Index of content:
Volume 24, Issue 2, 01 February 1956
24(1956); http://dx.doi.org/10.1063/1.1742453View Description Hide Description
An enhanced oxidation of platinum has been observed in moist activated oxygen, and the cause of this enhancement has been investigated. The surface oxidation was examined at 1000°C and 0.50 mm Hg pressure of oxygen, and the rate was found to be markedly increased by the oxygen atoms. The reaction was found to obey a linear law of the form ω= (k+k 2 n 0)t, where n 0 is the number of oxygen atoms striking unit area of the platinum per second. Oxygen atoms were shown to be at least 400 times more reactive than oxygen molecules.
24(1956); http://dx.doi.org/10.1063/1.1742454View Description Hide Description
A simple model, similar to the ``free electron'' theory of metals and conjugated systems, is shown to yield good values for the energies of most single covalent bonds. The model can be extended to multiple bonds and charged species, but not in its present form to excited states and unstable species. It can be correlated with the free electron theory of metals.
The significance of the success of this and other simple models in predicting bond energies is discussed.
24(1956); http://dx.doi.org/10.1063/1.1742455View Description Hide Description
The coloring of sodium azide (NaN3) by gamma‐ray and fast and slow neutron bombardment has been studied by reflection measurements.Gamma rays alone produce a broad absorption band at 3600 A, which is little affected by heating at 90°C, and poorly‐defined bands at 6600 A and 7600 A which decay completely at room temperature. Fast neutron irradiation at room temperature, or slow neutron irradiation at 100°C, as well as slow neutron irradiation at room temperature and subsequent heating at approximately 90°C give rise to a band at 6000 A. This also appears when material, which has been subjected to gamma‐ray irradiation, is heated at higher temperatures. When heated near the decomposition temperature, the spectra of NaN3 crystals which have been subjected to any of the above forms of irradiation are similar. At this temperature another band appears at 2800 A. Heat treatment alone colors the unirradiated material primarily near 3600 A, but much less intensely than in irradiated crystals. It appears that some of the observed bands are connected with the decomposition of this compound, brought about either by irradiation or thermal treatment.
24(1956); http://dx.doi.org/10.1063/1.1742456View Description Hide Description
A description of an experimental method of obtaining pressure‐time data for the decomposition of coarse TNT following partial detonation is given. This method consisted of photographing (with a streak camera) the displacement of a slug shot from a smooth bore cannon. The velocity and acceleration of the slug were obtained by numerical differentiation of the displacement‐time data derived from the photograph. Pressure‐time curves were obtained which exhibited pressure maxima at times that were dependent upon the particle size of the TNT detonated in the cannon. Peak pressures for TNT of 4—6 standard mesh particle size occurred between 140—200 μsec, peak pressures for 8—10 mesh occurred between 115—140 μsec, and pressure maxima for ``fine'' TNT occurred between 50—70 μsec. The pressure‐time curves were analyzed, and reaction times of the coarse TNT were calculated by two different methods. One method yielded a value of the reaction time for each pressure‐time coordinate and the other a reaction time in terms of the time at which maximum pressure occurred. The results obtained by these two methods were not the same. However, when corrections were made for gas leakage from the cannon, rather good agreement resulted. The most probable value computed (after leakage corrections were made) for the 4—6 TNT was found to be about 300 μsec and for the 8—10 TNT about 200 μsec. On the basis of these reaction times the grain erosion velocity for the TNT in the cannon was evidently much greater than linear burning rates at the same pressure obtained experimentally for explosive deflagration.
Study of Two‐Center Integrals Useful in Calculations on Molecular Structure. III. A Unified Treatment of the Hybrid, Coulomb, and One‐Electron Integrals24(1956); http://dx.doi.org/10.1063/1.1742457View Description Hide Description
The problem of the two‐center hybrid integrals is solved in a general way for Slater‐type atomic orbitals with integral effective quantum numbers. No other restrictions are placed upon effective quantum numbers and effective nuclear charges. The integrals are expressed linearly in terms of one type of auxiliary functions. A method for finding the coefficients is given, and the latter are computed for all cases involving orbitals with quantum numbers 1 and 2. The auxiliary functions are discussed in detail, and methods given for their computation. The treatment developed for the hybrid integrals is shown to be applicable also to the two‐center Coulomb integrals and to the one‐electron integrals.
