bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetically Induced Circular Dichroism and Birefringence in Single Lines of the Electronic Spectrum of ICl
Authors: Stalder Arnold F. , Eberhardt W. H.
Published: January 2005

The magnetically induced circular birefringence and dichroism of several bands in the electronic spectrum of ICl have been studed with a resolution of approximately 0.1 cm−1. The frequency dependence is in agreement with predictions based on the semiclassical dispersion formulas provided that each Zeeman component of a single zero-field line is treated separately. The line center is displaced by the Zeeman shift and the intensity is determined by first-order perturbation by the magnetic dipole-moment operator which mixes neighboring J states. Thus, although the qualitative aspects of the semiclassical treatment of the Faraday effect may be extended into regions of the spectrum in the immediate vicinity of sharp-line molecular spectra, the details of the spectrum depend in a very sensitive way on the molecular parameters and the rotational structure of the band.
Metastable Ions in the Mass Spectra of Propane and Deuterated Propanes
Authors: Ottinger Ch.
Published: January 2005

The metastable transitions of the three-carbon ions of propane, 2,2-dideuteropropane, and 1,1,1,2,3,3,3-heptadeuteropropane were investigated. Twenty-one transitions involving loss of one or two H or D atoms were detected. A very strong isotope effect which effectively suppresses D elimination for ions in which H elimination is a possible competitive process was also established, confirming earlier results for the methane system. Only secondary propyl ions are formed via a metastable decay, and little or no hydrogen-atom migration in the parent ion occurs prior to dissociation. In addition, elimination of the isotopic species in secondary reactions is far from statistical, suggesting that scrambling is also incomplete for these ions.
Method of Diatomics in Molecules. V. Theoretical Prediction of Stable Li2H+ and Almost Stable LiH2+
Authors: Wu Ay-ju A. , Ellison Frank O.
Published: January 2005

Diatomics-in-molecules theory is applied to the molecule—ions LiH2+ and Li2H+ using as a basis three canonical valence-bond wavefunctions in each case. The input for this theory consists of the valence-bond wavefunctions and potential-energy curves for the ground electronic states of H2, Li2, and LiH and for the ground and first excited states of H2+, Li2+, and LiH+. Experimental diatomic potential-energy curves are used if available; otherwise, best possible theoretical or semiempirical curves are used. Diatomics-in-molecules theory in this approximation leads to predictions that ground-state LiH2+ may be stable by about 2.5 kcal with respect to Li++H2 and that ground-state Li2H+ should be stable by about 10 kcal with respect to Li++LiH. The equilibrium shape for LiH2+ turns out to be a symmetrical isosceles triangle with RLiH=5.0 bohrs and RHH=1.4 bohrs; Li2H+ is symmetrical and linear with RLiH=3.4 bohrs. A stable linear excited state (1Σu+) is predicted at about 35 kcal above the ground state (1Σg+) of Li2H+.
Importance of Quadratic Force Constants in Fermi Resonance
Authors: Reichman Sandor , Overend John
Published: January 2005

If the intramolecular potential energy is written in internal valence coordinates, the transformation to normal coordinates is nonlinear. Consequently both the quadratic and cubic valence-coordinate force constants contribute to the cubic normal-coordinate force constant which is the coefficient of the Fermi—Dennison resonance operator. The contributions of the quadratic force constants have been evaluated in some simple cases; they appear to be more important than the cubic internal-coordinate force constants. Anharmonicity enters mainly through the cubic stretch—bend—bend interaction force constant.
Adsorption of Gases on Chromium Films
Authors: McElligott P. E. , Roberts R. W. , Engel T. W.
Published: January 2005

The adsorption behavior of O2, H2, CH4, C2H6, and C2H4 has been investigated on clean Cr films at 27° and 100°C. The gases adsorbed in the following order; O2>C2H4>H2>C2H6>CH4. No gaseous decomposition products were observed when CH4 adsorbed on a clean Cr surface, but C2H6 interacted with Cr at 100°C to produce appreciable amounts of gaseous H2. Ethylene was found to undergo extensive self-hydrogenation to C2H6 over Cr films at both 27° and 100°C. The presence of preadsorbed oxygen on Cr films at 100°C inhibited both H2 production from adsorbed C2H6 and the self-hydrogenation of C2H4.
Mechanisms of Energy Transfer Involving Trivalent Tb and Pr
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

The self-quenching of Tb emission, from the Tb5D3 manifold; the self-quenching of Pr emission, from the Pr3P0 manifold; and transfer from Tb5D3 or Tb5D4 to Pr involves dipole—quadrupole interactions in the scheelites. The lifetime for emission from Pr3P0 or Pr1D2 under dilute conditions is very short (∼5 μsec) compared to that for Tb5D3 (∼200 μsec) or Tb5D4 (∼565 μsec). Less than 1% of the excitation transferred from Tb to Pr appears as emission from Pr.
Two-Photon Laser Excitation of Polycyclic Aromatic Molecules
Authors: Dowley Mark W. , Eisenthal Kenneth B. , Peticolas Warner L.
Published: January 2005

