bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Free-Volume Model of the Liquid-Glass Transition
Authors: Turnbull David , Cohen Morrel H.
Published: February 2004

We have improved the free-volume model for molecular transport in dense fluids, as developed in earlier papers, by taking account of the variable magnitude of the diffusive displacement. The development is carried through in a way which may display more clearly the relation between the free-volume model and the Enskog theory. Implicit in the free-volume development is the association, on the average, of a correlation factor f(a) with each magnitude, a, of the displacement. It is assumed that f(a) is a step function which is zero, because of the predominance of back scattering, for a < a* and unity for a > a.* This corresponds to dividing the displacements sharply into two categories, one “gaslike” and the other “solidlike.” Molecular dynamics computations have shown that the self-diffusion coefficient in the hard-sphere fluid at the highest densities is falling precipitously, with increasing density, away from the Enskog values. It appears that this density trend, which was attributed to back scattering, if continued, would lead to a continuous solidification. It is shown that the magnitude and density trend of this deviation are described satisfactorily by the free-volume expression, where the free volume is referred to the specific volume of the Bernal glass. We conclude that at least the molecular transport manifestation of a liquid–glass transition can be deduced entirely within the framework of the van der Waals physical model for liquids with due corrections for the variation of the effective hard-core radius with temperature. The free-volume model results from a crude, but physically plausible, approach to this problem.
Interfacial Tension of 3-Methylpentane–Nitroethane near the Critical Point
Authors: Wims A. M. , Sengers J. V. , McIntyre D. , Shereshefsky J.
Published: February 2004

Experimental data are reported for the capillary rise of the interface between the two liquid phases of 3-methylpentane–nitroethane as a function of temperature. The data are interpreted in terms of a power law currently proposed for the behavior of the interfacial tension near the critical mixing point. The results seem to indicate that for 3-methylpentane–nitroethane the region of asymptotic behavior is limited to rather small values of ΔT* = (Tc − T) / Tc. For ΔT* ≥ 10−2 Sugden's parameter a2 can be represented by a power law a2 = A2ΔT*φ with an exponent φ = 1.00 ± 0.01. A comparison is made with the behavior of the surface tension of simple one-component liquids near the gas–liquid critical point.
Rotational–Translational Energy Transfer. II. Comparison of Action-Angle Solution in the Near-Static Approximation with Exact Results
Authors: Cohen Audrey O. , Marcus R. A.
Published: February 2004

In Part I, the differential equations for molecular rotational–vibrational–translational energy transfer were re-expressed in terms of action-angle variables. In the present paper, approximate integral solutions and exact results for rotational–translational transfer are compared for a wide range of collisional and molecular parameters at small fractional changes in translational energy. The results are in good agreement over the range investigated except at low moments of inertia. Thereby, conditions where the present approximation is best correspond to some which are least accessible by approximate or numerical quantum mechanical methods. The present approximation employs for zeroth order a classical analog of the static approximation in quantum mechanics, rather than the adiabatic approximation, and the results have implications for the ranges of molecular parameters where each should be preferable in the quantum case.
Quantum Mechanical Model of Three-Body Rearrangement Scattering. II. Calculations for a Resonance Energy
Authors: Dion David R. , Milleur Mac B. , Hirschfelder Joseph O.
Published: February 2004

In a companion paper, Robinson shows that the basis set which Hulburt and Hirschfelder used to obtain the transmission and reflection coefficients for a quantum mechanical model of reactive scattering of three atoms in a line was incomplete for a set of resonance energies. In the present paper, using Robinson's complete basis set, agreement is obtained with Tang, Kleinman, and Karplus's estimate of the transmission coefficient for E(8μl2 / h2) = 2. It is found that the “point matching” method of solution does not converge as rapidly as the truncated Fourier series. Graphs of the flux and particle density are given.
Electronic Spectrum of Carbonyl Fluoride
Authors: Workman Gary L. , Duncan A. B. F.
Published: February 2004

The complete electronic spectrum of carbonyl fluoride has been observed for the first time down to 1215 Å. At least four electronic transitions occur in this spectral region. The first three electronic transitions are associated with elaborate vibrational structures, which are analyzed. The transitions are interpreted as two n → π* types and one n → σ* type. A π → π* type transition is found at shorter wavelengths. Other unresolved transitions occur at still shorter wavelengths where the intensity increases continuously to the limit of observation. The ionization potential of carbonyl fluoride has been determined by electron impact in a mass spectrometer as 13.17 ± 0.1 eV.
Quenching of Benzene Fluorescence by Oxygen
Authors: Morikawa A. , Cvetanović R. J.
Published: February 2004

Molecular oxygen has been found to quench benzene fluorescence without noticeably decreasing the concentration of the benzene triplet (3B1u) although the fluorescing species, the excited singlet B2u1, is the precursor of the triplet. The most obvious explanation of this apparent anomaly is that the B2u1 state is converted to the triplet B1u3 when it is quenched by O2, perhaps with simultaneous conversion of O2 to the first excited singlet (1Δg). The estimated values of the quenching rate constants of benzene singlet (1B2u) and benzene triplet (3B1u) by oxygen are, respectively, k2d = 2.1 × 10−10cc/molecule·sec and k3c = 2.1 × 10−11cc/molecule·sec.
Deuterium Atom Distribution in Nb–D Solid Solutions
Authors: Fender B. E. F. , Henfrey A. W.
Published: February 2004

