Index of content:
Volume 39, Issue 8, 15 October 1963
39(1963); http://dx.doi.org/10.1063/1.1734563View Description Hide Description
The general cluster theory of inhomogeneous fluids is applied to the determination of ion and mean potential distributions in the interfacial region between electrolyticsolutions and metallic electrodes (specifically mercury), as well as in colloidal suspensions. The relevant electrostatic problem involving distinct inner and outer Helmholtz regions is solved in closed form. Summation of the linearized cyclic clusters appropriate to dilute solutions demonstrates for the first time the limitations of local Debye—Hückel activity corrections in the method called ``local thermodynamic balance.'' An explicit adsorption isotherm formalism results from proper treatment of cluster vertices confined to the inner Helmholtz plane; this permits proper deduction of the ``discreteness‐of‐charge'' effect, as well as nonelectrostatic ion size effects in this plane. It is furthermore shown that accounting for ion size to lowest order in the diffuse layer necessarily contradicts the local thermodynamic balance approach. The systematic cluster theory formulation of the colloid stability problem also suggests hitherto unused corrections to the relevant double‐layer free energies.
39(1963); http://dx.doi.org/10.1063/1.1734564View Description Hide Description
When lead is anodized in sulfuric acid at a constant ``half cell'' potential of 1.21 V with respect to hydrogen, an oriented film of tetragonal lead monoxide forms on the surface. If electrical contact is made to the dried surface of the resulting PbO, an open circuit voltage of about 0.5 V is found to exist between this contact and the lead substrate. The current is a nonlinear function of the voltage between the surface contact and the lead. The short‐circuit current and open‐circuit voltage depend on the atmosphere over the cell; the former is of the order of 1 μA in air saturated with water vapor, dropping by about four orders of magnitude after several days in vacuo. As the cell is dried, these quantities become increasingly dependent on the intensity of visible illumination, the current rising by as much as three orders of magnitude under intense illumination, and the voltage rising by about 0.2 V. The resistance of the cell to steady current flowing in a direction opposite to normal discharge is smaller than the discharge resistance, and varies only slightly with atmospheric conditions. The capacitance of the cell as measured at high frequencies corresponds to that expected for a parallel plate capacitor of thickness equal to the thickness of the cell. At lower frequencies, the capacitance is greater. A theory for the mechanism of the cell involves a diffusion of oxygen vacancies through the PbO, with the oxidation of lead to lead monoxide at the Pb/PbO interface furnishing the energy for the cell.
39(1963); http://dx.doi.org/10.1063/1.1734565View Description Hide Description
Infrared spectra of acenaphthene crystals measured with polarized radiation in the region 400–3000 cm—1 are reported. The unit cell contains four molecules. Splitting of bands in the crystal spectrum has been observed. However, because of the specific positions of molecules in the crystal lattice, a unique determination of the vibration symmetry is possible. An assignment of recorded frequencies is proposed.
39(1963); http://dx.doi.org/10.1063/1.1734566View Description Hide Description
Data on the 1–1 fluoride complex ion with noble‐gas‐type cations are examined for information on short‐range ion—ion and water—ion interactions. A four‐term numerical correlation of the standard free energies with the size and charge of the ion is developed based on the approach that electric saturation is not directly important to the complex formation. Deviations from the classical point charge Coulomb energy are expressed by a term independent of temperature and the dielectric medium, exponential in the separation distance, and containing only fundamental quantities which suggest wave‐mechanical interaction between cation and anion. The total standard entropy change separates into three terms; the temperature dependence of the macroscopic dielectric constant, the removal of coordinated water, and the cratic term for the change in the number of solute particles. A screened charge model of the hydrated ion is proposed in which hydration is the loss of the quantum‐mechanical free energy of the gaseous ions by the formation of covalent bonds with the water. The ion charge is delocalized, spreading out to the coordinated water. The degree of hydration depends on the free energy of the water, with the free energy for coordination of the last water molecule being less than 1 kcal.