24(1956); http://dx.doi.org/10.1063/1.1742458View Description Hide Description
The distribution of partially deuterated pentaborane species resulting from the reaction between B2D6–B5H9 and its converse B2H6–B5D9 has been examined mass spectroscopically. It was found that the deuterium is entering the pentaborane by two main processes; namely exchange and synthesis by pyrolysis of diborane. The number of readily exchangeable positions in the pentaborane under our experimental conditions is five. If the remaining four hydrogens are exchanging they are doing so at a very much slower rate. Examination of the mass spectrum indicates that the deuteriums are entering the molecule singly during exchange. Tracer studies with B10 indicate that borons are not involved in the exchange.
24(1956); http://dx.doi.org/10.1063/1.1742459View Description Hide Description
A modification of the Boltzmann equation is described in which the rotational motion of nonspherical molecules is considered classically. This Boltzmann equation leads to equations of continuity, motion, and energy balance similar to the equations applying when the molecules are spherical. An additional equation of change arises, however, because of the conservation of angular momentum in collisions. (When the molecules are spherical, this equation is redundant.) Associated with the additional equation of change, there appears an additional ``macroscopic variable'' related to the local density of angular momentum due to the rotational motion of the molecules and an additional flux vector representing the flux or transport of this angular momentum. The Boltzmann equation is solved by a perturbation method similar to the Chapman‐Enskog first approximation, and expressions are obtained for the various flux vectors and transport coefficients. Although the equations of change apply under more general conditions, the present treatment is restricted to molecules which may be idealized as rigid nonspherical bodies in which the center of mass is a center of symmetry.
24(1956); http://dx.doi.org/10.1063/1.1742460View Description Hide Description
Mixed halides of boron have been shown to exist in binary mixtures of the trihalides. Most of the fundamental frequencies of BF2Cl, BFCl2, BF2Br, BFBr2, BCl2Br, and BClBr2 for molecules containing boron‐10 and boron‐11 have been observed and assigned to the proper modes of vibration. With the aid of the trihalide frequencies a normal coordinate treatment has been made for the mixed halides. Some discussion of the validity of transferring force constants in this system has been given.
24(1956); http://dx.doi.org/10.1063/1.1742461View Description Hide Description
A previously given theory of the electronic spectra and structure of complex unsaturated molecules is further elucidated by listing specific formulas for the charge density, bond order, transition moment, and configuration interaction matrix elements.
The theory is then applied to give a number of simple rules for alternant hydrocarbons. These refer to the energies of the singly excited states and the effects of configuration interaction, the degeneracy between certain singlet and triplet states, the prohibition of certain electronic transitions which would be allowed from a group theoretical point of view, and the charge density distribution of the ground and singly excited states. A mechanism is proposed to explain some of the anomalously rapid singlet‐triplet radiationless transitions which are observed in connection with studies of the lower triplet states of complex molecules.
Quantitative application of the theory is made to the spectra of the polyacenes, benzene through pentacene, and to the bond orders of naphthalene and anthracene, employing a high‐speed digital computer. The calculated results are compared with experiment. Some previous assignments of electronic bands are confirmed, and some new assignments are suggested. The location of a number of excited states which have not, as yet, been observed is predicted.
Dynamics of Polymer Molecules in Dilute Solution: Viscoelasticity, Flow Birefringence and Dielectric Loss24(1956); http://dx.doi.org/10.1063/1.1742462View Description Hide Description
The problem of the motions of a chain molecule diffusing in a viscous fluid under the influence of external forces or currents is considered for a particular model. This model is a chain of beads connected by ideal springs. Hydrodynamic interaction between the beads is introduced in the approximate form due to Kirkwood and Riseman. It is possible to solve this problem exactly with the use of a transformation to a set of normal coordinates. The viscosity,birefringence of flow, and dielectric and tensile relaxation behavior are calculated explicitly. The intrinsic viscosity in steady flow is somewhat different from the Kirkwood‐Riseman result, and there is no change of viscosity with shear rate. The spectrum of relaxation times is similar to that found by Rouse and by F. Bueche, but has its maximum at a lower frequency than those obtained by Kuhn and Kuhn and by Kirkwood and Fuoss in other ways.