The diffuse scattering of long wavelength neutrons (7.0 Å) by niobium–deuterium solid solutions of composition NbD0.042 and NbD0.079 has been studied. The results indicate that within experimental error the hydrogen atoms are randomly distributed. An incoherent cross section of 2.78 × 10−2 ± 0.25 × 10−2 b is reported for niobium.
Simple Model for the High Energy Reaction of O+ Ions with N2
Authors: O'Malley Thomas F.
Published: February 2004

A rough semiempirical model is presented for the reaction O++N2→NO++N as it has been found experimentally to occur for either vibrationally excited nitrogen or high energy (≳1 eV) O+ ions. The model is based on an assumed crossing of potential-energy surfaces. It finds the rapid energy dependence of the reaction rate on both vibrational state and on kinetic energy in the Franck–Condon overlap integral. This integral is constructed by parameterizing initial and final potential-energy surfaces in their dependence on the N–N coordinate only, in such a way as to reproduce the experimental dependence on both vibrational and translational energy. The resulting συ(E) then allow extrapolation of the experimental results to any combination of vibrational and translational temperatures.
Variational Perturbation Theory Study of Some Excited States of Two-Electron Atoms
Authors: Aashamar Kjell , Lyslo Gudmund , Midtdal John
Published: February 2004

The Hylleraas–Scherr–Knight variational perturbation method has been applied to the two-electron states 1s3s 3,1S and 1s3p 3,1P. The calculations have been carried through to 20th-order wavefunctions, with 96-, 126-, and 162-term expansions of the Hylleraas type, thus yielding estimates of the energy through the 41st order. The perturbation energy coefficients are tabulated through the 21st order for the states 1s2s 3,1S, 1s2p 3,1P, 1s3s 3,1S, and 1s3p 3,1P, and the corresponding nonrelativistic energies are presented for the first 10 elements of the helium isoelectronic sequence, with the exception of H− to which the perturbation expansions do not apply. Where comparison is possible, our results are in fair agreement with those obtained from conventional variational calculations. A survey of the variational perturbation procedure is also given, presenting the basic formulas and phrasing two important theorems.
Linear Hard-Sphere Gas: Variational Eigenvalue Spectra of the Energy Kernel
Authors: Hoare M. R. , Kaplinsky C. H.
Published: February 2004

The relaxation problem for the linear hard-sphere gas is considered using a Rayleigh–Ritz expansion of the energy kernel for transitions in a test-particle/heat-bath system at variable mass ratio γ. The basis sets used are the “exact” eigenfunctions for the problem in the Rayleigh limit γ → 0 and the required expansion matrices can be obtained to order at least 20 × 20 by algebraic procedures. Good, converged eigenvalues λk are obtained in the discrete region 0 < λk < λ* so long as these are not within about 10% of the continuum threshold λ*. Where possible, unconverged “pseudoeigenvalues” in the continuum region λ > λ* are also determined and their use to “represent” the continuum in the initial-value problem is discussed. A number of applications are considered. We obtain the relaxation of distribution functions P(x,t) and mean energies 〈x(t)〉 and investigate the energy-autocorrelation function S(t) for equilibrium fluctuations, as a function of mass ratio. The latter proves to be very nearly Gaussian for all γ in the range 2−9 < γ < 29. The results also allow a detailed evaluation of the range of validity of the Rayleigh–Fokker–Planck (RFP) equation in energy space. For processes dominated by λ1 the RFP approximation is adequate from about γ < 1 / 20, but with progressive deterioration of the predicted higher eigenvalues. Where comparable the results agree with those of Shapiro and Corngold [Phys. Rev. 137, A1686 (1965)] obtained for the neutron thermalization problem with somewhat different methods and scope.
Heat Capacity of Silver Iodide. IV. Heat Content of Quenched Stoichiometric Material
Authors: Perrott C. M. , Fletcher N. H.
Published: February 2004

Experiments have been performed to measure the heat content of stoichiometric silver iodide, water quenched from the high-temperature (α) phase to room temperature. The data shows the retention of large amounts of energy during quenching, and this is shown to be consistent with a model of lattice disorder which was developed to explain anomalous thermal properties of annealed material.
Energy States and Intermolecular Interactions in Molecular Aggregates: Resonance Pair Spectra of Crystalline Naphthalene
Authors: Hanson David M.
Published: February 2004

Very high-resolution optical spectra reveal fine structure in the B2u1 → 1Ag and B1u3 → 1Ag electronic transitions of naphthalene isotopic mixed crystals, C10H8 as a guest in a C10D8 host. Extensive experimental data allow the spectral lines to be characterized and assigned. Some of the structure corresponds to the resonance splitting arising from neighboring pairs of guest molecules in the host lattice. In the Frenkel tight-binding approximation, this structure gives directly the intermolecular excitation transfer matrix elements responsible for the exciton mobilities and the energy band structures of both pure and mixed molecular crystals. For the B2u1 state the largest interchange equivalent interactions are approximately + 15.3 cm−1 and + 3 cm−1 while the largest translation equivalent interactions are approximately + 3.7, − 5.1, − 7.9, and − 3.3 cm−1. For the B1u3 state the largest interchange equivalent interaction is 1.25 cm−1.
Two-Electron Fractional Parentage Coefficients for the Configurations ln
Authors: Donlan Vincent L.
Published: February 2004

