bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonempirical Calculations on Excited States: The Ethylene Molecule
Authors: Dunning Thom. H. , McKoy Vincent
Published: January 2005

A series of nonempirical calculations are reported on the excited states of the ethylene molecule using a recent minimum basis set LCAO MO SCF wavefunction. For the lowest excited singlet state of ethylene (1B3u) the coupling between the π electrons and σ electrons is significant: the excitation energy being decreased from 11.98 to 10.17 eV and the oscillator strength from 1.03 to 0.73. This coupling has little effect on the triplet state. In the next higher approximation (the random-phase approximation) the excitation energy is further decreased to 9.44 eV and the transition moment to 0.51. With the use of accurate LCAO MO SCF wavefunctions, it is felt that the methods presented here will provide a basis for the theoretical interpretation of electronic spectra.
Vibrational Spectra of Molten Salts. II. Infrared Spectra of Some Divalent Metal Nitrates in Alkali-Metal Nitrate Solutions
Authors: Hester R. E. , Krishnan K.
Published: January 2005

Infrared spectra of thin films of Mg(NO3)2, Sr(NO3)2, Ba(NO3)2, Cd(NO3)2, and Pb(NO3)2, in molten KNO3 and equimolar KNO3–NaNO3 mixtures have been obtained over the spectral region 4000–200 cm−1. All the nitrates except those of Mg and Cd were in the anhydrous state. Even at temperatures of 300°C or more, the magnesium and cadmium nitrate melts retained small amounts of water. As the concentrations of the divalent metal nitrates were increased, some nitrate bands split, and new low-frequency lines were observed in some cases. These are located at 380 and 340 cm−1 for Mg(NO3)2 solutions, at 520 cm−1 for Cd(NO3)2, and around 420 cm−1 for Pb(NO3)2. The splitting of the ν3 line of free nitrate decreases in the order Mg2+>Cd2+>Ca2+>Pb2+>Sr2+>Ba2+. Except for Sr2+, this is the order of the ionic potentials. The observed bands are assigned and discussed in terms of complexes formed between metal and nitrate ions. Relative strengths of nitrate and chloride binding by Cd2+ and Mg2+ ions have been investigated by addition of Cl− ion to the mixed nitrate systems.
Radiolysis of Methane in a Wide-Range Radiolysis Source of a Mass Spectrometer. I. Individual and Total Cross Sections for the Production of Positive Ions, Negative Ions, and Free Radicals by Electrons
Authors: Melton Charles E. , Rudolph P. S.
Published: January 2005

The abundances of, and the total and individual cross sections for, primary products (positive ions, neutral species, and negative ions) resulting from elementary reactions induced by the absorption of energy by CH4 from ionizing radiation (100-eV electrons) have been measured. This was accomplished with the dual electron beam section of our wide-range radiolysis source. The results show that positive ions and free radicals are produced in nearly equal abundances, 45% and 55%, respectively. On the other hand, negative ions are less abundant by about four orders of magnitude. The total cross section for positive ionization (σI) by 100-eV electrons is 3.8×10−16 cm2 and that for the formation of neutral species (σN) is 4.7×10−16 cm2. To independently test the reliability of the dual electron-beam ion source, the total and individual cross sections for ionization of Ar by 100-eV electrons were measured for comparison with published values. Our value for the total cross section (σI) of 3.24× 10−16 cm2 is in satisfactory agreement with those reported by other workers, whose values range from (2.8 to 3.6)×10−16 cm2.
Shock-Tube Study of the Radiative Processes in Systems Containing Atomic Oxygen and Carbon Monoxide at High Temperature
Authors: Myers B. F. , Bartle E. R.
Published: January 2005

Absolute intensity measurements of the radiation emitted in systems containing atomic oxygen and carbon monoxide were made by shock heating gas mixtures containing O2, O3, CO, CO2, and Ar to pressures between 0.5 and 1.5 atm and to temperatures of 2679°±16°K and 2943°±26°K. The emission intensity was recorded as a function of time simultaneously in selected spectral intervals in the wavelength range between 2500 and 8000 Å. The absolute spectral intensity distribution for the radiative combination of O and CO was derived. Contributions to the measured emission intensity at wavelengths below 4500 Å by the radiative combination of oxygen atoms and by the radiation resulting from the electronic excitation of O2 were evaluated; at wavelengths greater than 7000 Å an unexpected rise in the emission intensity was found. The absolute spectral emission intensity for the O–CO combination was proportional to the concentration product, (O)(CO), at all wavelengths employed and at 2943°K, a rate constant of 3.80×105cm3 mole−1·sec−1 for the over-all radiative combination, O+CO→CO2+hv was calculated for the wavelength interval 2500 to 7200 Å. The activation energy for the radiative combination of O and CO was found to be 2.5±0.6 kcal mole−1 by combining the present results with low-temperature, discharge-flow-tube data over the common spectral interval between 3200 and 5000 Å; also, an activation energy of 31±12 kcal mole−1 was determined for the energy-transfer process CO2*+O2→CO2+O2*, where the starred quantities represent electronically excited molecules.
Hydrogen Bonding in Phosphonium Iodide: A Neutron-Diffraction Study
Authors: Sequeira A. , Hamilton Walter C.
Published: January 2005

