bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal Energy of Reaction Products by Velocity Analysis. I. Scattered KBr* from the Crossed Molecular Beam Reaction K+HBr
Authors: Grosser Arthur E. , Blythe Anthony R. , Bernstein Richard B.
Published: January 2005

The velocity distribution of excited KBr* formed in reactive collision between crossed beams of velocity-selected K and thermal HBr has been measured as a function of laboratory scattering angle for two different initial relative kinetic energies, E. The most probable value of the recoil velocity of the KBr* yields the final relative kinetic energy E′ and thus the value of the most probable ``collision-exothermicity'' Q ≡ E′ − E = ΔD0° − ΔEint, where ΔEint is the most probable value of the internal energy change. Results of a series of experiments at E = 1.9 kcal/mole gave Q = 0.5±0.5 kcal/mole (out of an a priori range from − 1.9 to +5.1 kcal/mole) and thus the most probable internal (excitation) energy for the KBr: E*KBr = 4.6±0.7 kcal/mole. The observed angular and velocity distributions of KBr imply that the reactive scattering in the center-of-mass (c.m.) system is predominantly confined to low angles (i.e., ``forward hemisphere,'' with the KBr* product preferring the direction of the incident K in the c.m.). Less extensive experiments at E = 3.4 kcal/mole served to confirm these conclusions.
Dielectric Behavior and Intermolecular Forces in Some Liquid Aromatic Methyl Ethers
Authors: Vaughan Worth E.
Published: January 2005

Measurements of the static dielectric constant and the density of o-methylanisole, m-methylanisole, p-methylanisole, 2,6-dimethylanisole, and 3,5-dimethylanisole from 20° to 60°C, are reported. These data are combined with estimates of the limiting dielectric constant at high frequency in order to obtain information about the interaction of a dipolar molecule with its neighbors. The dielectric constant and loss at 2-mm wavelength are also reported. These data are used to provide a partial characterization of the dielectric relaxation. The dielectric constants permit more accurate estimates of the high-frequency dielectric constants than possible previously.
Continuous Representations in the Statistical Theory of Electronic Energies. The Self-Consistent Field
Authors: Handler George S. , Golden Sidney
Published: January 2005

A self-consistent-field approximation has been applied to the continuous-representation version of statistical theory. Calculations have been carried out for He(3S and 1S), Be2+(1S), Be(1S), and Ne(1S). Binding energies are about 6% greater than experimental values. No shell structure in electron density was obtained, however, which reflects an inadequacy of the theory in approximating such properties. Nevertheless, the densities obtained gave relatively good estimates of the mean values of rn, −2≤n≤+2.
Gaussian-Type Functions for Polyatomic Systems. I
Authors: Huzinaga Sigeru
Published: January 2005

In view of rapid progress of computer capability, it is very desirable to have a reliable assessment of the usefulness of Gaussian-type orbitals as basis functions for large-scale molecular calculations. In the present paper several attempts are made to answer this question mainly at the level of atomic Hartree—Fock calculations. The necessary number of terms of Gaussian-type basis functions in the analytical Hartree—Fock expansion calculation is apparently more than twice as much as the number of terms needed in the expansion with Slater-type basis functions. However, this fact does not necessarily suggest a definite choice of Slater-type orbitals. Discussions pertinent to this point are presented in the latter part of the present paper.
Flash Evaporation
Authors: Saltsburg Howard
Published: January 2005

A study has been made of the behavior of thin metallic films when subjected to rapid heat pulses. Cadmium metal films, vapor deposited upon a tungsten ribbon, have been caused to evaporate in the form of a vapor pulse by rapidly heating the ribbon to temperatures in excess of the conventional boiling point of cadmium. The velocity of the emitted vapor pulse has been measured, in vacuum, using a time-of-flight technique involving the sequential scattering of two fixed electron beams. The dependence of the velocity has been measured as a function of a calculated tungsten-ribbon temperature. A detailed study of the shape of the observed scattering signal due to the vapor pulse suggests that the condensed phase of cadmium is superheated to the ribbon temperature. Further, the pulse so formed has a temporal distribution in density, at some distance from the ribbon, which is equivalent to a molecular velocity distribution of a modified Maxwell—Boltzmann type, characteristic of an equilibrium molecular beam of cadmium at the tungsten-ribbon temperature.
Tetrahedral and Cubic Three-Dimensional Free-Electron Networks
Authors: Rahilly W. Patrick , Duffey George H. , Schmidt John A.
Published: January 2005

In the boron cage of B4Cl4 and in the carbon cage of C8H8, valence orbitals hybridize to form an easy path along the edges of a symmetric polyhedron. On each structure, free-electron waves were constructed corresponding to the conventional delocalized molecular orbitals. Four different kinds of branching were observed. Energy levels were calculated without and with a delta-function singularity on each cage nucleus.
Nuclear Spin Coupling Between Geminal Hydrogen Atoms
Authors: Pople J. A. , Bothner-By A. A.
Published: January 2005

A molecular orbital theory of nuclear spin coupling between geminal hydrogen atoms is developed and found to give a satisfactory interpretation of substituent effects evident in experimental data. The theory suggests that the value of geminal coupling constants provides a means of distinguishing between inductive and hyperconjugative electron transfer. A number of geometrical rules are also proposed which should make these constants valuable in studies of molecular conformation.
Electron Spin Resonance of Semiquinones: Spin-Density Distribution and Carbonyl Sigma—Pi Parameters
Authors: Das M. R. , Fraenkel George K.
Published: January 2005

