bluuebunny/crossref_metadata_2025 huggingface dataset:
Dipole Moments of Dimethylsiloxane Chains
Authors: Mark J. E.
Published: February 2004

A rotational isometric-state model with neighbor dependence is used to calculate mean-square dipole moments and their temperature coefficients for dimethylsiloxane chains (CH3)3Si[OSi(CH3)2]xOSi(CH3)3 over a wide range of molecular weight. Chain conformational energies required in the calculations are obtained from a previous analysis of the random-coil dimensions of dimethylsiloxane chains in the limit of large x. Calculated dipole moments are in very good agreement with recently reported experimental results for oligomers corresponding to x = 1, 2, 3, and 5, at 25°, 40°, and 60°C. A simple physical picture for the predicted values of the dipole moments and their temperature coefficients is provided. As is the case in the interpretation of the dimensions of these chain molecules, the features of paramount importance are the inequality of the bond angles about Si and O atoms and the lower energy of trans, relative to gauche, states about Si–O and O–Si skeletal bonds.
Triplet → Triplet Fluorescence of Rubrene in Solution
Authors: Yildiz Attilà , Kissinger Peter T. , Reilley Charles N.
Published: February 2004

An unusual delayed emission is reported for solutions of 5,6,11,12-tetraphenyltetracene (rubrene). The first triplet state of rubrene can be populated by sensitization with biacetyl or benzophenone. In flash-photolysis studies of the properties of this state, an anomalous emission was observed. The anomalous emission is interpreted as triplet→triplet fluorescence within the triplet manifold of rubrene. Various data in support of this emission mechanism are presented.
Quadrupole Hyperfine Structure in the Microwave Spectra of Phosphorous Trichloride and Phosphoryl Chloride
Authors: Nave C. R. , Weatherly T. L. , Williams Quitman
Published: February 2004

The quadrupole hyperfine structures of the low rotational transitions in P35Cl3 and PO35Cl3 have been examined. Calculations of the hyperfine splitting and the Stark effect in the J = 1→ 2 transition have been made and compared with the experimental results. Measurements of the separation of the two strongest hyperfine components yielded the values −53.3 ± 1.0 and −55.4 ± 1.2 Mc/sec for the P–Cl bond axis quadrupole coupling constants eqQ in the molecules P35Cl3 and PO35Cl3, respectively. The Stark effect in the J = 1 → 2 and J = 2 → 3 transitions was analyzed to obtain the values 0.56 ± 0.02 and 2.54 ± 0.04 D for the dipole moments of PCl3 and POCl3, respectively. A phase-lock klystron stabilization technique was used in recording the spectra to improve the resolution of the spectrograph.
Perturbations between Electronic States in Aromatic and Heteroaromatic Molecules
Authors: Hochstrasser Robin M. , Marzzacco Charles
Published: February 2004

The low-temperature electronic spectra of several aromatic azines in regions of nπ* and ππ* overlap are presented and compared. It is shown that transitions to the higher-energy state are generally quite diffuse compared with those to the lower. Comparisons are made with aromatic hydrocarbons where ππ* states overlap and aromatic carbonyl compounds where nπ* and ππ* states overlap. The factors which determine the severity of broadening of higher states are discussed. It is concluded that when two states of different orbital type are nearby, there is a more severe breakdown of the Born–Oppenheimer approximation. This breakdown is less severe if the two states are far apart or if the molecule has a similar geometry in both states. The presentation includes accounts of the low-temperature singlet–triplet and/or singlet–singlet crystal spectra or mixed-crystal spectra of pyrazine, 2.6-dimethylpyrazine, tetramethyl pyrazine, pyrimidine, pyridazine, quinoxaline, phenazine, and diazaphenanthrene. The spectra of derivatives of benzene, naphthalene acetophenone, and benzophenone are discussed.
Studies with the Mössbauer Effect of the Formation of Xenon Bromides in Beta Decay
Authors: Perlow G. J. , Yoshida Hiroyuki
Published: February 2004

The reaction IBr2−129→βXeBr2129 has been observed for a pure sample of the potassium salt by use of the Mössbauer effect of the 39.48-keV gamma ray of 129Xe. With the assumption of pσ bonding, the quadrupole splitting leads to a value of 0.41 electron transferred to each Br. This is to be compared with 0.52 to each Cl in XeCl2 and 0.72 to each F in XeF2. An impure KIBr2 source shows a qualitatively different velocity spectrum—either due to a distribution of unknown xenon halides or to a molecular rearrangement observed in the act of occurring. If the latter is correct, the linewidth gives a mean life τm ≈ 3.5 × 10−10sec for the rearrangement. A source of CsIBr2 gives a broad singlet spectrum with no trace of XeBr2. The line represents either atomic xenon or a cubic rearrangement product such as XeBr64− or XeBr42−. Evidence from data on recoilless fraction and isomer shifts somewhat favors atomic xenon as the product but is not completely conclusive.
Dynamics of Krypton Atoms in Clathrate by the Mössbauer Technique
Authors: Hazony Y. , Ruby S. L.
Published: February 2004

The temperature dependence of the mean-square displacement 〈x2〉 of the Kr guest atoms in the hydroquinone–Kr clathrates has been studied by the Mössbauer effect. The results show that at all temperatures the observed 〈x2〉 is about twice as large as can be accounted for by the “rattling” frequency observed in the far infrared. This implies that low lattice frequencies contribute substantially to the motion of the Kr atoms and therefore the system cannot be described solely in terms of the van der Waals “particle-in-a-box” model.
Valence Excited States of NH and CH and Theoretical Transition Probabilities
Authors: Huo Winifred M.
Published: February 2004

