bluuebunny/crossref_metadata_2025 huggingface dataset:
New Combining Rule for Intermolecular Distances in Intermolecular Potential Functions
Authors: Good Robert J. , Hope Christopher J.
Published: February 2004

A geometric mean combining rule is proposed for intermolecular distances in potential functions of the Mie–Lennard-Jones or Buckingham types. It is shown to have considerable advantages over the Lorentz rule of additive diameters.
Mode Expansion in Equilibrium Statistical Mechanics. I. General Theory and Application to the Classical Electron Gas
Authors: Andersen Hans C. , Chandler David
Published: February 2004

A new expansion for the Helmholtz free energy of a classical system is presented. The potential energy of the system is assumed to be composed of two parts: a “reference system” potential energy and a perturbation potential, which is the sum of two-particle potentials. The two-particle perturbation potential energy is assumed to have a Fourier transform. Collective variables, which are the Fourier transforms of the single-particle density, are introduced, and the canonical ensemble partition function is expressed as an infinite series. The first term in the result for the Helmholtz free energy is the reference system free energy. The second is a mean field term, and the third is the random phase approximation. Subsequent terms involve correlations among the collective variables in the reference system. The general results are applied to the special case in which the reference system is the ideal gas. A density and temperature dependent renormalized potential arises from the analysis in a straightforward way. When the results are specialized to the case of the Coulomb potential, agreement with the ionic cluster theory is obtained, and the renormalized potential is the usual Debye–Hückel potential. Further applications of the technique are mentioned.
C
υ
(T)
Equation of State for Liquids. Calculation of the Shock Temperature of Carbon Tetrachloride, Nitromethane, and Water in the 100-kbar Region
Authors: Cowperthwaite Michael , Shaw Robert
Published: February 2004

The Cυ(T) model for calculating shock temperature in liquids is presented as an extension of the Walsh–Christian model for metals. The model is based on an analysis showing shock temperature to be more sensitive to variations in Cυ than in (∂p / ∂T)υ, and it takes account of the temperature dependence of Cυ. Measured shock temperatures for carbon tetrachloride are compared with calculated values as a test of the constant Cυ and Cυ(T) models. The constant Cυ model overestimates shock temperature and is inappropriate to polyatomic liquids. The agreement obtained with the Cυ(T) model suggests that it will be valuable for calculating more realistic values of temperature in shock initiation studies of liquids in the neighborhood of 100 kbar.
Heat Capacity of Dilute Polymer Solutions
Authors: Eichinger B. E.
Published: February 2004

Flory's treatment of the excluded volume integral for pairs of segments of polymer chains is extended to include temperature dependence of the enthalpy and entropy of mixing. The heat capacity term thereby introduced is evaluated from the known critical solution temperatures for polyisobutylene–benzene and polystyrene–cyclohexane. The ratio C¯p,1E / S¯1E at infinite dilution is calculated to be −3.1 and −4.1, respectively. A less accurate estimate of this quantity for polystyrene–decalin is employed in an analysis of data obtained by Berry. It is shown that partial draining effects are not as large as previously deduced, and that the results for this system are rationally interpreted by inclusion of temperature dependent thermodynamic functions for the mixture.
Phase Separation and the Critical Index for Liquid–Liquid Coexistence in the Sodium–Ammonia System
Authors: Chieux Pierre , Sienko M. J.
Published: February 2004

A precise determination of the liquid–liquid coexistence curve has been made for solutions of sodium in liquid ammonia. The critical index β, defined by the mole fraction vs temperature dependence, (x1 − x2) / 2xc = B(| T − Tc | / Tc)β, undergoes a rather abrupt change from 0.502 ± 0.010 to 0.34 ± 0.02 when T approaches to within 1.8°C of the consolute temperature. The validity range of Landau molecular field theory is used to deduce an interaction cluster extending over at least 140 ammoniated sodium centers.
Consistent Force Field Calculations. II. Crystal Structures, Sublimation Energies, Molecular and Lattice Vibrations, Molecular Conformations, and Enthalpies of Alkanes
Authors: Warshel Arieh , Lifson Shneior
Published: February 2004

A set of energy functions of internal coordinates and interatomic distances is used for calculating simultaneously and consistently many properties of alkanes. Comparison between calculated and experimental data is used as a means for systematically selecting energy functions and determining their parameters. Properties calculated are: unit-cell parameters; heat of sublimation; molecular and lattice vibrations; thermal expansion of the unit cell—all these for n-hexane and n-octane crystals. Enthalpy differences—for gauche–trans butane and for axial–equatorial methyl-cyclohexane. Excess enthalpies for the series cyclopentane through cyclodedcane and molecular conformations and vibrations for a selected number of cyclo- and n-alkanes molecules. Some of the results and conclusions from these calculations are: molecular vibrations in the crystal are in part higher than in the gas, and the corresponding enthalpy difference contributes to the heat of sublimation equally as much as the lattice vibrations. Anharmonicity of lattice and molecular vibrations contributes significantly to the calculated unit-cell parameters of crystals of n-hexane and n-octane at 0°K; thermal expansion is largest in the a1 direction. The Lennard-Jones and Coulomb (12–6–1) potential is inadequate to account simultaneously for intra- and intermolecular interactions; the 9–6–1 potential and the exp-6–1 potential are equally preferable. The intermolecular interactions exihibit an anisotropy not fully represented by functions of interatomic distances; anisotropy is the source of systematic discrepancies between the calculated and measured unit-cell dimensions.
Quenching of Phosphorescence by Paramagnetic Molecules in Rigid Media. II. Quenching of Perdeuderated Naphthalene by Co++, Cr3+, Cu++, and Ni++
Authors: Hill C. O. , Lin S. H.
Published: February 2004