An equation for computing the two-electron functional parentage coefficients of the configurations ln in terms of the one-electron fractional parentage coefficients of ln and ln−1 is derived. Abbreviated tables of the two-electron coefficients of the lowest lying terms of the dn and fn configurations are given. The orthogonality, charge conjugation, and symmetry properties of the two-electron fractional parentage coefficients are discussed briefly. The use of the coefficients in calculating matrix elements of two-particle operators is discussed, and the appropriate equations are given.
Alternative Technique for the Calculation of Single-Determinant Open-Shell SCF Functions Which Are Eigenfunctions of S2
Authors: Segal Gerald A.
Published: February 2004

The most general possible restriction is developed such that a single-determinant open-shell SCF wavefunction shall be an eigenfunction of S2. A method of satisfying this restriction by partitioning of the variational basis set is given. The method is computationally distinct from the equivalence restriction procedure of Roothaan, but yields results equivalent to it. A pilot calculation on the Σ+2 state of BO is carried out as an explicit example of the new method.
Shock-Tube Study of Radiation from S2
Authors: Bott J. F. , Jacobs T. A.
Published: February 2004

Absolute emission intensity measurements of the radiation from sulfur molecules S2 have been obtained in the temperature range from 2300 to 4800°K at six wavelengths spaced between 3132 and 5461 Å. The radiation intensities were proportional to the square of the sulfur atom concentration and were independent of the total pressure of the buffer gas, argon. In addition, the band structure was recorded for the wavelength interval 3600–4100 Å with an image orthicon camera mounted in a spectrograph. The intensities between 3650 and 5461 Å have similar activation energies and are interpreted in terms of the radiative transitions from the B 3Σu− state of molecular sulfur, this state being populated by the mechanism of inverse predissociation. Theoretical calculations of the B 3Σu− bands predicted the band shapes observed with the image orthicon and, together with the measured intensities, provide the electronic f value for the bands. The square of the transition moment [Re(r) / ea0]2 is estimated to have a value of 5.0, which corresponds to an f value of 0.16 on the basis of published Franck–Condon factors. The intensities at 3132 Å have a temperature dependence close to that predicted for transitions from the b 1Δu electronic state.
Dissociation of Diatomic Molecules from the Viewpoint of the Integral Hellmann–Feynman Formula: H2, LiH, and Li2
Authors: Marron Michael T.
Published: February 2004

The integral Hellmann–Feynman formula is used to compute the dissociation energies of H2, LiH, and Li2. The derivation of the transition densities and the method of taking the limit of the transition densities as one of the nuclei is removed to infinity, is discussed. The expression for the dissociation energy of LiH is examined in detail. While the results (except for H2) are inaccurate, it is argued that the essential characteristics of the transition density are correctly determined and that the method provides a basis for the physical interpretation of the factors which contribute to the dissociation energy.
Absorption, Fluorescence, and Thermoluminescence in Gamma-Irradiated Pr3+:LaF3
Authors: Gravely Ben T.
Published: February 2004

The thermoluminescence spectrum of gamma-irradiated Pr3+:LaF3 has been found to be identical to the unirradiated fluorescence spectrum. Three narrow-band glow curves are presented indicating agreement among the peaks in different spectral regions. An analysis of the trap depths is presented.
Temperature Dependence of Induced Electronic Transitions in Compressed Gaseous Oxygen
Authors: Gijzeman O. L. J. , Ogryzlo E. A. , Rettschnick R. P. H.
Published: February 2004

The absorption intensities of eight different induced transitions have been measured in the spectral region from 7500 to 28 000 cm−1 at constant densities (about 130 amagat units). The measurements were carried out at temperatures from 350°K down to 165°K. The results are discussed on the basis of a simple model for the gas in which it is assumed that the absorption is due to bound dimers as well as collision pairs. Absorption cross sections are evaluated for these two species.
Exact Calculation of the Partition Function for a Generalized Model of Two-Dimensional Polymer Crystallization by Chain Folding
Authors: Lauritzen John I. , Zwanzig Robert
Published: February 2004

A generalized model for two-dimensional polymer crystallization by chain folding is treated by equilibrium statistical mechanics. A generating function for the partition function is obtained in exact analytic form. The model leads to thermodynamically well-defined chain-folded polymer crystals. Under certain circumstances in the limit of an infinitely long polymer chain, the model shows a second-order phase transition from an “extended-chain” crystal to the chain-folded crystal.
Spin Relaxation Process of Chromium Ion in Potassium Alum
Authors: Candela George A.
Published: February 2004

The electron spin relaxation process of potassium chrome alum and potassium chrome aluminum alum was investigated at 14.5 GHz by measuring the change in the static dc magnetization as a function of the cw microwave power absorbed at electron resonance. At liquid-helium temperatures, the direct spin–lattice relaxation process is the dominant rate-determining process for magnetically dilute potassium chrome aluminum alum, but for the magnetically concentrated crystals, the spin–lattice process can easily be obscured by the lattice–bath relaxation process. The spin–lattice relaxation measurements at 14.5 GHz and those of other workers at 9 GHz are in agreement with the calculations made by Van Vleck in 1940.
Extrapolation to Single-Relaxation-Time Behavior in Solutions of Poly(n-butylisocyanate)
Authors: Bur Anthony J.
Published: February 2004

