bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent Field Corrections for Electric Dipole and Rotatory Strengths
Authors: Weigang Oscar E.
Published: January 2005

Quantum-mechanical perturbation theory is applied to the evaluation of the electric dipole strength and the rotatory strength of a condensed system of negligibly overlapped, randomly oriented solute and solvent molecules. Besides the traditional Lorentz field corrections, a correction factor is obtained which is a function of inductive and dipolar solute—solvent interactions.

An extension of the types of intermolecular force fields heretofore considered is achieved. In particular, the effect of solvent fields due to solvent molecule static dipole moment is predicted to be a decrease in solute absorption intensity and optical activity. The complexity of terms and level of approximation cannot be expected to yield more than semiquantitative relationships, but the important solvent and solute variables are identified.
Lower Electronic Levels of the Radicals PH and PH2
Authors: Jordan Peter C.
Published: January 2005

This paper describes a semiempirical quantitative theory of the low-lying electronic states of the radicals PH and PH2. The method is an extension of that developed by Jordan and Longuet-Higgins to treat Row II hydrides. It indicates that a small percentage of d character in the valence state may have a considerable effect on the equilibrium bond angle, if the d orbital is somewhat contracted by polarization. Including this effect, the results are in excellent agreement with experiment: PH2 in its excited 2A1 state is found to be strongly bent; PH3 is predicted to have an inversion barrier of 34.5 kcal/mole.
Appearance Potentials by the Retarding Potential-Difference Method for Secondary Ions Produced by Excited—Neutral, Excited Ion—Neutral, and Ion—Neutral Reactions
Authors: Melton C. E. , Hamill W. H.
Published: January 2005

A time-of-flight mass spectrometer with a retarding potential-difference ion source has been used to measure appearance potentials and ionization efficiency curves for secondary ions. Reaction types studied include excited neutral-molecule, charge-transfer, attachment and branching ion-molecule reactions. The systems investigated were argon, krypton, methane, acetylene, 1–3 butadiene, ethyl iodide, and methane—krypton mixtures. Rare-gas molecular ions from excited neutral-molecule reactions were observed for Ar2+ with appearance potentials at 14.94±0.02, 15.2±0.1, and 15.8±0.1 eV and for Kr2+ at 13.20±0.02, 13.8±0.1, and 14.0±0.1 eV. A charge-transfer reaction for Kr–CH4 produced CH3+ at 14.6±0.1 eV corresponding to Kr+(2P½). The activated complex formed by C4H6++C4H6 from butadiene produces six different secondary ions. Ionization efficiency curves of the six secondary ions showed the same structure in the energy range to 2 eV above onset. Similar results were observed for two competitive reactions formed by C2H2++C2H2 from acetylene, for energies below 14.5±0.2 eV. At higher energies, the ratio of secondary C4H3+/C4H2+ changed by a factor of two thereby demonstrating the influence of reactions of excited C2H2*+. The predominant excitation level for the excited reaction was 17.0±0.2 eV. Ionization efficiency curves of the primary and secondary ions in the energy range near onset for all systems were essentially identical except for the collision complex C4H10I2+ which was slightly different from that of the primary C2H5I+ ion. The technique greatly improves the reliability of correlating primary ions with secondary ions and provides detail not otherwise measurable.
Multiplicity of the Solution of the Vibrational Force-Constant Problem
Authors: Ruth John M. , Philippe Roger J.
Published: January 2005

When the secular equation in the form | H — Eλ | =0, where H is the matrix product GF or FG, is expanded into a polynomial equation of degree n in λ, a set of n algebraic equations in the n unknowns Ftt′ is obtained. The degrees of these equations are 1, 2, 3, ···, n, respectively. The number of solutions (sets of force constants) is n!, the number of possible sets of frequency assignments is also n!, and one set of force constants corresponds to each set of frequency assignments. When the frequencies are all different, the sets of force constants are all different, and in a diagonal F matrix all the force constants are real and positive. As an illustration, the six sets of force constants for the valence force treatment of a triatomic model of the ethyl chloride skeleton are computed, and the corresponding frequency assignments are determined.
Optical Measurement of the Specific Chromia Area of Chromia—Alumina Catalysts
Authors: Poole Charles P. , MacIver D. S.
Published: January 2005

The optical reflectances of chromia—alumina catalysts in the visible and ultraviolet regions have been determined and, at the same time, the specific chromia surface areas measured by oxygen chemisorption. A relationship was found between the intensities of the charge-transfer bands of Cr6+ and the extent of chromia area, which permits one to determine the chromia area of a chromia—alumina catalyst from the optical reflectance spectra.
Zeeman Effect of the 2F5/2, E5/2→2F7/2, E5/2 Transition in CaF2:Tm2+
Authors: Weakliem H. A. , Kiss Z. J.
Published: January 2005

The Zeeman spectrum of the 2F5/2, E5/2→2F7/2, E5/2 sharp-line fluorescence in CaF2:Tm2+ gives direct proof that the transition is a magnetic dipole one. The measured excited-state g value of 0.85 agrees with the Landé value. The line strength has been measured and was found to be significantly smaller than the calculated one.
Theory of Normal Vibrations of Chain Molecules with Finite Length
Authors: Matsuda H. , Okada K. , Takase T. , Yamamoto T.
Published: January 2005

