Index of content:
Volume 30, Issue 6, 01 June 1959
30(1959); http://dx.doi.org/10.1063/1.1730208View Description Hide Description
The infrared spectrum of gaseous CF3–CF2Br has been obtained with a Perkin‐Elmer double‐pass spectrometer equipped with CsBr, NaCl, and LiF prisms. The Raman spectrum of the liquid has been photographed with a 3‐prism glass spectrograph of reciprocal linear dispersion 15 A/mm at 4358 A. 17 vibrational fundamentals have been assigned as follows: Species a′: 1339, 1240, 1124, 949, 754, 634, 547, 370, 329, ca 297, and ca 167 cm—1; species a″: ca 1240, 1182, 591, 440, ca 297, and ca 152 cm—1. The torsional fundamental, which undoubtedly lies below 150 cm—1, could not be determined. The spectra have been interpreted in detail.
30(1959); http://dx.doi.org/10.1063/1.1730209View Description Hide Description
The rate of dissociation of oxygen behind strong shock waves in pure oxygen, in mixtures of oxygen and argon, and in air was determined over a temperature range from 2800°K to 5000°K. A long duration sparkinterferometer and drum camera were used to measure the shock speed and the variation of density behind the shock. The dissociation rate determined from the data can be represented by a collision theory equation, assuming that all of the available energy of vibration of the particles is transferred to dissociation in an inelastic collision. Oxygen atoms were found to be very effective in causing dissociation of oxygen molecules; the measured transition probability for energetically possible collisions between an oxygen atom and an oxygen molecule was 1.7, that for collisions between two oxygen molecules was 0.24. Collisions between nitrogen and oxygen molecules in air were found to be relatively ineffective in causing dissociation of oxygen; the measured rate of dissociation of oxygen in air was less than a factor of 2 larger than that caused by collisions between oxygen atoms and molecules alone.
30(1959); http://dx.doi.org/10.1063/1.1730210View Description Hide Description
The Al27 pure quadrupole resonances in AlBr3 are reported. With the addition of these data, the quadrupole coupling constants of all the atoms in the structure of five group III halides are known. For these cases it has been possible to determine complete self‐consistent electron distributions for the molecules. In addition, for two of the compounds it has been possible to determine bond angles and establish the existence of bent bonds in the molecules.
30(1959); http://dx.doi.org/10.1063/1.1730211View Description Hide Description
Approximate natural spin orbitals and the corresponding occupation numbers are obtained over a wide range of internuclear separations for the ground state and the excited state of the hydrogen molecule, using the Hirschfelder‐Linnett wave functions. The resulting natural expansions and their variation with internuclear separation are then discussed in terms of electronic configurations.
30(1959); http://dx.doi.org/10.1063/1.1730212View Description Hide Description
Approximate wave functions for the hydrogen molecule ground state previously available in the literature are analyzed quantitatively into approximate natural spin orbital functions with particular attention to the corresponding occupation numbers. The analysis demonstrates the very great similarity of all such trial wave functions, and especially the largely molecular orbital nature of the wave function. In addition it shows a close relationship between the molecular orbital and valence bond functions, and the importance for allowing for angular correlation of the electrons by including terms dependent upon the azimuthal coordinate. The analysis particularly demonstrates that approximate natural spin orbital occupation numbers are nearly invariant under a wide variety of choices of basis functions, and therefore are particularly suitable for comparison of different approximate functions and for discussion of their respective properties.
30(1959); http://dx.doi.org/10.1063/1.1730213View Description Hide Description
Small vibration shifts of usually 10 to 50 cm—1 can be observed superimposed on the electronic shifts of 200 to 1000 cm—1 which occur on solvation of aromatic polynuclear hydrocarbons. Vibration assignments for benzene indicate that the observed behavior of its vibration bands is due to the perturbation of a single vibration in the electronically excited benzene molecule. The change corresponds to an increase of frequency for the excited stateEg +3080‐cm—1 C–H vibration. A similar phenomenon can be detected in the naphthalene spectrum. The results are compared to the recent work of Fishman, Benson, Wiederkehr, and Drickamer on pressure perturbations of vibrations in electronic ground state molecules in solution.
30(1959); http://dx.doi.org/10.1063/1.1730214View Description Hide Description
A potential function describing the interaction between the ions of M2X+ molecules has been developed using a model suggested by Pauling. From this potential the energies and vibrational frequencies have been calculated for these molecules. The harmonic contributions to the bending frequencies are shown to be far from negligible based on this purely ionic model. The entropy and free energy changes for the reaction M(g)++MX(g) → M2X+(g) are considered.
