Index of content:
Volume 23, Issue 1, 01 January 1955
23(1955); http://dx.doi.org/10.1063/1.1740503View Description Hide Description
Atom bondpolarizabilities π r, st in alternant hydrocarbons (AH's) vanish identically. The calculation of π r, st in ions derived from AH's by addition or removal of one or more electrons (AHI's) is discussed, and the conditions under which they vanish are examined. Mutual atom polarizabilities π r, s and mutual bondpolarizabilities π rs, tu in AHI's are related to the corresponding quantities in the parent AH's. The dependence of all the polarizabilities on Coulomb and resonance integrals is examined.
23(1955); http://dx.doi.org/10.1063/1.1740562View Description Hide Description
Measurements have been made on the thermoelectric power of several nickel oxide samples containing foreign ions. Using an energymodel recently proposed for nickel oxide, the effect of the nature and concentration of additions on the Fermi level,hole concentration, and mobility is derived and discussed. For most of the samples hole concentration can be related to chemical composition. A case of change in valence of the addition induced upon introduction into the matrix is found. The use of the thermoelectric effect to determine impurity in nickel oxide is discussed. The energy scheme of nickel oxide which emerges from this work and that of Morin is emphasized as a drastic departure from the classical model of an electrical semiconductor.
23(1955); http://dx.doi.org/10.1063/1.1740504View Description Hide Description
The classical Soret diffusion problem is solved analytically for the case of unrestricted composition in a binary liquid system, taking account of the temperature‐variation of the density of the mixture. Previous treatments have neglected the phenomenon of thermal dilatation entirely and have not developed a unique general solution which applies both to dilute and to nondilute mixtures.
The rigorous solution derived in the present work is similar in form to de Groot's well‐known equation for dilute mixtures, but contains additional parameters characterizing the initial composition of the system and its coefficient of thermal expansion. These parameters disappear in the asymptotic approximation for a vanishing temperature gradient, but this approximation differs from that proposed by de Groot, even for dilute solutions. The asymptotic expression has practical importance for estimating the Soret coefficient and the ordinary diffusion coefficient of a system from experimental data taken during the thermodiffusional unmixing period; some examples of its application in this connection are discussed.
Photoconductivity and Crystal Imperfections in Cadmium Sulfide Crystals. Part I. Effect of Impurities23(1955); http://dx.doi.org/10.1063/1.1740514View Description Hide Description
The conductivity and photosensitivity of cadmium sulfide crystals can be controlled by the incorporation of suitable impurities. The conductivity and photosensitivity are increased by the incorporation of a halide or a trivalent cation, and decreased by the incorporation of copper or silver. A possible mechanism by which such impurities may produce the observed effects on the photoconductivity is presented.
Photoconductivity and Crystal Imperfections in Cadmium Sulfide Crystals. Part II. Determination of Characteristic Photoconductivity Quantities23(1955); http://dx.doi.org/10.1063/1.1740524View Description Hide Description
From measurements of photoconductivity on low conductivity ``pure'' cadmium sulfide single crystals, and on high conductivitycadmium sulfide crystals with chloride impurity, values for the following characteristicphotoconductivity quantities have been obtained: (1) concentration of levels in the forbidden gap, (2) energy distribution of such levels, (3) attempt‐to‐escape frequency for electrons in traps, (4) capture cross section of traps, (5) capture cross section of recombination centers, (6) mobility for electroncharge carriers, and (7) binding energy for the electron held in an orbit around the chloride ion in conducting crystals.
23(1955); http://dx.doi.org/10.1063/1.1740557View Description Hide Description
The properties of the hydrogen bond are discussed in relation to the equivalent orbital representation of lone pair electrons. The dependence of the energy of the hydrogen bond on the nature of the hybridized lone pair orbital is pointed out. On the basis of point charge models for the water and hydrogen fluoride molecules, and on the basis of a consideration of known hydrogen‐bonded structures, evidence is presented to show that the directional properties of the hydrogen bond are determined largely by the directional properties of the lone pair orbital, and that the strongest bonds result when the hydrogen bond direction is collinear with the lone pair orbital direction.