The electronic structure of the four lowest excited states of NH and CH was studied by means of single-configuration SCF calculations. The calculation located the singlet system of NH with respect to the triplet and predicted the location of the experimentally unknown a4Σ+ state of CH. A number of one-electron molecular properties was computed. The calculated electric dipole moments agreed well with experiment. The parameters for the hyperfine splitting of the ground state of CH was also calculated. The oscillator strengths computed for a number of transitions in NH and CH were shown to have order of magnitude accuracy only. The same situation is expected to hold in the calculation of oscillator strengths for other molecular systems with SCF wavefunctions.
Effects of X- and Γ-Ray Radiation on the Thermal Decomposition of Solid Orthorhombic Ammonium Perchlorate. II. Kinetics and Discussion
Authors: Herley P. J. , Levy P. W.
Published: February 2004

The experimental data obtained by thermally decomposing unirradiated and irradiated orthorhombic ammonium perchlorate in the temperature range 193°–238°C has been carefully analyzed. Most of this data consists of pressure vs time curves of the total evolved gas or that not trapped at −95°C or lower, obtained with powders and millimeter-size crystals. All of these curves can be described by the Avrami–Erofeyev equation. The increase in the acceleratory period rate, which is induced by, and is proportional to, x- or γ-ray irradiation prior to decomposition, can be attributed to the introduction of additional decomposition sites, an increase in the rate that each nucleus grows, or a combination of these. Independent microscopic examination of partially decomposed crystals also indicates that irradiation has increased the concentration of decomposition nuclei. In addition, the p vs t curve analysis shows that irradiation has increased the rate that potential decomposition sites are converted to active sites. The same activation energy, 28.4 ± 2.5 kcal mole−1, was obtained for both the acceleratory and decay periods from irradiated and unirradiated crystals. Irradiation also increases the duration of the acceleratory period, shortens the decay period, and reduces the induction period. In fact, the induction period I for irradiated NH4ClO4 can be described by the relation I = C1 − C2 log (dose). Taken together, these observations suggest that the same processes occur in both unirradiated and irradiated ammonium perchlorate, but the rate constants are increased by prior irradiation.
Magnetic Characteristics of Europium–Aluminum Intermetallics
Authors: Mader K. H. , Wallace W. E.
Published: February 2004

Bulk magnetic characteristics of EuAl2 and EuAl4 are reported for temperatures ranging from 4°–300°K and for field strengths up to 20 kOe. To evaluate the influence of electron concentration on the magnetic interactions a series of EuxLa1−xAl2 alloys, with x ranging from 0.1 to 0.8, was studied over the same interval of temperature and field strength. Between 50° and 300°K all samples exhibited Curie–Weiss behavior with an effective moment characteristic of dipositive europium. EuAl4, EuAl2, and Eu0.8La0.2Al2 become antiferromagnetic below 20°K, two types of antiferromagnetic order being indicated for the latter two intermetallics. Increasing the electron concentration by replacing Eu with tripositive La alters the interaction from predominantly antiferromagnetic to predominantly ferromagnetic as the electron concentration approaches 9. The change in sign of the interaction occurs at about 8.4 electrons per magnetic atom. Eu0.1La0,9Al2 and Eu0,2La0.8Al2 are ferromagnetic at 4°K with Eu moments of about 5 μB per formula unit. Eigenvalues of the spin–Hamiltonian are obtained for Eu++ in a site of tetragonal symmetry and used to interpret the saturation moments observed for the ferromagnetic ternaries and the deviations from Curie–Weiss behavior for EuAl2 and the (Eu, La)Al2 alloys. The bulk magnetic properties can be quite successfully accounted for on the basis of an over-all (Zeeman-like) splitting of 480°K.
Effect of Localized Lattice Vibration on the Matrix Spectra of Diatomic Molecules
Authors: Pandey Gopal Krishna
Published: February 2004

The effect of the interaction between the localized lattice vibrations and the rotational motion of a diatomic molecule trapped in rare-gas matrices on their matrix spectra is investigated theoretically. This results from the dependence of the crystalline field on the intermolecular separation. The instantaneous interaction between the molecule–rare-gas atom is expanded in powers of the displacements of the lattice points from their equilibrium positions, and then this is averaged over all the neighboring atoms. The resulting self-energy of the molecule is then treated as a perturbation to calculate the displacement of the rotational levels. Expressions for the resulting shifts in the frequencies of the rotational transitions are given and this has been calculated in some typical cases to demonstrate the importance of this coupling between the localized lattice vibrations and the rotational motion of the molecule in the matrix.
Proton NMR Relaxation Effects. Cross-Relaxation Processes in Pure Liquids
Authors: Brooks A. A. , Cutnell J. D. , Stejskal E. O. , Weiss V. W.
Published: February 2004

