bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-Crystal Infrared and Raman Spectra of Cyanuric Chloride
Authors: Thomas Dwaine M. , Bates John B. , Bandy Alan , Lippincott Ellis R.
Published: February 2004

The single-crystal infrared and Raman spectra of cyanuric chloride, 1,3,5-trichlorotriazine, were measured at 298 and 77°K. A complete assignment for the intramolecular fundamentals was made, including a study of a modified valence force field. Intensity predictions from the oriented gas model qualitatively agreed with the experimental results for the intensity of the free molecule Raman-active bands. Spectral measurements in the low-frequency region resulted in the assignment of several bands to the optically active lattice modes of cyanuric chloride.
Transform for Treating a Wide Class of Perturbation Problems, with Application to the Exchange Equations for H2+ and H2
Authors: Rosenthal Carey M.
Published: February 2004

A transform is introduced to solve the H2+ and H2 exchange functions of Certain and Hirschfelder. The solution obtained for H2+ is inverted numerically. The properties of this transform are derived and its applicability to other perturbation problems is discussed.
Reaction Rate Measurements of O(3P) Atoms by Resonance Fluorescence. II O(3P)+CO+M→CO2+M; M=He, Ar, N2
Authors: Slanger T. G. , Black G.
Published: February 2004

Absolute rate constants for the reaction O(3P)+CO+M→CO2+M have been determined at 300°K for M=He, Ar, and N2, using oxygen resonance radiation as a probe to monitor the relative atom concentration during decay time measurements. The rate constants are, in units of cm6 molecules−2·second−1, kHe = 6 ± 1.5 × 10−36, kAr = 7 ± 3.5 × 10−36, and kN2 = 1.4 ± 0.4 × 10−35. The O(3P) is produced by O2 photodisociation at 1470 Å, at which wavelength O(1D) is also formed. The observations indicate that the O(1D)–CO interaction results in O(1D) deactivation to O(3P), not CO2 formation.
Surface Tension in Lattice Models
Authors: Woodbury George W.
Published: February 2004

An expression is derived for the free-energy contribution at the edge of a lattice model which has nearest-neighbor interactions. The result is extended so as to give the surface tension between coexisting phases in the Ising Model. To test the formula, calculations are made for the two-dimensional lattice, where the surface tension is known. It is found the numerical results systematically approach the exact results of Onsager. The nature of long-range order in a lattice model with edges is also discussed in connection with the form of the asymtotic degeneracy of the largest two eigenvalues.
Studies on Triplet Radiative Lifetimes, Phosphorescence, and Delayed Fluorescence Yields of Aromatic Hydrocarbons in Liquid Solutions
Authors: Langelaar J. , Rettschnick R. P. H. , Hoijtink G. J.
Published: February 2004

The phosphorescence of phenanthrene, pyrene, and naphthalene in fluid solutions has been studied. The radiative lifetimes are calculated from the quantum yields and actual lifetimes and vary only slightly or not at all with temperature within the experimental error. For phenanthrene, pyrene, naphthalene, and anthracene the radiative lifetimes at 77°K in ethanol are 25, 30, 75, and 180 sec, respectively. The temperature dependence and the absolute value of the triplet–triplet annihilation efficiency vary from molecule to molecule. The results are discussed in terms of a re-encounter association of the annihilation partners to form an excimer.
Magnetic Resonance Studies of Biradicals. III. Verdazyl Mono- and Biradicals
Authors: Kopf Peter , Morokuma Keiji , Kreilick Robert
Published: February 2004

We have taken the NMR and ESR spectra of a series of verdazyl mono and biradicals. The susceptibility of each of the compounds was also measured. Zero field splitting parameters were determined from the ESR spectra while electron–nuclei coupling constants were determined from the NMR spectra. The coupling constants of nuclei contained in rings connecting the two monoradical halves proved to be the average of couplings from protons in corresponding positions in the monoradical while the coupling constants for nuclei in other parts of the molecules were one-half of the monoradicals couplings. The relative magnitudes of the various coupling constants were predicted by a simple perturbation calculation and by semiempirical MO calculations.
Calculation of the Exciton Band Structure of the 3800- and 2500-Å Singlet Transitions of Crystalline Anthracene
Authors: Philpott Michael R.
Published: February 2004

The exciton band structure of the 3800- and 2500-Å transitions of anthracene has been calculated in the dipole approximation. It is found that the branches of both transitions are flat for wave vectors k normal to the (001) plane. In other directions considered the exciton energy exhibits dispersion. The calculations also reveal that for all the directions considered the lowest energy of the 2500-Å exciton band is not a k = 0 state.
Rydberg States of Diatomic and Polyatomic Molecules Using Model Potentials
Authors: Betts Timothy , McKoy Vincent
Published: February 2004

We have used a simple model potential to calculate Rydberg series in N2, O2, CO, NO, ethylene, and benzene. The model potential for a molecule is taken as the sum of atomic potentials, which are calibrated to atomic data and contain no further parameters. Our results agree with experimentally measured values to within 5%–10% in all cases. We apply our results to several unresolved problems connected with the above molecules and indicate some of the applications which we foresee for model calculations.
Irreversible Statistical Mechanics of Polymer Chains. I. Fokker–Planck Diffusion Equation
Authors: Iwata Kazuyoshi
Published: February 2004