The spin-density distributions in the 1,4-benzosemiquinone and 2,5-dioxy-1,4-benzosemiquinone ions have been estimated by measuring the proton and 13C splittings and using reasonable choices for the values of the sigma—pi parameters which relate the splittings to the spin densities for C–C and C–H bonds. The determination of the signs as well as the magnitudes of the 13C splittings was required to obtain the spin densities. With QCHH=−27.0 G in the relation aiH=QCHHρi π between proton splitting aiH and carbon-atom—pi-electron spin density ρiπ, the sigma—pi parameters for the 13C splitting at a carbonyl position were found to be QCOC=17.7 G and QOCC=−27.1 G. The values of QCOC and QOCC depend on the value assumed for QCHH. Contrary to earlier predictions made on the basis of molecular orbital calculations, the sign of the 13C splitting from the 2 position of the p-benzosemiquinone ion was found to be negative. This discrepancy results because the MO calculations were performed so as to reproduce proton splittings rather than the entire spin-density distribution, a procedure that is insensitive to the spin densities on the carbonyl carbon and oxygen atoms. New MO calculations were performed to fit the spin densities at all the positions in the radical. The results show that calculations fitted to proton splittings alone are inadequate for predicting spin densities at ``blind'' positions such as those at the carbon and oxygen atoms of a carbonyl group, or the nitrogen and oxygen atoms of a nitro group. Carbon-13 splittings were also observed in the anthrasemiquinone ion in both ethanol and 1,2-dimethoxyethane (DME) solutions. The sign of the 9-position 13C splitting changes from +0.70 G in ethanol to −0.47 G in DME solution. By using the sigma—pi parameters for the carbonyl group carbon atom, the spin densities were determined for this radical and MO calculations performed to reproduce the spin-density distributions. The variation of the splittings in the p-benzosemiquinone ion with solvent composition could be accounted for quantitatively by using the newly determined sigma—pi parameters.
Isotopic Mixing in CO Chemisorbed on Tungsten. A Kinetic Study
Authors: Madey T. E. , Yates J. T. , Stern R. C.
Published: January 2005

When 12C18O and 13C16O were adsorbed together on tungsten, rapid isotopic mixing to form 12C16O and 13C18O occurred at temperatures above 850°K. These temperatures correspond to the desorption temperatures of the more strongly held adsorbed CO species (β states). No evidence was found for dissociation of CO into mobile adsorbed C and O atoms. A four-center bimolecular exchange intermediate on the surface is postulated. This is consistent with a model for molecular CO chemisorption on tungsten, which involves surface bonding through both the carbon and oxygen.

The rate constant for the bimolecular surface-exchange reaction is 1.9×10−10 exp(−30 000/RT) cm2/molecule·sec.
Uv Absorption Spectrum of Trapped S2
Authors: Brewer L. , Brabson G. D. , Meyer B.
Published: January 2005

The uv absorption spectrum of trapped S2 has been studied in N2, Ar, Kr, and Xe matrices at 4° and 20°K. Up to 26 vibrational bands of the v″=0 progression of the 3Σu—←3Σg— system were observed. In each of the matrices, the origin of the transition was shifted by an amount characteristic of the particular matrix; red shifts were observed for Xe, Kr, and Ar, while N2 yielded a blue shift. The vibrational spacing indicated distortion of the potential-energy curve under the influence of the matrix field. The absorption bands were slightly shaded towards the blue and had a half-width of about 150 cm−1. At low v′, doublet structure was observed. The ir absorption spectrum of the forbidden S2 vibration was also investigated.
X-Ray Investigation of a High-Pressure Phase of NH4F and ND4F
Authors: Morosin B. , Schirber J. E.
Published: January 2005

X-ray powder diffraction patterns were obtained for high-pressure modifications of NH4F and ND4F under purely hydrostatic conditions. The structure of both salts could be indexed in a tetragonal unit cell, a0=10.2 Å, c0=3.37 Å. The transition was observed at 3.64±0.02 kbar for both ND4F and NH4F. The zero-pressure lattice parameters were determined to be a0=4.4389±0.0004 Å, c0=7.1635±0.0004 Å, and a0=4.4378±0.0004 Å, for NH4F and ND4F, respectively.
Vibrational Analysis and Isotope Effects in Hydrogen Selenide
Authors: Hill R. A. , Edwards T. H.
Published: January 2005

Values of the band origins for the near-infrared rotation—vibration bands v1+v2, v2+v3, 2v1+v3, v1+2v3, 3v1, and 3v1+v3 of H280Se were determined directly from their respective PPJ (J) and RRJ (J) lines. A vibrational analysis of the band origins of these six bands, of four previously analyzed combination bands, and of the three fundamentals led to values for the zero-order frequencies, anharmonic constants, and the interaction matrix element for a second-order resonance between levels of the type (v1, v2, v3) and (v1−2, v2, v3+2). Values for the isotopic band center separations Δv0≡v0 (H280Se) —v0 (H2iSe) and for ΔC0≡80C0−iC 0, where i=82, 78, 77, and 76, were obtained from the observed isotopic separations of the PPJ (J) and RRJ (J) lines for several bands. These empirical values of Δv0 are compared with a set of theoretical values calculated using Krimm's approximate isotopic frequency rule and the vibrational constants for H280Se. Values of iA0, iB0, and iC0 were calculated by combining our values of 80A0, 80B0, and 80C0 with our empirical values of ΔC0 and with values of Δ(A0−C0) and Δ(A0−B0) obtained from Oka and Morino's analysis of the microwave data of Jache, Moser, and Gordy. An equilibrium H–Se–H bond angle of 90° 34′ and an H–Se bond length of 1.460 Å were calculated using a set of α's which were obtained from the rotational constants of 2v1, v1+v3, v1+v2+v3, and the ground state constants.
Microwave Absorption and Molecular Structure in Liquids. LXIII. Dielectric Behavior of Rigid Polar Molecules at 2.2-mm Wavelength and Atomic Polarization
Authors: Garg S. K. , Smyth C. P.
Published: January 2005

