Index of content:
Volume 22, Issue 9, 01 September 1954
22(1954); http://dx.doi.org/10.1063/1.1740441View Description Hide Description
The molecular polarization of ammonia is calculated quantum mechanically by taking account of the dipole matrix elements of inversion doubling in the first excited state as well as in the ground state of the symmetric deformation vibration. It is found to be reasonable that the dipole moment of this molecule decreases at higher temperatures. The atomic polarization is also calculated and the result, PA =0.65 cc, is in good agreement with the observed value.
22(1954); http://dx.doi.org/10.1063/1.1740442View Description Hide Description
The J=0→1 microwave rotational transitions in the states v=1 of the vibrations v 3(a 1) and v 6(e) in methyl chloride and the state v=1 of the vibration v 3(a 1) in methyl bromide have been studied. The quadrupole coupling constants eqQ of chlorine and bromine in these states were determined. These were compared with the values determined for the ground state. No variation of the quadrupole coupling constants with vibrational state was observed. The accuracy of the measurements requires the variation of eqQ with vibrational state to be less than 0.07 percent in methyl bromide. The rotational constants and vibration‐rotation constants for these states were also determined.
22(1954); http://dx.doi.org/10.1063/1.1740443View Description Hide Description
The real and imaginary parts of the complex dielectric constant of the liquid crystal and normal liquid phases of para‐azoxyanisole and para‐azoxyphenetole have been measured at a frequency of 15 300 Mc. A static magnetic field applied to the sample is capable of producing large changes in the observed values of the complex dielectric constant. The extent of this effect depends on the orientation and intensity of the static magnetic field and on the temperature.
22(1954); http://dx.doi.org/10.1063/1.1740444View Description Hide Description
A standing wave, single crystalinterferometer was used to measure the ultrasonic velocity in polystyrene having molecular weights from 4100 to 159 000. Most of the measurements were made with 2 g of polystyrene per 100 ml of solution, benzene being the solvent. Some measurements used similar concentrations with toluene as the solvent. In the range of temperatures from 8.95°C to 54.45°C the velocity attributable to the polystyrene had a negative temperature coefficient below 35°C and a positive one above 35°C. At a given temperature the velocity attributable to the polystyrene showed two minima when plotted as a function of molecular weight. These minima occurred at polystyrene molecular weights of 17 000 and 53 000. Suggestions, but no conclusions, are given for the cause of these minima or dispersive regions.
Free Radicals by Mass Spectrometry. VI. The Bond Dissociation Energies of Some Methyl, Allyl, and Benzyl Compounds by Electron Impact22(1954); http://dx.doi.org/10.1063/1.1740445View Description Hide Description
The appearance potentials for the radical ions from methyl, allyl, and benzyl halides and two other derivatives have been measured. Using previously measured values for the ionization potentials of the free radicals, the R–X bond dissociation energies in these compounds have been calculated. The results are in good agreement with published data for the methyl and allyl compounds, and in fair agreement for the benzyl halides.
22(1954); http://dx.doi.org/10.1063/1.1740446View Description Hide Description
Measurements on the thermoelectric power of pure AgBr and AgBr doped with CdBr2 have been interpreted in the light of the kinetic theories of Wirtz and de Groot. The ratio of the mobility of the interstitialsilver ions to that of the vacancies as determined by Teltow is reasonably consistent with the data reported here on thermoelectric power. Estimates are given for the heats of transport of the various species of moving imperfections. No evidence of a contribution by Schottky defects to the thermoelectric power is found.
22(1954); http://dx.doi.org/10.1063/1.1740447View Description Hide Description
The metastable ion suppressor on the Consolidated Engineering Corporation Model 21—103 mass spectrometer has been used as a retarding potential device to determine the excess kinetic energies possessed by the ions formed during appearance potential measurements. The suppressor setting at which an ion beam is extinguished is compared with the extinction setting for an ion beam with no excess energy. These settings are studied as a function of ionizing voltage, extrapolated back to the appearance potential, and converted into units of energy.
N+ from N2 was found to have no excess kinetic energy at the appearance potential. CH3 + from C2H6, CH3 + from C3H8, CN+ from C2N2, and CH3 + from C6H5CH3 were all formed with excess kinetic energy. The following quantities were deduced after taking the excess energy into account: D(CH3–CH3)=3.87 volts; D(CH3–C2H5)=3.70 volts; I(CN)=15.13 volts; I(C6H5)=9.90 volts; D(C6H5–CH3)=3.80 volts; D(C6H5–H)=4.64 volts.
22(1954); http://dx.doi.org/10.1063/1.1740448View Description Hide Description
The solution of the linearized equations appropriate for sound dispersion is presented. The limiting cases as the sound frequency becomes large or small is examined. The two state gas is exhibited as a special case and shown equivalent to previous work in the field when the appropriate assumptions are made.
