Index of content:
Volume 18, Issue 10, 01 October 1950
18(1950); http://dx.doi.org/10.1063/1.1747467View Description Hide Description
An experimental scheme to investigate the reduction equilibrium of barium oxide by carbon is described and analyzed critically. Exploratory results at 950° support the analysis and indicate equilibrium at carbon monoxide pressures below 100μ with bariumvapor pressures in the range 0.1 to 0.3μ. The resulting value for the free energy of formation of barium oxide is −114,000 cal. per mole.
18(1950); http://dx.doi.org/10.1063/1.1747468View Description Hide Description
The vapor phase infra‐red spectra of the molecules HCCCl and DCCCl have been investigated in the region 2μ to 30μ, and four of the five fundamentals have been identified for each molecule. Force constants have been calculated for the stretching modes of vibration assuming a linear structure. The bond stretching force constants have the values: f CH = 5.88, f CC = 14.9, f CCl = 5.51 all in units of 105 dynes/cm. The effect of resonance between the covalent structure, H–C≡C–Cl, and the structure H–C=C=Cl+ in stiffening the carbon‐chlorine bond is discussed.
18(1950); http://dx.doi.org/10.1063/1.1747469View Description Hide Description
Measurement of the absolute intensities of several infra‐red absorption bands of cyanogen and cyanogen chloride gives the following values in cycles per cm at N.T.P.
Values of the variation in bond moments with change in bond length are calculated on the basis of bond moment additivity. This leads to widely different values of this derivative for the CN bond in the two molecules.
The infra‐red spectrum of cyanogen chloride from 2 to 20 microns is reported.
Substituted Ethanes. II. Raman and Infra‐Red Spectra of 2,3‐Dibromo−2,3‐Dimethylbutane and 2,2,3,3‐Tetramethylbutane18(1950); http://dx.doi.org/10.1063/1.1747470View Description Hide Description
Raman displacements and infra‐red absorption wave numbers for 2,3‐dibromo−2,3‐dimethylbutane and 2,2,3,3‐tetramethylbutane (hexamethylethane) are reported, together with depolarization factors for the Raman lines and relative intensities for both the Raman lines and the infra‐red absorption bands. The spectra were obtained in both benzene and CCl4 solutions and the infra‐red measurements covered the region 400–5000 cm−1. The results indicate that both molecules possess a center of symmetry and that the structure is the same in the two solvents. The dipole moment of 1.01 D. obtained by Mizushima, Morino, and Miyagawa for 2,3‐dibromo−2,3‐dimethylbutane in CCl4 solution may be explained by oscillations of 48° amplitude about the equilibrium trans‐ position.
18(1950); http://dx.doi.org/10.1063/1.1747471View Description Hide Description
The isotopic composition of the products of the controlled thermal decomposition of ammonium nitrate has been studied. It has been found that small amounts of water are necessary to initiate the decomposition of ammonium nitrate. N15H4NO3 has been found to yield exclusively the isomer N15N14O. Some inferences are drawn from this observation regarding the mechanism of the reaction.
Oxygen and nitrogen isotope effects accompanying the decomposition have been studied with material of ``natural'' isotopic composition. Satisfactory agreement is found between the experimental results and theoretical calculations.
A method for the isotopic analysis of nitrates for O18 is outlined.
Ultrasonic Velocities of Sound in Some Metallic Liquids. Adiabatic and Isothermal Compressibilities of Liquid Metals at Their Melting Points18(1950); http://dx.doi.org/10.1063/1.1747472View Description Hide Description
The ultrasonic velocities of sound at 12 mc in 12 pure liquid metals at their melting points under atmospheric pressure and in 4 equi‐atomic liquid metallic mixtures have been determined by the use of the electronic pulse‐circuit technique.
For the pure metals the adiabatic and isothermal compressibilities have been computed. The compressibilities were generally found to be somewhat larger than for the corresponding solids at room temperatures. A calculation of Grüneisen's γ for the liquid metals shows that this quantity, in the case of normal metals, does not change appreciably on going from the solid state at room temperature to the liquid at moderately elevated temperature. These facts support the familiar view that the liquid metals at temperatures not far above their melting points are in a ``solid like'' state, and that equations of state for the solid state may be applicable to such liquids.
18(1950); http://dx.doi.org/10.1063/1.1747473View Description Hide Description
The solubility relations of n‐heptane with f‐heptane, iodine, sulfur, stannic iodide, and phosphorus are all accounted for within the usual limits of accuracy for regular solution theory by a solubility parameter 8.1 instead of the value 7.45 derived from its energy of vaporization per cc. Solutions of 2,2,4‐trimethyl pentane with f‐heptane and with iodine are similarly accounted for by the empirical value 7.45 instead of 6.85. Such an adjustment for paraffins is a practical alternative to the treatment used by Simons and Dunlap for the system n‐pentane, ``pentforane,'' which they recently reported upon, and is, at the same time, consistent with their assumption that the exceptional behavior of paraffins is to be attributed to an irregularity in their mutual repulsions.