This paper is concerned in the end effects on the normal vibrations of a chain molecule with finite length. In Part I we study the mathematical problem of how to solve the eigenvalue problem of the GF matrix of the chain molecule with finite length. Making use of the fact that the force range can be regarded finite we reduce the problem to solving a determinantal equation usually of much lower order than that of the GF matrix through the introduction of auxiliary variables and transfer matrices. We obtain the simple formula for giving an admissible phase difference in which the end effect is taken into account. In Part II, using this formula we analyze the infrared data of Snyder on crystalline normal paraffins C3H8 through C30H62. Our analyses indicate that the formula is generally useful for making extrapolation, interpolation, assignment, and determination of frequency-phase relations from the experimental data of homologous series of chain molecules.
Hyperfine Structure in the Microwave Spectrum of NH2D
Authors: Thaddeus P. , Krisher L. C. , Cahill P.
Published: January 2005

Hyperfine structure in the 313→303 rotation—inversion transition of deuterated ammonia NH2D at 18 807.7 Mc/sec has been studied with a beam maser microwave spectrometer giving a linewidth of 7 kc/sec. All details of the observed hyperfine structure have been accounted for in terms of the various quadrupole, spin—rotation, and spin—spin interactions of the four coupling nuclei. The hyperfine coupling constants which have been determined with the aid of a digital electronic computer are, for the 313 state: (eqJQ)D=—62.5±1.0 kc/sec, CD=—2.7±0.3 kc/sec, CH=—13.6±0.5 kc/sec; and for the 303 state: (eqJQ)D=—73.9±1.0 kc/sec, CD=—2.7±0.3 kc/sec, CH=—12.3±0.5 kc/sec. On the assumption that the electric field at the deuteron is cylindrically symmetric about the N—D bond direction ξ, we find that (eVξξQ)D=282±12 kc/sec, or Vξξ=1.38±0.06×1015 statV/cm2, where Vξξ is the second derivative of the electrostatic potential along ξ.
Normal Coordinate Analyses of Hydrogen-Bonded Compounds. I. Monomeric Formic Acid and Acetic Acid
Authors: Nakamoto Kazuo , Kishida Sanae
Published: January 2005

In order to obtain the Urey—Bradley force constants, normal coordinate analyses have been carried out for monomeric formic acid and acetic acid including their deutero analogs. Previous empirical band assignments have been confirmed or corrected on the basis of the calculation of the potential-energy distribution in each normal vibration.
Computation of Character Tables for Nonrigid Molecules
Authors: Stone A. J.
Published: January 2005

A simple method is described, by means of which it is possible to calculate character tables for the symmetry groups of molecules consisting of a number of methyl groups attached to a rigid framework. Character tables are given for the symmetry groups of neopentane C(CH3)4, and octahedral metal hexammine ions, M(NH3)6. The method can be generalized to apply to other nonrigid molecules.
Magnetic and Structural Characteristics of Lanthanide—Nickel Compounds
Authors: Walline R. E. , Wallace W. E.
Published: January 2005

The magnetic and structural characteristics of 11 intermetallic compounds represented by the formula LnNi are reported. The five compounds with Ln=Dy, Ho, Er, Tm, and Y are isomorphous and occur in the FeB structure. The others, with Ln=Ce, Pr, Nd, Sm, Gd, and Tb, form in the CrB structure, YNi and CeNi exhibit only Pauli paramagnetism down to 4.2°K. The others order magnetically with Curie temperatures ranging from 8°K for TmNi to 71°K for GdNi. Nickel appears to be nonmagnetic in the series and CeNi is nonmagnetic and hence Ce is quadripositive in CeNi. Curie—Weiss behavior is obeyed in the paramagnetic region for the compounds containing a magnetic Ln atom, except for TmNi, which exhibits a tendency toward Van Vleck-type temperature-independent paramagnetism at low temperatures. This and the fact that the observed saturation moments are well below the free tripositive lanthanide ion moments suggests that appreciable crystal field quenching of the orbital contribution occurs in these compounds. Except for TmNi, effective moments in the paramagnetic region are as expected for the free tripositive ions.
Pressure Dependence of the Resistance of VO2
Authors: Neuman C. H. , Lawson A. W. , Brown R. F.
Published: January 2005

The resistance of VO2 through the semiconductor-to-metal transition has been measured as a function of hydrostatic pressure. The transition has been studied in pure and partially hydrated single crystals of VO2 and in powdered VO2. The temperature of the transition is shifted by less than 0.5 C° by pressures up to 6×103 bars. The conductivity in both the semiconducting and metallic states is decreased by about 10—3%/bar. The effect of pressure on both the resistance and transition temperatures of VO2 is much smaller than that reported in previous measurements on V2O3. The relation between the pressure dependence of the energy gap in the semiconducting state and the pressure dependence of the transition temperature is examined and is shown to be consistent with Mott's mechanism for the transition to the metallic state.
Comparison of Experimental and Theoretical Vibrational Relaxation Times for Diatomic Gases
Authors: Parker J. G.
Published: January 2005

A comparison of theoretical and experimental vibrational relaxation times has been carried out for the halogens, nitrogen, oxygen and carbon monoxide. Reasonably good agreement is obtained for all gases except oxygen. For oxygen the predicted variation of the vibrational collision number with temperature appears to be correct; however, experimental values at high temperatures appear to be low by a factor of 0.55. Values obtained at room temperature on the other hand agree well with theory. It would seem therefore that an anomalous decrease in the vibrational collision number takes place in the temperature range from 300° to 500°K.

Since data for carbon monoxide could be fitted very well by theory, it is apparent that the effect of radiation is negligible, at least in the temperature range above 1000°K. This is consistent with the value of 0.03 sec for the radiative lifetime of carbon monoxide in the first excited vibrational state.

