Volume 33, Issue 2, 01 August 1960
Index of content:
33(1960); http://dx.doi.org/10.1063/1.1731144View Description Hide Description
A procedure is developed for inverting the linear laws of irreversible thermodynamics in spite of the singular nature of the admittance matrix when barycentric diffusion currents are employed. The procedure is symmetric in that it is unnecessary to identify one species as a reference solvent. Explicit relations are given for the new coefficients (resistance matrix, heats of transport, Soret thermal conductivity) in terms of the old. Constraints on the new coefficients are also obtained.
33(1960); http://dx.doi.org/10.1063/1.1731145View Description Hide Description
The shift in frequency of lines of the 2–0 band of HCl and of the ν1+ν3 band of C2H2 due to the presence of krypton and xenon as foreign gases has been measured. A marked J dependence was observed. The relative shifts in the upper and lower states of the transitions were calculated from the shifts in the Δ2 F″(J) and Δ2 F′(J) values obtained from the measured line shifts. In the case of HCl the shifts in the rotational levels were markedly different in the upper and lower states, the upper state shift being proportional to J, while the lower‐state energy‐level shifts approach an asymptotic value for high J. For C2H2 the shifts in both levels resembled the shift in the lower state of HCl.
33(1960); http://dx.doi.org/10.1063/1.1731146View Description Hide Description
The shape of absorption lines of HCl and C2H2 broadened with krypton and xenon as foreign gases is shown to be that due to collision broadening. Corrections for instrumental width are made in the manner described by Pigott and Rank to determine the half‐intensity width. These widths show a small J dependence with low‐J lines being the broadest. No difference between the widths of P and R lines of the same J could be detected. For high J's the quotient of the shift of the line and the width of the line is approximately constant for krypton and xenon. The breadth of HCl and C2H2 lines are not markedly different in spite of the difference in dipole moment. No asymmetry of lines perturbed by these foreign gases was observed.
33(1960); http://dx.doi.org/10.1063/1.1731148View Description Hide Description
The quadrupolar splitting of the B11nuclear magnetic resonance signal in a single crystal of inderite Mg2B6O11·15H2O at room temperature has been investigated in a magnetic field of 7187 gauss. The spectra obtained as the crystal was rotated in turn about three mutually perpendicular axes held normal to the magnetic field were interpreted on the basis that the six B11 sites per unit cell belong to three distinct types with the two sites of each type related by a center of symmetry. The electric quadrupole coupling constants C z and asymmetry parameters η at the three unique B11 sites were determined to beIt has been inferred from the foregoing values that two of the boron atoms in the asymmetric unit of inderite have tetrahedral coordinations whereas the third has triangular coordination. The orientations of the principal axes of the electric field gradient tensors at the B11 sites have also been determined.
Induction Studies in Several Groups of Halogen‐Containing Organic Compounds by Their Cl35, Br79, or Br81 Pure Quadrupole Resonance Spectra33(1960); http://dx.doi.org/10.1063/1.1731149View Description Hide Description
Induction studies have been carried out in several groups of halogen‐containing organic compounds by means of the halogen pure quadrupolespectra. In several straight‐chain compounds inductive effects have been examined as a function of the length of the chain in some monohalogenated‐paraffin hydrocarbons and as a function of the number of carbon atoms separating halogen atoms attached to either end of dihalogenated‐paraffin hydrocarbons. The effects of the hybridization of the carbon atom have also been examined in some aliphatic hydrocarbons. Chlorine pure quadrupole resonance frequencies from chlorine atoms bonded to atoms other than carbon, such as silicon, nitrogen, and sulfur, have been measured, and the effects of these different atoms upon the Cl35 resonance frequencies are qualitatively discussed.
Inductive effects have also been examined in different groups of aromatic compounds. The inductive effect in several chlorobenzyl compounds is found to be about ¾ of what it is in the corresponding chlorobenzene compounds as determined from a comparison of the Cl35 resonance frequencies. Definite discrepancies have been observed between the Cl35spectra obtained from several aromatic compounds which have molecular structures similar to anthraquinone and the Cl35 frequencies that can be predicted from data obtained from chlorobenzene compounds and Hammett σ values.
Employing the linear relationship between Cl35 resonance frequency and Hammett σ values, several Cl35 frequencies were predicted and compared to the measured frequencies in some chlorobenzene compounds. Some unknown σ values have also been predicted. A linear relationship between Br81 resonance frequencies and Hammett σ values has been developed from measured bromine quadrupole frequencies. Several halogen frequencies from some unrelated compounds have been measured and are tabulated in this paper.