A theory of the irreversible statistical mechanics of flexible polymer chains is developed on the basis of new ideas. The Brownian motion of polymer chains is assumed to be a Markoff random transition among their rotational isomeric states. The theory is described for ring polymer chains, for which the “normal coordinates” can be determined by the consideration of their symmetry alone. First, we derive the master equation which describes the discrete Brownian motion of a ring polymer chain. The master equation is averaged over all the configurations, fixed several normal coordinates to certain values. This averaging process is called “coarse graining.” By Taylor expansion of the coarse-grained master equation, we get a Fokker–Planck diffusion equation which is specified by two kinds of molecular constants, the diffusion constant Dα and the expansion parameter γα, both of which depend on the suffix α of the normal coordinates. For slow relaxation phenomena, the diffusion equation is reduced to that of the spring-bead model theory. The general behaviors of Dα and γα are discussed: The reduced diffusion constant D̃α(= Dα / D0) decreases rapidly as α increases, whereas γα2 / α2 remains roughly constant.
Hydrogen Bond Studies. XXXXVI. The Crystal Structures of Normal and Deuterated Sodium Hydrogen Oxalate Monohydrate NaHC2O4·H2O and NaDC2O4·D2O
Authors: Tellgren Roland , Olovsson Ivar
Published: February 2004

The crystal structures of NaHC2O4·H2O and NaDC2O4·D2O have been determined from three-dimensional single crystal x-ray diffractometer data obtained at room temperature. Two formula units crystallize in a triclinic unit cell with the dimensions: a = 6.503, b = 6.673, c = 5.698 Å, α = 85.04, β = 110.00, γ = 105.02° for the hydrogen compound and a = 6.501, b = 6.671, c = 5.716 Å, α = 84.91 β = 109.93 γ = 105.00° for the deuterated compund. The space group is P1̄. The hydrogen oxalate ions are linked end to end in infinite chains by hydrogen bonds (2.571 Å). The chains are cross linked to form layers by both O–H···O bonds from the water molecules (2.808, 2.826 Å) and by ionic bonds Na+···O. These layers are in turn held together by Na+···O bonds. The oxalate group is nonplanar with an angle of twist about the C–C bond of 12.9°. The only significant difference between the bond distances in the normal and deuterated compound occurs in the shortest hydrogen bond, which is 0.022 Å longer in the deuterated case.
Transfer of Protons through “Pure” Ice Ih Single Crystals. I. Polarization Spectra of Ice Ih
Authors: von Hippel A. , Knoll D. B. , Westphal W. B.
Published: February 2004

After a short introduction of the subject “proton transfer in ice” and some background information on previous polarization measurements, the growing and preparation of our single crystals and the instrumentation for a–c measurements from 105–8 × 10−3 Hz, 0 to − 180°C, are briefly described. By rigorous control of error limits and an improved computerized evaluation procedure it was possible to resolve the dielectric spectrum of these “pure” ice single crystals into several significant components: the intrinsic Debye spectrum, two weak spectra preceding it at a high frequency, and “space-charge-polarization” spectra. Important characteristics of these spectra and inherent difficulties in quoting their “accurate” parameters are presented. The interpretation of these data requires new molecular models; they are developed in Part II; the analysis of polarization data is resumed in Part III in conjunction with new transconductance measurements.
Transfer of Protons through “Pure” Ice Ih Single Crystals. III. Extrinsic versus Intrinsic Polarization; Surface versus Volume Conduction
Authors: Maidique M. A. , von Hippel A. , Westphal W. B.
Published: February 2004

In order to analyze the charge transport through ice Ih single crystals and over their surfaces, the a–c polarization studies of Part I were supplemented by d–c and transient measurements ranging from 10−2-4 × 104 V/cm, from nanoamperes to microamperes, and from 100μsec–3 h. After a brief description of techniques, the research focuses on “conductivity” as represented by an activation energy equation. In the literature, the activation energies quoted range from 33 ↔ 0 kcal/mole. Investigating the reasons for this confusion we found: (1) The value 33 kcal/mole is caused by surface conduction and can be reduced to ∼ 20 kcal/mole by pumping. (2) Zero activation energy characterizes the “initial” currents in the milli-second range. (3) Intermediate values (e.g., 12 kcal/mole) stem from apparent conductivities in space-charge distorted fields. The saturation current at high fields, measured by Eigen and co-workers (activation energy ∼ 22 kcal/mole), seems to be an extrinsic current produced by multicrystallinity and internal surface conduction; the true volume current through ice single crystals proves orders of magnitude smaller and Ohmic in that range. Instead of a saturation current, an extrinsic saturation charge can be extracted from ice single crystals; our best fresh samples contained about 3 × 1011 of these carriers per cubic centimeter. Their mobility is about 5 × 10−3 cm2/V·sec. This mobility is only 2–3 times larger than that of protons in water and gives no evidence for a special proton transfer mechanism across hydrogen bridges. The polarization spectra in ice single-crystal samples change dramatically on aging; after 10 months we observed six clearly separated relaxation spectra, three of them connected with space-charge phenomena; in fresh samples, the space-charge polarization can be drastically reduced by a high-voltage pulse and needs hours to recover completely. The results can be understood on the basis of the theoretical concepts developed in Part II about the behavior of intrinsic and extrinsic defects in ice single crystals.
Scattering of the Rare Gases (He, Ne, Ar, Kr, and Xe) from Platinum (111) Surfaces
Authors: Stoll A. George , Smith Donald L. , Merrill Robert P.
Published: February 2004