A three-dimensional single-crystal neutron-diffraction study of phosphonium iodide, PH4I, has confirmed the presence of weak P–H···I hydrogen bonds in this system. Each iodine is surrounded by four hydrogen atoms at a normal van der Waals contact distance of 3.35 Å and four others at a hydrogen-bond distance of 2.87 Å. The P–H bond length is 1.414 Å (σ0.008 Å), and the P–H···I angle is 171.6°. The thermal motion parameters derived from the diffraction study lead to a predicted librational frequency of 246 cm−1 in comparison with a value of 335 cm−1 observed by Rush in a neutron-inelastic-scattering experiment. This agreement may be considered good in view of the fact that crystal energy calculations reported here indicate that the barrier to rotation is possibly extremely anharmonic with a very high barrier height. That the potential curve is dominated by the repulsive term rather than the electrostatic term is strong evidence that the hydrogen bond is weak.
Raman Spectra and the Structure of Molten Stannous Chloride and Molten Mixtures of Stannous Chloride and Potassium Chloride
Authors: Clarke J. H. R. , Solomons C.
Published: January 2005

The Raman spectra of molten and crystalline stannous chloride and molten mixtures of stannous chloride and potassium chloride were measured at temperatures from 250° to 600°C. The results indicate that chain polymers of the type (SnCl2)n [with 3 coordination of Sn(II)] predominate in pure molten stannous chloride over a wide temperature range. The spectral changes observed on increasing the mole fraction of potassium chloride in the mixtures from 0 to 0.66 are interpreted as the result of gradual depolymerization with the ultimate formation of pyramidal SnCl3− ions.
Calculation of Magnetic Susceptibilities of Diatomic Molecules. VIII. Anisotropies and Rotational Magnetic Moments
Authors: de la Vega J. R. , Hameka H. F.
Published: January 2005

We evaluate the rotational magnetic moments and the anisotropies in the diamagnetic susceptibilities for a series of diamagnetic molecules from recently obtained susceptibility values. The molecules are Li2, Be2, C2, N2, F2, LiH, BH, HF, CO, BF, and LiF. Our results agree well with the experimental values except in the case of F2.
Enthalpies of Formation and Bond Energies of Some Fluoramines
Authors: Sinke G. C. , Thompson C. J. , Jostad R. E. , Walker L. C. , Swanson A. C. , Stull D. R.
Published: January 2005

From measurements of the enthalpies of explosion, the enthalpies of formation in kilocalories per mole of some fully fluorinated amines in the gas state were derived: F2C(NF2)2, −108.7; FC(NF2)3, −47.7; C(NF2)4, 0.5; FNC(NF2)2, 23.0; (F2N)2 CFNFCF(NF2)2, −84.4. The deviation of these values from those calculated from standard bond-energy terms is discussed.
On the Evaluation of Rate Coefficients from Limited Cross-Section Data
Authors: Hochstim A. R. , Shuler K. E.
Published: January 2005

An analysis is presented of the error involved in calculating rate coefficients from cross-section data in a limited energy range. For reactive cross sections of the form σ(E) = a(E—E*)n exp[—b(E—E*)], where E is the relative kinetic energy and E* is the threshold energy, it is shown that an upper bound on the error can readily be derived in terms of the parameters n, b, and E′—E*, where E′ is the largest kinetic energy for which σ(E) has been determined. For cross sections which can be represented by a polynomial of degree N in the range E* to E′, the m-point Laguerre integration formula yields exact results for the rate coefficient for m≥½(N+2), and also provides the criterion for the required energy range E* to E′.
Polarizations of the Low-Energy Sn←S Transitions in 9,10-Anthraquinone
Authors: Drott H. R. , Dearman H. H.
Published: January 2005

The polarizations of the transitions to the lowest n—π* and three π—π* singlet states of 9,10-anthraquinone have been measured relative to that of the phosphorescence by the method of photoselection. Assuming that the n—π* and two π—π* transition moments lie in the molecular plane and utilizing the previous result that the T1←S0 transition moment is parallel to the carbonyl axes (Z), the n—π* absorption is found to be polarized along Y and the first three π—π* transitions along Y, Z, Y, respectively. Y is the axis in the molecular plane perpendicular to the carbonyl axis. The ordering of the π* states is compared with the predictions of the two available SCF calculations and with the predictions of the Platt spectroscopic moment theory.
Vibration Frequencies of NO2− and NO3− Ions in KBr Crystals
Authors: Kato R. , Rolfe J.
Published: January 2005

Infrared-absorption spectra of doped KBr crystals at temperatures of approximately 8°K were measured in the wavelength range 2 to 15 μ. From the absorption spectra of crystals doped with NO2− and NO3− ions, and with ions enriched in the isotopes 15N and 18O, frequencies of normal vibrations of six isotopic NO2− molecules, and eight isotopic NO2− molecules were determined. These frequency values were used to calculate a set of force constants for NO2− and NO3− ions in the KBr lattice, using the most general harmonic force field (GFF). In mdyn/Å units, values obtained for NO2− were: fr=7.50, frr=1.66, frα=0.39, fα=1.67, and for NO3−: fr=7.62, frr=1.43, (fα—fαα)=1.09, (frα—frα′)=−0 .48, fγ=1.506.

