bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Diffusion-Controlled Reaction in Chemically Induced Nuclear-Spin Polarization II. General Theory and Comparison with Experiment
Authors: Adrian Frank J.
Published: February 2004

A more detailed study is made of an earlier proposal that the nuclear-spin polarizations observed in nuclear magnetic resonance studies of the products of free radical reactions are produced when a pair of radicals fail to react the first time they are together but instead diffuse apart and subsequently come together again. In this model the magnetic interactions within the radicals have ample time to produce a nuclear-spin dependent growth or decay of the singlet character of the radical pair during the interval between separation and return. Since the singlet character of the radical pair determines its recombination probability the products formed at the second encounter will be nuclear-spin polarized. This process is analyzed for the cases where the initial state of the radical pair is: (1) a triplet; (2) a singlet; and (3) uncorrelated electron spins. The predictions that sign of the nuclear-spin polarization is the same for the cases of a triplet and uncorrelated spins but is reversed for the singlet state are in agreement with experiment. The intensities of the polarized nuclear magnetic resonance lines are calculated for some typical reactions and the results are in good agreement with experiment.
Inelastic Neutron Scattering Spectra from Lanthanum Dihydride and Lanthanum Trihydride
Authors: Maeland Arnulf J. , Holmes Douglas E.
Published: February 2004

The optical hydrogen vibrations in lanthanum dihydride and lanthanum trihydride have been investigated by the energy-gain scattering of cold neutrons. The approximate frequency distributions, derived from the observed time-of-flight spectra, show peaks which correlate well with the known crystal structures. In fcc lanthanum trihydride the optical bands are peaked at 940 and 515 cm−1 corresponding to hydrogen vibrating at tetrahedral and octahedral sites, respectively, and in lanthanum dihydride there is a single peak at 825 cm−1 due to tetrahedral hydrogen. Other weak peaks have been observed and are thought to be due to vibrations of hydrogen atoms dissolved in the metal phase; this phase was identified by x rays in both samples. A large width of the optical levels, a common feature in all metallic hydrides, was also observed for LaH2 and LaH3.
PVT Properties of Water and Mercury
Authors: Grindley T. , Lind John E.
Published: February 2004

The PVT properties of water and mercury have been measured up to 8000 bar between 30 and 150°C with an accuracy of 0.01% of the volume by electromagnetically detecting the change in length of a column of fluid. Numerical differentiation yields thermal expansion coefficients and compressibilities accurate to 0.5% for water and 1.0% for mercury. The first and second derivatives of entropy with respect to volume for mercury are consonant with a hard sphere model, though (∂2U / ∂2)T requires a softer repulsive potential. Water, because of its structure, only approaches such a simple model above our maximum temperature.
Vibration Spectra of 1,3,5-Triamino-2,4,6-trinitrobenzene
Authors: Deopura B. L. , Gupta V. D.
Published: February 2004

Using Wilson's GF matrix method a normal coordinate analysis of the triamino-trinitrobenzene molecule is made and the Urey–Bradley force field is obtained. Inelastic neutron spectrum is obtained by the time-of-flight method and the frequency distribution is calculated in the one phonon and cubic approximation. Group frequency assignments are made and discussed.
Truncated Invariance Groups for Stable Molecules
Authors: Pedersen Thorvald
Published: February 2004

The concept of a concentrated wavefunction originally proposed by Watson has been elaborated into a theory of a Hilbert space of concentrated wavefunctions called the function space of square-integrable functions on a truncated support. When the operators of the full invariance group of the Hamiltonian are restricted to this function space a partial collapse of the group takes place leading in a natural way to a truncated group which is identical to the Longuet-Higgins group for the system. Hence a more precise meaning is attached to the concept of feasibility proposed by Longuet-Higgins. Another property of the Hilbert space mentioned is that it gives mathematical significance to the concept of a model so extensively used in molecular quantum mechanics.
Dielectric Properties of SF6–CClF3 Gas Mixtures at Nearly Liquid Densities
Authors: Nelson Ralph D. , Cole Robert H.
Published: February 2004

The second pressure virial coefficient and the second and third dielectric virial coefficients for SF6, CClF3, and mixtures of the two have been measured at 50°C and densities up to 5.3 mol l−1. For pure SF6, Bε = 64.1, for pure CClF3, Bε = 58.5, both ± 0.4 cm6/mol2. Analysis of the results using the Kielich multipole formalism gives a hexadecapole moment of 0.005 esu·nm4 for SF6 and an octopole component corresponding to 0.01 esu·nm3 for CClF3.
Reinvestigation of the Hanle Effect for the NO A 2Σ+ State
Authors: German K. R. , Zare R. N. , Crosley D. R.
Published: February 2004

The coincidence of the CdII 2144.38-Å line with the R1(25 / 2) and the RQ21 (25 / 2) lines of the (1, 0) band of the NO γ system A 2Σ+−X 2Π is used to perform a measurement of the molecular Hanle effect on the (υ′ = 1, N′ = 13) vibration-rotation level of the excited state. A linear fit to the pressure-broadening data yields an intercept of 4.25 ± 0.3 G for the zero-pressure linewidth and a slope of 16.3 ± 0.2 mG/mtorr. This is in disagreement with the value of 5.5 ± 0.5 G reported by Gouedard and Lehmann for the half-width at half-maximum. If we assume a g value calculated for Hund's case (b) coupling, the radiative lifetime calculated from our half-width at half-maximum is in good agreement with the work of Jeunehomme. The previous results of Crosley and Zare are shown to be spurious because of mercury vapor contamination.
Precise Measurements of W, the Mean Energy Required for Ion-Pair Formation in Gases I. Alkanes
Authors: Stoneham T. A. , Ethridge D. R. , Meisels G. G.
Published: February 2004

