bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of the magnetic anomalies in Cu(II):Ni(II) bis(diselenocarbamate) crystals
Authors: Buluggiu E. , Vera A.
Published: February 2004

A possible interpretation of the relevant magnetic anomalies, recently observed in Cu(II):Ni(II) bis(diselenocarbamate) mixed crystals, is presented. The Cu–Se bond is considered responsible for the large ``circularization'' (to the value for the free electron) of g about a twofold axis in the molecular plane. Thus it is possible that a weak C2h distortion of the D2h symmetry in the complex [mixing of (xz) into the (3z2−r2) ground state, or (y z) into the (x y) ground state] may produce both the characteristic angle of approximately 45° between the low values of g and the molecular plane and the appearance of a principal value of g slightly lower than the free electron value. It is also clarified why A does not exhibit an analogous rotating effect. Relevant expressions of g and A tensors are deduced in terms of a simple LCAO-MO formalism and implications on the covalent character of the magnetic bonds in the complex are finally discussed.
Observation of an electron transfer process
Authors: Budzinski Edwin E. , Lilga Kenneth T. , Box Harold C.
Published: February 2004

Electron transfer has been observed by ESR spectroscopy in x-irradiated single crystals of partially deuterated glycine hydrochloride. The crystals were irradiated at 4.2°K and the transfer occurs on warming to 77°K. It consists of the movement of electrons between carboxyl groups with the electrons exhibiting greater affinity for protonated carboxyl groups than for deuterated carboxyl groups. A slight perturbation of β-proton hyperfine couplings in carboxyl anion radicals due to substitution of a deuteron for a proton on the carboxyl group was also observed. The shift in coupling, which amounts to a fraction of a megahertz, was measured by ENDOR spectroscopy.
Laser stimulation of chemical reactions and scattered field detection
Authors: Goodman Myron F. , Stone James , Thiele Everett
Published: February 2004

We propose a model to account for some experimental observations on stimulating effects of light absorption on the rate of unimolecular chemical decomposition for gas phase molecules suffering collisions in a thermal bath. Our model calculations show a maximum in the rate constant when plotted against pressure at constant light intensity. A significant additional rate stimulation is predicted when molecules respond coherently to a laser field. This effect is most pronounced as the efficiency of energy transfer collisions increases. Numerical calculations applied to multilevel systems delineate the effects of temperature, pressure, light intensity, and efficiency of energy-changing collisions on the chemical rate constant. The dynamic behavior of a two-level system undergoing chemical decomposition is given in detail. We predict that the unimolecular rate constant appears as a linewidth for a broadened elastic component in the scattered electromagnetic field and the inelastically scattered band intensity is directly proportional to the energy-changing relaxation time. These scattered field measurements may be useful for measuring rapid chemical reactions and vibrational relaxation times.
Hund's basic potential from direct summation
Authors: Hajj Fuad Y.
Published: February 2004

The Coulomb potential at points inside NaCl and CsCl structures was calculated previously by a method of direct summation. This method consists, simply, of adding all the Coulomb potentials, at the point of consideration, due to the point charges of the ions in a piece of the crystal. The shape of the piece of crystal should be determined correctly. Although this method succeeded when applied to NaCl and CsCl structures, it failed when applied to ZnS, CaF2, and Cu2O structures; the reason is that the last three structures lack a certain type of symmetry. However, a hypothetical structure H was constructed such that this method succeeded when applied to it. Moreover, Hund's basic potential can be expressed in terms of the potentials of H and CsCl by a simple relation derived from Hund's identity. Thus, Hund's basic potential was computed at a grid of points of intervals a/16 and tabulated. The potential inside all structures having the cubic Bravais lattices as components can, therefore, be computed easily from this table.
75As Zeeman perturbed NQR in antiferroelectric NH4H2AsO4
Authors: Blinc R. , Mali M. , Osredkar R. , Parker R. , Seliger J. , Žumer S.
Published: February 2004

The 75As EFG tensors corresponding to the four ``nonferroelectric'' H2AsO4 Slater configurations have been determined and the correctness of the antiferroelectric proton ordering scheme proposed by Nagamiya is demonstrated. A comparison of the theoretical and experimental temperature dependences of the 75As NQR frequencies for T > Tc seems to show that the Slater parameter ε has the same sign in ADA as in KDA. The antiferroelectric transition thus seems to be triggered by long range dipole-dipole forces rather than by short range ones.
Lowest 5Σ+ state of FeO: An ab initio investigation
Authors: Bagus P. S. , Preston H. J. T.
Published: February 2004

Hartree-Fock and limited configuration interaction calculations were used to investigate the 5Σ+ and related states of FeO with equilibrium separation of [inverted lazy s] 3.2 bohr. Very extended configuration interaction calculations were then performed to determine the properties of the lowest 5Σ+ state. This lowest state is determined to be close to the Hartree-Fock state investigated. The dissociation energy is estimated to be 2.00 ± 0.14 eV. It is concluded that the ground state of FeO is not 5Σ+.
Electron spin relaxation and hyperfine line shape of manganese (II) in mixed-solvent systems
Authors: Burlamacchi L. , Martini G. , Romanelli M.
Published: February 2004

