bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-Spin Interactions in Nuclear Magnetic Resonance. Contact Contribution
Authors: Alexander S.
Published: January 2005

A method for calculating the contact contribution to spin-spin interactions between nuclei in nonaromatic molecules is described. The method is based on the valence bond model. The equivalent Hamiltonian of the Dirac vector model is used for a perturbation calculation in a representation where the total spin of the two electrons in each bond in the molecule is a good quantum number. The Ramsey-Purcell contact term in the interaction is calculated by a double perturbation method where only terms linear in the electron-nuclear interactions are considered but the perturbation is carried to higher order in the exchange integrals. In this way the interaction constants can be obtained explicitly in terms of the exchange integrals, and the calculation of the valence bond wave functions is avoided. It is then possible to see how the signs and magnitudes of the interaction constants depend on these integrals and what the dominant interaction mechanisms are. The perturbation series is evaluated explicitly with the electron nuclear contact interaction and the results are compared with the results of a similar calculation based on Ramsey's closure formula. In this way the objections against the closure procedure can be avoided. It is shown that Ramsey's formula can be used when different average energy separations are used for terms of different order in the expansion. The results of Ramsey for H2 and of Karplus et al. for hydrogen atoms separated by two and three bonds and the justification of the method of calculation used by them are discussed in detail. It is found that only perturbation terms of one type are important in each of the cases discussed by these authors and therefore their procedure can be justified. The results previously obtained by the author for spin-spin interactions in the allyl group are also discussed.
Moment Analysis of Magnetic Resonance Signals
Authors: Verdier Peter H. , Whipple E. B. , Schomaker Verner
Published: January 2005

A relation is given between the moments of a generalized convolution transform of a function, and the moments of the function itself. This relation is applied to the signal obtained with a field-modulated EPR spectrometer, a consequence being that the integrated intensity of an absorption line may be obtained from first moment measurements at any modulation amplitude, regardless of line shape or various instrumental nonidealities. This result has been verified experimentally to within a few percent with a Varian EPR spectrometer. Extension to measurement of higher moments is discussed.
Spin-Orbit Coupling in Orbitally Degenerate States of Aromatic Ions
Authors: McConnell Harden M.
Published: January 2005

It is shown that in the orbitally degenerate ground state of the benzene negative ion there is a first-order electron spin-orbit interaction associated with the electronic orbital motion around the ring. This first-order interaction may be as large as a few cm—1 and can give rise to enhanced electron spin-lattice relaxation in solution even though most of the time the electronic orbital motion is strongly quenched by electrostatic interaction with the solvent.
Effect of Pressure on the Spectra of Rare Earth Ions in Crystals
Authors: Keating K. B. , Drickamer H. G.
Published: January 2005

The effect of pressure to 180 000 atm has been measured on the absorption spectra of crystalline rare earth ions. The effects observed include:

(1) An increase of intensity due to increased mixing of 5d and 4f orbitals in the excited state due to an increase of the mixing potential with decreased interionic distance.

(2) Small shifts accompanied by increases in half-width. Except for the shifts of 3P0, 3P1, and 3P2 levels of Pr+3, these can be accounted for by an increase in the splitting of the individual levels due to intensification of the crystal field.

(3) Changes in shape of several of the bands, possibly due to changes in occupation of the various states which make up the bands.
Limit of Stability of Crystalline Helium
Authors: Radford Loren E.
Published: January 2005

The mobility of a vacancy in a crystal at the absolute zero of temperature is investigated. In this minimum energy configuration movement of the vacancy to an adjacent lattice site occurs by tunneling, the rate being determined by an approximation in which the barrier and adjacent potential wells are formed by nearest neighbor interactions only. There is found a critical volume at which the vacancy begins to move rapidly through the barrier. Identifying this increased mobility with the beginning of the melt, a criterion for stability of the crystalline structure is deduced. On applying this criterion to helium at the absolute zero, general agreement with experimental critical volumes is obtained.
Paramagnetism of Uranyl Ion. Effect of 6d Orbitals and Pi Bonding
Authors: Belford R. Linn
Published: January 2005

Second-order perturbation calculations of the paramagnetism of OUO++ ion were done. The contribution from pi bonds may be considerable. Although a bonding scheme utilizing only the 6d and 7s orbitals of U could account for experimental values, some involvement of 5f orbitals is suggested. There is no clear-cut evidence for strong involvement of 5f orbitals in bonds.
Low-Temperature Chemisorption. II. Flash Desorption of Carbon Monoxide
Authors: Ehrlich Gert
Published: January 2005

Flash desorption studies of the interaction of carbon monoxide with a tungsten surface indicate that this gas forms at an initial rate considerably higher than that for nitrogen (CO sticking coefficient: s∼0.5; N2 sticking coefficient: s∼0.25). This rate also remains independent of the amount adsorbed for higher coverages, up to n∼300×1012 molecules cm—2. Unlike nitrogen, CO does not dissociate on the surface. It retains its molecular identity in both the primary chemisorbed state β, and the weaker state of 20 kcal mole—1 binding energy α, which forms as the rate of β growth diminishes. At T=298°K, the α state reaches a concentration of ∼200×1012 molecules cm—2. No additional weak binding is found even at low temperatures, T∼115°K. The β state is itself made up of three subpeaks, arising from different surface structures, and designated β1, β2, and β3 in order of increasing binding energy. Only β2 and β3 form initially, with desorption energies of 75 and 100 kcal mole—1, respectively; β1 appears at higher coverages, at which the desorption energy of β2 has also diminished.
Molecular Statistics of Vinyl Polymers
Authors: Suzuki Yasutaka
Published: January 2005

