Volume 22, Issue 6, 01 June 1954
Index of content:

Effect of Pressure on Diffusion in Polymer Solutions
View Description Hide DescriptionDiffusion measurements have been made using two molecular weights of polysulfide polymer at 25°C and 59°C in toluene solution. One isotherm for the low molecular weight was obtained in chloroform solution.
The results indicate that there are two mechanisms of motion in solution. At low pressure the dominant mode involves the expulsion of a solvent molecule from the coiled polymer. At high pressure the motion is segmental.

Infrared Absorption Studies of Aqueous Complex Ions: I. Cyanide Complexes of Ag(I) and Au(I) in Aqueous Solution and Adsorbed on Anion Resin
View Description Hide DescriptionTechniques are described for obtaining infrared absorption spectra of complex cyanide anions in aqueous solution and adsorbed on anion resin. In the system AuCN–KCN–H_{2}O, only the soluble complex ion Au(CN)_{2} ^{—} is observed; the molar extinction coefficient (ε) is 477±25 mole^{—1} liter cm^{—1} at 2147±1 cm^{—1}. When Au(CN)_{2} ^{—} is adsorbed to the extent of 47 weight percent on Dowex‐A‐1 resin, its absorption maximum appears at 2138 cm^{—1}. Three distinct silver cyanide complex ions were observed in aqueous solution: Ag(CN)_{2} ^{—}, ε=264±12 at 2135±1 cm^{—1}; Ag(CN)_{3} ^{—2}, ε=397±23 at 2105±1 cm^{—1}; Ag(CN)_{4} ^{—3}, ε=556±83 at 2092±1 cm^{—1}. Approximate values (calculated in terms of activities) of the dissociation constants for the tri‐ and tetra‐cyanide complexes into the next lower complex are K_{3, 2}=0.20±0.05 mole liter^{—1}, and K_{4, 3}=13,4±4 mole liter^{—1}, respectively. Over ranges of silver concentrations from 0.1—1.0 formal and of free CN^{—} ion concentrations from 0.05—1.5 molar, the concentrations of Ag(CN)_{2} ^{—}, Ag(CN)_{3} ^{—2} and Ag(CN)_{4} ^{—3} can be calculated to within 5 percent (absolute) using values of the constants adjusted to best overall fit; in terms of concentrations, K_{3, 2} ^{ c }=0.108 and K_{4, 3} ^{ c }=2.85 mole liter^{—1}.

Order‐Disorder Phenomena
View Description Hide DescriptionThe thermodynamics of the order‐disorder transition in β brass is explored by making the assumption that the energy difference between the disordered and ordered state has the form E _{0}—BT ^{2}. Such a law suggests itself if the coupling of the thermal expansion to the order‐disorder transformation is emphasized and the effect of short range order is neglected. The constant B is shown to be related to the lattice vibrations of both the ordered and disordered phases. A very rough estimate of B was obtained from electrical resistivitymeasurements, the assumption being made that the connection between the resistivity and the vibrational frequency, ρ∝T/MΘ^{2}, holds. A heat capacityversus temperature curve, which was calculated on the basis of a nonconstant energy of disordering and which also includes the effect of lattice vibrations, is shown to agree well with the experimental one.
The usefulness of the form E _{0}—BT ^{2} is not confined to β brass and the same expression may be applied to systems other than solid‐solid.

Cross Sections for Charge Transfer Collisions of Low‐Energy Ions in N_{2} and O_{2}
View Description Hide DescriptionMeasurements have been made of the cross sections for charge transfer collisions between the low‐energy (9—250 ev) ions, N_{2} ^{+}, O_{2} ^{+}, O^{+} and N^{+}, and the molecules N_{2} and O_{2}. Two reactions (N^{+}, N_{2}; O^{+}, N_{2}) have been reported by other workers and are compared with present work.
The experimental method utilizes a radio‐frequency mass spectrometer as an ion source. The ions are collimated and enter a weak radial electric field of cylindrical symmetry. The secondary ions are separated from the primary beam and the ratio of the two currents is measured as a function of pressure.
Results are discussed in terms of the adiabatic collision condition and possible internal energy states of the ions and molecules.

