Index of content:
Volume 31, Issue 6, 01 December 1959
31(1959); http://dx.doi.org/10.1063/1.1730631View Description Hide Description
The 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.
31(1959); http://dx.doi.org/10.1063/1.1730632View Description Hide Description
An 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, α0=97°, β0=45°, γ0=48°, and α0=74°, β0=38°, γ0=127°. Apparently the hydrogens bond O5— —H–O5–H— —O1, where O5 are neighboring water oxygens and O1 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.
31(1959); http://dx.doi.org/10.1063/1.1730633View Description Hide Description
An 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.
31(1959); http://dx.doi.org/10.1063/1.1730634View Description Hide Description
A 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.
31(1959); http://dx.doi.org/10.1063/1.1730635View Description Hide Description
31(1959); http://dx.doi.org/10.1063/1.1730636View Description Hide Description
An 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.
31(1959); http://dx.doi.org/10.1063/1.1730637View Description Hide Description
It 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.
31(1959); http://dx.doi.org/10.1063/1.1730638View Description Hide Description
We have measured indirect spin‐spin couplings between protons and C13 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 CH3X 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.
31(1959); http://dx.doi.org/10.1063/1.1730639View Description Hide Description
We 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.
31(1959); http://dx.doi.org/10.1063/1.1730640View Description Hide Description
Thermionic 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.
31(1959); http://dx.doi.org/10.1063/1.1730641View Description Hide Description
The 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 C2 — 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.
31(1959); http://dx.doi.org/10.1063/1.1730642View Description Hide Description
Vibrational 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.
31(1959); http://dx.doi.org/10.1063/1.1730643View Description Hide Description
The 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, DJ =0.0035, DJK =—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 N14 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 Fields31(1959); http://dx.doi.org/10.1063/1.1730644View Description Hide Description
A 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 Fields31(1959); http://dx.doi.org/10.1063/1.1730645View Description Hide Description
31(1959); http://dx.doi.org/10.1063/1.1730646View Description Hide Description
The 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.
31(1959); http://dx.doi.org/10.1063/1.1730647View Description Hide Description
The 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.
31(1959); http://dx.doi.org/10.1063/1.1730648View Description Hide Description
The 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 Molecules31(1959); http://dx.doi.org/10.1063/1.1730649View Description Hide Description
The second virial coefficient for molecules interacting with a spherically symmetric potential is divided into three parts: (1) a contribution Bb , related to the equilibrium constant for the formation of bound double molecules; (2) a contribution Bm , related to the equilibrium constant for the formation of metastably‐bound double molecules; and (3) a contribution Bf , 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.
31(1959); http://dx.doi.org/10.1063/1.1730650View Description Hide Description
The 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.