Index of content:
Volume 22, Issue 4, 01 April 1954
22(1954); http://dx.doi.org/10.1063/1.1740127View Description Hide Description
The rate constant of the reaction between hydrogen peroxide and ferrous ions has been measured in sulfuric acid solutions, by direct spectrophotometric observations of the ferric salt produced at λ=304 mμ. It has been confirmed that the rate is independent of acidity (measurements were carried out from 0.05 N to 0.8 N H2SO4) and that the reaction is bimolecular within a wide range of the concentrations of the reactants; the hydrogen peroxide concentration was varied in the ratio 1:25 and the ferrous sulfate in the ratio 1:20. The rate constant, which has been measured within the temperature range of 15° to 40°C, can be represented by the equation
The Dielectric Properties of Some Long‐Chain Fatty Acids and Their Methyl Esters in the Microwave Region22(1954); http://dx.doi.org/10.1063/1.1740128View Description Hide Description
Measurements were made of the dielectric constant and loss of stearic, palmitic, and some other acids in the solid and liquid states between wavelengths of 1 and 50 cm. The loss was small in the solid state, and there was no absorption peak in the wavelength range covered; in the liquid state the loss was greater with evidence of a small absorption peak near 3 cm. The methyl esters show an absorption peak in the microwave region in both the solid and liquid states. The measurements on the liquid methyl esters indicate that resonance absorption is occurring at a frequency of about 6000 Mc/sec. Some ethyl esters were measured and were found to show a relaxation loss in the microwave region of the same order as the relaxation loss of the methyl esters but they showed no sign of resonance absorption loss. An attempt is made to explain both the relaxation loss and the resonance loss on the basis of a model which has already been used by Hoffman and Smyth.
22(1954); http://dx.doi.org/10.1063/1.1740129View Description Hide Description
22(1954); http://dx.doi.org/10.1063/1.1740131View Description Hide Description
The exchange energy of valence electrons in both monatomic and diatomic crystals is computed in the Bloch approximation for the case where the lowest electronic wave function in the band shows considerable spatial variation. Only ground‐state wave functions which are spherically symmetric in each atomic cell are considered, but within this limitation two types of spatial variation are considered: radial variation in the unit cell, and the variation in a diatomic lattice due to the wave function being more concentrated on one of the atomic species than on the other. The results of the calculation show that, for a monatomic solid, deviations from uniformity in the wave function have a relatively small effect on the exchange energy; in highly ionic diatomic solids, however, the exchange energy may be increased up to 50 percent in magnitude over the free‐electron value as a result of the electron density in anion cells being different from that of cation cells.
22(1954); http://dx.doi.org/10.1063/1.1740132View Description Hide Description
Measurements of the intensity and position of absorption from 45 000 to 64 000 cm—1 of butene‐1, cis‐butene‐2, trans‐butene‐2, and 2‐methylpropene were made on flowing vapors. All show a broad intense band which is most intense in the case of the cis‐isomer, and superimposed systems of narrow bands, both at shorter and longer wavelengths. Whereas the position of the last named is dependent on the number of alkyl groups adjacent to the double bond, the broad band maximum is not similarly displaced but rather depends on the molecular shape and seems related to the dipole moment vector. The vibrational structure of the bands is consistent with infrared and Raman data.
22(1954); http://dx.doi.org/10.1063/1.1740133View Description Hide Description
A general method has been devised to predict the viscoelastic behavior of plastics. A simplified model of the molecule is assumed and its general motion is treated by the method of normal coordinates. General equations have been developed such that when the manner of application of external forces to the molecule is known, the molecule's general behavior may be found in a convenient and straightforward fashion.
This method has been used to obtain theoretical curves for the viscoelastic behavior of cross‐linked polymers subjected to sinusoidal forces. Also, the similar problem for linear material has been solved together with the creep and stress relaxation problems. It is shown that the temperature‐time superposition procedure of Ferry and Tobolsky has a firm theoretical basis. In general, the theoretical curves appear to agree with the limited experimental data available. The method is also applied to the case of dilute solutions and comparison is made with the result obtained by Rouse using a different approach.