The scattering of He, Ne, Ar, Kr, and Xe from Pt (111) surfaces characterized by LEED has been measured for surface temperatures between 100°C and 500°C using effusive thermal energy beams of 23°C and 700°C. The LEED and helium scattering indicate that the surfaces are geometrically smooth, regular, and free from low molecular weight contaminants. Results are in qualitative agreement with some of the predictions of the “cube” scattering theories but at variance with the effect of incident angle and surface mass. Data agree qualitatively in these respects with the finite range interaction (FRI) models. Approximate mass balances between the total scattered flux and the incident flux permit estimates of the initial trapping probabilities. No diffraction of He was observed.
Molecular Structures and Motions in Solid Hexamethylethane by Proton Magnetic Resonance
Authors: Smith George W.
Published: February 2004

Proton magnetic resonance (PMR) studies of solid hexamethylethane reveal the existence of C3′ reorientation of the t-butyl groups (activation energy ∼ 3 kcal/mole) in the low-temperature phase. As the temperature is raised above the transition temperature (152.5°K) general molecular reorientation sets in abruptly. A further temperature increase leads to a gradual line narrowing due to self-diffusion above 270°K. The activation energy for self-diffusion is 15.0 ± 0.3 kcal/mole. The rigid lattice second moment (T < 80°K) is in accord with a molecular structure based on standard bond lengths and angles.
NMR Studies of Aqueous Electrolyte Solutions. IV. Hydration Numbers of Strong Electrolytes Determined from Temperature Effects on Proton Shifts
Authors: Vogrin Brother Ferdinand J. , Knapp Paul S. , Flint William L. , Anton Arthur , Highberger Gerald , Malinowski Edmund R.
Published: February 2004

Total effective hydration numbers for a variety of strong electrolytes are deduced from temperature dependence of proton shifts. Individual hydration of the cations and anions are speculated. The cations of all the alkali elements appear to have a relatively consistent hydration of 3 ± 0.5 when the concentrations are below 5m. Above this concentration ion pairing becomes important. For magnesium and calcium salts ion pairing is important above 2m.
Shock Tube Studies of Sulfur Tetrafluoride Dissociation
Authors: Bott J. F.
Published: February 2004

Shock tube studies of SF4 dissociation have been made in the temperature range 1650–1950°K. Rate constants for the initial fragmentation of SF4 have been determined from ir measurements and are explainable in terms of classical unimolecular reaction kinetics. The data were correlated with the Rice–Ramsperger–Kassel (RRK) theory; the values used were 79.0 kcal/mole for the SF3–F bond strength, 1013.63 sec−1 for the pre-exponential A factor, λDσm2 = 5.79 × 10−16cm2, and S = 6. Kinetic rates obtained from exponentially decaying radiation at 12.6 μ and temperatures of 2050–2800°K are attributed to SF3 and lie near the low-pressure limit of unimolecular reactions. The SF3 dissociation rates can be described by k = 4.29 × 1015exp(− 71.8 / RT) cc/mole·sec, where R is in kilocalories per mole·degree Kelvin.
Elastic Moduli and Stress Relaxation Times in Liquid Argon
Authors: Dexter A. R. , Matheson A. J.
Published: February 2004

The elastic shear and bulk moduli of liquid argon have been calculated for values of temperature and density along the saturation boundary. The temperature range was from 83.8–101.8°K and the density range from 1.414 to 1.300 g/cm3. The calculations were performed by allowing the array of atoms of the Bernal–Scott liquid model to interact with a Lennard-Jones pair potential function and studying the changes in energy of this array as a function of homogeneous strain. The density was varied by random removal of atoms from the array. Both the shear and bulk moduli decrease steeply with decreasing density as is observed in molecular liquids. The shear- and volume-stress relaxation times were calculated on the assumption of a single Maxwell relaxation mechanism. The average shear relaxation time τs = 2.22 × 10−13sec, and the average volume relaxation time τυ = 2.54 × 10−13sec. The relaxation times are practically independent of temperature in liquid argon under its saturated vapor pressure in the region of the triple point.
Microwave Spectra, Dipole Moments, and Torsional Potential Constants of cis- and trans-Cyclopropanecarboxaldehyde
Authors: Volltrauer H. N. , Schwendeman R. H.
Published: February 2004

Microwave spectra have been assigned for the ground state and three excited torsional states of species of cyclopropanecarboxaldehyde with the oxygen atom cis and trans to the cyclopropane ring. Dipole moments obtained by analysis of the Stark effect of the rotational transitions are as follows: cis species: μa = 2.02 ± 0.01 D, μb = 1.86 ± 0.01 D, μc = 0, μ = 2.74 ± 0.01 D; trans species: μa = 3.22 ± 0.01 D, μb = 0, μc = 0.49 ± 0.01 D, μ = 3.26 ± 0.01 D. From relative intensity measurements estimates of the torsional excitation energies of the two species and the cis–trans energy difference were obtained. By analysis of these energy values the first three coefficients in a Fourier series expansion of the torsional potential were deduced to be V1 = − 0.23 ± 0.12 kcal/mole, V2 = 4.39 ± 0.40 kcal/mole, and V3 = 0.28 ± 0.10 kcal/mole.
Microwave Spectra, Dipole Moments, and Torsional Potential Constants of cis- and trans-Cyclopropanecarboxylic Acid Fluoride
Authors: Volltrauer H. N. , Schwendeman R. H.
Published: February 2004