The theory of two-photon absorption is extended to include vibronic mixing between electronic states. Theoretical expressions are derived which relate the possible transition pathways with measured quantities. The experimentally determined quantities are: the relative absorption cross sections of linearly versus circularly polarized exciting light, and the polarization of the fluorescence resulting from two-photon excitation by linearly polarized light. The theory is applied to measurements on two molecules of D2h symmetry, anthracene and 9,10 dichloroanthracene. Utilizing the equations developed, the relative contributions of the three pathways, (1) both photons absorbed along the short axis, (2) both photons absorbed along the long axis, and (3) one photon absorbed along the long axis and the other photon absorbed along the short axis, are determined. From the deduced values of the transition pathways the relative contributions of different final vibronic states to the absorption of two laser photons (ℏω=14 400 cm−1) are determined.
Matrix-Isolation Study of the Reaction of Carbon Atoms with HCl. The Infrared Spectrum of the Free Radical HCCl
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: January 2005

The infrared spectrum of samples of cyanogen azide plus hydrogen chloride isolated in an argon or a nitrogen matrix at 14°K and subjected to photolyzing radiation under conditions previously shown to lead to the production of carbon atoms includes features at 815 and 1201 cm−1 which may be assigned to the free radical HCCl. 13C- and D-substitution experiments are consistent with this identification. A band system extending between about 7500 and 5600 Å corresponds to the band system previously reported for HCCl in the gas phase. These observations confirm the production of HCCl in the present experiments and indicate that the lower state of the transition observed for HCCl in the gas-phase studies is the ground state. The force constants and thermodynamic properties of HCCl have been estimated. Evidence is presented for the reaction of NCN, a photolytic intermediate in the production of carbon atoms from cyanogen azide, with HCl to produce an incompletely characterized species, probably either monochlorocyanamide or monochlorocarbodi-imide. HCCl reacts with HCl with little or no activation energy, leading to the stabilization of CH2Cl2.
Theory of Nucleation and Growth of a Thin Film. I. Equilibrium Two-Dimensional Liquid—Gas Phases
Authors: Kikuchi Ryoichi
Published: January 2005

As a preparation for the study of nucleation and growth of a film, the equation of state is derived for a system of atoms on a two-dimensional lattice using the cluster-variation method. Two cases are calculated. In the first portion of the paper the pair approximation is used for the case in which fixed impurities are scattered on the lattice. The isotherm is of the van der Waals type. In the second portion of the paper, a triangle is used as the basic cluster to show how the improved approximation works. It is significant that a flat portion in the pressure—density isotherm results in connection with the phase separation.
Theory of Nucleation and Growth of a Thin Film. II. Application of the Path-Probability Method
Authors: Kikuchi Ryoichi
Published: January 2005

Nucleation and growth of a thin film on a substrate by vapor deposition are studied theoretically using a statistical mechanical technique called the path-probability method for irreversible cooperative phenomena. The thin film is assumed a monolayer and is represented by a two-dimensional lattice system, each lattice point being either vacant or occupied by an adatom or an ``impurity.'' The atoms are supplied from the gas phase onto the film and may migrate on the film surface. The ``impurity'' acts as the prenucleation centers which attract adatoms; it can be either a defect in the substrate surface or a prenucleated atom and is assumed immobile in the analysis. Kinetic differential equations for three variables which specify the state of the film are derived as the most probable path. The limit of the stationary state leads to the gas—liquid isotherm identical to the one derived from the equilibrium theory, showing the internal consistency of the treatment. The stationary limit gives information on the maximum attainable density, and leads to the existence of a discontinuous ``deposition'' temperature; this temperature is lower for smaller impurity density. The process of film growth is calculated by integrating the kinetic equations for given pertinent parameters such as the rate of impinging atoms, density of impurities and the activation energies for migration and evaporation. Under certain parameters the density of the film stays on the first plateau value for some time before it increases suddenly to the second plateau. The first plateau is identified as the critical state of nucleation. The size of the critical nuclei is deduced; when the impurity density is larger, the film can grow with smaller rate of impingement and hence the critical size is larger.
Ion—Molecule Reactions in the Xenon-Sensitized Ionization of Ethylene
Authors: Kebarle P. , Haynes R. M.
Published: January 2005

Xenon was irradiated with alpha particles in the absence of electric fields at pressures up to 40 torr containing 10−3−5 torr ethylene. Part of the gas bleeds into a mass spectrometer. Experiments with a movable collimating slit and a theoretical treatment of the conditions in the ion source establish a qualitative picture for the sampling conditions and ionic reaction times. Most of the detected ions originate from a 1-mm-radius volume directly over the leak. The average ionic reaction times are a few milliseconds. Electrons are sampled with greatly reduced efficiency or not at all. The xenon-sensitized ionization of ethylene produces mostly C2H4+ as primary ion. The reactions of C2H4+ with ethylene at xenon pressures above 10 torr lead mainly to the simple chain CnH2n+ (n=even). Approximate rate constants for the addition reactions were determined. C4H8+ adds at least 100 times more slowly to ethylene than C2H4+. Further decreases of rate constants occur as the chain develops such that the rate constant for the C10H20+ addition to ethylene is some four orders of magnitude lower than that of C2H4+. At lower xenon pressures stabilization of the excited addition product (CnH2n*)+ is not sufficiently rapid and decomposition CkH2k−1 (k=odd) occurs. The stabilization to decomposition ratio is studied as a function of xenon pressure.
Reaction of O(1D) with CO2 at Low Temperatures
Authors: Weissberger Edward , Breckenridge W. H. , Taube Henry
Published: January 2005

