Index of content:
Volume 18, Issue 6, 01 June 1950
18(1950); http://dx.doi.org/10.1063/1.1747773View Description Hide Description
Measurements have been made of the temperature‐dependence of electrical conductivity and thermal e.m.f. on ZnF2 and ZnF2:Mn, and of the Hall coefficient and rectifying power at 25°C on ZnF2. Both ZnF2 and ZnF2:Mn are N‐type impurity semiconductors. The presence of MnF2 in ZnF2 decreases the electronic conductivity by a factor of about 103, indicating a decrease in the concentration of electron donors by oxidation. A marked dependence of the temperature variation of conductivity on heat treatment has been observed. Contrary to the simple theory, the absolute values of the thermal e.m.f. increase with temperature. From the Hall coefficient and conductance at 25°C of heat‐treated ZnF2, a concentration of free electrons of 3×1016 cm−3 and a mean free path of 6.7×10−8 cm are deduced. ZnF2 rectifies in the expected direction.
18(1950); http://dx.doi.org/10.1063/1.1747774View Description Hide Description
18(1950); http://dx.doi.org/10.1063/1.1747775View Description Hide Description
The kinetic behavior of Br80 produced by neutron capture has been investigated in gaseous systems containing ethyl bromide, ethylene and hydrogen bromide. The distribution of active bromine between organic and inorganic form has been shown to be principally dependent on the ethylene pressure. A kinetic scheme, incorporating a ``hot atom'' reaction, is postulated and shown to be in agreement with the experimental facts. Additional experimental tests of critical points in the proposed scheme have been successful.
18(1950); http://dx.doi.org/10.1063/1.1747776View Description Hide Description
Lithium,magnesium,calcium,aluminum, manganous, cobaltous, nickelous, cupric, zinc,cadmium and thorium nitrates, and nitric acid, show an absorption in tertiary butyl alcohol solution which is different from that of dilute aqueous solutions of nitrates. The most marked effects are shown by the transition elements with partially completed d shells. The variety of the spectra indicate that a single change, such as the rearrangement of the normally planar nitrate ion into a pyramidal form, cannot account for nitrate spectrum changes.
18(1950); http://dx.doi.org/10.1063/1.1747777View Description Hide Description
Thermodynamic equations are derived which should be useful in the analysis of experimental data and theoreticalmodels referring to the adsorption of a one‐component gas on an elastic adsorbent. This problem is closely related to the thermodynamics of adsorption of a solute from a liquid solution onto an elastic adsorbent immersed in the solution (e.g., a myosin thread).
18(1950); http://dx.doi.org/10.1063/1.1747778View Description Hide Description
The relative rates of the reactions of hydrogen iodide and deuterium iodide with methyl iodide were studied by a competitive method at 310° and 250°C. The analysis of hydrogen‐deuterium mixtures was accomplished by means of a simple viscometer with an accuracy of 0.5 percent. It was found that hydrogen iodide reacts about 1.4 times as fast as deuterium iodide at both temperatures. These results are discussed in terms of Eyring's theory of absolute reaction rates and a simple model.
18(1950); http://dx.doi.org/10.1063/1.1747779View Description Hide Description
The intensity of fluorescence of solutions of chlorophyll (either a or b) is sensibly independent of concentration, for values less than 2×10−3 m. At higher concentrations, the fluorescence decreases with increasing concentration, conforming to the empirical equation, If,max/If =1+4300m 2. The absorptionspectrum of chlorophyll a is the same at 0.02m as it is for very dilute solutions. These results, as well as the observed temperature coefficient of the fluorescent intensity, indicate that the self‐quenching of chlorophyll solutions is not due to the formation of non‐fluorescent dimers nor to collisions of the second kind, but is very probably related to the resonance exchange of excitation (16, 17) between an excited and normal chlorophyll molecule.
Measurements of the fluorescence intensity of solutions containing mixtures of chlorophylls a and b indicate that chlorophyll b can sensitize the fluorescence of chlorophyll a, and that the fluorescence of chlorophyll b is more strongly quenched by a than it is by itself.
18(1950); http://dx.doi.org/10.1063/1.1747780View Description Hide Description
Violanthrone, iso‐violanthrone, and pyranthrone have electrical conductance to a certain degree. This is due to the molecular structure of these compounds, which are made of the network planes of carbon atoms, and to the assumption that the π‐electron contribute to the electrical conduction.