Microwave spectra have been assigned for the ground state and several excited torsional states of species of cyclopropanecarboxylic acid fluoride with the oxygen atom cis and trans to the cyclopropane ring. Dipole moments obtained by analysis of the Stark effect are as follows: trans species: μa = 3.43 ± 0.03 D, μb = 0.44 ± 0.05 D, μc = 0, μ = 3.46 ± 0.03 D; cis species: μa = 2.85 ± 0.03 D, μb = 1.63 ± 0.03 D, μc = 0, μ = 3.28 ± 0.03 D. By analysis of estimates of the torsional excitation energies of the two species and the cis–trans energy difference, values of the first three coefficients of a Fourier expansion of the torsional potential have been obtained as follows: V1 = − 1520 ± 320 cal/mole, V2 = 5150 ± 700 cal/mole, V3 = 990 ± 260 cal/mole.
Magnetothermodynamics of CuK2(SO4)2·6H2O. II. Magnetic Moment, Heat Capacity, Entropy from 0.5 to 4.2°K with Fields to 90 kG along the γ Magnetic Axis
Authors: Giauque W. F. , Brodale G. E. , Hornung E. W. , Fisher R. A.
Published: February 2004

This is a continuation of our magnetothermodynamic study of a 3.912-cm-diam spherical single crystal of CuK2(SO4)2·6H2O. The magnetic moment and heat capacity have been measured over the range 0.5–4.2°K, with fields of 0, 0.5, 1.0, 2.5, 5, 10, 15, 25, 40, 65, and 90 kG directed along the γ magnetic axis. At 0.5°K the magnetic moment reached limiting values in the field range 45–90 kG. Mγ(limit) = Mγ(sat) + χγ(dia) H = 5782.3−2.45 × 10−4H G·cm3/mole,where − 2.45 × 10−4 is the molal diamagnetic susceptibility, and 5782 is the molal saturation value of the temperature-dependent paramagnetic system. Thus, gγ = 2.071. The heat capacities at 90, 65, and 40 kG approached zero below 1°K, thus giving a common zero reference for the entropy of the lattice and electron systems. The heat required to remove quanta of h / 2π from the saturated condition was slightly larger than the magnetic work gβH as expected for a ferromagnetic system. No evidence of hysteresis was observed at temperatures above 0.5°K. Temperature-field measurements on 31 isentropes, which connected the isoerstedic heat capacity series, evaluated the entropy over the experimental range. The total electronic entropy was found to be 1.379 gibbs/mole compared to the expected R ln2 = 1.3775 gibbs/mole. Smoothed values of the heat capacity, entropy, magnetic moment, enthalpy, internal energy, differential isothermal magnetic susceptibility, differential isoerstedic temperature co-efficient of magnetic moment, and the isothermal work of magnetization are tabulated.
Radiative and Radiationless Transitions from F45/2 State of the Nd3+ Ion
Authors: Pollack S. A.
Published: February 2004

The A45/2 → 4I9/2 fluorescence group of the Nd3+ ion in the CaWO4 matrix occurring at 8200 Å was studied and analyzed. From the intensity measurements versus temperature, it was concluded that the radiative transition from the F45/2 state to the ground competes with a nonradiative relaxation to the F45/2 state. The value of the nonradiative transition probability W was determined to be ∼ 106 sec−1.
Statistics of Randomly Branched Polycondensates
Authors: Kajiwara Kanji
Published: February 2004

The combinatorial theory of so-called “trail-weighting functions,” variously averaged over all trails in distributions of linear or branched molecules which are random (or at least lack long-range correlations) has been described and exploited for calculation of physical parameters in previous papers. A trail-weighting function is some arbitrary function φ(n) of the number of distinct trails of length n in the graph of a given molecule. By extending the use of univariate to bivariate generating functions, we here derive the moments of the distribution, the Stokes radii, and second virial coefficients for osmotic pressure and for light scattering of random f-functional polycondensates. It emerges that the z-average radius of gyration, the z-average reciprocal Stokes radius, and the second virial coefficient of osmotic pressure are related to the weight-average degree of polymerization, and the weight-average radius of gyration and the weight-average reciprocal Stokes radius to the number-average degree of polymerization.
High-Resolution Study of NMR Spin Echoes: “J Spectra”
Authors: Freeman Ray , Hill H. D. W.
Published: February 2004

The spin–spin relaxation of individual lines in a high-resolution NMR spectrum has been studied by a technique which extracts an essentially “monochromatic” component from the Carr–Purcell spin-echo response by means of a narrow-band filter. The resulting selectivity significantly reduces the complexity of the modulation of the spin-echo amplitude due to homonuclear spin–spin coupling, and further simplification may be achieved by double irradiation experiments. Echo modulation has been used as a precise measure of the 0.051-Hz long-range coupling in 3-bromothiophene-2-aldehyde, normally hidden by magnet inhomogeneity. It is proposed that modulation and spin–spin relaxation effects are best analyzed in the general case by calculating the Fourier transformation of the envelope of the spin-echo peaks. The general term suggested for this new mode of presentation is the “spin-echo spectrum.” It consists of a set of resonance responses with widths determined by the relevant spin–spin relaxation times, at freueqncies determined by the various modulation components of the spin-echo decay. The present study concentrates on operating conditions (low pulse repetition rate and “first-order” spin coupling) where the resonance frequencies correspond to one-half the sums and differences of the spin coupling constants. This special case of a spin-echo spectrum is called a “J spectrum.” When the spin-echo response appropriate to a single group of chemically shifted nuclei is observed selectively, the transformation gives a “partial J spectrum” which can be used as an aid to the assignment of the full spectrum. J spectra are illustrated for a typical first-order three-spin system—the ring protons of methyl furoate.
Hyperfine Interaction and Chemical Bonding in MgF, CaF, SrF, and BaF molecules
Authors: Knight L. B. , Easley W. C. , Weltner W. , Wilson M.
Published: February 2004