When O3 dispersed in a solid CO2 matrix, or a mixture of O3 and CO2 dispersed in solid argon is photolyzed using ultraviolet light, O3 disappears and a new substance forms. This substance shows infrared-absorption maxima at 2053, 1894, 1070, 975, and 564 cm−1. These absorption bands are ascribed to CO3. The molecule CO3 is capable of reacting with O2 to form O3. Experiments using 18O-labeled CO2 show that the oxygen in O3 formed by the reaction of O2 with CO3 is in part derived from the CO2.
Intermediate-Range Intermolecular Forces in H2+
Authors: McQuarrie Donald A. , Hirschfelder Joseph O.
Published: January 2005

A new type of molecular perturbation theory recently developed by Hirschfelder and Silbey is used to study intermolecular forces in the intermediate range where the wavefunctions overlap slightly and exchange must be taken into account. A method is outlined by which one can modify a nonexchange- or polarization-type first-order wavefunction to include the effect of exchange. Although the procedure seems to be general, for numerical convenience only the 1sσg and 2pσu states of H2+ are considered. The results are in good agreement with the exact energies for both states to approximately R=4 a.u., compared to about R=15 a.u. for a perturbation treatment without exchange.
Nonadditive Triple-Overlap Interactions among Rare-Gas Atoms in the Thomas—Fermi—Dirac Approximation
Authors: Present R. D.
Published: January 2005

Formulas for the nonadditive overlap energy of interaction among three atoms, based on the Thomas—Fermi—Dirac (TFD) approximation and the assumption of superimposed, unperturbed densities appropriate to the isolated atoms, have been developed for linear and isosceles arrays. Computations based on these formulas and employing March's variational, modified TF density have been performed for three Kr atoms in symmetric linear and equilateral triangular arrays, and also for three He atoms in symmetric linear arrays. For the case of Kr atoms in equilateral configurations, the ratio of the nonadditive energy to the sum of the repulsive pair energies (obtained in the TF approximation) is found to be −2.5% for an internuclear distance of 1 a.u. and to decrease rapidly with increasing separation. Smaller results are found for the symmetric linear arrays. Cancellation between the kinetic-energy and the exchange-energy contributions is partly responsible for the rapid falloff of the nonadditivity effect. The nonadditive overlap energy, as treated here, is appreciable only if the atoms are close enough to produce appreciable triple overlap of their charge distributions. Such close approach is ordinarily prevented by the repulsive part of the pair potential. The range of the nonadditive overlap interaction is enough shorter than the slow-collision diameter that the nonadditivity effects are negligible at physically significant distances—in agreement with results found previously for He arrays by Rosen and Shostak. We find, in both He and Kr, that the triple-overlap nonadditive interaction is smaller than the triple-dipole nonadditive interaction (Axilrod—Teller—Muto) at internuclear separations corresponding to the minimum of the van der Waals potential and the nearest-neighbor distance in the solid. The nonadditive overlap interaction appears too small to account for the anomalous crystallization of Kr into an fcc lattice or to produce a substantial correction to the third virial coefficient of the gas.
Quenching of the Tb3+ Fluorescence by Other Rare-Earth Ions in Aqueous Chloride Solutions
Authors: Holloway W. W. , Kestigian M.
Published: January 2005

The quenching of the Tb3+ fluorescence by Nd3+, Ho3+, or Er3+ ions has been studied by measurement of the fluorescence lifetime in aqueous chloride solutions. The probability for a quenching interaction Pint is found to be proportional to r−6, where r is an average distance between the fluorescent ion and the quenching ion. The overlap of the Tb3+ emission spectrum and the absorption spectra of several quenching ions has been measured. Pint, determined by the lifetime measurements for these ions, is approximately proportional to the value of the overlap integral. These results can be interpreted on the basis of a ``resonance'' (i.e., nonradiative) transfer of energy from the fluorescent terbium level to excited levels of the quenching ion through a dipole—dipole interaction.
Measurement of the Depolarization Ratio for the A1 Raman Line of Carbon Tetrachloride in Binary Mixtures
Authors: Murphy William F. , Evans Monroe V. , Bender Paul
Published: January 2005

A study of the depolarization ratio of the totally symmetric Raman line of carbon tetrachloride in a series of solutions has been made using a He–Ne laser for the source of incident light. A value for ρs (the depolarization ratio measured with linearly polarized incident light) of 0.0039±0.0002 was found for pure CCl4. The solution results provide experimental evidence that interaction between the molecules in the liquid is a major cause of the deviation from the zero depolarization ratio predicted from symmetry arguments. This conclusion is supported by a consideration of other possible causes of the deviation.
Th Symmetry in the Rare-Earth Double Nitrates
Authors: Devine S. D.
Published: January 2005

The symmetry of the crystal field about the rare-earth ion in the rare-earth double nitrates is known to be C3. While the major groupings of the crystal-field levels in the optical spectra may be understood by assuming the crystal-field symmetry is icosahedral, the structure within these groups can be explained by assuming an approximate symmetry of Th with a small distortion to C3. Tentative crystal-field parameters for Th symmetry are obtained for Nd2Mg3(NO3)12·24H2O and Ce2Mg3(NO3)12·24H2O.
Viscosity of Entangling Polydisperse Polymers
Authors: Graessley William W.
Published: January 2005