Ionization currents were measured for the complete stopping of 63Ni beta rays in N2 and in alkane isomers at temperatures 25–200°C and pressures between 400 and 2700 torr. The mean energy expended per ion pair formed, W (beta), was determined from the ratio of ion current in nitrogen to that in the sample at equal electron densities. No dependency of W upon temperature or pressure was observed within the experimental precision of ± 0.1%. Using W (N2) = 34.6 eV/ion pair for reference, relative values of W in electron volts/ion pair were found to be 26.94 for methane, 24.18 for ethane, 23.69 for propane, 23.19 for n-butane, 22.82 for n-pentane, 22.62 for n-hexane, 22.47 for n-heptane, 23.52 for 2-methylpropane, 23.07 for 2-methylbutane, 23.42 for 2,2-dimethylpropane, 22.80 for 2-methylpentane, 22.81 for 3-methylpentane, 22.81 for 2,3-dimethylbutane, and 22.88 for 2,2-dimethylbutane.
Shock Tube Investigation of Bromine Dissociation Rates in the Presence of Helium, Neon, Argon, Krypton, and Xenon
Authors: Warshay M.
Published: February 2004

The rates of dissociation of Br2 in the presence of He, Ne, Ar, Kr, and Xe are reported. The following rate constant expressions were obtained from experimental data measured by the light absorption method behind incident shock waves: kD, He = (2.15 ± 0.86) × 1011 T1/2exp[(− 31.9 ± 1.2 kcal/mole) / RT] cm3/mole·sec, kD, Ne = (1.04 ± 0.5) × 1011 T1/2exp[(− 29.1 ± 1.4 kcal/mole) / RT] cm2/mole·sec, kD, Ar = (2.14 ± 0.78) × 1011 T1/2exp[(− 31.3 ± 1.1 kcal/mole) / RT] cm3/mole·sec, kD, Kr = (3.32 ± 0.60) × 1011 T1/2exp[(− 32.8 ± 0.5 kcal/mole) / RT] cm3/mole·sec, kD, Xe = (6.92 ± 1.73) × 1011 T1/2exp[(− 35.5 ± 0.7 kcal/mole) / RT] cm3/mole·sec. In obtaining these rate constants, corrections were made for dissociation due to Br2–Br2 collisions and for the effects of boundary layer buildup. Molecular bromine was less than four times as effective as any of the noble gases in Br2 dissociation over the temperature range investigated, 1200–2000°K. Therefore, in the 1% Br2–99% noble gas mixtures studied, the corrections for the contributions of Br2–Br2 collisions were small. Boundary layer corrections shifted the rate constants to somewhat higher values, the percentage increase being greatest at the lower temperatures. In every single case the activation energy, Ea, was well below the dissociation energy of Br2, D0. The boundary layer corrections lowered Ea making the discrepancies between the Ea's and D0 even greater. The experimental data were used as a basis for evaluating five theoretical dissociation-recombination models (Nielsen–Bak, Light, Bunker–Davidson, Benson–Fueno–Berend, and Keck–Carrier). No single model excelled in predicting all three criteria: the rate constants, the effect of temperature upon kD, and the collision partner efficiencies.
Vibration→Rotation Energy Transfer in Hydrogen Chloride
Authors: Chen Hao-Lin , Moore C. Bradley
Published: February 2004

A pulsed HCl chemical laser source has been used to carry out laser-excited vibrational fluorescence experiments on HCl and mixtures of HCl with DCl, n-H2, p-H2, rare gases, and H2O. The following cross sections σA–B for vibrational deactivation of A by B at room temperature have been found: σHCl–HCl = (4.2 ± 0.4) × 10−19cm2, σDCl–DCl = (1.3 + 0.2, − 0.4) × 10−19cm2, σDCl–HCl = (2.9 ± 0.3) × 10−19cm2, σHCl–n-H2 = σHCl–p-H2 = (2.9 ± 0.5) × 10−20cm2, σHCl–rare gas < 10−21cm2, and σHCl–H2O = (2 ± 1) × 10−16cm2. The cross sections for HCl–HCl and DCl–DCl are about 16 times larger than predicted by linear extrapolation of the shock tube data between 2000° and 1000°K on a log σ vs T−1/3 plot. The isotopic changes in vibrational relaxation rates lead to the conclusions that: (1) Vibrational energy is transferred almost entirely into rotation in hydrogen chloride–hydrogen chloride collisions, and (2) for HCl–HCl and DCl–DCl collisions most of the vibrational energy is transferred into the rotation of the molecule which is initially vibrationally excited. A plausible explanation for these results is provided by the hydrogen-bonding interaction between two HCl molecules.
Anomalous Intensity Behavior in NMR Relaxation Data
Authors: Douglass D. C. , McBrierty V. J.
Published: February 2004

An explanation of the puzzling temperature dependent intensity behavior observed in the T1ρ data for isotropic FEP polymer is put forth in a simple model invoking spin diffusion between crystalline and amorphous phases. In order to explain similar data from fibers of FEP a more detailed model of a different morphology is proposed in which the interfacial geometry plays an important role. It appears that the morphological history of the samples is an important factor in the explanation of the observed relaxation behavior.
Spin–Spin Interaction and the Energy Splitting of the Rovibronic Levels of a Linear Triatomic Molecule
Authors: Chiu Lue-Yung Chow
Published: February 2004