The X-band ESR line shape of the six hyperfine components of manganese (II) has been investigated both in pure and in mixed solvents. The procedure used by Luckhurst and Pedulli [G. R. Luckhurst and G. F. Pedulli, Mol. Phys. 22, 931 (1971)] to account for the removal of the spin degeneracy by the nonsecular terms in the spin Hamiltonian has been used to compute the line shape as a function of (D:D) and of τc. In mixed solvents, large deviations from the theoretical line shape are due to the presence of differently coordinated complexes. A criterion for the determination of the selective solvation has been established.
Electronic absorption spectra of pyrene and its monopositive ion
Authors: Khan Z. H. , Khanna B. N.
Published: February 2004

The electronic absorption spectrum of pyrene in boric acid glass before and after irradiation with uv light has been studied in the region 200–1400 nm. The spectrum of the irradiated film of pyrene has been attributed to its monopositive ion. The results are in good agreement with those of the other workers. The effect of temperature during and after irradiation of the ionic species is also discussed and it has been found that the photo-oxidation of pyrene in the boric acid glass is a reversible process.
Dielectric and pressure virial coefficients of imperfect gases. Pure N2O
Authors: Kirouac S. , Bose T. K.
Published: February 2004

Dielectric and pressure virial coefficients of N2O have been measured at 6.5, 30.1, and 75.1 °C. The dipole moment and the polarizability determined from the first virial coefficient are, respectively, 0.18 D and 3.03 × 10−24cm3. In calculating the molecular quadrupole moment from the dielectric second virial coefficient, effects due to various interaction energy terms were taken into consideration. These energy terms are due to quadrupole-quadrupole interaction, dipole-dipole interaction, quadrupole-induced dipole interaction, reaction fields of induced moments, and anisotropic effects. Our experimental measurements lead to a molecular quadrupolar moment of 3.4 × 10−26 esu · cm2.
Semiclassical treatment of bound state systems: Trajectory calculations using an analytic approximation to the quantum momentum
Authors: Starkschall George , Light John C.
Published: February 2004

Using an analytic approximation to the quantum momentum previously derived to calculate single particle reduced density matrices in the semiclassical approximation, we have been able to construct equations of motion with which to perform trajectory calculations. Information calculated along these trajectories is used to calculate single particle reduced density matrices for one-dimensional systems. Charge densities for N fermions in a harmonic oscillator potential calculated using this quantum momentum approximation are in excellent agreement with the exact quantum mechanical calculations.
Nuclear quadrupole coupling constants of cis-propylene imine from the microwave spectrum
Authors: Schmidt Ronald , Beeson E. L.
Published: February 2004

The nuclear electric quadrupole hyperfine structure in the vibrational ground state of cis-propylene imine has been measured. The quadrupole coupling constants of the 14N nucleus with respect to the principal inertial axes of the molecule were found to be χaa = − 1.14 ± 0.06, χbb = + 2.01 ± 0.05, and χcc = − 0.88 ± 0.07 MHz.
ESR studies of anisotropic rotational reorientation and slow tumbling in liquid and frozen media. II. Saturation and nonsecular effects
Authors: Goldman S. A. , Bruno G. V. , Freed J. H.
Published: February 2004

Careful studies are described of the ESR line shapes and saturation behavior for the peroxylamine disulfonate (PADS) radical dissolved in a range of glycerol-water mixtures. This permitted studies where the rotational correlation time τR ranged from 3 × 10−12 sec to < 10−6 sec. The unsaturated line shapes for 10−10 < τR < 10−9 sec are, as in Paper I, readily interpreted in terms of anisotropic rotational diffusion, but for τR < 10−10 sec anomalous behavior of the linewidths, which could be attributed to nonsecular spectral densities, occurs. Supporting experiments at 35 GHz, and also on 17O-labeled PADS, are in excellent agreement with values of τR and N = 4.7 (the ratio of the two components of the axially symmetric diffusion tensor), and they supply further information on the anomalous behavior of the nonsecular spectral densities. A phenomenological treatment based on the memory function approach was found to qualitatively reproduce some observed features. The saturation studies were performed over both the motional narrowing and slow-tumbling regions. The motional narrowing results could be analyzed in a straightforward manner to yield values of We, the electron-spin flip rate, which are found to exhibit a weak dependence on τR, roughly as τR−(1/4) for the glycerol solvents. The stochastic Liouville method is applied to an analysis of slow-tumbling saturated spectra and generally reasonable agreement with experiment is achieved for the simplifying assumptions utilized. The rotationally invariant We obtained from the slow-tumbling analyses are found to agree with the values of We extrapolated from the motional-narrowing region. Other aspects of the slow-tumbling saturation experiments and analysis are discussed.
Photodissociation of gaseous olefinic cations
Authors: Kramer Jerry M. , Dunbar Robert C.
Published: February 2004

An ion cyclotron resonance spectrometer was used to study the wavelength dependence of the photodissociation of cations in propene and several isomeric butenes. Photodissociation onsets were determined and compared with electron impact and thermodynamic values. In all cases the photodissociation onsets were found to be above both the thermodynamic onset and the first excited state of the cation as determined by photoelectron spectroscopy. The onset results were compatible with a photodissociation mechanism that proceeds by initial excitation into the first excited state, followed by dissociation. A large increase in the photodissociation cross section for all the cations studied was observed at [inverted lazy s] 3.7 eV. This increase correlated with the second excited states of all the cations except 1-butene. Internal excitation of the parent cations was investigated by the addition of inert gas and by changing the electron beam energy. Photodissociation onsets were also found to be valuable in choosing between alternative structures for gas-phase cations. At least two noninterconverting isomers of C4H8+ were shown to exist.
Electric double layer across two media
Authors: Helmy A. K.
Published: February 2004