Experimental observation of the steady-state phosphorescence emission intensity of perdeuterated naphthalene as a function of paramagnetic quencher concentrations has been carried out in solid matrices of ethyl alcohol at liquid-nitrogen temperature. The paramagnetic quenchers chosen for study are the transition-metal ions, Co++, Cr3+, Cu++, and Ni++. The decay curves of phosphorescence are non-exponential, and the deviation from the exponentiality depends on the concentrations of quenchers. The experimental results are correlated and interpreted by using theoretical expressions derived from the Hoijtink's exchange interaction mechanism.
Chemical Accelerator Studies of Isotope Effects on Collision Dynamics of Ion–Molecule Reactions: Elaboration of a Model for Direct Reactions
Authors: Hierl P. M. , Herman Z. , Wolfgang R.
Published: February 2004

Crossed-beam studies on isotopic variants of the reaction Ar+ + H2→ArH+ are reported. Both velocity and angular distributions of the ionic product as a function of initial translational energy, down to 0.1 eV (center of mass), have been measured. At lowest energies there is a gain in the translational energy of the products over that of the reactants, but at higher energies there is increasing conversion of kinetic into internal energy. While this represents the most probable course of the reaction there is a fairly wide distribution about the median values. Results confirm that this reaction is predominantly direct at all energies and provide no evidence for intermediate persistent complex formation. They are also consistent with a model for direct reactions previously proposed. The data on reaction with HD permit further development of this mechanism. The reactants are mutually accelerated by their long-range attractive potential until hydrogen atom transfer occurs. The liberated H (or D) atom is reflected from the ArD+(ArH+ and the products separate, being decelerated in the process by the attractive potential acting between them. This “polarization–reflection” model yields a reasonable value for the radius at which transfer occurs, and it accounts quantitatively for the magnitudes of, and isotopic effects on, the median product velocities. It also predicts the significant back scattering observed at very low as well as very high energies. With appropriate modification for the attractive potentials involved the model can provide a simple representation of direct reactions in general.
Electron Spin Resonance Studies of Gamma-Irradiated Alkali Titanate Glasses
Authors: Kim Y. M. , Bray P. J.
Published: February 2004

Electron spin resonance (ESR) studies have been made of alkali titanate glasses gamma irradiated at liquid-nitrogen temperature. The radiation-induced spectrum can be separated into two distinct parts: One is located at a g value greater than that of the free electron, while the other has a lower g value. The latter spectrum consists of two different resonance lines, the broad and sharp spectra. They are identified as arising from Ti3+ centers formed in TiO6 units having one and two nonbridging oxygens, respectively. The high-g-value spectrum is also separated into two distinct resonance lines. Two different hole centers formed in titanium–oxygen units are proposed as being responsible for these resonances.
Intermolecular Interactions and the Weak Benzene–Halogen Complexes
Authors: Cook E. Gary , Schug John C.
Published: February 2004

We have calculated the interaction potential between benzene and halogen molecules as a function of intermolecular distance for approach of the halogens along the sixfold axis of benzene. The calculations were based upon the perturbation theory developed by Murrell and co-workers for intermolecular interactions in the region of small overlap. Emphasis was placed on the Coulombic and exchange terms. The former were calculated by numerical integrations over charge distributions developed from Slater-type atomic orbitals. The exchange interaction was expanded on the basis of determinantal wavefunctions for each molecule, using approximate self-consistent-field molecular orbitals. The dispersion and induction energies were calculated using approximations common to long-range theory. The charge-transfer resonance interaction was estimated semiempirically. Both the stabilization energies and the equilibrium separations obtained for the Cl2, Br2, and I2 complexes were reasonable in comparison with experimental data. It was concluded that all interaction terms must be considered in the over-all picture. If any one term can be singled out as playing a minor role in complex formation, it must be the charge-transfer interaction. Since it was the only repulsive term calculated, the exchange interaction is extremely important in determining the geometry and stability of complexes.
Electronic States of CH and NH
Authors: Liu H. P. D. , Verhaegen G.
Published: February 2004

Ab initio calculations (LCAO–MO–SCF) are performed on a series of valence levels of the molecules CH and NH+. Correlation energies are estimated semiempirically from corresponding atomic data. Close agreement with experiment is found for known states for a series of molecular properties such as equilibrium internuclear distances, vibration frequencies, term values, and dissociation energies. A low-lying Σ4− state in CH is calculated to lie 7500 cm−1 above the X 2Π state. No observable quartet transition could be found for CH, while for NH+ a Π4−Σ4− transition should occur in the region of 1000 Å. Other qualitative differences in the observed spectra of the two molecules are discussed. Finally a value of D00(NH+) = 3.4 eV is calculated.
Photoelectron Spectra of Methane, Silane, Germane, Methyl Fluoride, Difluoromethane, and Trifluoromethane
Authors: Pullen B. P. , Carlson Thomas A. , Moddeman W. E. , Schweitzer G. K. , Bull W. E. , Grimm F. A.
Published: February 2004