This paper presents a theory of viscosity in steady shearing flow for bulk polymers and concentrated polymer solutions. The basis for the theory is the supposition that intermolecular chain entanglements control the magnitude of the viscosity and that the decrease in viscosity with increasing shear rate is caused by shear-induced changes in the network of entanglements. It was found possible to represent the effect of entanglements by an additional term in the segmental friction coefficient, and to incorporate the effects of polymer concentration, molecular weight distribution, and shear rate in the final result. At low shear rates (γ̇→0) the viscosity reduces to η0=(const) (φn̄x)3.5 for highly entangled chains, where φ is the volume fraction of polymer and n̄x is an average chain length slightly greater than the weight average. The form of the viscosity—shear rate master curve was found to depend on the chain-length distribution of the polymer. Departures from Newtonian behavior occur at lower shear rates the broader the distribution, but at sufficiently high shear rates the behavior becomes similar for all distributions. The master curve for monodisperse polymers was in good agreement with measurements on solutions of narrow distribution polystyrene. The limiting power-law exponent in η=k|γ̇|−a was found to be 9/11 rather than ¾ as given by an earlier theory. The master curve calculated for most-probable distributions (M̄w/M̄n=2) agreed moderately well with the empirical master curve of Bueche and Harding and with data on solutions of unfractionated polystyrene.
Intersystem Crossing in Gaseous Molecules
Authors: Robinson G. Wilse
Published: January 2005

The theory of electronic relaxation in the solid phase is discussed in terms of gaseous molecules. Two limits are examined—the ``small-molecule limit'' (α limit), where electronic relaxation cannot occur in the free molecule, and the ``big-molecule limit'' (ω limit), where electronic relaxation at a rate virtually identical with that in the solid can take place in the absence of any external perturbation. An ``intermediate case'' (μ case) is described where no relaxation can occur in the completely free molecule, but where only extremely minute perturbations are required to induce such a process. Intersystem crossing B2u1→B1u3 in benzene is close to the borderline between the ω limit and the μ case. Although the concepts are somewhat inexact quantitatively because of the difficulty in estimating matrix elements and the vibrational density-of-state function, the theory does indicate that the zero-point level of the 1B2u state could behave like a μ case, while the excited vibrational levels of this electronic state, those mainly reached in past experiments, may lie in the ω limit. Available experimental data support the idea that the higher vibrational levels of the 1B2u state of benzene very likely lie in the ω limit, but cannot shed light on the behavior of the zero-point level.

Theoretical expressions for the rate of intersystem crossing, the fluorescence lifetime, and the fluorescence yield as functions of pressure are worked out. Theory shows that in both the α limit and in the μ case the absolute fluorescence yield approaches unity in the limit of zero pressure. For the ω limit, the absolute fluorescence yield can very well be less than unity even for a molecule in free space. Some new experiments are suggested by the theoretical conclusions.
Configuration of Isolated Polymer Molecules Adsorbed on Solid Surfaces Studied by Monte-Carlo Computer Simulation
Authors: McCrackin Frank L.
Published: January 2005

The configurations of adsorbed polymer molecules with excluded volume were simulated on a four-choice simple cubic lattice using a computer. The average values of the fraction of segments on the surface, loops off the surface, normal distance of the end of the molecule from the surface, root mean square of the normal distance, maximum normal distance from the surface, and root-mean-square end-to-end distance were calculated for various lengths of the molecules and various attractive energies between segments and the surface. When these averages over the configurations are compared with previous results which do not account for the excluded-volume effect, important differences are found.
Crystal Field in Rare-Earth Trichlorides. I. Overlap and Exchange Effects in PrCl3
Authors: Ellis M. M. , Newman D. J.
Published: January 2005

Overlap and exchange contributions to the crystal field of PrCl3 have been determined using an LCAO—MO model. The contributions to the parameters A60〈r6〉, A66〈r6〉 are found to be 8.5×greater than the magnitudes predicted by the simple point-charge electrostatic model. However, the calculated values of these parameters are still 21% less than the experimental values and several reasons for this discrepancy are suggested.
Very High Pressure Effects upon the EPR Spectrum of Ruby
Authors: Nelson H. M. , Larson D. B. , Gardner J. H.
Published: January 2005

The variation in the electron paramagnetic resonance (EPR) spectrum of ruby as a function of pressure has been observed to beyond 70 kbar for a magnetic field orientation parallel to the crystalline c axis. The data can be interpreted in terms of the usual spin Hamiltonian: H=g||βHzSz−12δ(Sz2−13S2), where the spectroscopic splitting factor g‖ has the same value as at ambient pressures, but where the zero-field splitting δ increases in a linear fashion from ∼0.38 to ∼0.43 cm−1. The experimental apparatus has been described previously, although important improvements in the pressure seal and in the pressure calibration have been made and are described in an Appendix.
Optical Anisotropy of Chain Molecules. Theory of Depolarization of Scattered Light with Application to n-Alkanes
Authors: Jernigan R. L. , Flory P. J.
Published: January 2005