Dielectric constants and losses of fluorobenzene, chlorobenzene, bromobenzene, α-chloro- and α-bromonaphthalene, thiphene, tetrahydrofuran, and chloroform have been measured at 2.2-mm wavelength at various temperatures between 20° and 55°C. The results have been used together with the existing lower-frequency data to construct Cole—Cole arc plots, from which relaxation times, distribution parameters and optical dielectric constants are obtained. In all cases studied the optical dielectric constant ε∞ has a value close to the square of the refractive index nD2, and there seems to be no evidence of the additional ultrahigh-frequency dispersion region suggested by the results of previous workers. The values of ε∞ obtained have been used to calculate atomic polarizations which generally agree well with the values determined for the molecules in the gaseous state.
New Cloud-Chamber Method for the Determination of Homogeneous Nucleation Rates
Authors: Allard Edward F. , Kassner James L.
Published: January 2005

A new technique has been developed for making precise measurements of homogeneous nucleation rates. Corrections may be made for the effect of vapor depletion by the growing droplets which do not require a knowledge of the droplet-growth law. This data also offers valuable information about the droplet-growth mechanism and affords a reasonably accurate determination of the nucleation-rate-versus-supersaturation curve which is provided by theory. A meager amount of data of a preliminary character is presented.
Diffusion in Organic Crystals. I. Self-Diffusion in Anthracene
Authors: Lee C. H. , Kevorkian H. K. , Reucroft P. J. , Labes M. M.
Published: January 2005

Self-diffusion in high-purity anthracene single crystals has been measured by means of a microtome sectioning technique with anthracene-9-14C as a tracer, in the temperature range from 140° to 196°. For diffusion perpendicular to the ab and ac planes, the data were respectively fitted as D(⊥ab)=3 exp (−22 kcal/RT)and D(⊥ac)=16 exp (−24 kcal/RT).The possible mechanism, the anisotropic nature of the diffusion process, and the results as compared with a previous investigation are discussed in detail.
Absorption Spectrum of Europium Iron Garnet between 1900 and 5400 cm−1
Authors: Koningstein J. A.
Published: January 2005

This article deals with an experimental and theoretical study on the split 7F manifolds of EuIG. Similarities have been established between the position of some of the energy levels of EuIG, Eu3+:YAlG, and Eu3+:YGaG. These similarities enable one (a) to assign bands in the absorption spectrum of EuIG in the infrared, which are due to the exchange field, and (b) to evaluate approximate crystal-field parameters. The best estimate of these parameters yields: A20 = +105 cm−1, A22 = ±95 cm−1, A40 = −140 cm−1, A44 = −700 cm−1, A60 = 30 cm−1, and A64 = +630 cm−1.
Some Excited States of He2++: Mixed Basis-Set Calculations
Authors: Browne J. C.
Published: January 2005

Quantum-mechanical calculations have been made which yield approximate potential curves for the lowest 1Σu+, 3Σu+, and 3Σg+ states and the first excited 1Σg+ state of He2++. The 3Σg+ and 3Σu+ states exhibit no minima in their computed potential curves, but the 1Σu+ and (1Σg+)* states are bound. Rigorous lower bounds of 0.29 and 0.24 eV are found for De of 1Σu+ and (1Σg+)*, respectively. The probable errors in these De are less than 0.1 eV.
Infrared-Emission Spectrum of HBr Excited in an Electric Discharge. Determination of Molecular Constants
Authors: James Thomas C. , Thibault Robert J.
Published: January 2005

The infrared-emission spectra of H79Br and H81Br have been observed by exciting HBr in an electric discharge. Lines in the 1–0, 2–1, and 3–2 bands have been measured to an accuracy of the order of 0.01 cm−1. Pure rotational transitions of H79Br and H81Br which were not resolved have also been observed and measured with an accuracy of the order of 0.2 cm−1. Values are reported for ωe, ωexe, ωeye (only limits for this constant), Be, De, αe, βe, γe, δe, and approximate values of H0 and H1 are also obtained. The results are found to be in agreement with Dunham's theory. Values of the potential constants a1, a2, and a3 are calculated. The Be values for H79Br and H81Br agree with calculations based on microwave measurements of D79Br and D81Br.
Paramagnetic Absorption of Single Crystals of Succinic Acid Irradiated at Low Temperature
Authors: Box Harold C. , Freund Harold G. , Lilga Kenneth T.
Published: January 2005

Electron spin resonance absorption was observed in single crystals of (–CH2–COOH)2, (–CH2–;COOD)2, and (–CH2–13COOH)2 irradiated at 77°K. The principal paramagnetic species observed at low temperature has an unpaired electron in a 2pπ orbital on the carbon atom of the carboxyl group. It is probably ionized succinic acid with the oxygen of the carboxyl group carrying a negative charge.
Use of Computer Programs in the Interpretation of Electron Paramagnetic Resonance Spectra of Dilute Radicals in Amorphous Solid Samples. I. High-Field Treatment. X-Band Spectra of π-Electron Unconjugated Hydrocarbon Radicals
Authors: Lefebvre Roland , Maruani Jean
Published: January 2005