An electron spectrometer which employs double focusing electrostatic plates is described. The photoelectron spectra obtained by bombarding methane, silane, germane, methyl fluoride, difluoromethane, and trifluoromethane with 21.22-eV photons are presented. The experimental ionization energies are compared with theoretical and other experimental data, and molecular-orbital assignments are made for the energy values obtained. Broad double maximum bands were observed in the case of methane, silane, and germane and are discussed in terms of Jahn–Teller distortion for the positive ions. Possible correlation of the methane spectrum with interstellar space data is also discussed.
Radiative and Predissociation Probabilities for the OH A 2Σ+ State
Authors: Smith William Hayden
Published: February 2004

Phase-shift lifetime measurements over a range of modulation frequency have provided data on the effects of the weak predissociation of the A 2Σ+ state. The υ′ = 0 radiative lifetime (850 ± 130 nsec) corresponds to an f(0–0) of 7.7 ± 1.1 × 10−4 in agreement with previous absorption measurements. The higher vibrational quanta show shortened radiative lifetimes due to predissociation.
Calculation of Spin–Orbit Coupling Constants and Other Radial Parameters for the Actinide Ions Using Relativistic Wavefunctions
Authors: Lewis W. Burton , Mann Joseph B. , Liberman David A. , Cromer Don T.
Published: February 2004

Relativistic self-consistent Dirac–Slater and Dirac–Fock wavefunctions have been used to evaluate the spin–orbit coupling constant and matrix elements of rn for most of the actinide ions and neutral atoms. Empirical corrections for the Dirac–Slater ζ5f constants based on experimental results are suggested which enable one to predict free-ion values more accurately. Values of ζ5f from crystal and solution spectra show reductions from these estimates which are independent of atomic number Z, but vary roughly according to ionic charge and ligand electronegativity. It is shown that 〈r−3〉 parameters from atomic beam measurements on Sm, Eu, Pu, and Am can be accounted for fairly well with relativistic Dirac–Slater wavefunctions and intermediate coupling eigenvectors; configuration interaction, core polarization, and other contributions to hyperfine coupling are neglected. Similar calculations with hyperfine coupling constants from crystal EPR spectra are less consistently satisfactory.
Oxidation of Carbon Monoxide by Oxygen in Shock Waves
Authors: Dean A. M. , Kistiakowsky G. B.
Published: February 2004

The oxidation of CO by O2, with and without small amounts of added H2, was investigated in very dilute mixtures with argon at about 5.4 × 1017 particles/cc total concentration. The reaction was followed in incident shock waves by measuring CO and CO2 infrared emissions for about 2000 μsec particle time over the 1700–2600°K range. The reaction shows an initial accelerating rate followed, in H2 mixtures, by a period of constant rate. The observed [CO2]-time profiles were compared to those calculated numerically on an IBM 360/65 computer. These calculations used two branching-chain mechanisms proposed by others. The one involving hydrogenous impurities is CO+O2=CO2+O, O+H2=OH+H, O+H2O=OH+OH, OH+CO=CO2+H, OH+H2=H2O+H, H+O2=OH+O, which describes all of the observations if the assumption is made that the total hydrogenous impurity (H2 and H2O) is approximately 40 ppm. This figure is in the range of the experimentally estimated impurity concentrations. In the calculations, least-squares averages of literature values of k3, k5, and k6 were used and best fits were obtained with: k1 = 5.8 × 10+12exp(− 50 000 / RT) cc molecule−1·sec−1, k2 = 1.5 × 10−10exp(− 10 000 / RT) cc molecule−1·sec−1, k4 = 1.9 × 10−12exp(− 1030 / RT) cc molecule−1·sec−1. With these values, which are consistent with literature data referring to high temperatures, quantitative agreement was obtained between calculated and observed rates of CO2 formation. The observed rates could not be explained by the other proposed mechanism, which postulated electronically excited CO2 as a chain carrier.
Hindered Rotation of Water Molecules in Potassium Oxalate Monohydrate: A Pulsed Deuteron Magnetic Resonance Study
Authors: Pedersen Bjφrn , Clark W. Gilbert
Published: February 2004

The spin–lattice relaxation time T1 of the deuterons in potassium oxalate monohydrate, K2C2O4·D2O, has been measured in the temperature range − 19 to 75°C. T1 decreases with temperature from about 70 sec at − 15°C to 0.02 sec at 75°C. The magnitude of T1 and the strong temperature dependence show that the spin–lattice relaxation is caused by fluctuations of the nuclear quadrupolar interaction resulting from the 180° flip motion of the water molecules in the lattice. The average waiting time between flips, τ, is determined directly at −15°C to be 1.0 ± 0.1 msec. The ratio T1 / τ is found to be (3.8 ± 0.3) × 104, in good agreement with the value calculated from the proposed relaxation mechanism, (4.00 ± 0.05) × 104. From the temperature dependence of T1 the potential barrier hindering the flip motion is found to be 16.3 ± 0.1 kcal/mol. This value is in good agreement with the value calculated earlier from a point-charge model by Pedersen.
Distribution Function for Excluded-Volume Problem
Authors: Kumbar Mahadevappa
Published: February 2004

The distribution function for mean-square end-to-end distance of the walks confined to lattice has been obtained. Reiss distribution function has been modified and represented in dipolar form which gives the correct answer to mean-square end-to-end distance of the walks confined to lattice. The mean-square length of the completely stretched chain also has been examined and represented as 〈rn2〉∝n2, where n is the number of bonds in the chain.
Momentum Autocorrelation Function of a Particle in a One-Dimensional Box
Authors: Deutch J. M. , Kinsey J. L. , Silbey R.
Published: February 2004