LCAO Self‐Consistent Field Calculation of the π‐Electron Energy Levels of cis‐ and trans−1,3‐Butadiene18(1950); http://dx.doi.org/10.1063/1.1747474View Description Hide Description
The π‐electrons of the molecules cis‐ and trans−1,3‐butadiene are treated by the method of antisymmetrized products of molecular orbitals, the molecular orbitals being taken as linear combinations of 2pπ‐Slater atomic orbitals with effective charge 3.18. The bestground stateLCAO molecular orbitals obtainable from these are found by application of a method recently proposed by Roothaan which is based on the variational theorem, and the π‐electron energy of the ground state is calculated. Including a correction for nuclear repulsions, the trans‐ form is computed to be 0.12 ev more stable than the cis‐form. Using the ground state orbitals to build up excited statewave functions, the energies of four singly excited singlet states and the corresponding triplet states are calculated, there resulting for the average of the lowest singlet and triplet states the excitation energy 5.4 ev for cis‐ and 5.7 ev for trans‐, the experimental value for the lowest singlet state (probably for trans‐) being 6.0 ev. The first ionization potential is computed to be 9.7 ev for both cis‐ and trans‐, whereas the observed value is 9.1 ev. No extra‐geometrical empirical data are used except in the calculation of ionization potentials, where the value − 11.28 ev based on atomic spectroscopic data is used for the energy of a 2pπ‐electron in a carbon atom in its valence state.
Ionization and Dissociation by Electron Impact: Cyanogen, Hydrogen Cyanide, and Cyanogen Chloride and the Dissociation Energy of Cyanogen18(1950); http://dx.doi.org/10.1063/1.1747475View Description Hide Description
The appearance potentials of CN+ in the mass spectra of HCN and (CN)2 have been remeasured and found to be 19.36±0.2 and 20.31±0.2 ev, respectively. Combination of the appropriate thermochemical data with the difference between these energies yields, D(NC–CN) = 6.88−2E(Z) ev where Z is the state of the CN radical either X 2Σ+ or A 2Π i , that accompanies CN+ from (CN)2, and E(X 2Σ+) = 0.00 ev and E(A 2Π i ) = 1.13 ev. The appearance potential of Cl+ in the mass spectrum of ClCN has also been measured and found to be 17.81±0.2 ev, which value gives D(NC–CN) = 6.92−2E(Y) when combined with the spectroscopicionization potential of the chlorine atom and the necessary thermochemical data. Here Y is the state of the CN radical that accompanies Cl+ from ClCN. In order that the two determinations of D(NC–CN) be consistent it is necessary that Y = Z and then the two permissible values of D(NC–CN) are 6.90±0.2 ev (Y = Z = X 2Σ+) or 4.64±0.2 ev (Y = Z = A 2Π i ). These results do not permit a choice between White's determination, 6.3±0.2 ev, and Pauling's estimate, 3.9±0.6 ev, but do serve to eliminate from further consideration the determination by Kistiakowsky and Gershinowitz, 3.3 ev. Neither value is compatible with the 5.2 ev suggested by Glockler. However, electron impact data on ethylene and methylene radical give 5.6 ev as the upper limit to energy of dissociation of ethylene into two methylene radicals, and this can be taken as an upper limit to the dissociation energy of cyanogen, suggesting the lower of the two possible values of D(NC–CN) to be correct. Corresponding to this lower value of D(NC–CN), 4.64±0.2 ev, the dissociation energies of H–CN and Cl–CN are 4.80±0.1 and 3.66±0.1 ev, respectively, and the ionization potential of CN is 14.55±0.2 ev.
The specific intensities of the various ions in the mass spectra of (CN)2, HCN, and ClCN characteristic of 75‐volt ionizing electrons are given with reference to that of A+ in the argon mass spectrum.
18(1950); http://dx.doi.org/10.1063/1.1747476View Description Hide Description
Ultrasonic absorption in various organic liquids at four different frequencies 1.00, 1.46, 2.89, and 4.00 Mc as well as their temperature coefficient of absorption (25°C to 60°C) have been studied by ultrasonicinterferometer.Liquids have been classified into four broad groups, Class I in which absorption due to changes in the heat content of the medium predominates, Class II in which absorption caused by structural changes in the quasi‐crystalline structure of the liquid state predominats, Class III in which viscosity of the medium alone accounts for absorption and Class IV where absorption is not proportional to the square of the frequency.