The classical Gouy double layer theory has been extended to include a double layer present across two media differing in their dielectric constants. Depending on the boundary conditions used for solving the Poisson equation, different conclusions are obtained. In one case, the double layer may be displaced in the outward direction from the surface without changes in the potential values. In the other case, the potentials across the double layers are lower than those of the classical monomedium model.
Formation of O2(a 1Δg) by electronic energy transfer in mixtures of NO2 and O2
Authors: Jones I. T. N. , Bayes Kyle D.
Published: February 2004

The production of O2(a 1Δg) has been observed when mixtures of NO2 and O2 are irradiated with light in the wavelength region 330–590 nm. The dependence of the signal on light intensity and concentrations suggests that the O2(a 1Δg) is produced by transfer of electronic energy from excited NO2 to O2. The absolute energy transfer efficiency was measured at 366 nm by direct calibration against the amount of NO produced simultaneously by NO2 photolysis. The efficiency measured at other wavelengths was then related to this absolute value. The O2(a 1Δg) production efficiency depended on the wavelength of the light used to excite the NO2, reaching a maximum of 4.5% at 390 nm. A plot of this efficiency as a function of wavelength did not show any apparent discontinuity at 398 nm, the wavelength that corresponds to the first dissociation limit of NO2.
Electric dipole moments of low J states of H2O and D2O
Authors: Dyke Thomas R. , Muenter J. S.
Published: February 2004

Molecular beam electric resonance spectroscopy has been used to make precision Stark effect measurements on the 111, 110, and 211 rotational states of H2O and the 111, 110, 211, and 313 states of D2O. These data have been analyzed using the dipole moment function of Clough, Beers, Klein, and Rothman [J. Chem. Phys. 59, 2254 (1973)] to obtain rotationless moments of 1.8546 ± 0.0004 D for H2O and 1.8545 ± 0.0004 D and D2O.
Electron affinities from endothermic negative-ion charge-transfer reactions. III. NO, NO2, SO2, CS2, Cl2, Br2, I2, and C2H
Authors: Hughes B. M. , Lifshitz C. , Tiernan T. O.
Published: February 2004

Translational energy thresholds have been measured for electron transfer reactions from various atomic negative ions to NO, NO2, SO2, CS2, Cl2, Br2, I2, and C2H2 using a tandem mass spectrometer. These thresholds, corrected where necessary for thermal broadening, were utilized with known thermodynamic data to calculate electron affinities for the molecules indicated. These results were also shown to be consistent with electron affinity limits established by observations of certain exothermic reactions of the molecular negative ions. The isotope distributions in the products from the reactions of monoisotopic Cl− and Br− with natural Cl2 and Br2, respectively, suggest that these reactions proceed via a linear X3− intermediate in which good ``mixing'' of the available energy occurs. The implications of this model with respect to the significance of the measured energy thresholds is discussed.
Electron affinities from endothermic negative-ion charge-transfer reactions. IV. SF6, selected fluorocarbons and other polyatomic molecules
Authors: Lifshitz C. , Tiernan T. O. , Hughes B. M.
Published: February 2004

Exothermic and endothermic negative-ion electron transfer reactions invloving SF6, C6F6, c-C4F8, 2-C4F8, C7F8, c-C6F10 C7F14, C6H5NO2, SiCl4, and SF4 were studied in a tandem mass spectrometer. Cross sections as a function of translational energy were determined for the reactions of various atomic negative ions with most of these molecules. Electron transfer reactions from molecular negative ions were also investigated and in general were found to exhibit very low rate coefficients. Dissociative electron transfer, atom pick-up and ion transfer reactions were observed in competition with electron transfer in several instances. From the translational energy thresholds measured for electron transfer and dissociative electron transfer reactions and from additional bracketing experiments, the following thermodynamic data were derived: E.A. (SF6) ≥ 0.6 ± 0.1 eV; E.A. (SF5) ≥ 2.8 ± 0.1 eV; D0¯(SF5− − F) = 1.1 ± 0.1 ev; E.A. (C6F6) ≥ 1.8 ± 0.3 eV; E.A. (C7F8) ≥ 1.7 ± 0.3 ev; E.A. (c-C6F10) ≥ 1.4 ± 0.3 eV; E. A. (C6H5NO2) ≥ 0.7 ± 0.2 eV.
Penning and associative ionization of triplet metastable helium atoms
Authors: Garrison B. J. , Miller W. H. , Schaefer H. F.
Published: February 2004

Potential energy curves for the ∑1g+, ∑1u+, and ∑5g+ states which arise from two triplet metastable helium atoms (1s 2s 3S) have been calculated by a large configuration interaction expansion. From the potential curves for the ∑1g+ and ∑3u+ autoionizing states, cross section for Penning and associative ionization have been calculated; the total ionization cross section for thermal energy (0.026 eV) collisions, for example, is computed to be 94 Å2. In this low energy region the orbiting model is seen to be adequate for determining the total ionization cross section, but not the more specific cross sections.
New alternative to the Dunham potential for diatomic molecules
Authors: Simons Gary , Parr Robert G. , Finlan J. Michael
Published: February 2004