The successive stages of the calculation of a high-field electron paramagnetic resonance line shape for a radical dilute in a polycrystalline or glassy sample from the parameters of its spin Hamiltonian have been fitted into a computer program. We have considered the general case where there may be a 32 tensor, anisotropic hyperfine couplings, and satellite lines arising from nuclei of any spin up to 32 and approximated the component line shape by a Gaussian function of constant width. Possible uses of such a program are: (1) determining the line shapes associated with some model radicals and establishing approximate rules to facilitate the interpretation of experimental spectra; (2) checking the validity of an assignment of tensors made on the basis of some plausible structure for a species under investigation; and (3) finding the parameters which make the best fit to an observed spectrum. Applications to some π-electron hydrocarbon radicals are presented, and the possibilities offered by such calculations are evaluated.
Use of Computer Programs in the Interpretation of Electron Paramagnetic Resonance Spectra of Dilute Radicals in Amorphous Solid Samples. II. Zero-Field Treatment for Several Nuclei of Spin 1/2
Authors: Lefebvre Roland , Maruani Jean
Published: January 2005

The successive stages of the calculation of a zero-field magnetic resonance spectrum for a radical with nuclei of spin ½ from its hyperfine coupling tensors have been fitted into a computer program. An application is made to two three-proton radicals studied by Cole, Kushida, and Heller.
Kink Poisons and the Reduction of Dissolution Rate at Crystal—Liquid Interfaces
Authors: Gallily Isaiah , Friedlander S. K.
Published: January 2005

The effect of contaminants on solubility and dissolution rate was studied in a system of a (100)-faced lithium fluoride single crystal and a very dilute solution containing ferric ions. The solubility of the crystal was determined in contaminant solutions of varying concentrations and at different temperatures. The dissolution-rate experiments were carried out in a rotating-disk apparatus. It was found that the reduction of the dissolution rate produced by ferric ions could be explained by the changed solubility of the (100)-faced crystals.
On the Difference between the Thermodynamic Behavior of Argon in D2O and H2O
Authors: Ben-Naim A.
Published: January 2005

The solubility of argon was measured in D2O (99.7%) at five temperatures: 5°, 10°, 15°, 20°, 25°C. The standard entropies, enthalpies, and free energies of solution were calculated, and compared with the corresponding values in H2O. The differences in the thermodynamic functions of solution in D2O and in H2O are interpreted in terms of the ``two-structure'' model for liquid water, and are attributed to the difference in the ``degree of crystallinity'' of the two solvents.
Search for a Charge-Transfer State in Crystalline Anthracene
Authors: Berry R. S. , Jortner Joshua , Mackie John C. , Pysh Eugene S. , Rice Stuart A.
Published: January 2005

In this paper we examine the calculation of the location of the charge-transfer state in crystalline anthracene. Also reported are the results of spectroscopic experiments designed to find the transition from the ground state to the charge-transfer state. No experimental evidence could be found for this transition, and it is thereby concluded that: (a) The CT state lies above the first exciton state in anthracene. (b) The polarization energy in the CT state is much less than that calculated on the basis of classical considerations. There is a brief discussion of the nature of the polarization in aromatic crystals, especially with respect to Conclusion (b).
Threshold Shapes and Resonances in the Photodetachment Cross Sections of Chloride, Bromide, and Iodide
Authors: Berry R. Stephen , David Carl W. , Mackie John C.
Published: January 2005

The photodetachment curves of Cl—, Br—, and I— have been examined in their threshold regions by absorption spectroscopy of shock-heated alkali halide vapors. The chloride curve appears smooth and normal in terms of threshold laws, but the bromide and iodide curves show maxima about 500 cm−1 above the thresholds, with widths of about 200 cm−1 at half-height. The threshold positions are not affected by changes in conditions. The anomalously large absorption or resonances seem to be due to the halide ions, but to be influenced to some degree by the alkali atoms or ions. Three explanations, none entirely satisfactory, are put forth for the maxima; these are (1) near-resonant transfer of energy from X+e— to M, giving X—+M*; (2) metastable autodetaching states of the halides; and (3) mixing of vacant alkali ion orbitals with continua of the halides. The third is considered most plausible.
Molecular Collision Cross Section Due to Quadrupole-Induced Dipole and Dipole-Induced Quadrupole Interactions
Authors: Krishnaji  , Srivastava Shyam Lal
Published: January 2005

A theory for molecular collision cross section due to quadrupole-induced dipole and dipole-induced quadrupole interactions has been developed following the Anderson—Tsao—Curnutte approach. The OCS–He, OCS–Ar, and HCl–Ar collisions are discussed. For HCl–Ar collisions, μ1q1α2 interactions have been found to be important, whereas in OCS–He and OCS–Ar collisions these are negligibly small.
Calculation of Zero Field Splitting in NH. I. One-Center Minimal Basis and Atomic Orbital Representations of the Ground State
Authors: Lounsbury John B.
Published: January 2005

The zero field splitting parameter D is calculated for the ground state of NH (3Σg—) using a variety of single Slater-type atomic orbitals and atomic SCF functions for nitrogen. A minimal basis (five basis functions) one-center expansion SCF calculation has been performed for 3Σg— NH. The resulting molecular orbitals produce D=1.6279 cm−1. Spin—orbit contributions to D are estimated and found to be small.
Splitting of 19F NMR Line in a Co2+-Doped NaF Crystal
Authors: Lovins Amory B.
Published: January 2005