Depolarization of light scattered by chain molecules is treated according to the valence-optical scheme which rests on the assumption that the polarizability tensor α for the molecule may be formulated as the sum of contributions of individual bonds, or of constituent groups. The anisotropy of the polarizability is described by the tensor invariant γ2 (proportional to the sum of the squares of the elements of the traceless part of α), which determines the depolarization ratio. This invariant (γ2) is averaged over all configurations of the chain molecule treated in the rotational isomeric-state approximation, interdependence of rotations about neighboring bonds being taken into account. Beyond the stated assumptions, the treatment is exact; it is applicable to chains of any length, and of any specified structure. Illustrative calculations for the n-alkanes are presented and compared with experimental depolarization results for liquids of this homologous series and for their solutions in solvents of low optical anisotropy.
Enthalpies of Mixing in Some Binary Alkaline-Earth Chlorides
Authors: Papatheodorou G. N. , Kleppa O. J.
Published: January 2005

The integral enthalpies of mixing in the six binary systems formed by MgCl2, CaCl2, SrCl2, and BaCl2 have been determined calorimetrically. The results are discussed in terms of the theories of Reiss, Katz, and Kleppa and of Davis and Rice, each suitably modified to take into account the higher charge on the cation. The molar enthalpies of mixing for the systems CaCl2–SrCl2, CaCl2–BaCl2, and SrCl2–BaCl2 can be represented by the following approximate expression which is simply related to the corresponding expression for the binary alkali halides, previously derived by Hersh and Kleppa: ΔHM=X1X2(U0++−Z2340δ122) kcal/mole. Here X1 and X2 are the mole fractions of the two components; δ12=(d1—d2)/d1d2, where d1 and d2 are the sums of the ionic radii of anion and cation in the two salts, while Z=Z1Z2, the product of the charges of the anion and cation in the component salts (here Z=2). The term U0++ represents an estimate of the contribution to the enthalpy of mixing arising from the London dispersion interaction between next-nearest-neighbor cations. The quoted expression does not hold for the three binary systems involving MgCl2, which are all much less exothermic and which exhibit considerable energetic asymmetry. In all cases the enthalpy of solution of MCl2in MgCl2 is more endothermic than the opposite process. The results for these three systems are interpreted to support the view, originally advanced by Førland, that pure MgCl2 has a certain tendency to form covalently bonded Mg–Cl–Mg bridges. The breaking of these bridges gives rise to a significant endothermic contribution to the enthalpy of mixing, over and above the contributions arising from Coulombic and dispersion forces.
High-Resolution NMR Spectra of Polycyclic Hydrocarbons. II. Pentacyclic Compounds
Authors: Cobb T. B. , Memory J. D.
Published: January 2005

The McWeeny theory has been used to calculate chemical shielding parameters for all even, alternant, pentacyclic hydrocarbons, and comparison with experiment was made where data were available. The spectra of two pentacyclic molecules, 1,2,3,4-dibenzanthracene and picene, not reported previously, were obtained and analyzed, and a complete analysis of the 1,2-benzpyrene spectrum is given. Agreement between theory and experiment is satisfactory for protons not subject to large van der Waals contact, and it is found that steric effects contribute an extra downfield shift of 0.54 ppm to angular phenanthrenic type protons. Additions and new interpretations are made for previously reported results of similar data on three- and four-ring molecules.
Approximate Self-Consistent Molecular-Orbital Theory. V. Intermediate Neglect of Differential Overlap
Authors: Pople J. A. , Beveridge D. L. , Dobosh P. A.
Published: January 2005

A new approximate self-consistent-field method for the determination of molecular orbitals for all valence electrons of a molecule is proposed. This method features neglect of differential overlap in all electron-interaction integrals except those involving one center only. The parameters involved in the calculation are generally obtained semi-empirically. The new method is known as the Intermediate Neglect of Differential Overlap (INDO) method, and may be regarded as an improvement over the CNDO method proposed in Part I, in that atomic term-level splittings and unpaired spin distributions are better accommodated. Calculations on geometries of AB2 and AB3 molecules are reported to substantiate the proposed method, and calculated unpaired spin distributions for methyl and ethyl radicals are discussed.
Treatment of the Normal Vibrations of Helical Polymers; Methods for Factoring theBMatrix and for Calculating Atomic Displacements
Authors: Sugeta Hiromu , Miyazawa Tatsuo
Published: January 2005

Theories on the degenerate normal vibrations of helical polymer chains were studied. A method for factoring the B matrix of infinite chains was worked out. For any phase difference, the factored B matrix is useful for calculating the G matrix and the atomic displacements. The atomic displacements for a degenerate vibration may be expressed with an ellipse that is common to all the repeat units. The atomic motion makes an elliptical locus when the pair of the degenerate vibrations take place with a phase shift. A refined method is presented for treating the normal vibrations of helical polymers of the dihedral group.
Molecular-Orbital Studies of Intermolecular Interaction Energies. II. Approximations Concerned with Coulomb Interactions and Comparison of the Two London Schemes
Authors: Pollak M. , Rein Robert
Published: January 2005