The electrical resistivity of violanthrone, iso‐violanthrone, and pyranthrone was measured. The values at 15°C are as follows; 2.3×1010 ohm‐cm, 5.7×109 ohm‐cm, and 3.9×1015 ohm‐cm respectively. The resistivity decreases with increasing temperature in every case, and a good linear relationships is observed between the logarithm of the resistivity and the reciprocal of the temperature. As the activation energy of the electrical conductance, the following values were observed; 0.39 ev, 0.375 ev, and 0.53 ev respectively. The values for violanthrone and iso‐violanthrone suggest that they can be assumed to be intrinsic semi‐conductors.
18(1950); http://dx.doi.org/10.1063/1.1747781View Description Hide Description
The infra‐red absorptionspectrum of gaseous tetrafluoroethylene between 2 and 22μ has been investigated with a prism spectrometer of high resolution, and the region from 20 to 37μ has been surveyed with a KRS−5 prism. The Raman spectrum of C2F4 gas has been photographed with a three‐prism glass spectrograph of linear dispersion 15 A/mm at 4358A, and semiquantitative polarization measurements have been made. All of the 12 fundamental vibration frequencies have been determined, although with some uncertainty for three frequencies obtained from combination bands. The spectra have been interpreted in detail.
18(1950); http://dx.doi.org/10.1063/1.1747782View Description Hide Description
The equations of hydrodynamics—continuity equation,equation of motion, and equation of energy transport—are derived by means of the classical statistical mechanics. Thereby, expressions are obtained for the stress tensor and heat current density in terms of molecular variables. In addition to the familiar terms occurring in the kinetic theory of gases, there are terms depending upon intermolecular force. The contributions of intermolecular force to the stress tensor and heat current density are expressed, respectively, as quadratures of the density and current density in the configuration space of a pair of molecules.
18(1950); http://dx.doi.org/10.1063/1.1747783View Description Hide Description
Using light scattering, the mean square molecular radius and length of a number of samples of polystyrene have been measured as a function of solvent and temperature. Molecular weights, intrinsic viscosities, and ``osmotic second virial coefficients'' have also been determined on many of the samples. From the data it may be concluded: (1) that polystyrene molecules are extended and stiffened by steric interactions of the phenyl groups; (2) that the molecules are largely unbranched; (3) that the heat of dilution is negative in some solvents, contrary to the usual situation in hydrocarbon systems; (4) that the osmotic second virial coefficient depends strikingly on molecular weight for a given solvent; (5) that there is a good correlation between this coefficient and the mean square radius at a given molecular weight; (6) that the intrinsic viscosity is strictly proportional to a power of the molecular weight over the molecular weight range from 2,000 to 2,000,000, but that deviations occur at lower molecular weights; (7) that the intrinsic viscosity and mean square radius are functions of solvent at high molecular weights but not at very low molecular weights. Theoretical concepts necessitated by these observations are discussed briefly.
18(1950); http://dx.doi.org/10.1063/1.1747784View Description Hide Description
A kinetic theory of phase transitions in two‐component systems is presented which is applicable to the transitions, vapor to liquid and liquid to liquid. The rate of the transition is characterized by a two‐dimensional vector which can be used in conjunction with the equation of continuity to develop a partial differential equation which determines the kinetics of the process.
A new type of energy surface is introduced, and an investigation of its salient features enables one to simplify the solution of the differential equation mentioned above. This purely kinetic treatment makes possible the evaluation of the unknown coefficient found in the older quasi thermodynamic treatment of transition rates in two component systems.
18(1950); http://dx.doi.org/10.1063/1.1747785View Description Hide Description
The temperature variation of the fractionation of oxygen in exchange reactions between dissolved carbonate and water and between calcite and water and calculated on theoretical grounds, and checked experimentally. In the course of the experiments it was necessary to investigate several methods of decomposing calciumcarbonate to carbon dioxide for mass spectrometeranalysis. A method was developed for growing calciumcarbonate from solution with the same isotopic composition as the carbonate shells of organisms produced at the same temperature from water of the same isotopic composition, and the results of these experiments at various temperatures are expressed in an equation relating the temperature of formation with the isotopic composition of the calciumcarbonate and of the water.