An empirical relationship is established between the interaction constant α and the molecular diameter σ, which reproduces the experimentally derived values quite closely.
Reformulation of the Virial Series for Classical Fluids
Authors: Ree Francis H. , Hoover William G.
Published: January 2005

The usual graphical representation of the virial coefficients is reformulated in terms of graphs containing not only Mayer f functions, but also f̃ functions [f̃≡f+1≡exp(−φ/kT)].

This reformulation has three main advantages:

(1) The number of integrals of topological graphs contributing to the virial coefficients is reduced; this simplifies numerical calculations.

(2) In Mayer's formulation none of the star integrals contributing to the virial coefficients (for hard potentials, at least) could be ignored; each made a nonnegligible contribution. In the new formulation (again, for hard potentials) many integrals make negligible (or even zero) contributions; the extensive cancellation of positive and negative terms found in Mayer's formulation is reduced.

(3) Several new ways of summing the virial series by successive approximation are suggested by the new formulation. One such way is worked out, in the first three approximations, for gases of hard parallel squares and cubes; the third approximation reproduces the first five virial coefficients exactly.

The reformulation is not restricted to the virial series alone. We also generalize our treatment to the radial distribution function. It can be applied to any series whose coefficients are integrals of graphs.
One-Center Wavefunction for the Ground State of the HeH+ Molecular Ion
Authors: Stuart J. D. , Matsen F. A.
Published: January 2005

The HeH+ molecular ion is a member of that class of diatomic hydride molecular ions which are one-center systems at R=0 and at R=∞. The total electronic energy of the ground state of HeH+ has been calculated over a wide range of R with a 30-term orbital product wavefunction centered on the helium nucleus. The results are compared with a James and Coolidge-type calculation and with a two-center orbital product calculation. The results in the order Evett, Anex, and present calculation are Re=1.432, 1.446, 1.464 a.u.; ωe=3600, 3378, 3184 cm—1; and E(R=1.4 a.u.)=—2.9730, —2.9742, —2.9691 a.u. The energy of the present calculation is the lowest for R greater than about 2 a.u. and is lower than the classical polarization energy for 2<R<4 a.u. For R>4 a.u. the one-center interaction energies [E(R)—E(∞)] lie quite close to the classical polarization energies.
Absorption and Photoionization Cross Sections of H2O and H2S
Authors: Watanabe K. , Jursa A. S.
Published: January 2005

Absorption and photoionization cross sections of H2O in the region 850–1110 Å and H2S in the region 1060–2100 Å were measured by photoelectric methods. The absorption curves support the photographic study of H2O and H2S by Price. The photoionization curves yielded the following ionization potentials: 12.62 eV for H2O and 10.46 eV for H2S.
Spectral Emissivities and Integrated Intensities of the 1.87-, 1.38-, and 1.14-μ H2O Bands between 1000° and 2200°K
Authors: Ferriso C. C. , Ludwig C. B.
Published: January 2005

Spectral emissivities of the overtone and combination bands of H2O in the 1- to 2-μ region have been measured between 1000° and 2200°K. The hot water vapor samples were produced in a small supersonic burner using H2 and O2. The measurements were made at the exit of the burner where the interactions of the hot gas jet with the ambient atmosphere are small. The variation of the spectral emissivities of H2O in the optically thin absorption region as a function of temperature are given for a total pressure of 1 atm and a constant amount of H2O in the optical path.

The integrated intensities of the bands have been determined from the emissivity spectra at the various temperatures. The values of the integrated intensities of the 1.87-, 1.38-, and 1.14-μ H2O bands at 273.2°K are 26.0, 21.2, and 1.92 (cm—2·atm—1), respectively. The integrated intensity variations with temperature of the bands have been used to determine the absolute intensity contributions from the numerous overtone and combination transitions which make up these bands.
Millimeter Wave Spectroscopy of Unstable Molecular Species. II. Sulfur Monoxide
Authors: Winnewisser Manfred , Sastry K. V. L. N. , Cook R. L. , Gordy Walter
Published: January 2005

Several spectral transitions of the gaseous free radical SO have been observed in the millimeter wave region. Analysis of the observed lines confirms that the molecule has a 3Σ ground state and leads to the rotational constants B0=21 523.75 Mc/sec and D0=0.0334 Mc/sec, also to the magnetic coupling constants λ=158 209.4 Mc/sec and γ=—164.52 Mc/sec. The assignments and analysis are confirmed by a close fitting, within approximately 1 Mc/sec, of all measured and calculated frequencies, and by the Zeeman effect which is measured and analyzed for several transitions.
Electrically Induced Perturbations of Halogen Nuclear Quadrupole Interactions in Polycrystalline Compounds. II. Microscopic Theory
Authors: Dixon R. W. , Bloembergen N.
Published: January 2005

The physical origins of electrically induced perturbations of quadrupole couplings in molecular solids are considered. Experiment and elementary theory are compared and it is concluded that polarizations of bonding electrons near the resonant nuclei are of dominant importance in determining the magnitudes of the electrically induced shifts.
Nuclear Magnetic Resonance Study of Cobalt—Chlorine Complexes in Methanol
Authors: Luz Z.
Published: January 2005

An NMR study of complex formation of Co+ + ion with Cl— ion in methanol between —80° and +80°C is reported. This work is an extension of the study reported in the preceding paper (referred to as IV) to a much wider temperature range. It is shown that, below +15°C in solutions containing up to 1M chloride ion, the monochloro octahedral complex is the only cobalt—chlorine compound formed. The equilibrium constant for the formation of this complex as function of temperature and chloride ion concentration was determined. From the broadening of the NMR peaks rate of methanol exchange between the solvation shell of the monochloro complex and the bulk solvent were obtained. Evidence for the formation of ion pairs of the form [Co(MeOH)6]+ +Cl— is presented.