39(1963); http://dx.doi.org/10.1063/1.1734567View Description Hide Description
The microwave spectrum of chlorobenzene has been observed in the frequency range between 8000 and 30 000 Mc/sec. An analysis of this spectrum gives the following values for the rotational constants for the two isotopic species, C6H5Cl35 and C6H5Cl37; A=5672.951 Mc/sec, B=1576.774 Mc/sec, C=1233.672 Mc/sec for the Cl35 isotopic species and A=5672.530 Mc/sec, B=1532.790 Mc/sec, C=1206.571 Mc/sec for the Cl37 isotopic species. The quadrupolar coupling constants which were obtained from the quadrupolar hyperfine structure are eqQ=—71.10 Mc/sec for Cl35 and eqQ=—56.10 Mc/sec for the Cl37. The quadrupolar asymmetry parameter η cannot be determined from the microwave spectrum. The observed dipole moment is 1.78±0.06 D.
39(1963); http://dx.doi.org/10.1063/1.1734568View Description Hide Description
Some comments are given on the construction of Polo's ρ vectors. Methods are reported for the construction of the (a) G —1 C α and (b) G —1 C α G —1 matrices by means of the (a) ρ and s vectors, and (b) ρ vectors alone. These matrices are important in the study of Coriolis interaction coefficients of rotation—vibration. For illustration of the theory the ethylene‐type molecular model is taken as an example.
39(1963); http://dx.doi.org/10.1063/1.1734569View Description Hide Description
The reaction of BF3(g) with B2O3(l) was studied by the transpiration method in the temperature range 600° to 1100°K. Results indicate the reaction to beΔH 298° was found to be 4.2 kcal, and leads to ΔHf 298°=—566.8±1 kcal/mole for (BOF)3(g).
The vapor above mixtures of MgF2 and B2O3 contained in a Knudsen cell was analyzed with a mass spectrometer and was found to contain BF3(g), (BOF)3(g), and BOF(g) in the range 980° to 1230°K. From studies of the temperature dependence of appropriate ion intensities the heat of the reactionwas derived as 131 kcal at 1125°K. Use of low ionizing electron energies was required to avoid fragmentation effects. The heat of formation of BOF(g) at 298°K was calculated to be —144±3 kcal/mole.
39(1963); http://dx.doi.org/10.1063/1.1734570View Description Hide Description
This work involves the alignment of molecules in the anisotropicliquid phase of p‐azoxyanisole due to externally applied dc and acelectric fields and walls of the sample holder. Microwave techniques involving dielectricmeasurements are used to provide a measure of the alignment. Results are discussed which suggest that for very pure samples an alignment should be produced with the long axes of the molecules perpendicular to the externally applied electric field. The alignment with the long axes parallel to the external field which is often observed appears to be due to an extremely small amount of impurity. This alignment appears to be associated with the conductivity, with an alignment produced such that the conductivity is a maximum in the direction of the field. Results are also discussed which suggest that small amounts of impurity are effective in producing an alignment of the molecules parallel to the walls of the sample holder.
39(1963); http://dx.doi.org/10.1063/1.1734571View Description Hide Description
The fluorine nuclear magnetic resonance spectra of the sodium,potassium,rubidium, and cesium hexafluorophosphates were studied between 77° and 400°K. It was found that in each of the salts the PF6 —ions are reorienting about the octahedral axes at random, or nearly so, for temperatures of 200°K and above. The broadening of the fluorine resonance in these solids at lower temperatures indicates that the ease with which the PF6 — groups reorient increases with increasing size of the alkali metal cation, so that for CsPF6 the fluorine resonance is still narrow at 77°K. A quantitative study of the potential barriers to PF6 — group reorientation was discouraged by the discovery that the fluorine line shapes and linewidths are remarkably sensitive to the physical state and, in the case of RbPF6, the thermal history of the sample. These effects are attributed to crystal imperfections which lower the potential barriers to PF6 — group reorientations and decrease the size of domains in which there is a cooperative ``freezing out'' of the reorientations. Thus, in the region of changing linewidth, we postulate domains with frozen‐out PF6 — groups and others with reorienting groups. In samples which should have relatively low imperfection concentrations and where such domains should be large, we find distinguishable broad and narrow components in the fluorine resonance, with one growing at the expense of the other as the temperature is changed. This two‐phase behavior disappears in finely powdered samples, in which high concentrations of imperfections were probably introduced by the mechanical grinding. Fluorine line‐shape studies reported previously for solid CF4 are reinterpreted in terms of a similar two‐phase, cooperative process for the freezing out of the CF4 reorientations.