22(1954); http://dx.doi.org/10.1063/1.1740449View Description Hide Description
An attempt has been made to observe the thermal dissociation of N2 in order to choose between the two values, 7.385 ev and 9.765 ev, for the dissociation energy of N2. At the highest available temperatures no dissociation could be observed, and a lower limit of 8.80 ev is set for D(N2).
22(1954); http://dx.doi.org/10.1063/1.1740450View Description Hide Description
The significance as a determinant of Joshi effect Δi in H2O vapor of the predischarge adsorption consisting of an instantaneous uptake of molecules due to van der Waal's forces and slow process of sorption on Langmuir sites was investigated. Joshi effect corresponding to 15—20‐percent reversible current suppression was detected with a predischarge interval = ½ min; it was not altered by increase of this last to 5 hr or favored by ``aging'' under discharge, which indicated that the instantaneous process, viz, van der Waal's adsorption, which was quite distinct from Langmuir sorption formed during the predischarge interval and/or under discharge, was the chief seat of Δi. It was suggested that under light, surface molecules dissociated into atoms and/or radicals which possessed large electron affinity, to increase the work function of the cathode and, therefore, to give Δi. Observation of Δi even with longer wavelengths than those corresponding to dissociation energy of H2O suggested that the adsorbed molecules possessed, prior to irradiation, certain energyh(vd—v ) obtained by ionic bombardment under applied fields (vd is the frequency corresponding to dissociation energy of a molecule, and v is that employed for observing Δi).
22(1954); http://dx.doi.org/10.1063/1.1740451View Description Hide Description
Experiments on the x‐ray excited fluorescence and thermoluminescence of pure ice and ice containing certain additives are described. The luminescent spectra are explained by a model in which the primary process is the radiative capture of electrons by impurity cations. The first‐order buildup of fluorescence and temperature dependence of luminous intensity are interpreted by the breakdown and formation of the dipole sheath surrounding the dissolved ions. From this viewpoint, the activation energy for rotation of a sheath ice dipole from the normal lattice position to the aligned configuration is calculated to be 0.07 ev. The principal trap depth determined from the glow curve is 0.32 ev, a correction for the luminous efficiency being incorporated in the calculation; the corresponding s value is 2×108 sec—1. Possible mechanisms for the first‐order thermoluminescence are given.
22(1954); http://dx.doi.org/10.1063/1.1740452View Description Hide Description
Kinetical studies were made at 167°C on the decomposition of methanol induced by methoxy radicals, by pyrolyzing a small amount of dimethyl peroxide in methanol. A considerable amount of ethylene glycol was found. The following mechanism was proposed, and the kinetical equations derived therefrom could express the most part of the reaction quantitatively:The dissociationrate constant of dimethyl peroxide is represented by 4.1×1015 exp (—36.9 kcal/RT) sec—1, and the activation heat of (a) is 3.0∼4.3 kcal higher than that of (b).
22(1954); http://dx.doi.org/10.1063/1.1740453View Description Hide Description
The calculations on the Ising lattice and the order‐disorder phenomenon indicate that the specific heat may become infinite at the λ temperature or transition point. The general thermodynamics of such a system in a variable magnetic field is considered, and the relation to the generalized theories of critical points of Tisza and of Semenchenko is indicated. The general import of these theories is that infinite values of the heat capacity at constant pressure Cp , or the analogous heat capacity in a system with variables other than p, V, and T, can become infinite in a one‐phase system only at a critical point. The existence of a locus of points where Cp = ∞ is thermodynamically possible in the pVT system, and equations analogous to the Clapeyron and Ehrenfest equations may be derived. However, the thermodynamic requirements show that such a locus is not likely to occur. Interesting possibilities occur where there is an interaction between several sets of variables. If an Ising lattice is compressible, for example, the transition temperature will depend on the lattice distance. In this case, the infinite heat capacity is to be considered as a singularity in Cv rather than in Cp . The effect of the compressibility is to change any transition in which infinite specific heats occur to a first‐order transition. If there is already a first‐order transition, even for an assumed incompressible lattice, the introduction of compressibility increases the latent heat and a discontinuity in lattice distance appears. This situation appears to arise in the order‐disorder transformation of an alloy like AuCu3, and the phases may also be expected to have different compositions; this latter phenomenon has also been considered from the point of view of this paper. If there is a λ point without infinite specific heats, the introduction of compressibility may or may not change it to a first‐order transition; in any event, the λ point is made ``sharper.'' There may be a critical point in this case. Various thermodynamic relationships are deduced, and the nature of the isotherms in all these cases is considered.