In crystals doped with divalent metal ions as well as NO2− and NO3− ions, new absorption bands appeared. These were perturbations of the vibrational frequencies of NO2− and NO3− ions, caused by association between divalent metal ions and NO2− and NO3− ions. In the case of NO3−, the doubly degenerate asymmetric stretching band was split into two nondegenerate bands by the perturbation, which is thus almost certainly caused by a nearest-neighbor association between metal and nitrate ions. While the other frequency shifts of nondegenerate vibrations can give no information about the symmetry of the surrounding lattice, they can also be explained by a nearest-neighbor interaction between divalent metal and NO2− and NO3 ions.
Microwave Spectra of Nitrogen-Containing Molecules. II. Structure, Dipole Moment, Quadrupole Coupling Constants, and Barrier to Internal Rotation of N-Methyl Ethyleneimine
Authors: Harmony Marlin D. , Sancho Michael
Published: January 2005

The microwave spectrum of N-methyl ethyleneimine has been studied in the region 8 to 28 GHz, and the following rotational constants have been obtained for the ground state: A=16443.15 MHz, B=7219.84 MHz, C=6152.69 MHz. Stark-effect measurements led to dipole-moment components of μa=0.07±0.02 D μc=1.234±0.015 D, and a total dipole moment of 1.236±0.02 D. Internal rotation splittings were observed in the v=1 torsional state and gave a barrier to internal rotation of 3462±35 cal/mole. The quadrupole coupling constants of 14N in the inertial axis system were found to be: χaa=3.35, χbb=0.63, and χcc=−3.98±0.02 MHz. The molecular structure has been described, and the previously mentioned results have been discussed with regard to other existing data. A tentative estimate has been made of the quadrupole coupling constants in the field-gradient principal-axis system.
Corresponding Orbitals and the Nonorthogonality Problem in Molecular Quantum Mechanics
Authors: King Harry F. , Stanton Richard E. , Kim Hojing , Wyatt Robert E. , Parr Robert G.
Published: January 2005

Given any two sets of spin orbitals ai and bj, there exist equivalent sets âi and b̂j such that their overlap matrix is diagonal, i.e., 〈âi | b̂j〉=d̂iiδij. This is the basis of the corresponding orbital transformation of Amos and Hall. Their transformation is shown to have widespread application to quantum chemistry. It leads to a simple generalization of the Slater—Condon rules for the expectation value of an operator between two determinantal wavefunctions when the spin orbitals of one function have no simple orthogonality relationship to those of the other function. In the case of single-determinantal wavefunctions, use of the corresponding orbital transformation and the integral Hellmann—Feynman formula leads to a very simple expression for the energy difference associated with two similar configurations of a molecular system. Extensions to limited configuration interaction expansions are discussed. Given single-determinantal wavefunctions for two related molecular systems, it is shown that the corresponding orbitals are those which are most nearly molecularly invariant in the sense of maximum overlap. A comparison of the Pitzer—Lipscomb wavefunctions for the staggered and eclipsed forms of ethane reveals that six of the nine corresponding orbitals have an overlap of no less than 0.999998 in the two configurations. Use of the corresponding orbital transformation overcomes various computational difficulties encountered with Löwdin's cofactor method for treating the nonorthogonality problem.
On the Excess Helmholtz Function of Isotope Mixtures
Authors: Byrns F. Louise , Mazo Robert M.
Published: January 2005

It is observed that, if one represents the Helmholtz function of an isotopic mixture by that of a pseudosingle component system with mass m*=παmαxα, where the mα are the masses of the components, and the xα their mole fractions, a good approximation is obtained. The Helmholtz function of the pseudosingle component system is obtained via the quantal law of corresponding states. Plausible, though nonrigorous, theoretical arguments for the validity of this observation are presented.
Molecular-Orbital Studies of Intermolecular Interaction Energies. I. On the Role of π Electrons in Intermolecular Interactions, with Some Application to DNA
Authors: Rein Robert , Pollak M.
Published: January 2005

A semiemphirical method, based on molecular orbitals, is presented for the treatment of intermolecular interactions which involve π-electron systems, as is common in biopolymers. In the application of the method, a numerical analysis is performed on the interaction energy between the bases of a guanine—cytosine homo-dinucleotide. The computed values of the exchange, the electrostatic, the polarization, and dispersion energies are given for an interaction between base pairs in configurations corresponding to some of the possible occurences in DNA. The following conclusions are based on the numerical results. It is incorrect to assume that the π-electron systems of the two monomers are separable. It seems acceptable, for the purpose of a perturbation treatment, to confine the set of wavefunctions to the π orbitals. The interaction energy between more distant monomers is not negligible relative to the interaction between nearest neighbors. While the energy of attraction between π-electron systems is significant, it cannot constitute the dominant part of the energy required for the stabilization of the double-helix structure.
Mössbauer Spectra of Some Tetrahedral Iron (II) Compounds
Authors: Edwards P. R. , Johnson C. E. , Williams R. J. P.
Published: January 2005

The 57Fe Mössbauer-effect spectra of a series of tetrahedrally coordinated Fe(II) compounds of general formula R2FeX4 have been measured over a wide temperature range. The absorption showed approximately a tenfold increase on cooling from 300° to 4.2°K, showing that the effective Debye temperature for the Fe(II) ion is low. The isomer shifts (1.0–1.1 mm/sec relative to iron) and quadrupole splittings (2.7–3.3 mm/sec at 4.2°K) reflect the degree of covalency in the anions and their distortion from cubic symmetry. The distortion was present in all the compounds studied, and was dependent both upon the ligand X and the cation R. For large cations the temperature variation of the quadrupole splitting can be understood in terms of a static distortion which splits the dz2 and dx2—y2 states by an energy Δ, where, e.g., Δ=470 cm−1 for R2=(N,N′-dimethyl-4,4′-dipyridyl)++. For (NMe4)2FeCl4 the quadrupole splitting cannot be accounted for simply by a temperature-independent ligand field splitting Δ. Measurements of the spectrum in a magnetic field showed that the sign of the electric field gradient is negative and hence that the groundstate orbital is dz2. This corresponds to the distortion being a compression along the z axis. Magnetic-susceptibility measurements were in accord with a splitting of this orbital state according to the spin Hamiltonian H=D[Sz2−13S(S+1)] where D=+9.0 cm−1, and with g‖=2.05 and g⊥=2.27. The component of the hyperfine magnetic field perpendicular to the distortion axis z was found to be −27 kG.
Thermal Study of Groups II—IV Semiconductors. Lattice Heat Capacities and Free Energies of Formation. Heat Capacity of Mg2Si from 15°—300°K
Authors: Gerstein B. C. , Jelinek F. J. , Habenschuss M. , Shickell W. D. , Mullaly J. R. , Chung P. L.
Published: January 2005