22(1954); http://dx.doi.org/10.1063/1.1740134View Description Hide Description
The status of the gel point equation, advanced by Flory, Stockmayer, and Walling for polyfunctional reactions, is briefly discussed. Two complicating factors in the chain polymerization of divinyl compounds, to which this equation has been applied, are reviewed: the admixture of a monovinyl compound of comparable reactivity, and the ``incestuous'' tendency for the two double bonds in a divinyl compound to enter the same polymerization chain. Contrary to the treatment by Simpson and co‐workers, these two factors are found to demand different theoretical approaches. The progress of polymerization enriches the monomer mixture in the monovinyl compound, while the incestuous tendency remains constant. Kinetic derivations are given for the gel point condition in both cases. The gel point in the ``incestuous'' polymerization of diallyl phthalate is calculated to lie at conversions 40 percent higher than estimated by Simpson and co‐workers, and much better agreement is thus achieved with their experimental measurements.
A simple network theory suffices to predict the gel point in two chain polymerization reactions. Substantial delays of the gel point, predicted by Walling's theory of diffusion control in such reactions, are not encountered.
22(1954); http://dx.doi.org/10.1063/1.1740135View Description Hide Description
The molecular structure of B5H11 has been determined from 299 x‐ray diffraction maxima which have been analyzed by three‐dimensional Fourier and least‐squares methods. There are four molecules in a monoclinic unit cell, in the space group P21/n, having parameters a=6.76, b=8.51, c=10.14A, and β=94.3°.
Although no molecular symmetry is demanded by the space group, the molecular dimensions indicate C8 symmetry for the isolated molecule. The boron skeleton is a fragment of the icosahedronlike arrangement in B10H14, and can also be derived from the tetragonal pyramid in B5H9 by opening up one of the basal B–B bonds. The apex boron BI is ``singly'' bonded to two hydrogens, one of which HVII, is very weakly bonded to the two outer borons BIII. Each BIII is ``singly'' bonded to two hydrogen atoms. Each of the remaining two borons BII is ``singly bonded'' to one hydrogen atom, and there are three bridge hydrogens, one bridging the BII–BIIbond and two bridging the BII–BIIIbonds. Molecular parameters are two BI–BIII=1.865, two BII–BIII=1.75, two BI–BII=1.72, one BII–BII=1.77A, seven B–H=1.07, six B–H (bridge) =1.24A, one BI–HVII=1.00 and two BIII–HVII=1.67A. The BIII–BI–BIII angle is 107°. Bond angles to hydrogen strongly resemble those in the other known boron hydrides.
Free Radicals by Mass Spectrometry. V. The Ionization Potentials of Methyl, Allyl, and Benzyl Radicals22(1954); http://dx.doi.org/10.1063/1.1740136View Description Hide Description
The ionization potentials of methyl, allyl, and benzyl radicals have been measured directly by electron impact. The values found were methyl 9.95±0.03 ev, allyl 8.16±0.03 ev, and benzyl 7.73±0.08 ev. The radicals were produced by thermal decomposition of suitable compounds in a mass spectrometer designed for the study of free radicals. Reactions of the radicals after formation led to the expected dimers, but the disproportionation reactions were found to be negligibly slow.
22(1954); http://dx.doi.org/10.1063/1.1740137View Description Hide Description
The critical regions of ethane, carbon dioxide, and xenon have been studied, using a Schlieren optical system. The material to be studied was confined in a thermostatted high pressure cell having optically flat windows, and placed in the test section of the optical system. At temperatures over a range of about two degrees, in the critical region, refractive index gradients within the cell were determined as a function of height along the cell. From these data were calculated the density distribution, the pressure distribution, and the shapes of the pressure‐volume isotherms at the various temperatures. The technique permitted detailed study of the isotherms over a narrow range of pressures, too small to be observed by usual experimental methods. Extensive visual observations were made throughout the course of the experiments. Particular attention was devoted to the question of the equilibrium state in the critical region and the process of equilibrium attainment.
