Index of content:
Volume 25, Issue 3, 01 September 1956
25(1956); http://dx.doi.org/10.1063/1.1742930View Description Hide Description
The mathematical description of a two‐bulb thermal diffusion experiment is extended to the case of multicomponents isotopic mixtures. A self‐consistent method of comparing two‐bulb data to theoretical predictions is developed and applied to the argon data of Stier. The best fit for the modified Buckingham exp‐six, α=14, intermolecular potentialmodel is obtained for a force constant, ε/k=110°K. Measurements of the thermal diffusion factor of krypton versus temperature are presented and compared to the Lennard‐Jones (9,5) and (13,7) and the modified Buckingham exp‐six, α=14 models, yielding the force constant values, ε/k=169, 395, and 470°K, respectively.
25(1956); http://dx.doi.org/10.1063/1.1742931View Description Hide Description
The ionization of all of the alkali metals on tungsten and on tungstenoxide surfaces follows the Saha‐Langmuir equation with no reflection. On platinum, however, a departure from this equation indicates partial reflection of the atoms. The reflection of Na is probably 0%, since the ionization efficiency is given closely by the Saha‐Langmuir equation with a value of 5.50 ev for the work function of Pt at 2000°K. The same value of the work function then indicates reflections of 18% for Li, 48% for K, 22% for Rb, and 8% for Cs, at 2000°K.
25(1956); http://dx.doi.org/10.1063/1.1742932View Description Hide Description
The ionization of the potassium halides on tungsten follows the Saha‐Langmuir equation and indicates the formation of stable partial films of halide. On platinum, however, reflection occurs amounting to more than 99% for KCl, KBr, and KI, and about 75% for KF.
25(1956); http://dx.doi.org/10.1063/1.1742933View Description Hide Description
25(1956); http://dx.doi.org/10.1063/1.1742934View Description Hide Description
This paper contains a detailed theory of ion pairing based on the viewpoint that the distribution of pairs is more fundamental than the density of ions in an ionic atmosphere. This distribution is then evaluated by considering the kinetic mechanism by means of which pairs exchange partners. The functions so derived, besides being applicable to nonequilibrium situations, are free of many of the inconsistencies which attend the simple theory of pairing based on mass action considerations. The present paper restricts attention to the properties at equilibrium.
25(1956); http://dx.doi.org/10.1063/1.1742935View Description Hide Description
This paper applies the nonequilibrium distribution function for ion pairs, derived in paper I of the series, to the case of ionic mobility in an external electric field. The results are in good agreement with the simple theory of Fuoss and demonstrate the virtue of the latter.
Microwave Absorption and Molecular Structure in Liquids. XIII. The Critical Wavelengths of Some Aliphatic Ethers and Long‐Chain Ketones25(1956); http://dx.doi.org/10.1063/1.1742936View Description Hide Description
The dielectric constants and losses of ethyl ether, n‐decyl ether, n‐heptanone‐2, n‐pentadecanone‐8, n‐heptadecanone‐9, and benzophenone, and of solutions of benzophenone in heptane and in a 50–50 mixture of heptane and benzene have been measured at wavelengths of 1.25, 3.22, and 10.0 cm at temperatures between 4 and 85°. The arc plots constructed from these data and the measured low‐frequency dielectric constants have been used to calculate the critical wavelengths at which the loss is a maximum. Several molecules of similar sizes and shapes are shown to possess similar viscosities and critical wavelengths. For the pure polar liquids, a rough proportionality between the critical wavelengths or dielectric relaxation times and the viscosities is observed.
25(1956); http://dx.doi.org/10.1063/1.1742937View Description Hide Description
The ignition phenomenon in a chemically reactive gas flowing about a heated body is discussed. Specifically the conditions at the forward stagnation point of the object are analyzed. A condition is formulated which relates the critical surface temperature for ignition with those parameters which control the heat and mass transport and the reaction kinetic mechanism.