A formula is proposed to describe the end-to-end distance and the total dipole moment of the vinyl polymer (CH2CHX)n. The interaction of neighboring X's is taken into account. The formula treats the general atactic polymer and includes the isotactic polymer and the syndiotactic polymer as special cases.
Vacuum Ultraviolet Absorption Spectrum and Dipole Moment of Nitrogen Trifluoride
Authors: La Paglia S. R. , Duncan A. B. F.
Published: January 2005

The electronic absorption spectrum of NF3 was investigated for the first time. At the lowest pressures, the long wavelength limit of absorption is at about 960 A in agreement with the lowest ionization potential of the molecule (939 A). Quantitative intensity measurements showed a smooth decrease of the absorption coefficients to effectively zero at about 1800 A, with no indication of even partly resolved electronic transitions. Comparisons with the electronic spectrum of ammonia are discussed. The molecular dipole moment is used to obtain an equivalent orbital representation of the NF3 wave function.
Infrared Spectroscopic Evidence for the Rotation of the Ammonia Molecule in Solid Argon and Nitrogen
Authors: Milligan Dolphus E. , Hexter Robert M. , Dressler Kurt
Published: January 2005

High-resolution infrared spectra (of the symmetric bending mode) of ammonia suspended at high dilution in solid argon and nitrogen have been obtained. More than a half dozen extremely sharp bands have been observed in the 950–1040 cm—1 region (in the spectrum of ammonia) in these materials under conditions where there should be little if any absorption due to polymeric species. The frequency separations of the bands, their temperature dependence, and their extreme sharpness appear to be compatible with a model in which the ammonia molecule executes quantized rotation in these solids.
Theory of the Two- and One-Dimensional Rigid Sphere Fluids
Authors: Helfand E. , Frisch H. L. , Lebowitz J. L.
Published: January 2005

The approximate theory of the three-dimensional hard sphere fluid developed by Reiss, Frisch, and Lebowitz has given astonishingly good predictions with little labor. In an attempt to investigate the reason for this result we adduce, in this paper, further evidence for the internal consistency of the approximations of this theory. Thus it is noted that the same equation of state of hard sphere fluid is obtained when one used the ``integral condition'' as when the ``infinity condition'' is used. We have then applied the theory to study the thermodynamic properties, in particular the equation of state, of the rigid sphere fluid in two and one dimensions. The approximate equation of state of the two-dimensional rigid sphere fluid is in good agreement over the range of fluid densities with the results of the machine Monte Carlo calculations by Jacobson and Wood and dynamical machine calculations of Wainwright and Alder. The exact Tonks' equation of state of the one-dimensional rigid sphere fluid is derived in a particularly simple manner.
Quadrupole Relaxation Effects in Nuclear Magnetic Double Resonance
Authors: Baldeschwieler John D.
Published: January 2005

The effects of quadrupole relaxation on the relative linewidths of the double resonance spectrum of a molecule in the liquid state are described. Only the special case is considered for which the broadening of individual components by quadrupole relaxation is not great enough to lead to complete collapse of a spinmultiplet. It is assumed that line separation is large compared to linewidth. The calculations are illustrated for the ammonia molecule.
Studies in Molecular Structure. III. Populations Analyses for Selected First-Row Diatomic Molecules
Authors: Fraga Serafin , Ransil Bernard J.
Published: January 2005

Electronic population analyses for selected diatomic molecules of the first row of the periodic table are tabulated. The tentative value of population analyses in relation to accuracy of approximation is discussed briefly.
Electron Spin Relaxation in Metal—Ammonia Solutions
Authors: Pollak Victor L.
Published: January 2005

The pulsed magnetic resonance technique was employed to measure the electron spin relaxation times T1 and T2 in solutions of sodium and potassium in liquid ammonia. Measurements were carried out over a range of temperatures from —50°C to +30°C, and for the concentration range of 10—4 to 10—2 mole metal per mole NH3. It was found that T1 and T2 are equal at all measured concentrations and temperatures, these times ranging from 1 to 3 μsec. For dilute solutions, the data are shown to be quantitatively consistent with the assumption that the relaxation is owing to the contact hyperfine interaction of the electrons with the N14 nuclei of ammonia. This interaction is modulated by the relative motion of the electrons and the ammonia molecules, the spin relaxation time being proportional to the modulation rate, as is typical in cases of extreme motional narrowing. An electron tunneling mechanism is proposed as a possible source of the modulation. That the electron-nitrogen hyperfine interaction is largely responsible for the spin relaxation in dilute solutions is verified by measurements on a sample prepared from isotopically substituted ammonia (N15H3). A qualitative explanation of the variation of the electron spin relaxation time with concentration is proposed.
Transients in the Blue and Green Luminescence of ZnS:Cu:Cl Crystals
Authors: Halperin A. , Arbell H.
Published: January 2005