Above +15° the blue tetrahedral complexes became progressively more important. In this temperature range the NMR and optical spectra can be correlated, but the large number of complexes allow only a qualitative analysis of the NMR results.
Unrestricted Hartree—Fock Calculations. I. An Improved Method of Computing Spin Properties
Authors: Amos Terry , Snyder Lawrence C.
Published: January 2005

Spin properties calculated using a spin-polarized single-determinant wavefunction in the unrestricted Hartree—Fock method can be unreliable because the wavefunction is not a spin eigenstate and contains unwanted spin components. New expressions are derived for the spin properties after the most important of these has been removed by an annihilator. Expressions are given for 〈S2〉 and for the spin- and charge-density functions, all in terms of the unrestricted bond-order matrices for electrons of α spin and of β spin. The cases of orthogonal and nonorthogonal atomic orbitals are included. The role of corresponding orbitals in the derivations is outlined. The results are illustrated by calculations on the pi-electron radicals, allyl, pentadienyl, naphthalene positive and negative ions, and the lowest-energy naphthalene triplet configuration. An estimate is made of the error due to the unwanted components which still remain in the wavefunction, and this will usually be small. A simple, approximate expression for the spin-density function is obtained.
Deuterium-Isotope Effect in the Chlorine Exchange between Hydrogen Chloride and Chlorine Atoms. A Study of Models for the Tunnel Effect
Authors: Klein Fritz S. , Persky Avigdor , Weston Ralph E.
Published: January 2005

The rates of the exchange reactions of chlorine atoms with hydrogen chloride and with deuterium chloride were measured as a function of temperature. Chlorine atoms were produced by photodecomposition of chlorine gas and their relative concentration was monitored by their reaction with deuterium: Cl+D2→DCl+D.The temperature dependence of the logarithm of the ratio of rates was found to be nonlinear in the temperature range of 30° to 150°C. Various attempts to calculate the isotope effect assuming different types of tunneling are discussed.
X 1Σg+—A 3Σu+ Excitation Energy in N2
Authors: Huber Lee M. , Thorson Walter R.
Published: January 2005

The valence-bond method is employed to calculate the energy separations of the potential surfaces for the X 1Σg+ and A 3Σu+ states of the nitrogen molecule for internuclear distances between the respective equilibrium positions (i.e., 1.094 to 1.29 Å). The radiative π—π* transition between these states gives rise to the well-known Vegard—Kaplan bands. The N2 molecule is treated as a 10-electron problem. Separation into σ and π groups of electrons is made and excitation assumed to affect only the latter. The self-energy of the σ core is not explicitly evaluated. The σ—π interactions are nearly insensitive to variations in the σ-core bonds, a result which justifies the variational calculation of the π energy plus σ—π interactions as a valid determination of the π-electron wavefunctions.

The resulting energy separation has an almost constant error, 1.1 to 1.3 eV lower than experiment; the energies themselves are more sensitive to the wavefunction than is the separation. The invariance of the error, both as obtained by several widely different calculations and as a function of internuclear separation, suggests strongly that it arises from correlation energy of two possible types, discussed below. Such an error may be ``typical'' of the error involved in a σ—π separation treatment for π—π* intersystem transitions. Within the error involved, the results justify the ``chemical'' description of these states of the nitrogen molecule.
Estimation of Soret Coefficients from Gouy Fringe Intensities
Authors: Becsey Julius G. , Bierlein James A.
Published: January 2005

Photometric scanning of Gouy diffraction patterns is used as the basis of a convenient method for measuring Soret coefficients. Experimental data on well-studied electrolyte systems yield values which are precise to about 1% and which agree closely with older determinations.
Gas-Phase Photolysis of Methyl Iodide. Reactions of Hot Methyl Radicals with Added Organic Compounds
Authors: Doepker Richard D. , Ausloos P.
Published: January 2005

The photolysis of CH3I and CD3I at 2537 and 3130 Å has been investigated in the presence of CD3CH3, C2D6, CH3CD2CH3, CD3CH2CD3, C4H10–C4D10 (1:1) mixtures, (CH3)3CD, (CH3)3CCD3, C6H6, C6H12, CH3OCH3, CH3COOCD3, CD3OH, C2D5OH, and CD3CH2OH. All mixtures were saturated with iodine in order to prevent the formation of methane by the reaction of thermal methyl radicals. It is shown that, under these conditions, the measured quantum yield of methane formation can be considered to be the probability that a ``hot'' methyl radical with 32 kcal will react with CH3I or the additive. The following observations were made: (1) Intramolecular and intermolecular isotope effects are of minor importance. (2) The probability of abstraction of an H or a D atom from a molecule by a ``hot'' methyl radical increases with the number of available H or D atoms, or with a decrease in the ΔH of the reaction. For instance, it is seen that the relative probabilities per atom for abstraction of a primary, secondary, or tertiary H atom in a hydrocarbon molecule are 1:3.6:10.0. A variation in wavelength, from 2537 Å to 3130 Å, lowers the methane quantum yield by a factor of 10 but does not greatly affect the relative probabilities of abstraction from different sites within a molecule. (3) The quantum yield of methane in the photolysis of CH3I or CH3I—hydrocarbon mixtures is nearly twice that observed for CD3I or the corresponding CD3I—hydrocarbon mixtures at the same wavelength.