Spin–spin interaction and spin–orbit interaction are both considered in studying the fine structure energy splitting of a rovibronic level. The molecule under study is linear triatomic and in the 3Π state. The first-order spin–orbit interaction is found to be zero except for the vibronic level with K = υ2 + 1, and the first-order fine structure splitting is therefore due to spin–spin interaction only. By nature of the second-rank tensor, the spin–spin interaction is also shown to split the over-all inversion symmetry pairs, namely the + and − of certain J levels. Hund's case a, case b and intermediate cases are considered. The energy of a fine structure level is expressed explicitly in terms of all the quantum numbers and coupling constants such that direct experimental comparison can easily be made. Examples of υ2 = 1 and υ2 = 2 are worked out in detail.
Self-Diffusion Coefficient of Supercooled Water
Authors: Pruppacher Hans R.
Published: February 2004

The self-diffusion coefficient D of liquid water was measured at temperatures between +30 and −25°C by means of a novel technique involving tritium as a tracer. At temperatures warmer than 0°C the present results agree well with the results of the most recent measurements of Wang who used 18O as a tracer. At temperatures below 0°C the present measurements for D are the only ones available. Using the present values for D and the most accurate values available in literature for the viscosity η and the dielectric relaxation time τ the quantities Dη/T, Dτ, and τ(η/T)−1 were found to be constants between +30 and −20°C. Based on this result values for D, η, and τ for temperatures between +40 and −40°C were computed. Interpretation of the present data in terms of Eyring's transition state theory of rate processes revealed that for liquid water self-diffusion, dielectric relaxation, and viscous flow involve at temperatures between +40 and −40°C the same activation mechanism with an activation energy that is strongly temperature dependent. It is further shown that the constancy of the quantities Dη/T, Dτ, and τ(η/T)−1 allow computing Eyring's structural parameters λ, λ1, λ2, and λ3.
Coupled Nuclear Spin Relaxation and Internal Rotations in Magnesium Fluosilicate Hexahydrate
Authors: Utton D. B. , Tsang Tung
Published: February 2004

Both proton and fluorine nuclear spin—lattice relaxations have been studied by the 180°-90° pulse method in MgSiF6 · 6 H2O at 25 and 13 MHz over the temperature range 170–350°K. Nonexponential behaviors have been observed. Both 1H and 19F relaxations may be characterized by the same pair of relaxation times, the shorter component due to the intermolecular H–F dipolar interaction. The results indicate that the SiF62− ions are reorienting with an activation energy, V = 31 ± 4 kJ/mole = 7.5 ± 1.0 kcal/mole, and a frequency factor τ0 = 10−14 ± 1sec. These values are consistent with other hydrogen-bonded fluorine compounds.
Monte Carlo Investigation of the Imprisonment of Resonance Radiation: The Doppler-Broadened Line
Authors: Klots Cornelius E. , Anderson Verner E.
Published: February 2004

Monte Carlo simulations of the transport of Doppler-broadened resonance radiation in certain ideal geometries are described. The results corroborate the usual local thermodynamic equilibrium assumption. Spectral line shapes, quenching probabilities, and resonance defects are discussed, and simple empirical formulations are noted.
Molecular Beam Study of the Oxidation of Deuterium on a (111) Platinum Surface
Authors: Smith Joe N. , Palmer Robert L.
Published: February 2004

The reaction D2+12O2→D2O occurring on a (111) Pt surface has been investigated using modulated molecular beam techniques. With a molecular beam of D2 and a (111) Pt surface immersed in an O2 ambient, the production of D2O was studied as a function of D2 flux and temperature, O2 pressure, Pt temperature and the angle of incidence of the D2 beam. From these data the rate of production of D2O can be expressed by a reaction rate proportional to PD 2 2.0 PO 2 0.8  exp[−3.6 (kcal/mole) / kTD 2]  exp[−12 (kcal/mole) / kTPt]in the pressure and temperature regime PD 2 ∼ 10 −7 torr, PO 2 ∼ 10 −5 torr, TD 2 ∼ 1200°K, and TPt ∼ 700°K. Further, a reaction mechanism which is consistent with this rate expression and also with the observed angular dependence is presented.
Lowest Triplet State of Substituted Benzenes. I. The Optically Detected Magnetic Resonance of para-Dichlorobenzene
Authors: Buckley M. J. , Harris C. B.
Published: February 2004

The optically detected magnetic resonance (ODMR) of para-dichlorobenzene in its first 3ππ* state is reported. The structures of the three zero-field transitions are interpreted in terms of a Hamiltonian incorporating the electron spin—spin, chlorine nuclear quadrupole, and chlorine hyperfine interactions. It is concluded from an analysis of the spin-Hamiltonian parameters that the triplet spin density in the chlorine out-of-plane orbitals is small, the chlorine electric field gradient is significantly reduced in the 3ππ* state as compared to the value for the ground state, and that the molecule most likely is distorted.
Rotational Isomerism in 1-Pentyne from the Microwave Spectrum
Authors: Wodarczyk Francis J. , Wilson E. Bright
Published: February 2004