Upon exciting the investigated ZnS crystals by the light of two wavelengths, 0.37 and 0.33 μ, in succession, their blue luminescence at low temperatures was found to rise to a maximum Im from which it decayed to its normal steady value I∞. The green luminescence band showed a similar effect above 170°K. A reduction in the degree of filling of the ``blue'' traps was found to take place during the decay of the transients at low temperatures. Results are discussed using a previously proposed energy model.
Interpretation of the Appearance Potentials of Secondary Ions
Authors: Wallenstein M. B. , Krauss M.
Published: January 2005

The statistical theory of mass spectra assumes that the excitation energy in a molecule-ion is essentially equipartitioned prior to unimolecular decomposition. Some of the consequences of this assumption have been deduced and the results have been used in interpreting the observed appearance potentials of secondary and tertiary ions of neopentane, n-butane, and 1-butene. Although the results are not quantitative, it is evident that considerable vibrational energy is removed with the neutral fragment. The problem of the detailed interpretation of appearance potentials is complicated by the fluctuation of the vibrational energy distribution in the products of a decomposition from the most probable value, i.e., equipartition. Some general considerations with regard to determination of minimum-energy decomposition paths and the significance of this study in relation to the statistical theory of mass spectra are also presented.
Effect of Pressure on the Spectra of Five Nickel Complexes
Authors: Stephens D. R. , Drickamer H. G.
Published: January 2005

The effect of pressure to 150 kbars has been measured on the absorption spectra of five nickel complexes. The results are discussed in terms of the change of 10 Dq and of the Racah parameter B, with pressure. In general 10 Dq, the crystal field strength, increased with pressure, but the increase noted was not the same when calculated for the different peaks of a given complex. This discrepancy may be described in terms of changes of covalency as measured by changes of the Racah parameter B. In general B decreased with increasing pressure showing increased covalency at high pressure. There were some discrepancies in the value of B obtained from different transitions. These may be the result of experimental error, but may also be associated with distortions of the field, or with weaknesses in the assumption of point charges or dipoles.
Infrared Spectrum of Single Crystals of LiOH, LiOD, and LiOH·LiOD
Authors: Hexter R. M.
Published: January 2005

High-resolution infrared absorption spectra of single crystals of LiOD and of the solid solution LiOH·LiOD are reported. These are compared with each other and with the spectrum of monocrystalline LiOH. Comparisons with the spectra of Mg(OH)2 and Ca(OH)2 are also made. The differences in selection rules for the two types of hydroxides are discussed together with differences in spectra to be expected upon changing the mass of the cation and upon deuterium substitution. The discussion is in terms of the current theory of the spectra of such crystals. It is concluded that the complex spectrum of these minerals in the high-frequency region (2000–5000 cm—1) is entirely due to OH— (or OD—) ion motion. The motion is quite localized; the motions of the several OH— ions of the crystal are poorly coupled. Difficulties with previous assignments due to unusual temperature dependencies of intensities are also discussed. The restricted rotational character of the localized motion of the OH— ions, previously proposed, may be used to rationalize these difficulties and to qualitatively account for the existence and similarity of the spectra of all three materials. Finally, the ``rotational'' model accounts well for the frequency shifts consequent on deuteration.
Evidence of Multiple Trapping Sites for Excited Nitrogen Atoms in Solid Molecular Nitrogen
Authors: Hemstreet R. A. , Hamilton J. R.
Published: January 2005

A study of glow curves and thermal effects indicates that both ground state and excited nitrogen atoms are trapped in discharged nitrogen condensed at 4.2°K. At elevated temperatures the recombination of ground state atoms is apparently governed by a single activation energy. The excited atoms are found in two types of traps; one associated with the ordered and the other with the disordered regions in the matrix and each has a distribution of energies.
Proton Magnetic Resonance Studies of Structure, Diffusion, and Resonance Shifts in Titanium Hydride
Authors: Stalinski B. , Coogan C. K. , Gutowsky H. S.
Published: January 2005

Measurements of the proton magnetic resonance at ∼26.9 Mc in titanium hydride samples, ranging in composition from TiH1.61 to TiH1.97, have been made in the temperature range from —196° to about 200°C. The second moment of the proton resonance at the lower temperatures shows that the hydrogen atoms are randomly distributed among the lattice sites which are located tetrahedrally with respect to the titanium atoms. Self-diffusion of the hydrogen atoms narrows the proton resonance above room temperature. The temperature dependence of the correlation frequency for the proton motions, obtained from the linewidths, leads to diffusional activation energies which increase with hydrogen content from 9.4 kcal/g atom for TiH1.607 to 10.2 for TiH1.923. Moreover, the diffusion rate is directly proportional to the number of unfilled tetrahedral holes in the metallic lattice, which indicates that the self-diffusion takes place via a vacancy mechanism.

