Volume 23, Issue 11, 01 November 1955
Index of content:
23(1955); http://dx.doi.org/10.1063/1.1740652View Description Hide Description
The HCN molecule is treated as a system of four π electrons moving in a suitable potential field. Its lower excited states are calculated, using both the molecular orbital method with configuration interaction and the Heitler‐London method including ionic‐homopolar resonance.
Slater atomic orbitals with effective charges 2δ=3.18 for the C atom and 3.85 for the N atom are employed.
The calculated energy levels with the 1Σ+ground state as zero are 3.53 ev (3Σ+), 5.60 ev (1Σ—), 7.71 ev (3Δ), etc. The effect of configuration interaction is remarkable, amounting to several electron volts, and ionic terms have almost the same weight as homopolar terms.
23(1955); http://dx.doi.org/10.1063/1.1740653View Description Hide Description
The infrared spectrum of gaseous fluorotrichloroethylene, FClC:CCl2, has been obtained in the range 3—50 microns. The Raman spectrum of a liquid sample has also been determined. Earlier data and new force constant calculations for some other fluorochloroethylenes are reviewed and used to establish a satisfactory vibrational assignment for FClC:CCl2. The planar fundamentals appear at 1645, 1181, 988, 857, 520, 407, 358, 250, and 174 cm—1; the out‐of‐plane vibrations occur at 537, 313, and probably near 130 cm—1. A necessary revision in the existing assignment for F2C:CCl2 is indicated. A table of the thermodynamic functions is given for FClC:CCl2 in the ideal gaseous state.
23(1955); http://dx.doi.org/10.1063/1.1740654View Description Hide Description
The infrared spectrum of gaseous CCl2:CClF has been observed from 2 to 22μ with NaCl and KBr prisms. The Raman spectrum of the liquid has been photographed with a three‐prism glass spectrograph of linear dispersion 15 A/mm at 4358 A, and the depolarization ratios of the stronger Raman bands have been measured. All but one of the fundamental vibration frequencies have been assigned, and the spectra have been interpreted in detail.
23(1955); http://dx.doi.org/10.1063/1.1740655View Description Hide Description
Concerning the Temperature Coefficient of the emf of Reversible Galvanic Cells Operated at Variable Concentration. II23(1955); http://dx.doi.org/10.1063/1.1740656View Description Hide Description
Heat Capacity of Zinc Fluoride from 11 to 300°K. Thermodynamic Functions of Zinc Fluoride. Entropy and Heat Capacity Associated with the Antiferromagnetic Ordering of Manganous Fluoride, Ferrous Fluoride, Cobaltous Fluoride, and Nickelous Fluoride23(1955); http://dx.doi.org/10.1063/1.1740657View Description Hide Description
The heat capacity of ZnF2 has been measured calorimetrically between 11 and 300°K. In addition to the direct experimental data, values of heat capacity,entropy,enthalpy, and free energy are tabulated at selected temperatures. The values of entropy, and enthalpy at 298.16°K are S 0=17.61±0.03 cal deg—1 mole—1 and H 0–H 0 0=2827±5 cal mole—1. The heat capacity of ZnF2 has been used, with a corresponding states argument, to estimate the lattice contributions to the entropy and heat capacity of the isomorphous fluorides MnF2, FeF2, CoF2, and NiF2 which exhibit heat capacity maxima associated with antiferromagnetic ordering at 66.5, 78.35, 37.70, and 73.22°K, respectively. The values of electronic entropy at the maximum in heat capacity are: MnF2, 0.85R ln6; FeF2, 0.87R ln5; CoF2, 0.80R ln2; NiF2, 0.71R ln3. The electronic entropies and heat capacities are compared with molecular field and spin wave theories of antiferromagnetism. At very low temperatures the electronic heat capacity on NiF2 is varying approximately as T ; whereas that of the other antiferromagnetic fluorides depends much more strongly on temperature. This behavior of the electronic heat capacity of NiF2 is believed to be associated with the small ferromagnetic moment found in magnetic anisotropy measurements on this salt.
