Index of content:
Volume 19, Issue 4, 01 April 1951
19(1951); http://dx.doi.org/10.1063/1.1748233View Description Hide Description
The Onsager and Kirkwood theories of polar dielectrics are extended to give expressions for the dielectric constant at high field strengths. The theory is applied in detail to water and simple formulas for the dielectric constant in terms of well‐known quantities are obtained. The results of the calculation are embodied in the formulawhere n is the optical refractive index,N 0 the number of molecules per unit volume, μ v the dipole moment of the water molecule, E is the field strength, and T the absolute temperature. L(x) is the usual Langevin function, and α and β are numerical factors which have the following values From these formulas it is shown that the reduction of the dielectric constant due to the saturation effect is of importance for fields greater than 106 volts per cm.
19(1951); http://dx.doi.org/10.1063/1.1748234View Description Hide Description
The electric moments of several imidazolidine derivatives in p‐xylene solution have been measured at various temperatures. It is suggested that the substances are mixtures of geometrical isomers which are in thermal equilibrium, the isomerism being due to the pyramidal arrangement of the valencies of the tervalent nitrogen.
From the temperature dependence of the moments, the energy difference between the two postulated isomers is calculated to be about 1.6 kcal/mole.
19(1951); http://dx.doi.org/10.1063/1.1748236View Description Hide Description
Following the theories of McMillan, Mayer, and Zimm, and extending the previous theories of the author, the second virial coefficient A 2 for high polymer solutions of the dumbbell model is calculated. The results are rigorous within the approximation of rigid‐body potential. A 2 varies smoothly with l/R, where R is the radius of spheres of the dumbbell and l is their separation. Based on the present results, comparisons between the gas and the lattice theories are made.
19(1951); http://dx.doi.org/10.1063/1.1748237View Description Hide Description
The mass spectra of the isotopic molecules CHCl3 and CDCl3 have been determined, using electron energies of 50 v and 70 v. It was found that the probability of dissociation of the C–H bond is approximately three times that for the dissociation of the C—D bond. The relative probability of dissociating H+Cl and D+Cl is the same as the relative probability of obtaining HCl+ and DCl+ ions, namely, about 1.6. Equal probability was observed for the dissociation of H+2Cl and D+2Cl. The probability of removing chlorine atoms is only slightly affected by the deuterium substitution.
19(1951); http://dx.doi.org/10.1063/1.1748238View Description Hide Description
The infrared spectra of CH2N2 and CD2N2 have been investigated in the gas phase between 4500 and 400 cm−1 using a Perkin‐Elmer spectrometer with LiF, NaCl, and KBr prisms.
The spectra have been correlated with a planar, nonlinear configuration for the diazomethane molecule with symmetry C 2v . The perpendicular type bands for both molecules are all overlapped or perturbed by neighboring absorption bands, so that no accurate values for the least moments of inertia have been obtained.
Two alternative schemes of assignments for the vibrational frequencies have been proposed and the thermodynamic functions for CH2N2 computed.
Potential‐function calculations have been carried out.
19(1951); http://dx.doi.org/10.1063/1.1748239View Description Hide Description
The structure of a microcrystalline platinum compound is derived from x‐ray data. Space group O h 3—Pm3n, a 0=5.69A, with 6 Pt at ±(¼ 0 ½, ↺), 8 O at ±(¼ ¼ ¼, ¼ ¾ ¾, ↺), and 2 Na at (000, ½ ½ ½), corresponding to the formula NaPt3O4. The coordinations are as follows: platinum 4 O and 2 Pt, oxygen: 3 O and 2 Na,sodium: 8 O. The substance is an ionic conductor.
