Argon mixtures

Gunther D, Heimich CA (1999) Enhanced sensitivity in laser ablation-ICP mass spectrometry using helium-argon mixtures as aerosol carrier. J Anal At Spectrom 14 1363-1368 Habfast K (1998) Fractionation correction and multiple collectors in thermal ionization isotope ratio mass spectrometry. Inti J Mass Spectrom 176 133-148... 

The zirconium sponge thus obtained is highly pyrophoric. The industrial practice is to condition this sponge by the controlled admittance of air-argon mixtures at around 50 °C. Such a treatment results in the formation of a thin, protective oxide film on the sponge this eliminates any major fire hazard in subsequent handling and crushing operations. 

Although dimethylberyllium is a coordination polymer in the solid state,27 it has long been known to be monomeric in the gas phase.28 It has also been found to be monomeric when synthesized from the co-condensation of laser-ablated beryllium atoms and a methane/argon mixture at 10 K.11 Formed in conjunction with several other species, including hydrides (see Section 2.02.2.4), (CH3)2Be was identified from its infrared absorption bands, which were compared to DFT-calculated frequencies (DFT = density functional theory). 

Numerous determinations of the heat of formation of carbon difluoride, a transient intermediate in the production of PTFE, for example, have been made. The most recent one has combined kinetic and equilibrium approaches. The equilibrium C2F4 2CF2 was studied at 1150-1600 K at 0.07-46 bar in dilute argon mixtures using incident and reflected shock waves. The carbene concentration was monitored at 250 nm after a careful study of the extinction coefficient over a wide temperature range. Rate parameters were found for forward and back... 

Fig. 50. TG curve showing the formation of alumina whiskers during oxidation of iron-aluminum alloy in wet hydrogen (2%)/argon mixture (isothermal at 1555 °C). Sample weight 1000 mg...

Temperature-Programmed Surface Reaction (TPSR) Experiments at 800 Torr. Pretreated and preoxidized silver exhibited no reactivity toward an ethylene/argon mixture at reaction temperatures (443 - 543 K) and atmospheric pressures (750-800 torr). The desorption spectrum of a pretreated sample showed no evidence of oxygen desorption when the sample was heated in vacuo to 673 K. These... 

Fig. 3.7. Spectral function of neon-argon mixtures at high densities, obtained with a constant neon density of 77 amagat the argon densities are 416 (o), 488 (x), 530 ( ), and 553 ( ) amagats, respectively. For comparison, the binary profile [75] (+) is also shown. All profiles are normalized so that intensities are equal at peak absorption (near 100 cm-1) after [252],...

Fig. 3.18. Comparison of the D2-Ar ( ) and H2-Ar (x) rotational spectra at 165 K, and 142 and 150 amagat argon density for deuterium-argon and hydrogen-argon mixtures, repectively, and a hydrogen concentration of 2 to 10% after [109],...

Fig. 3.30. Experimental reduced line shapes of the induced D2 So lines of deuterium-argon mixtures at 165 K argon density 142 ( ) and 650 amagat (o) after [109].

Fig. 3.39. Absorption spectrum of para-H2 in argon mixture at 77 K and 1.2 amagat after [267]. The diffuse lines shown in the upper portion of the figure are the collision-induced H2 Q (0) and Si(0) lines, and the sharp structures near the peaks are due to transitions of bound H2Ar complexes. The lower trace shows an enlargement of the Q branch region.

Later studies showed the same phenomena in deuterium and deuterium-rare gas mixtures [335, 338, 305], and also in nitrogen and nitrogen-helium mixtures [336] in nitrogen-argon mixtures the feature is, however, not well developed. The intercollisional dip (as the feature is now commonly called) in the rototranslational spectra was identified many years later see Fig. 3.5 and related discussions. The phenomenon was explained by van Kranendonk [404] as a many-body process, in terms of the correlations of induced dipoles in consecutive collisions. In other words, at low densities, the dipole autocorrelation function has a significant negative tail of a characteristic decay time equal to the mean time between collisions see the theoretical developments in Chapter 5 for details. 

Fig. 3.48. Enhancement of the absorption in the fundamental band in a hydrogen-argon mixture at low and high densities at 152 K the profiles are normalized to give Si(l) the same peak intensity. The argon density was 8 ama-gat (solid line) and 820 amagat (dashed line), respectively. The density splitting of the (overlap-induced) Q branch and the density narrowing of the S lines are apparent. A new (quadrupole-induced) Q line appears inthe wide absorption dip (between Qp and Qr) observed at high density. Reproduced with permission from the National Research Council of Canada from [137].

Fig. 3.51. Logarithmic plot of the normalized induced dipole moment correlation function, C(t), for hydrogen-argon mixtures at 165 K. Measurements at 90 amagat ( ) 450 amagat ( ) and 650 amagat (o). The broken lines at small times represents the portion of C(t) affected by the smoothing of the wings of the spectral profiles. Reproduced with permission by the National Research Council of Canada from [109].

Whereas the agreement of the SCF plus dispersion dipole model with spectroscopic measurements in neon-argon mixtures is impressive [44], it... 

The last column of Table 4.3 or, equivalently, Eq. 4.30 with the parameters as specified, probably represent the best induced dipole model for He-Ar pairs currently available. This model permits a close reproduction of the measured binary spectra of helium-argon mixtures in the far infrared, see Fig. 5.5 on p. 243. 

Helium-argon mixtures. For the He-Ar pair, an accurate ab initio induced dipole surface exists, Table 4.3 which, with the help of line shape calculations, was shown to reproduce the binary collision-induced absorption spectra within the accuracy of the measurement [278]. For the ternary moments, the SPFD2 He-Ar [12] and the HFD-C Ar-Ar [11] interaction potentials were input, along with this ab initio dipole surface. 

Table 5.2. Various computed binary and ternary moments M , with and without Wigner-Kirkwood corrections, for helium-argon mixtures at various temperatures. Units of Mo and Mi are 10 33 J amagat N and 10-20 W amagat N, where N = 2 and 3 for binary and ternary moments, respectively. The asterisk indicates that Wigner-Kirkwood corrections have not been made to the entries on that line [296].

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