Index of content:
Volume 19, Issue 3, 01 March 1951
Spectroscopic Moment: A Parameter of Substituent Groups Determining Aromatic Ultraviolet Intensities19(1951); http://dx.doi.org/10.1063/1.1748192View Description Hide Description
By the theory of Sklar and Förster, the added intensity produced in the benzene 2600A transition by monosubstitution is proportional to the square of a transition moment or ``spectroscopic moment'' induced by the substituent. The sign of the moment may be positive or negative. On disubstitution, para intensities are greater than meta and ortho if both signs are the same, less if they are opposite. The theory is used with available data to determine the relative spectroscopic moment for 25 different substituents. This moment is closely related to the ``mesomeric moment'' and to directing power, but the correlation is not perfect.
The theory is extended to account for intensity changes in the weak long‐wavelength transitions (1 A—1 Lb ) of derivatives of other cata‐condensed ring systems, such as naphthalene, phenanthrene, 1,2‐benzanthracene, etc. The increases of intensity produced by substituents, and their spectroscopic moments, appear to be almost identical with those found in benzene.
A Two‐Path Method for Measuring Flame Temperatures and Concentrations in Low Pressure Combustion Chambers19(1951); http://dx.doi.org/10.1063/1.1748193View Description Hide Description
The two‐path method for flame‐temperature determinations has been extended to discrete radiators observed with instruments of arbitrary resolving power. Representative calculations of radiant intensity have been carried out for low pressure combustionflames in order to ascertain the feasibility of experimental study with standard spectroscopic instruments. It is shown how experimentally determined temperatures and emissivities can be utilized to calculate the concentrations of emitters, provided the emitting species is known and the radiation emitted corresponds to the thermodynamic equilibrium for the local conditions of temperature and pressure.
19(1951); http://dx.doi.org/10.1063/1.1748194View Description Hide Description
The general theory of irreversible processes in solutions of macromolecules is employed to investigate the visco‐elastic behavior of solutions of rod‐like macromolecules. It is found that rotatory diffusional torques are responsible for three‐fourths of the stationary intrinsic viscosity. Under the action of periodic shear waves, the rotatory diffusional contribution to the stress exhibits relaxation phase lag and imparts a rigidity to the solution. As the frequency is increased, the intrinsic viscosity drops to one‐fourth of its stationary value and the rigidity modulus increases to an asymptotic value of 3RT/5 per mole/cm3 of solute.
19(1951); http://dx.doi.org/10.1063/1.1748195View Description Hide Description
The distribution of radicals at steady state has been computed for simple systems subject to heterogeneous and homogeneous reactions. Sample distributions are given. Expressions for two non‐steady‐state situations are derived for the case of a first‐order gas and first‐ or second‐order wall reaction. The effect of expansion and longitudinal diffusion on radical concentration in flow systems is discussed. Equations governing the former are derived and a method of estimating its effect rapidly is given. Expressions giving the upper limit of the latter are presented. It is shown that expansion may simulate a first‐order reaction, and may be of considerable importance in fast flow.
19(1951); http://dx.doi.org/10.1063/1.1748196View Description Hide Description
The rates of exchange between N2 28 and N2 30 obtained on doubly‐ and singly‐promoted iron catalysts is of the right order to be accounted for by assuming that all nitrogen evaporating from the surface of the catalyst is completely equilibrated with respect to the nitrogen isotope exchange. Large concentrations of hydrogen (50 percent H2 in N2) markedly accelerate the reaction. Small traces of surface oxides poison the iron catalysts severely for the isotope exchange.
19(1951); http://dx.doi.org/10.1063/1.1748197View Description Hide Description
The infrared spectra of gaseous and liquid CH3CN have been investigated in the region 1.6μ—20μ with a Perkin‐Elmer spectrometer using LiF, NaCl, and KBr prisms. The parallel type bands show, in general, a sharp Q branch and broad but more intense P and R branches. The perpendicular type bands are well resolved and show the expected intensity alternation ``strong, weak, weak, strong . . .'' of the subbands (Q branches).
All the fundamentals, except ν8(e), which is beyond the region investigated, have been definitely established and vibrational assignments have been made for all the observed bands.
Values for the rotational constants from microwave data have been used to obtain the Coriolis interaction constants,ζ i , from the observed separations of the subbands of the ⊥ bands. The following values have been obtained: ζ5=0.10, ζ6=−0.44, and ζ7=0.41.
19(1951); http://dx.doi.org/10.1063/1.1748198View Description Hide Description
The infrared spectrum of methyl chloroform has been investigated in the region 1.6μ—20μ with a Perkin‐Elmer spectrometer using LiF, NaCl, and KBr prisms. Vibrational assignments are given to all the bands observed, and all fundamentals except the torsional vibration have been fairly definitely established. Most of the bands, whether perpendicular or parallel type, show the same kind of PQR structure.