Spin–lattice relaxation in a liquid containing protons in two different molecular environments can proceed by three different routes. There is a route to relaxation associated with each of the environments resulting from interactions between protons within that same environment. The third route to relaxation results from interaction between protons in different environments and is called cross relaxation. In such a system, the total spin–lattice relaxation decay determined by pulsed NMR will be the sum of two exponentials. Three relaxation rate constants are derived from such data. When cross relaxation arises entirely from dipole–dipole interaction in the extreme narrowing limit, these rate constants may be associated with the three routes to relaxation. (The cross-relaxation rate can always be identified, regardless of the mechanism.) To illustrate such relaxation behavior and the methods for obtaining three independent relaxation rates, 1-phenylpropyne was studied as a function of temperature.
Analytical Treatment of Excluded Volume. III. Alternative Calculations of the Contacts Density in Chains
Authors: Alexandrowicz Z.
Published: February 2004

The excluded volume effect is expressed in terms of certain probabilities for segment contacts in the real chain, the derivation following a method recently described by Fujita et al. It is then assumed that these probabilities can be calculated from the Gaussian expressions for an “equivalent ideal chain.” On this basis an integral equation is derived for α(z), the asymptotic result being α5 ∼ z. While Fixman's theory [A], the author's previous theory [B], and the present theory [C] express the segment contacts in different ways, they have the common property of preserving the chain connectedness and of assuming contacts probability to be Gaussian. Dissimilar results are reached with the three theories and the reasons for the discrepancy are examined. It appears that the results obtained with the present theory [C], similar to [A] but in contradistinction to [B], do not agree with the original assumption of the contacts probability being Gaussian.
Effusion. III. Angular Number Distributions of Gaseous CsCl from Right-Circular Cylindrical Orifices into Vacuum
Authors: Adams J. Q. , Phipps T. E. , Wahlbeck P. G.
Published: February 2004

Angular number distribution in effusion is of concern to users of the Knudsen effusion cell, who frequently assume the validity of the Clausing theory. In this study a stationary surface-ionization detector in a high vacuum measured the angular number distribution of CsCl molecules effusing from a saturated vapor through a right-circular cylindrical orifice in the wall of a rotatable copper effusion cell. The variables were θ, the off-orifice-axis angle; D, the orifice diameter; L / D, the length-to-diameter ratio; and T, the effusion-cell temperature. Two orifices having D ≅ 0.28 mm were used, with respective L / D values of 0.49 and 1.3. For the short orifice, the range of p, the saturated vapor pressure, was 0.006–0.99 mm Hg, and that of T was 820°–1017°K; for the long orifice, p was 0.006–0.86 mm Hg and T was 820°–1010°K. At low T, where the Clausing theory was expected to be valid, the probability density P(θ), defined as the fraction steradian−1 effusing in direction θ, was in fair agreement with theory for θ > 35° for the short orifice and for θ > 20° for the long orifice. At θ near 0°, the largest deviations from the Clausing theory were observed. An unexpected deviation from theory was observed, namely, P(θ) at fixed θ showed fluctuation with the state of the gas. This fluctuation (1) had an L / D dependence, (2) was greatest at θ near 0°, (3) was least at θ near 45°, (4) was small but appreciable at θ near 90°, and (5) was reproducible upon cycling T and θ. High-pressure limits for molecular flow were found to be 2.1 > K (Knudsen number, ratio of mean free path to orifice diameter) >1.7 for the short orifice and 1.6 > K > 1.3 for the long orifice. In the transition region beyond the high-pressure limit of molecular flow, P(0°) decreased with increasing pressure for the long orifice, whereas P(0°) increased with increasing pressure for the short orifice, as did P(0°) for a near-ideal orifice.
Thermochemistry of Reacting Materials
Authors: Bowen Ray M.
Published: February 2004

This paper is concerned with the formulation of a thermomechanical theory of a mixture of chemically reacting materials without diffusion. The independent variables that influence the response of the mixture are assumed to be the temperature, the temperature gradient, the deformation gradient, the time rate of change of the deformation gradient, and the extent of reaction. The Clausius–Duhem inequality is used to derive a set of necessary and sufficient conditions that the constitutive functions must obey. Among these conditions are ones that determine the role of De Donder's chemical affinity in determining whether or not chemical reactions are present. In particular, a criterion is deduced that determines whether or not false equilibrium is possible. It is also shown under what circumstances vanishing of the chemical affinity is equivalent to vanishing of the reaction rate. The additional restrictions on the response of the mixture by the axiom of material frame—indifference and special types of material symmetry are also presented. It is also shown that if the free energy of the mixture satisfies a certain inequality, then any equilibrium state that has both a zero chemical affinity and a zero reaction rate is necessarily stable for chemical reactions taking place at constant temperature and deformation.
Thermodynamic Functions of Macroions of Rigid Core
Authors: Aono O. , Isihara A.
Published: February 2004

For a dilute system of macroions of rigid core a simple method is presented for the evaluation of the internal energy and other thermodynamic functions in the chain diagram approximation. The results, when expanded for high temperatures in dimensionless constants, are composed of terms representing the effects of the hard core only and those due to coupling between the hard core and the Coulomb force.
Molecular Charge Distributions and Chemical Binding. III. The Isoelectronic Series N2, CO, BF, and C2, BeO, LiF
Authors: Bader R. F. W. , Bandrauk A. D.
Published: February 2004