23(1955); http://dx.doi.org/10.1063/1.1740658View Description Hide Description
An ``apparatus'' is described in which, in a thought experiment, the whole of a sample of fluid may be subjected to a uniform electrostatic field under controlled conditions. The work done in such a process can be written into fundamental thermodynamic equations so as to enable the field strength E to be a variable of state in a way which is essentially symmetrical with the way in which P and T are variables of state. This enables a variety of differential coefficients to be obtained, some of which appear to be new. A discussion is given of the relationship between ``electrostriction pressure'' (as derived in electrostatics) and thermodynamic pressure. Application of the formalism to systems of more than one component is illustrated by discussion of the change in composition produced by charging the plates of a small condenser immersed in a large volume of binary fluid mixture. The customary representation of the ``energy density'' in a field as equal to E 2 K/8π is discussed, and found to be limited in formal validity when the field is nonuniform, when the charging process takes place under conditions which do not hold the volume constant, or when dielectric saturation is taken into account.
Dispersion and Absorption of Sound in Imperfect Gases in General Chemical Equilibrium and Its Application to Chemical Kinetics23(1955); http://dx.doi.org/10.1063/1.1740659View Description Hide Description
Previously, it was shown that there occur the dispersion and the absorption of sound owing to the chemical reaction in the gas in general chemical equilibrium such as aA+bB+···⇄qQ+rR+···. As the velocity and the absorption coefficient of sound are affected predominantly by the imperfection of the gas over other factors, the case of imperfect gases is considered. The velocity and the absorption coefficient are derived from the complex velocity of sound, and the characteristic of the dispersion and absorption curves are examined. The velocity and the absorption coefficient of sound are formulated in terms of the pressure, the density, the virial coefficients, the equilibrium constant, namely, the composition, the reaction heat at a constant volume, the molar heat at a constant volume, and the rate constant of the chemical reaction. By measuring the velocity and the absorption coefficient of sound, it is possible to calculate the rate constant of the chemical reaction and the reaction heat. As special cases, the formulas for the perfect gas and for a mixture of imperfect gases in which no chemical reactions occur, are derived. As an example of the calculation, the case of the dissociation equilibrium A⇄B+B was treated.
23(1955); http://dx.doi.org/10.1063/1.1740660View Description Hide Description
The J = 6←5 rotational transitions have been observed for 10 isotopic species of CH3CCCl, including four of the fully deuterated molecule. The values for DJ were calculated from the force constants of the molecule, and are tabulated with the resulting values for B 0. The structural parameters giving the best fit to the 10 moments of inertia IB are: r 0(C–Cl) = 1.6371 A, r 0(C≡C) = 1.2069 A, r 0(C–C) = 1.4584 A, r 0(C–H) = 1.117 A, ≰HCC = 110° 46′, r 0(C–D) = 1.114 A, and ≰DCC = 110° 30′. The quadrupole coupling constant eqQ was determined as —79.6 Mc/sec for Cl35 and —62.6 Mc/sec for Cl37. For CH3CCCl35, CH3CCCl37, CD3CCCl35, and CD3CCCl37 experimental values of DJK and HJKK were determined from the K structure. To fit the observed fine structure it was necessary to include the third‐order term HJKK in the expression for the rotational energy.
Equation of State of Gases by Shock Wave Measurements. I. Experimental Method and the Hugoniot of Argon23(1955); http://dx.doi.org/10.1063/1.1740661View Description Hide Description
An experimental method is described for the simultaneous measurement of the velocity of a plane shock through a gas and the associated particle velocity. Shocks are generated by a plate driven by a high‐explosive system. The velocities are recorded by a high‐speed rotating‐mirror smear camera with a precision of about ±½%. Data are presented defining the Hugoniot of argon between 200 and 1100 Los Alamos atmospheres. These data are compared with the theoretically predicted Hugoniot.
23(1955); http://dx.doi.org/10.1063/1.1740662View Description Hide Description
23(1955); http://dx.doi.org/10.1063/1.1740663View Description Hide Description
At temperatures below —180°C liquid ozone and liquid oxygen are not miscible in all proportions. Two liquid phases occur over a definite range in composition which depends upon the temperature. The solubility diagram at saturation pressures has been determined experimentally by measuringvapor pressureversus composition isotherms at —183.0°C, —185.7°C, and —195.6°C. The upper or oxygen‐rich liquid phase has been analyzed at —181.9°C, —182.9°C, —186.0°C, and —195.6°C. The critical solution temperature is —179.9°C±0.5°C. A liquid‐vapor equilibrium diagram at one atmosphere total pressure has also been determined experimentally.