19(1951); http://dx.doi.org/10.1063/1.1748199View Description Hide Description
The Curie temperature (θ) and intensity of magnetization of certain unreduced and reduced iron oxide catalysts have been determined. For the singly promoted unreduced systems of Fe3O4 containing small amounts of one of the following, Na2O, K2O, Cs2O, BaO, B2O3, Al2O3, or SiO2, θ was found to be practically the same as for Fe3O4, but large reductions in the saturation intensity of magnetization (Is ) were observed. The doubly promoted unreduced systems studied contained additions to Fe3O4 of Al2O3 and one of the following (in small amounts): Na2O, K2O, BaO, or SiO2. θ for these materials varied only slightly and was either equal to or less than that for Fe3O4. Large reductions in Is were found. Magnetic measurements on the reduced materials gave values of θ the same as for pure iron. The extent to which the promoters go into solid solution, both for the unreduced and reduced materials, is determined. Additional unreduced unpromoted iron oxides were investigated that had variable ratios (γ) of Fe++/Fe+++. Starting at γ=0.352, Is was found to increase with increasing γ to a maximum at γ=0.50, agreeing with the known value for magnetite, and then to decrease to a small value for large γ. The value found for Is at γ=0.352 is in agreement with Néel's theory of ``ferrimagnetism'' as applied to cubic Fe2O3 and Fe3O4. θ was found to be constant at about 583°C for γ from 0.352 to 1.276.
19(1951); http://dx.doi.org/10.1063/1.1748200View Description Hide Description
The concentration dependence of the conductivities of strong electrolytes is of interest in both theory and application. Older theoretical and empirical equations fail at high concentrations.
This article presents three empirical equations for the concentration dependence of conductivity. The first of these contains only a single fitted parameter (``a'' in Eq. (1) and Table I). Each of the other equations contains two parameters and follows the experimental curves up to high concentrations. However, Eq. (3) is the only one that shows the proper exponential concentration dependence at very high concentrations.
Also, a description is given of two anomalies in the behavior of tetramethyl ammonium salts.
19(1951); http://dx.doi.org/10.1063/1.1748201View Description Hide Description
Expressions are derived which predict satisfactorily the observed isomer and carbon number distribution of products from iron and cobalt catalysts in the Fischer‐Tropsch synthesis. These expressions are based on three schemes of stepwise addition of one carbon atom to the end or adjacent‐to‐end carbons of the longest carbon chain of the growing group at the catalyst surface. The implications of these schemes to some general aspects of the reaction mechanism are considered.
19(1951); http://dx.doi.org/10.1063/1.1748202View Description Hide Description
The mercury (3 P 1) photo‐sensitized decomposition of propane has been studied from room temperature to 450°C at pressures between 4 and 300 mm. The high temperature results are explained in terms of the decomposition of the propyl radical to form ethylene or propylene, and activation energies of 20 and 38 kilocalories, respectively, are assigned to these reactions. Experiments are also described where propane and propylene were in competition for hydrogen atoms, the relative rates of reaction being found at three temperatures. The difference in the activation energies of the two reactions is 4 kilocalories. The reactions at lower pressures are more complex and only a qualitative description of them can be given.
19(1951); http://dx.doi.org/10.1063/1.1748203View Description Hide Description
The mercury photo‐sensitized decomposition of ethane has been carried out with particular emphasis on the high temperature reaction. Evidence is given that under these experimental conditions the ethyl radical becomes unstable around 400°C. An activation energy of 39.5 kcal is assigned to the reactionon the basis of the proposed mechanism.
The Reactions of Methyl Radicals. IV. The Abstraction of Hydrogen Atoms from Cyclic Hydrocarbons, Butynes, Amines, Alcohols, Ethers, and Ammonia19(1951); http://dx.doi.org/10.1063/1.1748204View Description Hide Description
The photolysis of acetone in the presence of various compounds has been investigated between 70°C and 340°C. If the reactionhas no activation energy, then the activation energies in kcal for the reactions of the typeare cyclopropane 10.3, cyclobutane 9.3, cyclopentane 8.5, cyclohexane 8.3, benzene 9.2, toluene 8.3, 1‐butyne 9.1, 2‐butyne 8.6, methanol 8.2, ethanol 8.7, iso‐propanol 7.3, methyl ether 9.5, iso‐propyl ether 7.3, monomethyl amine 8.4, dimethyl amine 7.2, trimethyl amine 8.8, and ammonia 10.0. The collision theory steric factors are of the order of 10−3 or less for all these reactions.
A table is presented summarizing the results so far obtained on methyl radical reactions by the photolysis of acetone in the presence of other compounds. The accuracy of the method and some of the general implications of the results are discussed.