ESR spectra of MgF, CaF, SrF, and BaF molecules in their ground Σ2 states were measured while trapped in solid neon and argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with 19F, and in the case of SrF and BaF, with 87Sr and 137Ba, were determined. In all cases less than 4% of the spin density is on the F atom, supporting the evidence for their extreme ionicity. The variation in the anisotropic character of the 19F hfs probably indicates a slight increase in covalency in the lighter molecules. The hf interaction with the metal nucleus is quite anisotropic, demonstrating that the unpaired s electron on the M+ ion actually has appreciable p and d character, i.e., that the spherical s electron orbit in the free M+ ion is highly distorted by the F− ion in the molecule. This was supported by an approximate variational calculation considering the F− ion as a point charge. A negative Δg⊥ for the MgF molecule indicates that the lowest-lying Π2 state is regular, in support of Walker and Richards' reinterpretation of the λ-type doubling.
Approach of Certain Systems, Including Membranes, to Steady State
Authors: Hill Terrell L.
Published: February 2004

An investigation is made of the approach to steady state of a certain class of systems of independent subsystems. It is found that, roughly speaking, the variance, a matrix, approaches its steady-state functional dependence on the mean, a vector, at twice the rate that the mean approaches its steady-state value.
Kinetics and Mechanism of NO2 Fluorescence
Authors: Keyser L. F. , Levine S. Z. , Kaufman F.
Published: February 2004

NO2 fluorescence experiments with steady or modulated (8 and 20 kHz), monochromatic excitation at 4000–6000 Å and monochromatic observation have shown the process to be interpretable in terms of a single electronically excited state undergoing vibrational relaxation at gas-kinetic rate and electronic quenching about 100 times more slowly. An apparent radiative lifetime of about 55 μsec was found, independent of excitation frequency, but the possibility of mixing with vibrationally excited ground state makes this an upper limit to the lifetime of the hypothetical unperturbed B12 state. The average amount of vibrational energy transferred per collision was found to be 1000 · 500 cm−1 based on a simplified step-ladder model for the relaxation.
Calculation of Franck–Condon Factors for Radiationless Transitions Based on Selective Excitation of Single Vibronic Levels
Authors: Siebrand Willem
Published: February 2004

A theoretical framework is developed for a comparative study of rate constants of radiationless transitions originating from single vibronic levels in the manifold of the initial state. It is shown that in large molecules these rate constants show a characteristic relationship. Specifically, their ratios can be interpreted in terms of effective vibrational quantum numbers for the contribution of the oscillators excited in the initial state to the over-all Franck–Condon factor of the radiationless transition. The analysis is applied to recent data on singlet–triplet intersystem crossing in benzene and the contributions of two normal modes are calculated.
Simple Rules to Predict the Structure of Adsorbed Gases on Crystal Surfaces
Authors: Somorjai G. A. , Szalkowski F. J.
Published: February 2004

The surface structures of adsorbed gases on crystal surfaces which were detected by low-energy electron diffraction have been reviewed. From the analysis of the available structural data three rules of ordering have been proposed. The close-packing rule indicates that adsorbate–adsorbate interaction plays an important role in ordering. The rules of rotational symmetry and similar unit cell vectors are the consequence of the substrate–adsorbate interaction. Judicious application of these rules should allow one to predict the surface structures of adsorbed gases and condensable vapors which would form on crystal surfaces. It appears that both the heat of adsorption and the activation energy for surface diffusion of the adsorbed molecules influence ordering on surfaces.
Nuclear Magnetic Relaxation of 11B and F in BF3 Gas
Authors: Hinshaw Waldo S. , Hubbard Paul S.
Published: February 2004

The longitudinal nuclear magnetic relaxations of the 11B and F nuclei in BF3 gas have been measured as a function of pressure at temperatures of 270, 300, and 350°K, and the relaxation times T1 have been determined as a function of density. The purpose of the investigation was to determine whether or not there is a steplike dependence of T1 or T1 / ρ on density ρ for nuclei relaxed by quadrupole interactions in gas molecules. The T1 of 11B was found to increase linearly with density at low densities, and less rapidly than linearly at high densities, but no evidence of a steplike dependence on density was found.
Vapor Nucleation at a Liquid–Liquid Interface
Authors: Apfel Robert E.
Published: February 2004

The theory describing the conditions for the onset of homogeneous nucleation of the vapor phase in a liquid has been modified to include the possibility of nucleation at the interface between two pure liquids. In order to test these predictions, some experiments, which involve the measurement of the limit of superheat of a liquid, have been performed. In these experiments a droplet of one liquid is heated in an immiscible “host” liquid until the droplet explodes into its vapor. The results for the liquids tested (water droplets in silicone fluid and ether droplets in glycerine) are consistent with the theoretical predictions.
35Cl and 19F NMR Spin–Lattice Relaxation Time Measurements and Rotational Diffusion in Liquid ClO3F
Authors: Maryott A. A. , Farrar T. C. , Malmberg M. S.
Published: February 2004