In the semiempirical calculations of wavefunctions in molecules with π-electron systems, molecular orbitals are constructed from atomic orbitals that are assumed to be orthogonal to each other. Since the Slater orbitals are not orthogonal, the atomic orbitals are usually interpreted to be the Löwdin orbitals. The Löwdin orbitals are delocalized, and therefore a question arises of how to use the computed coefficients of these orbitals for calculating the electronic charge distribution. It is found that the charge distribution may be somewhat different from the distribution where Slater orbitals are used instead of Löwdin orbitals. The magnitude of the difference depends on the kind of approximation used for the product functions of two Slater orbitals centered on different atoms. The difference vanishes for the Mulliken approximation. Numerical analysis for a guanine—cytosine base pair indicates that when the Löwdin approximation, or a similar approximation, is used instead of the Mulliken approximation, the difference in atomic charges amounts to about 20%. The effect of this on the intermolecular Coulomb energy between two guanine—cytosine base pairs in a DNA-like arrangement amounts to about 20%. Of the two well-known London schemes for the calculation of intermolecular Coulomb energies, the second London scheme is much superior to the first one for application to many organic and biological molecules. The numerical analysis reveals a difference of 50% between the two schemes, when applied to the guanine—cytosine dimer.
Stress-Optical Coefficient of Polymeric Networks. Stereo-irregular and Multirepeat Polymers
Authors: Nagai Kazuo
Published: January 2005

Expressions for the optical anisotropy ΔΓ of Kuhn's random link (an equivalent to the stress-optical coefficient) of stereo-irregular and multirepeat polymers are derived on the basis of the additivity principle of bond polarizabilities and the rotational-isomeric-state approximation for rotations about skeletal bonds. By multirepeat polymers we mean ones in which a stereochemically identical structure repeats along the chain at an interval of an arbitrary number of skeletal bonds. Expressions for the unperturbed mean-square end-to-end distance 〈r2〉, which are required in the calculation of ΔΓ, are also obtained. All expressions are cast into compact form by use of Flory and Jernigan's method. Comparison is made of expressions for 〉r2〉 derived in this paper, with those given previously by Flory and his co-workers and by the present author.
Zero Field Splittings of t23 Cubic Terms
Authors: Macfarlane R. M.
Published: January 2005

We have investigated the possibility of obtaining good approximate analytical expressions for the zero field splittings of cubic terms belonging to the t23 configuration. Spin—orbit, and trigonal and tetragonal field perturbations are considered, and a perturbation expansion based on a strong cubic field zeroth-order Hamiltonian is used. Only in the case of 4A2 and a2E terms does the expansion converge sufficiently rapidly for a single order of perturbation theory to provide a useful approximation for octahedral Cr3+ or tetrahedral Co2+ complexes. In the case of trigonal symmetry, we investigate the range of validity of the perturbation expressions, by comparison with exact numerical solutions of the crystal-field eigenvalue problem for the complete d3 configuration.
Kinetic Theory of Dense-Fluid Mixtures. IV. Square-Well Model Computations
Authors: Palyvos J. , Luks K. D. , McLaughlin I. L. , Davis H. T.
Published: January 2005

Predictions are given for the viscosity, thermal conductivity, and thermal diffusivity of binary liquid mixtures composed of molecules interacting with a square-well potential. The theoretical formulas were derived by McLaughlin and Davis in Paper I of this series. The viscosity predictions are in good agreement with experiment for binary mixtures of methane, argon, krypton, and xenon liquids. The square-well results are compared with the small-step diffusion theory of viscosity developed by Rice and Allnatt. Thermal diffusivities predicted by the square-well theory are compared to those predicted by the hard-sphere theory. The latter theory predicts values about 25% smaller than those of the former theory. Three equations in McLaughlin and Davis' original work [J. Chem. Phys. 45, 2020 (1966)] contain certain errors. The correct forms of these equations are given in the Appendix.
High-Temperature Electrical Properties of Manganese Monoxide
Authors: Hed A. Z. , Tannhauser D. S.
Published: January 2005

The deviation from stoichiometry, the electrical conductance G, and the Seebeck coefficient Q of MnO were measured as function of temperature T and oxygen partial pressure, P(O2), where T varied between 1100° and 1557°C and P(O2) varied from 10−18 to 10−1 atm. We found that MnO is an oxygen-excess compound, the dominant defects being manganese vacancies. In the range of P(O2) which corresponds to P(CO2)/P(CO)<50, these vacancies are mainly doubly ionized, the concentration of holes is proportional to the one-sixth power of P(O2) and exceeds the concentration of free electrons in all or most of this range. The mobility of the free electrons was shown to be greater by a factor of 10 or more than that of the holes. This feature is responsible for the fact that for P(CO2)/P(CO)<1 the oxide behaves like an n-type semiconductor, i.e., Q is negative and G is proportional to a negative power of P(O2). The intrinsic point, where n=p, occurs at much lower oxygen pressures and may indeed fall outside the range of our measurements. The conductance and the deviation from stoichiometry plotted against 1/T, show a break near 1375°C, indicating a possible phase transition in MnO. The mobility of the holes was found to rise exponentially with temperature, the activation energy being 0.37±0.07 eV over the whole range of our measurements. This value is consistent with small-polaron theory. The analysis of Q supports the hopping model. The measurements of G and Q on single crystal gave the same results as on polycrystalline samples, except in the region of high temperature and high P(O2), where the G's differ. This difference is explained by the presence of grain boundaries in the polycrystalline samples.
Far-Infrared Spectra and Space Group of Crystalline Hydrazine and Hydrazine-d4
Authors: Baglin F. G. , Bush S. F. , Durig J. R.
Published: January 2005