Proton resonance shifts to higher applied magnetic fields were observed. They were measured at room temperature for all specimens and were found to increase from 0.01% for TiH1.607 to about 0.032% for TiH1.969. For these two extreme compositions, the temperature dependence of the shift was measured between —95°C and 190°C and was found to be similar to the bulk susceptibility, the shifts for TiH1.969 exhibiting an anomaly at about 13°C as does the susceptibility. These results are interpreted semiquantitatively in terms of exchange interactions which pair spins of electrons in the conduction band with those of electrons localized on the hydrogen. The results suggest that the hydrogen is held in the lattice by a combination of covalent and ionic bonding, the latter involving a net positive charge on the hydrogen. The general importance of exchange interactions in intermetallic compounds is commented upon.
Theoretical Molecular Transition Probabilities. I. The V–N Transition in H2
Authors: Ehrenson S. , Phillipson P. E.
Published: January 2005

Theoretical investigation of the oscillator strength of the V–N transition in H2 has been carried out employing the alternative length, velocity, and acceleration operator methods in the calculations. By successive improvements in the approximate molecular wave functions assumed for the two states, convergence of the results obtained by the three methods toward a unique f value is demonstrated. The best wave functions employed yield an f value of 0.27 for the V–N transition in H2. Because in general the three methods weight different spatial portions of the wave functions in the dipole strength integrals, comparison of the alternative numerical f values is shown to provide some insight into the goodness, over-all and regional, of these wave functions. Agreement among the three values is also shown to be a more sensitive test of the goodness of the wave functions than are the usual energy criteria. All integrals necessary in these computations are shown to be expressible in terms of Cαβγδε functions which are to be found in the literature. A systematic scheme for computing the oscillator strengths of any Σ—Σ transition involving one and two quantum-number Slater orbitals in terms of these C functions is outlined.
Measurements of the Diffusion Coefficient of Atomic Nitrogen in Molecular Nitrogen and the Catalytic Efficiency of Silver and Copper Oxide Surfaces
Authors: Young Robert A.
Published: January 2005

By utilizing the first positive bands of nitrogen to monitor the decay of atomic nitrogen caused by diffusion to a catalytic surface, the diffusion coefficient of atomic nitrogen in molecular nitrogen has been investigated, leading to a probable value of 280/p cm2 sec—1. The catalytic efficiency γ of silver and copper oxide surfaces is found to be of the general form γ=a/(bp+c), where p is the molecular nitrogen pressure, b and c are constants for each surface, and a is a constant independent of the surface.
Infrared Spectra and Potential Constants of Some Monohaloacetylenes
Authors: Hunt G. R. , Wilson M. Kent
Published: January 2005

The infrared spectra of gaseous HC≡CF, HC≡CCl, and HC≡CBr and their deutero-compounds have been obtained under prism dispersion between 250 and 3500 cm—1. All five fundamental vibrations have been identified for each of the hydrogen compounds and all but the lower bending mode for each of the deuterated compounds. Potential constants and vibrational amplitudes have been calculated.
Trimethylene Oxide. II. Structure, Vibration-Rotation Interaction, and Origin of Potential Function for Ring-Puckering Motion
Authors: Chan Sunney I. , Zinn John , Gwinn William D.
Published: January 2005

In the previous paper of this series, the microwave spectra of four isotopic species of trimethylene oxide were investigated and the potential function for the puckering of the four-membered ring was determined. Further analysis of the data has now enabled the molecular structure to be calculated. The structural parameters deduced from the rotational constants are: r(C–C) = 1.549±0.003 A, r(C–O) = 1.449±0.002 A, r(Cα–Hα) = 1.091±0.002 A, r(Cβ–Hβ) = 1.100±0.003 A, ∠Cα–Cβ–Cα = 84°33′±1′, ∠Cα–O–Cα = 91°59′±7′, ∠Cβ–Cα–O = 91°44′±3′, ∠Hα–Cα–Hα = 110°18′±10′, ∠Hβ–Cβ–Hβ = 110°44′±3′. The alphamethylene planes are slightly deflected towards the oxygen atom away from the bisectors of the ∠Cβ–Cα–O's. However, the actual angle of deflection is rather uncertain. Using these structural parameters, models have been constructed to calculate the vibration-rotation interaction due to the ring-puckering vibration. The experimentally observed rotational constant variations were found to be very well reproduced if the out-of-plane bending motion is assumed to follow a curvilinear path without any stretching of the C–C and C–O bonds. The potential function determined in the previous paper is also interpreted in terms of force fields within the molecule.
Pi Bonding in Uranyl Ion
Authors: Belford R. Linn , Belford Geneva
Published: January 2005

Overlap integrals were calculated for possible primary bonds of uranyl ion. The 6d σ and π overlaps are about the same and so great that considerable bonding of σd and πd types is indicated. The 5f σ and π overlap integrals are about the same and quite small, but strong σf bonding cannot be ruled out.
Reflectance Spectra of Terbium Oxides in the Range Tb2O3 to Tb4O7
Authors: Vratny F.
Published: January 2005

The diffuse reflectance spectra of terbium oxides (TbOx) have been studied in the composition range 1.5≤x≤1.75 from 300 to 1500 mμ. An ultraviolet cutoff was observed at about 325 mμ. A general decrease in reflectance was observed for an increase in the oxygen to metal ratio. A band was also noted in the 380 to 400-mμ region.
Cubic-Field Splitting and Cubic-Symmetry Orthonormal Sets of Wave Functions for J Manifolds (J Half-Integer)
Authors: Pappalardo R.
Published: January 2005

Energy level splittings of manifolds characterized by half-integer values of J have been derived in the case of a cubic crystal potential containing fourth- and sixth-order terms. Orthonormal sets of wave functions in cubic symmetry are tabulated for the same manifolds.
Derivation of Interelectronic Screening Parameters from Statistical Considerations
Authors: Bauman Robert P. , Considine James P.
Published: January 2005