The dielectric relaxation time of rodlike poly(n-butylisocyanate) (PBIC), (–CO–NR–)n, where R = C4H9, has been observed for dilute solutions as a function of the polydispersity in the PBIC molecular weight. The mode of relaxation is rotation about the minor axis of the rodlike molecule (end-over-end rotation). The dielectric relaxation time for this mode is a sensitive function of molecular weight, and a distribution of relaxation times Φ(τ) is observed whenever a distribution of molecular weights ψ(M) is present. A one-to-one correspondence between Φ(τ) and ψ(M) is established by observing the half-width W / 2 of the dielectric dispersion on a log frequency plot as a function of the ratio Mw / Mn, where Mn and Mw are the number and weight averages of ψ(M). Extrapolation of the W / 2 vs Mw / Mn data to the monodispersed case (Mw / Mn = 1.0) is carried out in order to determine whether or not a monodispersed sample has a single relaxation time. The accuracy of the extrapolated half-width suffers because the estimated uncertainty of the measured ratio Mw / Mn is ± 10%. The data do, however, satisfy a necessary condition for the presence of a single relaxation time. In the region Mw / Mn = 1.0 to 1.6, the experimentally observed Mw / Mn is in good agreement with Mw / Mn calculated from the observed Φ(τ). For these calculations it is assumed that each molecular species has a single relaxation time and that the molecular dipole moment is proportional to the molecular weight. A distribution ψ(M) may be obtained from the observed Φ(τ) if it can be assumed that all molecules have the same conformation.
Theory of Inelastic Collisions. II. The Proof of Conjectured Rules for the WKB-Type General Solutions
Authors: Eu Byung Chan
Published: February 2004

A set of the rules which were conjectured in the first paper of this series for obtaining the WKB-type general solutions of N-coupled radial Schrödinger equations are either derived or proved under an assumption of distinct eigenvalues of a matrix AN′ which is directly related to the coupled equations. These coupled radial Schrödinger equations occur in the multichannel approach in the theory of inelastic collisions of atoms and molecules.
Vibration Spectra of the Orthorhombic Alkaline-Earth Hydrides by the Inelastic Scattering of Cold Neutrons and by Infrared Transmission Measurements
Authors: Maeland Arnulf J.
Published: February 2004

The vibration spectra of the orthorhombic alkaline-earth hydrides have been investigated by measuring the energy distribution of cold neutrons which have been scattered inelastically from polycrystalline samples. In each case the measured spectrum consists of a band or bands primarily due to the metal atom vibrations (below ∼300 cm−1) and two broad optical hydrogen vibration bands (above ∼300 cm−1) presumably caused by hydrogen occupying two different sites in the metal lattice. An approximate frequency distribution has been derived for each hydride sample. The optical bands are peaked at 1050 and 720 cm−1 for YbH2, at 1010 and 690 cm−1 for CaH2, at 940 and 600 cm−1 for SrH2, and at 810 and 560 cm−1 for BaH2. Splitting and fine structure of the optical peaks have been observed and have been attributed to the asymmetry of the hydrogen sites in the metal lattice. Infrared transmission measurements on the same compounds are in good agreement with the neutron results. Additional splitting of the optical peaks have been observed in the infrared.
Chemical Applications of Metastable Argon Atoms. III. Production of Krypton and Xenon Metastable Atoms
Authors: Stedman D. H. , Setser D. W.
Published: February 2004

An inexpensive experimental technique has been developed for the production of argon, krypton, and xenon metastable atoms using a discharge-flow system. The reactions of these metastable atoms with N2, CO, and N2O were investigated in the pressure range 0.3–10 torr, and the emission spectra resulting from the reactions were identified. These spectra gave information about the collision event and also about some of the relaxation processes. Franck–Condon factors apparently do not control the molecular excitation processes in collisions of excited heavy atoms with light diatomic molecules. This discharge flow source of metastable atoms provides emission spectra of sufficient intensity from added CO and N2O for study of emission bands which currently are not well understood. Molecular emission from N2O has been observed, apparently for the first time.
ESR of TMPD–TCNQ: Spin Excitations of the Heisenberg Regular Linear Chain
Authors: Hoffman B. M. , Hughes R. C.
Published: February 2004

The detailed electron spin resonance of single crystals of the charge-transfer complex tetramethylphenylenediamine–tetracyanoquinodimethan (TMPD–TCNQ) at X band and Q band are reported. The ESR spectra are interpreted as resulting from the thermally excited (activation energy, 0.068 eV) spin excitations of the Heisenberg regular antiferromagnetically coupled chain. Although the exact solution to the excited states of the Heisenberg chain with antiferromagnetic coupling is not available, an approximate solution treating the quasiparticles as Wannier spin excitons is very successful at predicting the spin resonance properties of the excitations; fundamental to the Wannier spin exciton model is the absence of spin correlation in the excitations. The spin–spin (T2−1) and spin–lattice (T1−1) relaxation rates are observed as functions of temperature and are determined mainly by spin exchange between excitons. Exchange is proportional to exciton concentration, and the low activation energy in TMPD–TCNQ allows exchange frequencies on the order of the Larmor frequency to be achieved without decomposition. Nonsecular broadening of the linewidth is observed and interpreted in terms of the Kubo–Tomita formalism, modified for the uncorrelated spins of the excitations. Similar equations describe the spin–lattice relaxation. The form of the correlation function for spin fluctuations in one dimension can be deduced from the T1 data and is shown to be closely Lorentzian, rather than Gaussian. The crystal structure is known and both the g tensor and the principal parts of the dipolar secular moment for the excitations are shown to have the molecular rather than crystal symmetry.
Vapor Pressures of Some Deuterated Propylenes
Authors: McDaniel Robert L. , Van Hook W. Alexander
Published: February 2004

