bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate Hartree–Fock Wavefunctions, One-Electron Properties, and Electronic Structure of the Water Molecule
Authors: Aung Soe , Pitzer Russell M. , Chan Sunney I.
Published: February 2004

Several approximate Hartree–Fock SCF wavefunctions for the ground electronic state of the water molecule have been obtained using an increasing number of multicenter s, p, and d Slater-type atomic orbitals as basis sets. The predicted charge distribution has been extensively tested at each stage by calculating the electric dipole moment, molecular quadrupole moment, diamagnetic shielding, Hellmann–Feynman forces, and electric field gradients at both the hydrogen and the oxygen nuclei. It was found that a carefully optimized minimal basis set suffices to describe the electronic charge distribution adequately except in the vicinity of the oxygen nucleus. Our calculations indicate, for example, that the correct prediction of the field gradient at this nucleus requires a more flexible linear combination of p orbitals centered on this nucleus than that in the minimal basis set. Theoretical values for the molecular octopole moment components are also reported.
PMR Studies of the Solvation of Nickel(II) in CD3OH and CH3OD
Authors: Chmelnick A. M. , Fiat D.
Published: February 2004

Evidence is presented that the coordination number of the nickelous ion in methanol solutions is six. The chemical-shift temperature dependence and the linewidths of the PMR absorption-mode signals of CD3OH and CH3OD coordinated to the nickelous ion were measured. The hyperfine coupling constants for the interaction between the hydroxyl proton and the unpaired electrons of the nickelous ion were found to be A / h = (6.2 ± 0.3) × 105Hz and for the interaction with the methyl protons A / h = (6.4 ± 0.2) × 105Hz. The relaxation time of the unpaired electrons of the nickelous ion was estimated to be about 2 × 10−11 sec at −49°C. The ratio of the nickelous-ion–methyl-protons distance to the nickelous-ion–hydroxyl-proton one was found to be 1.32 ± 0.03. Earlier observations, relevant to those reported here are discussed and, in some cases, reinterpreted.
Adsorption of Barium onto Oriented Tungsten Surfaces
Authors: Hopkins B. J. , Smith B. J.
Published: February 2004

The Kelvin and the retarding-field contact potential difference techniques have been used to follow the work-function changes during the adsorption of barium onto both polycrystalline and single-crystal tungsten surfaces. A double-evaporation technique was devised in order to obtain conditions under which the barium could be evaporated without the pressure exceeding, at best, 3 × 10−10 torr. Contrary to the results of a previous similar investigation which used a thermionic method, the work functions of barium covered (110) and (100) tungsten surfaces differed considerably. For films, estimated to be greater than five monolayers in thickness, the final work functions on the (110) and (100) surfaces, respectively, were 2.955 ± 0.005 eV and 2.560 ± 0.005 eV. A model is suggested in which the barium on the (100) surface forms a polycrystalline deposit, while that on the (110) surface compares closely with a single-crystal (110) plane in barium metal but with a high density of defects. The shape of the work function vs coverage curves have been compared with those predicted by a recent semiempirical theory. Unfortunately, for a worthwhile comparison an accurate knowledge is required of the polarizability of the barium atom, the adsorbate density, and the monolayer position, none of which were determined in the present work. By allocating reasonable values to the polarizability and the monolayer position a fit between the experimentally and theoretically determined curves to within ±0.04 eV could be obtained on the (110) surface using the adsorbate density predicted by the proposed model. With no restriction on the adsorbate density for the (100) plane the fit could be improved to ±0.02 eV. Removal of this restriction for the (110) plane also improved the agreement between theory and experiment to within ±0.02 eV.
Infrared Spectrum of Ice VI in the Range 4000–50 cm−1
Authors: Bertie J. E. , Labbé H. J. , Whalley E.
Published: February 2004

The infrared spectrum of ice VI recovered at liquid-nitrogen temperature and atmospheric pressure has been investigated in the range 4000–50 cm−1. The spectrum closely resembles that of ice V, and shows conclusively that ice VI is orientationally disordered when recovered in this way.
Perturbation Theory for Exchange Interactions between Atoms or Molecules. II
Authors: Ritchie A. B.
Published: February 2004

A perturbation theory is developed for interacting atoms or molecules in the region in which exchange becomes important. Use of a set of linear operators which project out the components of the antisymmetrized state vector permits the derivation of a set of exact integral equations, each for a single component of the vector, which can be solved by ordinary perturbation–theoretic techniques. In this way, exchange can be treated exactly, without the necessity of obtaining an orthogonalized basis.
Combination Rules for Binary Gaseous Mixtures Deduced from Viscosity
Authors: DiPippo R. , Kestin J.
Published: February 2004

In this paper, the results are reported of two separate tests on the validity of three mixing rules that are commonly employed in determining the force parameters for unlike molecular collisions from those for like-molecular collisions where the interaction may be described by means of a two-parameterforcepotential. Both tests utilize the equations for the viscosity of dilute gases based on the Chapman–Enskog solution to the Boltzmann equation, together with highly precise experimental data on the viscosity of pure gases and binary gas mixtures. Both tests indicated that the experimental data are incompatible with the simple combination rules; that is, the arithmetic average for the distance parameter and the geometric mean for the energy parameter. The results of the second test show that the combination rule εijσij6 = (εiiσii6εjjσjj6)1 / 2 is not contradicted by the experimental data. All possible binary combinations of the gases He, Ne, Ar, N2, and CO2 were analyzed for this report.
Analysis of the Proton NMR Spectrum of Toluene
Authors: Williamson M. P. , Kostelnik R. J. , Castellano S. M.
Published: February 2004