23(1955); http://dx.doi.org/10.1063/1.1740558View Description Hide Description
23(1955); http://dx.doi.org/10.1063/1.1740559View Description Hide Description
It is shown in this paper how the conventional naive semiempirical molecular orbital approach for conjugated hydrocarbons may be complemented by means of theoretically computed electron repulsion integrals in a manner suggested by the more rigorously founded SCF procedure. This is shown to give satisfying results in three examples with a considerable reduction in labor as compared to the complete ASMO method. The method is carried over in a natural and simple manner to substituted hydrocarbons, providing unambiguous methods of evaluating empirical resonance and inductive parameters. The concept of ``weak'' and ``strong'' substituent is developed and it is shown how these provide simple intuitive approaches to the estimation of interaction parameters in the theory. The inductive and resonance effects upon the energy levels are shown to be far from additive, and indeed are dependent upon each other. The dependence is analyzed and it is indicated which ones are important (and determinable) from various experimental situations.
23(1955); http://dx.doi.org/10.1063/1.1740560View Description Hide Description
Raman displacements, relative intensities, and depolarization factors, as well as wave numbers and estimated relative intensities for the infrared absorption bands in the region 400—4000 K (K = kayser = cm—1), have been obtained. Tentative assignments are given for the observed wave numbers and the applicability of the sum and product rules of Mizushima and Bernstein is discussed.
23(1955); http://dx.doi.org/10.1063/1.1740561View Description Hide Description
The intermolecular potentials for a number of pairs of unlike molecules have been calculated from the known potentials for pairs of like molecules, by means of semi‐empirical combination rules. The intermolecular potential used was of the exp‐six form, . The validity of the combination rules were tested by calculating a number of properties of binary gas mixtures for comparison with experimental values. The resulting agreement was quite reasonable, and it was concluded that the combination rules can be used with some confidence.
23(1955); http://dx.doi.org/10.1063/1.1740564View Description Hide Description
Measurements have been made of the polarization effects in electrical conduction through isopropyl ether. This liquid was chosen because its conductivity is intermediate between that of dielectric liquids and water. Correlation of experimental results in this range with the Jaffé theory had not heretofore been checked. The present results provide a bridge across the gap which formerly existed in polarization measurements between conductivities of 10—6 ohm—1 cm—1 and 10—18 ohm—1 cm—1.
Observations were made of the time dependence of current following the application of various voltages to the electrodes of a cell containing the liquid.
Measurements in the present range broaden the pattern of agreement of the Jaffé theory with experiment. Such agreement now extends from semiconductors and aqueous solutions to dielectric liquids. In all cases good quantitative agreement is obtained provided part of the conductance is attributed to carriers of considerably lower mobility than the ordinary conductivity carriers.
23(1955); http://dx.doi.org/10.1063/1.1740565View Description Hide Description
A ``red shoulder'' on the N ← V absorption curve of olefins, observed at room temperature, but not at low temperature, results from the fact that the potential curves for twist about the double bond in the ground and excited states have slopes of opposite sign. The weaker absorption in the region 40—48 000 cm—1 is assigned to the N ← T absorption on the basis of its analogy to the N ← V transition in position, extinction coefficient, and oscillator strength.
Low‐Temperature Absorption Spectra of Benzene, Toluene, and Para‐Xylene in the Farther Ultraviolet Region23(1955); http://dx.doi.org/10.1063/1.1740566View Description Hide Description
The absorption spectra of the 2100 A and 1850 A transitions of benzene, toluene, and para‐xylene show sharp structure at low temperature. The sharp structure of the 1850 A transition shows that it is a π—π type transition, and not a dissociation band. Its correct assignment is 1 A 1g ← 1 E 1u , with analogous assignments in toluene and para‐xylene. The 2100 A transitions of these molecules can be assigned to 1 A 1g ← 1 B 1u and its analogs, while the 2600 A transitions are assigned to 1 A 1g ← 1 B 2u . Evidence presented indicates that there is no 1 A 1g ← 1 E 2g transition in this region of the spectrum.