Superimposed on the primary 19F nuclear magnetic resonance line from a room-temperature Co2+-doped NaF single crystal are 10 intense, evenly spaced, field-independent, strongly anisotropic secondary 19F lines of unknown origin. Neither these lines nor several additional anomalies of the NaF:Co2+ crystal are observable in an undoped but otherwise identical NaF crystal.
Molecular Orbital Theory of Diamagnetism. V. Anisotropies of Some Aromatic Hydrocarbon Molecules
Authors: Ferguson A. F. , Pople J. A.
Published: January 2005

Molecular orbital theory is used to calculate the diamagnetic susceptibility contributions of local intraatomic currents in a series of polycyclic aromatic hydrocarbons. It is found that a considerable part of the excess diamagnetism perpendicular to the molecular plane is due to the anisotropy of these local terms so that the contribution of interatomic ring currents is less than has been believed previously. The theory also reproduces the trend for the in-plane susceptibility to be (numerically) greatest along the long axis of the molecule.
Scattering of Slow Neutrons from Ammonia and Hydrogen Sulfide
Authors: Strong K. A. , Harker Y. D. , Brugger R. M.
Published: January 2005

Measurements of the scattering of slow neutrons from samples of gaseous ammonia and hydrogen sulfide have been made using the MTR phased-chopper velocity selector. The energies of incident neutrons were 0.025, 0.07, and 0.1 eV and the scattered neutrons were detected in counter banks in an angular range of 16° to 145°. The data obtained have been converted to reduced partial differential cross sections and have been compared with theoretical calculations based on scattering from a symmetric top molecule, from a spherical-top molecule and from a Krieger—Nelkin gas. The symmetric top gives the best fit to the data for both samples. This theory fits the ammonia data better than the hydrogen sulfide data; the deviation is at large energy transfers and is larger for hydrogen sulfide than for ammonia. The zeroth and first moments of energy transfer have been obtained from the data for the experimental range of momentum transfer. The zeroth moments for ammonia agree with the predicted values based on classical theory, but they are about 10% high for hydrogen sulfide. The experimental first moments for both molecules suggest an effective mass roughly 20% lower than the Sachs—Teller mass.
Spin-Echo Studies of Chemical Exchange. II. Closed Formulas for Two Sites
Authors: Allerhand Adam , Gutowsky H. S.
Published: January 2005

Closed expressions are derived for the decay in amplitude of successive echoes in nuclear magnetic resonance experiments for systems with two exchanging sites having different resonance frequencies but equal transverse relaxation times ``in the absence of exchange.'' The decay for a Carr—Purcell train of echoes is found to be the sum of two exponential terms and two ``pseudoexponential'' terms; the absolute values of the latter decay exponentially but the sign alternates from one echo to the next. For the case of two equally populated sites the decay simplifies to the sum of just one exponential and one ``pseudoexponential'' term. In most cases of experimental importance, a single exponential term is much larger than the rest and adequately describes the decay in echo amplitude.

An iterative computer procedure is described which uses the expressions to extract information about the system from measurements of the apparent decay time constant (1/T2) as a function of 180° pulse separation (tcp). In favorable cases the method yields values not only of the lifetime between exchanges (1/2τ) but also of the chemical shift (δω) and the relaxation time in the absence of exchange (1/T20). Moreover, it is applicable to both slow and fast exchange, whereas use of the approximate equation derived by Luz and Meiboom leads to inaccurate values for relatively slow rates with large chemical shifts between the sites. Our experience shows that the spin-echo technique can be very useful for the study of fast exchange processes, but even when closed expressions of appropriate accuracy are used the nature of these expressions is such that a high-speed computer is required for fitting the experimental data, unless some ``outside'' information is available about δω and 1/T20.
Luminescence and Energy Transfer in Solutions of Rare-Earth Complexes. I. Enhancement of Fluorescence by Deuterium Substitution
Authors: Kropp John L. , Windsor Maurice W.
Published: January 2005

Fluorescence yields and lifetimes of solutions of europium and terbium salts in solution are greatly enhanced by using deuterated solvents. The magnitude of increase varies from an 18-fold enhancement in yield and lifetime for an aqueous solution of europium nitrate to a twofold enhancement for europium ethylenediaminetetra-acetate dissolved in methanol. The enhancement is proportional to the fraction of deuterated solvent present. Results lead to conclusions that the dominant mode of radiationless deactivation of a rare-earth ion in solution is via loss of energy to hydrogen vibrations. Further, such loss is proportional to the number of hydrogen vibrations in the local rare-earth environment. Values for the rate constant for radiationless loss of energy to hydrogen vibrations are determined for the salts studied. The influence upon radiationless processes of complexing between the rare earth and anion is discussed. Likewise the dependence of the enhancement factor upon the rare-earth ion is considered. There is no evidence that the lifetime from the 5D1 level of europium nitrate is enhanced by deuterium substitution. This lifetime is ≤5 μsec in both D2O and H2O solutions.
Spin Echoes and Chemical Exchange
Authors: Bloom M. , Reeves L. W. , Wells E. J.
Published: January 2005

The amplitude of the nuclear induction signal is calculated for pulsed nuclear magnetic resonance experiments for systems in which chemical exchange takes place between two sites of different Larmor frequency. General expressions are given, within the scope of first order rate theory for one and two pulse experiments as well as multiple pulse (Carr—Purcell) sequences. It is proven that for a Carr—Purcell sequence the decay is always expressible as a sum of two exponentials. The two time constants are derived for the general case and some special cases are discussed in detail. The theory makes possible the measurement of exchange rate constants using spin-echo techniques without the use of computers and seems relatively easy to generalize to more complicated systems.
Temperature and Pressure Coefficients of Ionic Conductance in N ,N-Dimethylformamide
Authors: Brummer S. B.
Published: January 2005