It is concluded that systematic studies of this type may prove to be useful in determining a priori the probability of reaction with other related organic compounds.
ESR Studies and the Electronic Structure of Vanadyl Ion Complexes
Authors: Kivelson Daniel , Lee Sai-Kwing
Published: January 2005

The ESR spectra of vanadyl acetylacetonate and tetraphenylporphyrin have been studied in various liquid solvents and frozen glasses. The spectra have been analyzed and the components of the g tensor and of the vanadium hyperfine interaction tensors have been determined, and for the porphyrin the nitrogen extrahyperfine interaction tensor has been obtained. The unpaired electron is in the b2g* orbital. The extrahyperfine splitting is very isotropic which indicates that the b2g* orbital is localized on the vanadium in the porphyrin complex and the ``in-plane π bonding'' is slight. An explanation of the origin of this extrahyperfine splitting is discussed in terms of configuration interaction. An analysis of the vanadium hyperfine interaction indicates that the b2g* orbital is localized on the vanadium in the acetylacetonate also, and that the Fermi contact interaction depends upon a number of excited configurations and varies from complex to complex and with change of solvent. The g-tensor analysis suggests that the spin—orbit constant λ≥170 cm—1, that the in-plane σ antibonding and out-of-plane π antibonding orbitals are delocalized, the delocalization increasing in the order: VO(H2O)5+ +, vanadyl acetylacetonate, vanadyl porphyrin.
Pair-Correlation Effects in a System of Coupled Rotators
Authors: Tait W. C. , James Hubert M.
Published: January 2005

Orientational transitions in systems of coupled molecular rotators have previously been treated by methods that take account of pair-correlation effects, but only in the case of molecules with axial symmetry coupled by forces that do not depend on the direction of the line of centers between molecules. The theory is here generalized to the case of direction-dependent couplings. The resulting integral equations are treated by expanding in powers of Tb/T and 1/z, where Tb is the branching temperature of the ordered solution under consideration, and z is the number of next neighbors to which a molecule is coupled. The zero-order solution of the problem is related to the solution in the internal-field approximation. The first-order correction for pair-correlation effects is determined by an integral equation. The theory is applied to the James—Keenan model of solid methane, for which the integral equation is easily solved. Inclusion of the first-order pair-correlation correction increases the estimated octopole moment of methane by some 10% over that derived by the internal field method, to 0.55×10—24 electron·cm3. The effect of pair correlations on the orientational distribution of the molecules is discussed on the basis of this theory. The calculations on solid methane are of illustrative value only, since the small moment of inertia of even CD4 makes quantum effects important, whereas the present theory is based on classical statistical mechanics.
Hyperfine Structure in the EPR Spectrum of the Manganous Ion in Frozen Solutions
Authors: Allen B. T. , Nebert D. W.
Published: January 2005

EPR spectra of 10—3M MnCl2 were studied in various solutions at —180°C, and in 12M HCl or methanol the hyperfine structure was very similar. This hyperfine structure was then studied with respect to a changing Cl—/Mn++ ratio by addition of LiCl or HCl to the MnCl2 solution. These spectra may be explained in terms of a spin Hamiltonian by considering only the M = ½↔M = —½ transitions, and the occurrence of forbidden Δm = ±1 transitions.
Chemical Effects of Isomeric Transitions: The Separation of Tellurium Isomers in Different Chemical Media
Authors: Hahn Richard L.
Published: January 2005

The chemical separation of the nuclear isomers of 127Te and 129Te in different media has been studied. The variation of fj(127Te) with pH in aqueous solutions of HCl, HNO3, HClO4, and NaOH has been measured; fj is the probability that, if the parent metastable-state activity is in the telluric acid form, the daughter ground-state activity will be found as tellurous acid as a result of chemical interactions in a medium of substance j. The fj's for the different acids behave very similarly as the pH changes. In 6N acid solutions, fj is close to unity; it decreases monotonically with increasing pH and approaches the value for H2O, at pH of 6.0, of 0.760±0.017. In NaOH, fj increases with decreasing pH, and also approaches the value for H2O. The variation of fj with pH may be expressed by the relation, fj=exp(xj)/[1+exp(xj)], with xj=mj(pH)+bj; mj and bj are parameters which are obtained from the data. Also, relative fj values for 127Te and 129Te have been determined in solid telluric acid, H2O, and 6N solutions of HCl, HClO4, and NaOH. Although the absolute fj values for these nuclides change from substance to substance, the ratios of the fj's remain fairly constant, approximately equal to unity. Thus, fj appears to be mainly a function of the chemical, and not the nuclear, properties of the isomer separation process.
Conditions for Optimal Choice of Approximate Wavefunctions and the Hypervirial Theorem
Authors: Vetchinkin S. I.
Published: January 2005

The hypervirial theorem for the operator L does not guarantee the independence of the expectation value L from all essential errors of the approximate wavefunction. The more complete system of conditions includes the matrix elements of higher commutators (and anticommutators) L with the Hamiltonian. These conditions prevent the effect of approximate wavefunction errors and may be useful for evaluations of expectation values and transition probabilities. The problem is considered in terms of dynamics or statics. These treatments are shown to be equivalent only for the exact solution.
Properties of First-Row Atoms and Ions Calculated from ``Empirical'' Nonrelativistic Energies
Authors: Ellison Frank O.
Published: January 2005