The gas-phase microwave spectrum of 1-pentyne has been investigated in the region 8–40 GHz. The spectrum can be attributed to two rotational isomers in which the methyl group is, respectively, trans and gauche to the acetylene substituent. The rotational constants of the trans form are A = 23 340 ± 200, B = 2230.566 ± 0.020, and C = 2116.385 ± 0.020 MHz, and those for the gauche form are A = 9921.112 ± 0.030, B = 3172.780 ± 0.010, and C = 2634.025 ± 0.010 MHz. From these data a plausible structure has been derived which gives the gauche dihedral angle as 115° ± 3° from the trans position. For each form several vibrationally excited states have been assigned to the torsional motion around the central carbon—carbon bond, the methyl internal rotation, and the C–C≡C bending motion. The torsional vibration frequency is 106 ± 10 cm−1 in the trans form and 114 ± 10 cm−1 in the gauche. Stark effect measurements yield μ trans = 0.842 ± 0.010 D and μ gauche = 0.769 ± 0.028 D. The gauche-form ground state is 27 ± 36 cm−1 below the trans ground state. Four coefficients in the Fourier expansion of the potential energy for rotation about the central C–C bond have been derived: V1=0.940, V2=−1.045, V3=3.518, and V4=0.071 kcal/mole. It is suggested that the slightly greater stability of the gauche form may be due to an attractive dipole—dipole interaction.
Structure of the A 1 2″ State of NH 3 +
Authors: Harshbarger William R.
Published: February 2004

Franck—Condon factors for the transition from the ground state of ammonia to the A 1 2″ ionic state have been calculated. Calculations were made using three different descriptions of the excitation of the ion from the ground state. The results of these calculations were compared with the relative intensities for the transition observed in the photoelectron spectra of NH3 and ND3. This comparison indicates that in the A 1 2″ state, the ion has a planar configuration. The symmetric stretching mode of vibration of the ion, with a frequency of 2850 ± 100 cm−1 for NH 3+ and 2150 ± 100 cm−1 for ND 3 +, is excited in the transition, as well as the inversion mode of vibration. The N–H bond length for the A 1 2″ state of the ion is determined to be 1.07 ± 0.01 Å.
Infrared Spectrum of Propynyl Boron Difluoride
Authors: Reed P. R. , Lovejoy R. W.
Published: February 2004

Propynyl boron difluoride, CH 3C≡CBF2, has been synthesized for the first time and its infrared spectrum determined over the 4000–250-cm−1 region. All 20 fundamentals have been assigned based on band shape considerations, characteristic group frequencies, or isotopic splitting. The gas phase spectrum was compatible with a molecular model belonging to the G12 symmetry group for nonrigid structures. Resolved Q-branch structure was observed for the asymmetric methyl stretching fundamental ν8(e′) which resulted from the freely rotating methyl group. The Coriolis coupling coefficient for this mode was estimated to be ζ 8= +0.16.
Reactions in Crystalline Lattices: Spectroscopic Evidence for the Oxidation of Sm2+ to Sm3+ in KCl
Authors: Fenn J. B. , Cox D. E. , Fong F. K.
Published: February 2004

With varying concentrations of O2 and H2O, oxidation of Sm2+ to Sm3+ is observed. Experimental proof of the oxidation process is given by: (1) the disappearance of the characteristic absorption bands of Sm2+, accompanied by a dramatic decrease in the Sm2+ 5D0→7FJ fluorescence intensity; (2) the observation of the 5H5/2→4I13/2 absorption lines of Sm3+; and (3) the reappearance of Sm2+ fluorescence lines upon gamma irradiation of the oxidized sample. The discovery of a cubic Sm2+ site, which gives rise to a 5D0→7F1 fluorescence transition with a magnetic splitting factor of 1.48 ± 0.05 in excellent agreement with the Landé gλ factor of 1.5, is also reported. The significance of the hitherto unobserved cubic site is discussed.
Magnetothermodynamics of Antiferromagnetic, Ferroelectric β-Gd2(MoO4)3. I. Heat Capacity, Entropy, Magnetic Moment of the Electrically Polarized Form from 0.4 to 4.2°K with Fields to 90 kG along the c Crystal Axis
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2004

The magnetic moment of a 2.49-cm diam spherical single crystal of electrically polarized β-Gd2(MoO4)3 has been measured at stabilized fields of 500, 1000, 1500, 2000, 2200, 2300, 2500, 3500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G along the c crystal axis and over the range 0.3–4.2°K. The heat capacity has been measured at fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G over a similar temperature range. The temperature dependent magnetic moment reached saturation at the higher fields and low temperatures. As expected, any effect of reversing the magnetic field with respect to the electrical polarization was too small to be detected, i.e., less than 0.01% of the magnetic moment. The general character of the magnetic moment and its temperature derivatives vs field at 0.5°K and below indicates the development of an antiferromagnetic system. The fact that the heat of vaporization of momentum (h/2π) from the essentially saturated state exceeds 2MsatH/7, both at 90 and 65 kG, indicates that the energy of the j = ± 5/2 pair is above j = ± 7/2 in zero field. Temperature-field observations on 31 isentropes were used to correlate the entropies along 10 isoerstedic heat capacity series. The entropy zero of the electronic and lattice systems was located at magnetic saturation by means of the heat capacity series at 90 and 65 kG. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.4–4.2°K.
Localized and Delocalized 1s Hole States of the O 2 + Molecular Ion
Authors: Bagus Paul S. , Schaefer Henry F.
Published: February 2004

The hole states of O 2 +, obtained by ionization of the oxygen molecule, have been examined theoretically in three approximations: (i) The frozen orbital approximation, which consists of single configuration calculations in terms of the Hartree-Fock orbitals for the neutral O2 molecule; (ii) direct hole-state calculations in which g or u inversion symmetry is imposed on each molecular orbital; (iii) direct hole-state calculations without the restriction in (ii). For the 1s 4Σ− hole state the three approximations yield the following ionization potentials: (i) 563.5 eV; (ii) 554.4 eV; (iii) 542.0 eV. The experimental ionization potential is 543.1 eV, and it is concluded that the hole state is localized on one of the two oxygen atoms.
Structure of Dielectric Fluids. II. The Free Energy and the Kerr Effect in Polar Fluids
Authors: Nienhuis Gerard , Deutch J. M.
Published: February 2004