The proton NMR spectra of toluene recorded with and without decoupling of the methyl resonance have been completely analyzed in terms of chemical shifts and coupling constants. The procedures for the analyses of the spectra are illustrated, the results of the different calculations are compared, and the values of the spectral parameters obtained are discussed.
Dependence of Inertial Constants on Ordinary Vibrational Coordinates in Molecules with an Internal-Rotation Degree of Freedom
Authors: Kirtman Bernard
Published: February 2004

General expressions are developed for calculating first and second derivatives of inertial constants with respect to ordinary vibrational coordinates in molecules containing either a symmetric or an asymmetric internal rotor.
Second-Order Phase Transition in the VS One-Phase Region
Authors: Franzen H. F. , Burger T. J.
Published: February 2004

The lattice parameters and the densities of vanadium monosulfide samples have been determined by Guinier x-ray powder diffraction and pycnometry, respectively. The samples spanned the homogeneity range of vanadium monosulfide. The data obtained are consistent with sulfur vacancies in samples for which S / V < 1, and vandium vacancies for samples with S / V > 1. The lattice parameters were found to vary continuously through the transition from the NiAs structure type to the MnP structure type, indicating that the transition is second order.
Quadratically Convergent Iteration Procedure for Self-Consistent Calculations
Authors: Brown Thomas H.
Published: February 2004

An iteration procedure is described for self-consistent-type calculations which is quadratically convergent. As an illustration of the efficiency of the procedure, the results for an SCF LCAO MO calculation for the π electrons for napthalene are given. For this example, and for other cases tested, satisfactory convergence is obtained in one or two iterations. Convergence to machine accuracy usually takes no more than two or three iterations.
Low-Frequency Motions in Liquid Carbon Tetrachloride. II. The Raman Spectrum
Authors: Gabelnick Helene S. , Strauss Herbert L.
Published: February 2004

The low-frequency (0–130-cm−1 shifts) depolarized Raman spectrum of liquid carbon tetrachloride has been obtained. Comparison of the integrated intensity of this band with the allowed vibrational bands gives a value for a root-mean-square polarizability anisotropy of about 1 Å3. The derived correlation function is compared to the correlation function from previous infrared results. The data are consistent with a substantial root-mean-square distortion from tetrahedral symmetry although the time behavior is not explained.
Microwave Spectrum, Structure, and Dipole Moment of Cyclohexene
Authors: Scharpen LeRoy H. , Wollrab James E. , Ames Donald P.
Published: February 2004

The microwave spectra of cyclohexene, cyclohexene-d10, and 3,3,6,6-cyclohexene-d4 have been assigned. Subject to certain assumptions, the nine moments of inertia were least-squares fitted to obtain the structural parameters ∢C1–C2–C3 = 123.3°, ∢C2–C3–C4 = 111.6°, ∢C3–C4–C5 = 110.3°, ∢C–C–H (methylene) = 109.9°, ∢C–C–H (ethylene) = 119.5°, and θ=30.1°, where θ is the angle between the C1–us;C2 and C4–C5 bonds projected on the a–c principal axis plane. θ measures the deviation of the ring from planarity. The assumptions related to symmetry were (1) the molecular point group is C2; (2) the methylene groups are symmetric with equal C–C–H angles; and (3) the ethylene group and two adjacent carbons lie in a plane. The bond lengths were taken to be r(C1 –C2) = 1.34 Å, r(C2–C3) = 1.51 Å, r(C3–C4) = 1.53 Å, r(C4–C5) = 1.53 Å, r(C–H) (ethylene) = 1.09 Å, and r(C–H) (methylene) = 1.10 Å. Stark effect measurements yielded μb = 0.331 D for the common isotopic species and showed that μb is unchanged (within the experimental uncertainty) in the deuterated species. The Stark effect also confirmed the haclf-chair conformation and C2 symmetry by requiring μc to be less than 0.003 D.
Effect of cis–trans Isomerism on the Carbon-13 Chemical Shifts of Some Unsymmetrically Substituted Ethylenes
Authors: Savitsky George B. , Ellis Paul D. , Namikawa Keishi , Maciel Gary E.
Published: February 2004

The difference in shielding between the 13C nuclei of cis and trans isomers CHX = CHX for the series X = Cl, Br, I, CO2C2H5 was previously attributed to the inhibition of contributing resonance structures by bulky substituents in cis isomers. The present work, which includes the determination of 13C chemical shifts of cis and trans isomers with nonequivalent substituents, CHX = CHY, indicates that the previous interpretation must be modified considerably and that the tendency toward charge separation and reduced bond order in the C = C π bond of cis isomers may be the major factor in these differential shieldings. An application of the Pople–Karplus equations for 13C shielding is consistent with this view.
Thermal Conductivity and Rotational Relaxation in Some Polar Gases
Authors: Barua A. K. , Manna A. , Mukhopadhyay P.
Published: February 2004

Measurements of thermal conductivities of hydrogen sulfide, hydrogen chloride, and ammonia have been carried out over the temperature ranges −78.5°–200°, 0°–200°, and −26.2°–20.1°C, respectively, by the hot-wire cell method. The data have been interpreted by taking into consideration the effects of resonant exchange of rotational energy. The temperature dependence of rotational collision numbers Zrot derived from thermal conductivity values has also been investigated.
Enthalpies of Mixing in Binary Liquid Alkali Fluoride Mixtures
Authors: Holm J. L. , Kleppa O. J.
Published: February 2004

