Volume 49, Issue 8, 15 October 1968

Solubility and Diffusion of Hydrogen and Deuterium in Platinum
View Description Hide DescriptionThe diffusion and solubility of hydrogen and deuterium in monocrystalline platinum have been studied by a permeation method. The diffusion coefficient of hydrogen is , and the solubility in atom fraction H/Pt is given by . The isotope effects in permeation and diffusion are analyzed in terms of an earlier theory. An Appendix discusses quantitatively errors due to absorption of gas by the walls of the apparatus in this type of experiment.

Collision Broadening of Rotational Absorption Lines. III. Broadening by Linear Molecules and Inert Gases and the Determination of Molecular Quadrupole Moments
View Description Hide DescriptionA recently developed theory of the pressure broadening of microwave absorption lines resulting from transfer of rotational energy in molecular collisions has been applied to calculations of the linewidth of rotational absorption lines of a number of linear and symmetric‐top molecules broadened by collisions with linear molecules and inert‐gas atoms. In such cases, shorter‐range forces such as dipole–quadrupole, quadrupole–dipole, quadrupole–quadrupole, and dispersion interactions are important as well as dipole–dipole interaction. In general, the agreement between the theoretical calculations and previously reported measurements is quite satisfactory. The application of the experimental technique as a method for determining molecular electric quadrupole moments is analyzed, and values for the molecular quadrupole moments of OCS, N_{2}O, NO, CO_{2}, N_{2}, and H_{2} are obtained from earlier data.

Vibrational Assignment of Carbazole from Infrared, Raman, and Fluorescence Spectra
View Description Hide DescriptionThe infrared, Raman, and fluorescence spectra of carbazole are reported with as complete polarization information as possible. An experimental assignment of fundamentals is given and is reliable only for species, being incomplete or uncertain for the other symmetry species. Some lattice modes of the carbazole crystal were found both in the infrared and Raman spectra, and a partial assignment made. A crude normal‐coordinate calculation was made using a force field transferred from phenanthrene for the in‐plane problem and from benzene and anthracene for the out‐of‐plane problem. The observed and calculated frequencies are compared, and good agreement is found for the fundamentals.

Absorption Spectrum of Carbazole in a Fluorene Matrix
View Description Hide DescriptionThe polarized absorptionspectrum of carbazole in a single‐crystal matrix of fluorene at about 15°K is reported. Only the lowest‐energy transition of carbazole was studied, transitions to more highly excited states being obscured by the absorption bands of the matrix. The low‐energy transition of carbazole was assigned in agreement with earlier theoretical work. A vibrational analysis of the excited state is reported, and the assigned fundamentals are compared with those of the ground electronic state.

Structural Studies of Polyesters. II. Far‐Infrared Spectra of Aliphatic Polyesters: Comparison with α‐Polyamides
View Description Hide DescriptionPolarized far‐infrared spectra of aliphatic polyesters [–(CH_{2})_{ z }–CO–O–O]_{ n } with (, nonpolarized) and α‐polyamide (nylon 6 and its N‐deuteroderivative) have been measured in the region up to 80 cm^{−1}. All these polymers have essentially planar zigzag conformations. The normal vibrations of these polymers were calculated for the far‐infrared regions by using the Urey–Bradley force field with some modifications. For the series of polyesters, several far‐infrared bands were found to appear systematically at nearly the same positions with similar intensities. The similarities between these series of bands of the polyesters and those of polyamides were interpreted from the point of view of the normal modes of vibrations.

Low‐Temperature Thermal Properties of Calcium Tungstate
View Description Hide DescriptionThe heat capacity of a single crystal of CaWO_{4} was determined by adiabatic calorimetry from 5° to 350°K and found to be without transitions or thermal anomalies. Deviation of the curve from normal sigmate shape is shown to be due to internal vibrations of the WO_{4} ^{=} ions. Apparent Debye 's for the lattice‐only heat capacity and for that of the acoustical spectrum show “normal” deviation from simple Debye theory. Values of the heat capacity, entropy, enthalpy function , and Gibbs function at 298.15°K are 27.28, 30.21, 16.02, and −14.19, in calories per gram formula mass·degree Kelvin.