The heat capacity of Mg2Si has been measured from 15° to 300°K, and the lattice heat capacity, Debye temperature, and thermodynamic functions have been tabulated. The following values were found for the thermodynamic functions at 298.15°K: S°298.15=75.799 J (gfw·deg)−1, — (G°298.15—H°0)/T=33.830 J (gfw·deg)−1. A third-law ``reasonability check'' was made on a recently published heat of sublimination. A reduced temperature plot of Mg2Si, Mg2Ge, and Mg2Sn using the 0°K Debye temperature as the reducing parameter is used to predict the entropy of Mg2Pb at 273°K. The standard free energies of formation at 298°K are calculated for Mg2Si, Mg2Ge, Mg2Sn, and Mg2Pb and compared with previously published results. The relative stabilities of the compounds with respect to the elements are discussed.
Electron Paramagnetic Resonance of Mn(II) Complexes in Acetonitrile
Authors: Chan Sunney I. , Fung B. M. , Lütje Hans
Published: January 2005

Electron paramagnetic resonance has been observed for the systems (a) Mn(ClO4)2–Et4NClO4, (b) MnCl2–Et4NCl, and (c) MnBr2–(n-C4H9)4NBr in acetonitrile. EPR intensity measurements, linewidths of the hyperfine components, electrical conductance, and optical spectra have been used to characterize the species exhibiting the paramagnetic resonance as [Mn(CH3CN)6]++, [MnCl4]=, and [MnBr4]=. The 〈g〉 values and hyperfine interaction constants 〈A〉 for these complexes were determined to be: 〈g〉|〈A〉|G [Mn(CH3CN)6]++  2.003±0.00192±1 [MnCl4]=          2.007±0.00179±1 [MnBr4]=          2.008±0.00175±1.
Molecular Relaxation in a Fluctuating Environment
Authors: Anderson J. E. , Ullman Robert
Published: January 2005

This paper relates the symmetric and asymmetric correlation-time distributions found in various relaxation experiments to one another, and to the single correlation time. The reorientation probabilities of the individual molecules are taken as functions of an environmental parameter, loosely termed the ``free volume,'' which is presumed to fluctuate with time. This treatment leads to a symmetric correlation-time distribution when the rate of ``free-volume'' fluctuation is much less than the various rates of molecular reorientation; an asymmetric distribution when these rates are comparable; and a single correlation time when the rate of fluctuation is much larger than the rates of reorientation.
Test of Adam—Gibbs Liquid Viscosity Model with o-Terphenyl Specific-Heat Data
Authors: Greet R. J. , Turnbull D.
Published: January 2005

A differential scanning calorimeter has been used to determine the latent heat of fusion of o-terphenyl, 4.40±0.07 kcal/mole, the entropy of fusion, 13.4±0.2 cal/mole·°K, and the specific heat of the liquid, glassy, and crystalline states from 220°K to the melting temperature, 328.7°K. The constants of the Adam—Gibbs liquid viscosity model have been chosen to match the magnitude and slope of the experimental viscosity at the melting temperature (the highest temperature of directly measured configurational entropy) and also at −16°C (the lowest temperature of directly measured shear viscosity). Within this temperature range, the temperature dependence of viscosity predicted by the Adam—Gibbs model is compared with the measured temperature variation.
Fractionation of Boron Isotopes between Boron Trifluoride and Its Molecular Addition Compounds
Authors: Palko A. A. , Drury J. S.
Published: January 2005

Boron trifluoride adds to many Lewis bases to form 1:1 molecular addition compounds. Under favorable conditions, some of these adducts may be used to fractionate the isotopes of boron by means of the following reaction: Donor·11BF3(l)+10BF3(g)=Donor·10BF3(l)+11BF3(g).The equilibrium constants for this reaction vary with donor, donor substituents, and temperature. At 30°C the following order is observed: (C2H5)2S> (CH3)2S>(CH3)2Se>(C4H9)2S>(C2H5)2O>C6H5OCH3>(CH3)2O≥(CH2)4O>C6H5OH>(C2H5)3N. The ``anomalous'' concentration of boron-10 in the molecular addition compound may be explained by the unique chemistry of the boron and fluorine atoms. A model is proposed which accounts for observed variations in the isotopic fractionation factor when different donors are used, as well as when different substituents are present on a selected donor. The model also explains the isotopic behavior of other boron halides.
Ground State and Main Spectroscopic System of the Nitrogen-Molecule Positive Ion
Authors: Verhaegen G. , Richards W. G. , Moser C. M.
Published: January 2005

The ground state and first excited state of the nitrogen-molecule positive ion are calculated using the matrix Hartree—Fock approximation, which results in a reversal of the observed spectroscopic order of states. The inclusion of estimates of correlation-energy differences between the levels corrects this and leads to a calculated term value of the excited state (1.17 eV) in extremely close agreement with experiment (1.16 eV).
Interchange Symmetry. I. Molecules, Crystals, and Excitons
Authors: Kopelman Raoul
Published: January 2005

