Index of content:
Volume 22, Issue 11, 01 November 1954
22(1954); http://dx.doi.org/10.1063/1.1739920View Description Hide Description
The vapor above the SrO–Pt system was bombarded with electrons and the ion fragments analyzed by a mass spectrometer. Evaporator temperatures ranged from 1600°K to 1800°K. Log Sr+ vs 1/T plots were found to be time dependent initially. Eventually the plots became stable, and could be represented by two straight lines having a slope of 60 kcal/mole at the higher temperatures and of 138 kcal/mole at the lower temperatures. The appearance potential for Sr+ was approximately 5 volts. The ratio of Sr+ to SrO+ was between 10 and 100. These results indicate that thermal dissociation of SrO took place. An explanation based on a diffusion‐limited mechanism is offered for the smaller slope of the upper part of the log Sr+ vs 1/T plot. The behavior of the SrO–Pt system is compared with that of the BaO–Pt system. The latter system does not appear to exhibit thermal dissociation.
22(1954); http://dx.doi.org/10.1063/1.1739921View Description Hide Description
The absorption spectra of solid CH3COONa and CD3COONa have been observed from 350—5000 cm‐1. All of the fundamental frequencies of the acetate ion have been observed and assigned with the exception of that of the torsional oscillation. The assignments for CH3NO2 and CD3NO2 2,3 were used as an aid in assigning the CH3CO2 ‐ and CD3CO2 ‐ frequencies. An approximate force constant, 9.3×105 dynes/cm, is given for the C–O bond of CH3CO2 ‐ in solid sodium acetate. The spectra of the partially deuterated species were observed and assignments were made with the aid of the Decius‐Wilson sum rule and the Teller‐Redlich product rule.
22(1954); http://dx.doi.org/10.1063/1.1739922View Description Hide Description
The theory of charge‐transfer complex is applied to adsorption on metals and semiconductors. The heat of adsorption at zero coverage is given in terms of the ionization energy of the adsorbate, the electronic work function of the adsorbent, an image energy, and an interaction energy. For metals a linear relationship between heat (at zero coverage) and extent of adsorption is deduced from two of the simpler forms of theoretical isotherms. The functional dependence of the extent of adsorption on the ionization energy of the adsorbate is thus obtained.
The treatment for semiconductors is modified to take into account the space charge generated in the semiconductor on adsorption.
This treatment is shown to be consistent with reported experimental data for adsorption on ironpowder of long chain nitriles, esters, alcohols, amines, and thiols.
22(1954); http://dx.doi.org/10.1063/1.1739923View Description Hide Description
22(1954); http://dx.doi.org/10.1063/1.1739924View Description Hide Description
The assumptions necessary in deriving the equation for the dielectric polarization in the absence of short‐range interactions between the molecules, as represented by the Onsager equation, are made explicit. The equation derived by Harris and Alder for the general case of dielectric polarization of polar liquids is seen to involve an approximation not previously stated. The latter equation, when reduced to the limit represented by the Onsager equation, becomes identical to it when a further simplification is introduced.
22(1954); http://dx.doi.org/10.1063/1.1739925View Description Hide Description
The Raman spectra of CF3Br and CF3I have been obtained at —100°C and —40°C, respectively. The infrared spectra of both compounds have been obtained at 30°C, and some measurements have been made at 160°C. The observed frequencies were assigned to the fundamental modes of vibration, their combinations and differences. The frequencies were interpreted in correlation with other CF3X molecules in terms of the pertinent ``natural'' frequencies of vibration.
22(1954); http://dx.doi.org/10.1063/1.1739926View Description Hide Description
By applying symmetry considerations to intramolecular torsional barriers the over‐all barriers are resolved into contributions from the interactions of individual change distributions (i and k). This makes it possible to classify internal potential barriers and calculate their heights and shapes if the Fourier coefficients Cv ik are known. Some figures, mainly C 3 ik values, were obtained from experimental barriers others can be estimated by theoretical methods. The Lennard‐Jones potential with n = 12 and m = 6 appears to be altogether unsuitable for describing barriers of internal rotation, but a simple repulsive potential V = anR‐n with n∼5 furnishes a reasonable approximation.
22(1954); http://dx.doi.org/10.1063/1.1739927View Description Hide Description
The application of simple MO theory in the interpretation of electronic spectra is investigated. Certain simple theorems are derived and their applications, particularly with respect to configurational interaction in the polyacene series, are discussed. The potentialities and difficulties of this approach are enumerated, and it is concluded that the theory should only be used with caution.