The deuterium vapor pressure isotope effect has been measured for CH3CDCH2, CH2DCHCH2, CH3CHCD2, and CD2CDCD2 using mercury manometry. The samples were of high isotopic purity and were chemically purified using low temperature gas chromatography. Substitution at the ethylenic end of the molecule results in an inverse isotope effect of 0.5% per D near 240°K falling off to a normal effect of 1% per D near 150°K. At the higher temperatures the law of the mean was nearly obeyed but deviations, of course, occur around the crossover. The monodeuteromethyl compound shows an inverse effect of about 1% per D at 240°K and displays a very broad maximum around 1.3% per D near 160°K. The perduetero compound also displays a broad maximum. Its effect is larger than that predicted from the approximate theory.
Pure Quadrupole Resonance Study of 59Co, 35Cl, and 37Cl in [Co(NH3)5Cl]2+
Authors: Watanabe Ichiro , Tanaka Hideki , Shimizu Tatsuo
Published: February 2004

The quadrupole coupling constants of 59Co and the asymmetry parameters in [Co(NH3)5Cl]Cl2(e2qQ / h = 31.74 MHz, η = 0.251) and [Co(NH3)5Cl]SO4·H2SO4(e2qQ / h = 33.43 and 34.39 MHz, η = 0.042 and 0.089) have been determined. In the latter complex, two inequivalent sites of 35Cl and 37Cl resonances have also been observed. Their resonance frequencies are 15.484 and 15.521 MHz for 35Cl, and 12.203 and 12.232 MHz for 37Cl. The application of the Townes and Dailey method to the chlorine data gives the ionic character of about 67% for the Cl–Co bond. The contributions from the valence electrons of the cobalt and from the ionic charges at the ligands and crystal lattice to the field gradient at the cobalt site are discussed.
Bulk Trapping States in β-Phthalocyanine Single Crystals
Authors: Barbe D. F. , Westgate C. R.
Published: February 2004

From temperature dependence measurements of the SCLC and Ohmic current densities, the electron trapping levels in metal-free phthalocyanine have been determined in several ambients. In vacuum, traps with a density 5 × 1019 cm−3 located 0.38 eV below the conduction band have been observed. Associated with this level are donor sites with a density 2 × 1012 cm−3. In oxygen and hydrogen, trapping sites near the middle of the bandgap are observed. Thickness dependence measurements prove that the trapping sites are located at discrete energy levels. The results are extended to comment upon traps in copper phthalocyanine. The measurements indicate that the electron mobility is not temperature dependent up to 373°K.
Lattice Vibrations in Crystals with Deformable Molecules; a Calculation for Naphthalene
Authors: Pawley G. S. , Cyvin S. J.
Published: February 2004

A calculation has been done to show the effect of molecular distortion on the external modes of the molecular crystal naphthalene. This calculation also yields the dispersion relation for the internal modes caused by the crystalline forces. The method used is quite general. The force field for the isolated molecule comes from spectroscopic frequency fitting, and to this is added the effect of crystalline forces using a Buckingham atom–atom potential. The shift and splitting of all the modes calculated at zero wave vector are given, and also the dispersion relation for the lower modes for wave vectors parallel to the crystal screw-diad axis. A suggestion is made concerning the analysis of the results of neutron coherent inelastic scattering, which until now has assumed molecular rigidity.
Covalency and Electronic Structure of Cu2+ in ZnF2 by EPR
Authors: Swalen J. D. , Johnson B. , Gladney H. M.
Published: February 2004

With the aid of computer techniques, including a laboratory automation system, accurate computer simulation, and an accurate calculation method, the EPR spectrum of copper doped in zinc fluoride has been analyzed. The observed g values led by a new method to a determination of the coefficients of the Kramer's doublet. Copper hyperfine structure verified these values and fluorine transferred hyperfine structure gave a measure of covalency. The fractional orbital occupation showed predominantly σ bonding which is similar to other reported transition metal ions in ionic insulating crystals. Orbital reduction, though no doubt present, makes only an insignificant and undetectable contribution.
Infrared Lattice Bands of Trigonal and Cubic Mercury Sulfide
Authors: Riccius H. D. , Siemsen K. J.
Published: February 2004

The infrared reflection and transmission spectra of polycrystalline trigonal mercury sulfide have been measured between 800 and 40 cm−1 at room temperature and 77°K. From these measurements, in conjunction with the Raman data, the frequencies and symmetry character of the fundamental vibrational modes could be identified. The reststrahlen band in cubic mercury sulfide was observed at 177 cm−1 by using evaporated films for transmission measurements in the region of the transverse and longitudinal optical phonon frequencies.
X-Ray K-Absorption Edge of Niobium in Niobium Metal and Its Oxides
Authors: Bhide V. G. , Bahl M. K.
Published: February 2004