The Helmholtz free energy of a molecular fluid of rigid dipoles in the absence of any external field is studied. An explicit formal expression for the excess free energy due to the dipolar interaction is found. It is shown that the free energy per particle is independent of the shape of the sample, although shape-dependent long-range correlations are present in the fluid. For the special case of the Onsager model of polar fluids an explicit expression is obtained for the contribution to the free energy due to the dipolar interactions. Next, we study the long-range part of the three-particle correlation function for an arbitrarily shaped sample of the molecular fluid in the absence of an external field. This long-range part is dependent on the shape of the sample. The three-particle correlation function arises in the expression for the Kerr constant, which measures the birefringence of the fluid when a strong electric field is applied. We show explicitly that, in the lowest nonvanishing order in the field, the birefringence is proportional to the square of the resulting local macroscopic electric field with a proportionality constant (the Kerr constant) which is independent of the shape of the sample. A formal expression is given for the Kerr constant in terms of the local properties of the fluid.
Calculations on the ``Restricted Primitive Model'' for 1–1 Electrolyte Solutions
Authors: Rasaiah J. C. , Card D. N. , Valleau J. P.
Published: February 2004

This paper concerns the ``restricted primitive model'' of 1–1 aqueous electrolyte solutions at concentrations up to 2.0M. Monte Carlo data are compared with several recent theoretical treatments: those based on the hypernetted-chain (HNC) equation and the Percus—Yevick—Allnatt (PYA) equation, the mean spherical model, and the mode expansion and γ-ordering approaches. Some new theoretical calculations are reported. The hypernetted-chain treatment appears to be the most successful of the integral equation theories. Of particular interest is the observation of charge oscillation in the radial distribution functions in both the HNC and Monte Carlo calculations. It is also noted that the cube-root concentration dependence of the deviation from ideality, previously observed for real systems, occurs also in accurate treatments of the primitive model. When the diameter of the ions is sufficiently large, the thermodynamic properties of the restricted primitive model approach those of the corresponding uncharged system at very moderate concentrations.
Molecular Scattering Factors for H2, N2, LiH, and HF
Authors: Morrison Paul F. , Pings C. J.
Published: February 2004

X-ray molecular scattering factors for H2, N2, LiH, and HF have been calculated and expressed as spherical harmonic expansions. The coefficients of the expansion and corresponding gas scattering intensities have been tabulated and compared to isolated atom results. Gas scattering differences between molecular orbital results and isolated atom results are less than 1% for N2, about 16% for LiH, and 7% for HF when compared with zero valence isolated atom results. Expressions for the coefficients derived from two center Gaussian basis functions are presented. Four place convergence of the gas scattering intensity is shown to take place with thirteen coefficients for the worst case of LiH. This convergence rate and the applicability of two-center calculations to other molecules is discussed.
Penetration of Boundary Perturbations in Unstable Chemical Systems
Authors: Ortoleva Peter J. , Ross John
Published: February 2004

The effects of boundary perturbations of chemical species are investigated in a linear analysis for systems of coupled chemical reactions, with diffusion, which have instabilities. At marginal stability of one of the harmonic modes of such a system the penetration depth of the chemical boundary perturbation coupled to that mode approaches infinity at resonance, that is, at the frequency of boundary perturbation equal to the marginal oscillatory frequency of the mode. For the case of equal and diagonal diffusion coefficients for all chemical species the penetration of the perturbation is homogeneous at resonance. In general inhomogeneous penetration occurs in association with symmetry-breaking instabilities of the system. The propagation of an impulse boundary perturbation is derived. Some possible applications of the theory are suggested but not demonstrated: (1) analysis of chemical instabilities; (2) analogies of electronic devices such as tuned amplifiers, transmitters, and receivers (chemical radio); (3) communication in aggregates of biological systems; and (4) mechanism of pheromone emission and reception.
Response of Unstable Chemical Systems to External Perturbations
Authors: Ortoleva Peter J. , Ross John
Published: February 2004

For a system of coupled chemical reactions, with diffusion and in a homogeneous steady state near marginal stability, the response to a periodic external perturbation is derived in a linear analysis and shown to be a resonance phenomenon. Responses to perturbations of external variables with small effects on the rate coefficients are large at resonance. Suggested applications of the theory are: (1) study of kinetic parameters and their dependence on external variables; (2) use of marginally stable systems as analogs of electronic devices; (3) use of marginally stable systems as sensors and receptors; and (4) double resonance experiments.
Interference Effects in the Rydberg Spectra of Naphthalene and Benzene
Authors: Scheps Richard , Florida Donald , Rice Stuart A.
Published: February 2004

We report new studies of (portions of) the Rydberg spectra of naphthalene and benzene. The anti-resonances in the Rydberg spectrum of naphthalene are analyzed in terms of the theoretical line-shape parameters A [Eq. (3)], q [Eq. (4)], and Γ [Eq. (6)]. The values of the parameters deduced, together with a simple physical argument, imply that the matrix element coupling the zero-order Rydberg state φR and the isoenergetic inhomogeneously broadened background levels {ψi} is less than 1 cm−1. The available data do not permit an unambiguous determination of the nature of the background transitions, and hence of the coupling mechanism. Two limiting cases are considered, one requiring strict compliance with symmetry properties of the zero-order states, and one disregarding said symmetry properties because of vibronic mixing prior to the interaction of φR and {ψi}. Both schemes can be made to fit the experimental data, and both have deficiencies. A possible intermediate scheme is suggested; it requires the background intensity to arise from at least two electronic transitions, possibly including σ−sgr;* and σ−π* excitations.
Invariant Expansion for Two-Body Correlations: Thermodynamic Functions, Scattering, and the Ornstein—Zernike Equation
Authors: Blum L. , Torruella A. J.
Published: February 2004