Energy Transfer in the Photo‐Sensitization of Silver Halide Photographic Emulsions: Optical Sensitization, Supersensitization, and Antisensitization19(1951); http://dx.doi.org/10.1063/1.1748240View Description Hide Description
Many facts concerning optical sensitization of silver halide photographic emulsions point to the importance in the sensitization process of the migration of excitation energy from a dye molecule primarily excited by radiation to neighboring molecules in a cooperative layer. Individual dye molecules, however, appear capable of transferring energy to the silver halide without the intervention of energy migration, often with high efficiency, as is shown by relatively high quantum yields of sensitization at low concentrations of dye. If, as a result of increase in the concentration of dye, the sharp absorption bands indicative of exciton migration appear, the efficiency of transfer tends, in fact, to fall. Dyes in the cooperative state, however, are most susceptible to the increase of sensitization caused by supersensitizers. The regular periodic field which favors exciton migration decreases the probability of energy transfer to the halide, and the supersensitizer appears to act as a perturbation of this field at which the moving exciton is slowed down so as to facilitate transfer. Consistent with this explanation is the high quenching power of supersensitizers on the fluorescence sometimes exhibited in solution and in the adsorbed state by cooperative aggregates of dye molecules. The inverse of supersensitization, antisensitization by relatively small amounts of nonplanar dyes, is also observed. Here the migrating energy in the cooperative layer is dissipated as heat by the perturbing molecule, and is prevented from reaching the silver halide. Experimental evidence supporting these conclusions is furnished in detail, including correlations between optical sensitization and supersensitization with the type of absorptionspectrum of the adsorbed dye; the relations between the concentration of sensitizer, supersensitizer, and antisensitizer, and the efficiency of super‐ and antisensitization; the quenching of fluorescence of sensitizers by both types of perturbing molecules; and effects of nonplanar dyes on the photoconductivity of optically sensitized silver halide emulsions analogous to their photographic effects.
19(1951); http://dx.doi.org/10.1063/1.1748241View Description Hide Description
Shock front thicknesses in argon and nitrogen have been measured at Mach numbers of approximately 1.12, 1.28, and 1.40 by the reflectivity method. These thicknesses are significantly greater than predicted by Thomas and demonstrate the need for an improved theory which will cover the whole range of shock strengths. Reflectivitymeasurements have also been used to detect distortions of shock fronts in nitrogen owing to the lag of the rotational heat capacity. About 20 collisions are required for the rotational relaxation of nitrogen at room temperature.
19(1951); http://dx.doi.org/10.1063/1.1748242View Description Hide Description
The quantum properties of a Bose‐Einstein gas give rise to a critical adsorption into a mobile film. If the energy of adsorption is assumed to decrease with thickness according to a simple power law, the theory gives an isotherm in good agreement with observations on heliumadsorption at temperatures above the lambda‐temperature of liquid helium, for all gas pressures higher than 10 percent saturation.
With mixtures of He3 and He4isotopes the theory predicts appreciable adsorption of He3 only in the first or localized monolayer; all mobile monolayers should be practically pure He4 at all gas pressures. Comparison is suggested with the known isotopic constitution of the Rollin film below the lambda‐temperature.
19(1951); http://dx.doi.org/10.1063/1.1748243View Description Hide Description
The optical rotation of quartz has been observed in the infrared from 2.2 to 9.7μ. The measurements were made with a selenium film transmission polarizer and a similar analyzer; a Perkin‐Elmer Model 12B infrared spectrometer was used as the monochromator and detector. Anomalous rotatory dispersion was found at wavelengths longer than 3.7μ. A tentative qualitative interpretation of the anomaly is suggested.
19(1951); http://dx.doi.org/10.1063/1.1748244View Description Hide Description
The products of the reactions of sodium vapor with methyl and ethyl iodide vapors have been analyzed. It has been found that in the reaction with methyl iodide the principal product is ethane, but considerable amounts of methane, ethylene, and hydrogen are also formed. With ethyl iodide the principal product was butane, with lesser amounts of ethane, ethylene, methane, and hydrogen. It was also noted that in the latter system considerable amounts of propane appeared which could be accounted for as a pyrolysis product of the butane formed. The results have been compared with those obtained by others with similar systems and with the results obtained in the photolyses of mercury dimethyl and mercury diethyl. It is concluded that at low temperatures the dominant reaction for both ethyl and methyl radicals is for two to combine to form a saturated hydrocarbon. At higher temperatures, disproportionation reactions and reactions of the radicals with other molecules must be taken into account and eventually become the dominant reactions.