A model for helium and two-electron ions has been found in which assumptions similar to that of the Bohr model for the hydrogen atom lead to ionization energies and atomic radii in agreement with observed values and values calculated by the Hartree-Fock method, respectively. An effective screening potential is found by quasi-classical statistical arguments. The angular momentum of each electron is fixed at one unit and the two electrons constrained to move on the same sphere. The interelectronic distance is assumed to follow an exponential distribution expressed in terms of the Coulombic repulsion. When the distance between electrons is then fixed at its most probable value according to this distribution function, no adjustable parameters remain. The method can be extended to excited states.
Pressure Dependence of Fluorescence Spectra
Authors: Wilson David J. , Noble Barbara , Lee Betty
Published: January 2005

The pressure dependence of the fluorescence spectra of molecules in the gas phase is calculated for two models; one involving a strong collision mechanism for transferring vibrational energy, the other involving a stepwise collision mechanism. The fluorescence spectra of the two models show very marked differences at pressures between the low pressure region of resonance fluorescence and the high pressure limit.
Complex Cyclotron Resonance in Dilute Gases
Authors: Collins R. L.
Published: January 2005

An X-band electron spin resonance spectrometer has been used to analyze the products of an electrodeless discharge in flowing gases at low pressure. During a search for polyatomic free radical fragments, a multiple signal was found near g=2.0000. Three poorly resolved peaks were found for a variety of paraffins and olefins, while methane, ammonia, methylamine, and sulfur dioxide yielded doublets. The structure was best resolved at low pressure. The spacing of the peaks increased with ESR microwave power. Evidence is presented that the signal is caused by cyclotron resonance of photo-ionized electrons. It is suggested that this multiple resonance is more apparent than real, and arises from either a velocity-dependent capture process or from dephasing of electrons upon collision with gas molecules.
Expected Square of the Length of Isotactic Vinylic Hydrocarbon-Type Chains
Authors: Meyer Victor E. , Kinsinger Jack B. , Parker Paul M.
Published: January 2005

The mean square length of long isotactic vinylic hydrocarbon-type chains is calculated. The Markov chain formalism is employed for this calculation. The problem of excluded volume is not considered.
Quantum Mechanics of Mobile Electrons in Conjugated Bond Systems. V. Empirical Determination of Integrals between Carbon Atomic Orbitals from Experimental Data on Benzene
Authors: Ruedenberg Klaus , Layton E. Miller
Published: January 2005

It is shown that the experimental information given in the ultraviolet spectrum of benzene uniquely determines the two-center Coulomb integrals between the 2pπ atomic orbitals of carbon as a function of the internuclear distance. The calculations are carried out including all terms involving neighbor overlap. For the many-center electron-interaction integrals, the Mulliken approximation and the London approximation are both considered with little difference in the results. Some peculiar properties of the empirically determined distance dependence are compared with the theoretical behavior of two-center Coulomb integrals. The empirical values for the resonance integral and the Coulomb integral are also found. The investigation differs from similar work of Pariser by the inclusion of overlap effects.
Energies of Excited Electronic States as Calculated with the Zero Differential Overlap Approximation
Authors: Murrell J. N. , Salem L.
Published: January 2005

It is shown that electronic excitation energies, calculated using the zero differential overlap approximation, can always be expressed in terms of the difference between two-electron Coulombic integrals. These differences can then be used as empirical parameters for the calculation of excitation energies.
Potential Curves for Doubly Positive Diatomic Ions
Authors: Hurley A. C. , Maslen V. W.
Published: January 2005

An integral form of the quantum-mechanical virial theorem, applicable to ionic as well as neutral systems, is established. This theorem is used to derive an approximate expression for the potential curve for a doubly positive diatomic ion in terms of the corresponding curve for a related neutral molecule. The appearance potentials of a number of these ions are calculated and compared with values obtained from electron-impact measurements. Satisfactory agreement is found, but a crucial test of the theory is vitiated by uncertainties in the experimental value of either the appearance potential of the doubly charged ion or the dissociation energy of the corresponding neutral molecule. The accuracy of the approximations underlying the theory is estimated by a series of calculations on two-electron systems.
Effect of Pressure on the Resistance of Iodine and Selenium
Authors: Balchan A. S. , Drickamer H. G.
Published: January 2005

The effect of pressure from 60 to over 400 kbar has been measured on the resistance of selenium and iodine. Selenium exhibits a very rapid drop in resistance between 60 and 128 kbar; at 128 kbar it shows a discontinuous drop. At higher pressures its behavior is apparently metallic. Iodine shows a rapid drop in resistance from 60 kbar to the region of 225–255 kbar where there is relatively abrupt change of slope. At higher pressures the change in resistance with pressure is much smaller. It is interesting to note that the optical energy gap of selenium extrapolates to zero at about 130 kbar, while the optical gap for iodine extrapolates to zero at 240 kbar.
Theory of Solutions. III. Thermodynamics of Aggregation or Polymerization
Authors: Hill Terrell L.
Published: January 2005

Polymeric and colloidal systems are usually polydisperse, containing possibly hundreds or thousands or more, of subspecies differing only in degree of polymerization n. The required thermodynamic approach is that appropriate to a highly multicomponent system. Let P(n) be the fraction of polymer molecules of size n. The distribution function P(n) will depend on one or more parameters, for example, the mean n̄ and standard deviation σ in the case of a Gaussian distribution. The thermodynamic problem becomes tractable if we replace, as composition variables, the numbers of molecules of all the polymer subspecies by the total number of polymer molecules N and the parameters of P(n). The new set of variables may be only two, three, etc., in number. Our main interest in this paper is to investigate how the thermodynamic functions of the system change when the distribution function P(n) changes, as, for example, in a kinetic study in which P(n) evolves sufficiently slowly with time or in thermodynamic studies on different samples of the same polymer.
Entropy of Mixing of Interconvertible Species. Some Reflections on the Gibbs Paradox
Authors: Noyes Richard M.
Published: January 2005