22(1954); http://dx.doi.org/10.1063/1.1740139View Description Hide Description
Various theoretical and semi‐empirical methods for determining electron affinities of atoms have been applied to fluorine. All results indicate a low value of the electron affinity consistent with recent experimental data, and with the value implied by the recently determined dissociation energy of the fluorine molecule. An extrapolation of the type suggested by Hellmann and Mamotenko appears to give the most reliable value and indicates EF =83.2±0.3 kcal/mole.
22(1954); http://dx.doi.org/10.1063/1.1740140View Description Hide Description
Quantitative measurements of the absorption spectra of the six isomeric pentenes in vapor phase have been made in the region 45 000—65 000 cm—1. The maximum of the intense band (N→V) is the same for 1‐pentene, cis‐2‐pentene, and 2‐methyl‐2‐butene, with one, two, and three alkyl substituents, respectively. The results show that in a series of hydrocarbons, where the molecular weight is unchanged and the number of alkyl groups is the only variable, the position of the N→V maximum is not a function of the number of alkyl substituents. From the standpoint of methyl substituents, there is no shift between cis‐2‐pentene with one methyl group and 2‐methyl‐2‐butene with three. In the absence of such a shift, spectral evidence in support of hyperconjugation in the substituted ethylenes is lacking.
The N→V maximum for trans‐2‐pentene is less intense and at somewhat longer wavelength than for the cis‐isomer. The greatest shift in this band is with 2‐methyl‐1‐butene, where the two alkyl groups are on the same carbon atom. These results indicate the importance of molecular shape in determining the energy of the N→V transition in the monoolefins.
The positions of the shallow bands (N→R) on the long wave side of the N→V band are in substantial agreement with earlier measurements and confirm the conclusion that the energy of this transition is dependent on the number of alkyl substituents on the carbon atoms of the double bond. The possibility of other Rydberg bands on the short wave side is discussed briefly. Oscillator strengths for the N→V band are given for the six pentenes; these vary from 0.26 in 2‐methyl‐1‐butene to 0.45 in cis‐2‐pentene but their value for testingtheoretical predictions is doubtful because of the overlapping of different electronic transitions.
22(1954); http://dx.doi.org/10.1063/1.1740141View Description Hide Description
The protonmagnetic resonance absorption has been measured in NH4Cl, NH4Br, and NH4I crystal powders from —195°C to room temperature, and for NH4Cl to 200°C. Line width transitions were found at —144, —171, and about —198°C in the chloride, bromide, and iodide, respectively. The N–H distance in the ammonium ion was determined to be 1.035±0.01A from the second moments of the broad, low‐temperature absorption lines observed in NH4Cl and NH4Br, with allowance for broadening by modulation effects and narrowing by zero‐point torsional oscillations. The relatively narrow room temperature line shapes are consistent with the broadening estimated for inter‐NH4 + interactions, the intra‐NH4 + interactions averaging to zero over the hindered rotational motions of the NH4 + ions. No appreciable line shape changes were found at the λ temperatures. An electrostatic calculation is made of the potential barriers to rotation of the NH4 + ion giving values comparing favorably with experimental inferences. The results clarify the motions which narrow the absorption line at low temperatures and emphasize the dynamic aspects of the order‐disorder process.
22(1954); http://dx.doi.org/10.1063/1.1740142View Description Hide Description
The nuclear resonanceabsorptionspectrum has been calculated theoretically for a tetrahedral 4‐spin system, with I of ½, for orientations in which the external magnetic field coincides with a two‐ or three‐fold symmetry axis of the tetrahedron or with a tetrahedral edge. Comparison of the theoretical results with the protonresonance observed at —195°C in a single crystal of ammonium chloride demonstrates that the NH4 + ion is oriented with the N–H bonds pointed essentially towards corners of the unit cube. An N–H distance of 1.032±0.005A is determined from the low‐temperature second moments of the resonance line with the applied magnetic field in the (1,0,0) and (1,1,0) directions. At room temperature, the anisotropy of the resonance results from inter —NH4 + interactions, with intra —NH4 + interactions averaged to zero by hindered rotational motions; free rotation of the ammonium ions does not occur. A small decrease with temperature of the second moment of the resonance line at the λ‐point agrees with the order‐disorder model for the transition. The motion of the NH4 + ion is discussed.