39(1963); http://dx.doi.org/10.1063/1.1734572View Description Hide Description
Wavefunctions and energies for both the eclipsed and staggered forms of ethane have been calculated in the limited basis set, self‐consistent‐field approximation. The basis functions are a minimum set of Slater orbitals. All integrals have been evaluated to the necessary accuracy. The calculated value of the barrier to internal rotation is 3.3 kcal/mole in good agreement with experiment. The sensitivity of the value to improvements in the wavefunctions cannot be estimated readily. The bearing of this calculation on proposals of the origin of the barrier is discussed. A transformation to localized molecular orbitals will be necessary for a more detailed discussion of the barrier.
39(1963); http://dx.doi.org/10.1063/1.1734573View Description Hide Description
The mean lifetime of the amino group τ of aqueous solutions of sarcosine in the zwitterion form was measured using the NMR technique at 21°±1°C. The zwitterion can participate in the following exchange reactions: From the experimental results, i.e., the dependence of 1/τ on 1/ a H+ and the concentration of the amino acids, the following rate constants were determined:and
Discussing and comparing the above rate constants with the rate constants for similar reactions enables one to estimate the value of each of the rate constants given as a sum.
39(1963); http://dx.doi.org/10.1063/1.1734574View Description Hide Description
The absorptionspectrum of naphthacene vapor is similar to that in solution. There is an absorption band with pronounced vibrational structure running from about 5000 to 3500 Å and a second stronger band from 2700 Å to shorter wavelengths. We have examined the fluorescencespectrum of the vapor at low pressures, such that molecules have no collisions during the lifetime of the excited state. By selective excitation with either the 3650 Å line or the 2537 Å line of the mercury lamp it is possible to excite molecules into either the first excited singlet state or into the second excited singlet state. The fluorescence emission appears to be from the first excited singlet state in both cases even though the molecules suffer no intermolecular collisions in the excited state.
39(1963); http://dx.doi.org/10.1063/1.1734575View Description Hide Description
A variation‐perturbation method is employed for the calculation of the electric polarizabilitytensor of a series of diatomic molecules (H2, Li2, N2, LiH, HF, LiF, CO). The SCF—LCAO—MO functions of Ransil are used as unperturbed solutions and appropriately orthogonalized perturbation functions are introduced to account for the effect of the electric field. For the three molecules (H2, N2, CO) for which experimental data are available, reasonable agreement between the theoretical and the measured values is obtained. However, the calculations appear to somewhat overestimate the electric polarizability, particularly so for the parallel component of the tensor; possible theoretical refinements to reduce this error are discussed.
39(1963); http://dx.doi.org/10.1063/1.1734576View Description Hide Description
High‐resolution chemical shift measurements were carried out on electrolyticsolutions in 50% dioxane—water mixtures. Whereas the water protonresonance position was displaced significantly by the addition of electrolyte, the dioxane signal in all mixtures remained unperturbed. Further, the results, particularly those obtained with chloride solutions of the small or highly charged Be, La, and Th ions indicated that strong selective solvation of cations by the water was occurring. This conclusion was substantiated by differences in the dioxane and the water linewidths observed in several solutions, including those of paramagnetic salts.
Self‐diffusion coefficients of dioxane in these electrolytic mixtures were also measured by the nuclear magnetic resonance spin‐echo technique. The observed diffusion data could be interpreted solely on a hydrodynamical basis, again indicating that no significant interaction was occurring between dioxane and the added electrolyte.