The Interaction of Rare Gas Atoms with Surfaces
View Description Hide DescriptionThe apparent volumes of vessels containing high surface area powders have been measured with rare gases and analyzed. The interaction energies and distances of closest approach have been evaluated. A new method for the estimation of surface area is presented.

Structures of the Boron Hydrides
View Description Hide DescriptionEvidence for the structures of B_{2}H_{6}, B_{4}H_{10}, B_{5}H_{9}, B_{5}H_{11}, and B_{10}H_{14} is reviewed. Correlations of the boron arrangements with known structures have been pointed out, and a systematic discussion of the boron‐hydrogen distances is given.

The Valence Structure of the Boron Hydrides
View Description Hide DescriptionA set of extended valence postulates is presented including the concept of the localized three‐center bond. These postulates are applied systematically to the boron hydrides and account for their unusual geometry, their unexpected dipole moments, and the fact that they are not ``electron‐deficient.''

The Bipyramidal XY _{3} Z _{2} Molecular Model. Part I. Classical Vibration Problem
View Description Hide DescriptionSymmetry coordinates are set up from the standpoint of group theory for describing the normal modes of oscillation of the XY _{3} Z _{2} molecular model in such a manner that maximum factorization of the secular determinant is accomplished. The cubic and quartic portions of the anharmonic potential function are derived, and the components of vibrational angular momentum are set down. The complete valence‐type potential function is discussed. Explicit relations are derived between the force constants occurring in the secular determinant and the physical valence force constants.

The Frequency of the Irradiating Light as a Determinant of the Joshi Effect in Oxygen under Silent Electric Discharge
View Description Hide DescriptionCeteris paribus, the negative Joshi effect —Δi in oxygen under electrical excitation increases linearly with the frequency v of the irradiating light:where i_{D} is the rms current in dark, v_{m} the minimum threshold frequency, and Λ a constant dependent upon the nature of the electrode surface, gas pressure, applied potential V, etc. v_{m} decreases with increase in V because of the occurrence of the photoelectric analog of the Schottkyeffect. The increase in —Δi with v(>v_{m} ) is the consequence of a similar variation in the photoelectric yield. Superimposed on this are factors which tend to reduce —Δi: (1) the increase in photoelectron energy with v, which diminishes the probability of attachment, and (2) reduction in emission because of the negative space charge and the image force.

Temperature Dependence of the Ultraviolet Absorption Spectrum of Naphthalene in Solution
View Description Hide DescriptionThe absorptionspectrum of naphthalene solutions has been measured, in the region 3300—2400A, at temperatures between +60°C and —185°C. Particular attention was given to the long‐wavelength vibrational bands of the first electronic transition (3200—2900A), in order to locate and establish the identity of the band origin. The band acquires most of its intensity through the participation of an active vibration, whose ground‐state frequency measured from two observed vibrational bands, is 525±20 cm^{—1}, in adequate agreement with the value 544±60 cm^{—1} found from the temperature dependence of intensity of the 0←1 band in this frequency. This is probably the Raman a_{g} frequency 512 cm^{—1}, which identification, in conjunction with previous polarizationmeasurements, assigns the transition as B _{2u }← A_{g} . Frequency and intensity data are given for 26 bands of this and the next transition (2900—2400A); the latter appears, vibrationally, to be allowed.

Semiempirical Potential Energy Functions. I. The H_{2} and H_{2} ^{+} Diatomic Molecules
View Description Hide DescriptionAfter setting up certain theoretical criteria for a semiempirical potential energy function, two such functions for H_{2} ^{+} and H_{2} are constructed, the simplest of which has the formwhere V is the potential energy with its zero corresponding to infinite separation. R is the internuclear distance, e the electronic charge, and a and b parameters. This function is used to correlate the experimental quantities: dissociation energy, equilibrium internuclear distance, force constant, third and fourth derivatives of V with respect to R, united atom energy, and critical distance.
A more complicated function is also presented which with one molecular parameter fixed by the dissociation energy is capable of then predicting internuclear distance and force constant.

