Volume 16, Issue 3, 01 March 1948
Index of content:
16(1948); http://dx.doi.org/10.1063/1.1746825View Description Hide Description
The Seeger‐Teller theory of dielectric breakdown for the alkali halides has been extended to account for the effect of trapping at low temperatures. The cross section of ionized F‐centers has been estimated classically, as well as from recent experiments of Domanic on the photoelectric yield of F′‐centers, to be about 3×10−13 cm2 near liquid air temperatures. The increase in the breakdown field for NaCl is given as a function of the concentration of vacant halogen ion sites. An observable increase, of about 10 percent, in breakdown voltage is predicted at a concentration of 2×1018 centers per cm3.
Studies of Surface Films by Reflection of Polarized Light. I. A More Rigorous Algebraic Method for Computing Results16(1948); http://dx.doi.org/10.1063/1.1746827View Description Hide Description
Plane‐polarized light is in general elliptically polarized by reflection. Since the molecules in a very thin surface layer are those chiefly concerned in the process of reflection, the ellipticity is very sensitive to the interface conditions such as the presence of thin films. Since light changes phase 360° in a single wave‐length, determination of phase changes to within a few minutes of arc should allow film thickness measurements to the nearest angstrom unit. The method has been used for many years to treat problems of wide variety. The instruments and techniques employed have, on the whole, been adequate, but the interpretation of results has often been more or less unsatisfactory. The algebraic relationship between instrument readings and film constants is not exactly known. Reasonably precise graphical solution is tedious. Algebraic solutions have been preferred by most workers.
This paper reports an algebraic method containing fewer approximations than used hitherto and compares results with values found by two prior methods. Drude's original equations give results in rather poor agreement with those of the more precise equations developed in this paper. Results obtained with the equations of Tronstad, on the other hand, agree fairly well in a favorable case.
16(1948); http://dx.doi.org/10.1063/1.1746829View Description Hide Description
X‐ray powder patterns on anhydrous sodium palmitate show that the five phases already known to occur between crystal and isotropic melt can be grouped into two basic structures. Both structures are liquid crystalline, i.e., crystalline in the direction of the long spacing and liquid‐like laterally. Between the lower temperature ``waxy'' structure, which includes the previously known subwaxy, waxy, and superwaxy phases, and the higher temperature ``neat'' structure, which includes subneat and neat, there is a pronounced break in the curve of long spacing vs. temperature; in addition, the three waxy phases exhibit two diffuse short spacing rings, whereas the neat phases exhibit only one. These pattern differences lead to the interpretation that the waxy phases contain structural restraints on molecular position and motion not present in the neat phases.
Statistical Mechanics of Multimolecular Adsorption. IV. The Statistical Analog of the BET Constant a 1 b 2/b 1 a 2. Hindered Rotation of a Symmetrical Diatomic Molecule Near a Surface16(1948); http://dx.doi.org/10.1063/1.1746831View Description Hide Description
An approximate study is made of the restricted rotation of a symmetrical diatomic molecule near a surface. This makes possible some calculations concerning the BET constant C=R exp(ε1—Λ)/kT, and especially the factor R (which is customarily set equal to unity). Cassie has pointed out that if this factor is set equal not to unity but to about 1/50 or even less, the low values of the heat of adsorption usually found on putting R=1 in the analysis of data are accounted for. The results obtained here indicate, unfortunately, that this factor is of the order of, say, 5–10, and that another explanation of the low heats of adsorption mentioned above will have to be found. An alternative method of estimating the area occupied per molecule in a completely filled monolayer is mentioned in an appendix.
The temperature dependence of the quantity R is of some experimental interest, and a brief discussion of this dependence as predicted by the present approximate treatment is included.
16(1948); http://dx.doi.org/10.1063/1.1746833View Description Hide Description
Values are computed for the viscosity,thermal conductivity, and coefficient of self‐diffusion, as functions of temperature, for the following gases: neon (60°−200°K), argon (110°−290°K), krypton (150°−370°K), and xenon (210°−550°K). The method of calculation is the same as that previously developed for gaseous helium and involves the use of classical scattering theory within angular regions where diffraction effects are absent, to obtain appropriate classical transport cross sections for insertion into the exact formulas of Chapman and Enskog.
The average absolute deviations between calculated and experimental values are 5.5 percent for viscosity and 5.9 percent for thermal conductivity. In the case of self‐diffusion, only two experimental values are available for comparison with calculated values, one each for krypton and xenon. The absolute deviations are 9.7 and 10.3 percent, respectively.
A procedure is suggested for obtaining approximate values of the mutual diffusion coefficient of a binary gas mixture from the self‐diffusion coefficients of the constituents.
16(1948); http://dx.doi.org/10.1063/1.1746834View Description Hide Description
(1) It is postulated that the interaction between starch and iodine in the amylose‐iodine complex is of dipolar nature.
(2) A model for such dipolar interaction is proposed and the necessity for a cooperative effect is discussed.
(3) The interaction energy is calculated as a function of a parameter x and it is shown that this parameter possesses a critical value at which a ``condensation'' of iodine into the complex occurs.
(4) It is demonstrated that it is physically reasonable for this parameter to attain its critical value.
(5) It is shown that additional stabilization may occur as a result of the formation of a resonating ``polyiodine'' chain at high dipolar interaction having a I–I distance and heat of formation which compares favorably with experiment.