Expressions are derived for the change of state when two separated but interconvertible species are allowed to mix and come to chemical equilibrium. These expressions are unaffected by the possible existence of an exchange process involving simultaneous interconversion of two molecules. The results emphasize that entropy concepts are intimately connected with the distinguishability of chemical species and that the original concern of Gibbs arose because distinguishability is usually employed as a discontinuous concept. The discontinuity could be removed in specific cases by recognizing the finite limits to distinguishability imposed by existing analytical procedures.
Analysis of the Absorption and Fluorescence Spectrum of NdCl3 Diluted with LaCl3
Authors: Wong Eugene Y.
Published: January 2005

The Stark splitting of the identified levels of Nd+3 in LaCl3 were calculated by first-order perturbation. Intermediate coupling wave functions and crystal-field interaction parameters reported by Judd were used. The calculated spectrum agrees with the spectrum observed by Carlson to 5 cm—1.
Crystallography of the Ru–B and Os–B Systems
Authors: Kempter C. P. , Fries R. J.
Published: January 2005

The Ru–B and Os–B systems were investigated by x-ray powder diffraction. In addition to Aronsson's hexagonal Ru7B3 phase, two new hexagonal Ru–B phases were found: RuB2(D6h1—P6/mmm, a0=2.852 A, c0=2.855 A) and Ru2B5(D6h4—P6/mmc, a0=2.89 A, c0=12.81 A. In the Os–B system, two new hexagonal phases, isomorphous with the latter Ru–B phases, were found: OsB2(a0=2.876 A, c0=2.871 A) and Os2B5 (a0=2.91 A, c0=12.91 A). RuB2 and OsB2 are isomorphous with MoB2; Ru2B5 and Os2B5 are isomorphous with W2B5.
Electrical Properties of Organic Solids. IV. Charge Carrier Diffusivity in Metal-Free Phthalocyanine
Authors: Kearns David R. , Calvin Melvin
Published: January 2005

The pulsed light technique has been applied to determine the charge carrier mobility in microcrystalline or amorphous, metal-free phthalocyanine layers. This appears to be of the order of 10—3 to 10—2 cm2 sec—1 v—1, and the positive holes are the majority carriers. The low values are attributed to the physical state of the layer.
Solid State Ionization Potentials of Some Aromatic Organic Compounds
Authors: Kearns David R. , Calvin Melvin
Published: January 2005

The ionization potentials of a number of solid aromatic organic compounds have been determined by photoelectric threshold measurements. These are compared with literature values of the gaseous ionization potentials and the solid-state surface values seem to be approximately 1¼ v smaller. The relation between the ionization potential of a molecule within a crystalline lattice and that in the surface of the lattice is described, and the significance of the bulk ionization for conductivity of organic molecular lattices is discussed.
Color Centers in ZnS Single Crystals
Authors: Halperin A. , Pinker R.
Published: January 2005

Absorption bands induced in ZnS crystals by uv (0.366 μ) are described. The two main absorption bands peaked at or below 0.6 μ and at 1.2 μ. Two weaker bands at 0.8 and 1.35 appear as shoulders of the main bands. Thermal and optical bleaching properties are also described, and the results are shortly discussed in light of a formerly proposed model.
Deviations from Thermal Equilibrium among Reactant Molecules
Authors: Widom B.
Published: January 2005

A model of a chemically reacting system is considered in which the reactant molecules are dilutely dispersed in an inert gas and reaction is the result of binary collisions between inert and reactant species. It is noted that during reaction the distribution of reactants over their internal states is not that characteristic of equilibrium. It is shown that if κ is the rate constant of the reaction and κeq the rate constant that would have characterized the reaction had the reactants been in equilibrium, then κ=κeq—τ̄( 〈q2〉—〈q〉2), where τ̄ is a mean relaxation time, q is the reaction probability per unit time from a particular reactant state, and 〈 〉 is an average over reactant states with an equilibrium distribution. The rate constant κeq is itself 〈q〉. A number of illustrations are given, and it is concluded that in real chemical systems 〈q2〉 is probably of the order of magnitude of 〈q〉1+γ with 0<γ<1. This has as a consequence that κ is of the form (1 — Bκeqγ)κeq. The quantity in parentheses describes the effect on κ of deviations from equilibrium, and it is a decreasing function of temperature. It is suggested that this might possibly be the explanation of the observed temperature-decreasing pre-exponential factor in the rate constant for dissociation of diatomic molecules.
``Floating'' Hydrogen Densities in Some Molecules of the Type XHn
Authors: Banyard K. E.
Published: January 2005