The infrared spectra of crystalline hydrazine and hydrazine-d4 have been recorded from 33 to 400 cm−1. All spectral bands have been assigned to lattice vibrations according to whether they arose primarily from a translational motion or a librational mode. However, there is strong evidence that these two motions are coupled and thus may not be described accurately as one motion or the other. An attempt is made at correlation between the observed and calculated shifts upon deuteration and some simple force constant calculations have been made. Finally, the far-infrared spectrum distinguishes between the two proposed crystal structures (C2h2 and C22) and the results are consistent only with the C22 structure.
Error Bounds for Expectation Values: Some Applications and Extensions
Authors: Jennings Philip , Wilson E. Bright
Published: January 2005

The error-bound procedure of Bazley and Fox is extended as in a previous paper and applied to the expectation values of some quantum-mechanical operators of physical interest. The quality of the bounds is discussed and it is found to be possible to improve them under certain conditions. An attempt is made to use these error-bound formulas as variational principles for expectation values. Some special cases such as Fermi contact terms and electron densities are discussed separately. Errors in Hartree—Fock expectation values are considered from the point of view of Brillouin's theorem and some qualitative predictions of their magnitudes are made. Transition probabilities are also treated and some qualitative conclusions are made concerning the accuracy of the alternative length and velocity formulas.
Anisotropy of Molecular Optical Rotation. I. Transparent Media
Authors: Disch R. L. , Sverdlik D. I.
Published: January 2005

An examination is made of the experimental problem of measuring the optical rotation of an anisotropic fluid, with particular reference to the application of an electric field to an optically active medium. Exclusion of the rather large effects of induced linear birefringence (Kerr effect) and the provision of an adequate single-to-noise ratio are the most important considerations. Two cases are discussed: the ``parallel'' and the ``perpendicular,'' in which the direction of propagation of the light is respectively parallel and perpendicular to the applied electric field. The former permits a rigorous exclusion of the Kerr effect with inherent limitation of signal-to-noise ratios, and the latter, while providing signal-to-noise ratios of the order of 50 to 100 times greater, requires special care in the exclusion of the Kerr effect. The perpendicular case, which has heretofore received little attention, is analyzed in detail, and it is shown that in most instances satisfactory results cannot be obtained with a single pair of plane-parallel electrodes. The use of two pairs of electrodes, having different azimuths, is suggested, and an analysis is given of the conditions under which exclusion of the Kerr effect may be obtained. Approximate calculations are made of signal-to-noise ratios which could be obtained in the perpendicular case with regard to both the Faraday effect and natural optical activity.
Deuterium Isotope Effects in the Electron Spin Resonance Spectra of Naphthalene Negative Ions
Authors: Lawler Ronald G. , Bolton James R. , Karplus Martin , Fraenkel George K.
Published: January 2005

High-resolution electron spin resonance spectra have been obtained of the anion radicals of naphthalene and of 10 different deuterium substituted naphthalenes. The ratio of the proton (aH) to deuteron (aD) hyperfine splittings was found to be different from the value aH/aD=6.514 expected on the basis of the magnetic moments and spins of the two isotopes and, furthermore, it was also found to be different at the α and β positions. These anomalous aH/aD ratios have been qualitatively interpreted in terms of vibrational effects which alter the sigma—pi interactions at the substituted positions. The data indicate that the sigma—pi parameters (Q's) for the two isotopes and at the α and β positions are all different, even when account is taken of the magnetic moments and spins. Deuterium substitution at one position was found to alter the hyperfine splittings of the protons at other positions. The magnitude and sign of these changes, which depend on the position and number of substituted deuterium atoms as well as on the position of the proton, have been shown to obey an additivity relationship. The changes in splittings are interpreted as resulting from a redistribution of spin density throughout the radicals. Hückel molecular-orbital calculations have been performed in which the resonance integral for bonds adjacent to a deuterium-substituted position have been altered by a small amount in order to account for this redistribution in spin density. Good agreement between the experimental and calculated changes was obtained, while similar calculations in which the presumed weak electron-donating effect of deuterium was accounted for by a change in the Coulomb integral at the substituted position were in systematic disagreement to a significant extent with the spin densities at certain positions. It was concluded that ESR data provide a more direct means of evaluating the vibrational perturbations introduced by deuterium substitution than do studies of chemical kinetics. Some of the spectra were of such high resolution that anomalies were introduced because of second-order shifts. These could not be analyzed by the usual approximations, and an Appendix is included on the detailed procedures which had to be employed.
Resonant States of H2−
Authors: Eliezer I. , Taylor H. S. , Williams James K.
Published: January 2005

Detailed quantitative calculations are reported for different resonant states of H2−. Results tie in quantitatively with dissociative attachment experiments and electron-scattering experiments, and qualitatively with vibrational-excitation experiments. Preliminary results on other states which have not as yet been experimentally observed are also discussed. Wavefunctions and energies are reported.
Diffuse Continua-Emitting Discharges in the Rare Gases with and without Nitrogen
Authors: Kenty Carl
Published: January 2005