22(1954); http://dx.doi.org/10.1063/1.1739928View Description Hide Description
The partial molal volumes of benzene, methane, ethane and propane in water solution have been determined at temperatures ranging from 10—40°C. All the volumes measured were less than those of the same hydrocarbons in nonpolar solvents. This decrease in volume is explained in terms of the abnormally high internal pressure of water, which decreases the free volume available to the hydrocarbon molecules. The temperature dependence of the partial molal volumes of the aliphatic hydrocarbons differs sharply from that of benzene. It is suggested that this is caused by a difference in solution structure in the two cases.
22(1954); http://dx.doi.org/10.1063/1.1739929View Description Hide Description
A band at 2.57μ wavelength has an absorbance which depends upon the product of the partial pressures of hydrogen fluoride and chlorine trifluoride and is hence attributable to a molecular complex HF·ClF3. This complex is present only in low concentration. The temperature variation per unit product of the pressures indicates a heat of reaction of 3.9 kcal per mole for the reaction HF+ClF3⇄HF·ClF3. The band is a hydrogen‐fluorine stretching vibration. The complex probably does not contain a hydrogen bond.
22(1954); http://dx.doi.org/10.1063/1.1739930View Description Hide Description
The appearance potentials of C+, CH+, and CH2 + in the mass spectra of methylene, methyl, and methane are found to be mutually consistent and when combined with the spectroscopic value of the ionization potential of the carbon atom (11.26 ev) lead to 15.5±0.5 ev/molecule for the heat of atomization of methane. This value (15.5) when further combined with the heat of formation of methane (—0.78 ev/molecule) and the dissociation energy of H2 (4.48 ev/molecule) yields 5.76 ev/atmos or 133 kcal/mole for the heat of sublimation of graphite.
The set of appearance potentials confirmed the spectroscopic value for the heat of dissociation of CH+ (3.6 ev/molecule) and yield the following additional energetic quantities: D(CH2–H) = 3.75±0.3 ev/molecule, D(CH–H) = 3.99±0.3 ev/molecule, D(CH3 +–H) = 1.34±0.1 ev/molecule, D(CH2 +–H) = 5.54±0.2 ev/molecule, and D(CH+–H) = 3.37±0.2 ev/molecule. Earlier determinations of Iz (CH4), Iz (CH3) and D(CH3–H) are confirmed (within the experimental error) and the ionization potential of the methylene radical, Iz (CH2), is found to be 11.75±0.1 ev/molecule.
Combination of the appearance potentials of CH2 + in the methane and diazomethane mass spectra gives 46±6 kcal/mole for the heat of formation of diazomethane.
Frequency Assignments for Normal Aliphatic Compounds: I. The Normal Paraffins in the Range 1450 cm—1 to 650 cm—122(1954); http://dx.doi.org/10.1063/1.1739931View Description Hide Description
It is assumed that the normal aliphatic hydrocarbons in their crystalline forms belong to the symmetry groups C2v (odd number of carbon atoms) or C2h (even number of carbon atoms), and that the selection rules for these symmetry groups hold exactly. It is then possible to work out a ``theoretical distribution pattern'' for the carbon‐stretching modes, and for most types of the hydrogen deformation modes. Comparison of these patterns with available experimental data leads to a complete assignment of frequencies of these types in all the normal hydrocarbons for which data are available, and accounts satisfactorily for all spectral features for these materials in the solid and liquid state. The results might evidently be extended to other aliphatic series.
22(1954); http://dx.doi.org/10.1063/1.1739932View Description Hide Description
The infrared absorption of tetrakis(ethylenethiocarbamide)copper(I) nitrate, ethylenethiocarbamide, and potassium nitrate have been measured by the potassium bromide disk method. The assignment of the frequencies of ethylenethiocarbamide explains that part of the spectrum (the wavelength region between 7 and 13 microns) in which various CH2 deformation frequencies are expected to appear. Generally speaking the infrared spectrum of tetrakis(ethylenethiocarbamide)copper(I) nitrate can be regarded as the superposition of the spectra of ethylenethiocarbamide and potassium nitrate, except for the absorption peaks at 9.6 and 14 microns, which do not appear in the infrared spectra of ethylenethiocarbamide and potassium nitrate. It is interesting to note that these wavelengths correspond to the Raman frequencies (1050 cm—1 and 720 cm—1) of potassium nitrate, which should be infrared‐inactive. The appearance of these frequencies in the absorptionspectrum is explained by the distortion of the nitrate ion in tetrakis(ethylenethiocarbamide)copper(I) nitrate.
22(1954); http://dx.doi.org/10.1063/1.1739933View Description Hide Description
A partly phenomenological, one‐dimensional theory is presented of the double layer formed at an ideal polarized electrode in uni‐univalent aqueous electrolytes showing no specific adsorption. The system analyzed consists of the metallic electrode with its surface charge density, a charge‐free layer next to the electrode, and a diffuse layer containing positive and negative charges in unequal concentration extending into the body of the electrolyte. The theory includes the effect of dielectric saturation in both layers due to the field produced by an applied negative bias potential, and compression of the charge‐free layer by this field is also taken into account.