The momentum autocorrelation function of a particle in a one-dimensional box is calculated both classically and quantum mechanically. The classical function is found by using the eigenfunctions of the Liouville operator for the system. The quantum-mechanical function is calculated and shown to be a non-analytic function of ℏ.
Relativistic Effects in Diatomic Molecules: Evaluation of One-Electron Integrals
Authors: Matcha R. L. , Kouri D. J. , Kern C. W.
Published: February 2004

One- and two-center matrix elements over the kinetic-energy-shift, the spin–orbit, the Dirac, and the Fermi-contact operators are evaluated for arbitrary combinations of Slater orbitals. The analysis is compatible with previous treatments of the two-electron Breit–Pauli operators.
Convolution Analysis of Electron Impact Experiments
Authors: Cowperthwaite Ronald L. , Myers Howard
Published: February 2004

Electron impact experiments are analyzed from the standpoint of the influence of the electron beam energy distribution on the measurements. A generalized electron energy distribution function is formulated. Special cases of this distribution function yield analytical representations of operational electron guns. The energy distribution of the gun is found to strongly affect the salient features of the cross section. A procedure is thence developed for unfolding the true cross section from impact measurements by removing the distortion of the electron beam. Comparisons with measured data are presented.
Shock Wave Compression of Three Polynuclear Aromatic Compounds
Authors: Warnes R. H.
Published: February 2004

Polycrystalline samples of anthracene, phenanthrene, and pyrene have been stressed with shock waves to pressures of 550 kbar. States in the stressed samples were determined by measuring shock wave velocities in the samples and in an 1100 aluminum base plate used as a standard. An abrupt increase in the compressibility was noted for each material: it occurred at 176 kbar for anthracene, 201 kbar for phenanthrene, and 234 kbar for pyrene. This increase is believed to be associated with an intermolecular coupling reaction. Recovered samples of anthracene did exhibit this coupled structure. The Hugoniot and calculated isotherm both indicate that anthracene is more compressible than was previously thought. The equation of state of 1100 aluminum was determined during this work.
Isotherms of Carbon Monoxide to 10 kbar and 300°C
Authors: Robertson Stanley L. , Babb Stanley E.
Published: February 2004

The isotherms of carbon monoxide have been determined between 35 and 300°C at pressures from 1500 to 10 000 bar.
Isotherms of Ethylene and Propane to 10 000 bar
Authors: Babb Stanley E. , Robertson Stanley L.
Published: February 2004

A single isotherm of ethylene at 35°C between 1500 and 8000 bar and of propane at 35, 100, and 200°C extending to almost 11 000 bar, are reported.
Cation Self-Diffusion and Semiconductivity in NiO
Authors: Volpe Milton L. , Reddy John
Published: February 2004

Nickel self-diffusion and semiconductivity in single-crystal NiO have been measured as functions of temperature and O2 pressure over ranges of 1182–1762°C and from one to 5 × 10−7 atm. Atmospheres of pure O2, pure CO2, O2–Ar mixtures, and CO–CO2 mixtures have been used. In pure O2 and in pure CO2 the results can be expressed with a standard deviation of less than 4% by equations of the form D = D°exp(− ED / RT ) and σT = (σT)0exp(− Eσ / RT). In pure O2, D° = (4.8 ± 1.3) × 10−2cm2/sec, ED = 60.8 ± 0.6 kcal/mol, (σT)0 = (7.5 ± 0.8) × 106Ω−1·cm−1°K, Eσ = 24.7 ± 0.2 kcal/mol. In pure CO2, D° = (2.1 ± 0.4) × 10−2cm2/sec, ED = 62.7 ± 0.3 kcal/mol, (σT)0 = (65 ± 11) × 106Ω−1·cm−1/sz/K, Eσ = 36.4 ± 0.6 kcal/mol. Both semiconductivity and diffusion coefficients are proportional to Pβ. For diffusion, β increases with temperature, being 0.16 at 1245°C and 0.20 at 1380°C; for conductivity, β is between 14and16 and decreases with temperature. The results can be interpreted in terms of simple models invoking noninteracting defects. Using these models, approximate values have been calculated for the migration and formation energies of the defects.
Raman Spectrum of Graphite
Authors: Tuinstra F. , Koenig J. L.
Published: February 2004

Raman spectra are reported from single crystals of graphite and other graphite materials. Single crystals of graphite show one single line at 1575 cm−1. For the other materials like stress-annealed pyrolitic graphite, commercial graphites, activated charcoal, lampblack, and vitreous carbon another line is detected at 1355 cm−1. The Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k-selection rule. The intensity of this band allows an estimate of the crystallite size in the surface layer of any carbon sample. Two in-plane force constants are calculated from the frequencies.
Stark Spectroscopy of 15NH3 ν2 Band by 10-μ Lasers
Authors: Shimizu Fujio
Published: February 2004

Ninety-five coincidences between 15NH3 ν2-band lines with J ≤ 7 and CO2 and N2O laser lines are obtained by Stark tuning of NH3 lines. Accurate relative positions between NH3 and laser lines are calculated for these coincidences. Further, the molecular constants related to the ν2 band are determined using the wavelengths of the laser lines as standard.
Electron Traps in Irradiated Water–Ethylene Glycol Glass at 4 and 77°K
Authors: Higashimura Takenobu , Noda Masato , Warashina Tetsuo , Yoshida Hiroshi
Published: February 2004