24(1956); http://dx.doi.org/10.1063/1.1742463View Description Hide Description
An eigenvalue problem encountered in the dynamical theory of chain molecules isThis is solved by three methods: use of a Fourier series for α, expansion of α in associated Legendre polynomialsP m 2, and by a variation method. The eight smallest eigenvalues are calculated explicitly and an approximate formula is found for the remaining ones. Formulas are found also for the eigenfunctions.
24(1956); http://dx.doi.org/10.1063/1.1742464View Description Hide Description
Solutions of the zero‐temperature Thomas‐Fermi equation for an atomic system have been obtained by numerical integration with the aid of the IBM 701 Defense Calculator. The complete range of atomic volumes of physical interest has been covered in sufficient detail to permit accurate interpolation to intermediate regions. Tables of the potential distributions are given as well as of the important physical properties.
Infrared Absorption Studies of Aqueous Complex Ions. II. Cyanide Complexes of Cu (I) in Aqueous Solution24(1956); http://dx.doi.org/10.1063/1.1742465View Description Hide Description
In the system CuCN–KCN–H2O, we have observed infrared absorption spectra of three distinct complex ions:At 29°C, the constants for the dissociation of Cu(CN)4 ≡ into Cu(CN)3 =+CN— are: K 4, 3 c = 0.0076±0.0005 mole liter—1 [in terms of concentrations at 0.1—0.2f Cu(I)] and K 4, 3 a = 0.026 mole liter—1 (in terms of activities). Analogous values for the dissociation of Cu(CN)3 = into Cu(CN)2 —+CN— are K 3, 2 c = (2.44±0.36)×10—5 mole liter—1, and K 3, 2 a = 4.2×10—5. The above values are calculated from approximately 100 determinations. At 25°C, the corresponding values of these constants are approximately K 4, 3 c = 0.0057 and K 3, 2 c = 1.5×10—5.
Using the activity constants determined in this paper and a value of 1×10—24 for the constant: [Cu+][CN—]2/[Cu(CN)2 —] we derive the following values: [Cu+][CN—]3/[Cu(CN)3 =] = 2.6×10—29 and [Cu+][CN—]4/[Cu(CN)4 ≡] = 5×10—31. The free energies of formation of the complex ions are thus: Cu(CN)2 —, ΔFf 0 = 58.5 kcal/mole; Cu(CN)3 =, ΔFf 0 = 91.8 kcal/mole; and Cu(CN)4 ≡, ΔFf 0 = 129 kcal/mole.
24(1956); http://dx.doi.org/10.1063/1.1742466View Description Hide Description
Two possible ways in which intramolecular overcrowding in dianthrone can be relieved are shown to lead to two stable, interconvertible molecular configurations, separated by a potential barrier. The two molecular configurations are briefly described. The height of the potential barrier is estimated, and found to agree well with that observed between the two isomers—referred to as chromic isomers—responsible for the thermochromic behavior of dianthrone. It is therefore suggested that the two molecular configurations described are identical with the two chromic isomers, and that this model applies also to analogous compounds. Some observed phenomena are discussed in support of the proposed model.
24(1956); http://dx.doi.org/10.1063/1.1742467View Description Hide Description
The infrared spectra of liquid and crystalline CHBr2CHBr2 and CHCl2CHCl2 have been obtained in the 2 to 36μ region. It has been observed that CHBr2CHBr2 will crystallize as either trans‐or gauche molecules, depending upon the method of cooling employed. To date, crystalline CHCl2CHCl2 has been prepared in the gauche‐form only. On the basis of these data and previously reported Raman spectra, a partial assignment of the fundamental frequencies has been made.
24(1956); http://dx.doi.org/10.1063/1.1742468View Description Hide Description
Nickelferrite, as ordinarily prepared, has a dc resistivity of 104 to 106 ohm‐centimeters. It has been found that by incorporating small amounts of manganese or cobalt, the resistivities can be increased to 1010 or 1011 ohm‐centimeters. Presumably, replacing Fe++ or Ni+++ with Mn or Co ions eliminates the easy conduction paths otherwise provided by the former ions. Further work is required to elucidate the exact mechanism.
24(1956); http://dx.doi.org/10.1063/1.1742469View Description Hide Description
Influences of substituents on the ultraviolet and infrared absorptions of acetophenone and benzoic acid are investigated from theoretical and experimental points of view. In the present paper, all theoretical considerations are made by the molecular energy‐level diagram method developed by the authors.