19(1951); http://dx.doi.org/10.1063/1.1748205View Description Hide Description
The infrared spectrum of F2O has been re‐examined from 2–25μ with a prismspectrometer and selected regions further examined with a grating spectrometer. Several bands observed by Hettner, Pholmann, and Schumacher have been shown to be caused by impurities. Other bands observed by them have been resolved, and an assignment of fundamental modes has been made which is consistent with dimensions of the molecule obtained from electron diffraction data. Two new bands have been observed and assigned to combinations of the fundamentals. The present observed frequencies and their assignments are: ν1=928 cm−1, ν2=461 cm−1, ν3=831 cm−1, ν1+ν3 and 2ν2+ν3 at 1731 cm−1, 3ν3=2460 cm−1, 2ν1+ν3=2643 cm−1.
19(1951); http://dx.doi.org/10.1063/1.1748206View Description Hide Description
An infrared absorption cell for compressed gases was constructed and used at pressures up to 600 atmos. In the cell, which was of the reflection type, the length of the absorbing path could be changed from 5×10−4 cm to 4 cm by means of metal spacers placed between the window and the mirror. The influence of high pressures of helium, argon, and nitrogen on the intensity of the methane band at 3.3μ was investigated. It was found that the absolute absorption coefficient for the band increases linearly with the density of the foreign gas. With nitrogen at 600 atmos the absorption coefficient is 20 percent greater than that of the free methane molecule. The magnitudes of the coefficients of induced absorption are compatible with the assumption that the vibrating dipole of the absorbing molecule is increased by the reaction field of the polarizable foreign gas molecules in its neighborhood. The coefficient of absorption for the free molecule was found by extrapolating the measured coefficients to zero density of the foreign gas. The values derived from measurements with the three foreign gases agree closely, and give an average value of 1075×1010 sec−1 cm−1 at NTP.
19(1951); http://dx.doi.org/10.1063/1.1748207View Description Hide Description
The infrared and Raman frequencies are calculated for the fundamental vibrations of an infinite n‐paraffin chain. Valence force constants, chosen to give agreement between the calculated and observed infrared frequencies, give calculated Raman frequencies which are correlated with observed Raman lines. The difference in frequency to be expected for the Raman and infrared bands of the CH2 out‐of‐plane rocking vibration is discussed. The CH2 frequencies of propane are calculated from the infinite paraffin chain force constants and are compared with previous assignments.
19(1951); http://dx.doi.org/10.1063/1.1748208View Description Hide Description
LCAO molecular orbitals and ionization potentials have been calculated for the ground state of CO2 using Roothaan's LCAO self‐consistent field method. The interactions of all electrons have been explicitly considered, and no extra‐geometrical empirical data have been used. The calculated molecular orbitals are in general agreement with those predicted by Mulliken and Moffitt from semi‐empirical considerations. The calculated ionization energies are 11.5 ev for a 1π g electron and 17.9 ev for a 2σ u electron, compared with the experimental 13.8 ev, and 18.0 ev, respectively. The evaluation of the large number of integrals over atomic orbitals that occur, is discussed in an appendix. All the larger integrals were calculated exactly, the smaller ones approximated. Useful approximation methods for some of these integrals are considered.
19(1951); http://dx.doi.org/10.1063/1.1748210View Description Hide Description
Observations have been carried out on the splitting of thorium stars in photographic emulsions. It is found that this process is caused entirely by the Brownian motion of the thoron atoms produced in the course of successive decays. Applying the classical statistical theory, the diffusion coefficient of thoron in gelatin and the viscosity of dry gelatin at room temperature have been deduced. The results are discussed in the light of our present knowledge of the structure of gelatin.
19(1951); http://dx.doi.org/10.1063/1.1748211View Description Hide Description
This article describes a proposed new type of adsorption potential associated with surface strain induced in the elimination of unbonded electron orbitals (``first‐order strain''), and strain due to surface (chemical) heterogeneities, or surface impurities (``second‐order strain''). These surface strains are assumed to give rise to a ``semi‐chemical'' adsorbate‐adsorbent attachment in the first layer of multimolecular films. This is termed ``structural adsorption'' and is considered to be largely responsible, along with ordinary van der Waal's potentials, for the low pressure region of the type II isotherm.
The theory is applied in the calculation of the adsorption isotherms for pure nitrogen, pure oxygen, and mixtures of nitrogen and oxygen on anatase. It is further applied in determining the composition of the adsorbate in mixed gas adsorption and in the computation of the surface pressure of these films over the entire range of relative pressures from zero to p/p 0=1.0. Excellent agreement with experimental observations is achieved.
- LETTERS TO THE EDITOR
19(1951); http://dx.doi.org/10.1063/1.1748212View Description Hide Description