Volume 31, Issue 6, 01 December 1959

Vibrational Assignment and Potential Field of Iron Pentacarbonyl
View Description Hide DescriptionThe fundamental frequencies of iron pentacarbonyl were assigned using recent vibrational data. The results show that iron pentacarbonyl possesses a trigonal bipyramidal structure. Valency force constants were evaluated for a force field consisting only of the diagonal F‐matrix elements.

Proton Magnetic Resonance Study of Lithium Sulfate Monohydrate
View Description Hide DescriptionAn extended protonmagnetic resonance study of lithium sulfate monohydrate is presented. An oddity in the resulting Pake curves appears. Some of the curves show a shift so that they are described by equations of the form, +constant shift.
There are two orientations of the hydrated water molecule. For these the direction angles of the proton‐proton axes with respect to the crystallographic a, b, and c axes are, respectively, α_{0}=97°, β_{0}=45°, γ_{0}=48°, and α_{0}=74°, β_{0}=38°, γ_{0}=127°. Apparently the hydrogens bond O_{5}— —H–O_{5}–H— —O_{1}, where O_{5} are neighboring water oxygens and O_{1} is a sulfate oxygen.
Several possible origins of the shifts in the Pake curves are discussed with limited success. An adequate theoretical explanation is lacking.

Valence Bond Calculation of the Barrier to Internal Rotation in Molecules
View Description Hide DescriptionAn approximate calculation of the barrier to internal rotation in ethane was made using a set of covalent valence bond structures involving only s and p orbitals.
The calculated result is sufficiently great that it does not appear that other effects are needed to explain the barrier height.

Potential Function of Boric Acid
View Description Hide DescriptionA normal coordinate treatment was carried out for the planar X (YZ)_{3} molecule (symmetry point group C _{3h }) by means of Wilson's F‐Gmatrix method, using the most general harmonic force field. Ten of the most important force constants of boric acid were determined from existing infrared and Raman data.

X‐Ray Diffraction Study of Bismuth Polymer in Aqueous Perchlorate Solution
View Description Hide DescriptionX‐ray diffraction study of an aqueous solution of bismuth perchlorate has established the presence of a polymeric species containing six bismuth atoms in octahedral arrangement. The bismuth‐bismuth distances are 3.70 and 5.23 A.

Nonequilibrium Kinetics and Chromatography
View Description Hide DescriptionAn effort is made here to deal with the complex kinetic processes which determine the structure of component zones in chromatography. The problem is approached by assuming that the various steps are proceding near equilibrium. In order to facilitate the analysis an approximation is made in which each derivative of a concentration is replaced by the derivative of the equilibrium concentration. The latter derivatives are evaluated in terms of the concentration profile. This yields a set of linear algebraic equations from which an equilibrium departure term, ε, can be found for each species. The diffusion of the zone is then obtained as a function of the various ε's.
The simplicity introduced by this method allows one to obtain the zone diffusion term for complex kinetics in contrast to the rigorous theories where only the simplest kinetic schemes have been treated. The results for a simple kinetic example are the same, however, as obtained in the limit of large times by the rigorous methods. The validity of the assumptions made is established independently of this comparison. Various applications of the method are discussed which extend beyond the range of chromatographic analysis.

Use of the Self‐Consistent Field in the Treatment of the Vibrations of Crystals
View Description Hide DescriptionIt is shown that quantum‐mechanical average equilibrium positions and average normal coordinates of ordered crystals are useful quantities. It is found that the wave functions calculated using these average quantities are more tractable approximations than those calculated from the true potential function with neglect of cubic and higher terms. A self‐consistent field treatment is used to show how the average equilibrium positions and average normal coordinates could be obtained in principle. The wave functions derived from the self‐consistent field coordinates are still very poor approximations to the exact wave functions in the sense that the projections of an approximate wave function on any exact wave function is extremely small.