23(1955); http://dx.doi.org/10.1063/1.1740567View Description Hide Description
The conventional valence‐bond treatment, by being put upon a more frankly empirical basis, can be modified in such a way that the difficulties arising from the nonorthogonality of the atomic orbitals centered about different atoms are largely bypassed. Although the extension of the new treatment to molecules more complex than that of benzene is rendered impracticable by the increased mathematical difficulties, the results obtained for 1,3‐butadiene, cyclobutadiene, and benzene suggest that many of the essential features of the older calculations can be given a better theoretical justification than hitherto seemed possible. On the other hand, the importance of the relatively unstable structures with formal bonds appears to have been overrated.
23(1955); http://dx.doi.org/10.1063/1.1740568View Description Hide Description
Appearance potentials and excess kinetic energies have been determined for the ions produced by the ionization and dissociation of nitromethane by electron impact in a mass spectrometer. Bond dissociation energies and mechanisms of fragmentation have been deduced where possible. D(CH3–NO2) has been found to be 2.56 volts, a value in agreement with thermochemical data. The dissociation and ionization process yielding NO+, the most abundant ion in the nitromethane mass spectrum, is believed to yield, at the same time, a CH3O radical. A new value for the ionization potential of NO2, 9.91 volts, is reported.
Measurement of the Molecular Weights of Vapors at High Temperature. II. The Vapor Pressure of Germanium and the Molecular Weight of Germanium Vapor23(1955); http://dx.doi.org/10.1063/1.1740569View Description Hide Description
The vapor pressure of germanium and the molecular weight of germanium vapor have been determined by use of an apparatus for the simultaneous measurement of the weight of vapor effusing through two small orifices and of the force exerted by the effusing vapor. The molecular weight of germanium vapor at 1750°K was found to be 58±16 compared to the atomic weight of 72.60. The heat of sublimation of germanium at 298°K is 91.5±3.0 kcal.
23(1955); http://dx.doi.org/10.1063/1.1740570View Description Hide Description
Single ion free energies of hydration were assigned by Latimer, Pitzer, and Slansky by choosing a set of ion radii which made both negative and positive ions fall on the theoretical Born curve in a plot of ΔF against 1/r′. The r′ values were the crystal ion radii plus 0.1 A for negative ions and plus 0.85 A for positive ions. It is now shown that this assignment of single ion free energies is consistent with the single ion entropies of hydration if S̄ H+ is —2.1 (the Eastman value). The ΔS values are proportional to Z/r′ and the tentative suggestion is made that it is the temperature coefficient of r′ which leads to the Z/r′ function. It is proposed that the ΔF values be used to calculate a consistent set of radii of aqueous ions which will take into account coordination numbers and polarization.
23(1955); http://dx.doi.org/10.1063/1.1740571View Description Hide Description
Pyridine and pyrrole react together to form a 1:1 complex as shown by infrared, heat of reaction, viscosity,refractive index, and density data. The heat of formation of this complex is 3.8 kcal/mole. Pyrrole itself is associated, but, like the simple alcohols, cannot be represented by a simple equilibrium. The heat of dilution of pyrrole in CCl4 is 1.4 kcal/mole at infinite dilution.
23(1955); http://dx.doi.org/10.1063/1.1740572View Description Hide Description
The multiple origin method has been utilized for the selection of initial coordinates for the description of the normal vibrations of N‐dimethylaminodiborane. Symmetry considerations were then used in order to obtain symmetry coordinates from these MOM coordinates, and, under the assumption of a diagonal potential function, these coordinates were assigned to vibrational frequencies which have been recently reported by Mann. The valence force constants for the methyl‐N‐methyl framework vibrations were then calculated and the results compared with similar constants obtained from the dimethylamine molecule.