Index of content:
Volume 21, Issue 7, 01 July 1953
21(1953); http://dx.doi.org/10.1063/1.1699148View Description Hide Description
It is shown that an electric potential exists between the surface and the bulk of ionic crystals. The potential is expressed in terms of the energies necessary for formation of lattice defects. The distribution of the potential and of lattice defects near the surface is calculated. The difference between the concentration of lattice defects near the surface and that in the bulk leads to a ``surface conduction.'' The magnitude of the potential, the thickness of the space‐charge layer near the surface and the ``surface conduction'' are calculated for NaCl crystals using numerical values, calculated by Mott and Littleton [N. F. Mott and M. J. Littleton, Trans. Faraday Soc. 34, 485 (1938)] for the energies of formation of lattice defects. The effect of charged impurities in the crystals on the surface potential is discussed. The importance of the surface potential on diffusion, photoelectric effect, and photographic effect is mentioned.
An Application of Perturbation Theory to the F and G Matrix Method of Calculating Molecular Vibration Frequencies21(1953); http://dx.doi.org/10.1063/1.1699150View Description Hide Description
The F and G matrix form of the secular equation for molecular vibrations may be split into two approximate equations, of which one has as its roots the high frequencies (corresponding to relatively rigid bonds, etc.), the other the low frequencies (corresponding to relatively weak bonds, etc.). With the aid of the eigenvectors of these two equations, the exact equation is transformed into a form which yields the corrections to the approximate frequencies by a straightforward application of perturbation theory. The use of the correction terms so derived and the convergence of the perturbation series are illustrated by a discussion of the totally symmetric modes of ethylene.
21(1953); http://dx.doi.org/10.1063/1.1699151View Description Hide Description
The rate of combination of methyl radicals produced by the thermal decomposition of mercury dimethyl has been studied with a free radical mass spectrometer over a large range of temperature (161° to 814°C) and at one temperature (735°C) over a range of total pressure from 4.8 mm to 18.5 mm. The combination was found to be complex, consisting of a second‐order homogeneous reaction and a first‐order, presumably heterogeneous reaction. Only the second‐order reaction was studied in any detail. The rate constant or collision efficiency of this reaction was found to increase with decreasing temperature but showed no dependence on the carrier gas pressure. A negative temperature coefficient was found for the combination which, if expressed as an activation energy, was −2.2±0.5 kcal. It seems, however, more reasonable to regard this effect as a change in the effective collision diameter of the methyl radicals with temperature, the change being due to the van der Waals energy of attraction between the radicals.
21(1953); http://dx.doi.org/10.1063/1.1699152View Description Hide Description
Studies on the low temperature specific heat of crystalline selenium have been extended down to 15°K. The data are compared with a calculation based on a one‐dimensional‐continuum model with which good agreement is shown to exist down to about 37°K. Below this temperature, deviations are described in terms of an anisotropic continuum which considers the ``interaction'' between atom chains.
The values of the thermodynamic functions,entropy,enthalpy, and free energy have been evaluated and tabulated at regular integral values of temperature up to 300°K. The entropy of crystalline selenium at 298.16°K is 10.15±0.05 cal/g‐atom/deg, of which 0.22 was obtained by extrapolating below 15°K. For this extrapolation, the anisotropic‐continuum model was used.
21(1953); http://dx.doi.org/10.1063/1.1699153View Description Hide Description
The intermolecular force constants of gaseous fluorine have been determined from measurements of the second virial coefficients in the region 80–300°K. On the assumption that gas imperfection results only from binary collisions of spherical nonpolar molecules whose potential is of the form given by Eq. (1), the force constants obtained were r 0=3.61±0.04A and ε0/k=121±3°K. These force constants yield viscosities in good agreement with the experimental data of Kanda if the high temperature point is discarded.
21(1953); http://dx.doi.org/10.1063/1.1699155View Description Hide Description
Carbon 14‐labeled CO was used in a study of the carbiding of reduced iron in the temperature range 170–231°C. It was shown that the percarbide forms around nuclei scattered throughout the iron, that carbon in percarbide volumes is held firmly in place, and that a substantial fraction of the surface of partially carbided iron is occupied by percarbide.