C^{13} Splittings in Proton Magnetic Resonance Spectra. II. Bonding in Substituted Methanes
View Description Hide DescriptionWe have measured indirect spin‐spin couplings between protons and C^{13} nuclei in a variety of substituted methanes. As found earlier for hydrocarbons, the coupling constants, J _{C–H}, appear to be linearly related both to the percent s character of the carbon atomic orbital participating in the C–H bond and to the bond length. On the basis of the large variations of the J _{C–H} values and of the C–H bond lengths in these compounds we conclude that the state of hybridization of the carbon atom cannot be reliably inferred from the observed, essentially tetrahedral valence angles. This means that the bonds must in many cases be considered as somewhat bent.
We investigated the dependence of the C–H bond hybridization in compounds of type CH_{3}X upon the properties of the substituent group. The results can be correlated on the assumption that the effective electronegativity and the size of the atom directly attached to the methyl carbon primarily determine the hybridization.

Overhauser Effect in Asphalt Solutions
View Description Hide DescriptionWe have discovered that solutions of asphalt in a suitable solvent will show an Overhauser effect. The effect is qualitatively similar to that in crude oil. It arises from a dipolar interaction between the unpaired spins in the asphaltic free radicals, and the protons of the solvent molecules. The contribution to proton relaxation from the asphalt is a linear function of asphalt concentration. The function relating proton signal enhancement to electron saturating rf field strength is found to vary with asphalt concentration. A plot of enhancement versus electron‐stimulating frequency at constant H _{0} yields a curve similar to the EPR absorption line. The large size of the asphalt radicals does not appear to have any direct significance with respect to the Overhauser interaction.

Thermionic Properties of Uranium
View Description Hide DescriptionThermionic measurements were made on uranium metal in the form of drawn wire and on films of uraniumdeposited on tungsten by evaporation in ultrahigh vacua. Measurements of the emission current as a function of accelerating potential and of the work function of the bulk material indicated that the surface was never completely freed of oxide. Measurements of the work function and emission constant A as a function of the thickness of the evaporated films showed both φ and A to increase with increasing depth of deposit up to 15 atom layers and to reach constant values of 3.47±0.03 ev and 114±12 amp cm^{—2} deg^{—2}, respectively, for deposits 15–200 atom layers deep. Qualitative measurements of the ionization potential of uranium by means of surface ionization showed the positive ion current to increase with increasing temperature indicating the ionization potential to be greater than 4.53 ev. The magnitude of the positive ion currents suggested an ionization potential of 4.5–5.0 volts.

Negative Ion Mass Spectra of Hydrocarbons and Alcohols
View Description Hide DescriptionThe complete negative ion mass spectra and relative sensitivity for positive and negative ion formation in various organic compounds are herein reported for the first time. These compounds include methane, the C_{2} ^{—} hydrocarbons, n‐butane, and all of the alkyl alcohols through the butyls. A limited comparison of the observed ionic patterns with molecular structure and chemical properties manifests a correlation. Relative sensitivities for positive and negative ion formation in these compounds show that formation of positive ions is about four orders of magnitude more probable than formation of negative ions under the conditions used in this study.

Lattice Vibrations in Alkali Halide Crystals. I. Lithium and Sodium Halides
View Description Hide DescriptionVibrational frequency distributions for the lithium and sodium halides have been evaluated on the basis of the Born lattice theory by the use of Blackman's numerical‐sampling technique. Both room temperature and extrapolated 0°K parameters have been used in the calculation. Specific heats, the corresponding Debye characteristic temperatures, and the moments of the distributions have been evaluated directly from the frequencies. Comparison is made with experimental data and with other theoretical work.

Microwave Spectrum and Internal Rotation of Ethyl Cyanide
View Description Hide DescriptionThe microwave spectrum of ethyl cyanide has been studied in the region from 17–36 kMc. Both parallel and perpendicular transitions have been assigned. Rotational constants (Mc) for the ground vibrational state are a _{0}=27 663.30, b _{0}=4714.14, c _{0}=4235.14, D_{J} =0.0035, D_{JK} =—0.0496. From Stark effects the dipole moment is calculated to be μ_{ a }=3.78 D, μ_{ b }=1.38 D, μ=4.02 D.Hyperfine splittings lead to a value of —3.3 Mc for the quadrupole coupling of the N^{14} nucleus along the a axis. Rotational transitions of molecules in several excited vibrational states have also been measured. A Coriolis interaction between the torsional mode and the in‐plane CCN bend has been found and is discussed. Splittings of transitions of molecules in the first excited torsional state show that the barrier hindering internal rotation of the methyl group is 3.05 kcal/mole.