The chemical binding and properties of the two isoelectronic series N2, CO, BF, a 14-electron series, and C2, BeO, LiF, a 12-electron series, are discussed in terms of the molecular charge distributions and the forces which they exert on the nuclei. It is found that the formation of the chemical bond in the 14-electron series results in a transfer of charge from the bonding to the nonbonded regions of both nuclei in the molecule, the amount transferred increasing with the increasing asymmetry of the nuclear potential field. The larger and more diffuse nonbonded charge increase on B in BF as compared to that on C in CO suggests that BF may be superior to CO in its ability to act as a ligand in metal complexes. The increasing asymmetry of the potential field in the 12-electron series results in a parallel increase in the asymmetry of the molecular charge distributions. Unlike the 14-electron series, the charge transfer in BeO and LiF is unidirectional. The Δρ(ε, η) or density difference contour maps [ρ(molecule) − ρ(atoms)] show that the atomic densities of atoms which employ p orbitals in their bonding exhibit a large quadrupole polarization. The Δρ(ε, η) maps for BeO and LiF indicate that the radial excitations of the pσ charge density of O and F, predicted by Sternheimer antishielding theory, are quenched by the exchange repulsions with the residual core densities on Be and Li.
Relaxation of the Molecular Charge Distribution and the Vibrational Force Constant
Authors: Bader R. F. W. , Bandrauk A. D.
Published: February 2004

The force constants are calculated from Hartree–Fock wavefunctions for the molecules N2, CO, BF (isoelectronic with 14 e−), and BeO, LiF (isoelectronic with 12 e−) by a polynomial fit of the forces exerted on the nuclei as a function of the internuclear separation. The magnitude of the force constant and its variation through the two series of molecules are interpreted in terms of the relaxation of the molecular charge distribution which accompanies a displacement of the nuclei. It is found that the charge distribution of a covalently bound molecule relaxes in such a way as to facilitate the motion of the displaced nuclei. In a molecule with the characteristics of ionic binding, the relaxation of the charge density localized on the cation opposes the nuclear displacement while the charge density on the anion facilitates its nuclear displacement. The relaxations are illustrated in the form of density difference maps between the extended and equilibrium molecular charge distributions. Such relaxation diagrams show a striking correlation with density difference maps which depict the change in the atomic density distributions which result from the formation of a chemical bond. Thus the dominant characteristics of the relaxation, whether it opposes or facilitates the motions of the nuclei, may be inferred from a knowledge of the polarizations present in the static charge distribution when these polarizations are measured relative to valence-state distributions of the undistorted atoms.
Diffraction Pattern and Structure of the System Water–Ammonia at 4°C
Authors: Narten A. H.
Published: February 2004

The scattering of x rays from the free surface of liquid solutions of ammonia in water and of pure ammonia at 4°C has been analyzed. Intensity and radial distribution functions have been calculated for a model structure and compared with those derived from experiment. This model, similar to that proposed for liquid water, assumes an anisotropically expanded ice I structure, surrounded by a continuous distribution of distances, as an adequate description of the short-range order in these liquids. Occupancy of the large dodecahedral cavities typical for this structure was permitted. The model intensity and radial distribution functions are in quantitative agreement with those derived from experiment.
Force Constants and Dipole-Moment Derivatives of Molecules from Perturbed Hartree–Fock Calculations. I
Authors: Gerratt J. , Mills I. M.
Published: February 2004

General expressions for the force constants and dipole-moment derivatives of molecules are derived, and the problems arising in their practical application are reviewed. Great emphasis is placed on the use of the Hartree–Fock function as an approximate wavefunction, and a number of its properties are discussed and re-emphasised. The main content of this paper is the development of a perturbed Hartree–Fock theory that makes possible the direct calculation of force constants and dipole-moment derivatives from SCF–MO wavefunctions. Essentially the theory yields ∂φi / ∂RJα, the derivative of an MO with respect to a nuclear coordinate.
Force Constants and Dipole-Moment Derivatives of Molecules from Perturbed Hartree–Fock Calculations. II. Applications to Limited Basis-Set SCF–MO Wavefunctions
Authors: Gerratt J. , Mills I. M.
Published: February 2004

The perturbed Hartree–Fock theory developed in the preceding paper is applied to LiH, BH, and HF, using limited basis-set SCF–MO wavefunctions derived by previous workers. The calculated values for the force constant ke and the dipole-moment derivative μ(1) are (experimental values in parentheses): LiH, ke = 1.618(1.026) mdyn/Å, μ(1) = −18.77(−2.0±0.3) D/Å BH, ke = 5.199(3.032) mdyn/Å, μ(1) = −1.03(−)D/Å; HF, ke = 12.90(9.651) mdyn/Å, μ(1) = −2.15(+1.50) D/Å. The values of the force on the proton were calculated exactly and according to the Hellmann–Feynman theorem in each case, and the discrepancies show that none of the wavefunctions used are close to the Hartree–Fock limit, so that the large errors in ke and μ(1) are not surprising. However no difficulties arose in the perturbed Hartree–Fock calculation, so that the application of the theory to more accurate wavefunctions appears quite feasible.
Solution of the One-Dimensional Schrödinger Equation by the Method of Continued Fractions
Authors: Vescelius Lee , Neff Vernon D.
Published: February 2004

The one-dimensional Schrödinger equation is solved for a general polynomial type of potential function by the method of continued fractions. The inherent computational difficulties of the problem are overcome by the use of a digital computer. Energy levels and matrix elements are reported specifically for the quartic oscillator and for a double minimum potential.
Charge Transfer between Positive Alkali Ions and Atoms
Authors: Gentry W. R. , Lee Yuan-tseh , Mahan Bruce H.
Published: February 2004