(6) Application of the theory is made in discussing the stability of the polyvinyl alcohol‐iodine complex.
(7) The color of these complexes is discussed in terms of the theory.
16(1948); http://dx.doi.org/10.1063/1.1746836View Description Hide Description
An investigation of the structure of the nitrogen dioxide molecule has been made by the electron diffraction method. The interpretation of the photographs, which showed rings extending to values of q of nearly 100(q = 40/λ sinτ/2), leads to the following structural parameter values: N–O = 1.20±0.02A, <O–N–O = 132±3°. These values are discussed briefly and compared with those obtained by other methods.
16(1948); http://dx.doi.org/10.1063/1.1746838View Description Hide Description
If infra‐red absorption by a sample gas is measured at low resolution in the presence and absence of pressure broadening by a non‐absorbing gas, information may be obtained concerning breadth and fine structure of individual rotational lines. Data on 590—cm−1 and 1285‐cm−1 bands of N2O indicate self‐broadening coefficients of about 0.21 and 0.13 cm−1 per atmosphere, respectively. These values may be compared with 0.20 cm−1 per atmosphere obtained by Adel and Barker by direct measurement on the 590‐cm−1 band.
16(1948); http://dx.doi.org/10.1063/1.1746840View Description Hide Description
Valence‐type force constants, including several interaction terms, have been deduced from some of the experimentally observed fundamental vibration frequencies of the molecular sequence CX 4, CX 3 Y, CX 2 Y 2, CXY 3, and CY 4 in which X may be chlorine or bromine, Y hydrogen or deuterium. By assuming that the force constants are invariant for the different molecules and by neglecting several interaction constants associated with two bending motions, the number of distinct constants was reduced to 28, from which, after slight adjustment, 100 vibration frequencies were calculated. The quality of the fit with the experimental frequencies is indicated by a reasonably low root mean square deviation between calculation and observation (1.1 percent for 82 frequencies) and by the success of the constants in predicting 22 of the frequencies which were not used in the initial numerical evaluation of the constants.
16(1948); http://dx.doi.org/10.1063/1.1746843View Description Hide Description
16(1948); http://dx.doi.org/10.1063/1.1746845View Description Hide Description
An investigation of the acetone photolysis in the ``continuum'' and in the ``banded'' region has been made in clean quartz vessels and in vessels coated with potassium chloride and with lead. No appreciable change in the C2H6/CO ratio occurs in the coated vessels. This is surprising since biacetyl formation is apparently at least partly heterogeneous, and the ratio would be expected to be sensitive to the condition of the surface.
A few experiments were also made on the mercury photosensitized decomposition of acetone. Very high C2H6/CO ratios were found. It is concluded that this is due merely to higher absorbed intensities for a given incident intensity.
16(1948); http://dx.doi.org/10.1063/1.1746847View Description Hide Description
A table of constants is given whereby one may at once write down, knowing the vibrational frequencies, the best approximation of the form Cp o = A 0+A 1 T+A 2 T 2 to the heat capacity of a gas with translational, rotational, and vibrational (harmonic) degrees of freedom.
16(1948); http://dx.doi.org/10.1063/1.1746849View Description Hide Description
Poisoning films of exceptional thermal stability are formed on a platinum catalyst when heated in a silicone vapor (hexamethyldisiloxane) at pressures of the order 10−3 mm. These films prevent the combination of hydrogen and oxygen at low pressures and are not removed until heated to about 1440 K in the presence of hydrogen (or to higher temperatures in oxygen). It is suggested that the film may consist of a silicon oxide oriented with the silicon atoms attached directly to the platinum and presenting an outer layer of oxygen atoms, effectively shielding the catalyst.
A New Method of Preparing Strongly Luminescent Thallium Activated Alkali Halides and Some Properties of These Phosphors16(1948); http://dx.doi.org/10.1063/1.1746851View Description Hide Description
Phosphors with a bright visible fluorescence and a long lasting afterglow can be prepared by grinding potassium chloride with small amounts of a thallous salt in a mortar. The character of the luminescence spectra and the phosphorescence decay depends on the thallium concentration. The behavior of other alkali halides under the same treatment and some conclusions concerning the probable carriers of the luminescence are discussed.
16(1948); http://dx.doi.org/10.1063/1.1746853View Description Hide Description
The ultrasonic velocity for the temperature range 10° to 30°C has been measured for seven members of a 1‐olefin series. Densities and refractive indices were also measured. From the measurements, values of the molecular sound velocity, adiabatic compressibility, and molecular refractivity were computed. The ultrasonic velocity is found to vary linearly with temperature, while the molecular constant, MV ⅓/d, remains substantially constant. The constant is found to be strictly additive for the series members studied.
An Asymptotic Expression for the Energy Levels of the Asymmetric Rotor. II. Centrifugal Distortion Correction16(1948); http://dx.doi.org/10.1063/1.1746855View Description Hide Description
It has been found possible to develop perturbation operators for the centrifugal distortion terms that permit an approximate evaluation to be made of their contribution to the asymmetric rotor energy levels for large values of J. The procedure is based upon the asymptotic (J→∞) similarity between the matrices of the asymmetric rotor and that obtained from Mathieu's differential equation.
- LETTERS TO THE EDITOR
16(1948); http://dx.doi.org/10.1063/1.1746858View Description Hide Description
16(1948); http://dx.doi.org/10.1063/1.1746860View Description Hide Description