The enthalpies of mixing in the binary liquid systems LiF–NaF, LiF–KF, LiF–RbF, and LiF–CsF have been determined over wide ranges of composition in a high-temperature calorimeter suitable for temperatures up to 1100°C. A few measurements near the 50–50 composition are reported for the systems NaF–KF, NaF–RbF, and KF–RbF. The results are compared with comparable data for the alkali nitrates, chlorides, bromides, and iodides previously studied by Kleppa and Hersh. On the whole the enthalpies of mixing of the fluorides are somewhat less exothermic (or more endothermic) than predicted from the earlier results. It is suggested that this may be related to the lower polarizability of the fluoride anion with the attendant weakening of the nearest-neighbor cation–anion ion–induced-dipole–ion interaction, and to the radius ratio effect, i.e., to the core repulsion between next-nearest-neighbor cations in the presence of the small fluoride anion.
Heat Capacity of Tetrauranium Enneaoxide (U4O9) from 1.6° to 24°K. The Magnetic Contribution to the Entropy
Authors: Flotow Howard E. , Osborne Darrell W. , Westrum Edgar F.
Published: February 2004

The heat capacity of UO2.250 has been determined calorimetrically from 1.6° to 24°K and found to be significantly higher than that of UO2 or ThO2. There is no λ-type thermal anomaly in the region of the maximum in the magnetic susceptibility near 6.4°K. The heat capacity is proportional to T2 below 2.7°K. An approximate resolution of the entropy into lattice and magnetic components indicates that the magnetic entropy is about 70% that of UO2 near 200°K.
Neutron Diffraction Study of Ice Polymorphs. I. Ice IX
Authors: Rabideau S. W. , Finch E. D. , Arnold G. P. , Bowman A. L.
Published: February 2004

The neutron diffraction spectrum of polycrystalline D2O ice IX has been obtained and it is in agreement with a proton-ordered structure for this ice. Values of the tetragonal, pseudocubic lattice parameters were found to be a0≃c0 = 6.745 ± 0.004 Å at 80°K. A computer-generated least-squares fitting of the intensities of the 38 observed reflections gave the scale factor, thermal parameter, and the oxygen and deuteron position parameters. The O–O–O bond angles are appreciably distorted from the tetrahedral angle in this high-pressure polymorph.
Perturbation Treatment of the Helium Ground State with Correlation in Zeroth Order
Authors: Lebeda C. F. , Schrader David M.
Published: February 2004

Pluvinage's method for calculating correlation energies of two-electron atoms is modified so that a consistent perturbation calculation becomes possible. Correlation is thereby introduced into the wavefunction in zeroth order, and the cusp conditions between all pairs of particles are satisfied in zeroth order. The first-order wavefunction is estimated variationally, and the resulting energy to third order is compared with that of Scherr and Knight and Midtdal for the systems H−, He, and Li+. The sensitivity of certain calculated properties to the accuracy of the first-order wavefunction is examined in the case of He.
Vibronic Coupling in the Dimer
Authors: Young John H.
Published: February 2004

A displaced oscillator model of vibronic coupling in the dimer is presented. Interpolation formulas for the vibronic eigenvalues and intensities are derived which are valid in both limits of weak intermolecular and weak vibronic coupling. The characteristic function of the intensity distribution function is also derived. The physical interpretation of these expressions is given.
Flash Photolysis of Hydrogen Iodide in the Presence of Deuterated Hydrocarbons
Authors: Biordi Joan C. , Rousseau Yves , Mains Gilbert J.
Published: February 2004

The reactions of hot hydrogen atoms in the range 0.8–2.4 eV with perdeuterated and partially protonated hydrocarbons have been studied. The hot atoms were produced in C2D6, C3D8, n-C4D10, and various isotopically mixed ethanes by flash photolyzing HI-RHD mixtures. Graphs of product ratio H2/HD vs the initial reactant ratio HI/RD were characteristically linear. These and similar graphs for mixtures containing a rare gas were analyzed using the kinetic theory of hot-atom reactions developed by Estrup and Wolfgang and also by a simpler approach. Where comparison was possible, the results of the two methods of analysis showed good agreement. The following parameters were evaluated: average relative reaction probabilities for H*–HI and H*–RD collisions (where the asterisk denotes the hot species), the fraction of H* moderated to that reacting hot in pure RD, and β, the average fractional energy loss by H* is collision with RD. The most important conclusions which can be drawn from the results are: (a) a simple interpretative scheme employing average reaction and moderation probabilities serves to give nearly quantitative estimates of the parameters involved; (b) in all cases the probability of H* reaction with HI is considerably larger than with RD, although several times smaller than the corresponding reaction probabilities of thermal hydrogen atoms; (c) deuterium abstraction by H* from the six partially deuterated ethanes is simply statistical; (d) collisions between H* and RD are quite inelastic, the values for β being greater than 4, 6, and 12 times the respective rigid-sphere values for perdeuterated ethane, propane, and n-butane.
Zero-Field Resonance of Gd3+ in YVO4 and YPO4
Authors: Kahle H. G. , Koch V. , Plamper J. , Urban Wolfgang
Published: February 2004

