Index of content:
Volume 36, Issue 2, 15 January 1962
36(1962); http://dx.doi.org/10.1063/1.1732497View Description Hide Description
The manner in which molecular additives inhibit the reaction of (n, γ) activated I128 with CH4 was determined in an effort to observe indirectly reactions of I128 with the additives. The data suggest that (1) O2, N2, and CF4 serve only to remove excess I128 kinetic energy; (2) the ionization potential of O2 is greater than 12.16 ev, the potential energy of I+(1 D 2); (3) the ionization potential of C2F6 is less than 12.16 ev; (4) CH3I, CF3I, n‐C3H7I, and C6H6 inhibit the reaction principally as a result of I++additive ion‐molecule reactions and/or physical quenching.
36(1962); http://dx.doi.org/10.1063/1.1732498View Description Hide Description
The absorption of infrared radiation by carbon monoxide has been measured at wavelengths of 4.60, 4.67, and 4.72 μ for temperatures from 1160° to 2300°K. The test gas was heated to the desired temperatures by shock compression. The carbon monoxide optical density varied from 4 to 11 atm‐cm; total gas pressures ranged from 1.40 to 3.60 atm. Absorption coefficients, presented as averages over slitwidth and total pressure, varied from 0.091 to 0.040 atm—1 cm—1 at 4.60 μ, 0.057 to 0.031 atm—1 cm—1 at 4.67 μ, and 0.065 to 0.026 atm—1 cm—1 at 4.72 μ, with higher values corresponding to lower temperatures. A pressure dependence of absorption was observed and an empirical correction assuming the logarithm of transmission proportional to the fourth root of total pressure was found to render Beer's law plots linear. Absorption coefficients were calculated by averaging over slitwidth an expression requiring a knowledge of the pressure dependence of integrated absorption. A comparison of these calculations with the observed values indicates quantitative agreement for 4.60 and 4.72 μ, and qualitative agreement for the temperature dependence of absorption at 4.67 μ.
36(1962); http://dx.doi.org/10.1063/1.1732499View Description Hide Description
The cubic to hexagonal phase transformation of the systems Nd2O3–Sm2O3 and Nd2O3–CeO2 has been studied by x‐ray diffraction methods for zero to 20% atomic substitution of Nd by Sm or Ce. Diffraction patterns were obtained at room temperature after heat treatments between 600° and 1400°C. The patterns indicate that at elevated temperature the oxides containing Ce form a solid solution of the approximate cation composition 75% Nd—25% Ce together with excess Nd2O3. At 1400°C the solid solution was found to be cubic and the excess Nd2O3 to be hexagonal. The oxides containing Sm form solid solutions with cation ratios corresponding to those of the original mixture. They transform into the hexagonal phase via a monoclinic phase which is isomorphous with the B form of Sm2O3. Preferred orientation effects were observed on pressed powder disks of Eu2O3 and Nd2O3 below and above their respective transition temperatures. They support an approximate identification of the monoclinic a, b, and c axes with the cubic [11̄0], , and  directions and suggest the equivalence of the hexagonal c axis and cubic  direction.
36(1962); http://dx.doi.org/10.1063/1.1732500View Description Hide Description
The mass spectra of some 10 representative organic compounds were obtained by using electrons with an energy up to 12 kev. Modifications of the ion source were made to reduce field penetration by the filament potential and emission of secondary electrons in the ion box. The mass spectra showed some small changes from 50 to 1000 ev. The changes were due to decreases in the abundance of ions of low relative intensity. These were ions which could be produced only by a succession of fragmentation processes. The mass spectra remained remarkably constant with further increase of the voltage. The significance of the results for gas phase radiolysis by α particles and β rays is briefly considered.
36(1962); http://dx.doi.org/10.1063/1.1732501View Description Hide Description
The probability distribution of the radius of gyration of unbranched polymer chains is discussed. The characteristic function of the distribution is presented in closed form, and calculations are the made of the semi‐invariants, moments, and behavior of the probability at very large and very small values of the radius of gyration.
36(1962); http://dx.doi.org/10.1063/1.1732502View Description Hide Description
A theory is given of the sharp viscosity rise in mixtures in the critical mixing region. Good agreement with the experimental dependence of viscosity on composition and temperature is found. The method involves a calculation of the entropy production through diffusion which results when a mixture in a state of composition fluctuation is caused to have a velocity gradient. The long wavelength part of the spectrum of composition fluctuations is intense and very easily distorted by a velocity gradient in the critical region. The return to uniform composition through diffusion dissipates energy, and the loss is interpreted as an excess viscosity. It is shown that this method, which requires no knowledge of the intermolecular potential but only of the long‐range part of the radial distribution function, correctly gives the viscosity of a dilute 1–1 electrolyte.