In order to study the mechanism of electron trapping in irradiated glasses of water–ethylene glycol mixture, they were subjected to γ rays and examined by optical absorption and electron spin resonance measurements at 4 and 77°K. Most trapped electrons formed at 4°K give an optical absorption band in infrared region around 1800 nm and a single-line electron spin resonance spectrum with the width of 3 G, while the trapped electrons formed at 77°K give an absorption band in visible region (λmax = 585 nm) and an electron spin resonance spectrum with the width of 15 G. By warming the glass to 77°K after the irradiation at 4°K, the trapped electrons transformed to those observed for the irradiation at 77°K. Results indicate that the nature of trapped electrons formed at 4°K is very similar to that of trapped electrons in irradiated nonpolar alkane glasses. Even in the polar glass of water–ethylene glycol, the orientation of molecular dipoles is not needed for the formation of electron traps at 4°K, where the molecular movements are highly restricted. By raising the temperature to 77°K, the molecular dipoles in the vicinity of trapped electrons orient favorably to deepen the traps. The yield of trapped electrons, for 100 eV energy absorbed, at 4°K is estimated to be larger than 0.6. However, it is possibly less than 2.0, the yield for the irradiation at 77°K.
Emission Cross Sections of N2 in the Vacuum Ultraviolet by Electron Impact
Authors: Ajello Joseph M.
Published: February 2004

The electron beam excitation spectrum of N2 at low pressure (0.12–0.18 μ) in the wavelength range 1200–2000 Å was recorded for monoenergetic electron impact energies from 10 to 208 eV. The spectral features observed were the Lyman–Birge–Hopfield vibrational transitions (a1Πg → 1Σg and several atomic nitrogen multiplets produced by dissociative excitation of N2. The emission cross sections of the Lyman–Birge–Hopfield vibrational transitions were measured and summed to give the cross section for the entire electronic transition. The energy dependence of all vibronic transitions was the same. The atomic nitrogen transitions studied were the multiplets at 1200 Å (4P → 4S0), 1493 Å (2P → 2D0) and 1743 Å (2P → 2P0). These emissions originated from dissociative excitation of molecular nitrogen. The emission cross sections of these transitions typically have two thresholds, corresponding to dissociative excitation of N2 into two nitrogen atoms and to dissociative ionization excitation into an atom and an ion.
Supercritical Viscosity Anomaly in Oxide Mixtures
Authors: Simmons Joseph H. , Napolitano Albert , Macedo Pedro B.
Published: February 2004

The viscosity anomaly, previously detected above the critical point of some fluid binary mixtures, is investigated in the sodium–borosilicate oxide system. At the sodium–borosilicate dome, the critical composition is selected with small CaO and Al2O3 doping additions to obtain samples whose critical temperatures range over 190°C and have minimum high-temperature structural differences. Viscosities between 102 and 109 P (10−1 N·sec/m2) are measured. A fractional excess viscosity is defined as the difference between the viscosity of each melt and a normal viscosity function, divided by the normal viscosity. The normal viscosity function is taken to have the form of the viscosity curve from the sample with the lowest critical temperature. The fractional excess viscosity then shows an anomalous increase near the critical point. The fractional excess viscosity, Δη / η0, attains a value of 2 near the consolute temperature but appears to remain finite at the critical point. This critical-point effect can be detected 200°C above the critical temperature. Such results indicate that the viscosity is quite sensitive to the presence of composition fluctuations above the critical point of this system, and represents a good tool for investigating supercritical phenomena.
ESR Spectra of NO2 in Inert Matrices
Authors: Myers G. H. , Easley W. C. , Zilles B. A.
Published: February 2004

The ESR spectrum of NO2 in neon at 4°K has been re-examined at improved resolution. The spectrum is interpreted in terms of three distinct sites: (1) a rigid site with preferred molecular orientation as observed by Kasai et al. [J. Chem. Phys. 42, 1120 (1965)], (2) a rotational site with motion of the N atom about the O···O axis (which is oriented parallel to the matrix deposition surface), and (3) a hindered rotation about the C2v symmetry axis. The relative concentrations of these sites is estimated to be of the same order of magnitude. The NO2/argon spectra are irreversibly changed by annealing at 30°K, populating the latter rotational site at the expense of the former sites.
Intrinsic Viscosity of Short Chains. I. Extension of the Theory of Kirkwood and Riseman
Authors: Perico A. , Rossi C.
Published: February 2004

The hydrodynamic theory of Kirkwood and Riseman is extended to include chains with a small number of bonds. The dependence of the intrinsic viscosity on the variation of the frictional coefficient, the chain statistics, and the number of bonds is analyzed.
Classical Collisions of Dipoles and the Transport Properties of Polar Molecules
Authors: Clarke A. G. , Smith E. B.
Published: February 2004

Classical trajectories for the collisions of dipolar molecules have been calculated for many initial conditions by stepwise integration of the equations of motion. The molecules were represented by hard spheres with point dipoles at their centers and the motion was confined to a plane. Molecular parameters representing, very crudely, the interactions of CHF3, CH3F, and HCl were used and most of the calculations were carried out for relative velocities equal to the mean relative velocity for each gas at 300°K. The translation–rotation energy exchange and the scattering angle are found to be very sensitive to the initial dipole orientations. The mean scattering angle χ and translation–rotation energy exchange ΔE, averaged over the two dipole orientations, are shown to be insensitive to the difference of the angular velocities and to be determined mainly by the sum of the angular velocities. Many of the qualitative features of the collisions are found to be predicted by the rough-sphere model. In the second half of the paper the quantitative results are applied to the transport properties of polar gases using the kinetic theory equations of Wang Chang and Uhlenbeck. The effect of energy exchange terms in the viscosity formula is estimated and various methods of calculating transport cross sections for dipolar molecules are compared.
Ground-Term Energy Levels of Triply Ionized Holmium in Calcium Tungstate
Authors: Wortman D. E. , Sanders David
Published: February 2004