The interchange-symmetry concept for molecules and crystals is introduced. In a molecule it is the minimal symmetry establishing the physical equivalence among a given set of its constituent fragments (nuclei or collections thereof). In a crystal it is a minimal symmetry establishing the physical equivalence among a set of constituents (atoms or molecules) within the unit cell. The chief application of the interchange symmetry in this paper is for the classification of eigenstates and the interpretation of spectroscopic data encountered in investigations of molecular crystals. The existence of n-1 pure, inequivalent, interchange elements in ideal crystals is proven group theoretically, where n is the number of molecules or atoms per primitive unit cell. The relations among interchange symmetries and interchange groups, site groups, unit cell groups, translation groups and space groups are discussed. These are related to crystal splittings, intermolecular coupling constants (including signs), selection rules and exciton theory (including k≠0). Examples: the benzene molecule (Höckel theory), the benzene, naphthalene, and anthracene crystals (exciton coupling constants and their signs), methyl halides, N2, CO, and CO2 crystals (interchange splittings), and the CS2 crystal (ground and distorted excited state). Nonhexagonal benzene and its energy splittings is the example in a separate chapter on isotopically substituted molecules that get distorted in excited states and/or in condensed phases like matrices and crystals.
Paramagnetic Relaxation of Triplet Molecules Randomly Oriented in a Rigid-Glass Matrix
Authors: Brown I. M. , Sloop D. J.
Published: January 2005

Investigations have been made of the paramagnetic relaxation of the triplet molecules zinc 2,2′-biquinoline randomly oriented in a rigid-glass matrix of 2-methyltetrahydrofuran. The saturation and relaxation behavior of these molecules is qualitatively consistent with the inhomogeneous nature of the ΔM=1 line-shape. The relaxation times are such that a hole burned in the line can recover by spin—lattice relaxation and by cross relaxation to adjacent spin packets. The temperature dependence of the spin—lattice relaxation time is given by T1−1=1.37×105 exp(−22/T)+2.94T2.

We interpret the exponential as indicating an Orbach process between the ground-state triplet and the first excited singlet. The Orbach exponent implies that the triplet—singlet separation, which is determined by the value of the intramolecular exchange integral, is 15.5±1 cm−1. An expression for T1 similar to that derived by Scott and Jeffries has been used to identify the dominant interaction participating in this process. From crude estimates of the spin-vibronic matrix elements it seems unlikely that this interaction is large enough to account for the experimental value of T1=1.3 msec at 4.2°K. The only interactions which are large enough to explain this value are second-order vibronic effects which involve singlet—triplet mixing through static spin—orbit coupling. At this time we can offer no explanation of the T2 dependence which predominates below 2°K.
Thermodynamic Temperature and Heat Capacity of NiSiF6·6H2O without Heat Introduction below 0.35°K. Magnetic Moment and Internal Energy from 0.05° to 4.2°K. Fields 0–90 kG Perpendicular to the c Axis
Authors: Giauque W. F. , Hornung E. W. , Fisher R. A. , Brodale G. E.
Published: January 2005

Values of the magnetic moment of a 3.5-cm-diam spherical single crystal of NiSiF6·6H2O have been determined over the range 0.3°—4.2°K and 0–90 kG. The field was perpendicular to the c crystallographic axis. The differential isothermal magnetic susceptibility and the isothermal work of magnetization are given. The data have been combined with our previous related measurements of heat capacity and entropy to evaluate the changes in internal energy and enthalpy. All of the data apply to a spherical crystal without correction for the demagnetizing effect. The temperature-independent magnetic moment was estimated as 3.4×10−4H G·cc/mole from the high-field observations. Using this value to correct the data, ga,b=2.233, and a similar correction of our previous data with H ∥ c axis gives gc=2.241 for the temperature-dependent moment. Measurements of magnetic moment as a function of field on 40 adiabatics have been used to extend the thermodynamic temperature and heat capacity below the region of heat introduction, thus avoiding problems of thermal contact and thermal conductivity at very low temperatures.
Upper and Lower Bounds on the Second-Order Energy Sum
Authors: Goodisman Jerry
Published: January 2005

Modifications of well-known procedures allow the generation of hierarchies of upper and lower bounds to the second-order energy of perturbation theory. Our results are extremely good for the polarizability of H, fair for the H–H van der Waals interaction, and discouraging for the He interelectronic repulsion.
Field Inhomogeneity Correlation Effects in Nuclear Magnetic Double-Resonance Detection of Very Small Spin Coupling Constants
Authors: Freeman R. , Gestblom Bo
Published: January 2005

Double-irradiation techniques may be used to detect nuclear magnetic resonance splittings that are so weak as to be obscured by the broadening due to spatial inhomogeneity of the applied magnetic field. The basis for these experiments is the fact that the observable double-resonance effects result from interactions on the molecular scale (such as spin—spin coupling) with the result that the two nuclear sites, A and X, experience almost exactly correlated local fields due to nonuniformity of the applied magnetic field. One such correlation effect is the partial compensation of field inhomogeneity broadening of lines that are regressively connected to the irradiated line. A second correlation effect may be observed if the intensity of a given line with a radio-frequency field so weak that its influence is restricted to sample regions very close to the resonance condition. A comparative study of double irradiation methods based on these effects has been carried out by applying them to the problem of resolving the 0.05-Hz splitting in the 60-MHz proton magnetic resonance spectrum of 3-bromothiophene-2-aldehyde, attributed to long-range spin coupling of the aldehyde proton with the ring proton at Position 4.
Theory of Saturation and Double Resonance Effects in ESR Spectra. III. rf Coherence and Line Shapes
Authors: Freed Jack H. , Leniart Daniel S. , Hyde James S.
Published: January 2005