If a current the order of 1 mA is passed through 50–750 torr of a pure rare gas in a 10-cm-diam tube a diffuse discharge results filling the tube and emitting mainly a continuous spectrum, strong in the vacuum uv, weak in the near uv, visible and ir. The discharge is characterized by a very high voltage gradient and a substantially flat volt—ampere characteristic. The ion and electron concentration is 108−109 cm−3 and the electron energies are high. Energy losses are principally elastic and the ions and electrons reach the wall by ambipolar diffusion. The continuous spectra are of molecular origin. Continua from Xe, Kr, and Ar are whitish, that from Ne a light blue. In any of the above discharges if a critical current is exceeded the discharge goes to a filamentary form. The addition of 0.1% N2 to the pure rare gas has profound effects, lowering the gradient in Xe 18-fold and bringing out the arc lines of Xe. New spectral structures are found at 3466 Å, 3650 Å, and at 1.3 μ which are believed to be due to complex molecules of Xe and N2. There is an afterglow lasting up to 10 sec that is spectroscopically much the same as the discharge itself. A high concentration (1013−1014 cm−3) of long-lived energy carriers is indicated and are believed to be mainly N2(3Δu). Collisions of pairs of 3Δu with Xe as a third body and/or of 3Δu with N2(A) produce the higher excited states of Xe and probably Xe2+ and higher excited states of N2 and N atoms. Blue fluorescence of a Pyrex wall indicates strong vacuum uv in Xe. The Vegard—Kaplan (VK) bands are developed with fair intensity indicating a population of N2(A) of the order of 1010 cm−3. The discharges have a positive characteristic indicating that the ions and electrons are disappearing by recombination and that the metastable energy carriers are partially saturated with respect to current. Interruption of the current is followed by an abrupt fall in luminosity to ∼⅓ of the initial intensity, followed by a recovery to ∼¾ initial, and then a slow decay of ∼½ sec. In N2+Kr the first negative system of N2+ is strongly developed perhaps indicating the presence of a high-energy metastable state of N2.
Quantum Theory of Stimulated Raman Scattering
Authors: Freedhoff Helen S.
Published: January 2005

The stimulated Raman scattering of radiation is studied as an illustration of the fact that a correct quantum description of the interaction of a laser beam with matter is obtained by representing the field by means of Glauber coherent states. Any attempt to represent the field by means of incoherent, occupation-number representation states will yield an incomplete description of the physical situation.
Mixed Excimer Fluorescence; The Importance of Charge-Transfer Interaction
Authors: Chandross Edwin A. , Ferguson J.
Published: January 2005

Mixed excimer fluorescence is observed when any one of a variety of aromatic hydrocarbons is added to solutions of 9-cyanoanthracene or 9, 10-dicyanoanthracene. The formation of a mixed excimer appears to be markedly dependent upon the ionization potential of the donor. The emission maxima of the 9, 10-dicyanoanthracene mixed excimers vary linearly with the polarographic oxidation potentials of the donors, a results corresponding to that found for charge-transfer absorption bands. It is concluded that charge-transfer interaction is important in the excimer state.
Ion Motion in Tetrafluoroborate Salts. I. NH4BF4 and ND4BF4
Authors: Caron A. P. , Huettner D. J. , Ragle J. L. , Sherk L. , Stengle T. R.
Published: January 2005

Proton and fluorine NMR data in NH4BF4 and its totally deuterated analog reflect the presence of isotropic and rapid BF4− tumbling as well as onset of isotropic NH4+ ion motion in the orthorhombic phase. A linewidth transition in the 19F spin system from 19±1 G2 at 133°K to 2.5±0.5 G2 at 198°K and 19F thermal relaxation times measured in ND4BF4 from 210° to 478°K yield a span of 19F correlation times from 3×10−4 sec (168°K) to 6.4×10−11 sec (472°K). The transition to the cubic modification at 472°K decreases the 19F correlation time to 2.6×10−12 sec (478°K). Above 318°K, fluorine relaxation in NH4BF4 is dominated by intraionic dipolar interactions, while below this temperature cross relaxation with protons located on neighboring ammonium ions becomes evident. Deuteration removes this contributor to the 19F relaxation. The apparent activation energy for BF4− motion is slightly dependent upon temperature, and increases somewhat with increasing temperature. The pre-exponential factor associated with 19F correlation times above 318°K is abnormally small, possibly reflecting a decrease in the effective moment of inertia by mechanical coupling between BF4− motion and NH4+ motion. Crystallographic measurement of the orthorhombic unit cell parameters from 190° to 296°K shows rapid linear expansion of a and c axes in the range 190° to 260°K, with a marked decrease in the rate of variation of these axis lengths with temperature above 260°K. In the same temperature region a shallow proton T1 minimum is observed, which may be associated with the modification of NH4+ ion motion by lattice expansion or simply due to cross relaxation with the 19F spin system. Proton T1 data also show a shallow plateau at higher temperatures due to interionic dipolar coupling and the BF4− motion. The x-ray data suggest the possibility of a subtle crystallographic change at low temperatures. A small linewidth transition is observed for the proton spin system in the range 173°K (4.0±0.1 G2) to 223°K (2.9±0.1 G2) apparently associated with interionic dipolar coupling.