The frequency variation spectrometer described earlier by one of the authors has been completed to cover three octaves from 2 to 16 GHz. This spectrometer is used to measure the zero-field splittings of trivalent gadolinium in yttrium vanadate and yttrium phosphate.
Percus–Yevick Equation for Hard Spheres with Surface Adhesion
Authors: Baxter R. J.
Published: February 2004

It is shown that the Percus–Yevick approximation can be solved analytically for a potential consisting of a hard core together with a rectangular attractive well, provided that a certain limit is taken in which the range of the well becomes zero and its depth infinite. The results show a first-order phase transition which appears to be of the type observed numerically for the Lennard-Jones 12–6 potential.
Millimeter Wave Spectrum and Molecular Force Field of Tetratomic C2υ Molecules: NO2F
Authors: Mirri A. M. , Cazzoli G. , Ferretti L.
Published: February 2004

The millimeter rotational spectrum of NO2F has been measured in the frequency range 90–200 kMc/sec. By centrifugal distortion analysis, based on the Kivelson and Wilson first-order perturbation treatment, the following values of the ground-state parameters were obtained: A = 13 201.31 B = 11 446.25 C = 6118.99 τaaaa = − 0.039814 τbbbb = − 0.078638 τaabb = 0.012452 τabab = −0.048868. Two different methods were used in order to determine the general quadratic force field, by combination of infrared and microwave data. The first method is based on the complete consistency between force constants and vibration frequencies of the normal species and on the best fit of the rotational spectrum. The second method uses the least-square determination of the corrections on some starting set of force constants. All the isotopic- and normal-species vibration frequencies measured by Bernitt, Miller, and Hisatsune and all the centrifugal distortion contributions on millimetric rotational transitions were used as experimental data, taken with appropriate weights. The two methods yield very similar results. The agreement between observed and calculated rotational and vibration frequencies is of the order of magnitude of the experimental errors. Two different sets of force constants were obtained, corresponding to an exchange of ν2 and ν3 vibration frequencies in the diagonalization of the GF matrix.
Medium Effects in NMR. VI. Vapor-Phase Studies of Hydrogen Bonding between Dimethyl Ether and Hydrogen Chloride
Authors: Govil G. , Clague A. D. H. , Bernstein H. J.
Published: February 2004

The hydrogen chloride–dimethyl ether system has been chosen as an example to demonstrate that NMR can be used to study hydrogen bonding in the vapor phase. An analysis of the temperature and pressure dependence of the proton signal in HCl gives the following values for the thermodynamic quantities: ΔH = − 7.1 ± 0.8 kcal / mole, ΔS = − 25.7 ± 1.3 e.u. The effect of hydrogen bonding is to deshield the HCl proton by about 3 ppm, which agrees with the value calculated from an electric-field model.
Ionizing Photolysis of Methane
Authors: Jensen C. A. , Libby W. F.
Published: February 2004

The photolysis of methane using a filtered 584-Å light source yields primarily ethylene and a polymer with small amounts of other products. An interpretation of the meaning of these results is offered. Information on the use of thin aluminum films to obtain pure 584-Å light is given.
Superhyperfine Interaction Due to 13C in the ESR Absorption Spectrum of Mn2+ in Single-Crystal Calcite
Authors: Hodges J. A. , Marshall S. A. , McMillan J. A. , Serway R. A.
Published: February 2004

The superhyperfine structure spectrum of Mn2+ interacting with 13C nuclei in single crystal calcite has been examined by electron spin resonance absorption spectroscopy at 77°K. An analysis of the spectrum performed in three mutually orthogonal planes of the calcite structure indicates that the core polarization of Mn2+ is 134 kOe.
Concentration Dependency of the Fluorescence from Solutions of 2-Phenyl Indole and Derivatives of 2-Phenyl Indole. I. Fast-Electron Excitation
Authors: Horrocks Donald L. , Wirth Hermann O.
Published: February 2004

The relative scintillation yield for excitation with fast electrons was measured as a function of the concentration of the solute. The property of self-quenching of a series of 2-phenyl indole and 2-phenyl indole derivatives was correlated with the structure of the compound. It was shown that destroying the ability of the chromophore of the molecule to obtain a coplanar configuration would eliminate self-quenching in most cases. The exceptions were those derivatives which had an H atom on the N atom of the indole ring. It is believed that in these cases self-quenching may proceed through a hydrogen-bonding mechanism. The substitution on long-chain alkyl groups on the N atom of the indole did not eliminate self-quenching even for a 12-carbon-atom chain. There was a gradual decrease in self-quenching upon increasing the substituent from methyl to n-hexyl.
Concentration Dependency of the Fluorescence from Solutions of 2-Phenyl Indole and Derivatives of 2-Phenyl Indole. II. uv Radiation Excitation
Authors: Horrocks Donald L.
Published: February 2004

The fluorescence spectra and fluorescence yields were measured as a function of solute concentrations for uv excitation of 2-phenyl indole and some derivatives of 2-phenyl indole. Correlations between structure and self-quenching were similar to the correlations obtained with fast-electron excitation. The formation of excimers was demonstrated as the concentration of certain derivatives of 2-phenyl indole was increased. A common pathway of excimer formation and self-quenching was indicated from the results.
Two-Temperature van der Waals Potentials
Authors: Rosenkrans J. P. , Linder B. , Kromhout R. A.
Published: February 2004