Electron—electron repulsion energies C̄, electron—nuclear attraction energies L̄, and nuclear magnetic shielding constants σ for atoms and ions with number of electrons n=2 to 10 and nuclei of charge Z=n—1 to 10, calculated from ``empirical'' nonrelativistic energies E for isoelectronic series, are reported and compared with theoretically computed values.
Energy Transfer between Molecules and Electronically Excited Atoms
Authors: Shahin M. M. , Lipsky S. R.
Published: January 2005

The technique of competitive quenching has been used to determine the relative rate constants of O2, N2, H2, CO2, and CH4 for quenching of excited argon atoms formed both by the action of β radiation from a tritium source and also by low-energy electron impact. Calculations based on the mean lifetime of these species in the system show that with the exception of nitrogen the quenching process for all the other molecules is highly efficient and energy transfer occurs on every collision. Evidence is also presented to suggest that the excited species formed by collision with β rays are primarily in the 1P1 state and not the 3P0,2 metastable states.
Constant Energy and Minimum Energy Orthogonalization
Authors: Joy Hubert W. , Schaad L. J. , Handler George S.
Published: January 2005

The problem of orthogonalizing a set of orbitals is considered, noting that the energy calculated for a determinantal wavefunction is often changed by such a procedure. Rules are given for finding whether a particular determinantal wavefunction will, in fact, yield different results on orthogonalization of its basis set. A new orthogonalization procedure, minimum energy orthogonalization, is illustrated, and some of its possible uses are examined.
Isotope Effect in the Ionization of Polyatomic Gases by Metastable Atoms
Authors: Jesse William P.
Published: January 2005

An isotope effect in the probability of ionizing a polyatomic molecule by energy transfer from a metastable noble-gas atom has been investigated for a large number of gases, especially in an attempt to relate the magnitude of the observed effect to the quantity of energy transferred from the metastable atom. In the experiments the current in an ionization chamber was measured for an initially highly purified noble gas under bombardment by beta particles from a 63Ni or 3H source, as successive measured concentrations (up to 1% by volume) of the gas investigated were introduced. The increase in ionization, relative to that found initially in the pure noble gas, gives a measure of the number of ion pairs resulting from collisions of the second kind between metastable atoms and molecules of the contaminant gas. This relative increase varies through wide limits with the nature of the polyatomic contaminant gas introduced. Moreover, the increase is found consistently larger for a fully deuterated hydrocarbon sample than for an undeuterated one. The isotope ratio, i.e., the ratio of the current increase for a deuterated to that for an undeuterated sample, has been found in ethylene, n-butane, benzene, and toluene to decrease as the metastable state energy increases (in benzene from a ratio 1.16 for an energy of 9.4 eV to 1.04 at 20.2 eV). Over a smaller range, ethane and methane show increases in the ratio with increasing energy. In general, the present values for this isotope ratio are in good accord with the theory of Platzman, which predicted such an isotope effect.
Emission Properties of Tetracene—Pyrene and Pentacene—Pyrene Mixed Crystals
Authors: Kawaoka Kenji , Kearns David R.
Published: January 2005

Studies of the emission spectra of tetracene- and pentacene-doped pyrene crystals reveal that tetracene is soluble in pyrene crystals only to the extent of one part in 104, whereas pentacene is soluble only to less than one part in 105. These results explain why tetracene and pentacene are ``anomalously'' poor quenchers of pyrene fluorescence and resolve an apparent conflict with current theories of energy transfer.
Remarks on the Determination of Electric Dipole Moments from Rotational Magnetic Moments. The Dipole Moment of Hydrogen Fluoride
Authors: Chan Sunney I. , Ikenberry Dennis , Das T. P.
Published: January 2005

The determination of electric dipole moments from isotopic variations of the rotational magnetic moment is considered. It is pointed out that appreciable errors in the dipole moment can result if one neglects the effects of vibrational motion on the high-frequency part of the magnetic susceptibility. Thus, a current discrepancy in the dipole moment of HF determined from the rotational magnetic moments of HF and DF and by the molecular beam electric resonance method is resolved by such vibrational corrections. When these vibrational corrections are made, the dipole moment of HF as determined from the rotational magnetic moments of HF and DF is 1.83±0.05 D (H+F—) instead of 1.65 D, and is in good agreement with the value of 1.818±0.008 D obtained by electric resonance.
Dissociative Ionization of N2 and N2O by Rare-Gas Ion Impact
Authors: Maier William B.
Published: January 2005

Cross sections for the reactionsNe++N2→N++N+Ne,Kr++N2O→O++N2+Kr,Ar++N2→N++N+Ar,Kr++N2O→N+NO++Kr,are measured as functions of primary ion kinetic energy. All of these reactions exhibit thresholds, and a semiempirical formula is fitted to the data near to the threshold energies. Despite the isoelectronic character of the products of Kr++N2O→O++N2+Kr and Kr++N2O→N+NO++Kr, their behavior differs in that the former reaction proceeds by the energetically most favorable channel while the latter does not; the reaction Kr++N2O→N+NO++Kr is energetically allowed for all primary ion kinetic energies but appears not to proceed below kinetic energies of about 2.4 eV in the center-of-mass coordinate system. The cross sections of reactions involving only atomic products do not exhibit any striking, qualitative differences from those cross sections involving molecular products.
Electron Spin Resonance Study of the Sym-Trinitrobenzene Anion and Related Radicals
Authors: Glarum Sivert H. , Marshall James H.
Published: January 2005