30(1959); http://dx.doi.org/10.1063/1.1730215View Description Hide Description
The Hg199 and H1nuclear magnetic resonance spectra of a series of dialkylmercury compounds have been obtained. The Hg199 results indicate that the shielding of the mercury increases along the series Me<n—Pr< Et<i—Pr. This increased shielding seems to be connected with an interaction of Hg199 and the β protons, as evidenced by the H1 resonance peaks and the Hg199–H1 spin‐spin coupling constants.
30(1959); http://dx.doi.org/10.1063/1.1730216View Description Hide Description
A collisional approach, somewhat similar to the Wang‐Chang and Uhlenbeck treatment for the transport properties of polyatomic molecules, is used to obtain a general expression for the rate of a bimolecular chemical reaction in terms of reaction cross sections.
Specialization is then made to the case where a Maxwell‐Boltzmann velocity distribution may be assumed for the reactants. This leads to a Laplace transform relation between the rate constants for reaction of molecules in definite internal quantum states and the reaction cross sections. The further assumption of a Boltzmann distribution among the internal energy states of the reactant molecules then leads to a rate equation of the usual form and to an explicit expression for the single over‐all rate constant. This expression is used to rederive the results of the old ``simple'' collision theories.
Finally, a collisional approach is used to rederive the usual rate expression of the Eyring theory of absolute reaction rates. The rather drastic approximations which seem to be necessary for such a derivation are pointed out and discussed.
Optical and Electrical Properties of Single Crystals of Tri‐p‐Methoxy Phenyl Methyl Perchlorate and Triphenyl Methyl Azide30(1959); http://dx.doi.org/10.1063/1.1730218View Description Hide Description
Measurements have been made of the optical and electrical properties of single crystals of tri‐p‐methoxy phenyl methyl perchlorate and triphenyl methyl azide. These include the absorption spectra,photoconduction behavior, low‐frequency dielectric constants, and refractive indices. In the case of tri‐p‐methoxy phenyl methyl perchlorate where the electron affinity of the acid radical is high the solid is ionic and an estimate has been made of the energy required to raise an electron from the full band to the conduction band. The properties of triphenyl methyl azide are consistent with a covalent type solid. The stability of these compounds is considered in outline.
30(1959); http://dx.doi.org/10.1063/1.1730219View Description Hide Description
By means of a new experimental technique, the drift mobility of electrons in liquid n‐hexane has been measured at field strengths below 2 kv/cm and at several temperatures in the range +27° to —47°. The drift mobility is found to vary with temperature as , where μ0=0.3±0.2 cm2/volt‐sec and Δε=0.14±0.02 electron volt. The results indicate that electrons injected into the liquid neither behave as free particles nor are they permanently attached to form negative ions. It is proposed that the injected electrons are alternatively trapped and thermally untrapped many times during their drift through the liquid. The experimental quantity Δε is interpreted as the average energy with which an electron is trapped. The origin of the traps is not evident, but possible trapping mechanisms are discussed.
30(1959); http://dx.doi.org/10.1063/1.1730220View Description Hide Description
It is illustrated that the formal theory of transport processes developed by Kirkwood, Irving, Zwanzig, and Ross can be extended to fluids composed of polyatomic molecules. In Secs. II and III the hydrodynamical equations are established for the case of classical mechanics and in IV these same relationships are shown to obtain in the quantum theory. Section VI is devoted primarily to the equations of change for the classical distribution functions, special attention being given to cases where the intermolecular forces are impulsive. In V and VI the quantum theory is formulated in terms of generalized Wigner functions, i.e., Fourier transforms of the density matrix. In terms of these functions the transport properties of a dilute polyatomic fluid may be represented as those of a mixture whose components are molecules with different internal quantum states. Finally, in VII we consider the equations of change for the Wigner functions and the quantum analog of the Boltzmann integro‐differential equation.
30(1959); http://dx.doi.org/10.1063/1.1730221View Description Hide Description
The effect of bond orientation in ice, which leads to its residual entropy, is also found to be important in its heterogeneous nucleation. Any substrate which orients ice dipoles at its surface parallel to one another is a poor nucleating atent, because it reduces the entropy and hence raises the free energy of any small embryos growing upon it. Critical temperatures are calculated for surfaces of this type, and it is shown that for crystals like AgI or PbI2 the basal faces are poor ice crystal nuclei, and activity is mostly confined to the prism faces. This result leads to improved agreement between observed and theoretical nucleation thresholds and gives an explanation of some of the phenomena observed in nucleation by monocrystalline substrates.