The model of ``floating'' hydrogen densities was suggested initially by McDonald in an analysis of the electron density for NH4+. The model, as used here, is an attempt to represent the molecular radial distribution as a superposition of the radial densities obtained from the ``best'' electronic wave functions (in the sense of the variation method) for the constituent atoms, the centers of the unperturbed hydrogen distributions being allowed to ``float'' inward along the bonds. The model was applied to H2O and CH4 and the molecular and bond dipole moments were calculated. Thus for H2O, which alone possesses a resultant moment, some insight could be obtained into the accuracy of the angular dependence of the density pref dicted by such a model. Comments were also made on NH4+ and NH3. Further, the application of an approximate formula of Carter enabled a determination to be made of the paramagnetic contribution to the molar diamagnetic susceptibility.
Studies in Molecular Structure. IV. Potential Curve for the Interaction of Two Helium Atoms in Single-Configuration LCAO MO SCF Approximation
Authors: Ransil Bernard J.
Published: January 2005

Single-configuration LCAO MO SCF wave functions and corresponding total energies were calculated for two ground-state He atoms interacting over an extensive range (0.4 to 12.0 A). Comparison with available experimental data is made; remarkably good agreement is obtained for distances greater than 1.5 A. For the first time, it is believed, an a priori account is given of both the van der Waals minimum and the repulsion region with a wave function of sufficient flexibility to deal with both. The details of repulsion and of bonding in the van der Waals region are analyzed in terms of atomic and overlap populations.
Electrostatic Binding Energy in a Body-Centered Structure of Parallel Charge Doublet Chains
Authors: Jackson P. J.
Published: January 2005

The binding energy between chains in a body-centered tetragonal structure, consisting of infinite charge doublet chains parallel to the c axis, is considered as a function of two lattice parameters. Graphs are plotted of the variation of the binding energy with these parameters. The results are applied to the particular case of metaldehyde.
Twist in Alumina Whiskers
Authors: Sears G. W. , DeVries R. C. , Huffine C.
Published: January 2005

Eshelby twists have been microscopically observed at the tapered tips of alumina whiskers grown by the reaction Al2O(g)+2H2O(g)⇌2H2(g)+Al2O3(s).It has been found that the twist and associated screw dislocation can be removed by nonuniform bending occurring during breakage of the whisker from its base.
Development of the Liquid Equation and the Partial Structure of Water
Authors: Ginell Robert
Published: January 2005

In a previous publication where the derivation of the Tait equation for liquids is given, the number average degree of association and the volume of holes depended on a sum φ= ∑ x=1∞sx(1/v)x·This sum is transformed here into a closed expression. Hence, these quantities can now be evaluated numerically along any isobar or isotherm in terms of one undetermined constant at a particular reference temperature. In terms of this development, the structure of water is analyzed along an isobar (1 atm) from 20°—75°C and along an isotherm (20°C) from 1–200 atm.
Diffusion and Heterogeneous Reaction. IV. Effects of Gas-Phase Reaction and Convective Flow
Authors: Wise Henry , Ablow Clarence M.
Published: January 2005

The kinetics of atom recombination by homogeneous and heterogeneous reaction are examined. The analysis includes the combined effects of first-order surface reaction and third-order gas-phase reaction in a system undergoing diffusive and convective flow. On the basis of this model the rate constants for the homogeneous rate of recombination of oxygen atoms and of hydrogen atoms are derived from published experimental measurements.
Separation of Boron Isotopes. V. The Phenol-BF3 System
Authors: Palko A. A. , Drury J. S. , Bull W. E.
Published: January 2005

The exchange of boron between BF3(g) and BF3·phenol(l) was studied. The single-stage isotopic fractionation factor varied according to the equation, logα= (10.315/T) —0.02423, over the temperature range —8°C to 37°C. B10 is concentrated in the liquid phase. Vapor-pressure measurements of dilute and concentrated solutions of BF3 in phenol were made at various temperatures from —10°C to 40°C. The freezing point of the BF3·phenol complex was approximately —15°C; that for the BF3·2 phenol, —5°C.
Electronic Structure, Spectra, and Magnetic Properties of Oxycations. III. Ligation Effects on the Infrared Spectrum of the Uranyl Ion
Authors: McGlynn S. P. , Smith J. K. , Neely W. C.
Published: January 2005

A series of uranyl complexes KxUO2Ly(NO3)2, where L is the variable ligand (or ligands), has been prepared; it has been shown that a ligand series may be defined using the antisymmetric stretching frequency of the uranyl entity, and this series exhibits a remarkable parallelism with the spectrochemical series defined by Δ in octahedral complexes of transition metals of the 1st and 2nd series. This parallelism has been rationalized using a mixed ligand field theory in which the uranyl ion is considered subject to bonding with ligands which are arranged hexagonally in a plane equatorial to the O–U–O axis. It is shown that the large changes of ν3 and ν1 are due primarily to electron population of the φu and δu atomic orbitals of uranium. Such population is physically equivalent to the reductions AmO2+ +→AmO2+ and NpO2+ +→NpO2+, which cause a decrease of approximately 100 cm—1 in ν3. It is further shown that Δν̄3 = — electrostatic effect — σ(L→M) — π(L→M) ± π(M→L), where in the last term the plus sign is the more probable, and the results obtained have been rationalized using this equation.