21(1953); http://dx.doi.org/10.1063/1.1699156View Description Hide Description
Association of Joshi effect Δi with electronic part ie of the discharge current i was investigated by elimination principle. ie was suppressed under transverse magnetic fieldH. In agreement with Joshi's theory, negative effect (—percent Δi) in water and iodine vapor was maximum in i and negligible in i—ie ; comparatively, positive effect was unaffected by H.
21(1953); http://dx.doi.org/10.1063/1.1699157View Description Hide Description
Penner's method of calculating effects of absorption on measured OH (2Σ+) rotational distributions has been applied to the R 2 branch and the results compared with intensity measurements of acetylene‐oxygen flames at atmospheric pressure. It is shown that distributions in the hot gases above the reaction zone are in agreement with calculated distributions and that for isothermal regions the method can give both emissivity and rotational ``temperature,'' even when there is appreciable self‐absorption. Measured intensities in the reaction zone indicate that there is a rotational ``temperature'' several hundred degrees in excess of the adiabatic temperature and that the ``temperature'' of the emitters is greater than that of the absorbers.
21(1953); http://dx.doi.org/10.1063/1.1699158View Description Hide Description
Pyridine‐d 5 has been prepared by exchange between pyridine vapor and heavy water in the presence of a palladium catalyst. Infrared and Raman spectra are reported for pyridine and pyridine‐d 5 over the spectral range 300–4000 cm−1. Interpretation of the spectra with the help of the product rule and by analogy with the fundamental frequencies of benzene and benzene‐d 6 leads to complete sets of frequencies for the 27 vibrational degrees of freedom of pyridine and of pyridine‐d 5. The frequency assignment for pyridine does not differ greatly from previous ones, but is believed to be more reliable because of the additional spectroscopic data.
Investigation of the Surface Reaction of Oxygen with Carbon on Tungsten with the Field Emission Microscope21(1953); http://dx.doi.org/10.1063/1.1699159View Description Hide Description
The adsorption of oxygen and carbon on tungsten and the surface reaction between carbon and oxygen on tungsten have been studied by means of the field emission microscope. Emission patterns for oxygen on tungsten,carbon on tungsten, and oxygen and carbon together on tungsten under a variety of temperature pretreatment conditions have been obtained. Average work functions over all exposed crystallographic planes, calculated from measured voltages and emission currents on the basis of the Fowler‐Nordheim equation, give a measure of surface coverage in the case of oxygen on tungsten. The similarity of the emission‐pattern changes in the evaporation of oxygen from tungsten with those found in the reaction between carbon and oxygen on tungsten suggests that the rate‐controlling step in the reaction is desorption of oxygen from the tungstensurface. Diffusion of carbon into the tungsten lattice plays no role in the pattern changes since, in the absence of oxygen, the carbon‐on‐tungsten surface is found to be very stable.
21(1953); http://dx.doi.org/10.1063/1.1699160View Description Hide Description
The near ultraviolet solution spectra of twenty one mono‐, di‐, and triamino derivatives of symmetric triazine are reported. The addition of amino groups to the s‐triazine ring introduces electrons which can interact with those of the ring, with resultant changes in the intensity and position of the absorption bands. The spectra of mono‐, di‐, triamino‐s‐triazine may be arranged in a Platt sequence along with that of trichloro‐s‐triazine and that expected for s‐triazine.
21(1953); http://dx.doi.org/10.1063/1.1699161View Description Hide Description
An investigation has been made of the chemical forms assumed by I131 initially in the form of iodide ion at low concentration (the order of 10−7 M) when it is oxidized under various conditions. Oxidation at room temperature in 1f sulfuric acidsolution by dichromate ion or cerium(IV) results in the formation of I2 and three additional, unidentified, chemical fractions which are not readily exchangeable with I−, I2, or IO3 −. Two of the unidentified fractions are extracted from aqueous sulfuric acidsolution by organic solvents, one fraction being converted by aqueous sodium hydroxide to water‐soluble forms exchangeable with I2. At least some of the unidentified fractions probably are the products of reactions between trace impurities, molecular or colloidal, and iodine in an oxidized reactive form such as HIO. These unidentified fractions are quite inert toward oxidation and reduction.