Thermodynamics, Stationary States, and Steady‐Rate Processes. I. Introduction and Migrational Equilibrium in Isothermal and Monothermal Fields
View Description Hide DescriptionA method of obtaining thermodynamic relationships for systems in stationary states, for steady‐flow processes, and for steady‐rate processes in general is outlined. The method is shown to be applicable to equilibrium systems, and a monothermal concentration field is treated briefly.

Thermodynamics, Stationary States, and Steady‐Rate Processes. II. Migrational Equilibrium in Thermal Fields
View Description Hide DescriptionThe thermodynamic method outlined in paper (I) for treating stationary states and steady‐rate processes is applied to a discussion of nonisothermal systems. Thermomolecular pressure, thermo‐osmotic and thermal diffusion effects are treated in detail.

Thermodynamics, Stationary States, and Steady‐Rate Processes. III. The Thermocouple Revisited
View Description Hide DescriptionThe thermodynamic properties of the thermocouple are treated according to the principles developed in the first two papers of the series. The steps in the derivation of the Thomson relations seem to imply that a homogeneousthermoelectric effect does not exist.

Thermodynamics, Stationary States, and Steady‐Rate Processes. IV. Steady Monothermal Rate Processes
View Description Hide DescriptionThe procedure outlined in paper (I) of the series is applied to such steady monothermal rate processes as forced vaporization,diffusion,Poiseuille flow, and chemical reaction. In the case of forced vaporization, numerical values of a coefficient defined in terms of entropy production are computed from the data of Alty pertaining to the vaporization of water and of carbon tetrachloride.

Effect of Pressure on the Melting Points of Eight Alkali Halides
View Description Hide DescriptionThe melting curves of the alkali chlorides and the sodium halides have been determined at high pressures. The results can be represented within experimental error by Simon's equation. Comparison of the slope of the melting curve at low pressure with measurements of the changes of volume and entropy upon fusion suggests that the latter data are systematically in error.

Contribution of Bound, Metastable, and Free Molecules to the Second Virial Coefficient and Some Properties of Double Molecules
View Description Hide DescriptionThe second virial coefficient for molecules interacting with a spherically symmetric potential is divided into three parts: (1) a contribution B_{b} , related to the equilibrium constant for the formation of bound double molecules; (2) a contribution B_{m} , related to the equilibrium constant for the formation of metastably‐bound double molecules; and (3) a contribution B_{f} , due to molecules which interact but are free to separate after the interaction. Equations are given for determining each of the three parts of the second virial coefficient. A detailed treatment of these three contributions together with numerical tables on a reduced temperature basis is given for the square‐well, Sutherland, and Lennard‐Jones (6–12) potentials.
The mean lifetimes of metastably bound double molecules are discussed, and numerical values are given for the special case of argon. Tables for computing mean lifetimes in other Lennard‐Jones gases are given. It is found that most metastably bound double molecules have mean lifetimes considerably longer than the mean time between collisions at ordinary pressures. Finally, an equation is developed for the number of vibrational levels of a double molecule.

Initial Pressure Dependence of Thermal Conductivity and Viscosity
View Description Hide DescriptionThe initial pressure dependence of thermal conductivity and viscosity of gases is considered to arise from molecular association and collisional transfer. Since only the initial pressure dependence is investigated, clusters larger than dimers can be neglected. The effect of dimer formation can be calculated from a knowledge of the equilibrium constant for the reaction 2A⇌A _{2}. The effect of collisional transfer is obtained by a semiempirical modification of Enskog's theory. In the case of thermal conductivity, it is found that at low temperatures molecular association is more important than collisional transfer, while at high temperatures collisional transfer predominates. For viscosity, the initial pressure dependence is due primarily to collisional transfer.
Detailed equations for the initial pressure dependence of both thermal conductivity and viscosity are given in terms of dimensionless groupings which include the intermolecular potential parameters. Tables of these dimensionless groupings as functions of a reduced temperature are given for molecules obeying the Lennard‐Jones (6–12) potential. Comparisons between theory and experiment are included. It is found that the numerical results are sensitive to the choice of force constants for the interaction of a monomer with a dimer.