The limiting conductance of a number of salts in N ,N-dimethylformamide (DMF) was determined from measurements of the electrolytic conductance, in the range 1–100×10−4M, 25°—65°C and 1–1900 atm. The results are discussed in terms of transition-state concepts. An important parameter is the heat of activation at constant volume Ev, which is substantially smaller than the usually determined heat of activation at constant pressure Ep. Both Ev and Ep are independent of temperature. Ev, which decreases with increase in ion size, is sensitive to the density (packing) of the solvent and, in the range investigated, varies inversely with the free volume. A change in the dependences of Ev and of the pre-exponent on solvent volume is observed at a volume of about 75 ml mole−1. At densities greater than this, Ev extrapolates to infinity (i.e., the conductance process ceases) at about the normal freezing point. Below this density, Ev would become infinite at about the close-packed solvent density. In harmony with the behavior of Ev, the pre-exponent is a simple function of ion size and solvent density at densities less than 75 ml mole−1; at greater densities, its behavior is more complex. The volume of activation ΔV‡, which is between 8 and 12 ml mole−1, increases with solvent volume and ion size and decreases with increases of temperature. The value of ΔV‡ for picric acid suggests that the H+ ion is monosolvated in DMF.
Nuclear Resonance in Solid Nitrogen Trifluoride
Authors: Matzkanin G. A. , Scott T. A. , Haigh P. J.
Published: January 2005

A combined NQR and NMR study has been made of solid NF3. The quadrupole coupling constant and asymmetry parameter of 14N have been determined and the low-temperature torsional oscillation frequencies of the molecule in the solid calculated by fitting the temperature dependence of the resonance frequencies to Bayer theory. The constants obtained are: 3e2q0Q/4h = 5.3012±0.0005×106 sec−1, η0 = 0.00112±0.00002, vx = 1.505±0.005×1012 sec−1 and vy = 1.003±0.003×1012 sec−1, respectively, where the first two parameters are for the rigid lattice at 0°K. Above about 35°K, and particularly near the phase transition at 56.6°K, Bayer theory is inadequate to explain the observed temperature dependence. The linewidth of the 19F magnetic resonance undergoes a precipitous decrease above 35°K and becomes very narrow before the solid melts. A consistent interpretation of the data may be made if one assumes the onset of hindered rotation of the NF3 molecule about its triad axis below the transition temperature and the occurrence of additional large amplitude motions above the transition, but this speculation requires further proof.
Irreversible Thermodynamics of Vectorial Phenomena. I. The Second-Order Transport Equations of Thermal and Electrochemical Diffusion
Authors: Hurle D. T. J. , Mullin J. B. , Pike E. R.
Published: January 2005

A phenomenological description of transport processes in concentrated multicomponent systems driven by generalized thermodynamic driving forces of vectorial character is derived by the methods of classical irreversible thermodynamics. The approach differs from that used in previous work in two major respects, first, in an emphasis in the first-order equations on the use of experimentally measurable quantities, and, second, on mathematical consistency in the derivation of the second-order equations. This second requirement is shown to lead to the introduction of a number of new transport coefficients which are analogous to the already known Thomson coefficient. A further difference lies in the fact that electroneutrality is not assumed and Poisson's equation is incorporated.

A discussion of the nature and use of phenomenological transport coefficients is included, and an extension of the theory to large systems is made.
Energy-Band Calculations for Periodic DNA Models in the Hückel Approximation
Authors: Ladik J. , Biczó G.
Published: January 2005

The energy-band structures of different periodic models of DNA poly(A−T),  poly(G−C),  poly(A−TG−C),  poly(A−TC−G),  poly(A−TT−A),  and  poly(G−CC−G) have been calculated in the Hückel approximation. The characteristic features of the results are compared with those previously obtained for homopolynucleotides and for the most simple heteropolynucleotides.

The widths of the energy bands make possible a small conduction in DNA. For the forbidden bandwidth between the highest filled band and the lowest unfilled singlet band the value 3.46 eV has been obtained in the case of the most complicated model systems, which do not differ too much from real DNA.
Normal Coordinate Analyses of Hydrogen-Bonded Compounds. III. The Acid Maleate Ion
Authors: Nakamoto Kazuo , Sarma Y. Anantarama , Behnke George T.
Published: January 2005

The infrared spectra of the acid maleate ion and its two deutero analogs have been obtained from 4000 to 160 cm−1. In order to estimate the Urey—Bradley force constants, a normal coordinate analysis has been carried out on the C2v model of the acid maleate ion. The antisymmetric and symmetric O–H–O stretching and O–H–O bending bands have been assigned at 2008, 310, and 1700 cm−1, respectively. The O–H–O stretching and bending force constants used are 1.10 and 0.60 mdyn/Å, respectively. Calculations of potential-energy distribution reveal that strong vibrational coupling makes it virtually impossible to assign group frequencies in the low-frequency region.
Production of Free Radicals in Organic Solids by Hydrogen-Atom Bombardment
Authors: Cole T. , Heller H. C.
Published: January 2005

A beam of hydrogen (or deuterium) atoms, produced by a microwave electrodeless discharge, has been found capable of producing free radicals upon striking polycrystalline samples of malonic acid, malonamide, methyl malonic acid, and methyl malonamide. The radicals produced in these compounds, identified by means of their electron magnetic resonance signals, arise from the removal of a methylene hydrogen of the parent molecule. Only one radical species is produced in each compound, in contrast to x irradiation which often produces several types of radicals. The present study strongly suggests that the impinging hydrogen atoms (a) abstract methylene hydrogens from the organic molecules to form radicals and H2 and (b) penetrate several molecular layers of the crystallites before they react.