25(1956); http://dx.doi.org/10.1063/1.1742939View Description Hide Description
Two of the 3 Raman‐active fundamentals of UF6 have been observed at 666.6±0.3 (ν1) and 535±5 cm—1 (ν2) for a gaseous sample. The new value for ν2 is in good agreement with the value 532 cm—1 obtained earlier by Gaunt from infrared combinations. The sample of UF6 was contained in a Pyrex Raman tube and was irradiated for many hours with 4358 A light with no visible deterioration. Gaunt's thermodynamic functions remain valid.
25(1956); http://dx.doi.org/10.1063/1.1742940View Description Hide Description
A discussion of the phenomenon of dielectricsaturation is presented, and Debye's theory for an assembly of independent molecules is extended to include the field dependence of the molecular polarizability. Also, a rigorous theory of the field‐dependent dielectric constant of a dense medium is deduced. It is found that a relationship valid at all densities exists between this dielectric constant and the molecular Kerr constant, and the experimental data on liquidcarbon disulfide are in good agreement with the theory. The saturation effect in dilute solutions of anisotropically polarizable substances with large dipole moments is also discussed, and the experimental results for dissolved nitrobenzene agree well with the theory.
25(1956); http://dx.doi.org/10.1063/1.1742941View Description Hide Description
The complex dielectric constant for wool‐water systems has been determined at a frequency of 26 000 Mc by a cavity resonator method similar to the method employed at 3000 and 9300 Mc. At 26 000 Mc, measurements on single wool fibers and at relative humidities as high as 98% have proved feasible.
The complex dielectric constant of the wool‐water system increases with increasing water content. Curves for the dielectric constant and loss factor of the wool‐water systems at 26 000 Mc are presented and analyzed in terms of a new theory of water sorption by wool. According to this theory, which is based upon a theory originally proposed by Cassie, the water sorbed by wool consists of three distinct molecular species: (1) localized water irrotationally bound to polar sites in the wool, (2) mobile water with bulk liquid properties, and (3) intermediate water with a potential energy of absorption which lies between those for localized and mobile water. The analysis of the measurements at 26 000 Mc for the higher relative humidities in terms of this theory has resulted in a more thorough description of the properties of the sorbed water than was possible for the data obtained at 3000 and 9300 Mc.
25(1956); http://dx.doi.org/10.1063/1.1742943View Description Hide Description
The Schwartz, Slawsky, and Herzfeld method for the calculation of vibrational relaxation times of gases has been extended in its application to polyatomic molecules. A general method is developed for the calculation of the effective relaxation times and the associated constants of the sound velocity relaxation equation. Calculations have been made for the bimolecular collisions of methane and the chloromethanes involving changes of one, two, and three quanta. A normal coordinate treatment is used to obtain the atomic vibrational amplitudes. The effect of an intermolecular potential function, embodying a dipole interaction term, is included for the polar molecules of this investigation.
Calculated results are compared with experimental data. For CH4 and CH3Cl the calculations agree well with experimental results. For CH2Cl2, CHCl3, and CCl4 the calculated relaxation times are higher than selected experimental values by factors of 8–9. For CH2Cl2, CHCl3, and CCl4 two major relaxation times are calculated. In the case of CH2Cl2 the two relaxation areas have been observed. The experimental data on CHCl3 and CCl4 remain inconclusive in respect to the two predicted relaxation areas. Collisions involving three quanta are shown to be important for CH2Cl2, CHCl3, and CCl4.
25(1956); http://dx.doi.org/10.1063/1.1742944View Description Hide Description
Burning velocity measurements of the CO–O2–N2–H2O system were made with the flat‐flame burner technique. The plan of experimentation was to vary the H2O content, the equivalence ratio, and the pressure, while holding the flame temperature constant by controlling the proportion of N2 in the mixture. The results could be represented empirically by the relation:where vu is burning velocity (cm/sec), (CO) u and (H2O) u are mole fractions in the unburned gas, P is pressure, and Tb is burned‐gas temperature. The Zeldovich, Frank‐Kamenetsky, and Semenov equation was used to obtain an ``over‐all'' activation energy (20 kcal) and frequency factor for the process, and the CO oxidation rate in this type of flame was then compared with the rate at which the CO forming as an intermediate in a lean hydrocarbon‐air flame is oxidized in the downstream portion of such a flame. The comparison showed that, at comparable conditions, the CO oxidized 5.6 times as fast in the CO flame as in the hydrocarbon flame. Temperature traverses in hydrocarbon‐air flames to which large proportions of H2O have been added showed the rate of CO oxidation to be slightly increased thereby.