The Linder formulation of the van der Waals potential, expressed in terms of susceptibilities, between two weakly interacting molecular systems at different temperatures is applied to a simple model. The model molecules are assumed to have the low-frequency characteristics of rigid rotors and the high-frequency characteristics of harmonic oscillators. It is shown that the induction potential is always attractive; the orientation potential becomes repulsive when the temperature difference is large. The dispersion potential becomes repulsive when the temperature difference is large provided the hotter system has the higher natural frequency.
Studies of the Evaporation Mechanism of Sodium Chloride Single Crystals
Authors: Lester J. E. , Somorjai G. A.
Published: February 2004

The vacuum evaporation rate of the (100) face of pure sodium chloride single crystals has been measured with a vacuum microbalance in the temperature range 450°–650°C. The steady-state vaporization rates of pure crystals with dislocation densities of ∼1 × 106/cm2 were lower by about a factor of two than the maximum thermodynamic rate (ᾱυ ≈ 0.5). When the dislocation density was increased an order of magnitude (to ∼ 107/cm2) by straining the crystals, the steady-state evaporation rate increased to approximately the thermodynamic rate (ᾱυ ≈ 1.0). The relative vaporization rates of monomer and dimer were measured using a quadrupole mass spectrometer. Vaporization activation energies ED* = 53 ± 1 kcal/mole and ED* = 62 ± 1 kcal/mole were found for the monomer and dimer, respectively, in the temperature range of the experiments for low dislocation crystals. No dependence of the monomer to dimer ratio on the dislocation density was detected. The presence of the divalent cation impurity, Ca2+, in the NaCl crystals markedly reduced the vaporization rate and increased the activation energy of vaporization. Crystals doped with 300 ppm Ca2+ exhibited vaporization rates approximately an order of magnitude lower than the maximum thermodynamic rate (ᾱυ ≈ 0.1). The average activation energy of vaporization for these crystals was Ē* ≈ 63 kcal/mole as computed from the total rate of vaporization. The monovalent impurities, Br−, OH−, O2−, had no detectable effect on the vaporization rate. An evaporation mechanism was postulated which could account for the experimental observation.
Ionization Potentials of Free Radicals Formed by Electron Impact. Methylstannyl Radicals
Authors: Lampe F. W. , Niehaus A.
Published: February 2004

The vertical ionization potentials of the (CH3)3Sn, (CH3)2Sn, and CH3Sn radicals have been measured using a double-pulsed mass-spectrometric method in which the radicals were formed by the impact of electrons on hexamethylditin. As a check on the internal consistency of the method and measurements, the vertical ionization potentials of several alkyl radicals, R, produced by electron impact on compounds of the type (CH3)3Sn–R, were measured. The values found were generally somewhat higher than recent measurements using photoionization and pseudomonoenergetic electron-impact methods, but were in excellent agreement with the vertical ionization potentials obtained by the impact of nonmonoenergetic electrons on thermally-produced alkyl radicals.
Radial Integrals for the Atomic Many-Body Problem
Authors: Roberts P. J.
Published: February 2004

A full analysis is presented of the radial integrations arising from certain two-, three-, and four-electron integrals for correlated wavefunctions, assuming only pair correlations between the electrons in an atom.
Temperature Dependence of Surface Tension for Liquid Metals
Authors: Bohdansky J.
Published: February 2004

The surface-tension temperature dependence is calculated for liquid metals. In this calculation the ion motion is taken as a harmonic oscillation and it is shown that the difference in oscillation frequencies for surface and inner ions is mainly responsible for the temperature dependence of the surface tension. There is, however, a second influence caused by the change of particle density due to thermal expansion. An expression for the surface tension is derived and comparison is made with experimental values. The change of oscillator frequency, the surface tension at zero temperature, and a characteristic temperature corresponding to the critical temperature are calculated.
Intensity Law for Microwave Spectroscopy: Theoretical and Experimental
Authors: Harrington Howard W.
Published: February 2004

A method is described for extracting accurate molecular information from pure-rotational absorption-line-intensity data. This method can be applied successfully to the relative intensity of two or more lines even when these lines occur at widely separated frequencies. It is shown that the experimental function, log spectrometer signal amplitude at the line frequency vs log corresponding incident microwave-power level can be superimposed on a theoretical intensity function called the intensity law by a translation of the origin. This origin displacement is related to the molecular concentration of the absorbing species and the rotational broadening–relaxation time associated with the particular transition. The intensity law is independent of the line frequency or sample pressure and depends only on the microwave power density distribution in the sample. This distribution varies as function of frequency in the Stark cell due mainly to waveguide wall losses. Neglect of this variation can result in large errors in molecular quantities calculated from relative intensity data.
Diagrammatical Derivation and Representation of Rayleigh–Schrödinger Perturbation Theory
Authors: Salzman W. R.
Published: February 2004

A method is presented for obtaining the various terms in the Rayleigh–Schrödinger perturbation theory to arbitrary order by means of diagrams. The prescription for obtaining the Nth-order correction to a particular zero-order eigenvector is to construct all diagrams of a certain type and associate an operator with each diagram. The method provides for the easy construction and display of Rayleigh–Schrödinger perturbation-theory corrections. The relationship of the present method to other work is discussed.
Explicit Formulas for Molecular Integrals over Hermite–Gaussian Functions
Authors: Živković T. , Maksić Z. B.
Published: February 2004

A new basis set of functions of the form Hn1[(a)1/2x]Hn2[(a)1/2y]Hn3[(a)1/2z] exp(− ar2) is proposed for molecular calculations. Explicit formulas for overlap, dipole moment, and kinetic-energy integrals as well as nuclear-attraction and electron-repulsion energy integrals are given. Numerical integration is completely avoided. All integrals are analytical functions of parameters, and only two auxiliary functions are required.
Equation of State of the Hard-Disk Fluid from Approximate Integral Equations
Authors: Lado F.
Published: February 2004