The theory is compared with experimental data of D. C. Grahame on 0.916 N to 0.001 N NaF, which shows little or no adsorption on negative polarization. Good agreement is found both for the dependence of the differential capacitance of the entire system on negative polarizing potential (measured from the electrocapillary maximum) and on concentration. Such agreement allows several constants of the charge‐free layer to be obtained relatively accurately. In particular, values for its initial thickness, modulus of linear compressibility, initial dielectric constant, and dielectric saturation constant are obtained. Comparison of these results with corresponding results for bulk water affords strong evidence that the charge‐free layer consists of a single molecule of water and thus that cations nearest the polarized electrode are hydrated.
22(1954); http://dx.doi.org/10.1063/1.1739934View Description Hide Description
Vapor pressuremeasurements on solid magnesium oxide show that the solid vaporizes mainly into molecular species. Spectroscopic experiments have been conducted and have shown that the known gaseous 1Σ electronic state of MgO is not the principal vaporizing species. A study of the ultraviolet bands, produced originally by magnesium burning in air, proves the lower electronic level of the molecule involved in this transition is more important than the 1Σ state of MgO. Within experimental uncertainty the heat of sublimation obtained from vapor pressuremeasurements agrees with a spectroscopically determined heat of sublimation of the molecule involved in the ultraviolet transition. The ultraviolet bands are shown to originate from a gaseous monomer of MgO. The vapor pressure of MgO at 2200°K is 3.8×10—4 atmos, and the vapor pressure over MgO reaches 1 atmos at 3040±60°K. The D 0 value for MgO gas is 4.7 ev.
Free‐Electron Network Model for Conjugated Systems. V. Energies and Electron Distributions in the FE MO Model and in the LCAO MO Model22(1954); http://dx.doi.org/10.1063/1.1739935View Description Hide Description
A comparative study is made of the LCAO MO model (including overlap) and the FE MO model. Energies and electronic distributions are examined and the concepts ``atom population'' and ``bond population'' are analyzed. A close correspondence is found to exist between the two theories.
Electron Impact Studies of Some Aromatic Hydrocarbons. Implications Regarding Certain Aromatic Reactions22(1954); http://dx.doi.org/10.1063/1.1739936View Description Hide Description
The ionization potential of several alkyl‐substituted aromatics have been measured by an electron impact method, and the results are found to agree with values predicted by equivalent orbital calculations. The appearance potential of several alkyl‐substituted benzyl ions have been measured, and the results show that the energies of these ions are independent of ring substitution. The appearance potential of several alkyl‐substituted phenyl ions were measured, and the results appear to be anomalous. The results can be understood if it is assumed that the ions rearrange during decomposition to the isomeric benzyl ions. The implications of these results in terms of several chemical reactions are discussed. The heat of formation of the phenyl and ethyl phenyl radicals were found to be approximately 66 and 49 kcal/mole, respectively.
22(1954); http://dx.doi.org/10.1063/1.1739937View Description Hide Description
Para‐xylyl radicals were generated by pyrolysing para‐xylyl bromide in the presence of toluene or of para‐xylene. Investigation of their behavior led to the conclusion that the quinonoid hydrocarbon CH2:C6H4:CH2 is formed by the disproportionation process. Further information about this reaction was secured by studying the pyrolysis of ω, ω′ dibromo para‐xylene (Br·CH2·C6H4·CH2·Br). Semiquantitative treatment of the data indicates that the activation energy of the dissociation processis of the order 70 kcal/mole. Consequently, the dissociation process is too slow to account for the formation of the quinonoid hydrocarbon, at temperatures below 1100°K. We therefore attribute the formation of the quinonoid hydrocarbon to the disproportionation reaction.
Reinvestigation of the pyrolysis of benzyl bromide confirmed the past results and particularly the value for D(C6H5·CH2–Br). It was shown that the rate constant for the decomposition of para‐xylyl bromide is essentially equal to the rate constant for the decomposition of benzyl bromide, and it appears that the rate constant for the decomposition of ω, ω′ dibromo para‐xylene is higher by statistical factor of 2 from the rate constant of the decomposition of para‐xylyl bromide.
22(1954); http://dx.doi.org/10.1063/1.1739939View Description Hide Description
An analytical elaboration of von Neumann's model of the detonation wave is presented. A hydrodynamic argument for the well‐known Chapman‐Jouguet condition is advanced, and the sound speed to be used therein is identified as that obtained with frozen chemical equilibrium, in agreement with a recent result of Brinkley and Richardson. Possible situations in which the classical Chapman‐Jouguet hypothesis might be incorrect are very briefly discussed.