The NMR spin–lattice relaxation times of 35Cl and been 19F have measured by pulse techniques over the entire liquid range of ClO3F (130–368°K). The chlorine relaxation which is due solely to the nuclear quadrupole interaction can be used together with the known quadrupole coupling constant to determine the correlation time for molecular orientation, τθ,2. The fluorine relaxation is dominated by the spin–rotation interaction with only a small intermolecular dipole contribution at the lowest temperatures. In order to obtain the angular momentum correlation time, τJ, an independent estimate of the spin–rotation tensor was made by combining gas-phase measurements of T1(19F) with previous data on the chemical shift and gas-phase dielectric relaxation. The results for this quasispherical molecule are in accord with rotational diffusion theory and Hubbard's relation, τθ,2τJ = I / 6kT, at the lowest temperatures and agree over the entire range with the extended treatment of McClung.
Ionic Interactions in Volatile Lanthanide Chelates
Authors: Boeyens J. C. A.
Published: February 2004

In order to allow estimation of the electrostatic and dipolar contributions to the cohesive forces in volatile lanthanide β-diketonates, these compounds are considered to be purely ionic. The relevant lattice sums can then be computed directly and underestimation of the ionic contributions is avoided. Even without considering the effect of shielding by bulky substituents, the calculations, based on crystallographic results, show that the electrostatic contributions to lattice forces are negligible and do not influence the volatility. The electrostatic stabilization of the dimers, known to occur in the case of some chelates of 2,2,6,6-tetramethyl-3,5-heptanedione, is, however, sufficient to account for the observed trends in heats of vaporization, heats of sublimation, and gas chromatographic retention times.
Molecular Beam Measurement of the Magnetic Susceptibility Anisotropies and Molecular Quadrupole Moment in H2CO
Authors: Kukolich Stephen G.
Published: February 2004

The molecular Zeeman effect in formaldehyde was studied using a molecular beam maser spectrometer in fields to 17 kG. The molecular resonance linewidth was 5 kHz. ΔM = 0 and ΔM = ± 1 transitions were observed for the 110 → 111 rotational transition. The measured susceptibility anisotropies (in units of 10−6 erg/G2·mole) are 2χaa − χbb − χcc = 25.4 ± 0.2 and 2χbb − χaa − χcc = − 4.1 ± 0.15. The molecular quadrupole moment obtained from this data (in units of 10−26 esu·cm2) are Qaa = − 0.06 ± 0.16, Qbb = 0.33 ± 0.12, and Qcc = − 0.27 ± 0.20. The Stark effect produced by the motion of the molecules in the magnetic field (ῡ × B̄) was clearly observed.
Defect Phosphorescence of Pyrazine Crystal. II. The Nature of the Defect
Authors: Azumi Tohru
Published: February 2004

The phosphorescence of pyrazine crystal is due to the emissions from various crystalline defects. In this paper the nature of the crystalline defects which causes the emission and also quench the emission is investigated. Both the emissive defects and quenching defects are classified into impurity-induced resonance defects and structural defects. The concentration of the impurity-induced resonance defects may effectively be decreased by zone melting. The structural defects, on the other hand, are removed by annealing. The emissive impurity-induced resonance defects seem to be responsible for many sharp bands around the onset of the spectrum. The emissive structural defects are responsible for the broad bands often observed at somewhat longer wavelength region of the sharp bands. The analyses of the temperature dependence of the phosphorescence intensity yield the rate of triplet exciton migration to be larger than 5 × 1013 sec−1. Finally, suggestions are given as to in what ways one has to endevor to obtain crystals which exhibit genuine exciton phosphorescence.
Nuclear Magnetic Resonance of the Aquated Proton: Hydronium Perchlorate
Authors: O'Reilly D. E. , Peterson E. M. , Williams Jack M.
Published: February 2004

The deuteron and proton nuclear magnetic resonance of polycrystalline hydronium perchlorate has been examined by continuous wave and pulse techniques from 100 to 300°K particularly in the vicinity of the phase transition at 243°K. Above 243°K the deuteron resonance is a single sharp line for which relaxation times have been determined. Below 243°K the deuteron resonance is broadened by the quadrupolar interaction with a quadrupolar coupling constant (QCC) of 72 · 2 kHz. At 131°K the rigid-lattice QCC is 212 · 5 kHz. Proton spin–lattice relaxation times (T1) demonstrate that below 243°K and H3O+ ion is reorientating about the threefold axis and above 243°K is undergoing essentially isotropic reorientation. In agreement with the results of the Hennel and Pollack-Stachura the proton second moment is constant below 243° K down to 160°K and is equal to 10 · 2 G2 and below 130°K is equal to 31 · 2 G2. The hydronium ion exists as a shallow pyramid with the DOD angle equal to 118.5 · 0.7° and the OH distance 1.01 · 0.02 Å. Thermal hysteresis was encountered in the proton and dueteron resonance on traversing the phase transition at 243°K (Tc). Chlorine-35 nuclear magnetic resonance was observed above Tc as a single sharp line which disappeared below Tc. This is consistent with a large distortion of the ClO4− tetrahedron below Tc.
Vibrations of Glasslike Disordered Systems. I. Diatomic Chains in Two Dimensions
Authors: Bermudez Victor M.
Published: February 2004

A computer program has been written to generate disordered, two-dimensional chains of randomly oriented B–A–B V-shaped units with a Gaussian distribution of bond angles between successive units. The radial distribution function of the system shows it to be essentially vitreous in that it exhibits only short-range order. The equations of motion are derived using a simplified valence force potential function, and the distribution of squared normal mode frequencies is obtained using the negative eigenvalue theorem. The frequency spectra are discussed in terms of the ordered chain in two dimensions and the glasslike disordered chain in one dimension. The existence of a band gap is confirmed, but the size and position are complicated by the disorder of the system, as is the over-all shape of the spectrum. A feature in the spectra, near the LO zone-edge frequency of the ordered chain, is found to be the result of wavelength-dependent coupling between “transverse” and “longitudinal” vibrations. The more general results of the present calculations appear applicable to three-dimensional models.
Identification of the Lower Transitions in the Spectra of Uranyl Complexes
Authors: Görller-Walrand C. , Vanquickenborne L. G.
Published: February 2004