A new systematic procedure for constructing potential curves for diatomic molecules is developed. The procedure is similar to the well-known Dunham method, except that the expansion parameter is (R-Re)/R instead of (R-Re)/Re. The new expansion, which has a formal theoretical basis, is shown to be superior in terms of both rate of convergence and region of convergence. It is shown how the expansion coefficients may be obtained from spectroscopic data, and the proper behavior of the potential at large R is shown to allow one to determine additional coefficients and to determine dissociation energies. To illustrate the method, the ground states of hydrogen flouride and carbon monoxide are treated. Possible extensions to polyatomic molecules are briefly discussed.
Kinetics of decay of hydroxyl radicals at low pressure
Authors: McKenzie A. , Mulcahy M. F. R. , Steven J. R.
Published: February 2004

The kinetics of decay of OH radicals in excess He at 298 °K and about 1 torr pressure have been studied in a flow tube by ESR spectrometry and computer simulation. In agreement with previous work [Breen and Glass, J. Chem. Phys. 52, 1082 (1970); Mulcahy and Smith, J. Chem. Phys. 54, 5215 (1971)], a first order reaction of OH at the surface was found to accompany the gas-phase reactions OH + OH → H2O + O and OH + O → O2 + H. When [OH] is about 10−10 mole cm−3 or less, the rate of the heterogeneous reaction can be comparable with that of the homogeneous reaction. After allowing for the effects of diffusion resistance on the radial concentration profile, the nonsteady state concentration of O atoms, and the difficulties associated with accurate kinetic analysis of a system of simultaneous first and second order reactions, the rate constant for OH + OH → H2O + O was found to be k2 = (1.3 ± 0.3) × 1012cm3 mole−1 · sec−1.
Theoretical study of the perturbation parameters in the a 3Π and A 1Π states of CO
Authors: Hall J. A. , Schamps J. , Robbe J. M. , Lefebvre-Brion H.
Published: February 2004

Completely ab initio calculations of the perturbation parameters of the a 3Π and A 1Π states of CO have been carried out and compared with the recent experimental results of Field et al. Use has been made of a new program for calculating off-diagonal matrix elements of the B L · S and spin-orbit coupling operators. By including configuration interaction functions built from Hartree-Fock orbitals optimized for each state, good agreement has been obtained between calculated and experimental constants in most cases. Our results show that the perturbations have a strong dependence on R and that they are different for different pairs of states. The single configuration approximation gives a relative error up to 40% and the constancy of perturbation values found by Field et al. cannot be attributed to dependence on a single, constant parameter.
Phosphorescence lifetimes of cationic dyes: Concentration and temperature effects
Authors: Berg Robert A. , Ron A.
Published: February 2004

Experiments have been performed to determine the effect of the concentration of various anions on the phosphorescence lifetimes of cationic dyes in ethanol solution. The three dyes studied were 1,1′-diethyl 2,2′-cyanine; 3,3′-diethyl thiacyanine; and acridine orange. At 77 °K in a glassy solvent the chloride form of the dye salts decays exponentially. In two cases the decay time is independent of concentration; however, the lifetime of the thiacyanine dye increases from (0.35 ± 0.02) sec at infinite dilution up to a maximum of (0.55 ± 0.02) sec at 10−4M. In the presence of heavy ions the decay becomes nonexponential and the lifetime decreases in the order Cl− > Br− > I−. The relative strengths of the perturbation within this series of anions are nearly the same for all three dyes. Below its melting point, ethanol can be prepared either as a supercooled liquid (and glass) or in a crystalline state. The study of phosporescence lifetimes as a function of temperature reveals two different behaviors, depending only on the phase of the low-temperature solution. The phosphorescence lifetime can be used to detect the glass transition and also the development of crystallization in the supercooled liquid.
Electronic energy transfer in rare gas mixtures
Authors: Cheshnovsky Ori , Raz Baruch , Jortner Joshua
Published: February 2004

In this paper we present the results of an experimental study of electronic energy transfer in xenon-argon and xenon-krypton gaseous mixtures excited by an α source. Spectroscopic evidence is presented for molecule-atom energy transfer from Ar*2(1,3Σu) to Xe(1P1) and from Kr*2(1,3Σu) to Xe(3P1). These two electronic energy transfer processes are characterized by large ∼ 10−14 − 10−13 cm2 cross sections. Information has been obtained for collision-induced energy conversion processes of the Xe energy acceptor involving 1P1 → 3P1 conversion and the formation of Xe*2(1,3Σu) at moderately low (≤ 200 ppm) Xe concentrations. A new emission band, observed in the xenon-krypton system, peaking at 1530Å, is tentatively assigned to a heteronuclear (KrXe)* diatomic molecule.
Collinear collision between a particle and a harmonic oscillator with a Morse potential interaction
Authors: Storm David , Thiele Everett
Published: February 2004

The model problem of a collinear collision between a particle and a harmonic oscillator interacting via a Morse Potential is considered. The Devonshire formula, or the distorted wave formula, for the transition probabilities is corrected and a new formula is obtained which yields improved results. The origin of the correction is the improved treatment of the matrix elements of the interaction potential, and the correction is analogous to that made in the corresponding model problem in which the interaction potential is a repulsive exponential. The differences in scattering from the Morse potential and a purely exponential potential are discussed. A new correction factor to account for attractive forces is given; the result is similar to one given previously in simplicity, but yields a more accurate correction.
Herzberg-Teller interactions and spectra of dimers: Stable anthracene dimer
Authors: Zgierski Marek Z.
Published: February 2004