Perturbation Theory and the Equation of State of Mixtures of Hard Spheres
View Description Hide DescriptionThe equation of state of a mixture of hard spheres of diameter and is evaluated by expanding the free energy of the mixture to second order in powers of the differences , where and is the diameter of the unperturbed hard spheres. The parameter is chosen to make the sum of the first‐order terms zero. The second‐order terms are evaluated using the superposition approximation, and the equation of state is determined by analytic differentiation. The agreement of this perturbation calculation with quasiexperimental Monte Carlo and molecular dynamics results is excellent, even for quite large values of , but becomes less satisfactory as becomes very large.

ESR Linewidths in Solution. V. Studies of Spin–Rotational Effects Not Described by Rotational Diffusion Theory
View Description Hide DescriptionWe have measured the ESRlinewidths of ClO_{2} as a function of temperature in a number of solvents. The dominant spin relaxation mechanism is the motional modulation of the spin–rotational interaction; therefore, the measurements yield the autocorrelation times for angular momentum. The experimental data can be correlated with the aid of the relation where is the autocorrelation time for the component of angular momentum along the αth molecular axis is the moment of inertia about the αth axis, is the coefficient of viscosity for the solvent, is a translational hydrodynamic radius which is determined experimentally by means of diffusion experiments, is the frequency of precession of the αth component of angular momentum, a frequency which vanishes for spherical tops and linear molecules and can be calculated entirely in terms of known components of the moment of inertia, and is an adjustable parameter which is assumed to be independent of temperature and viscosity but dependent upon solvent. There are three such equations for the three correlation times , and they can be combined with linewidth formulas to yield the ESRlinewidth as a function of , and . The linewidth‐versus‐(T / η) curves can then be fitted by adjusting the value of the single parameter for each solvent. The parameter is a measure of the anisotropy of the intermolecular potentials; it approaches unity for very anisotropicinteractions and zero for hard‐sphere interactions. A derivation of the equation above is given along with an analysis of the relation between and the intermolecular potential. Various corrections to the results are presented together with a critique of the present theory and a comparison with other work.

Double Perturbation Theory Applied to Frequency‐Dependent Polarizabilities. I
View Description Hide DescriptionThe work of Tuan et al. is extended to the calculation of second‐order frequency‐dependent properties. Under certain circumstances, our previous method of calculating dispersion interactions can be simplified to the point where the two‐electron equations may be solved by inspection. The simplified method is applied to a model system previously used to study the effect of intra‐atomic correlation, and the results of the method are compared with those of an exact calculation and those of coupled time‐dependent Hartree–Fock theory.

Double Perturbation Theory Applied to Frequency‐Dependent Polarizabilities. II
View Description Hide DescriptionTwo theorems are presented which increase the scope of double perturbation theory. First, an interchange theorem is found for polarizabilities at complex‐valued frequencies. Second, a form of double perturbation theory is developed which does not assume the existence of an unperturbed Hamiltonian relating the unperturbed and perturbed wavefunctions.

Vibration–Translational Energy Transfer According to the Morse Potential
View Description Hide DescriptionA quantum‐mechanical analysis of molecular vibration–translational motion energy transfer is obtained using the Morse potential, a one‐dimensional model, and the method of distorted waves. All wavefunctions and transition matrix elements are obtained in closed form. In the limit of high temperatures, the results are identical to the Landau–Teller expression. At low temperatures, resonances are found to result from the attractive part of the molecular interaction which can lead to transition probabilities that increase with decreasing temperature. The theory is compared with experimental data for the deactivation of O_{2} by various collision partners. The agreement is excellent, though some uncertainty in the interaction well depths is found due to a lack of very low‐temperature data. A comparison with the results of classical and semiclassical theories is given.