The Photoconductivity of Anthracene. I.
View Description Hide DescriptionPure crystals of anthracene became photoconducting when illuminated with wavelengths lying within their fundamental absorption band. The majority carriers were positive holes, which, as they drifted through the crystal, took part in trapping processes. From the variation of the photocurrent with temperature it was concluded that the number of positive hole traps fell off exponentially as their height above the valence band increased. From the behavior of the photocurrent at various applied fields and light intensities, it was concluded that the conventional energy band diagram as used for inorganic substances could be applied to organic compounds also. Evidence was found, however, indicating that there were large potential irregularities in the energy levels throughout the crystal.

The Effect of Oxygen on the Photoconductivity of Anthracene. II
View Description Hide DescriptionThe photoconductivity in the surface layers of crystalline anthracene has been found to increase considerably over its vacuum level when it is measured in the presence of oxygen or air. Replacing the oxygen by nitrogen or argon causes no such increase. The increased photoconductivity is attributed to the photooxidation of the surface, both the light and the oxygen being necessary to produce the effect. No reaction takes place in the dark. The oxide formed is fairly unstable and dissociates in the dark. Its rate of dissociation is considerably increased when the crystal is illuminated in the absence of oxygen. The experiments indicate that the peroxide is formed by a two‐stage process, the highly unstable intermediate product being formed very rapidly while the final peroxide is formed much more slowly. The nature of the intermediate product is not known for certain. The end product is very likely the oxide formed by an oxygen bridge across the 9, 10 carbon atoms of the anthracene molecule. Apparently, both the oxidation products modulate the photocurrent solely by their effect on the mean free path of the carriers; the intermediate product producing a relatively large increase while the end product produces a smaller decrease in the mean free path.
It is suggested that the technique of photoconductivity measurements might prove to be useful in the study of the kinetics of certain photochemical reactions.

Symbolic Structural Formulas for Boron Hydrides
View Description Hide DescriptionA structural convention is proposed, intended to serve the same function for boron hydrides that the standard valence bond convention serves for organic compounds. It involves the auxiliary concept of the ``valence cone,'' which is the cone swept out by three tetrahedral orbitals rotating about the fourth as an axis. The known open boron hydrides B_{ n }H_{ n+p } then appear to be even‐electron molecules with the boron atoms approximately in a close‐packed equilateral‐triangular network on the convex surface formed by their overlapping valence cones; with n single B–H bonds normal to this surface; and with p (even) added peripheral hydrogen in the surface located so that every boron atom has neighbors in all three sectors of its valence cone. As long as this network does not form a complete polyhedron, we may represent it on paper by a flat triangular network having the same topology.
This prescription gives uniquely and correctly the structures and formulas for the known B_{2}, B_{4}, B_{5}, B_{6}, and B_{10} hydrides and predicts other possible open compounds up to B_{11}. It would be consistent with the existence of closed inert polyhedral hydrides B_{ n }H_{ n } up to B_{12}H_{12} and with chains and lattices of such polyhedra.

Statistical Computation of Mean Dimensions of Macromolecules. I
View Description Hide DescriptionThe configurations of flexible coiling type polymer molecules have been investigated statistically with a high‐speed electronic digital computer by generation of large numbers of ``random walks.'' These walks were carried out subject to the excluded volume effect in simple cubic and tetrahedral lattices. It was found that the walk attrition obeys an exponential decay law with a half‐walk of 6.7 steps in the cubic lattice and 17.3 steps for the tetrahedral. Mean square end‐to‐end separations, 〈r_{n} ^{2}〉_{Av}, were also obtained, and two distinct kinds of empirical formulas have been fitted to the data. So far, the statistical data are insufficient to establish unequivocally the nature of the functional dependence of 〈r_{n} ^{2}〉_{Av} for large values of n, the number of steps. A study was also made on the probabilities of ring closures for restricted random walks in the cubic system. It was found that for rings greater than 6 steps, the probability of formation varies inversely as the square of the ring size.

