The argon spectrum in the range of 1200–2000 cm<Superscript>–1</Superscript>

Atomic argon spectrum in the range of 1200–2000 cm^–1 has been recorded by time-resolved Fourier transform spectroscopy. The lines have been identified using the oscillator strengths calculated by the quantum-defect method. Previously unknown energies of the 6h levels of Ar I have been found from the spectrum.