The theory of vibronic coupling in dimeric systems is extended to include mixing between electronic states of the same symmetry via a totally symmetric vibrational coordinate in the monomer. The inclusion of such mixing removes the discrepancy between theory and experiment in the intensity distribution in the fluorescence spectra of the stable anthracene dimer.
Polarizability calculations on water, hydrogen, oxygen, and carbon dioxide
Authors: Nir S. , Adams S. , Rein Robert
Published: February 2004

Based on the semiclassical model of damped oscillators, a procedure is developed for the calculation of the dispersion of refractive index, polarizability, and dielectric permeability, which are treated as complex quantities. Using experimental values of refractive indices and employing the frequencies of strong absorption bands, a least squares fit is used to determine oscillator strengths and damping factors. The absorption coefficient and the imaginary part of the refractive index are also calculated at the corresponding wavelengths. The procedure is applied for the cases of water, hydrogen, and oxygen in both the liquid and gaseous states and for gaseous carbon dioxide, and a good agreement is obtained between calculated and observed values of refractive indices. Results are also compared with those of previous calculations. Calculated absorption coefficients agree well with experimental values in the region of absorption bands. The calculated values of oscillator strengths and damping factors are discussed. The previously determined values for the polarizability extrapolated to infinite wavelength agree with the present results for the contribution of the electronic motion to the polarizability, this contribution being about the same for both the liquid and gaseous states of hydrogen, oxygen, and water. The value obtained in the present work for the polarizability of liquid water is about 2.8-fold greater than the results of previous calculations; most of the contribution is due to atomic and molecular motions. Onsager's theory is shown to yield the experimental value of the permanent dipole of water from the dielectric constant of liquid water when our result for the polarizability of liquid water is employed.
ESR and ENDOR studies of the main radical created by gamma irradiation at 300 °K in the imidazole crystal
Authors: Lamotte B. , Gloux P.
Published: February 2004

ESR studies of room-temperature gamma irradiated single crystals of imidazole and of its derivatives deuterated in several different positions have permitted us to identify the main radical produced by such irradiation. It is a π radical formed by the addition of one hydrogen atom on a carbon of the ring. Moreover, we show that the hydrogen atom which is added to form the radical comes from hydrogens involved in the hydrogen bond chains. The subsequent ENDOR study enables us to deduce the spin density distribution in the radical from the determination of all the proton hyperfine tensors.
Reaction paths on the H4 potential energy surface
Authors: Silver David M. , Stevens Richard M.
Published: February 2004

Portions of the electronic potential energy surface corresponding to various nuclear geometries of the H4 molecular system have been studied. The variational calculations employed double-zeta basis sets (1s and 1s′ Slater-type orbitals on each center) to form configuration interaction wavefunctions. At selected points on the surface, the effects of exponent optimization and increased basis set size (1s, 1s′, and 2p orbitals per center) were assessed. A low energy reaction path allowing a bimolecular mechanism for exchange, requiring less energy than a single H2 dissociation, was not found. However, a path leading from trapezoidal to linear structures (and vice versa) was found to offer the possibility of exchange with less than 6 kcal/mole of energy above this dissociation limit.
Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) of hyperfine interactions in solutions of α, α′-diphenyl-β-picryl hydrazyl (DPPH)
Authors: Dalal N. S. , Kennedy D. E. , McDowell C. A.
Published: February 2004

The high resolution of the electron-nuclear double resonance (ENDOR) technique has been utilized to obtain precise values for the twelve proton hyperfine couplings and to estimate the various nitrogen hyperfine couplings in solutions of the stable free radical α, α′-diphenyl-β-picryl hydrazyl (DPPH). The results enable us to explain for the first time the rather complex hyperfine structure in the electron paramagnetic resonance (EPR) spectra of DPPH solutions. Assignment of the various couplings was aided by comparison of the observed EPR spectrum with the computer-simulated spectra and by comparison of the available theoretical and magnetic resonance data with our ENDOR data. The results provide an accurate measure of the spin densities over the entire molecule. They also provide an experimental basis for a model proposed recently to account for the ``combination'' lines observed in electron-electron double-resonance (ELDOR) spectroscopy.
Anomalous osmosis: Solutions to the Nernst-Planck and Navier-Stokes equations
Authors: Wyman C. E. , Kostin M. D.
Published: February 2004

The phenomenon of anomalous osmosis is studied by using the coupled Nernst-Planck and Navier-Stokes equations to investigate diffusion of an electrolyte through a pore of an ion-exchange membrane. Exact solutions to these equations show that a concentration gradient can produce fluid motion. It is found that the velocity profiles may be significantly different from those of Poiseuille flow.
Dielectric studies of 1-chloro-2-bromoethane in the liquid state
Authors: Ghatak A. , Das A. , Hasan A.
Published: February 2004

