E. A. Mason

Scattering of High Velocity Neutral Particles. X. He–N2; A–N2. The N2–N2 Interaction

Total collision cross sections have been measured for helium atoms with energies between 500 and 2100 ev, and for argon atoms with the same energies, scattered in room temperature nitrogen. The results have been analyzed to obtain the average potential between a helium atom and a nitrogen molecule, 〈V(r)〉Av=1.19×10−10/r7.06u2009ergs, for r between 1.79 A and 2.29 A, and the average potential between an argon atom and a nitrogen molecule, 〈V(r)〉Av=1.21×10−9/r7.78u2009ergs, for r between 2.28 A and 2.83 A.A procedure which takes into account the noncoincidence of the center of mass and the centers of force in the N2 molecule has been developed for expressing these average atom‐molecule interactions as functions of the atom‐atom potential between the beam particle and either of the nitrogen atoms. These interatomic potentials have been combined with potentials previously determined for He–He and A–A to obtain a hypothetical potential between two nitrogen atoms in different N2 molecules. The following average intermo...

Scattering of High‐Velocity Neutral Particles. III. Argon‐Argon

Total collision cross sections have been measured for argon atoms, with energies between 700 and 2100 ev, scattered in room temperature argon. Results obtained with two detectors of different geometric aperture are shown to be in accord when allowance is made for beam shape, intensity distribution, and scattering to a detector which is narrower than the beam, in accordance with procedures previously used for helium scattered in helium.Potential energy information derived from the cross sections may be represented by V(r)=1.36×10−9/r8.33u2009ergs for values of r between 2.18A and 2.69A, and appears to be consistent with that derived from measurements of gaseous compressibility, viscosity, and crystal properties.

Scattering of High Velocity Neutral Particles. VIII. H–He

Total collision cross sections have been measured for hydrogen atoms with energies between 700 and 2100 ev, scattered in room temperature helium. The results have been analyzed to obtain potential energy information for the interaction between a hydrogen atom and a helium atom. The potential function, which may be represented by V(r)=3.75×10−12/r3.29u2009erg for r between 1.16 A and 1.71 A, gives values which agree with those calculated quantum mechanically by Mason, Ross, and Schatz.The H–He potential has been combined with a potential previously obtained for He–He to obtain a function which, it is suggested, represents the repulsive interaction between two hydrogen atoms. The derived function is in fair agreement with theoretical calculations of Hirschfelder and Linnett for the repulsive 3Σ state of the hydrogen molecule.

Diffusion Coefficients of the Systems CO2–CO2 and CO2–N2O

The radioactive tracer, C14O2, has been used to measure diffusion coefficients for the systems CO2–CO2 and CO2–N2O in the temperature range −78° to 90°C. The apparatus, which is the Loschmidt type, uses saturation ionization currents as a measure of the extent of diffusion. The characteristics of this type of apparatus have been analyzed in detail to obtain working equations which permit use of experimental measurements at both small and large values of the time.The present results, whose accuracy is estimated at 1.5 percent, agree with those obtained by other investigators using different experimental methods. Although the difference is small, 2.6±0.3 percent, the diffusion coefficient for the system CO2–N2O is consistently larger than that for CO2–CO2 over the entire temperature range.

SCATTERING OF HIGH VELOCITY NEUTRAL PARTICLES. VII. XENON-XENON

Measurements have been made of the scattering of xenon atoms with energies between 700 and 2100 ev in room temperature xenon. The interaction potential for two xenon atoms, deduced from the variation of total collision cross sections with energy, may be expressed as V(r)=1.13×10−8/r7.97u2009ergs for r between 3.01 A and 3.60 A. This potential is consistent with others, valid at larger separation distances, which have been obtained from measurements of gaseous compressibility, transport, and crystal properties, within the limits of uncertainty of the potentials at the larger distances.

Scattering of High Velocity Neutral Particles. V. Neon‐Neon

Total collision cross sections have been measured for neon atoms with energies between 500 and 2100 ev scattered in room temperature neon. The experimental results have been treated to obtain potential energy information for the interaction of two neon atoms. The analytical relation, which may be represented by V(r)=5.00×10−10/r9.99erg for r between 1.76 A and 2.13 A, is consistent with the potential, valid at larger separation distances, which has been derived from measurements of gaseous compressibility, viscosity, and crystal properties.

Scattering of High Velocity Neutral Particles. VI. Krypton‐Krypton

Total collision cross sections have been measured for krypton atoms with energies between 700 and 2100 ev, scattered in room temperature krypton, to obtain potential energy information for the interaction of two krypton atoms. The potential function may be represented by V(r)=2.55×10−10/r5.42u2009ergs for r between 2.42 A and 3.14 A.The present potential appears to be consistent with potentials, valid at larger separation distances, which have been derived from measurements of gaseous compressibility, transport, and crystal properties, within the limits of uncertainty of these larger distances potentials.

Growth of Potassium Chloride Crystals from Aqueous Solutions. I. The Effect of Lead Chloride

Single crystals of potassium chloride were grown from aqueous solutions under carefully controlled conditions of supersaturation, agitation, and impurity lead chloride concentration. The growth rate of the (100) face was determined.It was found that PbCl2 concentrations as low as 10−8 moles PbCl2/mole KCl decreased the rate of growth, and the retardation increased markedly with increasing PbCl2 concentration. The growth process changed from a layer type to a dendritic form over a small supersaturation range. Mass transfer rates of both KCl and PbCl2 from the solution to the crystal face were estimated and conditions delineated where each may be the rate‐controlling step. A mechanism is proposed to account for the formation of crystal clusters on the surface of KCl at slow stirring rates.

Intermolecular Potentials for the Systems CO2–CO2 and CO2–N2O

Experimental values of self‐diffusion and mutual diffusion coefficients, in the range −78° to 90°C, have been used to determine the intermolecular potentials for the systems CO2–CO2 and CO2–N2O. It has been assumed that a spherically symmetric potential of the form V (r)=4e[(σ/r)12—(σ/r)6] may be used and that the dynamics of the diffusion process are adequately described by the classical Chapman‐Enskog transport relations, which consider only elastic, binary collisions.The potential parameters derived from diffusion measurements have been compared with those obtained from measurements of viscosity, compressibility, the critical temperature, and the critical volume. It was not possible, for either system, to obtain a single set of parameters which could satisfactorily reproduce all the gaseous properties. It has been concluded that, for the present systems, the failure is due to one or both of the following: (1) inadequacy of the assumed potential form, (2) importance of inelastic collisions.

Calculation of Obstruction Effects on Rarefied Particle Streaming through Short Tubes

A numerical technique has been developed to study the behavior of the flow conductance through a cylindrical channel for various types of rarefied particles. The present method has the characteristics of being accurate and more efficient than the conventional Monte Carlo. In comparison with Clausing and DeMarcuss approaches of solving integral equations, the method is superior by being both versatile and flexible. The channel obstruction effects are characterized by a dimensionless parameter K which is computed in TUBNOF code. Some of the effects investigated are the specular reflection, adsorption, and absorption. The finite molecular mean free path effect on the rarefied particle flow is also considered. The technique can be very useful in studies involving sublimation, molecular beams, cold gas jets, and radiation streaming.