The electron spin resonance spectra of anion radicals generated by the electrolytic reductions of sym-trinitrobenzene, trinitromesitylene, trinitrobenzoic acid, trinitrotoluene, trinitroanisole, picramide, and the picrate ion are reported and discussed. Measurements were carried out in three solvents; dimethylformamide, dimethylsulfoxide, and acetonitrile. In addition, perturbations in the spectrum of the trinitrobenzene anion produced by the presence of various monovalent and divalent cations were studied. The trinitrobenzene and trinitromesitylene anions show an alternating linewidth effect which increases as the interaction between the anion and its environment increases. This effect implies correlated fluctuations in the spin densities of three equivalent nitrogroups.
Spin-Density Calculations for the Azulene Positive and Negative Ion Radicals
Authors: Brown Thomas H.
Published: January 2005

The valence bond method has been used to calculate the spin densities in the positive and negative ions of azulene. Though there is some question as to what value of QCH H should be used in the expression ρiπ=aiH/QCH H, the experimental hyperfine constants for the azulene negative ion are converted to spin densities through the use of 13C–1H spin-coupling data. The results of the valence bond calculations, when the parameters are chosen to minimize the error in the three largest spin densities, are in as good agreement with experiment as are the results of several molecular orbital calculations. A previously determined parameter was used to compute the effect of methyl substitution. Though the spin densities themselves are in no better agreement with experiment than in the case of the unsubstituted ion, the change in spin density at the unsubstituted positions is correctly predicted in both direction and magnitude. Since the spin densities in the azulene positive ion should be quite different from those in the azulene negative ion, these quantities are calculated as well. The results for the azulene positive ion do not agree with the results of available molecular orbital calculations, and thus some experimental values are needed to evaluate the relative merits of the methods.
First-Order London Dispersion Forces and Microwave Spectral Linewidth
Authors: Krishnaji  , Srivastava Shyam Lal
Published: January 2005

A theory for the collision cross section due to first-order London dispersion forces has been developed on the basis of the Anderson—Tsao—Curnutte's theory of pressure broadening. The widths of OCS J = 1→2 line broadened by helium and argon are explained.
Radiolysis of Cyclohexane—Cyclohexene-1-14C Solutions
Authors: Cher Mark , Hollingsworth C. S. , Browning B.
Published: January 2005

Radiolysis of solutions of 1% cyclohexene-1-14C in cyclohexane with 60Co γ rays yields radioactive cyclohexane, bicyclohexyl, cyclohexylcyclohexene, and bicyclohexenyl. Measurements were made of the total yield of these products, their specific activity, the total yield of hydrogen, and also the yield of hydrogen from pure cyclohexane. It is shown by material and radioactive balance considerations based on a simplified free radical mechanism, together with some known kinetic data, that a major fraction of the decrease in the H2 yield relative to that in pure liquid cyclohexane can be accounted for in terms of the reactions of H atoms with cyclohexene and the resulting formation of the radioactive C6H11 and C6H9 radicals. Detailed analysis shows that the specific rate of addition of H atoms to cyclohexene is 41 times greater than the specific rate of abstraction by H atoms from cyclohexane, and that the molecular (unscavengeable) and free radical yields in the irradiation of pure cyclohexane are, respectively, 1.7 and 3.7 molecules/100 eV. The latter conclusion is in fair agreement with results obtained by a number of other workers, but is in sharp contrast with recent results of Dyne. A plausible explanation is suggested to reconcile the discrepancy between the two sets of results.
Solutions of the Thomas—Fermi—Dirac Statistical Model of Atoms
Authors: Latter Richard
Published: January 2005

Numerical integration of the zero-temperature Thomas—Fermi—Dirac equation has been carried out on the IBM 701 for atomic numbers Z = 1 to 100. Compressed, expanded, and isolated atoms were treated, the latter using the boundary condition suggested by Jensen. Physical properties of interest for compressed and expanded atoms are presented graphically and, in the case of isolated atoms, tabularly as well.
Electrolytic Reduction of Trivalent Rare-Earth Ions in Alkaline-Earth Halides
Authors: Fong Francis K.
Published: January 2005

Trivalent dysprosium, thulium, and holmium ions in calcium fluoride, strontium chloride, and barium bromide have been successfully reduced to the divalent state by solid-state electrolysis. In contrast with similar samples reduced by gamma irradiation which are unstable with respect to light and heat, the electrolytically induced divalent rare-earth ions are optically and thermally stable. Unlike the gamma-reduced samples, recombination hole centers are believed to be absent in these samples. The majority of trivalent ions have been reduced, and the concentration of divalent rare-earth ions obtainable by the electrolytic process far exceeds that by gamma irradiation in all the samples, with or without charge-compensating monovalent cations. The completeness of the reduction, the stability of the reduced samples and, therefore, the apparent absence of recombination hole centers suggest that the reduction of the rare-earth ions follows the migration of the corresponding halide ions (which, in the case of calcium fluoride, served as charge compensators for the trivalent ions) to the anode, where they are presumably oxidized to the neutral state and escape from the crystal lattice. This mechanism is not unlike that proposed for the electrolytic coloration of alkali halides.
Flash Photolysis Measurement of the Kinetics of CF2 Reactions
Authors: Dalby F. W.
Published: January 2005

The second-order rate constant k for the combination of CF2 radicals to tetrafluoroethylene (C2F4) has been determined to be k=[(1.3)108](T/300∘K)12exp(−1.2/RT) liters/mole·sec.The reactivity of CF2 radicals towards olefins and towards oxygen was found to be surprisingly low.
Chemical Shifts, Ring Currents, and Magnetic Anisotropy in Aromatic Hydrocarbons
Authors: Dailey B. P.
Published: January 2005

Both the chemical shifts of nuclear magnetic resonances and molecular diamagnetic susceptibilities have their origin in the electronic currents induced by an external magnetic field. For the aromatic hydrocarbons detailed chemical-shift measurements and extensive measurements of the magnetic anisotropies are available to aid in a study of the validity of various theories connecting magnetic properties with magnetic electron currents.