An invariant expansion of the two-body statistical correlation function of a fluid is proposed. This expansion does not depend on any particular reference frame used to define the orientation of the molecules, and therefore can be reduced to the expansions of the literature in a simple way. The new expansion permits a rather convenient way of including the effects of molecular symmetry into it. The expressions for a few thermodynamic properties in terms of this expansion are obtained. The equations for x-ray, neutron, and light scattering are somewhat simpler using this expansion. The Ornstein—Zernike equation has a very convenient form, and is given in Fourier transformed form in terms of 6j angular recoupling coefficients.
Analytical Evaluation of Three-Center Nuclear-Attraction Integrals with Slater-Type Atomic Orbitals
Authors: Bosanao S. , Randio M.
Published: February 2004

The general three-center one-electron nuclear attraction integral with integer n Slater-type orbitals is evaluated analytically. The formula is derived using Neumann expansion of 1/rc in elliptic coordinates and by subsequent use of ξ/ξc→ξ substitution in order to restore the integration limits in integrals involving ξ. For the expression [ξ2—1]M/2 binomial expansion is used. The final results is expressed as a multiple summation of terms built from the well-known auxiliary functions An (p), and Bm (pt) appearing in overlap integrals between Slater-type orbitals. In addition the generalized exponential function En(p) = ∫ 1∞ x−nexp(−px)dx=A−n(p)appear. Numerical results are given for several combinations of orbitals with quantum numbers n=1, 2, 3 and l=0, 1, 2, while the quantum number m was restricted to zero. The results are compared and are in a satisfactory agreement with those of Yoshimine which are based on numerical integration.
Ion—Molecule Experiments Involving Negative Ions of Tungsten and Rhenium Oxides
Authors: Center R. E.
Published: February 2004

Rate constants for the reactions of ReO3− and (WO3)n=1,2,3− with Cl2 and NO2 have been measured in a drift tube/mass spectrometer apparatus from thermal energies (295°K) to ∼ 0.07 eV in the center of mass system. The rate constants for these reactions involving atom exchange agreed to within a factor of 2 with the theoretical orbiting rate constant of approximately 7 × 10−10cm3/sec for both reactants. ReO4− did not react with either NO2 or Cl2. Ordinary charge transfer was not observed, implying electron affinities in excess of 2.5 eV for these metal oxides. The mass-identified zero-field mobilities of these ions in Ar were measured at 295°K and were found to be 1.94, 1.67, 1.96, 1.50, and 1.20 cm2 V−1·sec−1 for ReO3−, ReO4−, WO3−, (WO3)2−, and (WO3)3−, respectively.
Temperature Dependence of Specific Rates of Benzene Monomer and Excimer Fluorescence
Authors: Gregory T. A. , Helman W. P.
Published: February 2004

The specific rates which describe the fluorescence behavior of benzene have been determined from lifetime measurements of excited benzene in methylcyclohexane solution in the temperature range 169–298°K. Particular attention is directed to the rates at 195°K, because at this temperature the rates for excimer association and dissociation can be directly measured by pulse techniques described. It is confirmed that excimer is formed at a diffusion-controlled rate, but it is also found that excimer dissociation proceeds more rapidly in dilute solutions than in concentrated solutions of benzene. Specific rates of fluorescence for both monomer and excimer are found to have the same temperature dependence on change from 298 to 195°K, although the magnitudes of the rates differ. Refined values of other specific rates have also been obtained and, when comparison can be made, have been shown to have the same value in solution as in the vapor phase at pressures of several torr or above.
Theory of Three-Dimensional Reactive Collisions Using Natural Collision Coordinates
Authors: Wyatt Robert E.
Published: February 2004

Starting from the classical kinetic energy expressed in natural collision coordinates, the Hamiltonian operator is derived for three dimensional reactions of the form AB+C→near linear intermediate→ A + BC. After writing the wavefunction as a sum of products of symmetric top wavefunctions (which provide for orientation of the plane of the three particles) times internal functions (which determine the size and shape of the three particle triangle), a system of coupled equations is obtained for the internal functions. Coupling mixes states of different K (component of angular momentum along rotating z axis). At large distances, K± 1 coupling is important even though the bending potential vanishes. At small distances, K ± 2 coupling is most important but even this should be small for a near linear intermediate. After expanding the internal functions in a perturbed stationary state basis, coupled differential equations (containing only local potentials) are obtained for the translational functions. The rotational part of the basis is then treated in more detail. At large atom—molecule distances, the free rotator states are obtained. At smaller distances, where internal rotation is slightly hindered, rotator functions are obtained as expansions in free rotator states. For the near linear intermediate, bending states are obtained using continued fraction techniques. The asymptotic form of the total wavefunction is then examined. Formulas are obtained for the nonreactive and reactive scattering amplitudes, and for the degeneracy averaged total reaction cross section. The latter has a form which in the classical limit becomes integration of the reaction probability over the impact parameter.
Accurate Calculation of the Vibrational Force Constant of the Hydrogen Molecule by Variation–Perturbation Theory
Authors: Chang S. Y.
Published: February 2004