Comparison of the Effects of High Pressure and Low Temperature on the Absorption Spectra of Some Condensed‐Ring Aromatics33(1960); http://dx.doi.org/10.1063/1.1731150View Description Hide Description
A comparison of the spectral shifts obtained by lowering the temperature of a solution to those obtained by increasing its hydrostaticpressure shows that the temperature shift is composed of two oppositely directed components. The larger one is the red shift due to solvent density increase with temperature decrease and the accompanying increase in dispersion forces. The second and usually smaller effect is a blue shift that results from a change in the shape of the band as a result of a decrease in the population of the higher vibrational levels with a decrease in temperature.
33(1960); http://dx.doi.org/10.1063/1.1731151View Description Hide Description
Measurements of viscosity and electric conductivity in liquid zinc chloride indicate that at temperatures near the melting point, the melt is associated. The degree of association diminishes rapidly with increasing temperature as shown by the decreasing energies of activation for both viscous flow and conduction. Liquid ZnCl2 is thus not a normal fused salt such as CdCl2 or MgCl2. From the crystal structure and Raman absorption spectra, a mechanism of fusion and the structure of the melt are postulated. The ease of glass formation is discussed in terms of the liquid structure.
33(1960); http://dx.doi.org/10.1063/1.1731152View Description Hide Description
By two methods, a linearization and a variational principle, the Born‐Green‐Kirkwood equation for the radial distribution function is solved approximately and the osmotic pressure of chain polymer solutions computed at arbitrary concentration. The gaussian intermolecular potential energy of Flory and Krigbaum is used, and this restricts the range of validity of the theory to volume fractions less than one‐tenth. It is shown how the distribution of polymer molecules in the solvent becomes random as the concentration is increased. For good solvents, the quantity [(P/c 2)—RT/Mc], where P is the osmotic pressure and M the molecular weight, is predicted to increase rapidly with concentration c, and then to level off rapidly, the whole effect being accomplished at quite low concentrations as the molecules are forced to overlap. Some experimental corroboration is displayed. Severe doubt is cast on the practicality of the virial expansion of P, and possibly on the validity, beyond quite low concentrations.
33(1960); http://dx.doi.org/10.1063/1.1731153View Description Hide Description
The T→S and S→S′ spectra of pyrazine and 2,5‐dimethylpyrazine in hydrocarbon and EPA glasses has been measured. The S→S′ and S→T spectra of the same compounds in ethanol and isopentane are also reported. When due correction is made for the effect of the rigid media, solvent shifts (from hydrocarbon to EPA) of 60 cm—1 to the red in emission and the same amount to the blue in absorption are obtained for the 0–0 band. The absorption maximum is shifted by approximately 1200 cm—1 to the blue and the emission maximum by about 600 cm—1 to the red. The data is explained in terms of the weak hydrogen bonding and the Franck‐Condon strain resulting therefrom. It is suggested that due to the change in the extension of the n orbitals in nitrogen atoms of N heterocyclics, a Franck‐Condon destabilization energy results in protonic solvents. The role of the Franck‐Condon principle in the n→π*blue shift phenomenon is found to be of considerable importance in accordance with Pimentel's views. The previously reported discrepancy of 500 cm—1 in the 0–0 bands of the T→S emission and S→T absorption of these compounds is entirely explained by media effects.
Heat Capacity of Uranium Tetrafluoride from 1.3° to 20°K and the Thermodynamic Functions to 300°K. Calorimeter for the Range 0.8° to 20°K33(1960); http://dx.doi.org/10.1063/1.1731154View Description Hide Description
The heat capacity of uranium tetrafluoride has been determined from 1.3° to 20°K in an isothermal calorimeter with an integral gas thermometer and vapor‐pressure bulb for calibration of a carbon resistance thermometer. The enthalpy,entropy, and free‐energy functions were evaluated from these data and previous measurements at higher temperatures. At 298.15°K, the values of S°, (H°–H 0°)/T, and — (F°–H 0°)/T are 36.25±0.04, 18.08±0.02, and 18.17±0.02 cal mole—1 deg—1 for uranium tetrafluoride. A Schottky‐type anomaly occurs in the heat capacity at 6.4°K, presumably as a consequence of ligand‐field splitting of the electronic energy levels.