30(1959); http://dx.doi.org/10.1063/1.1730222View Description Hide Description
The vapor pressure for hexaborane over the temperature range —40°C to 16°C can be expressed by the equation log10 Pmm=5.2124— (1566.3/T) +0.005841 T. The melting point is —63.2°C; the extrapolated boiling point equals 82.2°C. The vapor pressure at 0°C is 11.85 mm instead of the published literature value of 7.2 mm. The purification of the hexaborane has been followed by infrared and mass spectra. A discussion of these spectra is given.
30(1959); http://dx.doi.org/10.1063/1.1730223View Description Hide Description
The structure of 12‐silico‐tungstic acid, H4SiW12O40, in aqueous solution has been investigated by x‐ray diffraction. The results indicate that 12 tungsten atoms are contained in a monodisperse species with arrangement similar to that found in the crystalline acid. Each tungsten atom has two near tungsten neighbors at each of the distances 3.36 A and 3.71 A.
30(1959); http://dx.doi.org/10.1063/1.1730224View Description Hide Description
The vibrational analysis of 4,4‐dimethylcyclopentene has been carried out by a normal coordinate calculation based on the Wilson FGmatrix method. Assignments of the infrared and Raman bands were made with the help of the calculated fundamentals. The model used in the calculation was assumed to be planar and to possess C 2v symmetry. The good agreement between calculated and observed frequencies justified this assumption.
A matrix iteration program was used on an IBM—650 digital calculator to find the roots of the secular determinant. It worked very well considering the large number of modes caused by the low symmetry of the molecule.
30(1959); http://dx.doi.org/10.1063/1.1730225View Description Hide Description
The mechanism of the addition of radicals to aromatic and olefinic compounds is discussed in terms of a potential energy diagram which explains the linear relation between localization energy and the logarithm of methyl affinity per reactive center. It is pointed out that such a linear relation is expected for series of compounds, each having the same type of reaction center, e.g.,in a series of aromatic hydrocarbons orin a series of substrates like ethylene, styrene, butadiene, etc.
The relation between the slope of such a line and the nature of the reactive center is discussed.
The foregoing treatment is extended to explain the effects caused by hyperconjugation, and an excellent agreement is found between theory and experiment.
It is shown that compounds having a methyl substituent on the reactive center are less reactive. This inhibitory action of the methyl substituent is explained in terms of steric hindrance, and it is shown that for a particular center the inhibitory effect amounts to a constant factor independent of the original reactivity of the center. Still greater steric effects are caused by phenyl groups and by two methyl substituents located on a reactive center.
The utility of this ``blocking'' technique for determining the most reactive centers is pointed out.
30(1959); http://dx.doi.org/10.1063/1.1730226View Description Hide Description
A theory of the response of a burning solid to a sound wave is developed, based on time‐dependent solutions of the transport equations relevant to a combustible having idealized physical and chemical properties. The development is restricted to small perturbations about the steady‐state conditions for a rather simple model whose parameters have either a direct physical significance, or are experimentally determinable. The introduction of ad hoc time delays, or other phenomenological parameters has been entirely avoided. Time‐dependent reaction rate chemistry also has been avoided, by considering only sufficiently fast reactions that the volumetric rate of reaction corresponds to the steady‐state rate appropriate to the instantaneous local conditions as described by solution of the time‐dependent transport equations. The predictions of the theory are discussed briefly, and several rather general observations are made. However, in view of the complexity inherent in the phenomenon and the present state of inadequate available empirical knowledge regarding this phenomenon, it is not yet possible to make a quantitative comparison between the theory and experiment.
30(1959); http://dx.doi.org/10.1063/1.1730227View Description Hide Description
The frost points of argon‐krypton mixtures at various pressures and compositions of the gas phase have been determined. These results have then been analyzed by a generalized form of regular solutiontheory, where the energy of mixing parameter wAB has been allowed to vary with mole fraction as well as temperature. The results have been compared with an exact expansion in terms of Mayer cluster sums of the lattice‐solution (Ising) model. The model does not entirely account for the data.
30(1959); http://dx.doi.org/10.1063/1.1730228View Description Hide Description
The charge transfer spectra of , quinhydrone, and chloranil‐hexamethyl‐benzene have been measured as a function of pressure. The shifts of the peaks for the inorganic complexes can be explained in terms of the effect of pressure on the acceptor levels of the metal relative to the ligand levels. The large red shifts observed in the peaks for the organic complexes can be explained in terms of solid‐state band theory.