Showing papers on "Argon published in 1972"

Viscosity of the Noble Gases in the Temperature Range 25-700°C

Abstract: New relative measurements of the viscosity of xenon at a pressure P=1 atm and in the temperature range T=25–700°C are reported. The viscosity of argon has also been remeasured. A careful analysis of the long‐term reproducibility of the oscillating‐disk viscometer employed in the work is presented together with best estimates of the viscosity of all the noble gases. Standard reference values of the viscosity of the gases at atmospheric pressure and at zero density at 25°C are given. The data for all the monatomic gases are represented by means of a single empirical correlation.

Absorption Spectrum and Reaction Kinetics of the HO2 Radical in the Gas Phase

Abstract: HO2 radicals were produced in the gas phase by flash photolysis of water vapor (3%) in an atmosphere of hydrogen, helium, or argon containing ∼ 2% oxygen. Water is dissociated in the first continuum to H and OH, and O2 converts the H atoms to HO2. Hydrogen nearly doubles the amount of HO2 produced by converting OH to H. The absorption spectrum of HO2 is a broad band with a peak at 2050 A. The molar extinction coefficient, emax, based on measurement of the H2O2 formed in the hydrogen system, is 1770 ± 150 M−1· cm−1. The rate constant for the bimolecular combination reaction, HO2+HO2 → H2O2 + O2, was evaluated as 5.7 ± 0.5 × 109 M−1· sec−1 at 298°K and for the reaction HO2+OH→ H2O+O2, k = 1.2 ± 0.2 × 1011M−1. sec−1. From auxiliary measurements of the rate of O3 formation it was also found that, in the flash photolysis of O2 (2%) in H2, hot O atoms react with H2 to form OH and H which are then converted to HO2.

Infrared Absorptions of Interstitial Hydrogen Atoms in Solid Argon and Krypton

Abstract: Infrared absorptions are reported in the spectra of inert gas‐hydrogen matrix samples which were deposited after the gas mixture passed through a glow discharge. For hydrogen in argon, absorption is recorded at 905 cm−1. This band shifts to 644 cm−1 for deuterium in argon and no new bands are observed with hydrogen‐deuterium mixtures. With krypton matrix, similar absorptions are observed at 852 cm−1 (H2–Kr) and at 607 (D2–Kr). Prolonged infrared irradiation in the spectral range of the absorptions causes them to disappear, the hydrogen absorptions more rapidly than the deuterium features. No similar bands could be detected when xenon or neon matrixes were used. The very small 36Ar–40 Ar isotopic shift (0.2±0.1 cm−1) shows that the argon absorptions cannot be attributed to HAr, to HAr+ or to HAr2+. The evidence is consistent with the interpretation that both in argon and in krypton, the absorptions are due to hydrogen atoms trapped in Oh interstitial sites in an undistorted inert gas lattice. This interpre...

Scattering of Helium, Neon, Argon, Krypton, Xenon, and Deuterium from a Tungsten (110) Surface Characterized by LEED

Abstract: Rare gas (He, Ne, Ar, Kr, and Xe) scattering distributions have been measured from a tungsten (110) surface at an incidence angle of 45°. The gas temperature was 295°K, while the surface temperature varied between 375 and 1300°K. The positions of the peak maxima and the broadening of pseudospecular scattering of He and Ne correlate with the FRI models, whereas the Ar–Xe results are anomalous in that these aspects of the scattering do not correlate with either the FRI or soft‐cube models because Ar, Kr, and Xe are dominated by trapping at the surface. An estimate of the fraction of the rare gas atoms initially trapped at the surface has been made. Deuterium scattering distributions have been measured and are characterized by a relatively large diffuse fraction which is attributed to an internal excitation of the diatomic molecule rather than to trapping at the metal surface. Comparisons of these data with scattering from the (111) face of fcc crystals suggests three phenomenologically distinguishable scattering regimes, quasielastic, inelastic, and trapping dominated scattering.

Evidence for Rb‐Rare‐Gas Molecules from the Relaxation of Polarized Rb Atoms in a Rare Gas. Experimental Results

Abstract: Relaxation experiments have been performed between 0–200 G on optically polarized Rb atoms in argon, krypton or xenon, at pressures ranging from 0.1 to 20 torr. They clearly show the existence of Rb–Ar, Rb–Kr and Rb–Xe molecules of low binding energy (smaller than kT). Molecular parameters such as lifetime, spin‐orbit coupling constant, formation rate, constant of mass action, etc., are measured, or evaluated when they cannot be directly measured. Experimental values of the diffusion coefficient of Rb in the gas (except xenon) and of the disorientation cross sections by usual binary collisions are also obtained.