19(1951); http://dx.doi.org/10.1063/1.1748245View Description Hide Description
A simple molecular orbital treatment is presented to explain the bonding in trihalide ions, X3 −, XY2 −, and XYZ−, and bifluoride ion, HF2 −. The M.O.'s are formed from linear combinations of npσ halogen orbitals, and the 1s hydrogen orbital and stable bonding M.O.'s are obtained without the introduction of higher atomic orbitals. Applications are suggested in prediction of other stable species and low energy reaction intermediates.
19(1951); http://dx.doi.org/10.1063/1.1748246View Description Hide Description
Polarized radiation is used to study the pleochroism of aligned specimens of polythene, Nylon, polyvinyl alcohol, polyvinyl chloride, and polyvinylidene chloride, in the 0.8–2.5μ overtone and combination region. Assignments of observed absorption bands to various vibration modes of (coupled) >CH2, N–H, and C=O groups are attempted. The symmetry of an infinite planar‐zigzag >CH2 chain is discussed as an approximation to that of polythene and, to a lesser extent, Nylon. Some limitations in the interpretation of observed pleochroism and in the application of selection rules are discussed. A pleochroism study, with unpolarizedradiation, is made of the molecular alignment in oriented ``Parowax.'' A study is made also of the rupture of the intermolecular N–H≡O bonds in molten and premolten Nylon.
19(1951); http://dx.doi.org/10.1063/1.1748247View Description Hide Description
The absorption and emission spectra of the thallium‐activated potassium chloride phosphor at various temperatures has been computed theoretically. An ionic model is used. The radial charge densities of free Tl+ in the ground 1 S 0 state and in the excited 3 P 1 0 state are evaluated using the Sommerfeld modification of the Fermi‐Thomas method for the core and the Hartree self‐consistent field method for the two outershell electrons. From these wave functions and from the known ionic radius, polarizability, and repulsion energy constant ρ for the ground state, these parameters are evaluated for the Tl+ in the excited state interacting with Cl−. The variation of repulsion energy with interatomic distance a is shown to be equal to the variation of S 2/a with a, where S is an overlap integral. The Tl+ in the 1 S 0 and the 3 P 1 0 states are substituted in dilute concentrations for the K+ in KCl, and the change in total energy of the system is calculated as a function of the change in the Tl+ nearest Cl− distance Δa with the condition that the remainder of the lattice rearranges to minimize the total energy. Madelung, exchange repulsion, van der waals, ion‐dipole and coulomb overlap interactions are included. The absorptionspectrum is computed by recognizing that the various atomic configurations of the system in the ground state have probabilities in accord with a Boltzmann function. The emission spectrum is similarly determined by summing over configurations of the system in the excited state. The computed spectra at various temperatures are found to be in good agreement with experiment. In addition, new insight is obtained on the detailed mechanism of solid‐state luminescence.
19(1951); http://dx.doi.org/10.1063/1.1748248View Description Hide Description
A simple form for the expansion of the distribution function in phase space, by means of modified hermite polynomials, is set up. Expressions for the density, temperature and the components of the mass current, of the strain tensor, and of the heat current, in terms of the coefficients in the expansion, are obtained. A simple method for obtaining the infinite set of integro‐differential equations imposed upon the coefficients in the expansion of the distribution function by the Gibbs' principle of conservation of density‐in‐phase is outlined. Results obtained for the dissipative processes of heat conduction and of viscosity in liquids are summarized.