When iodide ion at low concentration is treated with a hot sulfuric acidsolution of cerium(IV), the principal product is IO3 −, or a species readily exchangeable with IO3 −. The IO3 − formed in this way is readily reduced at room temperature to I− by a sulfuric acidsolution of iron (II).
21(1953); http://dx.doi.org/10.1063/1.1699162View Description Hide Description
The theory of molecular size distributions which are intrinsically Poisson in character is extended to cover two complementary aspects of copolymerization which are specifically adapted to polypeptide synthesis via the N‐carboxyamino acid anhydride (Leuchs monomer). The statistical aspects for (1) discrete monomer reacting with a Poisson ensemble of initiators and (2) the circumstance of an array of monomers copolymerized by a discrete initiator are delineated. Explicit relations for the number and weight average molecular weights are derived.
21(1953); http://dx.doi.org/10.1063/1.1699163View Description Hide Description
The principal polarizabilities of a flexible paraffin hydrocarbon molecule may be calculated from the bond polarizabilities. The result will depend upon the average configuration of the molecule. The light scattering depolarization which is calculated from these polarizabilities may be compared with measured values. The comparison favors a configuration requiring preferential trans‐arrangements about carbon‐carbon single bonds.
21(1953); http://dx.doi.org/10.1063/1.1699164View Description Hide Description
Group theoretical methods are used to separate the rotational coordinates from the N‐particle Schroedinger equation and obtain a set of equations which are particularly applicable to the study of collisions involving two sets of particles or two molecules. The coordinates used to describe the configuration of the N particles in a center of gravity coordinate system are those describing the orientation of the system as a whole, the relative orientation and separation of the two molecules, and the internal configuration of each of the molecules. Coupled differential equations involving only the coordinates describing the internal configuration and separation of the molecules are obtained. As a special case the equations are applied to a system consisting of two diatomic molecules.
21(1953); http://dx.doi.org/10.1063/1.1699165View Description Hide Description
This paper contains a theoretical account of the possible effects which the ionization of donor and acceptor impurities can induce in the thermodynamic phase relations involving their solutions with semiconductors. These effects reflect the energyband structure of the semiconductor. Furthermore, the phenomenon has an interest of its own, for within a certain range of experimental conditions the effects can be attributed to a chemical‐like, mass action behavior of the electrons which play the roles of negative ions.
Section V is a brief discussion of a fine point concerning the Fermi level. It is shown that although the Fermi level is certainly the electronic electrochemical potential, it is not the Gibbs free energy per electron unless the density of electronenergy levels is linear in the volume of the system.
21(1953); http://dx.doi.org/10.1063/1.1699166View Description Hide Description
2,2‐dinitropropane forms face‐centered, cubic crystals at room temperature, with a 0=8.78±0.05A, and 4 molecules per unit cell. Molecular disorder is necessarily present in the cell, and several models are examined. Excellent agreement is obtained with a model in which the molecule possesses complete orientational disorder. Although the distinction between ``rotational'' disorder in time and in space is not possible, the following mechanism is suggested: while the disorder is complete at long range, there is a high degree of order at short range.
21(1953); http://dx.doi.org/10.1063/1.1699167View Description Hide Description
A variational principle is formulated for diffusional processes such as heat and matter diffusion which is a modification of Onsager's principle of minimum dissipation. Also a variational principle is given for the flow of viscous incompressible fluids which has some analogy to Onsager's principle.
21(1953); http://dx.doi.org/10.1063/1.1699168View Description Hide Description
The possibility of observing the rotational spectra of allene‐type molecules was suggested by the present author and Venkateswarlu. In this paper the effect of nuclear spin on the statistical weight of each rovibrational levels and the transition probability between them are calculated.