Paramagnetic‐Resonance Studies of Irradiated High‐Density Polyethylene. I. Radical Species and the Effect of Environment on Their Behavior33(1960); http://dx.doi.org/10.1063/1.1731155View Description Hide Description
Linear polyethylene (Marlex‐50) was irradiated at different temperatures with 800‐kv (peak) electrons. It was examined for paramagnetic resonance at +25° and —196°C to determine the radical species and their postirradiation behavior as well as that of the crystalline trapping medium. At low doses the spectrum is composed of two radical species which decay at different rates at room temperature. The predominant radical decays to zero in about five days; its six‐line hyperfine structure is attributed to –CH2–CH–CH2–. The fast decay supports a previous suggestion that the polymer radicals are formed in pairs on adjacent chains. The other radical has a basic five‐line spectrum with additional ``very fine'' structure. It lasts for months at room temperature. The behavior of the ``very fine'' structure on cooling to liquid‐nitrogen (LN) temperature and the initial low concentration of the radical suggest its probable structure to be . The relative numbers of each radical trapped at room temperature depend on the rigidity of the crystal and, therefore, on temperature during irradiation. The six‐line radical pairs exist as several groups decaying at different rates at room temperature. The half‐life of the fastest decaying group was 10 sec, that of the slowest, 25 hr. The fastest group comprises pairs in which the two radicals are formed nearly opposite each other on adjacent chains. They cause spin‐spin line broadening in the time‐zero LN spectrum. The decay rate of the radical pair is determined by the rigidity of the crystal. An apparent transition point for the crystal exists at —70°C, below which there is only a slight decay of the closest‐spaced radicals. The total number of radicals produced and trapped by 40 megaroentgens at LN temperature was 6.2×1019/g which corresponded to a G(total radicals) = 3.0.
Paramagnetic‐Resonance Studies of Irradiated High‐Density Polyethylene. II. Effect of Irradiation Dose on the Radical Species Trapped at Room Temperature33(1960); http://dx.doi.org/10.1063/1.1731156View Description Hide Description
The previous paper presented a study of the radical species in irradiated Marlex‐50 at low dose levels. This paper extends that study to a level of 4000 megaroentgens. The kind and relative number of each radical trapped at room temperature (RT) depends on the degree and tightness of the crystalline and crosslinked fractions during irradiation. At least two of three distinct species, having different hyperfine structures (six‐, five‐, and a single‐line) are present in varying concentrations at all doses. The six‐ and five‐line radicals are trapped in the crystal, whereas the single‐line radical is trapped in the highly crosslinked medium. During irradiation at RT and liquid‐nitrogen (LN) temperature, the crystal is not as effective in trapping the six‐line radical as in the absence of irradiation. At 640 megaroentgens the six‐line radical does not survive during irradiation at RT, leaving the five‐ and single‐line radicals above this level. The single‐line radical appears at 320 megaroentgens and increases until at 3000 megaroentgens, where crystallinity is zero, it accounts for about 70% of the total.
Heating the irradiated samples causes all radicals to disappear; the ``extinction temperatures'' for the six‐, five‐, and single‐line radicals were 90°, 135°, and about 250°C, respectively. The relative effectiveness of the preirradiated annealed samples compared to the nonirradiated Marlex‐50 in trapping radicals at RT was 0.5 for the 20‐megaroentgen, 1.0 for the 320‐megaroentgen, and 1.4 for the 4000‐megaroentgen preirradiated material. There is evidence in the uv spectrum for conjugated double bonds in the highly irradiated samples. It is proposed that the single‐line radical is initially formed adjacent to the conjugated sequence and then becomes trapped within the sequence by resonance. The radical could be represented as.
33(1960); http://dx.doi.org/10.1063/1.1731157View Description Hide Description
In earlier experiments, we have shown that it is possible to relate sparking potentials of saturated hydrocarbon gases to certain molecular properties. From measurements of electric breakdown in a series of these gases, it has been found that the effective molecular cross section for electron scattering is proportional only to the number of carbon‐hydrogen bonds in the molecule and is independent of their disposition. The lack of a contribution by the carbon‐carbon bonds has been attributed to a shielding effect.