The energy levels of the I5 ground term of Ho3+ in single crystals of CaWO4 were established by absorption and fluorescence spectra measurements. The measurements were made using crystals at temperatures near 2, 20, and 85°K. Most of the observed transitions can be accounted for by the electric dipole selection rules. Magnetic dipole selection rules cannot be ruled out for some of the lower energy transitions, however. Calculations were made to determine the effects of the crystalline host material on the Ho3+ energy levels. An effective Hamiltonian of the form suggested by Karayianis was diagonalized in a basis of Russell–Saunders wavefunctions to obtain the calculated energy levels and wavefunctions for Ho3+. Such a calculation takes into account the complete J mixing of the states within the ground term and is equivalent to determining the effects of the spin–orbit interaction to better than second order. In the calculation, an rms deviation of 10 cm−1 was found as the best agreement between the theoretical and experimental energy levels using the Hamiltonian, H = λ1(L·S) + λ2(L·S)2 + λ3(L·S)3 + ΣlmBlm+Clm. The empirically determined parameters yielding this rms deviation are (in cm−1): λ1 = − 487.9, λ2 = − 6.601, λ3 = − 0.1801, B20 = 436, B40 = − 664, B44 = 779, B60 = − 33, ReB64 = 558, and ImB64 = 196. The g‖ factor for the ground state of Ho3+ in CaWO4 was calculated to be 13.675. This is in agreement to within 0.12% of the experimental value of 13.691 ± 0.006 reported by Kirton.
Ultrasonic Relaxations in a Vitreous Ca(NO3)2–KNO3 Mixture
Authors: Weiler R. , Bose R. , Macedo P. B.
Published: February 2004

Ultrasonic relaxations have been studied in a vitreous 60% KNO3–40% Ca(NO3)2 mixture (mol%) from 1 to 185 MHz in the temperature range 90–130°C. The spectrum of longitudinal relaxation times has been found to be symmetric, fitting a Gaussian distribution in the logarithm of relaxation times, and having a temperature dependent width which narrows remarkably at the high-temperature end. The occurrence of a high-temperature sharp distribution of relaxation times in a molten salt system raises a major objection to the currently held belief that the origin of such sharp, high-temperature distributions, found in molten oxides for example, originate from the covalent nature of the molecular bonds. It has been shown in this paper that a topological model previously proposed by Simmons and Macedo, correlating the distribution of relaxation times to the distribution of molecular environments, provides an excellent qualitative description of the characteristics of the observed relaxation spectra.
Scattering of Low Velocity Neutral Particles: The Cs–He, Cs–Kr, and Cs–Xe Interactions
Authors: Colgate S. O. , Imeson T. C.
Published: February 2004

Total scattering cross sections Q were measured for Cs atoms velocity selected from thermal beams scattered by He, Kr, and Xe gases. Over the available range of relative velocities, the observed Cs–Kr and Cs–Xe cross sections vary in accordance with scattering by a central field attractive potential of the form U(r) = − C6r−6. Observed values of C6 in units of 10−58 erg·cm6 are 4.7 ± 0.4 and 8.1 ± 0.7 for the Kr and Xe interactions, respectively, and are in good agreement with available theoretical estimates. The velocity range of the Cs–He measurements was too small to permit accurate determination of the force law, but the total cross section at a relative velocity of 1.30 × 105 cm/sec was found to be 177 ± 9 Å2.
ESR Study of Complex Formation and Electronic Relaxation of Fe3+ in Aqueous Solutions
Authors: Levanon H. , Stein G. , Luz Z.
Published: February 2004

ESR measurements of aqueous solutions of Fe3+ containing various electrolytes were made at X- and Q-band frequencies. It was found that the line shape and integrated intensity depend on the pH and on the type and concentrations of counteranions in the solution. Addition of LiCl and NH4NCS result in reduction in the integrated intensity and subsequent disappearance of the ESR signal. This is interpreted in terms of the formation of monosubstituted complexes which give signals too broad to observe. From the results, formation constants have been calculated. Successive addition of NH4F results in the formation of complexes of the type [Fe(H2O)6−nFn]3−n having different ESR linewidth ranging from 10 to 1000 G. There is a strong reduction in the linewidth on going from X- band to Q-band frequencies. The results are explained in terms of electronic relaxation via the modulation of the zero field splitting (zfs) parameter. From the analysis of the data it was possible to derive values for the zfs interactions and the associated correlation times. The results indicate that the modulation of the zfs interaction is due to collisions between complex and solvent molecules rather than diffusional tumbling.
Viscosity of Binary Polar-Gas Mixtures: CH3Cl–H2S and CH3Cl–SO2
Authors: Bhattacharyya P. K.
Published: February 2004

Viscosities of the binary polar-gas mixtures, CH3Cl–H2S and CH3Cl–SO2, have been measured in the temperature range from − 35 to 35°C with an oscillating-disk viscometer. The data have been utilized to derive information on unlike polar–polar interactions. The results show the remarkable success of effectively spherically symmetric potentials and semiempirical combining rules in representing mixture viscosities of polar systems.
Analysis of the Determination of Rotational Relaxation Numbers from Thermal Transpiration
Authors: McConville G. T. , Taylor W. L. , Watkins R. A.
Published: February 2004