The Percus–Yevick, hypernetted-chain, and “pressure-consistent' integral equations have been solved, using numerical Hankel transforms, for a fluid of two-dimensional hard cores. The thermodynamic quantities obtained from these solutions are presented and compared among themselves and with the results of other theories; a comparison of computed pair distribution functions g with a Monte Carlo g is also presented. The Percus–Yevick equation is found to give the best over-all results.
Hydrogen Dichloride Radical: Infrared Detection through the Matrix Isolation Technique
Authors: Noble Paul N. , Pimentel George C.
Published: February 2004

When hydrogen chloride–chlorine–argon mixtures are passed through a glow discharge and the products are condensed at 14°K, two conspicuous infrared absorptions at 956 and 696 cm−1 result. Concentration dependence of intensities, isotopic labeling, and force-field calculations lead to assignment of these bands to hydrogen dichloride. The force field calculated supports a linear, centrosymmetric (D∞h) structure with hydrogen bond strength apparently comparable to or exceeding those attributed to HCl2− in various crystals.
Significant-Structure-Theory Compressibility Coefficients, Thermal-Expansion Coefficients, and Heat Capacities of Alkali Metals in the Liquid Phase
Authors: Vîlcu Rodica , Misdolea Constantin
Published: February 2004

Some thermodynamic characteristics of molten alkali metals, at various temperatures, were calculated with the help of the significant-structure theory. The coefficients of the thermal expansion and of the isothermal compressibility are correlated to heat capacities, at constant volume and pressure. The computation results, considered in comparison with the available experimental data, show the validity limits of the theory.
Proton Magnetic Resonance Spectra of a Three-Spin System: Oxalic Acid Dihydrate
Authors: Håland Kjell , Pedersen BjO/rn
Published: February 2004

Theoretical proton magnetic resonance spectra have been fitted to experimental room-temperature spectra of a single crystal of oxalic acid dihydrate by least-squares methods. The theoretical spectrum used is the seven-line spectrum calculated by Andrew and Bersohn for a magnetic dipole–dipole coupled three-spin system with each line in the spectrum broadened by a Gaussian function. The three-spin system consists of two protons from a water molecule and one proton from a hydroxyl group. From the marked temperature dependence of the spectrum in certain orientations it is concluded that the water molecules are flipping fast at room temperature equalizing the coupling between the hydroxyl proton and each of the two protons in the water molecule. The theoretical line shapes are found to be in good agreement with the experimental spectra in crystal orientations where the fine structure is well resolved. From the analysis the interatomic distances and the orientation of the three-spin triangle in the unit cell are determined. The intramolecular proton–proton distance is found to be 1.595 ± 0.004 Å, and the distances to the hydroxyl proton 2.046 ± 0.010 Å and 2.131 ± 0.017 Å. All distances are uncorrected for atomic vibration. The intramolecular distance is equal to the length as usually found in NMR studies of hydrates, and the other two distances are within the experimental uncertainty equal to the corresponding distances found in a neutron diffraction study. The broadening parameter β, which is a measure of the coupling between the three-spin systems, is found to be smaller than expected from the calculated Van Vleck second moment.
Studies in Configuration Interaction. II. Determination of Charge- and Spin-Density Functions in π-Electron Systems
Authors: Cooper I. L. , McWeeny R.
Published: February 2004

Results of calculations of spin- and charge-density functions are presented for some small π-electron systems, using a configuration-interaction procedure which applies equally well to both molecular-orbital and valence-bond approximation methods, and thus provides a direct comparison of the two methods.
Electron Attachment in N2O
Authors: Phelps A. V. , Voshall R. E.
Published: February 2004

Electron attachment coefficients in N2O at 300°K have been measured using drift-tube techniques. For ratios of electric field to gas density, E / N, below about 2 × 10−17V·cm2 attachment occurs by an apparent three-body process. Extrapolation to thermal electron energies yields an attachment rate coefficient of (6 ± 1) × 10−33 cm6 sec−1, in good agreement with the value obtained by Fessenden and Warman from microwave afterglow studies. For E / N > 2 × 10−17V·cm2 attachment occurs by a two-body process, presumably the dissociative attachment process leading to O− as observed in electron beam experiments.
Optical Activity of Vibrational Origin. I. A Model Helical Polymer
Authors: Deutsche C. W. , Moscowitz Albert
Published: February 2004

Measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) in the visible and ultraviolet region of the electromagnetic spectrum are common. Largely due to technical difficulties, however, few measurements of Cotton effects have yet been made at infrared frequencies. If the usefulness of such measurements could be demonstrated, it might be that the experimental difficulties would be overcome in the near future. It is such a demonstration which is undertaken in this paper. The model system studied is an infinite helical polymer of point masses each with an effective charge. The normal modes of vibration for the polymer are calculated using a valence-force approximation, and using these normal-modes expressions for molecular polarizability and optical rotatory dispersion are derived for infrared frequencies. It is seen that under certain conditions there will be normal vibrations which are not easily observed in the absorption spectrum but which should exhibit Cotton effects which are more readily observable. Also, the chirality of the helix is implicitly given by the signs of the Cotton effects. These results are analogous to what is found in ORD spectra at visible frequencies. In addition to these effects, however, a frequency dependence proportional to (ω02–ω2)−2 appears in the infrared ORD spectrum at frequencies corresponding to the “perpendicular” band of the absorption spectrum. It is possible that the identification of such a band in the ORD spectrum could be used to identify helical conformations of polymers in solution.
ESR and Optical Studies of Acyl Radicals Produced from Acyl Chlorides by Dissociative Electron Attachment in γ-Irradiated Organic Glasses at 77°K
Authors: Noda Shoji , Fueki Kenji , Kuri Zen-ichiro
Published: February 2004