36(1962); http://dx.doi.org/10.1063/1.1732503View Description Hide Description
Dielectric constants in the density range 0 to 4 moles/liter have been measured at temperatures between 25° and 75°C. Both gases show significant increases of the Clausius‐Mossotti function with density attributable to pair interactions. In CO2, these are consistent with the theory of quadrupole‐induced dipoles for a molecular quadrupole moment of about 5×10—26 esu cm2. In ethylene, the increased effect at higher temperatures is contrary to the theory, which is given in a more general form suitable at high temperatures for molecules such as ethylene, which lack axial symmetry. It is shown that for both gases the theory may be somewhat inaccurate at ordinary temperatures because effects of quadrupole coupling energies have not been adequately treated. Measurements of mixtures with a second gas of highly symmetrical molecules are proposed as a promising means of studying the questions raised by those results.
Infrared Spectra of Metal Chelate Compounds. VI. A Normal Coordinate Treatment of Oxalato Metal Complexes36(1962); http://dx.doi.org/10.1063/1.1732504View Description Hide Description
The infrared spectra of 10 oxalato complexes have been obtained in the frequency range 4000 to 300 cm—1. A normal coordinate treatment made on the 1:1, metal:ligand model of the chelate ring of tris‐(oxalato)‐Cr(III) resulted in the assignment of metal‐oxygen stretching bands in the range between 600 and 300 cm—1 for various oxalato complexes. The force constants and the band assignments obtained are compared with those of the previous normal coordinate analysis based on the free oxalato ion. Relationships between the metal‐oxygen and the carbon‐oxygen stretching frequencies are discussed.
Infrared Spectra of Metal Chelate Compounds. VII. Normal Coordinate Treatments on 1:2 and 1:3 Oxalato Complexes36(1962); http://dx.doi.org/10.1063/1.1732505View Description Hide Description
Normal coordinate treatments have been made on the square planar 1:2 oxalato complex of Pt(II) and the octahedral 1:3 oxalato complex of Cr(III), and the results were compared with those obtained with simple 1:1 complexes. It was found that coupling between the ligands in the square planar 1:2 complex is small whereas coupling between the ligands in the octahedral 1:3 complex is appreciable. Observed differences of the spectra between 1:1 and 1:2 oxalato complexes of Pt(II) and between 1:1 and 1:3 oxalato complexes of Cr(III) and Co(III) are in good agreement with the results of these calculations.
36(1962); http://dx.doi.org/10.1063/1.1732506View Description Hide Description
The infrared spectra of twenty Co(III) carbonato complexes have been measured in a range between 4000 and 300 cm—1. Normal coordinate treatments were made with a model based on the unidentate and bidentate forms of the 1:1 (metal/ligand) complex. The theoretical band assignments and force constants obtained by these calculations confirm the validity of the previous qualitative conclusions based on the differences of symmetry and the frequency shifts of the unidentate and bidentate complexes. The Co(III)‐O stretching bands were located at 440∼380 (antisymmetric) and at 400∼350 (symmetric) for the bidentate complexes, and at 360∼340 cm—1 for the unidentate complexes.
36(1962); http://dx.doi.org/10.1063/1.1732507View Description Hide Description
When a distribution of relaxation times is associated with thermally activated processes in a material and arises solely from a distribution of activation energies, the form of the relaxation‐time distribution may be restricted. In this case, the temperature dependence of some of the parameters which enter into the distribution function will be uniquely determined. The Wagner relaxation‐time distribution function may be made entirely consistent with a distribution of activation energies by taking its shape parameter temperature dependent, but the Cole‐Cole, Fuoss‐Kirkwood, and Davidson‐Cole distribution functions can only be made approximately consistent in the separate limits of very wide and narrow distributions of relaxation times. The temperature dependences of their parameters found experimentally for thermally activated processes is compared where possible with that required for the distribution of activation energies situation. A new relaxation‐time distribution is proposed which is completely consistent with a distribution of activation energies in an activated process and which can describe a variety of experimental data.
36(1962); http://dx.doi.org/10.1063/1.1732508View Description Hide Description
Vapor pressures of zirconium over zirconium diboride have been measured by the Knudsen technique over the temperature range 2150° to 2475°K. A new type of apparatus was constructed and used successfully in the study.
Zirconium diboride was determined to evaporate congruently at a composition of ZrB1.906(+0.025 or —0.010) by heating solid pressed plugs of both zirconium‐rich and boron‐rich material to constant composition at 2400°C to 2500°C. The over‐all reaction isThree series of measurements were made using tungsten crucibles and different orifice sizes. Second‐law and third‐law treatments of the data did not agree. Thermodynamic calculations were made which indicated that water vapor at low background pressures would produce volatile oxides of both zirconium and boron. This reaction was investigated by adding water vapor to the system and the increased transport of zirconium was clearly demonstrated. Accordingly, each pressure measurement was corrected by a factor β, constant for each series, related to the background pressure.
From the corrected pressures, values of ΔH 0 o for the reaction were computed by the third‐law treatment. From the three series a vaporization coefficient of 0.025±0.010 was computed, leading to an equilibrium ΔH 0 o of 458.3±6.5 kcal/mole for reaction 1, or a partial pressure of Zr over ZrB1.906 of 2.38×10—10 atm±20% at 2000°K. The variance between this and an expected value of 477.4 kcal/mole is presumed to be related, at least in part, to discrepancies in the heat of vaporization of zirconium.