The total cross sections for resonant charge exchange have been measured as a function of energy in the range from 10 to 500 eV for the Cs+–Cs, Rb+–Rb, and K+–K systems. The agreement with certain data obtained at higher energies for these systems and with theoretical cross sections of Smirnov is satisfactory.
Lattice Models of Hard-Core Molecules with Attractions: The Phase Diagram
Authors: Orban J. , Van Craen J. , Bellemans A.
Published: February 2004

Two different lattice models of hard-core molecules with attractions are discussed. Both of them refer to a square lattice, and the excluded range around a molecule covers first-, second-, and third-neighboring sites. For Model I the attractive range corresponds to fifth neighbors only; for Model II it includes fourth neighbors as well as fifth neighbors, with a slightly more pronounced attraction on fourth neighbors. The exact properties of finite lattices 10 × ∞ are investigated by the matrix method for both models, and it is shown that they exhibit (at least) two phase transitions in some temperature range. These transitions are apparently first-order ones and seem to correspond to the gas–liquid and fluid–solid phase changes. Model I leads to a rather unphysical phase diagram similar to that of helium. On the other hand, Model II gives a phase diagram essentially similar to the one observed for simple classical substances.
Fluorescence and Phosphorescence of SO2 Vapor
Authors: Mettee H. D.
Published: February 2004

Stern–Volmer constants for SO2 fluorescence [Ã(1B1)→X̃1A1] for six optically exciting wavelengths (3130, 3020, 2960, 2850, 2750, and 2650 Å) show a regular decrease in going to shorter exciting wavelengths in the pressure range 1–1000 μ Hg. Due to earlier work by Douglas, it is inferred that the principal change is occurring in the fluorescence lifetime, which decreases accordingly. If electronic quenching takes place at every gas–kinetic collision, then any amount of vibrational relaxation which occurs prior to emission has a larger-than-gas–kinetic cross section. The fluorescence yields (Qf)λ go to unity at zero pressure, within liberal error limits, for all exciting wavelengths. The phosphorescence [ã(3B1)→X̃1A1] essentially disappears at pressures below 10 μ and does not originate from vibrationally excited triplet levels even at low pressures. The phosphorescence yields (Qp)λ pass through a minimum at an exciting wavelength of 2850 Å, and the corresponding values at the exciting wavelength extreme are about the same.
Bis(Thiosemicarbazone) and Other Nitrogen and Sulfur Ligated Complexes of Copper(II)
Authors: Blumberg W. E. , Peisach J.
Published: February 2004

We have measured the electron paramagnetic resonance and optical absorption properties of several complexes of copper(II) in which the ligands of the copper atom are two nitrogen and two sulfur atoms. Chelate structures varying from two saturated rings to a three-condensed-ring pseudoaromatic system have been explained. The effect of different degrees of protonation of the chelate rings has been investigated. The experiments show that, apart from varying the magnitude of the nitrogen superhyperfine interaction, these variables do not significantly affect the magnetic properties of the Cu(II), except for one case where protonation promotes dimerization. The relevance of these chelate structures to the unique Cu(II) sites in the copper-containing proteins is discussed.
Vibrational Spectra of IF7 and ReF7
Authors: Claassen Howard H. , Gasner Earl L. , Selig Henry
Published: February 2004

Raman spectra of IF7 and ReF7 have been observed for the first time in the vapor state. Infrared spectra of the vapors have also been re-examined. Earlier difficulties regarding possible coincidences in the IF7 spectra have been removed. The data suggest that both molecules belong to symmetry group D5h, although there are some significant as yet unexplained differences between them.
Effect of Molecular Identity on Two-Temperature Potentials
Authors: Linder Bruno , Kromhout Robert A.
Published: February 2004

The potential of interaction between molecules at different temperatures is analyzed from a fundamental point of view, starting with the equation of motion of the quantum-statistical operator. A simple model is utilized taking account of the interaction of two molecules with each other and with their respective heat baths. It is shown that the matrix elements of the statistical operator depend generally on the coupling with the two heat baths. Canonical distributions are recovered in several limiting cases. In case of nonidentical particles the distributions are canonical to first order in the intermolecular interaction. The free energy of interaction, defined as the isothermal work of polarization, is shown to be the same in this case as the adiabatic work to second order and the resulting interaction potential is correctly given by the reaction-field technique formulated previously. Canonical distributions are also obtained when the temperatures are high (classical limit) regardless of whether the interacting particles are identical or not. In case of near identity (e.g., isotopic species), very high temperatures are required to give the classical limiting forms.
Amine–Halogen Charge-Transfer Interactions: Vibrational Spectra and Intramolecular Potentials
Authors: Gayles J. N.
Published: February 2004

Spectral data are presented for three acceptor complexes of trimethylamine and for two of their perdeuteroisotopes over the range 33–4000 cm−1. Data were taken both at 300° and 83°K over the near-infrared region. This has allowed a complete assignment of all intramolecular motions and the discovery of several of the weaker lattice intercombination frequencies. Data are reported in all three cases for low-lying degenerate bending motions in the frequency range 33–80 cm−1. The revised assignments reported here have permitted a complete description of the skeletal intramolecular potential which predicts properly the observed isotope effects. The model proposed suggests a revision of previous considerations regarding force fields in charge-transfer complexes. In particular, it is necessary to account for skeletal stretch–bend interactions.
Magnetothermodynamics of Single-Crystal CuSO4·5H2O. IV. Properties over the Range 0.4°–4.2°K with Fields to 90 kG ‖ to the β Magnetic Axis
Authors: Giauque W. F. , Brodale G. E. , Fisher R. A. , Hornung E. W.
Published: February 2004