Equilibrium concentrations of the species H, OH, and O in the burned gases were calculated for a variety of CO–O2–N2–H2O mixtures, all at the same flame temperature, and correlations with burning velocity were sought. The square of the burning velocity was found to be directly proportional to (OH) b (CO) b 0.72; alternatively, the group (H) b (O2) b 0.136 gave equally good correlation. A third successful grouping was [(H) b +0.15(OH) b ]½. The writers are not convinced that correlations of this type reveal the burning mechanism.
25(1956); http://dx.doi.org/10.1063/1.1742945View Description Hide Description
Lewis‐Rayleigh afterglow in nitrogen has been examined by simultaneous observation with a mass spectrometer and a photomultiplier. Afterglow intensity was found to be proportional to the square of the ground‐state nitrogen atom concentration under a variety of conditions. The proportionality constant was essentially unaffected by small oxygen addition, but was somewhat increased with admixture of noble gases. Evidence is presented for a linear dependence of afterglow intensity on total pressure of nitrogen. Addition of nitric oxide to the afterglow results primarily in the production of nitrous oxide. From a rough calibration of the atomic concentration (ca 1%) and the afterglow radiation intensity, (1013 photons/cc‐sec) a termolecular rate constant of 2×10—33 cc2‐molecule—2‐sec—1 is obtained.
The experimental data point to a termolecular reaction involving two 4 S nitrogen atoms. The detailed mechanism probably involves the intermediate formation of the 5Σ g + molecular state, followed by a collision‐induced, radiationless transition into the 3π g state.
25(1956); http://dx.doi.org/10.1063/1.1742946View Description Hide Description
It is shown that for every transition in its individual residues, a helix has two transitions whose moments are respectively parallel and perpendicular to the screw axis. The largest contributions to the rotational strengths of these bands are equal and opposite in the two cases. As a result, their net effect on the optical activity contains a term proportional to the interval between the two upper states. This term shows abnormal dispersion and its magnitude and sign are more easily interpreted than any other component of the rotatory power.
25(1956); http://dx.doi.org/10.1063/1.1742947View Description Hide Description
The infrared spectrum of formic acid vapor at 150°C has been studied over the 1800–1250 cm—1 region. A vibrational assignment has been made for monomeric formic acid and the anomalous frequency shifts in the three deuterated isotopic acids explained on this assignment by considering vibrational interaction.
First Singlet‐Singlet Electronic Transition in the Phenanthrene Molecule and the Band Structure of the Phenanthrene Crystal25(1956); http://dx.doi.org/10.1063/1.1742948View Description Hide Description
The absorption and emission spectra of single crystals of phenanthrene have been studied at 20°K. The data show that the transition moment in the molecule is short‐axis polarized, and that the factor group splitting in the crystal is 47 cm—1. The emission originates in a region of very weak absorption at a frequency below the main absorption in analogy to several other molecular crystals whose spectra have been studied. It is suggested that the emitting level corresponds to a distorted lattice site.
25(1956); http://dx.doi.org/10.1063/1.1742949View Description Hide Description
Effective flame speeds of turbulent free flames were measured by photographic, ionization gap, and photo‐multiplier tube methods; they were found to have a statistical distribution attributed to the random nature of the turbulent field. The effective turbulentflame speeds for the free flame were found to be less than those previously measured for flames seated on Bunsen burners and bluff bodies. The statistical spread of the effective turbulentflame speeds was markedly wider in the lean and rich fuel‐air regions. This is attributed to the greater sensitivity of laminar flame speed to flame temperature in the lean and rich regions.
25(1956); http://dx.doi.org/10.1063/1.1742950View Description Hide Description
The absolute intensities of the fundamental bands in CH2Br2 and CH2I2 of species B 1 and B 2 have been measured. The intensities observed are, in cycles/sec at NTP,The bond moments and bond derivatives calculated from this data arewhere the ambiguity in signs that led to alternate values of ∂μCH/∂r CH could not be resolved.