The theory of saturation in the electron spin resonance spectra of dilute solutions of free radicals has been employed to analyze in detail several possible effects in ENDOR spectra that are due to the coherent nature of the applied nuclear rf and microwave fields. These effects are implicitly contained in a ``coherence matrix,'' although their observation also depends on the details of the relaxation terms. It is shown that (1) strong nuclear rf fields can split ESR lines, a phenomenon similar to ``spin-tickling'' in NMR double resonance, (2) strong microwave fields in the presence of weaker, but saturating, nuclear rf fields can split ENDOR lines, and this latter effect is demonstrated experimentally. A subtle coherence effect requiring nuclear spins of I>½, or more than one equivalent spin of I=½, and dependent upon nuclear rf field strength is carefully analyzed. It is predicted to significantly affect only the ENDOR line obtained from saturating the M = 0 hyperfine line for two or four equivalent protons. The theory for this effect appears to be in very good agreement with detailed experimental studies on Coppinger's radical. Other radicals are also found to exhibit such coherence effects. The ability to distinguish and analyze them is deemed important in applying ENDOR as an analytical tool. Computer simulations of the line shapes in the presence of coherence effects are also presented.
Application of the NMR Method to Rotational Isomerism. Limitations Revealed by Temperature-Dependent Studies on CHBr2–CFBr2
Authors: Govil G. , Bernstein H. J.
Published: January 2005

NMR and thermodynamic parameters for the two rotational isomers of CHBr2–CFBr2 have been obtained from their low-temperature 1H and 19F spectra. The results are in variance with those obtained from the conventional method which utilizes the temperature dependence of the time-averaged spectra at higher temperatures. Limitations of the second method have been discussed. The signs of the coupling constants in the two rotamers have been established.
Ultrasonic Determination of Rotational Collision Numbers and Vibrational Relaxation Times of Polyatomic Gases at High Temperatures
Authors: Carnevale E. H. , Carey C. , Larson G.
Published: January 2005

An ultrasonic method has been used in experimentally determining the rotational collision numbers, and vibrational relaxation times of polyatomic gases at high temperatures. An ultrasonic (∼1–3 MHz) pulse method has been used to measure both sound velocity and sound absorption in nitrogen, oxygen, and carbon dioxide in the temperature range of 300°—1300°K. All of the measurements were obtained at a pressure of one atmosphere. Vibrational relaxation times of carbon dioxide have been determined from the sound absorption measurements from 300° to 1300°K. Rotational collision numbers have been obtained as a function of temperature in oxygen and nitrogen and are in reasonable agreement with the theoretical values given by Parker. This agreement has established that the transport properties of nondissociated diatomic molecules (homonuclear) can also be determined from ultrasonic measurements.
Nonadditive Interactions between Molecules in a Statistical Treatment of Dilute Gases
Authors: Baer Shalom
Published: January 2005

A dilute gas is treated by the method of diagrammatic perturbation expansion for a system of electrons and nuclei. A reinterpretation of the diagrams in terms of interacting molecules leads to their re-expression as functionals of intramolecular particle correlation functions. The first-order diagrams depend on the single-electron and electron-pair distributions in the molecule.
Use of the WKB Method for Obtaining Energy Eigenvalues
Authors: Krieger J. B. , Lewis M. L. , Rosenzweig C.
Published: January 2005

A simple, general method is derived for evaluating the second- and third-order WKB energy integrals by rewriting the integrals having nonintegrable singularities in terms of derivatives, with respect to the energy, of integrals having integrable singularities. As an example, it is shown that the higher-order WKB integrals vanish for the one-dimensional linear harmonic oscillator. A calculation of some eigenvalues using this method is made for potentials of the form V(x)=λx2ν and the results are compared to the ``exact'' results obtained from a numerical integration of the Schrödinger equation. It is observed that inclusion of the third-order integral improves the accuracy of WKB eigenvalues.
Molecular-Orbital Calculation of 10Dq in Some Transition-Metal Fluorides
Authors: Offenhartz Peter O'Donnell
Published: January 2005

Using the ionic Hamiltonian model, the antibonding orbital separation 10Dq has been calculated for the tripositive metal hexafluorides CrF63− and FeF63−, and for the dipositive metal hexafluoride NiF64−. The calculated 10Dq is found to be about half of the experimental value in all three cases. Isotropic and anisotropic spin densities at the fluoride nuclei have also been calculated; the agreement between theory and experiment is poor in all cases. The results are discussed in the light of the approximations made in the ionic Hamiltonian model. A comparison of the present molecular-orbital method with the configuration-interaction approach of Hubbard et al. is given; it is shown that molecular-orbital theory is capable of taking into account all relaxation and polarization effects included in the configuration-interaction approach.
Theory of Diffusion-Controlled Processes. II. Consideration of Conceptual Framework
Authors: Yguerabide Juan
Published: January 2005

The fundamental concepts and equations used in describing diffusion-controlled processes in liquids are defined and analyzed in terms of the behavior of an ensemble of reacting molecules. Rate equations are derived and written in forms familiar in reaction kinetics. The physical meaning of the various forms of these equations is discussed in terms of a priori and a posteriori probabilities. The probabilistic equations are also expressed in terms of particle concentrations; the measurables of experiments, in reaction kinetics. The final equations constitute the correct formal description of the reaction of molecules in liquids under conditions explicitly specified.