Some evidence in favor of linearity of the UO2+ + has also been induced, and a general criterion for distinguishing the difficulty observable ν1 has been reestablished. It has also been shown, although not discussed extensively, that the stability of uranyl complexes should increase, roughly as ν̄3 (or ν̄1) decreases. The discussion of similar effects in vanadyl, titanyl, chromyl, and other oxycations has been deferred to a later time.
Internal Rotation of Cis 2,3-Epoxybutane from the Microwave Spectrum
Authors: Sage Martin L.
Published: January 2005

The microwave spectrum of cis 2,3-epoxybutane was investigated in the region from 8000 to 29 000 Mc. The spectrum consists of singlets and triplets. The ground torsional state shows a pseudo rigid-rotor spectrum with rotational constants 8057.71, 4461.36, and 3468.60 Mc. The triplets yield a barrier to internal rotation of 1607±150 cal/mole independent of a range of assumptions concerning the coupling of the two methyl groups. The dipole moment was found to be 2.03±0.02D with 2.01±0.02D in the plane of the ring. A group theoretical discussion of double rotors with one rotor on each side of a plane of symmetry is given.
ESR Spectra of Solid Phthalocyanines
Authors: Neiman Robert , Kivelson Daniel
Published: January 2005

Phthalocyanine complexes of paramagnetic metal ions show ESR spectra characteristic of the metals; phthalocyanine complexes of diamagnetic metal ions show strong single ESR lines characteristic of free radicals. The source of this latter resonance is not understood. Intimate molecular mixtures of ``paramagnetic'' copper and ``dimagnetic'' zinc phthalocyanines exhibit exchange between the copper unpaired electron and the ``free radical'' electron in the zinc phthalocyanine. Nickel and zinc phthalocyanine also exhibit a single sharp resonance in dilute solutions of concentrated sulfuric acid.
Experimental Townsend Ionization Coefficients for Isopentane
Authors: Heylen A. E. D.
Published: January 2005

Townsend α and γ values have been measured over the range 60≤E/p0≤3000 for isopentane using the dc method of measuring the ionization current. The experimental apparatus and procedure are described. It is shown that Townsend's law α/p0=A exp (—Bp0/E) is obeyed within 80≤E/p0≤500. Positive ion action at the cathode sets in at E/p0≥500. The results agree with previous breakdown measurements. It was found possible to follow the current growth due to ionization of the gas over a multiplication range exceeding eight orders of magnitude. The influence of space-charge distortion within single avalanches and that due to neighboring ones has been examined. No space-charge reduction of the avalanche multiplication was observed until eαd≥107.
Dissociation Energy of Cyanogen and Related Quantities by X-Ray Densitometry of Shock Waves
Authors: Knight Herbert T. , Rink John P.
Published: January 2005

Density ratios across shock waves in a 0.85 Kr+0.15 C2N2 mixture at an initial pressure of 50 mm Hg and room temperature, have been determined with an x-ray densitometer as a function of shock velocity. The heat required to dissociate cyanogen into two CN radicals D(C2N2) has been determined to be 145±6 kcal/mole by comparing the experimental data with curves of density ratio vs shock velocity calculated as a function of D(C2N2). Dissociation energies of 174±3 kcal/mole for CN and 129±3 kcal/mole for HCN forming H and CN, and a heat of formation of 109±3 kcal/mole for CN, were obtained by the application of Hess's law to the appropriate chemical reactions using this value of D(C2N2) and the currently accepted values for the dissociation energy of nitrogen (225 kcal/mole) and the heat of sublimation of graphite (170 kcal/mole). The value of D(HCN) was confirmed by analogous density-velocity measurements on shock waves in a 0.85 Kr+0.15 HCN mixture. A rate constant for the recombination of CN to form C2N2 at 2900°K was deduced from the variation of density with time behind the shock. The value obtained was of the order of 1×109 (mole/liter)—2 sec—1.
Shock Wave Studies by Mass Spectrometry. I. Thermal Decomposition of Nitrous Oxide
Authors: Bradley J. N. , Kistiakowsky G. B.
Published: January 2005

An apparatus is described in which the reacting gas behind a reflected shock wave is sampled continuously and analyzed at intervals of 50 or 100 μsec by a time-of-flight mass spectrometer. The thermal decomposition of N2O in the temperature range 1780–2000°K has been used as a test case to demonstrate that the experimental technique is valid. It has also been shown that the mechanism and rate constants of this reaction at high temperatures are consistent with earlier measurements at much lower temperature.
Intermolecular Coupling of Vibrations in Molecular Crystals. II. Intermolecular Forces in CH3Cl and CD3Cl
Authors: Dows David A.
Published: January 2005

The effect of isotope substitution on band splittings caused by dipole coupling between molecules is examined. For methyl chloride and methyl bromide, the results support the contention that the theory of dipole coupling in its present form is not sufficient to explain the splittings in most bands.

The theory of atom-atom interactions presented in part I of this series is applied to various possible potentials coupling the motions of normal and deuterated methyl chloride molecules. A repulsive potential acting between hydrogen atoms of neighboring molecules accounts for the splittings of several bands. Certain types of coupling potentials seem ruled out by the results of these calculations, while others are left as possible factors in band shifts which occur when a gas is condensed.
Maximum Overlap Atomic and Molecular Orbitals
Authors: Lykos Peter G. , Schmeising Howard N.
Published: January 2005

The eigenvectors of the overlap matrix are shown to be maximum overlap orbitals (MO–O's). Naive MO methods, such as that due to Hückel, are shown often to reduce to the MO–O problem. The potential usefulness of MO–O's in the determination of atomic hybrid orbitals and as starting orbitals for SCF calculations is considered.