New thermal transpiration data are given for He, Ar, N2, and CO in the temperature region between 77 and 300°K. These data are analyzed in terms of the “dusty-gas” flux equation and its differential approximation and in terms of a modified Weber–Schmidt equation. These models produce from the data values of the translational Eucken factor, which is related to the rotational relaxation number in a gas. The analysis indicates that a precise representation of the temperature dependence of the viscosity and independent information about the gas–tube surface interaction must be used to determine unambiguous values for the translational Eucken factor from these measurements.
Dissociation Energy of F2
Authors: DeCorpo J. J. , Steiger Ronald P. , Franklin J. L. , Margrave J. L.
Published: February 2004

The dissociation energy of F2 has been determined mass spectrometrically. The heat of formation of fluorine, ΔHf°(F), was determined from measurements of both the appearance potentials and translational energies of the products resulting from electron impact, including both positive and negative ions. One can derive values for the dissociation energy from each of the possible processes, namely: (1) dissociative electron attachment, (2) ion-pair formation, and (3) dissociative ionization. The values are in excellent agreement and establish D°(F2)=37.5 ± 2.3 kcal/mol.
Application of Tight-Binding Method to Disordered Systems
Authors: Popielawski Jan
Published: February 2004

The Green's function method, in the perturbational version, has been applied to description of the nearly bounded electron limit in disordered systems retaining some degree of spatial ordering, as described by the pair correlation function. The series expansion for the Green's function has been approximately summed up, both for the systems at absolute zero temperature and for the systems at finite temperatures described by Born–Oppenheimer approximation. The approximate dispersion relations (E ∼ k relations) have been given explicitly, and a general way of the calculation of density of states and electrical conductivity for the systems mentioned has been indicated. Applications of the presented formalism to a study of the dynamics of Frenkel excitons in liquids and disordered solids and electron properties of dense metallic vapors have been briefly discussed.
Modification of the Electronic Structure of Ferrous Iron in Hemoglobin by Ligandation and by Alterations of the Protein Structure Inferred from Mössbauer Measurements
Authors: Trautwein A. , Eicher H. , Mayer A. , Alfsen A. , Waks M. , Rosa J. , Beuzard Y.
Published: February 2004

Mössbauer effect measurements were performed on rat hemoglobin enriched in vivo with 57Fe to about 70%. The low-energy term scheme (5B2, 3E, 5E, 1A1) of ferrous iron in deoxyhemoglobin compounds (hb) was inferred from the temperature dependence of the quadrupole splitting and chemical shift by ligand field calculations. The low-energy term schemes of oxyhemoglobin (hbO2) and carbonylhemoglobin (hbCO) were suggested from the magnitude of the experimental quadrupole splittings, and were compared with the calculated low-energy term scheme of hb. It is concluded that the ground state of hbCO (1A1) lies considerably lower in energy than the ground states of hbO2 (Γ) and hb (5B2). This is in agreement with the equilibrium behavior of hb with CO and O2. The effect of a variation of pH and of the binding of hemoglobin to haptoglobin on the low-energy term scheme was investigated.
Exciton Theory of the Electronic States of Dye–Polymer Complexes. I. Linear Polymers
Authors: Philpott Michael R.
Published: February 2004

A theory is developed for the excited electronic states of dye–polymer complexes in which dyes with many vibronic states are bound to infinite linear polymers with one excited state per monomer. Overlap of wavefunctions of monomers and dyes is neglected. Two aspects of the coupling of excited dye levels to the exciton states of the polymer are considered. First, dye transitions are assumed not to overlap the exciton band of the polymer. Problems considered include the perturbation of dye levels by the polymer (primary trap states), the formation of discrete states below the exciton band due to secondary interactions between dye and monomer, coupling of vibronic dye levels by the polymer, and the many-dye problem, including the case where the dyes have a series of vibronic levels. In the latter it is shown how the degree of the secular equation reduces to the number of dyes present and how this is equivalent to a Frenkel exciton moving on a lattice with holes since the whole of the dye–polymer interaction can be incorporated into an effective dye–dye resonance interaction. The more subtle problems of exciton scattering by the dye molecule and the time development of prepared states, which arise when dye levels fall inside the exciton band, are considered using the techniques of second quantization.
Rate Constants for the Thermal Energy Reactions of H−. with O2, NO, CO, and N2O
Authors: Dunkin D. B. , Fehsenfeld F. C. , Ferguson E. E.
Published: February 2004

The reaction of H− with O2 has been measured in a flowing afterglow system at 278°K. The reaction is found to be associative detachment, H−+O2→HO2+e, with a rate constant 1.2 ± 0.2 × 10−9 cm3/sec. A careful search was carried out for the possible heavy negative ion products, O2−, OH−, O− with negative results. Such products are believed to contribute less than 1% to the reaction if they contribute at all. Also, the reaction H−+N2O→OH−+N2 has a rate constant 1.1 ± 0.3 × 10−9 cm3/sec, the reaction H−+NO→HNO+e has a rate constant 4.6 × 10−10 cm3/sec, and H−+CO→HCO+e has a rate constant 4.6 × 10−10 cm3/sec, and H−+CO→HCO+e has a rate constant ∼5 × 10−11 cm3/sec.
Fluorescence of Fluorobenzene
Authors: Nakamura Kenichiro
Published: February 2004