The results derived here are compared with those of a previous paper in which the macroscopic behavior of a system of reacting molecules is expressed in the form of a power series derived from consideration of molecular diffusion and microscopic molecular distribution. It is shown that the fundamental rate equation previously used is only approximately correct and that higher-order terms of the power series arise from the approximate nature of the rate equation.
Excitation of Nitrogen Gas by Fission Fragments along the Entire Track
Authors: Sears John T. , Rodgers Robert
Published: January 2005

Luminescence produced in nitrogen in small segments of the tracks of fission fragments was studied with a pulse technique. The amount of formation of the C3πu state of nitrogen per unit distance, L*, was measured over the entire path length of the low-mass fragment group as a function of track length. The energy loss per unit distance dE/dr can be approximated by L* over the entire fission fragment path length. The observance of light produced from the second positive group (C3πu→B3πg) near the end of the track, despite a major change in the primary mode of energy deposition by the fission fragments, indicates that a more detailed theory of chemical production from the deposition of energy by a heavy charged particle needs to be formulated in the regime of nuclear elastic collisions which exists at the end of the particle's range.
Line Shape and Collision Effects in the Microwave Wing of Far-Infrared Rotational Lines
Authors: Maryott A. A. , Birnbaum George
Published: January 2005

The microwave absorption very far in the low-frequency wing of the pure rotational spectra of HCl, DCl, and HBr has been measured in order to investigate the applicability of pressure-broadening theory in the region many linewidths removed from the resonant frequencies. Data for mixtures of HCl and HBr with the foreign gases He, H2, Ar, N2, CH4, C2H6, CO, SF6, and CO2 are also reported. Experimental results are compared with the Van Vleck—Weisskopf equation, which is used to indicate an upper limit of the absorption. Data for the mixtures with He and H2 are in accord with this line shape. Data for the remaining mixtures and the pure gases are not in agreement, the observed absorption being from 2 to 8 times greater than predicted. These results suggest the presence of an additional absorption region which is centered at a lower frequency than the normal rotational spectrum and which may be attributed to interacting molecular pairs.
Difference Bands in the Raman Spectrum of Carbon Tetrachloride
Authors: Kenney J. T. , Powell F. X.
Published: January 2005

The difference bands of carbon tetrachloride are analyzed and it is found that, in the Raman spectrum at room temperature, the complex at 775 K is essentially all difference bands. This band has been previously assigned as the fundamental ν3, ν1+ν4 with a spacing of 28 K; the fundamental is present in the complex but its spacing is 15 K and it is weak. The difference bands of titanium tetrachloride are mentioned briefly.
Electron Spin Resonance of Thortveitite
Authors: Datars W. R. , Calvo C.
Published: January 2005

The ESR spectra of the mineral thortveitite, (Y, Sc)2Si2O7 are reported in the temperature range 77° to 300°K and at 1.4°K. The spin-Hamiltonian parameters of Fe3+, situated at Sc3+ sites, are found to be |D|=2390 G, |E|=110 G, g∥=g⊥=2.00 with one magnetic axis constrained parallel to the b crystallographic axis. For Mn2+, g = 2.01 and a hyperfine splitting of 85±10 G is found. Possible space groups of thortveitite are discussed. The C2/m space group is consistent with the data in the temperature range 77° to 300°K.
Shock-Tube Study of the Vibrational Relaxation of Nitrogen Using Vacuum-Ultraviolet Light Absorption
Authors: Appleton J. P.
Published: January 2005

The results of a shock-tube study of the vibrational relaxation of nitrogen over the approximate temperature range 3000° to 9000°K are presented. Measurements were made using a vacuum-ultraviolet light-absorption technique at 1176 Å which monitored the rate of populating vibrational level v″≃10. The good agreement of the present results with earlier interferometric measurements demonstrates the validity of the assumption that the populations of vibrational levels from the ground state up to at least v″ = 10 relax via a continuous sequence of ``near'' Boltzmann distributions which are described by a single time-dependent vibrational temperature. At temperatures in excess of about 5500°K, where no shock-tube data have previously been reported, the results indicate that the local value of the characteristic vibrational relaxation time becomes increasingly dependent on the degree of vibrational excitation, such that it decreases within the relaxation region as equilibrium is approached.
Scintillation Studies of Organic Compounds in a Supercooled Molten State
Authors: Horrocks Donald L. , Wirth Hermann O.
Published: January 2005

When the crystals (obtained by crystallization from certain solvents) of a number of low-molecular-weight organic compounds (11 derivatives of 2-phenylindole and two derivatives of p-quaterphenyl) were melted and recooled to room temperature, rather stable nonrecrystallizing, supercooled melts were obtained. The consistency of these at room temperature varied from rather viscous oils to rigid glasslike masses. Their stability also varied over a wide range; from one day to at least several years.

The response of these amorphous, pure scintillators to excitation by energetic electrons was measured relative to a standard liquid scintillator solution (gas-free, 3-g/liter PPO—toluene solution) which was assigned a value of 100. The very stable (at least several years) and rather rigid melt of 12,23,32,43-tetramethyl-p-quaterphenyl exhibited a relative response of 92. The supercooled melt of N-isoamyl-3,2′-ethyleno-2-phenylindole showed a relative response of 125 and remained amorphous with a consistency at room temperature of a thick grease for greater than nine months if maintained under evacuated conditions.