The value of the activation energy for dielectric relaxation in 1-chloro-2-bromoethane in the liquid state obtained from dielectric studies in different microwave regions and at different temperatures is found to be 1 kcal/mole which is in good agreement with the calculated value of the difference of electrostatic energies of 0.9 kcal/mole between the gauche and trans isomers in the liquid state. This activation energy is also almost equal to the amount of lowering of the energy difference (940 cal/mole) between trans and gauche isomers of the molecule from the vapor to the liquid state obtained from spectroscopic studies. The energy difference of 550 cal/mole between the two isomers of the molecule in the liquid state calculated from the measured dipole moment values at different temperatures agrees fairly well with the spectroscopic value of 490 cal/mole.
Mobilities and longitudinal diffusion coefficients of mass-identified hydrogen ions in H2 and deuterium ions in D2 gas
Authors: Graham E. , James D. R. , Keever W. C. , Albritton D. L. , McDaniel E. W.
Published: February 2004

We have measured in a drift tube mass spectrometer the mobilities and longitudinal diffusion coefficients of H+, H3+, and H− ions in H2 gas and D+, D3+, and D− ions in D2 gas. These measurements were made at 300°K and over a substantial range of E/N, where E is the electric field intensity and N is the gas number density. The zero-field reduced mobilities of the ions in H2 were determined to be 16.0 ± 0.3, 11.3 ± 0.2, and 43.0 ± 1.3 cm2/V · sec, respectively; the values for the ions in D2 were 11.7 ± 0.4, 8.07 ± 0.25, and 30.1 ± 0.9 cm2/V · sec, respectively. The fact that the mobilities of H− and D− are so much larger than those of the corresponding positive ions, H+ and D+, is unexpected and thus far has not been quantitatively explained. Measurements of the longitudinal diffusion coefficients as a function of E/N are in fair agreement with the theoretical predictions of Whealton and Mason. The low-field diffusion coefficients are in good agreement with the values predicted from the measured mobilities by use of the Einstein equation.
Generalized product expansions for pair-correlated wavefunctions
Authors: Mehler E. L.
Published: February 2004

A correlated wavefunction in the form of a linear combination of generalized products is proposed for describing electron correlation in N-electron systems. The generalized product configurations are group functional products describing the correlated behavior of a pair of electrons in an N-2-electron independent particle sea. The linear expansion includes terms for all possible pairs and thus includes correlation effects for every pair of electrons. The structure of the wavefunction is given, the matrix elements of the Hamiltonian are determined, and some of the variational equations determining the optimal total wavefunction are discussed. The relation between second-order Nesbet-Bethe-Goldstone calculations and the pair at a time CI method of Sinanoğlu and the pair-correlated wavefunction developed here is discussed, and a method is given for obtaining a complete generalized product wavefunction from these type independent pair approximations.
Correlated Gaussian wavefunctions for H3+
Authors: Salmon Lydia , Poshusta R. D.
Published: February 2004

Quantum chemical calculations have been performed on H3+ using correlated Gaussian wavefunctions of a type suggested by Singer. The resulting upper bound energy, E = −1.34335 a.u., is lower than all previous results except those of Conroy. Vibrational frequencies were calculated to be ω1 = 3272 cm−1 (symmetrical stretch) and ω2 = 2735 cm−1 (bending mode). The kinetic energy, nuclear repulsion energy, interelectronic repulsion energy, nuclear-electronic attraction energy, virial, and squared electronic position expectation values were computed.
Measurements of the O+ + N2 and O+ + O2 reaction rates from 300°K to 2 eV
Authors: Johnsen R. , Biondi Manfred A.
Published: February 2004

The rates and energy dependences of the reactions O+ + N2 → NO+ + N and O+ + O2 → O + O2+ have been studied in a drift tube/mass spectrometer apparatus. At 300°K rate coefficients of (1.2 ± 0.2) × 10−12 and (2.0 ± 0.2) × 10−11 cm3/sec are found for the reactions with N2 and O2, respectively. The rate coefficients at 300°K and their variation with ion energy are in satisfactory agreement with previous results of flowing afterglow studies carried out at temperatures up to 600°K. At ion energies above ∼ 0.15 eV for O+ + N2 and ∼ 0.25 eV for O+ + O2 the rates are observed to increase sharply, a behavior anticipated on the basis of extrapolations to low energies of ion beam results. Both reactions are of particular importance in converting atomic O+ ions in the Earth's ionosphere (E and F regions) into molecular ions. The present measurements extend previous rate coefficient determinations to ion energies appropriate to F region conditions (500°K < T < 2000°K).
Shock wave measurements on solid hydrogen and argon
Authors: Lagus Peter L. , Ahrens Thomas J.
Published: February 2004

Hugoniot data for solid argon (initially at 77°K and 1 bar) and solid hydrogen (initially at 5°K and 1 bar) have been obtained to 143 kbar and 6.4 kbar, respectively, using the projectile impact method. The argon data (at volumes of 15.28, 14.84, and 14.64 cm3/mole) are in fair agreement with previous shock data, and in excellent agreement with the most recent theoretically predicted Hugoniot. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cm3/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the shock and isothermal data are self-consistent under the assumption γ/V is constant. To compressions of V/V0≈0.65, the previous isothermal compression measurements on solid hydrogen are consistent with the present shock data.
Vibrational relaxation of CO2 by O atoms
Authors: Center R. E.
Published: February 2004