22(1954); http://dx.doi.org/10.1063/1.1740454View Description Hide Description
Infrared and Raman spectra have been obtained for hexafluoro‐2‐butyne, including qualitative depolarizations and gaseous state frequencies for the stronger Raman lines. The data provide good evidence that D 3d selection rules are followed. From this it appears that there must be hindered rotation between the CF3 groups, with the ``staggered'' configuration being stable. An assignment of fundamental frequencies has been made for this model. The origin of the potential barrier is not known. (See note added in proof at end of paper.)
22(1954); http://dx.doi.org/10.1063/1.1740455View Description Hide Description
The emission, excitation, and absorption spectra of silver‐activated alkali halides have been investigated. Three absorption bands due to ionic silver have been observed in NaCl, NaBr, KCl, and KBr, and the growth of these bands with silver concentration has been studied. In each of these crystals the two shorter‐wavelength bands are ascribed to isolated silver ions, while the band of longest wavelength is ascribed to pairs of silver ions.
Upon x‐ray irradiation as many as five new absorption bands arise in certain alkali halides in addition to the F band. Excitation into three of these bands (designated as the B, C, and D bands) produces luminescence, the emission spectrum being different for each band. The B band is attributed to a center consisting of an electron trapped at a silver ion adjacent to a halogen‐ion vacancy; the C band to an electron trapped at a complex of two silver ions adjacent to a halogen‐ion vacancy; and the D band to a hole trapped at an alkali‐ion vacancy adjacent to a silver ion.
22(1954); http://dx.doi.org/10.1063/1.1740456View Description Hide Description
The rate of reaction of tritium and oxygen, initiated by the tritium beta radiation, has been investigated at 25°C, in the absence of mercury vapor, by using a sensitive Bourdon gauge as the manometer. The rate is not linear with time, but shows a small continual decrease as the reaction proceeds. The initial reaction rate was found to be directly proportional to the tritium pressure, and hence proportional to the radiation intensity. It was independent of the oxygen concentration over the range investigated. The reaction rate shows a slight dependence on the isotopic composition of the hydrogen reactant, tending to rise with increase in the mole fraction of protium. The initial reaction rate may be represented bywhere Ct 2 is the tritium concentration in moles/liter or other absolute concentration units, and mH is the mole fraction of protium in the hydrogen reactant. On the basis of a requirement of 33 ev per ion pair in the reactant mixture, the initial ion‐pair yield for tritium disappearance or water formation is (M/N)0=3.25 for the reaction of pure tritium with oxygen. Material balance measurements indicate that little or no peroxide appears in the product.
22(1954); http://dx.doi.org/10.1063/1.1740458View Description Hide Description
The composite piezoelectricoscillator method has been employed to study the temperature dependence of the velocity of ultrasonic waves in Perspex and polystyrene plastics. While confirming a previously reported transition in Perspex at 60°C, the results show the existence of a transition in polystyrene also at 70°C for the first time.
Photoionization and Total Absorption Cross Section of Gases. I. Ionization Potentials of Several Molecules. Cross Sections of NH3 and NO22(1954); http://dx.doi.org/10.1063/1.1740459View Description Hide Description
Ionization potentials determined by examining the long wavelength limit of the ionization continuum for H2S, CS2, C6H6, toluene, p‐xylene, C2H4, butadiene, and CH3I agreed with spectroscopic values obtained by Price and co‐workers. Values are reported also for NH3, NO, acetone, methyl‐ethyl‐ketone, CH3OH, and C2H5OH.
Improved energy measurements showed that photoionization cross sections of NO in the region 1070—1340A obtained earlier were about 40 percent too low. At 1215.6A the photoionization and the total cross sections are 2.0×10—18 and 2.4×10—18 cm2, respectively, the difference being ascribed to an absorption band. The photoionization cross section of NH3 was found to rise rather gradually with decreasing wavelength in the region 1220—1060A and to reach a value of 9×10—18 cm2 at 1060A.
Influence of Rate of Shear on the Apparent Viscosity of A—Dilute Polymer Solutions, and B—Bulk Polymers22(1954); http://dx.doi.org/10.1063/1.1740460View Description Hide Description
The measuredviscosity of bulk polymers and their solutions varies with the magnitude of the applied shearing stress. In this paper we show that this is a natural consequence of the fact that the molecules are caused to rotate by the shearing action. This rotation gives rise to sinusoidal forces which alternately stretch and compress the molecules. The viscous behavior of such a system is shown to be analogous to that of a spring immersed in a viscous medium and being acted upon by sinusoidal viscous forces. We have treated the problem quantitatively using the method of a previous paper. Good agreement is obtained between theory and experiment without the aid of adjustable parameters. It is found that, if the molecule is considered shielded, the theory accurately represents the experimental data for dilute solutions. The behavior of the bulk polymer is well represented by means of the free draining approach. It is pointed out that the variation of the viscosity of dilute polymer solutions with the rate of shear may provide a convenient method for determining molecular weights of coiling type polymers.