The position and fine structure of the x-ray K-absorption edge of niobium in niobium metal and in its oxides have been investigated using a 400-mm bent crystal (mica) spectrograph. The K-absorption edge of niobium in its oxides shifts towards higher energy with respect to that in niobium metal; the shift is greater the higher the valence state of niobium.
Hydrogen Bonding in Some Hydrated Manganese Chlorides
Authors: Saffar Z. M. El
Published: February 2004

The H coordinates are given for eight hydrated manganese chlorides, all of which become antiferro-magnetic at low temperatures. These coordinates are obtained from Baur's electrostatic model, and in the case of one compound (MnCl2·4H2O), from a precise three-dimensional neutron-diffraction study. The latter study appears to confirm the validity of Baur's model. The results indicate that the H bonds are normal bonds for all but three of the O–H- - -Cl bonds which are found severely bent.
Experimental Observation of Singlet–Triplet Absorption in Pure Crystalline Benzene
Authors: Burland D. M. , Castro G. , Robinson G. W.
Published: February 2004

The B1u3 ← A1g1 intrinsic absorption spectra of C6H6 and C6D6 at 4.2°K have been obtained for the first time at high resolution using the phosphorescence–photoexcitation method. The spectrum exhibits very clear evidence of a pseudo-Jahn–Teller distortion of the normally hexagonal benzene molecule upon excitation to the triplet state. Factor-group splitting of the 0–0 and 0–0 + ν1 exciton bands have also been observed. The position of the mean of the 0–0 exciton band of C6H6 when compared to the phosphorescence origin of a C6H6 guest in a C6D6 crystal, indicates that the “static” intermolecular interactions between guest and host are different for C6H6 and C6D6 hosts. This result has important implications for the applicability of mixed crystal theories to benzene.
Adiabatic Corrections to Long-Range Born–Oppenheimer Interatomic Potentials
Authors: Pack Russell T , Hirschfelder Joseph O.
Published: February 2004

The rotationally coupled electronic equations of the previously derived “best adiabatic” (BA) approximation are solved variationally at large values of the internuclear distance. Adiabatic interatomic potentials result which contain all first-order corrections to the Born–Oppenheimer approximation and change smoothly as the internuclear distance changes. The angular momenta smoothly couple and uncouple resolving difficulties of earlier treatments with corrections to the centrifugal potential. Selection rules for the long-range corrections to the Born–Oppenheimer (BO) approximation are given. And the long-range adiabatic potentials in H2 and OH are calculated as examples.
Ab Initio AMO Calculation of the Lowest Singlet–Triplet Separation in Benzene
Authors: Gilman Robert R. , de Heer J.
Published: February 2004

The A1g1 and B1u3 states of benzene have been described by a wavefunction built up from π-alternant molecular orbitals and ordinary σ molecular orbitals. The resulting energy expressions have been cast in a form directly comparable to that obtained from semiempirical theories. From a basis of 48 (contracted) Gaussian-type orbitals, a σ core has been chosen and assumed common to both states. The π orbitals were then optimized separately for each state. The resulting energy separation is in good agreement with experiment.
Laser Raman and Infrared Spectra of the Tetrahedral Co(CO)4− Ion
Authors: Edgell Walter F. , Lyford John
Published: February 2004

The laser Raman spectrum of water solutions of NaCo(CO4) was obtained from 50 to 4000 cm−1 with results which differ in significant ways from those of an earlier study. Further, they show the Co(Co)4− ion here to be in an effectively tetrahedral site environment. An assignment of frequencies to the fundamental modes of the anion in this kind of environment was made on the basis of a laser Raman study and an infrared study over the above spectral range for the salt dissolved in dimethylformamide.
Bound-State Calculation of Scattering Resonance Energies
Authors: Weiss A. W. , Krauss M.
Published: February 2004

Resonance energies in electron scattering are estimated by calculating bound trial functions which represent electron attachment to the lowest Rydberg state. The trial functions are kept orthonormal to a single-configuration description of the target state and so represent an approximation to the Feshbach procedure. Correlated trial functions are used for He−(2S), Ne−(2P), and Ar−(2P). The resonant-energy predictions are in good agreement with observation. In addition, the correlation energy for the ns2 pairs range from 0.55 to 0.75 eV. These correlation energies are used to correct Hartree–Fock estimates of resonance energies computed for the HF, H2O, and N2 molecules. Energy curves obtained for HF−(2Π) indicate a dissociative attachment process is possible that leads to production of the H− ion. Only single points are calculated for H2O but the B12 resonance state is assigned to a dissociative attachment at 6.5-eV incident electron energy that yields the H− ion. In addition to the attachment to Rydberg excited states, two N2 valence-type Feshbach states are calculated. The results for σgπg2, 4Σg−, and Δg2, when used with correlation energy estimates lead to the conclusion that valence-type Feshbach states are not bound relative to their concomitant neutral excited valence state. Sharp resonances would not then be expected below such neutral states.
Applications of Variational-Perturbation Theory to Molecules. I. The Water Molecule
Authors: Montgomery H. E. , Bruner Buddy L. , Knight Robert E.
Published: February 2004

The energy of the ground state of the water molecule is obtained through the second order using the Rayleigh–Schrödinger variational-perturbation method. The resultant value of − 75.9935 a.u. differs from the exact nonrelativistic energy by 0.6%. The method is applicable to other hydrides.
Comparisons of the Reflection and Diffraction of 3He, 4He, H2, and D2 from the (001) Surface of LiF
Authors: O'Keefe D. R. , Smith Joe N. , Palmer R. L. , Saltsburg Howard
Published: February 2004