Collision‐Induced Dissociation of Low‐Kinetic‐Energy Ions
View Description Hide DescriptionDissociativereactions of H_{2} ^{+}, O_{2} ^{+} and NO^{+} molecule–ions with various atoms and molecules have been measured for reactant ions having kinetic energies less than 50 eV. Initial velocity components of the reactant ions in these experiments are axial to the slit system of the analyzingmass spectrometer which serves to discriminate against charged reactants but allows for effective collection of the slow reaction products. The cross sections for the production of low‐kinetic energy H^{+}, N^{+}, and O^{+} ions range from 0.01 to 1.0 Å^{2} near threshold. Reasonably sharp kinetic‐energy thresholds for atomic ion formation measured in these experiments approximate known molecule–ion dissociation energies.

Vibrational Spectra and Structure of Organogermanes. IV. Normal Vibrations and Free Rotation in Phenylgermane
View Description Hide DescriptionThe infrared spectra of liquid phenylgermane, phenylgermane‐d _{3}, phenylgermane‐d _{5}, and phenylgermane‐d _{8} have been recorded from 4000–33 cm^{−1}. The Raman spectra of the liquids have also been recorded and depolarization values have been measured. The vapor‐phase spectra show that the germyl group is freely rotating for these molecules. Thus, the local symmetry of the phenyl ring is and the vibrations have been assigned according to this symmetry. The effective symmetry of the GeH_{3} and GeD_{3} groups is essentially . All spectra have been interpreted in detail, and the 39 fundamental vibrations have been assigned based on previous assignments of benzene and its isotopic derivatives, depolarization ratios, and vapor‐phase infrared band contours. The assignments are shown to be consistent by means of the Teller–Redlich product rule and by application of the sum rule. The free rotation of the germyl group shows that the sixfold barrier to internal rotation around the C–Ge bond is negligibly small.

Spin State of Divalent Iron. I. Magnetic Properties of Phthalocyanine Iron (II)
View Description Hide DescriptionThe magnetic properties of phthalocyanine iron (II) have been investigated in the temperature ranges 1.25°–20°K and 100°–300°K. Between 100° and 300°K the magnetic susceptibility obeys the Curie–Weiss law accurately, but the measured value of μ_{eff} at 25°C is , which is intermediate between the theoretical spin‐only values for and states. However, in the range 1.25°–20°K the susceptibility is virtually independent of temperature, and this result has been used to show that the ground state of the central iron atom is an orbital singlet, with a real spin triplet state. This is split by second‐order spin–orbit coupling into a singlet ground state and a doublet state at 70 cm^{−1}, to give .

Spin State of Divalent Iron. II. A Mössbauer‐Effect Study of Phthalocyanine Iron (II)
View Description Hide DescriptionMeasurements of the ^{57}Fe Mössbauer spectrum of phthalocyanine iron(II) made at 4.2° and 100°K, with the sample in applied magnetic fields of 30 kOe, show that the electric field gradient at the iron nucleus is of positive sign and that there is no large asymmetry in the electric‐field‐gradient tensor. The major axis of the field‐gradient tensor does not appear to be colinear with the magnetic symmetry axis, indicating that there is no orbital degeneracy in the molecule. The hyperfine field at the iron nucleus, measured in the plane of maximum magnetization, is estimated to be + 270 kOe.

^{14}N Nuclear Quadrupole Resonance in Substituted Pyridines
View Description Hide DescriptionNitrogen‐14 nuclear quadrupole resonance has been observed in 15 substituted pyridines, including cyano, acetyl, and chloro derivatives and the methyl esters of the pyridine monocarboxylic acids. The substituents produce variations of 5%–10% in the field gradient at the nitrogen. The and charge densities at the ring nitrogen are discussed in terms of the relative electrophilic properties of the substituents and excellent qualitative agreement with the classical ideas of chemistry is obtained. Correlation of the nitrogen NQR data with the Hammett values and with chlorine‐35 NQR results is also considered. The charge distribution of the cyano group is analyzed and discussed in connection with the ring nitrogen. The ionic character of the cyano C–N bond is found to be approximately 17%.