23(1955); http://dx.doi.org/10.1063/1.1740664View Description Hide Description
Original absorption spectra of halides and a large body of literature absorptionspectrum data are assembled. Certain characteristic features are pointed out which can be ascribed to transitions of electrons localized on the halide portion of a molecule or ion, such that their removal to an excited condition essentially leaves a neutral halogen atom as part of the excited state configuration. Recognition of this portion of the spectrum should assist understanding of halide spectra.
Absorption Spectrum and Quantum States of the Praseodymium Ion. I. Single Crystals of Praseodymium Chloride23(1955); http://dx.doi.org/10.1063/1.1740665View Description Hide Description
The structure of the polarization spectra exhibited by single crystals of anhydrous praseodymium chloride permitted the assignment of quantum states of the praseodymium ion because of the fact that the symmetry of the crystal fields had previously been determined by x‐rays. The crystals which were diluted with isomorphic, colorless lanthanum chloride, were grown from melts.
Observations of transitions over the range from 2200 A to 18 000 A at the temperatures of liquid nitrogen and liquid helium led to the identification of seven upper states as well as the substates into which they were split by the crystal fields. The four lowest substates of the ground state also were characterized. The F triplet was found inverted.
All the transitions were forced electric dipole in nature.
Absorption Spectrum and Quantum States of the Praseodymium Ion. II. Anhydrous Praseodymium Fluoride in Films23(1955); http://dx.doi.org/10.1063/1.1740666View Description Hide Description
The absorption spectra of anhydrous praseodymium fluoride were examined to confirm term designations derived from the spectra of anhydrous praseodymium chloride. In the fluoride, praseodymium ion is at the center of a micro‐field of C2V symmetry and in the chloride it is in a field of C3h symmetry. There was complete consistency in the interpretations of the spectra of the two compounds.
A new phenomenon appeared in the spectrum of the fluoride, however. The selection rules prohibiting some of the possible transitions of an ion in a field of C2V symmetry valid at the temperature of liquid nitrogen were lifted at the temperature of liquid helium, where in fact all possible transitions occurred. There is evidence against any gross crystallographic transformation.
It is surmised that the positions of energy minimum for the ions lie slightly off the symmetric positions possibly due to higher order interactions such as occurs in the case of bariumtitanate.
23(1955); http://dx.doi.org/10.1063/1.1740667View Description Hide Description
Angular parts of p‐ and d‐orbitals are hybridized to form a set of tetrahedrally oriented π orbitals. These orbitals are suitable for explaining partial double bond character in compounds such as nickel tetracarbonyl. It is shown that up to three of these orbitals may exist, each possessing the required properties of orthogonality and linear independence. The maximum partial double bond character allowed is, in this way, 75%. The strength of these orbitals, according to a modified Pauling's criterion, is discussed. Also the cases of trigonal bipyramidal and octahedral symmetry are discussed. An attempt is made to interprete semiquantitatively bond lengths in Cr, Fe, and Ni carbonyls.
Localizability of Electrons in Atoms and Molecules—Application to the Study of the Notion of Shell and of the Nature of Chemical Bonds23(1955); http://dx.doi.org/10.1063/1.1740669View Description Hide Description
The importance of the correlations existing between the positions of electrons in atoms and molecules has recently been stressed. A new method for the study of these correlations is presented here. It consists in the decomposition of the space of an electronic system into small parts where there is a very large probability of finding one and only one electron of a given spin. This method allows the association of spherical rings to the shells of atoms and the association of space to the atomic core and to the bonds of molecules.
23(1955); http://dx.doi.org/10.1063/1.1740670View Description Hide Description
23(1955); http://dx.doi.org/10.1063/1.1740671View Description Hide Description
An isotopic tracer experiment, using carbon 13, has been performed to determine whether the excited C2 radical in acetylene flames comes directly from the carbon pair of the acetylene burned. In the flame studied, the greater part of the C2 * which radiates does not come from this source, but is produced in some series of reactions in which the —C≡C— bond is broken prior to the appearance of C2 *. It is shown further that most of the C2 * cannot arise from the random breakup of polymers or incipient carbon particles formed by direct polymerization of acetylene. The results appear to favor the choice of a reaction between single‐carbon fragments as the predominant source of C2 *.