Diffusion of Boron from Shallow Ion Implants in Silicon

Abstract: The use of shallow ion implants as diffusion sources was studied on bare (111) silicon wafers implanted at room temperature with 30 keV, 31014 cm−2 boron. Samples were annealed in purified argon at 900°, 1000°, and 1100°C. The diffusion profiles of boron are determined by in‐diffusion into the silicon and by dissolution, to equilibrium, in the thin oxide layer on the surface. The amount of boron retained in silicon decreases during the initial period of an anneal and then remains constant. More boron is retained the higher the temperature and the lower the oxygen content in the ambient gas. With ~10 ppm O2 in argon, losses range from 15 to 35% of the implanted dose. Experimental results are reasonably well represented by the mathematical formalism developed. The experimental data indicate that the values listed in the literature for sheet conductivity mobilities of holes are too low.

Emission Spectra of Deep Impurity States in Solid and Liquid Rare Gas Alloys

Abstract: We have measured the spectral distribution (in the region 1100–2000 A) of the α excited luminescence from solid and liquid dilute rare gas alloys. Emission was observed from the lowest deep impurity state of xenon in liquid and in solid argon, which provides evidence for medium relaxation resulting in a ``cavity'' formation around the excited impurity in dense rare gases.

Beam-Foil Spectroscopy at Low Initial Ion Energies. Radiative lifetimes measurements for Na, Ne, Ar, Kr and Xe

Abstract: The possibility of determining atomic mean-lives of excited levels in heavier atoms by the beam-foil technique using low initial ion energies was investigated with emphasis on correct energy-loss determinations. Cascade corrections are facilitated at low energies, especially for excited states with long lifetimes. The mean-life of the 3p2P01 level in Na I was determined at 50 keV to be 16.2?0.5 ns. A number of mean-lives of excited levels in neutral and ionized neon, argon, krypton, and xenon were measured at ion energies ranging from 50 to 300 keV. The present xenon mean-lives are considerably shorter than reported in previous beam-foil studies.

Velocity Dependence of the Ionization of Ar, Kr, and Xe on Impact of Metastable Neon Atoms

Abstract: Measurements of the velocity dependence of the total ionization cross section of argon, krypton, and xenon on impact of thermal‐energy metastable neon (Ne*) atoms have been made using a velocity‐selected beam of the metastable atoms. The composition (3P2/3P0 ratio) of the Ne* atomic beam has been measured using an inhomogeneous‐field deflecting magnet and found to be about 5/1, assuming equal detection efficiency for the two metastable species. The ionization measurements were of sufficient precision to allow simultaneous determination of both the secondary‐electron‐ejection efficiency and the cross section. The secondary‐electron‐ejection efficiency from an argon‐covered gold surface on impact of metastable neon atoms was found to be 0.27± 0.14. In the relative velocity range investigated (g=320–1700 m/sec) the cross section Q was found to vary as g−m below g=650 m/sec and to rise at higher relative velocities. The value of m obtained is 0.622 for Ne*–Ar, 0.728 for Ne*–Kr, and 0.874 for Ne*–Xe. A simple ...

Molecular Structure Effects on the Free-Ion Yields and Reaction Kinetics in the Radiolysis of the Methyl-Substituted Propanes and Liquid Argon: Electron and Ion Mobilities

Abstract: The free‐ion yields in liquid alkanes increase with increasing molecular sphericity and increasing temperature, in agreement with earlier observations. The Arrhenius temperature coefficient of free‐ion formation is 0.8 kcal/mole in propane and 0.7 kcal/mole in 2‐methylpropane. The free‐ion yield in purified argon at 87°K appears to be Gfi=2.0. Addition of oxygen to liquid argon decreased the free‐ion yield, mainly because the efficiencies of electron energy loss processes with the diatomic oxygen molecules were much greater than those with monatomic argon molecules; the oxygen served to decrease the ion—electron separation distance more by de‐energizing the electron than by scavenging it before it reached the end of its normal track. In pure liquid oxygen at 87°K, Gfi=0.013. The ion—electron neutralization rate constant equals 8 × 10−5 cm3/ion · sec in pure argon at 87°K and 3.1 × 10−4 cm3/ion · sec in liquid methane at 120°K. The mobility of electrons in liquid methane is 300 cm2/V · sec and decreases in...

Argon Matrix Raman Spectra of Oxygen Difluoride and the Oxygen Fluoride Free Radical

Abstract: The argon matrix Raman spectra of oxygen difluoride and oxygen‐18 difluoride at 16°K have been observed; frequencies within one wavenumber of analogous infrared studies were measured. Laser photo‐detachment of fluorine atoms has provided significant yields of the OF and 18OF free radicals; the Raman observations confirm the earlier infrared work. Temperature cycling operations and depolarization ratio measurements provide aid in identifying new chemical species and making vibrational assignments.

Dependence of X-Ray Yields in Argon, Krypton, and Xenon upon the Charge State of Fluorine Ions at 35.7 MeV

Abstract: In high-velocity ion-atom single collisions, a strong dependence of target x-ray production cross sections upon the ionic charge state has been observed. Experiments were performed in thin gas targets of argon, krypton, and xenon with 35.7-MeV fluorine ions incident in charge states +5 to +9. Production cross sections for Ar $K$, Kr $L$, and Xe $L$ characteristic lines increase by as much as a factor of 5 with increasing incident charge state but cannot be fitted by a ${q}^{2}$ dependence.