In the present paper, we describe and discuss the results of a similar investigation of breakdown in unsaturated hydrocarbon gases. It was found that, for a series of olefin gases, the cross section associated with the carbon‐carbon double bond is greater than three times that of the carbon‐hydrogen bond, while that of the carbon‐carbon single bond is essentially zero as it was in the alkane series. An attempt is made to interpret this observation in terms of (1) a decrease in the shielding effect, and (2) the larger spatial configuration of the π‐electron orbitals associated with the ethylenic linkage. Variations in the position of the double bond within the molecule has little or no effect upon its contribution to the total cross section.
Breakdown measurements in butadiene‐1,3 and benzene indicate that conjugation results in an increase in the effective cross section of each double bond, as might be expected. Evidence of a small but measurable amount of double‐bond character was also found in cyclopropane from sparking potential measurements. This is in agreement with the predictions of other investigators.
33(1960); http://dx.doi.org/10.1063/1.1731158View Description Hide Description
The molecular structure of methane, ethane, ethylene, acetylene, ethyl fluoride, benzene, butadiene, allene, butatriene, propylene, cyclooctatetraene, methyl acetylene, diacetylene, methyl cyanide, methyl isocyanide, vinyl cyanide, carbon dioxide, formaldehyde, acetaldehyde, propynal, acrolein, formic acid, methyl formate, formamide, and acetyl cyanide (25 molecules) have been correlated by means of a set of empirical parameters, the physical meaning of which is discussed in part.
33(1960); http://dx.doi.org/10.1063/1.1731159View Description Hide Description
The order‐disorder theory of Hijmans and de Boer is adapted to a description of equilibrium between a gas and a phase forming a localized submonolayer on an energetically uniform surface. Isotherm equations are derived for adsorption in the absence of lateral interactions, and in the presence of nearest‐ and next‐nearest‐neighbor interactions. The Langmuir and Fowler‐Guggenheim equations result as special cases of the present treatment. The general theory is then applied to adsorption processes on sites in hexagonal configurations. A discussion of the resulting isotherm equations is presented.
33(1960); http://dx.doi.org/10.1063/1.1731160View Description Hide Description
The rotational analysis of the n+4, 3 band of the ``Y'' system of N2 shows that the initial state is a 3Σ u — level with B n+4 = 1.3325. The band has exactly the structure to be expected from a 3Σ u —→3II g transition and all expected 27 branches have been observed. The triplet separation of the 3Σ state degenerates into a doublet for all but the lowest values of K as the two states with J = K±1 nearly coincide.
33(1960); http://dx.doi.org/10.1063/1.1731161View Description Hide Description
An investigation of the vibrational spectra of IrF6 has failed to reveal the anomalies found for OsF6 that were attributed to a Jahn‐Teller coupling. This is taken to indicate that the Γ8ground electronic state of IrF6 has a strong spin character. For the vapor in the NaCl range the observed absorption frequencies (cm—1) and their assignments were: 720 (σ3), 852 (σ2+σ6), 921 (σ2+σ4), 979 (σ1+σ4), 1364 (σ2+σ3), and 1425 (σ1+σ3). A Raman shift of 651 cm—1 ascribed to σ2 was obtained for a solution of IrF6 in n‐C7F16.
33(1960); http://dx.doi.org/10.1063/1.1731162View Description Hide Description
The dissociation of a simple model of a linear four‐atomic molecule is treated classically by considering the motion of configuration points in the configuration space of the molecule. The usual configurational criterion for dissociation, i.e., the crossing of a critical surface in configuration space, is used. The specific problem studied here is the effect of the recrossing of a critical surface by a configuration point corresponding to the ``healing'' of a ``dissociated'' bond. It is shown that, for the model considered here, the above effect results in a greater probability of breaking of the exterior bonds as compared to the interior one.
33(1960); http://dx.doi.org/10.1063/1.1731163View Description Hide Description
Ehrenfest equations for the constant‐volume phase transitions from the mixed liquid‐vapor or liquid‐solid system to pure liquid or vapor have been derived and applied in the case of He4. Such processes serve as a model of second‐order phase transitions. The reasonably good agreement found indicates that these equations may be used to check experimental data at the boundaries of two‐phase regions and to determine unknown quantities entering into them.
33(1960); http://dx.doi.org/10.1063/1.1731164View Description Hide Description
Urey‐Bradley force constants have been fitted by least squares to the vibrational frequencies of CH3F, CH3Cl, CH3Br, CH3I, and their fully deuterated isotopes. Both observed and zeroth‐order frequency data have been used and the corresponding sets of force constants have been compared.