The heat capacity, magnetic moment, and entropy of CuSO4·5H2O have been measured in stabilized magnetic fields of 0, 1, 3, 5, 10, 20, 30, 50, 70, and 90 kG, over the range 0.4°–4.2°K. The field was directed along the β magnetic axis of a 3.700-cm-diam spherical single crystal. The heat capacity measurements show that the nuclear spin polarization at 90 kG is in equilibrium with the lattice at temperatures down to 0.75°K. The data are uncorrected for the demagnetizing effect of the spherical sample. Temperature-independent paramagnetism is much smaller than the diamagnetism as shown by a net temperature-independent susceptibility of −1.0 × 10−4 cm3/mole. The gyromagnetic ratio, gβ = 2.259, may be compared with our previously determined values gα = 2.081 and gγ = 2.269. The electronic entropy was found to be R ln 2 in agreement with previous work. Conditions during a temperature range in which equilibrium between the nuclear spin system and the lattice is lost are described.
Radiationless Transitions in Polyatomic Molecules. III. Anharmonicity, Isotope Effects, and Singlet-to-Ground-State Transitions in Aromatic Hydrocarbons
Authors: Siebrand W. , Williams D. F.
Published: February 2004

The work on Franck–Condon factors for radiationless transitions in polyatomic molecules, as reported in Parts I and II of this series, is extended and generalized, starting from the theoretical expression for Franck–Condon factors in aromatic hydrocarbons, which was derived and applied to triplet-to-ground-state transitions in Part II. The role played in this expression by the anharmonicity and symmetry of CH-stretching modes is clarified. As a preliminary step towards application of this expression to singlet-to-ground-state transitions in aromatic hydrocarbons, the appropriate Franck–Condon factors are studied spectroscopically by measuring the long-wavelength part of the fluorescence spectra of anthracene-h10 and -d10. These experimental Franck–Condon factors are used to determine the anharmonicity parameter in the theoretical expression for the singlet-to-ground-state radiationless-transitions rate constant. Theoretical rate constants for the transition calculated on this basis compare favorably with the scarce experimental data. They tend to justify the commonly made assumption that these transitions contribute a negligible amount (about 1% or less) to singlet decay in most simple aromatic hydrocarbons, but with some notable exceptions. Thus, for benzene and tetracene, and possibly also for coronene, contributions of about 10% are obtained, whereas in azulene and all of its known derivatives, the transition dominates the other decay processes of the first excited singlet state. The calculations also account qualitatively for the broadening of the first singlet absorption system and the anomalous fluorescence of azulenes. The isotope rule derived in Part I is corrected for anharmonicity. In its new form it does not account quantitatively for the observed deuterium effects. This indicates that CD-stretching modes, which are much less efficient in taking up electronic energy than CH-stretching modes, have about the same efficiency as some of the skeletal modes, so that these skeletal modes will contribute substantially to the Franck–Condon factors of perdeuterated aromatic hydrocarbons. The analysis of singlet-to-ground-state transitions leads to rate constants of 1013–1014 sec−1 for transitions between closely spaced electronic energy levels of the same multiplicity. Comparison with the results for triplet-to-ground-state transitions indicates a spin-prohibition factor of 108. The dependence of spin-prohibition factors on the energy of the electronic states involved in the transition is briefly discussed.
Formaldehyde Molecule in a Gaussian Basis. A Self-Consistent Field Calculation
Authors: Winter N. W. , Dunning Thom. H. , Letcher John H.
Published: February 2004

Accurate LCAO–MO–SCF calculations have been carried out for the formaldehyde molecule using (73/2) and (95/3) Gaussian basis sets. The energy parameters, molecular orbitals, dipole moments, and population analyses are reported. The results are compared to a previous calculation with a minimum Slater basis and to experiment.
Inadequacies of Viscosity Theories for B2O3
Authors: Macedo P. B. , Napolitano A.
Published: February 2004

The viscosity of B2O3 glass was measured from 1010–1014 P by the fiber-elongation method and found to be Arrhenius with an activation energy of 94 kcal/mol. These new data were combined with previously reported rotation data (101–1010 P) and gave a smooth plot. The complete viscosity data were used to test the equations of the best-known viscosity theories but no reasonable fits were found. Therefore, an examination of the validity of the basic assumptions underlying these theories was made. As a result of this study, it was found that the temperature dependence of the viscosity is not controlled by structural effects such as free volume, configuration entropy, etc., but by activation energy effects in the viscous flow process. The onset of the non-Arrhenius region is a direct consequence of the appearance of a symmetric distribution of relaxation times and/or a distribution of activation energies which cannot be explained by existing viscosity theories. Finally, all theories are in error in predicting that the viscosity goes to infinity (in the annealing region) much faster than the measured values indicate.
Crystal Structure of α-Fluorine
Authors: Meyer Lothar , Barrett C. S. , Greer Sandra C.
Published: February 2004