Thermal Expansions of Solid Argon, Krypton, and Xenon above 1 K

Abstract: A differential parallel-plate capacitance dilatometer has been used to measure the linear thermal-expansion coefficients of free-standing samples of solid argon (1-35 K), krypton (1-45 K), and xenon (1-105 K). The present data for argon and krypton are systematically larger than existing x-ray lattice-parameter data above 20 K by a constant proportionality factor which varies from 1 to 3% for different runs and different samples and which most likely is due to bonding of the samples to the capacitor plates. These data have been normalized using the x-ray results. The xenon results agree with other published data without the use of a scale factor. Temperature-dependent Gr\"uneisen parameters $\ensuremath{\gamma}$ are calculated for these solids using available thermodynamic data. These calculations give ${\ensuremath{\gamma}}_{0}=2.7\ifmmode\pm\else\textpm\fi{}0.1$ for argon, 2.67 \ifmmode\pm\else\textpm\fi{} 0.07 for krypton, and 2.5 \ifmmode\pm\else\textpm\fi{} 0.1 for xenon, with the major uncertainty occurring through the bulk-modulus data.

Atomic and Molecular Diffraction and Scattering from a Tungsten Carbide Surface Characterized by LEED

Abstract: The scattering of collimated beams of helium, deuterium, neon, and argon are reported from two tungsten carbide surfaces which form on the (110) face of tungsten. On a (3× 5) surface both helium and deuterium give sharp, well‐defined diffraction peaks corresponding to the (2, 0), (1, 0), (0, 0), (1, 0), (2, 0) directions along the 5 spacing. No diffraction is observed on the (1× 1) carbide surface or the clean metal surface which is also (1× 1). Fractions scattered in the specular ray, (0, 0), as high as 55% have been observed from the carbide surfaces. The scattering of neon is in the inelastic regime and argon is trapping dominated. Analysis of the scattering in combination with the LEED suggests a dense carbide, perhaps WC, with a Debye temperature of 1200°K or higher. This diffractive scattering is the first reported on a surface other than alkali halides and some comments on the sort of periodic potential which is likely to give rise to diffractive scattering of atoms are given.

Three body conversion reactions in pure rare gases

Abstract: Measurements of the conversion reaction coefficients, beta , for the three body conversion of krypton and xenon atomic to molecular ions in pure rare gas afterglow plasmas have been made The values for beta at 300 K are (342+or-15) Torr-2s-1 in krypton, and (447+or-22) Torr-2s-1 in xenon Preliminary investigations in the case of krypton indicate that beta is essentially the same at gas temperatures of 180 K and 300 K, but that there is a marked decrease in beta as the gas temperature is increased to 510 K These results, coupled with the previous measurements, in this laboratory, of beta in helium, neon and argon have allowed an assessment to be made of the validity of several theoretical models It is shown that good agreement exists between the experimental values and those calculated using the theoretical approach of Mahan (1965)

Experimental Investigation of Normal Shock Wave Velocity Distribution Functions in Mixtures of Argon and Helium

Abstract: The electron beam fluorescence technique for measuring simple one‐dimensional moments of helium velocity distribution functions has been extended for use with argon. Measurements made in argon‐helium gas mixture shock waves at low Mach numbers are presented. Parallel and perpendicular temperature profiles are shown for each gas. Macroscopic velocities for each gas were measured by determining the blue shifts in the line profiles when the line of sight was directly upstream. The results are compared with existing theories and other experimental results.

Photoionization of helium, neon and argon in the 60-230 eV photon energy range

Abstract: The photoionization absorption coefficients of helium, neon and argon have been measured by single beam photometry in the 60-230 eV photon energy range using a synchrotron radiation source and channel electron multiplier photodetection. The accuracy of most of the data is +or-3% rising to +or-5% for a few cases in helium. Agreement with theory is typically better than 20% for photon energies up to 150 eV with greater discrepancies at higher energies especially for helium and argon.

Study of Relaxation in Free Jets Using Temperature Dependence of n‐Butane Mass Spectra

Abstract: Molecular beam studies of the temperature dependence of n‐butane fragmentation patterns were carried out under several conditions. Under effusive‐flow molecular‐beam formation, the temperature dependence of fragmentation to several ions from n‐butane agrees well with conventional studies. Under free‐jet expansion molecular beam formation, the fragmentation of n‐butane to several ions indicates substantial vibrational relaxation of the neutral molecule. Dilution of n‐butane with argon at room temperature gives rise to parent/fragment ion ratios that suggest that the dimer or higher clusters are contributing substantially to ion peaks normally attributed to the monomer. The unusual ions (C4H10)n+ are readily generated. Implications of the large observed vibrational cooling and its method of detection are discussed.