The available experimental data seem to present a definite paradox. The chemical shifts due to ring currents are theoretically directly proportional to the values of Δχ, the anisotropy in the diamagnetic susceptibility; yet the experimental values of Δχ are much larger than those calculated from theory, while the experimental chemical shifts are substantially smaller than the theoretical ones.

Hoarau has suggested that only a part, χL, of the total anisotropy Δχ arises from the π electrons involved in the ring current and that one should add Δχσ, a contribution from the electrons in the σ bonds, and Δχp, the contribution due to the localized p electrons. The SCF—MO calculations of χL for benzene give a value of approximately —30×10—6, which is only about half the experimentally observed value of —59.7×10—6. Rough calculations are presented which indicate that the contributions of the σ and localized p electrons are large enough to account for the observed values of Δχ and χz for the aromatic hydrocarbons.

An analysis of the chemical shifts of the aromatic hydrocarbons shows that they are in agreement with a Δχ value for benzene of approximately —31×10—6 in good agreement with the SCF—MO value of χL. Calculations of the chemical shifts due to localized magnetic anisotropies show that they are quite small and can frequently be neglected. In calculating ring current contributions to the chemical shift in NMR spectroscopy it is recommended that the SCF—MO value of χL, —30×10—6, be used in place of the classical value, —49.5×10—6.
Study of Molecular Orbital Degeneracy in C7H7
Authors: Silverstone H. J. , Wood D. E. , McConnell H. M.
Published: January 2005

The paramagnetic resonance of the cycloheptatrienyl radical (C7H7) has been observed in single crystals of thiourea and naphthalene and in polycrystalline thiourea, naphthalene, cycloheptatriene, and argon at temperatures ranging from 4.2° to 300°K. The spectra are of two types: (a) high-temperature spectra—eight equally spaced lines with splittings in the range 3.5–4.1 G; (b) low-temperature spectra—highly anisotropic spectra which are markedly different for each crystalline environment. The transitions from (a) to (b) occur within 5°K, and the transition temperatures are 40°, 20°, and around 13°K in thiourea, naphthalene, and cycloheptatriene, respectively.

The high-temperature spectra are readily accounted for in terms of seven equivalent protons and a uniform electron spin distribution about the ring. The high-temperature spectra thus provide evidence that there is no significant static (Jahn—Teller) distortion of C7H7. The uniform spin distribution around the molecular ring is brought about by the combined effects of rapid molecular reorientation about the seven-fold axis, plus the crystalline electric-field splitting of the orbital degeneracy. That is, in a sense, the crystal field splitting ``locks'' the spin distribution to the lattice, and molecular reorientation moves the nuclei relative to a fixed spin distribution. The low-temperature spectra correspond to the electronic ground state of (nonreorienting) C7H7, as determined by the crystalline electric field. The observed low-temperature spectra of C7H7 in naphthalene are compared with spectra calculated using the Hückel, valence-bond, approximate unrestricted Hartree—Fock LCAO—MO, and Pariser—Parr approximations to the molecular electronic structure of C7H7. The observed spectra appear to be in semiquantitative agreement with calculations based on the Hartree—Fock and Pariser—Parr approximations. However, detailed comparisons between these theoretical calculations and experiment are uncertain since both vibronic interactions as well as torsional molecular oscillations have an effect on the low-temperature spin distribution.
Crystalline Field Stress Dependence
Authors: Stettler John D. , Veigele Wm. J.
Published: January 2005

A tensor theory for crystalline field stress dependence has been developed and the components expressed as matrix elements of ground-state electronic wavefunctions which contain the type of crystal bonding. The theory is applied to ruby and an approximate form of the theory is compared with an ionic model theory and with NMR experiments on 27Al in ruby from which (1/T| |)(Δq/q)| |=+2.8×10−12 (dyn/cm2)−1 and (1/T⊥)(Δq/q)⊥=−2.7×10−12 (dyn/cm2)−1 were determined. From the approximate form of the theory it is concluded that not more than 15% covalency is present in ruby. A splitting of an 27Al satellite NMR line under stress at 20° to the c axis was observed and is explained by the C3 site symmetry of ruby.
Approximate Computation of the Energy Band Structure of Native DNA
Authors: Beleznay F. , Biczó G.
Published: January 2005

A new method for the determination in the Hückel approximation of the band structure of a periodic native DNA has been devised. First the method is described, its applicability for DNA is analyzed, after which the band structures of two periodic DNA models and of eight different DNA macromolecules are determined. The results show that realistic computations can be performed only if in addition to the nearest-neighbor frequencies of the bases within the single DNA helices, also the frequencies of all the 16 possible combinations of superimposed base pairs are known. Failing such experimental data, the computations on native DNA of different compositions will lead to oversimplified band structures.