The crystal structure of α-fluorine, stable below 45.6°K, has been investigated from x-ray powder-diffraction patterns. Alpha fluorine is monoclinic, probably space group C2 / m, but space group C2 / c cannot be ruled out completely. There are four molecules per unit cell. At 23°K, the cell dimensions are: a = 5.50 ± 0.01 Å, b = 3.28 ± 0.01 Å, c = 10.01 ± 0.01 Å, β = 134.66° ± 0.02°. The unit-cell volume at 23°K is 128.4 Å3, the calculated density is 1.97 g/cm3, and the calculated molar volume is 19.3 cm3/mole. The structure is very similar to α-O2, the main difference being that the molecules are tilted, probably only by about 11° to alternate sides of the normal to the basal plane in alternate layers, leading to a doubling of the unit cell in the c direction as compared to α-O2. The fact that the unit cell contains four molecules admits the possibility of space group C2 / c with the molecules tilted out of the ac plane.
Rotational Zeeman Effect in Methyl Iodide
Authors: Hüttner W. , Flygare W. H.
Published: February 2004

We have observed the molecular (J) and nuclear (I) Zeeman effects in the strongly coupled (F) methy iodide molecule. The shielded g value of the 127I nucleus in methyl iodide is (1 − σ)gI = 1.1220 ± 0.0025 and the molecular g values parallel and perpendicular to the symmetry axis are g‖ = + 0.271 ± 0.015 and g⊥ = − 0.010 ± 0.002. An upper limit of | χ‖ − χ⊥ | = 20 × 10−6erg/G2·mole has been obtained for the magnetic-susceptibility anisotropy. Evidence is also presented on a possible observation of the magnetic-shielding anisotropy.
Molecular Collisions. VIII
Authors: Curtiss C. F.
Published: February 2004

The set of integral equations describing the molecular scattering process developed in the previous papers of this series is reformulated as a set of differential equations, in which the coupling is associated with a Hermitian matrix. Exact eigenvectors and eigenvalues of this matrix are developed. These eigenvectors may be used as the basis of a numerical solution of the equations. They also lead to an approximate solution which is valid when the difference of the wavenumbers in the entrance and exit channels is small. The approximate solution may be considered as the lowest-order term in a series development.
Calculated Collision-Induced Absorption Spectrum for He–Ar
Authors: McQuarrie D. A. , Bernstein R. B.
Published: February 2004

Computations (exact within the classical framework) are presented of the translational absorption spectrum for a model system of dissimilar rare-gas atoms chosen to simulate the He–Ar pair. The treatment makes use of the classical theory of Levine and Birnbaum. However, the procedure takes proper account of the nonlinear collision trajectories (evaluated on the basis of a realistic interaction potential derived from beam scattering experiments) and the theoretical form of the dipole-moment function (i.e., the ab initio computations of Matcha and Nesbet). The calculations reproduce the experimental (Bosomworth and Gush) line shape for He–Ar fairly well, provided the “dipole range parameter” is altered by some 7% from its ab initio value.
ESR and NMR of Mn(II) Complexes in Methanol
Authors: Levanon H. , Luz Z.
Published: February 2004

ESR spectra of Mn2+ in methanol solutions of Mn(ClO4)2 containing various amounts of LiCl, NaNCS, LiBr, LiNO3, and LiClO4 were studied. In all solutions, variations in the integrated intensity of the ESR signal upon addition of the electrolyte were observed. This effect was interpreted in terms of the formation of asymmetrically substituted octahedral Mn2+ complexes, in many of which the zero-field splitting interaction causes fast electronic relaxation and therefore an ESR signal too broad to observe. Some of the mixed solvent-anion complexes do however yield resolved ESR signals; in particular, a well-defined spectrum due to [Mn(MeOH)4(NCS)2] could be characterized. From the decrease of the ESR signal the equilibrium constants for the formation of monosubstituted octahedral complexes, [Mn(MeOH)5X]+, were estimated. The equilibrium constants for Cl−, NCS−, Br−, NO3−, and ClO4− are respectively >100, >100, 10, 5, and 1M−1. At high LiCl concentrations tetrahedral [MnCl4]2−, exhibiting resolved ESR lines, is formed. In the ESR spectrum of the system Mn(ClO4)2–LiCl–methanol there is, in addition to the intense sextuplet, also a very broad background signal which is attributed to the monochloro complex. From the over-all width of this signal an estimate of the zero-field splitting energy in this complex was made. Proton magnetic resonance measurements were made in methanol solutions of Mn(ClO4)2 containing various amounts of LiCl. There is a strong dependence of the proton linewidth on temperature and on LiCl concentration. The results were interpreted in terms of exchange of methanol molecules in and out of the solvation shells of [Mn(MeOH)6]2+ and the various mixed chloro complexes, but only for [Mn(MeOH)6]2+could a quantitative analysis be made. The kinetic parameters for the exchange reaction of this complex are 1 / τM(25°C) = 9.5 × 105sec−1 and ΔE‡ = 7.4 kcal mole−1. In the monochloro complex the exchange rate is about twice as high.
Librational Amplitudes: Raman and Nuclear Quadrupole Resonance Spectra of p-Dichlorobenzene and p-Dichlorobenzene-d4
Authors: Stidham Howard D.
Published: February 2004