By using the Parr and White perturbation scheme for the diatomic potential energy as a function of internuclear distance, the quadratic force constant ke of the ground state of the hydrogen molecule is calculated by solving a perturbation equation in which the electronic kinetic energy is the perturbation. The first- and second-order energies in the force-constant expression are calculated by a second perturbation expansion with electron correlation as perturbation. The zeroth-order uncorrelated wavefunction is determined from the Distorted Atoms in Molecule Model. The first- and second-order perturbation equations involving kinetic-energy perturbations are solved exactly. By applying accessible correlation expressions, all of the perturbation energies are evaluated without explicit determination of the correlation wavefunctions. The value of ke found is 0.35–0.37 a.u., in good agreement with the experimental value 0.368 a.u.
Gas-Phase Absorption Spectrum of Triplet Naphthalene in the 220–300-nm and 410–620-nm Wavelength Regions
Authors: Hunziker H. E.
Published: February 2004

A recently developed method for kinetic spectroscopy based on modulated excitation of mercury-photo-sensitized reactions was employed to investigate the gas-phase triplet absorption spectrum of naphthalene in the visible and ground-state absorption regions of the spectrum. At least four distinct electronic transitions were observed and assigned as follows (transition energy in electron volts, symmetry species of upper state, oscillator strength where determined): 2.25, Ag+3; 2.93, Ag−3; 4.86–5.06, Ag−3; 5.46, B1g−3, f=0.50. A value of f=0.14 was found for the well-known B1g−3 transition at 3.12 eV. Extinction coefficients were estimated from the observed ground-state depopulation signal. The spectrum appears to be in essential agreement with the theoretical predictions by de Groot and Hoytink.
Vibrational Spectra of Fluoronium Ions, FH2+, FD2+, and FHD+
Authors: Couzi Michel , Cornut Jean-Claude , Huong Pham Van
Published: February 2004

The first direct observation of fluoronium ions, FH2+, FD2+, and FHD+, is reported. The method of production of the fluoronium salts is described, and their infrared spectra are analyzed. The structure of the fluoronium ions is shown to be angular. The force constants have been evaluated. In the presence of liquid hydrogen fluoride, the fluoronium ions are strongly solvated by hydrogen bonds in the form (HF)nH+.
Electronic Structure of the Silver (1+)—Ethylene Complex
Authors: Basch Harold
Published: February 2004

The electronic structure of the silver (1+)—ethylene complex has been calculated using the nonempirical self-consistent field theory in an extended Gaussian orbital basis set and in a top-complex geometry corresponding to Dewar's original two-way donor-acceptor model. A purely electronic binding energy of just under 1.0 eV is predicted for this complex in the gas phase. For comparison purposes an identical calculation was carried out on ethylene in the presence of a unit point charge replacing the Ag+ ion. Based on an examination of core electron binding energies and basis orbital populations it is concluded that (a) the point charge model is capable of describing most of the ethylene intramolecular electron rearrangement in the complex, and (b) the metal olefin σ bond is more important than the π bond. The energy ordering of the excited states of the complex is found to be dominated by the upper orbital energy. A number of considerations and results mitigate against the alternative side complex as the most stable geometric configuration for AgC2H4+.
Random-Coil Dimensions and Dipole Moments of p-Chlorostyrene Chains
Authors: Mark J. E.
Published: February 2004

Mean-square dimensions and dipole moments of p-chlorostyrene chains CH3–[CH(p-C6H4Cl)–CH2–] xH have been calculated as a function of their stereochemical structure, degree of polymerization x, and temperature. Theoretical arguments and experimental evidence indicate that p-chlorostyrene and styrene chains differ little in conformational energy. Therefore, the present investigation employs conformational energies of styrene chains recently obtained by Flory and co-workers from analysis of the stereochemical equilibrium compositions of styrene dimers and trimers. The calculations indicate that at large x the dimensions of p-chlorostyrene, or styrene, chains and the dipole moments of p-chlorostyrene chains should increase with increasing isotacticity and decreasing temperature. The marked differences in the configurational characteristics of p-chlorostyrene and vinyl chloride chains are shown to result from the large difference in size between p-C6H4Cl groups and Cl atoms. Theoretical results calculated for large x are, in general, in satisfactory agreement with published experimental results on poly (p-chlorostyrene). Several experimental results, as yet unconfirmed, seem however to evade interpretation in terms of the present model. Additional experimental investigations would be required to resolve this discrepancy and to provide a more definitive test of the calculated results.
Determination by Gas-Phase EPR of the Absolute Concentration of Species Undergoing Electric Dipole Transitions
Authors: Breckenridge W. H. , Miller Terry A.
Published: February 2004

An experimental investigation of the theoretical expressions relating gas-phase EPR signal strengths and absolute concentration of species undergoing electric dipole transitions has been carried out. Absolute concentrations of SO(3Σ−) have been determined by EPR using NO as a calibrant gas. Concomitant determinations by titration of SO(3Σ−) with known amounts of NO2 are found to be in excellent agreement with the EPR results, once inconsistencies in the published values for the transition moments of NO(2Π) and SO(3Σ−) are reconciled. The agreement supports the validity of each technique, but the EPR method is more convenient once a correct calibration factor is established. Several methods for determining the signal strength from an observed EPR line (first moment, double integral, width squared times height) have been critically examined. All of the methods were found to yield consistent results when properly applied. A choice among them will be dependent upon the particular requirements of any given experiment.
Phosphorus-31 Nuclear Magnetic Relaxation Times in the PBr3–PBr2Cl–PBrCl2–PCl3 System
Authors: Jordan A. D. , Cavell R. G. , Jordan R. B.
Published: February 2004