The fluorescence spectra of these compounds in the undiluted, supercooled state and in a toluene solution (mole fraction of about 0.001) were measured for excitation by 315-mμ radiation. In some cases there were differences in the measured spectra depending on the type of sample.
Reaction of Oxygen Atoms with Chlorine
Authors: Niki H. , Weinstock Bernard
Published: January 2005

The reaction between O(3P) atoms and Cl2 has been studied in a fast flow reactor coupled to a time-of-flight mass spectrometer. The reaction is first order in O and Cl2 and can be described by the mechanism, O+Cl2=OCl+Cl,O+ClO=Cl+O2.The rate constant for Reaction (1) is (7.5±0.6) × 10−14 cc molecule−1·sec−1 at 300°K. In the Cl2-rich system, the over-all rate constant is twice this value indicating that Reaction (2) is much faster than Reaction (1). A lower limit has been obtained for the rate constant of Reaction (2) of 10−11 cc molecule−1·sec−1. The apparent gas-phase catalytic effect of Cl2 for the recombination of O atoms previously reported has been shown to be incorrect and to arise from a rapid regeneration of Cl2 molecules on HF ``poisoned'' walls.
Thermal Diffusion of Gas Mixtures in Chemical Equilibrium
Authors: Brokaw Richard S.
Published: January 2005

Theoretical expressions are developed for thermal-diffusion ratios or factors in reacting gas mixtures. In general, these parameters can be related to λr, the increase in thermal conductivity due to chemical reaction. Calculations on the N2O4⇄2NO2—argon system predict thermal-diffusion factors as large as 2 and in satisfactory agreement with experiment. Reduced thermal-diffusion factors are computed for separation of noble-gas isotopes in the presence of the (HF)6⇄6HF equilibrium and are predicted to be as much as an order of magnitude greater than factors which have been observed without added hydrogen fluoride. Reduced separation factors for argon, krypton, and xenon are negative, which means that the heavy isotope migrates to the hotter regions of the gas mixture. (In mixtures of isotopes alone, separation factors are always positive.) Finally, separation of reactants in a mixture without inerts is considered. Separation factors as large as 1 are predicted for the dissociation of PCl5.
Observations of Phosphorescence in Plastic Scintillators Excited by 60Co γ Irradiation
Authors: Kropp John L.
Published: January 2005

The γ-induced luminescence of chrysene-d12, coronene-d12, and p-terphenyl has been studied in plastic hosts (DER-332 and polymethylmethacrylate). Both phosphorescence and fluorescence are observed. The variation of phosphorescence and fluorescence as a function of solute concentration is determined. From the concentration dependence, Q parameters can be calculated for the phosphorescence (QP) and fluorescence (QF) of the compounds studied. The ratio of phosphorescence to fluorescence under γ irradiation (Rγ) is compared to that observed under uv irradiation (Ruv) and a kinetic scheme is developed that relates (Rγ/Ruv) to QP and QF assuming only excitation transfer. From the fit of the kinetic treatment to the experimental points, it is concluded that triplet coronene-d12 is formed mainly via excited solvent triplets. Triplet p-terphenyl is not formed via excited solvent but is formed by other processes probably involving ions.
Geometry of Some Refractory Metal Dioxides
Authors: Kaufman M. , Muenter J. , Klemperer W.
Published: January 2005

The deflection by an electrostatic quadrupole of molecular beams of SiO2, TiO2, ZrO2, CeO2, ThO2, TaO2, and UO2 has been measured. Of the above species only SiO2 was found to be nonpolar while the remaining species were found polar. This sequence (with the exception of TaO2 and UO2) together with CO2 forms an isoelectronic sequence with previously investigated alkaline-earth difluorides. In each instance the geometry of isoelectronic partners is similar.
Molecular Charge Distributions and Chemical Binding. II. First-Row Diatomic Hydrides, AH
Authors: Bader R. F. W. , Keaveny Ian , Cade Paul E.
Published: January 2005

An interpretation of the binding in the first-row diatomic hydrides AH is presented, based upon the molecular charge distribution and the forces which it exerts on the nuclei. The density distributions are discussed in relation to ``molecular'' size and the partitioning of the total charge between different spatial regions. Density difference maps are employed to compare the molecular charge distribution with that of the separated atomic charge densities and the charge density of the corresponding united atom. The molecular-orbital charge densities are classified as binding, nonbinding, or antibinding with respect to the forces which they exert on the nuclei. The orbital forces provide a quantitative assessment of the relative binding abilities of the orbital charge densities; for a given molecule, or through the complete series of molecules. On the basis of the total charge distributions, the density difference distributions and the forces exerted on the nuclei, the bonding in LiH is classified as ionic, that in BH→HF as covalent. The binding in BeH is found to be transitional between the limiting classifications of ionic and covalent.
Calculation of Cartesian Coordinates and Their Derivatives from Internal Molecular Coordinates
Authors: Thompson H. Bradford
Published: January 2005

An algorithm is described for rapid calculation of cartesian coordinates of atoms from internal molecular coordinates. Two procedures are given for efficient calculation of first derivatives of the Cartesian coordinates with respect to internal coordinates, and the manner in which higher derivatives may be obtained is indicated.
Operation of Thermal-Diffusion Column with Mixtures of Gases Having Equal Molecular Weights (CO2–N2O)
Authors: Srivastava B. N. , Batabyal A. K. , Roy A. N. , Ghosh A. K.
Published: January 2005

Steady-state separation factors of 1:1 carbon dioxide—nitrous oxide mixture at mean temperatures 363°, 401.5°, and 435.5°K and at pressures ranging from 0.30 to 0.95 atm have been measured by operating a coaxial thermal-diffusion column. It has been found that the variation of separation factor with pressure agrees qualitatively with Furry—Jones' theory for isotopic mixtures. A detailed comparison of the experimental results with the theory has been made on the Maxwellian and Lennard-Jones (12:6) models and values for the thermal-diffusion factor for this polyatomic gas mixture have been estimated.