The vibrational relaxation in CO2–Ar, CO2–O2–Ar, and CO2–O–O2–Ar mixtures was studied over the temperature range 2000–4000°K. Infrared emission measurements were made of the 4.3 μ asymmetric stretch mode and the 2.7 μ combination bands. Since all the modes of CO2 have been shown to exhibit the same relaxation time, the present measurements could be directly related to the relaxation rate for the translation-vibration excitation excitation of the bending mode. The experimental results indicate that O-atoms are approximately an order of magnitude more efficient than Ar in the relaxation of the bending mode with a collisional probability of the order of 10−2 at 3000°K.
S matrix elements for excited rotational state transitions
Authors: Eastes Walter
Published: February 2004

Exact S matrix elements are presented for atom-rigid rotor scattering for transitions between the j = 6, 8, and 10 rotational states. Enough channels are included in the close coupling scheme to ensure convergence. It is found that one may neglect the lower lying rotational states if one is interested only in S matrix elements for transitions between excited states.
Velocity dependence of the cross section for the quenching of Ar(3P0,2) and Kr(3P0,2) by O2
Authors: Gersh Michael E. , Muschlitz E. E.
Published: February 2004

Measurements of the velocity dependence of the absolute cross sections for the quenching of metastable Ar(3P0,2) and Kr(3P0,2) by molecular oxygen were performed using a velocity selected metastable beam and a collision chamber. The Ar(3P0,2)−O2 cross section was equal to 35 Å and was independent of velocity for average relative velocities ḡ = 500–1700 m/sec. The Kr(3P0,2)−O2 cross section decreased as ḡ−1/5 from 500–1200 m/sec with a value of 39.5 Å2 at 600 m/sec. Application of an inhomogeneous magnetic field to the metastable beam showed that the 3P0 cross sections were larger than the 3P2 cross sections by 30 ± 20% and 60 ± 30% for Ar* and Kr*, respectively.
Single crystal magnetic susceptibility measurements on the linear chain polymer copper (II) pyrazine nitrate
Authors: Losee D. Bruce , Richardson H. Wayne , Hatfield William E.
Published: February 2004

Magnetic susceptibilities have been measured in the temperature region 1.7–60°K both parallel and perpendicular to the chemical chain on single crystals of Cu(pyrazine)(NO3)2. It has been shown that there is qualitative disagreement between experiment and theory if the appropriate equations derived for the Ising model in one dimension are applied. On the other hand, excellent agreement exists for the Heisenberg model with J/k = −5.3°K down to the lowest temperature achieved, along with closer agreement between the g values determined in this experiment and those obtained by EPR. A comparison is also made between the exchange pathway in Cu(NO3)2 · 2.5H2O and the probable pathway in Cu(pyrazine)(NO3)2.
Kinetic isotope effects in the reaction of fluorine atoms with molecular hydrogen. I H2/D2 kinetic isotope effect
Authors: Persky Avigdor
Published: February 2004

The kinetic isotope effect in the reaction of fluorine atoms with H2 and D2 was measured as a function of reaction temperature in the range of 163 to 417°K. The isotope effect can be expressed as an Arrhenius type equation: kF+H2 / kF+D2 = (1.04 ± 0.02) exp[(370 ± 10)/RT]. Experiments were carried out in a flow system with direct mass spectrometric analysis of reaction products. Fluorine atoms were produced by dissociating SF6 or CF4 in a microwave discharge.
Graphlike state of matter. V. Theory of Rayleigh scattering from randomly cross-linked chains of arbitrary primary distributions
Authors: Kajiwara K. , Gordon M.
Published: February 2004

The concepts and vocabulary of graph theory provide a simpler and more systematic approach to the combinatorics of branched polymer systems than the usual ad hoc methods based on probability theory. Formulas of remarkable simplicity are derived for the experimentally accessible z -average particle scattering factor Pz (θ) of polymer distributions arising from (a) the random condensation of distributions of star-shaped monomers of variable functionality and (b) randomly cross-linked systems of arbitrary primary chain distributions (vulcanizates). As usual, the weight average degree of polymerization and the mean square radius (and higher moments) are simply obtained from Pz (θ) when the subchains obey Gaussian statistics.
Classical study of rotational excitation of a rigid rotor: Li+ + H2. II. Correspondence with quantal results
Authors: LaBudde R. A. , Bernstein R. B.
Published: February 2004

Further classical trajectory calculations of the rotational excitation of H2 in collision with Li+ have been carried out in order to assess several alternative classical-quantal correspondence relationships. The results are compared with exact quantal cross sections computed for the same model system by Lester and Schaefer.
Study of laser-supported detonation waves by time-resolved spectroscopy
Authors: Wei P. S. P. , Hall R. B. , Maher W. E.
Published: February 2004

Temporal developments of sparks generated by a pulse CO2 laser from solid surfaces in air have been studied by time-resolved spectroscopy in the range from 3800 to 6200 Å. The plasma front appears to be a detonation wave during the early part of the pulse when the laser intensity exceeds about 2 × 107 W/cm2. With decreasing laser intensity, the plasma which contains N+ and O+, expands both forwards and backwards to become a luminous column in a way similar to the combustion wave described by Raizer. Stimulated emission from AlO has been observed in the vapor from an alumina sample.
Role of attractive forces in self-diffusion in dense Lennard-Jones fluids
Authors: Kushick Joseph , Berne Bruce J.
Published: February 2004