22(1954); http://dx.doi.org/10.1063/1.1740143View Description Hide Description
The infrared gratingspectra of σ2 for B10F3 and B11F3 have been reexamined from 650 to 750 K. Two samples of BF3, one composed of 93.4 percent B10F3 and 6.6 percent of B11F3, and the other of the normal abundance ratio 20 percent B10F3 and 80 percent B11F3 were secured for the investigation. Complete resolution of the rotational fine structure of this parallel‐type band was achieved. The following constants were obtained by means of the usual sort of rotational analysis: for B10F3, σ0 = 718.23 K, B 0 = 0.35272 K, B(v 2 = 1) = 0.35288 K, DJ = 13.72×10—7 K. For B11F3, σ0 = 691.45 K and the rotational constants are the same for the two isotopic species.
22(1954); http://dx.doi.org/10.1063/1.1740144View Description Hide Description
Total collision cross sections have been measured for helium atoms, with energies between 500 and 2100 ev, scattered in room temperature helium. Measurements were made with two detectors of different geometric aperture, 13.4 and 0.96 minutes. In order to obtain meaningful potential energy information from such results, it is necessary to determine effective apertures by taking into account beam shape, intensity distribution, and for the case where the beam is wider than the detector,scattering to the detector from external regions of the beam. Potential energy functions have been derived from the cross sections obtained with the two detectors. The functions agree within a factor of about 1.3 as compared with 0.17 when geometric apertures are used directly. The results from both detectors have been represented by an average function, namely,for values of r between 1.27A and 1.59A.
The potential energy information obtained from the present experiments is in agreement with theoretical calculations of P. Rosen and H. Margenau within the uncertainty of such calculations. The information also appears to be consistent with that derived from measurements of gaseous compressibility and viscosity, for values of r between 1.90A and 2.30A.
22(1954); http://dx.doi.org/10.1063/1.1740145View Description Hide Description
Total collision cross sections have been measured for argon atoms, with energies between 700 and 2100 ev, scattered in room temperature argon. Results obtained with two detectors of different geometric aperture are shown to be in accord when allowance is made for beam shape, intensity distribution, and scattering to a detector which is narrower than the beam, in accordance with procedures previously used for helium scattered in helium.
Potential energy information derived from the cross sections may be represented byfor values of r between 2.18A and 2.69A, and appears to be consistent with that derived from measurements of gaseous compressibility, viscosity, and crystal properties.
22(1954); http://dx.doi.org/10.1063/1.1740146View Description Hide Description
An investigation has been made of the mercury‐6(3 P 1)‐photosensitized decomposition of cyclohexane at 29.30±0.01°C, under static conditions. The products of the reaction are hydrogen, bicyclohexyl, and cyclohexene, in order of decreasing importance. The mean quantum yields of cyclohexane disappearance, hydrogen formation, and cyclohexene formation were found to increase slightly with increasing substrate pressure; at 90‐mm cyclohexane pressure, the values are 0.83, 0.43, and 0.03, respectively. Extrapolation to initial conditions of data on the variation of mean quantum yield with time at constant substrate pressure gave 0.55 for the initial quantum yield of hydrogen formation, and 0.17 for cyclohexene formation, independent of substrate pressure. From the foregoing initial quantum yield data, taken in conjunction with the stoichiometry of the reaction, a value of 0.93 was obtained for the initial quantum yield of cyclohexane consumption.
Absence of hexane, dodecanes, n‐hexylcyclohexane, and low molecular weights products was taken as evidence of the stability of the cyclohexane ring during reaction.
The results of the investigation can be adequately accounted for by the following simple mechanism:(1) (2) (3) (4) (5)
Steps (1) to (4) describe the reaction under initial conditions.
From the initial quantum yield data the ratio k 4/k 3, the ratio of the rates of recombination to disproportionation for cyclohexyl radicals, was evaluated at 2.2. In short, recombination is approximately twice as fast as disproportionation for cyclohexyl radicals.