The NMR transverse and longitudinal relaxation times of 31P in a liquid mixture of PCl3 and PBr3, and in a liquid mixture of PBr3, PBr2Cl, PBrCl2, and PCl3 were measured at 40.5 MHz as a function of temperature from 80 to −100°C. Transverse relaxation times of 35Cl in a liquid mixture of PCl3 and PBr3 and in neat liquid PCl3 were measured over the temperature region 70–29°C. The 35Cl relaxation time in PCl3 is entirely due to a quadrupolar interaction mechanism, thus the reorientational correlation time of the PCl3 molecule is determined from the 1/T2 values and the known quadrupole coupling constant. The 31P transverse relaxation time is controlled by a scalar coupling interaction mechanism while the longitudinal relaxation time is controlled by a spin—rotation interaction mechanism at high temperatures and a combination of dipolar, scalar coupling, and anisotropic chemical shift interaction mechanisms at lower temperatures. The scalar coupling constants calculated for P–35Cl in PCl3 and P–79Br in PBr3 are 127 and 296 Hz, respectively. The value for PCl3 is in excellent agreement with previous work, while that for PBr3 is believed to be more accurate than the value reported from previous studies. The spin—rotation coupling constants for PBr3, PBr2Cl, PBrCl2, and PCl3 are 3.49, 4.41, 5.95, and 9.09 kHz, respectively. The values for PBr3 and PCl3 do not agree with those obtained from previous relaxation measurements, but are in excellent agreement with the theoretical values.
Heat Capacity and Thermodynamic Properties of o-Terphenyl Crystal, Glass, and Liquid
Authors: Chang S. S. , Bestul A. B.
Published: February 2004

The heat capacity of o-terphenyl has been measured with an adiabatic calorimeter for the crystal from 2°K to Tm (329.35°K), for the glasses from 2°K to Tg (around 240°K) and for the liquid from Tg to 360°K, on a sample with less than 0.005 mole % impurity. The heat of fusion and the entropy of fusion are 17 191 J mole−1 and 52.20 J°K−1· mole−1, respectively. The residual entropy of the glasses at 0°K is about 15 J°K−1· mole−1. Above 170°K, the heat capacity of the o-terphenyl crystal is nearly proportional to the temperature to within 1%. Configurational entropy of the supercooled liquid, estimated from the result of this investigation, is used to relate the relaxation properties of glass-forming liquids according to the theory of Adam and Gibbs. Good agreement is found for both viscosity and NMR correlation frequency data.
Resonant Transport Properties of Polyatomic Gases in Oscillating Magnetic Fields
Authors: Fleming Paul D. , Martin Paul C.
Published: February 2004

The transport properties of a polyatomic gas in collinear static and oscillating magnetic fields are discussed qualitatively and studied quantitatively using a microscopic kinetic equation. With no adjustable parameters, resonances recently observed in the thermomagnetic torque (the Scott Effect) are quantitatively reproduced. Related resonant phenomena are predicted for the viscosity, thermal conductivity, and various Burnett coefficients. The calculations are performed for molecules with a unique magnetic moment and for molecules with a distribution of moments. The measured moment distribution is essential for explaining the results on NO, on which the most careful and varied dynamic measurements have been performed. Agreement between theory and experiment for N2 and NO is satisfactory. The calculation entails the evaluation of correlation functions for a steady state in an oscillatory external field. Limiting values of the functions determine the ordinary and Burnett transport coefficients. The details of the identification are treated briefly and separately since equivalent results may be obtained alternatively (specifically, by using the Waldman-Snider equation). With only a static field but no oscillating field, the expressions obtained in this article for molecules with a unique g factor reduce to those derived and applied to N2 by Levi and Beenakker. In particular their explanation of the thermomagnetic torque in terms of a Burnett coefficient is also utilized in the dynamic generalization reported here.
Kinetics of Vaporization of Potassium Chloride Containing Calcium Impurity
Authors: Grimes Carol , Hinkley Jeffrey , Lester Joseph E.
Published: February 2004

The vaporization rates of the (100) face of single crystals of KCl have been measured in the temperature range 430–550°C for crystals containing from less than 2–700-ppm calcium impurity. The vaporization rates of all Ca2+-doped crystals were higher than the rate of the ``pure'' crystal at all temperatures in the range studied. The activation energy for vaporization of ``pure'' crystals taken from the slope of the log rate vs. T−1 curves is 48 ± 2 kcal/mole solid. The behavior of these samples with respect to divalent ion doping is opposite to that observed in Ca2+-doped NaCl.
Reassignment of the n→π* Transitions of Phthalazine
Authors: Hochstrasser Robin M. , Wiersma Douwe A.
Published: February 2004

We have measured the dipole-moment changes for excitation to different vibronic levels of the near ultraviolet, 4200 Å, absorption bands of phthalazine (2, 3-diazanaphthalene). The value of |Δμ| is found to be 3.05 ± 0.10 D (for Ec′ = 0.54 Eeff) for all vibronic transitions including bands associated with the so-called second nπ* state. Armed with this new information we have revised the previous analysis and show that the main bands belong to just one nπ* state (1A2) and not to two nπ* states as previously asserted. The analysis leads us to some new ideas on nonradiative processes in azines, especially 1,2-diazines.
Precise Method for Measuring Absolute Values of Diffusion Coefficients of Binary Gas Mixtures
Authors: Carson P. J. , Dunlop Peter J. , Bell T. N.
Published: February 2004

An apparatus is described for determining binary diffusion coefficients of gases as a function of temperature, pressure, and concentration. Binary diffusion coefficients are reported for the systems H2−N2 and He−Ar at 300°K and 1 atm. The data are believed to be precise to approximately 0.2%, and show a linear dependence on concentration for the system H2−N2.