Ultraviolet absorption spectra of some substituted acetophenones are measured in n‐heptane, alcohol, water, and sulfuric acid. It is found that most molecules studied here have absorption bands corresponding to the n→π* transition of the carbonyl group, A 1g →B 2u and A 1g →B 1u transition of the benzene ring, and intramolecular charge‐transfer absorption. Especially concerning last absorption, a somewhat quantitative theoretical consideration is presented and satisfactory agreement is obtained between the theoretical and observed excitation energies.
Infrared absorption spectra of carbonyl groups in substituted acetophenones are measured in carbon tetrachloride. The observed carbonyl frequencies are compared with the bond orders of this bond calculated on the basis of the above method. Good correlation is also found between these two quantities. A similar consideration is also made with substituted benzoic acids.
24(1956); http://dx.doi.org/10.1063/1.1742470View Description Hide Description
The absolute absorption intensities of the fundamental vibration bands in ammonia and phosphine have been measured. Normal coordinates are calculated for each of the vibrations and the intensities interpreted in terms of bond moments μ and their derivatives ∂μ/∂r.
Values of ∂μ/∂r for the NH and PH bonds in the A 1 mode are 0.6 and 1.2 D/A, respectively; in the E mode the corresponding values are 0.2 and 0.8 D/A.
Values of the vibrational bond moments found are 1.0 D (A 1) and 0.5 D (E) for the NH bond; 0.7 or 0.5 D (A 1) and 1.2 or 0.6 D (E) for the PH bond.
The relation of these vibrational bond moments to the molecular dipole moment and the moment (μu.p.) of the unshared pair of electrons is discussed in detail. After corrections have been applied for changes in magnitude and direction of μu.p. during the vibrations, the results for NH3 are compatible with the following static moments:The data for PH3 are less internally consistent. ``Likely'' moments, taken from the A 1 bending vibration, are
24(1956); http://dx.doi.org/10.1063/1.1742471View Description Hide Description
The chain model for polyelectrolytes developed in the preceding papers of this series is extended to polyampholytes composed of a regular alternation of acidic and basic groups. Included in this model are the effects of counter ion binding, dissociation equilibria among the acidic and basic groups, and electrostatic interactions among the charges of the polymer. The electrostaticfree energy of interaction between neighboring charges of the chain was computed including interactions between both nearest and next nearest neighboring charge sites by a simple extension of the methods previously employed. The equilibrium conditions are then expressible as a set of simultaneous equations which may be solved by a convenient iterative method.
The end‐to‐end extension may be calculated by previously described methods except in the vicinity of the isoelectric point (i.p.), near which point the effects of charge fluctuations become relatively more important. It is shown how both charge fluctuation and the distribution of monomer units along the polymer chain are related to its end‐to‐end extension. However, for a regularly alternating copolymer the skeletal distribution effect vanishes.
Calculations for a hypothetical polymer indicate that the expansion is nearly independent of ionic strength, and that the fluctuations produce a negligibly small contraction at the i.p. However, it is found that added salt acts, primarily by reducing the electrostatic forces, to alter the titration curves in the same manner as has been observed experimentally in dilute protein solutions.
24(1956); http://dx.doi.org/10.1063/1.1742472View Description Hide Description
The chain model for polyelectrolytes developed in the preceding papers of this series is extended to equimolar polyampholytes of general skeletal structure. The present development differs from that for copolymers consisting of a regular alternation of acidic and basic groups in that the environments of the individual groups will depend upon the local skeletal distribution. This inhomogeniety affects both the titration and configurational properties, primarily through a displacement of the acid‐base equilibria. In addition, locally inhomogeneous skeletal structure can cause either an expansion or contraction at the isoelectric point, although strong deviation from random copolymerization is necessary to realize a large effect. No experimental data are available with which to compare the theory, but a calculated titration curve and expansion ratio are presented for a hypothetical polyampholyte of random skeletal structure. It is found that the titration curve of the random copolymer exhibits more buffer action near the isoelectric point than does a similar regularly alternating copolymer, but that the configurational properties and the effect on the titration curve of increased ionic strength are quite similar to the corresponding effect for the regularly alternating copolymer. It is pointed out that substantial change in titration properties may be realized by alterations in the skeletal structure of a copolymer.