The behavior of the first excited singlet state of monofluorobenzene in the gaseous phase has been examined with aid of spectroscopy and of emission quantum yields. Some resonance emission occurs at short wavelengths of incident radiation at a pressure of 1 torr. This resonance radiation is quenched by foreign gases and a linear plot of 1 / Qrf vs p is obtained. Absolute emission yields were obtained by use of benzene, for which Qf at 253 nm is assumed to be 0.18. The total yield of fluorescence is constant over the range λ > 258 nm, but below 258 nm the yield decreases. Addition of iso-C4H10 enhances the yield at short wavelengths. An apparent diffuseness of the spectrum at short wavelengths may indicate some process such as isomerization or even dissociation.
Polarized Electronic Absorption Spectrum of Tetragonal NiCl42− Cs3(MgCl4)Cl
Authors: Couch Thomas W. , Smith G. Pedro
Published: February 2004

The optical absorption spectrum (4000–17 000 Å) of crystals of Cs2(Mg0.996Ni0.004Cl4)Cl was measured at approximately 5 and 80°K. The host material was found by x-ray diffraction to have the Cs3(CoCl4)Cl structure (I4 / mcm) at temperatures down to at least 10°K. In the solid solution the spectra showed that nickel(II) substituted for magnesium, which lies at sites of D2d symmetry with the principal axis aligned with the c axis of the tetragonal crystal. Spectra were measured in both E ⊥ c and E ‖ c polarizations, and the results were in accord with a ligand-field model having B, C, ξ, B02, B04, and B44 as parameters. Numerous phonon-creation bands were observed that provided information about excited state potential wells and nuclear motions. In some band systems the individual bands were unusually narrow and well resolved.
Surface Work Function of Gadolinium
Authors: Ramey R. L. , Katzberg S. J.
Published: February 2004

A contact potential difference measurement of gadolinium against platinum yielded a work function of 2.90 ± 0.06 eV.
Fourth Picture in Quantum Mechanics
Authors: Marcus R. A.
Published: February 2004

A quantum-mechanical counterpart to the classical mechanical variation of constants method is derived, with initial values of coordinates and momenta as “constants.” Use is made of a formal operator solution for nonautonomous or autonomous systems in classical mechanics, which we published earlier, and of the correspondence between Poisson brackets and commutators. An alternative unified Lie-algebraic derivation is also given. It is shown that the Schrödinger, Heisenberg, and interaction pictures in quantum mechanics do not correspond directly to the method of classical mechanical variation of these “constants.” A fourth picture, termed “mixed interaction,” is introduced and shown to so correspond. It complements the previous three in a symmetrical manner, bearing the same relation to the Heisenberg picture that the Schrödinger picture bears to the interaction one. The group-theoretic relationship to the interaction picture is noted, as is the relation to the usual variation-of-constants method in wave mechanics. For completeness, the classical counterparts of the Heisenberg and interaction pictures are also given. The present results arose from a comparison of quantum and classical treatments of collisions.
On the Proton Affinity of Water
Authors: Long John , Munson Burnaby
Published: February 2004

Ion–molecule reactions of proton transfer from H3O+ and to H2O were studied with several mixtures in a Bendix TOF mass spectrometer at pressures of 0.05–0.10 torr and in a CEC 21-110B mass spectrometer at pressures as high as 0.25 torr. Proton transfer was observed from H3O+ to C3H6, cis-2-C4H8, and CH2O; proton transfer was observed to H2O only from C2H5+, and not s-C3H7+ or s-C4H9+. These observations support the value of P.A. (H2O) = 164 ± 4 kcal/mole.
Orientation Dependence of the Electron Spin Resonance Spectrum of Di-t-butyl Nitroxide
Authors: Libertini Louis J. , Griffith O. Hayes
Published: February 2004

Comparisons of theoretical calculations and experimental results are reported for the anisotropy of the hyperfine splitting and g value of the di-t-butyl nitroxide free radical. Extensive experimental data were collected with a microwave frequency of 9.5 GHz with supplementary data collected at 35 GHz. Several approximations to the Hamiltonian are discussed and compared to the results of the exact solution. Explicit equations for several approximations are given in terms of the principal values of the splitting and g-value tensors and the orientation of the nitroxide in the external magnetic field. The more accurate approximations should prove useful in the interpretation of nitroxide ESR spectra by decreasing the programming difficulties and the time requirements involved in computer simulation of nitroxide spectra.
Combined SCF and CI Method for the Calculation of Electronically Excited States of Molecules: Potential Curves for the Low-Lying States of Formaldehyde
Authors: Buenker Robert J. , Peyerimhoff Sigrid D.
Published: February 2004

The success of various ab initio methods for the calculation of electronic spectra for polyatomic molecules is discussed with reference to the formaldehyde system. It is found that a limited CI calculation based on the SCF MO's of the ground-state wavefunction yields inaccurate potential curves for the excited states of H2CO and overestimates their transition energies from the ground state. It is concluded that the major cause for these deficiencies lies in the fact that the ground-state MO's do not represent a good starting point for the description of the excited states, and thus a second series of calculations is carried out using open-shell SCF techniques in an attempt to improve upon this situation. The resulting excited-state potential curves do show the proper angular behavior expected from experimental studies, but the calculated transition energies are too low because the correlation energy error in the SCF treatment is greater for the closed-shell ground state than for the open-shell excited species. To correct this shortcoming a limited CI calculation is carried out for each excited state based on the SCF MO's of its parent or main configuration. This combined SCF and CI treatment leads to excellent results for both transition energies and potential curves of ground and excited states and also produces relatively good dipole moments for both types of states.