Substituted Methanes. XX. Potential Constants and Calculated Thermodynamic Properties for Some Dibromomethanes
View Description Hide DescriptionUsing previous infrared and Raman data, a reasonable set of potential constants were obtained for CH_{2}Br_{2} and CD_{2}Br_{2}, by means of the Wilson FG matrix method, with a potential energy function containing all possible second degree terms. Fundamental frequencies for CHDBr_{2} were then calculated using the potential constants found for CH_{2}Br_{2} and CD_{2}Br_{2}. Finally the heat content, free energy,entropy, and heat capacity for the ideal gaseous state at 1 atmos pressure were calculated for these three molecules for twelve temperatures from 100°K to 1000°K with a rigid rotator harmonic oscillator approximation.

The Solution of the Boltzmann Equation for a Shock Wave using a Restricted Variational Principle
View Description Hide DescriptionUsing a variational method and the Mott‐Smith velocity distribution function, the thickness of a plane shock wave is calculated for various Mach numbers. The results compare fairly well with those obtained by Mott‐Smith. It is also shown that the Mott‐Smith distribution function becomes a better choice as the Mach number increases.

The Infrared Spectrum of Ketene
View Description Hide DescriptionThe infrared spectrum of gaseous ketene has been reinvestigated in the 500—1200 cm^{—1} region with a recording prismspectrophotometer using KBr and NaCl optics. Because of an experimental procedure which enabled us to subtract the absorption of the impurities, a ketene absorption curve was obtained, probably more correct than that found by previous investigators. An interpretation of the numerous lines in the 500—1000 cm^{—1} interval is given, resulting in a reassignment of some of the fundamental vibrational frequencies. Thermodynamic functions are recalculated.

Diffusion across an Interface
View Description Hide DescriptionIdeal diffusion in the sense of Fick's law in a heterogeneous system composed of two liquids is discussed by means of a three‐region model where the two bulk liquid regions adjoin a third region which characterizes the liquid‐liquid interface. When diffusional resistance terms are defined in the usual manner, three classes of interfacial diffusion may be conveniently described by our model. It is found that extraordinary resistance to diffusion at the interface gives rise to perturbations in the observed concentration profile of the bulk regions; these perturbations diminish with time and disappear in the limit of vanishing resistance.

PVT Relations of Liquid Carbon Tetrachloride and n‐Perfluoroheptane and a Test of the Clausius‐Mosotti Equation
View Description Hide DescriptionValues of (∂P/∂T)_{ v } for CCl_{4} and n‐C_{7}F_{16} have been measured over a range of approximately 20° and 160 atmospheres. The linear relation between P and T found in earlier studies to hold over 20 atmospheres for a number of liquids and solutions is here confirmed over the much larger range. One corollary is that (∂C_{ v }/∂V)_{ T }=0; another is that the isothermal compressibility of C_{7}F_{16}, not hitherto known, is 2.38×10^{—4} atmosphere^{—1} at 25° and 1 atmosphere, and could easily be calculated for other temperatures. The terms in the equation (∂E/∂V)_{ T }=T(∂P/∂ T)_{ v }—P are given, also the function V^{2}(∂E/∂V)_{ T }, shown in the earlier studies to be constant. Its value for CCl_{4} confirms the earlier studies; for n‐C_{7}F_{16} it is 101.5 atmospheres×liters.^{2}
The dielectric constant of n‐C_{7}F_{16} has been measured at 16.0° and at 38.4°, and over a pressure range of 115 atmospheres. The values obtained conform closely to the Clausius‐Mosotti equation, giving a molar polarization of 49.1 cc.