Helium argon

A gun is used to direct a beam of fast-moving atoms or ions onto the liquid target (matrix). Figure 4.1 shows details of the operation of an atom gun. An inert gas is normally used for bombardment because it does not produce unwanted secondary species in the primary beam and avoids contaminating the gun and mass spectrometer. Helium, argon, and xenon have been used commonly, but the higher mass atoms are preferred for maximum yield of secondary ions. 

Argonaut Argon difluoride Argon fluoride Argon-helium Argon ion lasers Argon-oxygen... 

For distributing larger quantities of gaseous helium, argon, and occasionally neon, a number of large, horizontal, compressed gas cylinders are manifolded on tmck semitrailers (called tube trailers) or railroad cars. Like individual cylinders, these serve both as transport containers and rental storage containers. Capacities of tube trailers range from about 300 to 5,000 m (10,000—175,000 fT) of gas. 

Gas-phase deposition In this process, a halide of the solute metal is passed in vapour form over the surface of the metal to be coated, which is heated to a temperature at which diffusion can take place. Temperatures of 500-1 300°C or more can be used, depending on the particular system considered. Generally, filler atmospheres are provided to carry the halide vapour these atmospheres are usually reducing gases such as hydrogen, cracked ammonia, etc. or inert gases (helium, argon). 

Properties Oxygen is a colorless, odorless, and tasteless gas, that makes up about 21% of the Earth s atmosphere. It is essential to life for almost all living matter. It is found in nature in combination with all elements except the so-called rare gases (helium, argon, and neon). It can be liquefied under pressure. 

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... 

Arc discharge [25] is initially used for producing C60 fullerenes. Nanotubes are produced by arc vaporization of two carbon rods placed in a chamber that is filled with low pressure inert gas (helium, argon). The composition of the graphite anode determines the type of CNTs produced. A pure graphite anode produce preferably MWNT while catalyst (Fe, Co, Ni, Y or Mo) doped graphite anode produces mainly SWNT. This technique normally produces a complex mixture of components, and requires further purification to separate the CNTs from the soot and the residual catalytic metals present in the crude product. 

Strip lighting in a classroom, hospital, business hall or kitchen is often called fluorescent lighting, although in fact it is a phosphorescent process, as above. Each bulb consists of a thin, hollow glass tube that is sealed at both ends. It contains gas such as helium, argon or krypton, and a drop of liquid mercury (about 0.5 mg of mercury per kilogram of lamp, or 0.5 parts per million). Like the neon and sodium lamps above, the pressure inside the tube is about 30 Pa, so the mercury evaporates to become a vapour. It is the mercury that yields the light, albeit indirectly. 

The principal laws for the fluorination of polymeric hydrocarbons are the same as those described above for the simple case. Direct fluorination has been used extensively in organic chemistry (but only since the early 1970s) in low-temperature methods, where the fluorine is strongly diluted with some inert gas (helium, argon, nitrogen, krypton). One can note the La Mar, aerosol-based, and liquid-phase fluorination methods. 

These experiments were extended by Hamill et a .12, who used helium, argon and hydrogen as inert diluents. Addition of these gases also produced an increase in k3fk2, which approached a limiting value, (k3jk2)[Pg.145]

From On the Position of Helium, Argon, and Krypton in the Scheme of the Elements , Proceedings of the Royal Society, 63 (1898), 408-11... 

Mobile phases are generally inert gases such as helium, argon, or nitrogen. The choice of carrier gas is often dependent upon the type of detector used. Gas is obtained from a tank, or sometimes from an electrolysis cell, and is passed through a series of reductors, equalizing valves, and traps to ensure constancy of pressure or flow and elimination of impurities as well. 

For example, a helium-argon laser with a power of 2 x 10-8 W at 632.8 nmwill emit 6.37xlO15quanta s-1m- or 1.66x 10-8einstein s 1 m 2. 

Stace and Murrell [535] numerically simulated the reaction of iodine atoms in the inert gases, helium, argon and xenon using a method similar to that of Bunker and Jacobson above. Most of their interest was in the reaction process at low inert gas pressures. At high inert gas pressures, a cage effect was noted over times longer than 50 ps. 

Fig. 3.1. Measurements of the binary absorption coefficient of helium-argon [75], neon-argon [75] and argon-krypton mixtures [104], at room temperature, normalized by the product of relevant densities.

Fig. 3.2. The (smoothed) spectral functions derived from the measurements, Fig. 3.1, of the normalized binary absorption coefficients of helium-argon, neon-argon and argon-krypton mixtures at room temperature in a semi-logarithmic grid, Eq. 3.2.

Fig. 3.35. Absorption profiles, a = av, of the enhancement of the H2 fundamental by helium (bottom), argon (center) and xenon (top) at 298 K. Hydrogen densities were 10.3, 4.5, and 11.1 amagat, and the helium, argon and xenon densities were 105, 113 and 51 amagat, for the lower, middle and upper curve, respectively after [187],...

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. 

Comparison of ternary moments with measurements. The density dependence of the helium-argon collision-induced absorption spectra has been studied at the temperature of 165 K, helium densities from 66 to 130 am-agats, and argon densities from 156 to 280 amagats. Ternary moments of... 

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].

B. C. Freasier and N. D. Hamer. Density effects in collision-induced light absorption in helium-argon mixtures. Chem. Phys, 58 347, 1981. 

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