The typical low-energy spectra of the uranyl complexes—both in solution and in the solid state—are interpreted by using group theory and qualitative molecular orbital theory. A comparative study of the effects of ligation on the spectrum shows that the observed facts can be rationalized by means of only one possible identification scheme. The band system situated at 20 000–22 000 cm−1 is due to a Σg+1 → Φg1 transition, while the band system at 22 500–27 000 cm−1 is due to a Σg+1 → Δg1 transition.
Self-Consistent Molecular Orbital Methods. XI. Molecular Orbital Theory of NMR Chemical Shifts
Authors: Ditchfield R. , Miller D. P. , Pople J. A.
Published: February 2004

Ab initio molecular orbital calculations of first row atom (C, N, O and F) NMR chemical shifts are presented for a variety of polyatomic molecules. Both minimal and extended basis sets are used and it is shown that at the minimal level, basis sets at the Hartree–Fock atomic level give a better description of magnetic shielding than do Slater-type (exponential) orbitals. The extended basis set also gives a good description of magnetic shielding, features associated with anisotropic molecular environment being some-what more adequately treated at this level. Calculated chemical shifts of nuclei which have similar positions relative to the origin of the vector potential describing the magnetic field are in good agreement with experiment. Agreement for the chemical shifts of nuclei which have markedly different positions relative to this origin is not as good.
Fluorine-19 Nuclear Magnetic Resonance of the Liquid and Solid Phases of Fluorine
Authors: O'Reilly D. E. , Peterson E. M. , Hogenboom D. L. , Scheie C. E.
Published: February 2004

Fluorine-19 NMR has been studied from 105 to 4.2°K in elemental fluorine. In the liquid phase the spin–rotational interaction determines the spin–lattice relaxation time (T1) except within about 17°K of the melting point, where the effect of a small amount of dissolved molecular oxygen becomes evident. Self-diffusion coefficients have been measured in the liquid from 105°K to the melting point (53.5°K) and are well represented by the expression (6.6 ± 0.3) × 10−4exp[− (510 ± 30) / RT] cm2sec−1. Spin–rotational (τ1) correlation times have been calculated from the experimental relaxation times. Nuclear dipolar (τ2) correlation times have been estimated from the quasilattice-random flight model. The product τ1τ2 is a factor of 20 longer than predicted by the continuum theory of rotational diffusion. A root mean square angular jump of 2.6 rad is estimated from comparison of the experimental data with the large angular jump model of molecular rotation. T1, rotating frame (T1ρ), and spin–spin relaxation times were measured in the β phase from 53.5 to 45.5°K. The β phase is a plastic crystal with relatively rapid translational diffusion and very rapid, but anisotropic, rotational diffusion. T1 is essentially unchanged from the liquid to the β phase. The self-diffusion coefficients are accounted for entirely by an increase in the work required to create a vacancy in going from the liquid to the β phase. In the α phase, below 45.5°K, a small amplitude mode of molecular motion persists. A 15° “tilt” motion of the molecules is assigned to the minimum observed in T1ρ in the α phase. A shallow minimum in T1 is assigned to spin diffusion to molecular oxygen impurities and occurs due to the proximity of the oxygen electronic spin–lattice relaxation rate to the fluorine larmor frequency.
New High-Density Equation of State for Gases
Authors: Babb Stanley E.
Published: February 2004

A new equation of state is proposed for the high-density region of gases. This equation is applied to the recent measurements of a number of gases and fits well within experimental error. The equation is characterized by five constants: three which are substance and temperature dependent, and two which are both substance and temperature independent. Values of all constants are given for the gases considered. Two liquid isotherms are also examined and also are fit by the equation, as are the calculated isotherms for soft spheres and Lennard-Jones spheres.
Time-of-Flight Spectroscopy of CO2 Photodissociation in the Vacuum Ultraviolet. Electron Emission from Cesium Surface by Metastable Singlet Oxygen Atoms
Authors: Welge K. H. , Gilpin R.
Published: February 2004

Time-of-flight spectroscopy has been employed in conjunction with metastable photofragment detection by electron emission from metal surfaces to study the photodissociation of CO2 in the vacuum ultraviolet at wavelengths longer than 1050 Å. Irradiation was performed by unfiltered light. However, some wave-length selection was provided by the CO2 absorption itself and by choice of window material, LiF and CaF2. The metastable detector was coated with cesium. The photodissociation, CO2 + hυ→CO(X 1Σ)+O*, has been observed where O* can be O(1S) and/or O(1D) only. The result implies that the deactivation of metastable singlet oxygen atoms at a cesium surface produces electron emission. The analysis of the flight time distribution of O* shows that in the wavelength range from about 1160–1050 Å more than 50% of the dissociation leads to internally excited CO(X 1Σ) with considerable amounts of vibration-rotation energy.
Normal Mode Calculation of Grüneisen Thermal Expansion in n-Alkanes
Authors: Broadhurst M. G. , Mopsik F. I.
Published: February 2004