Comparisons of the reflection and diffraction of thermal energy beams of 3He, 4He, H2, and D2 from the (001) surface of LiF are reported. Intense diffracted beams, including those of the second order, result from a freshly cleaved LiF surface without heating, and large exposures of H2O vapor do not reveal any measurable change in either the intensity, normalized to constant incident beam intensity, or location of such beams. The intensity and location of the individual beams are examined, taking into account the influence of adjacent beams. The locations of beams not so influenced display good agreement with the predictions of simple diffraction theory. The shapes and intensities of the diffracted beams are compared for the four gases with reference to possible inelastic effects. The decreasing intensities of diffracted beams for the same incident de Broglie wavelength are found to be in the order 4He, H2, and D2, i.e., in the order of increasing rotational energy coupling with the surface; 3He diffracted beams have intensities approximately the same as for 4He. The order of decreasing specular intensity, on the other hand, changes, depending on angle of incidence, but 3He is consistently more intense than for 4He, implying a mass collisional dependence. Preferentially scattered beams, similar to those reported for the heavier rare gases, are also evident although the presence of these beams only becomes apparent when conditions are such that the influence of other beams (diffracted and specular) is small. Selective adsorption studies reveal the presence of one or more bound energy states for each of the gases. The energy states for 3He and 4He are found to be significantly different, which is consistent with the results for the adsorption of these gases on charcoal. The energy states for H2 and D2 are identical, within the experimental error, and considerably greater in magnitude than for either 3He or 4He.
Lower Bounds for the Overlap of Approximate Wavefunctions
Authors: Wang P. S. C.
Published: February 2004

A set of intermediate resolvents is constructed from the intermediate Hamiltonians introduced by Weinstein. From these intermediate resolvents we obtained a new formula for the lower bound of the overlap between the approximate and exact wavefunctions of a quantum-mechanical system. Special examples of these bounds are given and discussed. A new lower bound for the expectation values of positive Hermitian operators was derived in a similar way and included as an Appendix.
van der Waals Forces across Triple-Layer Films
Authors: Ninham B. W. , Parsegian V. A.
Published: February 2004

It is shown that Lifshitz' theory can be used to calculate dispersion forces across a triple-layer film. The general expression is derived and numerical estimates obtained specifically for soap films in air. The theory predicts clear deviation from single-film behavior for very thin films and a marked solute effect. This may explain “anomalies” observed in experimental studies.
Volumetric Properties of Molten and Crystalline Alkali Fluoroborates
Authors: Cantor Stanley , McDermott Dana P. , Gilpatrick L. O.
Published: February 2004

The densities of the molten alkali fluoroborates were each measured over a temperature interval of approximately 150°C using a dilatometric method. The molar volumes and expansivities derived from these measurements exhibit the order predicted from the periodic table. At equal corresponding temperatures, molar volumes of molten alkali fluoroborates were found to be slightly larger than the molar volumes of molten alkali iodides. For LiBF4, RbBF4, and CsBF4, melting points and solid-state transition temperatures were determined. At the solid-state transition temperature, volume changes are predicted on the basis of analogous behavior of MBF4 and MClO4. The indices of refraction of the crystalline compounds were also measured; an electronic polarization averaging 2.77 Å3 for BF4− was calculated from these measurements. The polarization of BF4− appears to decrease with increasing alkali cation size.
Ligand ENDOR of Metal Complexes in Powders
Authors: Rist Gunther H. , Hyde James S.
Published: February 2004

Magnetically dilute crystalline powders of the following metal complex systems have been prepared by coprecipitation: copper salicylaldoxime in palladium salicylaldoxime, copper dimethylglyoxime in nickel dimethylglyoxime, copper picolinate in phthalic acid and also in zinc picolinate, copper 2-methylpicolinate in zinc 2-methylpicolinate, copper quinaldinate in zinc quinaldinate, copper 8-hydroxyquinolinate in phthalimide and also in zinc 8-hydroxyquinolinate, and silver picolinate in phthalic acid and also in zinc picolinate. These samples have been investigated with electron–nuclear double-resonance (ENDOR) spectroscopy. At some settings of the magnetic field, single-crystal-type ENDOR spectra are obtained which arise substantially from molecules in a single orientation with respect to the magnetic field. At other settings of the field, powder-type ENDOR spectra are found which arise from molecules in many orientations. In either case the spectra are simpler and easier to interpret than the EPR powder spectra of the samples. Hyperfine and quadrupole couplings of the ligand nuclei have been measured. In all cases it has been established that the unpaired spin density in the ligand molecules resides in σ orbitals, and that the spin densities at the ligand nuclei have the same sign as the spin density at the metal ion. The nitrogen hyperfine couplings are larger and the quadrupole couplings smaller in the silver complexes, indicating stronger metal–ligand interaction. In samples containing water molecules which coordinate with the metal ion, the in-plane metal–ligand interaction is weaker. The hyperfine couplings in copper salicylaldoxime are unusually large, compared with the other copper systems with mixed oxygen–nitrogen ligands.
Electronic Structure and Low-Lying Triplet States of CaO
Authors: Carlson K. Douglas , Kaiser Kurt , Moser Carl , Wahl Arnold C.
Published: February 2004