Mean-squared angular amplitudes of vibration are calculated for a one-dimensional crystal model with torsional nearest-neighbor interaction. Vibrational modes with nonzero wave vector are all included in the averaging, and the effect is shown to be amplification of amplitude of magnitude dependent on the extent of interaction. Raman spectra for the 0–100-cm−1 region of crystalline p-dichlorobenzene and p-dichlorobenzene-d4 are reported and an assignment suggested for these librational fundamentals. Raman frequencies so assigned are used in an approximate calculation of the temperature dependence of nuclear quadrupole resonance frequencies of p-dichlorobenzene and the results compared with experiment. An interpretation is given of the result of Dinesh and Narasimhan for the nuclear quadrupole resonance frequency of HgCl2.
One-Electron Properties of Near-Hartree–Fock Wavefunctions. I. Water
Authors: Neumann D. , Moskowitz J. W.
Published: February 2004

Self-consistent-field calculations are reported for the ground state of the water molecule in a contracted and uncontracted Gaussian basis set. The uncontracted set is shown to be near the Hartree–Fock limit for water. One-electron properties were computed from both wavefunctions. Our best estimates for several of these quantities are: dipole moment, μz = 1.995 D; quadrupole moment, θzz = − 0.108 and θxx = − 2.422 in buckinghams; octupole moment, Ωxxz = − 1.337 and Ωzzz = − 0.960 in units of 10−34 esu·cm3; average diamagnetic shielding at the proton, σAvd = 102.9 ppm; quadrupole coupling constant at the deuteron, (eqQ / h)AA = 343.9 kc/sec, and at the oxygen, (eqQ / h)aa = − 8.34 Mc / sec. The effect of including d-type Gaussian functions in the basis is examined.
Spectroscopy and Mechanisms of the Photo- and Thermal Reactions of Photochromic Anils
Authors: Richey W. Frank , Becker Ralph S.
Published: February 2004

The principal emission from the salicylideneanilines, salicyclidene-2-aminoanthracene, and 2-hydroxynaphthylideneaniline is assigned as a fluorescence originating from a π, π* singlet state of a short-lived intermediate, cis†. The cis† arises as the first product of the photochemistry and is a species in which proton transfer has occurred but essentially retains the geometry of the enol tautomer. The cis† species, in the salicylideneanilines and salicylidene-2-aminoanthracene, converts to the final photocolored product. This final product is a nonequilibrium form of the true cis–keto tautomer. The latter is produced from the photocolored species by a thermal reaction. The cis–keto tautomer cannot be produced by a photoreaction from either the enol or the photocolored species. However, for the 2-hydroxy-naphthylideneaniline, the cis–keto tautomer is the final photocolored product from the enol. No photocolored products can be produced from the nitrosalicylideneanilines. Viscosity barriers are present that affect both the forward and reverse photochemical reactions for all molecules considered.
Infrared and Raman Investigation of Condensed Phases of Methylamine and Its Deuterium Derivatives
Authors: Durig J. R. , Bush S. F. , Baglin F. G.
Published: February 2004

The infrared spectra of solid and matrix-isolated methylamine, methylamine-d2, methyl-d3-amine, and methyl-d3-amine-d2 have been recorded from 4000 to 250 cm−1. The Raman spectra of the four isotopic species have also been recorded and depolarization values measured. The elusive NH2 twisting vibration has been located in the solid-phase infrared spectra of CH3NH2 and CD3NH2, and the assignment is in agreement with both the product rule and earlier assignments for this normal mode in hydrazine. A temperature-dependent hydrogen-bonding study has been carried out and ΔH° for H-bond formation in methylamine-d2 was found to be −660 cal/mole.
Fluctuation Theory and Critical Phenomena
Authors: Chandler David , Oppenheim Irwin
Published: February 2004

Singularities in equilibrium properties at critical points are related to the asymptotic forms of averages of products of ν(r), the deviation from the mean density at position r. Thus the forms of the singularities of the thermodynamic properties at the critical point can be obtained in a simple fashion from any theory that describes the forms of correlation functions like 〈ν(r1)ν(r2) 〉 for large r12. As a particular example of such a theory we use the Landau–Lifshitz fluctuation theory to obtain the results Cυ∼κ−1, KT∼κ−2, and ∼(T − Tc)1/2κ for T near Tc. We demonstrate that the predictions of the fluctuation theory are consistent in the sense that the prediction of the form of Cυ from four-particle correlations is the same as that obtained from a temperature integration of ∂Cυ / ∂T in terms of six-particle corrections.
Electron Correlation and the Nuclear Spin–Spin Coupling Constant. II. The Generalized Product Approximation with Intergroup Configuration Interaction
Authors: Barfield Michael
Published: February 2004

A generalization of a number of existing theoretical descriptions of contact nuclear spin–spin coupling is presented in terms of a density matrix formalism and the generalized product approximation. The recognition of distinct groups such as bonds, σ electrons, or π electrons by this method permits a simplification of the discussion of many electron systems, but for an adequate description of spin coupling in many cases in which there is more than one group, it is essential to introduce intergroup configuration interaction. The resulting theoretical expressions provide a generalization of those descriptions which use second-order perturbation theory and do not invoke the approximation of a “mean excitation energy” in the second-order perturbation sum. The applicability of the method is demonstrated for cases in which the groups are described by both molecular-orbital and valence-bond (VB) wavefunctions. Using VB wavefunctions, specific π-electron coupling constant results are reported for fragments of the butadiene and allene molecules. In the generalized product approximation, each of these fragments is described in terms of two groups of four electrons. Although considerably less computational effort is required by this method, the calculated results are in substantially good agreement with previous results based on eight-electron VB calculations. With the computational simplification provided by the generalized product approximation, theoretical results are obtained for the π-electron coupling between protons separated by from two to nine bonds in octatetraene.