Radicals were also formed by impinging hydrogen atoms in naphthalene, hexamethylene tetramine, calcium malonate, calcium formate, and aluminum acetyl acetonate. However, no positive identification of these radicals could be made on the basis of their powder EMR spectra. On the other hand, several other organic powders gave no radicals by the hydrogen-bombardment technique.
Symmetry Numbers and Statistical Factors in Rate Theory
Authors: Bishop David M. , Laidler Keith J.
Published: January 2005

It is shown that for any chemical equilibrium the ratio of symmetry numbers is equal to the ratio of statistical factors; these statistical factors represent the number of different sets of products that can be formed if identical atoms in the reactant are labeled. In arriving at rate expressions one must use not simple symmetry numbers but the statistical factor l‡ for the formation of the activated complex from the reactants. This procedure takes account of the special situation that arises if the formation of the activated complex produces an optical enantiomer. The application to the Bro/nsted relationships is considered, and it is shown that Bro/nsted's original formulation is the correct one.
Positron Annihilation in Liquid Crystals
Authors: Cole George D. , Walker William W.
Published: January 2005

Positron lifetimes have been measured, as a function of temperature, in the following liquid crystalline substances: cholesteryl benzoate, cholesteryl stearate, cholesteryl myristate, and p-azoxyanisole. The value of τ2 was observed to vary at the melting point of each compound and at smectic transitions. No change in τ2 occurred at nematic isotropic and cholesteric isotropic transitions. Possible explanations for the behavior of τ2 are suggested.
Excitation Energies of Azulene and Naphthacene Triplets
Authors: Lamola Angelo A. , Herkstroeter William G. , Dalton J. Christopher , Hammond George S.
Published: January 2005

The high-frequency phosphorescence emission previously attributed to naphthacene is found to be due to 5,12-naphthacenequinone. Naphthacene triplets are not quenched by azulene although the latter is a good quencher for anthracene triplets. Consequently, we infer that the excitation energy of azulene triplets lies between 31 and 39 kcal/mole (11 000–14 000 cm−1).
Ethylene Molecule in a Gaussian Basis. I. A Self-Consistent-Field Calculation
Authors: Moskowitz J. W. , Harrison M. C.
Published: January 2005

A series of nonempirical calculations are reported for the ethylene molecule, using the LCAO—SCF method with Gaussians as the basic expansion functions. Ground-state calculations on the planar molecule at its experimental equilibrium position are reported for ten basis sets of different sizes. The pi orbitals are found to be relatively independent of the sigma orbitals, with excitation energies for the lowest 1Ag and 3B3u states giving fair agreement with experiment, the lowest 1B3u state being too high. Calculations on the twisted and stretched molecule using a small basis set give structural parameters in good agreement with experiment.
Ground-State Energy and Excitation Spectrum of Molecular Crystals
Authors: Mavroyannis C.
Published: January 2005

The Green's function method has been used to investigate the properties of the Frenkel excitons in molecular crystals at zero temperature. Excitation energies have been determined for crystals having one or more excited molecules in the unit cell. Configuration effects resulting from the interaction between different molecular states have been included. General formulas are developed for the ground-state energy of a molecular crystal, first without and then with mixing of different electron configurations. It is found that the interaction between two different exciton states contributes appreciably to the ground-state energy of the crystal.
Determination of Ground-State O, N, and H by Light Absorption and Measurement of Oscillator Strengths
Authors: Morse F. A. , Kaufman F.
Published: January 2005

Vacuum-ultraviolet absorption measurements of the resonance lines of O, N, and H by the line-absorption method are described. They lend further support to the correctness of the gas-titration reactions of O and N by NO2 and NO. Line-shape difficulties are reduced by means of an optically thin light source. Based on a simple Doppler emission—Doppler absorption model, oscillator strengths, Σgf, of 0.3±0.1 are obtained for the oxygen-resonance triplet near 1300 Å, and lower limits of 0.2 and 0.6 for the nitrogen triplet near 1200 Å and the Lyman alpha doublet. Preliminary experiments on the detection of metastable excited states of O and N are also described.
Decyclization of Cyclohexene, 4-Methylcyclohexene, and 4-Vinylcyclohexene in a Single-Pulse Shock Tube
Authors: Tsang Wing
Published: January 2005

Several cyclohexene compounds have been decomposed in a single-pulse shock tube. Rate constants for the decyclization reactions C6H10(cyclohexene)→C2H4+C4H6,(1,3−butadiene)C7H12(4−methylcyclohexene)→C3H6+C4H6,(1,3−butadiene)C8H12(4−vinylcyclohexene)→2C4H6,(1,3−butadiene)are compared with the rate of dehydrochlorination of hydrogen chloride from isopropyl chloride. The Arrhenius expression for the latter reaction has previously been found to be k(i−C3H7Cl)=1013.64exp(−51 100/RT).On this basis, the following rate expressions have been obtained: k(C6H10)=1015.02exp(−66 700/RT)sec−1  (900∘−1150∘K),k(C7H12)=1015.13exp(−66 600/RT)sec−1  (900∘−1150∘K),k(C8H12)=1015.20exp(−62 000/RT)sec−1  (900∘−1050∘K).
Shrinkages of the Internuclear Distances by Molecular Vibrations
Authors: Nagarajan G. , Lippincott E. R.
Published: January 2005