Precise symmetry-restricted Hartree–Fock calculations based on the method of Roothaan have been carried out to provide information not previously available on the existence of low-lying triplet states of the CaO molecule and new information on its normal electronic structure. It is shown that in the Hartree–Fock approximation the lowest states in order of increasing energy are 3Π, 1Π, 3Σ+, and 1Σ+, with 3Π being the Hartree–Fock ground state. In their general features, these states in both structure and order are similar to those calculated earlier by others for BeO and MgO in the same series. In contrast with the conclusions of earlier studies, however, an open-shell configuration of σσ structure is shown to be the true variational reference state for the lowest 1Σ+ term. This may be the case also for the other alkaline-earth monoxides. On the grounds of straightforward arguments, it is then demonstrated that strong configuration interaction is necessarily an essential feature of the lowest experimental 1Σ+ state. It is suggested that this configuration interaction is likely to depress 1Σ+ below 3Π, giving an X 1Σ+ ground state in agreement with experimental evidence.
Relativistic Long-Range Interactions between Atoms and Molecules
Authors: Chang T. Y. , Karplus M.
Published: February 2004

Lower and upper bounds for the coefficients of the leading term of the relativistic long-range two-body interactions are obtained by use of Padé approximants. Although the bounds are approximate, they provide an estimate of the importance of this contribution to the interaction energy for a variety of atoms and molecules.
Scalar Spectral Characteristics of One-Dimensional Solids
Authors: Pysh E. S.
Published: February 2004

A simple restatement is given for the description of polymer optical properties in terms of the interaction matrix coupling monomers. Two- and three-state solutions are given explicitly and in detail for the polypeptide alpha helix, beta sheets, and polyproline helices. The results are compared with perturbation-theory results. Agreement with experimental data is good except for polyproline II. The role played by the amide band recently observed in the gas phase is discussed, as is the extension of the calculations to other regular polymers and amorphous polymers.
External Field Dependence of Transport Properties. II. Thermal Conduction in a Fluid of Loaded Spherocylinders
Authors: Klein William M. , Dahler John S. , Cooper Eugene , Hoffman David K.
Published: February 2004

Classical kinetic theory is used to determine the influence of a magnetic field upon thermal conduction in a gas of linear molecules. To account for the effects of inelastic collisions it is assumed that the molecules are rigid and smooth, loaded spherocylinders. The geometrical parameters which characterize the interactions between these particles are obtained from comparisons of experimental and theoretical values for certain properties of the thermal conductivity tensor. The agreement between theoretical and experimental values of the phenomenological coefficients λ‖, λ⊥, and λtr is quite satisfactory for N2, CO, and NO, the three gases for which there are extensive experimental data.
High-Order Time-Dependent Perturbation Theory for Classical Mechanics and for Other Systems of First-Order Ordinary Differential Equations
Authors: Marcus R. A.
Published: February 2004

A time-dependent perturbation solution is derived for a system of first-order nonlinear or linear ordinary differential equations. By means of an ansatz, justified a posteriori, the latter equations can be converted to an operator equation which is solvable by several methods. The solution is subsequently specialized to the case of classical mechanics. For the particular case of autonomous equations the solution reduces to a well-known one in the literature. However, when collision phenomena are treated and described in a classical “interaction representation” the differential equations are typically nonautonomous, and the more general solution is required. The perturbation expression is related to a quantum mechanical one and will be applied subsequently to semiclassical and classical treatments of collisions.
Theory of Molecular Interactions. I. Molecular Orbital Studies of Water Polymers Using a Minimal Slater-Type Basis
Authors: Del Bene Janet , Pople J. A.
Published: February 2004

Ab initio minimal basis LCAOSCF molecular orbital calculations have been performed to determine the energies and configurations of small groups of water molecules, with particular emphasis on those aspects which are relevant to the structure of liquid water. An intermolecular potential which spans the complete range of possible relative orientations for the dimer is presented. The predicted equilibrium form of the dimer is found, together with estimates of some of the intermolecular force constants. Results of calculations on both open and cyclic polymeric water structures containing up to six molecules are included. It is found that polymers having OH···OH···OH··· chains are preferred, and that hydrogen-bond energies deviate considerably from additivity. Cyclic structures are predicted to be most stable for the trimer and higher polymers.
EPR Studies on Heme Oriented in an Organic Crystalline Environment
Authors: Scholes Charles P.
Published: February 2004

Heme containing high-spin ferric ion has been doped into perylene, and EPR orientation studies of single crystals have given: (a) g values and orientation of principal g axes; (b) ligand hyperfine structure from heme pyrrole nitrogens. Formulas are derived to explain the angular behavior of the ligand hyperfine structure. Certain hyperfine constants are then obtained and related to iron pyrrole nitrogen covalency.
Internal Rotation in Two-Top Molecules. I. A General Theory
Authors: Knopp John V. , Quade C. R.
Published: February 2004

The dynamics is developed for internal rotation in two-top molecules where both internal rotors may, or may not, be asymmetric. A framework fixed axis method (FFAM) is used for the formulation. The explicit α1 and α2 dependence of the moments of inertia is obtained for over-all rotation, internal rotations, and coupling between over-all and internal rotations. The Hamiltonian in proper Hermitian form is derived. Inertial parameters and rotational coefficients are calculated for two representative molecules.