The Lennard-Jones potential is separated into a purely repulsive and a purely attractive part, VR and VA, respectively. The velocity correlation function (vcf) is computed by molecular dynamics separately for (VR + VA) and for VR in both isotropic and nematic liquids for several thermodynamic states. It is found that in dense fluids, the results for these two different potentials are in qualitative agreement. The role of the attractive force is discussed. This work is motivated by the recent success of perturbation theories in connection with the equilibrium properties of fluids.
Triplet transfer integrals in aromatic hydrocarbon crystals. Influence of nonorthogonality corrections
Authors: Tiberghien A. , Delacote G. , Schott M.
Published: February 2004

The influence of different choices of atomic and molecular wavefunctions, the role of multicenter integrals, and the effect of intermolecular orthogonalization on calculated triplet Davydov splitting in aromatic crystals have been studied. It is shown that the influence on the charge-transfer configuration is dominant.
Dynamical aspects of helix-coil transitions in biopolymers. II
Authors: Tanaka Toyoichi , Wada Akiyoshi , Suzuki Masuo
Published: February 2004

A dynamical theory of the helix-coil transitions in polypeptides and in polynucleotide-polynucleotide complexes with arbitrary lengths is presented, which uses an Ising model in a static magnetic field. From time-dependent spin correlations calculated, it is shown that quite similar modes of the helix-coil transitions are mainly contributing to all experiments of NMR, tritium-hydrogen exchange, sonic measurements, and temperature-jump methods. Thus the explanation for the variety of orders of relaxation times obtained in these experiments rests on other causes, such as polydispersity of polypeptides or solvating effects.
Relative contributions of ΔJ = 2 and ΔJ = 1 transitions in rotationally inelastic collisions of polar molecules
Authors: Verter Michael R. , Rabitz Herschel
Published: February 2004

Previously developed first- and second-order semiclassical perturbation theory is employed to treat rotationally inelastic collisions between pairs of linear molecules. The dependence of the cross sections σ (ΔJ = 1) and σ(ΔJ = 2) on the rotational constants, dipole and quadrupole moments, and reduced masses of the colliding molecules is investigated. It is shown that the rotational constant has a dominant role in determining the relative magnitude of the cross sections ΔJ = 2 compared to ΔJ = 1. Much of the observed cross section behavior can be explained through collisional resonance effects. The conditions for significant ΔJ = 2 transitions are discussed and illustrated with rotational transitions in the molecules HF, HCl, DCl, HBr, OCS, HCN, ClCN, and BrCN. Each of these molecules interacted with a thermal bath of molecules of the same species. Results are also presented for the systems HCl:DCl and DCl:HCl where the first molecule in each pair is the observed species. The resulting cross section ratios σ(ΔJ = 2)/σ(ΔJ = 1) in these studies ranged from 0.14 for HF to 0.73 for DCl:HCl.
Influence of electron capture decay of 57Co on the Mössbauer emission spectrum of hydrated cobalt chlorides
Authors: Friedt J. M. , Shenoy G. K. , Abstreiter G. , Poinsot R.
Published: February 2004

The Mössbauer emission spectra of 57Co in CoCl2 · 2H2O and CoCl2 · 6H2O measured from 1.6 to 300 °K exhibit both the divalent and the trivalent charge states of 57Fe associated with numerous defect configurations. A close comparison of these spectra with the absorption spectra of 0.1 at.% 57Fe in the same hydrated cobalt chloride hosts is made. We demonstrate that the anomalous charge states and the defect species are a consequence of the self-radiolysis of the water ligands by the low energy electrons and x rays produced from the electron capture decay. The experiments in the antiferromagnetic state of these compounds suggest that the damage occuring from the self-radiolysis in the neighborhood of the decaying ion breaks the magnetic superexchange paths.
Kinetics and statistics of occupation of linear arrays. A model for polymer reactions
Authors: Boucher Ernest A.
Published: February 2004

A model has been analyzed for the kinetics by which a one-dimensional array of m sites, representing polymer substituents (pendant groups), reacts (or the sites become occupied) with a mechanism randomly and irreversibly involving three adjacent sites at a time. Equations are derived for the time dependence (a) of the number Nx of sequences obtaining x unreacted substituents, (b) of the extent ξ of reaction, and (c) of the rate ξ̇ of reaction. (The analysis could equally well represent occupation of an array of sites.) Results are given for arrays initially containing a finite as well as an infinite number m of unreacted substituents. In the limit of reaction, t → ∞, a fraction 0.17635 of the substituents become isolated as singletons or in pairs for infinitely long arrays. Of this fraction, the proportion in pairs is 2e−3 (= 0.09957). It is suggested that in addition to being relevant to intramolecular reactions of polymers, the results may be applicable to reactions of, or interactions involving, two-dimensional systems, e.g., spread monolayers, where molecular packing produces parallel one-dimensional arrays. A similar kinetic description would also result from a mechanism where reaction of one substituent renders unreactive its two adjacent neighbors by, for example, an umbrella effect.
Midinfrared spectra of the plastic crystal phases of t -butyl bromide-h9 and -d9
Authors: Bertie John E. , Sunder Sham
Published: February 2004

The midinfrared spectra of the two plastic phases of t -butyl bromide are identical to each other and are very similar to that of the liquid, except for small decreases in the half-widths of the bands as the temperature is lowered. It is shown that molecular reorientation and intermolecular vibrational coupling contribute to the half-widths, and the residual width is attributed to site effects.