Ar-H2 Mixture Research Articles

Massenspektrometrie am negativen Glimmlicht einer zylindrischen Hohlkathode / Mass Spectrometric Studies of the Negative Glow of a Cylindrical Hollow Cathode Discharge

Abstract Positive ions were extracted from the negative glow (NG) of a cylindrical hollow cathode discharge (h.c.d.) through a plane sampling probe (diameter 1 mm, orifice dia. 50 [xm, Molyb-denum) and analyzed in a 60° mass spectrometer. The discharge was operated in pure Argon with an admixture of about 0.1% of H20. The principal ions were Ar+, Ar++,r2 +, ArH+ , H20+ and H3O+ . The individual ion currents were measured as functions of the probe potential U\>, at dif-ferent discharge currents (2 - 7 mA) and of the gas pressure (0,05 - 0,5 torr). The reaction scheme for the production and conversion of these ions in the NG could be established. In general, the ions were extracted from the axis of the h.c.d. When the sampling probe was mounted excentrically (3 mm out of the axis), the ratio of secondary to primary ions was higher in the axis. At probe potentials above +15 v referred to anode no ions from the NG reached the probe, but electrons were accelerated so that ionization of the neutral gas could arise in and behind the orifice. The Ar++ current as a function of Ub together with other results suggested the presence of very fast electrons (energy > 100 v) in the sampling orifice. They could be identified as electrons from the cathode fall region which were scattered into the orifice. Studies of the ion currents from Ar-H2 mixture proved the sampling probe suitable as an electron impact ion source.

Chemical Lasers from the Reactions of ClF and ClF3 with H2 and CH4: A Possible Chain-Branching Chemical Laser

Both HF and HCl chemical laser emission have been observed from the flash photolysis of ClF–H2–Ar and ClF3–H2–Ar mixtures. In contrast, only HF laser emission is produced by flash photolysis of ClF–CH4–Ar or ClF3–CH4–Ar mixtures. For the ClF–H2 system, the presence of 3→2 HF transitions and the appearance of HCl transitions show that the H+ClF reaction divides to form very roughly equal amounts of HCl and HF. For HCl, equal–gain temperature measurements place k2/k1 in the range 1.2–3.8. The ClF3–H2 chemical laser is extremely intense, but it displays much lower vibrational excitation of HF than that of ClF–H2 or of ClF3–CH4. There is evidence that chain-branching reactions occur, which enhances the potentiality of the ClF3–H2 system as a possible high-power, continuously operating chemical laser.

Hydrogen Etching of Silicon Carbide

The etch rate of SiC crystals with hydrogen was investigated as a function of the reaction temperature, the hydrogen flow velocity and the hydrogen partial pressure in the H2-Ar mixture. An etching reaction mechanism and calculated expressions for the etch rate have been developed based on thermodynamical considerations. The experimental results are well explained from the approximate expression at the etch rate region higher than about 3 µ/min.

Experimental Measurements of the Diffusion Coefficients of H Atoms in H2 and in H2–He and H2–Ar Mixtures

The catalytic sink technique previously described was used to measure the diffusion coefficients of H atoms in H2 over the temperature range 202°–364°K and in H2–He and H2–Ar mixtures at 275°K. The rigid-sphere collision diameters of H atoms in H2, He, and Ar were 1.89, 1.94, and 1.84, respectively. However, the temperature dependence of the H–H2 diffusion coefficients does not fit the rigid-sphere equation but can be represented by the use of the Lennard-Jones parameters ε / k = 85°K and σ′H,H2 = 2.32 Å. Comparisons are made with values derived from viscosity data and with theoretical calculations.

Determination of Eucken Factor from Relative Change in Thermal Conductivity of Gas Mixtures. Ortho–Parahydrogen Mixtures at 77°K

At 77°K the measured change in thermal conductivity of hydrogen caused by a change in the relative proportions of ortho- and parahydrogen can be used to determine the dimensionless parameter δ (introduced by Hirschfelder in his formula for the “modified Eucken correction”) which is a measure of the contribution of rotational energy to the thermal conductivity of a polyatomic gas. The present method, which is very reproducible and is not sensitive to systematic errors in the measurement of absolute thermal conductivity, yields δ = 0.73 ± 0.04. An analogous method, using the variation of thermal conductivity at 311°K of a H2–Ar mixture as the proportion of H2 is increased, yields δ = 0.76, which is in excellent agreement with values previously obtained by other investigators from absolute measurements of thermal conductivity and Prandtl number. These experimental values of δ are lower than Hirschfelder's theoretical values. Possible reasons for this discrepancy are discussed.

Kinetics of Decomposition of HF in Shock Waves

The decomposition of HF in HF–Ar and HF–H2–Ar mixtures was studied behind incident shock waves over the temperature range 3800° to 5300°K employing infrared emission techniques. For HF dissociation, a rate k1=1019.053T−1 exp (−134 100/RT) or, alternatively, k1=1022.710×T−2 exp (−134 100/RT) was found to best represent the experimental data; the exchange rate for H+HF was found to be k2=1013 exp (−35 000/RT); the recombination rate for H2 was best represented by k−3=1018.30T−1 (all rates are in cubic centimeter—mole units). Rates derived for H–F recombination were found to be in good numerical agreement with the theory of Benson and Fueno.