39(1963); http://dx.doi.org/10.1063/1.1734577View Description Hide Description
It has been shown by the deflection of beams of alkaline‐earth dihalide molecules by inhomogeneous electric fields that the following compounds have permanent electric dipole moments and are therefore assumed bent: BaF2, BaCl2, BaBr2, BaI2, SrF2, SrCl2, CaF2. No polarity was observed for the following compounds investigated: CaCl2, CaBr2, SrBr2, SrI2. The absence of deflection of beams of BaCl2 by inhomogeneous magnetic fields shows that this molecule has no electronic magnetic moment and hence is in a singlet ground state.
39(1963); http://dx.doi.org/10.1063/1.1734578View Description Hide Description
From high‐resolution protonmagnetic resonance experiments, absolute magnitudes of J C13–H and J X–C–H have been determined for compounds of the type X(CH3)4, where X=Si, Ge, Sn, and Pb. The J C13–H values yield the s characters of the carbon orbitals in the C–H and C—X bonds as well as the Juan—Gutowsky s character affinity ΔX. Rough calculations of J X–C–H based on the Fermi contact term give widely varying results depending on the value of the effective charge used. A straight line correlation of J X–C–H with n 3 can be explained crudely on the basis of the Fermi contact term.
39(1963); http://dx.doi.org/10.1063/1.1734579View Description Hide Description
The absorption bands of water in the 1.1‐to‐1.3‐μ region have been measured. From the extinction coefficients, concentrations of water species involving 2,1, and 0 hydrogen bonds per molecule were calculated. The temperature dependence of these concentrations yielded a value of 3.7–4.5 kcal for the energy involved in breaking one mole of hydrogen bonds in water. On melting, 46% of the hydrogen bonds originally present in ice are broken; by 72°C the percentage broken has increased to 61. Further, the results were used in conjunction with the flickering cluster model of Frank and Wen to obtain an upper limit for the average size of the water polymers of 90 molecules of H2O at 20°C.
39(1963); http://dx.doi.org/10.1063/1.1734580View Description Hide Description
The infrared absorption bands of water in the 1.1‐ to 1.3‐μ region have been studied. Variations in intensities of three bands have been used to calculate for ionic solutions the mole fractions of water molecules in which zero, one, and two of the hydrogens are involved in hydrogen bonding. The average sizes of water clusters in HCl, HBr, HNO3, HClO4, H2O2, NaOH, KOH, NaNO3, and NaClO4 solutions were calculated. From this and from qualitative evaluations for other solution systems, it was possible to assign the following effect on the water structure to the ions:
39(1963); http://dx.doi.org/10.1063/1.1734581View Description Hide Description
Electron—electron repulsion energiesC̄ and electron—nuclear attraction energiesL̄ are computed from the nonrelativistic total energiesE for isoelectronic series of two‐, three‐, and four‐electron atoms in their lower electronic states. A limited variational approach to atomic structure is then described which uses in effect rescaled eigenfunctions (for two or more electron systems) as a basis; the ``empirical'' C̄ and L̄ obtained in the first part are employed in these calculations. Use of the eigenfunction for an atom with nucleus of charge Z+1 to predict the energy of an isoelectronic system with nucleus of charge Z yields results which are in error by about 0.3 to 0.7 eV for two‐ to four‐electron atoms, respectively. A semiempirical correction scheme of this approach gives results which are in error by 0.01 to 0.1 eV, respectively. Energies for some states of H, He, and Li negative ions are predicted.
39(1963); http://dx.doi.org/10.1063/1.1734582View Description Hide Description
The transformation graphite to diamond is catalyzed by the Group VIII metals, manganese and chromium. The fact that these metals are good solvents for carbon tends to obscure their catalytic role in this transformation. It was found that copper‐rich copper—nickel alloys capable of dissolving less than 0.06 at. % carbon catalyzed the formation of diamond whereas lead and antimony having about equal solvent capacity did not. The diamondnucleation rate increased exponentially with nickel concentration in the copper‐rich alloys. Hence, on the basis of the theory that nucleation catalysts provide surfaces of low interfacial energy, one important role of the nickel in these alloys may be interpreted as that of reducing the interfacial energy between diamond and alloy.