Analytical expressions for shrinkage effects in linear and nonlinear conformations are outlined. Schematic representations of linear as well as nonlinear shrinkages for various systems are given. The computed numerical values of the linear and nonlinear shrinages at different temperatures for various molecules with different symmetry are reported.
Composite Diffusion Mechanisms and Diffusional Anisotropy of Helium in Beryl, Aquamarine, Quartz, and Related Glasses
Authors: Brandt W. W. , Hattori M.
Published: January 2005

The rates of desorption of helium from several types of beryl, from aquamarine, and from quartz have been measured using a mass-spectrometer-type leak detector of high sensitivity. The rates measured on beryl or aquamarine slabs cut perpendicularly and parallel to the hexagonal axis of symmetry at 680°C are very different but conform to the appropriate solution of the diffusion equation. Diffusion through the channels present in the beryl crystal structure is probably the controlling process at this temperature. The extent of anisotropy, the conformance to the ideal curve shape, and the sample to sample reproducibility correlate with the quality of the various beryls investigated. At low temperatures relatively little helium is evolved and the process does not conform to the solution of the diffusion equation mentioned above, probably because grain boundaries of various dimensions furnish the preferred diffusion paths. Fused beryl and quartz yield very anomalous (nonconforming) rate curves while crystalline quartz is intermediate between the glasses and the crystalline beryls. Defect diffusion is probably of considerable importance in these cases. Results obtained on a beryl powder indicate that surface desorption is negligibly small in comparison to bulk and defect diffusion.
Microwave Spectrum of 1,3-Cyclohexadiene
Authors: Butcher Samuel S.
Published: January 2005

The microwave spectrum of 1,3-cyclohexadiene has been investigated in the frequency region 20–36 Gc/sec with a conventional Stark modulation spectrometer. The rotational constants and the orientation of the dipole moment suggest that the equilibrium conformation has C2 symmetry. The dipole moment μ=μa=0.437±0.014 D has been obtained from the observed Stark effect. A semiquantitative estimate of the degree of nonplanarity has been made from an analysis of the ground vibrational state rotational constants.
Microwave Spectrum of 1,3,5-Cycloheptatriene
Authors: Butcher Samuel S.
Published: January 2005

The microwave spectrum of 1,3,5-cycloheptatriene has been investigated in the frequency region 17–35 Gc/sec. A quantitative estimate of the nonplanarity of the ring has been made using the ground-state rotational constants of the normal isotopic species. The components of the total dipole moment are μa=0.24±0.04 D and μc=0.060±0.002 D. The vibrational satellites and other aspects of the microwave spectra of molecules of this type are discussed.
Nuclear Magnetic Dipole—Dipole Relaxation in Molecules with Internal Motion
Authors: Woessner D. E.
Published: January 2005

The nuclear magnetic dipole—dipole relaxation for nuclei of spin ½ has been calculated for a model in which the length, as well as the orientation, of the internuclear separation vector varies as a result of internal molecular motion. In liquid molecules the internal motion increases the relaxation times, the effect of internal motion is to split the average of the inverse sixth power of internuclear separation into more terms, and most of these terms have shorter correlation times than for a system of rigid molecules with the same distribution of internuclear separation values.
Quantum Effect in the Diffusion of Gases in Liquids at 25°C
Authors: Nakanishi Koichiro , Voigt Eva M. , Hildebrand Joel H.
Published: January 2005

The study of the diffusion of gas solutes in CCl4 by Ross and Hildebrand is extended and refined to give the following figures for 105D in square centimeters per second at 25°C: in CCl4: He, ∼20; Ne, ∼6.3 (subject to determination of solubility) ; O2, 3.8; SF6, 1.7. In (C4F9)3N; He, ∼13; H2, 6.5; D2, 5.55; Ne, ∼5.3; N2, 2.35; Ar, 2.75. The method is shown to yield not merely relative but absolute values of diffusivity.

The product 1021Dσ2, where σ is the molecular diameter, rises in CCl4 from 45 for the heavier gases to 132 for He; in (C4F9)3N from 32 to 86 for He. There is a linear relation between these values and the square of the quantum parameters of de Boer. The quantum effect is much stronger in CCl4 than in (C4F9)3N in accord with their internal pressures, 3350 and 2170 atm, respectively.
Scattering from Fluids of Nonspherical Molecules. I. X Rays and Neutrons
Authors: Steele William A. , Pecora R.
Published: January 2005

The general theory of the statistical mechanics of nonspherical molecules is applied to the problem of the scattering of x rays and slow neutrons from a fluid composed of nonspherical molecules. Expressions for the differential scattering cross sections are derived for the cases of both elastic and inelastic scattering. General properties of the time-dependent correlation functions are discussed, and a short-time approximation is given and applied to the calculation of the inelastic neutron scattering cross section.
Scattering from Fluids of Nonspherical Molecules. II. Light
Authors: Pecora R. , Steele William A.
Published: January 2005

The statistical mechanical theory of nonspherical molecules is applied to the problem of the scattering of light from fluids composed of optically nonspherical molecules. Expressions for the scattered light intensity in the elastic and inelastic scattering cases are expressed in terms of angular moments of the generalized pair distribution function of the fluid. The special case of axial symmetry is considered, and comparison with previous theoretical and experimental work is briefly made.
Quantum Cell Model for Solids at Low Temperatures
Authors: Reed Robert D. , Henderson Douglas , Chen Ru-Yong
Published: January 2005

The cell model has been widely applied to classical liquids and has recently been applied to quantum liquids. In the cell model it is assumed that each molecule moves independently in a cell formed by the neighboring molecules. This assumption is more reasonable for the solid state than for the liquid state. In the present investigation the cell model is applied to solids at low temperatures. Results are reported for Ar, H2, D2, and 4He. Agreement with experiment is good.