Dissociative electron attachment by acyl chlorides in γ-irradiated organic glasses at 77°K has been investigated by ESR and optical absorption measurements. The MTHF and 3MP glasses containing acyl chlorides (CH3COCl, C2H5COCl, C6H5CH2COCl, C6H5COCl, C6H5CH=CHCOCl) display a similar ESR singlet. 3-Methylpentane glass containing CH3COCl exhibits an ESR singlet or triplet depending upon solute concentration. γ-irradiated MTHF glasses containing these solutes give the optical absorption spectra having the characteristic absorption bands in the visible and uv region. These ESR and optical absorption spectra have been assigned to acyl radicals. Illumination of γ-irradiated samples with visible light yields alkyl radicals from CH3CO· and C2H5CO·, benzyl radicals from C6H5CH2CO·, and brings about no change in C6H5CO· and C6H5CH=CHCO·. The decay of alkyl radicals formed in 3MP has been measured at 77°K.
Thermoluminescence and Phase Transitions of Irradiated Fluorinated Polymers
Authors: Mele A. , Site A. Delle , Bettinali C. , Domenico A. Di
Published: February 2004

Polytetrafluoroethylene and polytetrafluoroethylene oxide have been irradiated under vacuum and in the presence of oxygen and helium. The thermoluminescence glow curves of the polymers have been examined from liquid-nitrogen temperatures up to about 60°C. The polymers irradiated in vacuo show very weak thermoluminescence emission. The presence of gas during irradiation has the effect of inducing a strong emission. The temperature of the thermoluminescence peaks coincides with the appearance of molecular motions. The spectral distribution of the thermoluminescence glow peaks has been determined. The results have been interpreted on the basis of the electron-trap theory. It is suggested that thermoluminescence at low temperature is associated with a continuous structural change in the amorphous regions which occurs on warming the polymers and that the trapping levels are uniformly distributed over a wide range of energy. The thermoluminescence glow peaks near room temperature correspond to well-defined crystalline transitions in the two polymers.
Polarized Spectra and Crystal-Field Parameters of Eu3+ in YPO4
Authors: Brecher C. , Samelson H. , Riley R. , Lempicki A.
Published: February 2004

Single crystals of yttrium phosphate doped with Eu3+ were investigated by means of polarized emission and absorption spectroscopy. The spectra are consistent with the known D2d site symmetry of the Eu3+ ion, and most of the observed transitions have been assigned. The energy-level structure of the 7F multiplet and the lower part of the 5D multiplet has been defined, and the former has been described in terms of a crystal-field model. The optical parameters for such a model have been calculated, and comparisons are made with similar calculations on yttrium vanadate.
Collision Broadening of Rotational Absorption Lines. III. Broadening by Linear Molecules and Inert Gases and the Determination of Molecular Quadrupole Moments
Authors: Murphy Joseph S. , Boggs James E.
Published: February 2004

A recently developed theory of the pressure broadening of microwave absorption lines resulting from transfer of rotational energy in molecular collisions has been applied to calculations of the linewidth of rotational absorption lines of a number of linear and symmetric-top molecules broadened by collisions with linear molecules and inert-gas atoms. In such cases, shorter-range forces such as dipole–quadrupole, quadrupole–dipole, quadrupole–quadrupole, and dispersion interactions are important as well as dipole–dipole interaction. In general, the agreement between the theoretical calculations and previously reported measurements is quite satisfactory. The application of the experimental technique as a method for determining molecular electric quadrupole moments is analyzed, and values for the molecular quadrupole moments of OCS, N2O, NO, CO2, N2, and H2 are obtained from earlier data.
Double Perturbation Theory Applied to Frequency-Dependent Polarizabilities. II
Authors: Deal Walter J. , Young Ralph H. , Kestner Neil R.
Published: February 2004

Two theorems are presented which increase the scope of double perturbation theory. First, an interchange theorem is found for polarizabilities at complex-valued frequencies. Second, a form of double perturbation theory is developed which does not assume the existence of an unperturbed Hamiltonian relating the unperturbed and perturbed wavefunctions.
Dissociation of N2 in Weak rf Discharge
Authors: Young Robert A. , St. John Gilbert A.
Published: February 2004

It has been established that the production of nitrogen atoms from molecular nitrogen by a weak rf discharge is due predominantly to dissociation of a metastable state of N2 by electron impact.
Nonideality and Association in Binary Mixtures of Molten Salts
Authors: Braunstein Jerry
Published: February 2004

Equations are derived for the composition dependence of activities to be expected in binary molten-salt mixtures if association with ideal mixing of the associated and unassociated species is the cause of the deviations from ideality. Relations are derived between the association constants and the coefficients in the Margules expansion for binary mixtures of nonelectrolytes or of molten salts. Contrary to previous reports, the formation of the anionic associated species MgCl42− cannot account quantitatively for the observed deviations from ideality in alkali chloride–magnesium chloride mixtures.
Optical Spectra of Divalent Manganese Salts. II. The Effect of Interionic Coupling on Absorption Strength
Authors: Lohr Lawrence L. , McClure Donald S.
Published: February 2004