Magnetic‐Rotation Spectra of the 1–0 Vibration–Rotation Band of Nitric Oxide
View Description Hide DescriptionMagnetic‐rotation spectra of the 1–0 band of ^{14}N^{16}O and ^{15}N^{16}O as a function of pressure, path length, and field intensity have been obtained. A phenomenological theory of magnetic‐rotation spectra applicable to this case is outlined. Computer predictions made on the basis of this theory, including the effects of finite resolution, explain the major features of the observed magnetic‐rotation signals. These features include the doublet structure of the lines at high pressure and the intensity contour of the 2 subband.

Millimeter‐Wave Rotational Spectrum of HSSH and DSSD. I. Branches
View Description Hide DescriptionThe Q‐branch rotational lines of H_{2}S_{2} have been measured in the frequency range 80–200 Gc/sec, those of D_{2}S_{2}, in the range from 60 to 220 Gc/sec. For HSSH, measurements were made on the torsional vibrational state, and the S–S bond‐stretching vibrational state as well as on the ground state. The molecules are the most nearly accidentally symmetric tops of any so far reported. Wang's asymmetry parameter for the ground vibrational state of H^{32}S^{32}SH is found to have the value ; for H^{32}S^{34}SH, ; for D^{32}S^{32}SD, . The asymmetry increases markedly with the torsional oscillation: for H^{32}S^{32}SH when ; it decreases with the S–S stretching: for H^{32}S^{32}SH when . The molecule is found to have the nonplanar chain structure HSSH, with the structural parameters having the values: , and the dihedral angle . The barrier to relative internal rotation of the two SH groups is evidently very high, much higher than in H_{2}O_{2}. The internal rotational splitting of the ground vibrational state is too small to be resolved. In the torsional vibrational state it was found to be . The near orthogonality of the bond angles, the S–S length, and the high barrier to internal rotation indicate significant bonding through the mechanism of hyperconjugation.

Atomic Binding of Transition Metals on Clean Single‐Crystal Tungsten Surfaces
View Description Hide DescriptionThe binding energy of single atoms of the Period‐6 transition elements on atomically perfect single‐crystal planes of tungsten was measured by utilizing low‐temperature‐pulse field desorption, in a ultrahighvacuum field‐ion microscope. For any given adatom, the dependence of the binding energy on surfacecrystallography was observed to be inconsistent with a pairwise interaction model. A new model incorporating a surface‐charge redistribution into a pairwise potential is shown to be consistent with the data. The variation in binding energy with electronic configuration of the adatom is interpreted in terms of an electron‐energy band model. The binding energy depends upon the electron occupancy of two subbands assumed to exist in the levels of the atom, when it is adsorbed on the surface. Finally, the abnormal field‐desorption properties of adatoms on the (110) plane are discussed in terms of its anomalous work function.

Electrical Transport Processes in Beryllium Oxide
View Description Hide DescriptionThe electrical resistivity was determined for polycrystalline and single‐crystal BeO between 1200°–1700°C. Analysis was made of the effects of oxygen partial pressure, aliovalent impurities, and microstructure. Conductivity and relevant diffusion coefficients were calculated with these data. The results show the BeO samples to be impurity‐controlled ionic conductors, and establish the need for higher‐purity material to study intrinsic properties. Electrical migration is independent of grain boundaries and crystallographic direction. Creation of cation defects by varying the oxygen activity in the specimens is not an important process in this material. At high temperatures, above a critical roll‐over temperature determined by the impurity content, electrical transport processes occur by a vacancy mechanism with an activation energy of 65 ± 5 kcal/mole. At lower temperatures, the electrical transport process is more complex and no simple theory is applicable. It is suggested that precipitation of impurities may be a more important process than the association of vacancy–impurity complexes in this system. The activation energy for this process depends inversely on the amount of aliovalent impurities present in the sample, and has a value of 73 kcal/mole at the lowest concentration studied.