19(1951); http://dx.doi.org/10.1063/1.1748249View Description Hide Description
A liquid bireactant system, consisting of a stoichiometric mixture of anhydrous hydrazine and hydrogen peroxide, is evaluated in terms of the resultant equilibrium temperature‐pressure‐density relationship corresponding to chamber pressures over the range 10,000 to 185,000 pounds per square inch. The analysis is based on the use of the reactants both at constant volume and at constant pressure, and data pertaining to the mole fractions of components of the product gas, its molecular weight and covolume are included for each case.
19(1951); http://dx.doi.org/10.1063/1.1748250View Description Hide Description
The reaction of methylcyclopentane with photo‐excited Hg 6(3 P 1) atoms was investigated in a static system at 29.35±0.01°C, over a range of initial pressures of 5–110 mm. After an initial slight pressure rise, the reaction exhibited a linear pressure decrease, the magnitude of which increased linearly with initial pressures of methylcyclopentane above 15 mm. The average rate of hydrogen formation also increased with initial pressure of methylcyclopentane and decreased with time in the course of a run. The products found were hydrogen, methylcyclopentenes, and a heavy fraction with the formula C12H22. Upon the basis of chemical and physical properties, strengthened by kinetic considerations, it was concluded that the C12H22compound was predominantly dimethyldicyclopentyls. Quantum yields reached a maximum of 0.44 for hydrogen formation and 0.42 for methyl‐cyclopentane consumption.
The mechanism postulated proceeds through an initial carbon‐hydrogen bond split, thus:
This mechanism yields rate expressions which confirm the trends observed in the experimental work.
19(1951); http://dx.doi.org/10.1063/1.1748251View Description Hide Description
Recently, much interest has been focused upon the preparation of monodispersed colloids using the ``growth by diffusion'' process. Although these colloids are useful tools in experimental procedures, no well‐established reason has been given to explain why the ``growth by diffusion'' method should produce such uniform dispersions. In this paper it is shown that an assembly of competing particles, growing by diffusion, develop the squares of their radii at equal rates. This condition provides a mechanism leading towards uniformity.
A method, based on this equal square rule, is suggested for the determination of size distributions in polydispersed systems.
19(1951); http://dx.doi.org/10.1063/1.1748252View Description Hide Description
If the specific heatC(T) of a solid is given as a function of temperature from T=0 to ∞ with infinite accuracy, the frequency spectrum f(ν) is uniquely determined. What information about f(ν) can be derived from specific heat data of experimental accuracy? The following conclusions give the answer.
(1) Experimental specific heats determine accurately the low frequency part of the frequency spectrum but allow a latitude, wide enought to fit almost any theory, for its high frequency part.
(2) In a Debye plot (effective Debye temperature θ versus T) peaks and dips in the region 0<T<θ/10 represent dips and peaks in the low frequency part of the frequency spectrum. The correspondence is so simple that it can be interpreted at a glance. The peaks and dips are superimposed on a simple Debye spectrum and presumably have a direct physical meaning, in terms of lattice irregularities. Only their centers and total weights are obtainable, so that they act effectively as single Einstein frequencies.
(3) In the region θ/5<T<∞ all information obtainable about f(ν) consists of the first few even moments (three for specific heat errors of order one percent, five for 0.1 percent). These can be represented respectively by two or three weighted equivalent Einstein functions without direct physical meaning.
(4) The region θ/10<T<θ/5 corresponds to the high frequency part of the frequency spectrum, but hardly any information can be derived here.
19(1951); http://dx.doi.org/10.1063/1.1748253View Description Hide Description
Most studies of the excitation of molecular vibrations in gas mixtures have been carried out using very low concentrations of the B type ``impurity'' gas to excite basic gas A. It is pointed out in this paper that such studies very likely fail to detect the possible importance of triple collisions of the AAB type. Indeed, data of Eucken and Aybar on mixtures containing quite high concentrations of B molecules is felt to furnish strong evidence for the triple collision excitation of COS molecules by argon and by nitrogen molecules.