18(1950); http://dx.doi.org/10.1063/1.1747477View Description Hide Description
For reversible reactions close to equilibrium the net reaction rate (rf —rb ) is shown to be proportional to ΔX, where X is any one of the thermodynamic functions, e.g., the Gibbs free energy,F, governing equilibrium under the conditions of the reaction, e.g., (rf —rb )=rf ·—ΔF /RT. The derived relationships are independent of the manner in which small displacements from equilibrium may be brought about. Equations are derived by which the magnitude of the forward (or backward) reaction rate at equilibrium may be determined with the aid of observations of the net reaction rate close to equilibrium. Since the magnitude of the former is a function of the kinetics of the reaction, measurements of the net reaction rate near equilibrium over a range of conditions may be used within specified limits to determine the kinetics of reversible reactions.
18(1950); http://dx.doi.org/10.1063/1.1747478View Description Hide Description
The problem of determining the rate of cataphoresis of a solid spherical particle in an electrolyte when relaxation effects are neglected, is solved completely by using Oseen's equations. The bearing of the results on the usual methods of finding zeta‐potentials from cataphoretic velocities is discussed.
18(1950); http://dx.doi.org/10.1063/1.1747479View Description Hide Description
It is shown that Pauling's ionic and atomic radii may be correlated with the ionic heat of hydration in a manner which provides a method of intercomparison of the different radii and demonstrates their self‐consistency. The correlation also indicates significant differences between ionic and atomic radii which may be interpreted in terms of the ion‐dipole interaction theory of solutions.
18(1950); http://dx.doi.org/10.1063/1.1747480View Description Hide Description
The accommodation coefficients of nine gases on platinum at various temperatures in six different tubes are presented as a function of pressure. In all cases the accommodation coefficients show a constant value as the pressure is lowered toward zero, which is in contradiction to results reported by Amdur and co‐workers. Reasons for disagreement are suggested and criticism of an earlier paper from this laboratory is answered. Presumably specially reliable values of the accommodation coefficients of argon and krypton taken in Tube B are given and this tube and method of operation are described in detail.
18(1950); http://dx.doi.org/10.1063/1.1747481View Description Hide Description
18(1950); http://dx.doi.org/10.1063/1.1747482View Description Hide Description
Based on Meixner's thermodynamics for irreversible processes, and the work of Haase, an equation for the thermal diffusion ratio α, which can be evaluated from the equation of state, is presented.
Using van der Waals' equation, α's are calculated in the critical region and compared with data for ethane‐xenon. The equation reproduces all the essential features of the experimental results.
Calculations made for a mixture of isotopes indicate that the effect of pressure on α cannot be attributed to selective clustering.
18(1950); http://dx.doi.org/10.1063/1.1747483View Description Hide Description
New measurements of the infra‐red absorptionspectrum of acetylene between 16 and 2.5μ have established many new bands. A cooling experiment has demonstrated that the central line of the parallel band ν4 1+ν5 1 (1328.18 cm−1) belongs to a difference band, 2ν4 0+ν5 1—ν4 1 (1328.46 cm−1). Resolution sufficient to distinguish the center of the fundamental ν3 (3282.5 cm−1) from the combination band ν2+ν4 1+ν5 1 (3295.56 cm−1) has been obtained. An interesting Π u —Π g ‐band, identified as ν1+ν5 1—ν4 1, is shown. Frequencies of the infra‐red inactive fundamentals are derived and many anharmonic coefficients are evaluated. Diagrams of the absorption regions and tables of the line frequencies are included.
18(1950); http://dx.doi.org/10.1063/1.1747484View Description Hide Description
The third virial coefficient for non‐polar gases has been calculated with great accuracy by means of punched‐card techniques. The Lennard‐Jones potential, with inverse twelfth‐power repulsion and inverse sixth‐power attraction, was used in the calculations. Excellent agreement between our computations and those of Kihara was obtained at very high temperatures; in the moderate temperature region our calculations agree moderately well with those of Montroll and Mayer and those of de Boer and Michels. A comparison with experimental data indicates fairly good agreement for the approximately spherical molecules argon, methane, and nitrogen. In other cases there are discrepancies suggesting deviations from the form of the interaction energy which we assumed. There is considerably difficulty in obtaining accurate third virial coefficients from the equation of state data. A method is suggested whereby the third virial coefficients for mixtures of gases may be estimated. The functions which are tabulated should be particularly useful for extrapolating the equation of state to very high temperatures, where no experimental data are available. The zero‐pressure derivative of the Joule‐Thomson coefficient with respect to pressure provides additional means for comparing our tabulated functions with experimental data, and the deviations are consistent with those discovered by comparison of the third virial coefficients themselves.
Fluorescence Studies of Some Simple Benzene Derivatives in the Near Ultraviolet: II. Toluene and Benzonitrile18(1950); http://dx.doi.org/10.1063/1.1747485View Description Hide Description
The fluorescence spectra of toluene and benzonitrile have been studied using various sources of excitation. In both cases, discrete spectra have been observed in the near ultraviolet. The spectrum of toluene shows about 100 bands while that of benzonitrile shows about 140 bands. In both cases, there is good agreement with the absorption spectra. Progressions are noted and assignments are made for some of the vibrations in accordance with the symmetry properties of the molecules.