18(1950); http://dx.doi.org/10.1063/1.1747786View Description Hide Description
The hypothesis is made that the thermodynamic energy and the virtual work done in a reversible process are statistical averages of the corresponding mechanical quantities and that the averages comply with the laws of thermodynamics. These assumptions are shown to be sufficient for deriving the canonical distribution so far as the distribution on the energy scale is concerned.
18(1950); http://dx.doi.org/10.1063/1.1747787View Description Hide Description
Integrated intensities of the 2900, 1460, and 1370 cm−1 infra‐red absorption bands have been measured for twelve aliphatic hydrocarbons. The results are interpreted on the basis that the hydrocarbon molecule behaves like a non‐interacting mixture of [Complex chemical formula] structural groups. The unit structural group intensities are 4.41×10−7, 3.81×10−7, and 1.39×10−7 cm2/(molecule second) for the CH3, CH2 and CH groups respectively in the 2900 cm−1 band; 0.544×10−7 and 0.232×10−7 for the CH3 and CH2 groups in the 1460 cm−1 band; and 0.394×10−7 for the CH3 group in the 1370 cm−1 band. Values calculated for the CH bonddipole moment divided by the equilibrium CH bond length vary from approximately 0.2×10−18 to 0.4×10−18 c.g.s. units. Values of approximately −0.75×10−10 are obtained for the change in CH bonddipole moment with change in CH bond length.
18(1950); http://dx.doi.org/10.1063/1.1747788View Description Hide Description
The fraction of the radioactive energetic chlorine atoms, formed by radiative neutron capture, that react with inactive carbon tetrachloride to give radioactive carbon tetrachloride, or with a solvent to give other radioactive organic halides, was studied as a function of composition in solutions of carbon tetrachloride in silicon tetrachloride, cyclohexane, and benzene. The reactions of similarly formed atoms were also studied for solutions of chlorine in cyclohexane and in benzene.
No significant effect of the temperature of the bombarded solution or of the energy of the neutrons was found.
The results are examined in terms of a theory which predicts the concentration dependence of some of the observed reactions, and alternative descriptions are suggested. It is concluded that the observed reactions occur before the recoil atoms are reduced to thermal equilibrium, and that particular reactions predominate in certain energy ranges.
18(1950); http://dx.doi.org/10.1063/1.1747789View Description Hide Description
A probability function has been derived which characterizes the variation of an interatomic distance affected by the restricted internal rotation of a molecule. The probability function takes into account the general vibration of the molecular frame in addition to the internal libration. The theory and practice are developed for determining the values of the parameters in the probability function directly from experiment. In addition the contribution from this probability distribution to the intensity of electron scattering is derived.
18(1950); http://dx.doi.org/10.1063/1.1747790View Description Hide Description
A calculation, involving vibrational potential functions of a general quadratic type restricted to small displacements, has been used to evaluate force constants, singly or in linear combination, for the fluoromethanes, and simultaneously, to confirm new assignments of the fundamentals of CF3H and CF2H2 arising from a detailed experimental study of their Raman spectra. The results indicate considerably greater bond strengths than expected from a mere extrapolation of the properties of analogous halogen derivatives. Particularly significant is the order of interaction terms involving the C–F stretching and the F–C–F bending motions of the molecules.
18(1950); http://dx.doi.org/10.1063/1.1747791View Description Hide Description
Depolarization measurements have been made on the Raman spectrum of fluoroform and difluoromethane. Several new lines were observed, all of which had previously been found in infra‐red absorption. Several weak lines reported previously could not be found and presumably must be ascribed to impurities in the material used by earlier investigators. The analyses given for the vibration spectra now seem to be in plausible agreement with all the known spectroscopic data on these molecules.
18(1950); http://dx.doi.org/10.1063/1.1747792View Description Hide Description
Color centers have been formed in alkali halide crystals by exposing them to x‐rays, electron bombardment, and pile irradiation, and their stability with respect to temperature and light bleaching has been investigated. In general such crystals contain centers of non‐uniform stability. The lower the temperature at which the color centers have been produced, the more unstable they are on the average. In the absorption spectra taken at low temperature of crystals irradiated at low temperature new bands appear on the short wave‐length side of the F‐band which are never observed in crystals irradiated at room temperature and which, on warming the crystal to room temperature, vanish together with a part of the F‐centers. It is suggested that the instability of some of the color centers formed at low temperature is connected with the presence of these new absorption bands.