The normal mode problem is solved for a semirigid chain of beads in a quasiharmonic potential in order to separate the inter- and intrachain parts of the specific heat. The effects of lattice vibrations are included in an approximate way. The usual Grüneisen relation, αBT = γCυ / V, valid only for acoustical modes, is generalized for optical modes to give αBT = Σj(γj / V) (∂Sj / ∂lnωjmax), where Sj and ωjmax are the entropy and frequency cutoff of mode j. The predicted thermodynamic properties of the system are unusually sensitive to chain length because of interchain thermal energy effects. The parameters are given values from independent solid n-alkane data, and the calculated results are shown to predict quite well experimental Cp and V–T behavior of the n-alkanes.
Effects of the Langer Transformation on the Calculation of Internuclear Potential Curves
Authors: Howard Russell A.
Published: February 2004

The Langer transformation is applied to the radial equation for internuclear motion. The quantization integral is obtained and applied to the calculation of the effective potential curve by the Rydberg–Klein–Rees method. First- and second-order RKR expressions for the turning points are derived. It is shown that the Langer transformation affects the RKR method in all orders.
Superhyperfine Interactions in CdF2:Yb
Authors: Chang Te-Tse , Cohen M. I. , Hosler W. R.
Published: February 2004

The superhyperfine structure of Yb3+ in CdF2 has been observed. Fitting of the structure was done according to the model of Ranon and Hyde. The principal values of the interaction tensor T were approximated to be − 16.7 MHz for T⊥ and 37.8 MHz for T‖.
Time Lag in Nucleation
Authors: Frisch H. L. , Carlier C. C.
Published: February 2004

We obtain exact expressions for the (Daynes) time lags L for the Becker–Döring and the Zeldovich modified Becker–Döring theory of nucleation. Our exact mathematical expressions for L are obtained without solving for the transient concentration of embryos of the new phase. L depends on the initial distribution of embryos. We find from numerical evaluation of L for two reasonable initial distributions, for at least vapor–liquid transitions, that these initial distributions did not produce the previously found effect on the magnitude of L.
NMR Study of Na3UF8 Structure and Hyperfine Effects
Authors: Fukushima Eiichi , Hecht Harry G.
Published: February 2004

Nuclear magnetic resonance spectra of polycrystalline Na3UF8 were studied experimentally. The magnetic field dependence of the 19F second moment allowed a separation of its field-dependent and field-independent parts. The temperature dependence of the field-independent part exhibits no discontinuities attributable to phase transitions and only a slow transition at about 250°K attributed to hindered molecular rotation of the isolated UF8 units. The temperature dependence of the field-dependent part also exhibits no discontinuities. It does reflect the paramagnetic susceptibility which obeys, to within the accuracy of the experiment, the Curie law. The isotropic chemical shift is small, i.e., − 0.07% ± 0.01% with respect to F2 at 292°K and − 0.11% ± 0.01% at 175°K. The even smaller chemical-shift anisotropy is approximately 25% of the isotropic shift. These shift data are consistent with a system containing one 5f electron as the unpaired spin. The 19F spectra and the temperature dependence of the field-dependent second moment require the existence of inequivalent 19F nuclei. This is not consistent with the published crystal structure of Na3UF8 characterized as I4 / mmm.
Nonequilibrium Contributions to the Rate of Reactions. II. Isolated Multicomponent Systems
Authors: Shizgal B. , Karplus M.
Published: February 2004

The nonequilibrium rates of reaction in multicomponent reactive systems are obtained by solving the Champman–Enskog equation. A Sonine polynomial expansion is used for the solution and its convergence is demonstrated for a wide range of system variables. It is found that the perturbation of the velocity distribution function for each reactive component depends on the deviation of the reactive collision frequency R(0)(cγ) from a special form R̄(0)(cγ). A model reactive system was examined with line-of-centers reactive cross sections and hard-sphere elastic cross sections chosen to fit the available data for the reaction H2+Cl=HCl+H. The deviation of the ratio of the forward and reverse rate coefficients (kf / kr) from the equilibrium value (kf(0) / kr(0)) was shown to be much smaller than the experimental deviation; this suggests that translational nonequilibrium is not significant, but does not exclude vibrational effects which could be more important.
Nonequilibrium Contribution to the Rate of Reaction. III. Isothermal Multicomponent Systems
Authors: Shizgal B. , Karplus M.
Published: February 2004

The nonequilibrium contribution to the reaction rate of an isothermal multicomponent system is obtained by solution of the appropriate Chapman–Enskog equation; the system is composed of reactive species in contact with a heat bath of inert atoms M. It is found that the perturbation of the velocity distribution functions is determined by the extent of the departure of the reactive collision frequency R(0)(cγ) for each reactive component γ from R̄(0)(cggr), the collision frequency that leaves the distribution function unaltered by reaction; the function R̄(0)(cγ) obtained for an isothermal systems is different from that introduced previously for an isolated system. An illustrative application is made to a model system corresponding to the H2+Cl⇆HCl+H reaction without internal degrees of freedom; the deviation of the rate coefficient ratio (kf / kr from the equilibrium value (kf(0) / kr(0)) is a few percent.
Third-Order Constitutive Equations for a Monatomic Gas
Authors: Cha C. Y. , McCoy B. J.
Published: February 2004

Third-order transport relations are developed by applying the Chapman–Enskog method to the Krook equation. A simple correction factor is introduced which gives results for rigid sphere molecules. The pressure tensor and the heat flux vector are presented in an irreducible form in terms of gradients of density, velocity, and temperature.