The visible absorption spectrum of Mn++ salts consists of spin-forbidden transitions. It is found that the intensity of these transitions in different salts depends on the interionic coupling, being too great for vibronic effects and lacking the temperature dependence expected for a vibronic mechanism. The discovery of magnon sidebands in several Mn++ salts provides detailed insight as to the nature of this coupling. It is proposed that the spin-forbidden transitions in salts (not only Mn++ salts), in which the metal ions are bridged by a single anion, occur by way of a simultaneous electronic transition in one ion and a spin deviation in the neighbor.
Reduction Parameters for an Unspecified Intermolecular Potential. II. Core Potential Calculations Including Nonadditivity
Authors: Ng Wing Y. , Walkley John
Published: February 2004

The zero-point properties of the inert-gas solids are used to determine the parameter values for a range of m:6 Kihara core pair potential functions. Calculations are made with the inclusion of a long-range non-additivity term in the static lattice potential. It is found that when the experimental properties are satisfied this nonadditivity term becomes zero. The resulting pair potential parameters are then shown to give “best” reduction parameter values for Ar, Kr, and Xe, which allow the second virial and viscosity, two-body, gas-phase properties to be reduced to a pattern of corresponding-states behavior.
Theoretical Investigation of Reactive Collisions in Molecular Beams: K+Br2
Authors: Godfrey M. , Karplus M.
Published: February 2004

A quasiclassical trajectory calculation is performed on a simplified interaction potential approximating that for the K+Br2→KBr+Br reaction. Various scattering attributes are computed; they include differential and total cross sections, energy, and angular-momentum partitioning. A qualitative attempt is made to relate some of these to the interactions along the reactant and product portions of the collision trajectory.
Theory of Diffusion-Controlled Chemical Reactions in Porous Media. II. Two-Phase Diffusion
Authors: Reck R. A. , Reck G. P.
Published: February 2004

Rigorous upper and lower bounds are set on the effective rate constant ke of a diffusion-controlled chemical reaction which occurs in a random two-phase system. A reactive species B* is formed at a uniform rate σ everywhere within one phase and diffuses into the second phase where it reacts chemically according to an empirical first-order rate law with a rate constant k. The bounds are given in terms of two- and three-point configurational correlation functions. An analytic form for a cruder upper bound in a dilute bed of spheres gives ke < A1 + A2φ + (A3 / φ) + (A4 / φ2) + (A5 / φ3), where the constants Ai depend on the reaction rate constant k, the diffusion coefficient, and potential of B* in the two phases, as well as on the radius of the spheres which comprise the bed (φ being the void fraction).
d
Orbitals in the sp3d, sp2d2, and p3d2 Configurations of Phosphorus
Authors: Chandler G. S. , Thirunamachandran T.
Published: February 2004

Wavefunctions and energy matrices for spectroscopic terms of phosphorus in the sp3d configuration are reported. Using a two-term Slater function for 3d orbitals and orthogonalized Slater functions for other orbitals, term energies are optimized with respect to 3s, 3p, and 3d orbital parameters. The core wavefunction is kept unchanged. Calculations on the lowest terms and configuration averages of sp2d2 and p3d2 of phosphorus are also reported. d Orbitals for the multiplets of phosphorus in the sp3d configuration are diffuse and have mean radii upwards of 3.66 Å (6D0), while in the lowest terms of sp2d2 and p3d2 they are compact, the mean radius being 2.03 Å. d Orbitals in the excited configurations of phosphorus are compared with those of sulfur. The applicability of Slater's rules to excited configurations is examined. A computer method for performing all the calculations, including the algebra, is given in an Appendix.
Repulsive Potential-Energy Curves for the Rare-Gas Atoms
Authors: Dymond J. H.
Published: February 2004

An inversion technique is described for the determination of the repulsive part of the potential-energy curve from experimental dilute-gas transport-coefficient data. Potential curves determined by this method for the rare gases agree closely over the energy range 0.2–0.5 eV with the results obtained from molecular-beam data. A comparison of these curves with the results of calculations based on the simple Thomas–Fermi–Dirac model of the atom shows the theoretical curves to be remarkably accurate.
Physical Properties of Aromatic Hydrocarbons. IV. An Analysis of the Temperature Dependence of the Viscosity and the Compliance of 1,3,5 Tri-α-naphthylbenzene
Authors: Plazek D. J. , Magill J. H.
Published: February 2004

The viscosity measurements on 1,3,5-tri-α-naphthylbenzene have been extended to 407°C, in order to establish the limiting high-temperature Arrhenius activation energy. Diverse functions have been used to fit the viscosity results on this material which range over 15 orders of magnitude. From the temperature dependence of viscosity and crystal-growth rate in the transport-controlled temperature region below the growth-rate maximum, a temperature dependence of the limiting high-frequency modulus (for the dominant viscoelastic relaxation process) is predicted.
Four-Body S-State Coordinates
Authors: Carter Benjamin P.
Published: February 2004

Inequalities on interparticle distances are derived, and various coordinate systems are described for even-parity four-particle S states. The region D corresponding to tetrahedra is shown to be nonconvex in the space of interparticle distances, which proves that D is not characterized by linear inequalities. Expressions are derived for the volume element and for the metric coefficients gαβ which appear in atomic kinetic-energy integrals.