The results verify the prediction that the Zr–B system exhibits a congruently evaporating phase and suggest that the congruently evaporating composition in many high‐temperature systems will occur at nonstoichiometric compositions.
36(1962); http://dx.doi.org/10.1063/1.1732509View Description Hide Description
Electron‐coupled spin‐spin interaction constants J C–H for a series of formyl compounds are presented and interpreted. It is concluded that J C–H is essentially independent of the polarity of the C–H bond and provides the best experimental measure of the hybridization of the carbon atomic orbital used in the bond. Some of the C–H bonds involve carbon orbitals of surprisingly high s character, especially in view of the available data on the bond lengths. It is suggested that the electrostatic interaction between the C–H proton and the π electron density may play an important part in fixing the lengths of these C–H bonds.
36(1962); http://dx.doi.org/10.1063/1.1732510View Description Hide Description
Apparent molar volumes of some metals and salts in dilute liquid ammonia solutions at 0° have been measured with a direct‐mixing dilatometer. There is little volume change involved in dissociation of diamagneticmetal species, but a large volume decrease results from dissociation of ion‐pairs in salt solutions. Volumes are estimated for single ions and the solvated electron.
36(1962); http://dx.doi.org/10.1063/1.1732511View Description Hide Description
Heats of solution in ammonia at 25° have been measured for Li, Na, and K at concentrations down to 0.005 M, and for Na in the presence of NaI. Dilution is endothermic, and the heat of dilution is greater in the presence of added Na ion; these results support the Becker‐Lindquist‐Alder theory of the solutions.
36(1962); http://dx.doi.org/10.1063/1.1732512View Description Hide Description
Sm2+ which occurs as impurity in very small concentrations in LaCl3 has a very distinctive fluorescencespectrum which resembles in all details that of Eu3+. Excitation is through the very strong continuous absorption to 4f 55d in the visible. The energy is transferred to the stable states 5 D 0 and 5 D 1 of the 4f 6 configuration separated by 1330 cm—1 from which emission to the components of the ground multiplet 7 F is observed. The fact that in all cases the spatial degeneracy is completely removed shows that the field around the Sm2+ ion has low symmetry even though the La3+ ion which it replaces is in an hexagonal field.
36(1962); http://dx.doi.org/10.1063/1.1732513View Description Hide Description
The electron spin resonancelinewidth for Mn(H2O)6 ++ in aqueous solution is examined in the temperature range 15° to 90°C, at frequencies of 9.4 and 24 kMc. The results are interpreted on the assumption that the linewidth is a measure of the spin‐lattice relaxation rate. As expected from previous NMR measurements of proton nuclear relaxation in such solutions, the linewidth decreases with increasing temperature, and is smaller at 24 kMc than at 9.4 kMc. The ESR results are approximately in agreement with the NMR results if the electronic relaxation time is assumed to follow a Bloembergen equation with the correlation time behaving with temperature according to an activation energy of 2.5 kcal/mole.
36(1962); http://dx.doi.org/10.1063/1.1732514View Description Hide Description
The theoretical relationships involved in thermal diffusion have been re‐examined. It has been shown from strictly thermodynamic considerations that in dilute solid solutions the quantity ``heat of transport,'' or Q *, can be expressed as the sum of two distinct contributions.
One of these is the partial molal heat of solution of the solute, referred to pure solute as the standard state. The second is a portion, designated the thermal gradient effect, which exists independent of solubility relationships. The latter has been shown to be obtainable from a plot of log solute activity vs reciprocal temperature when the activity is referred to pure solute as the standard state. Comparison of heat of transport with heat of solution in interstitial solid solutions where data are available indicate that the thermal gradient effect is small in these systems.
Electron‐Molecule and Electron‐Atom Collision Cross Sections from a Cyclotron Resonance Study of Flame Gases36(1962); http://dx.doi.org/10.1063/1.1732515View Description Hide Description
Low‐pressure (6–40 mm Hg) acetylene‐oxygen flames, diluted with various proportions of nitrogen and the rare gases, were investigated. The temperature range covered was 1600–2400°K. At 2200°K, the following results were obtained for the collision cross sections: undiluted, near‐stoichiometric C2H2–O2flame gases, 40 A2; nitrogen 30 A2, decreasing with temperature; helium, 27 A2, decreasing with temperature; argon, 7 A2; neon, 5 A2; water, about 80 A2; carbon dioxide about 37 A2. These values are up to three‐fold larger than the cross sections for collisions with electrons reported for systems other than flame gases.
36(1962); http://dx.doi.org/10.1063/1.1732516View Description Hide Description
X‐ray diffraction patterns obtained from liquid neon at six conditions of temperature and pressure ranging from the triple point to the critical point were used to calculate the corresponding radial atomic distribution functions. Areas and locations of the first peaks in the distribution curves varied from 8.4 atoms at 3.18 A near the triple point, to 4.3 atoms at 3.26 A near the critical point. Experimental intensity patterns for temperatures nearest the triple and critical points were compared with intensity patterns calculated by the method used by Fournet. Small‐angle scattering patterns obtained at 15 conditions of temperature and pressure near the critical point were used to calculate corresponding radii of gyration and characteristic functions.