bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR modulation-spectrum study of an x-ray irradiated fused quartz
Authors: Swann Jack T. , Miyagawa Ichiro
Published: July 2002

The modulation-spectrum method which had previously been developed in the audiofrequency range for double modulation was extended to the radiofrequency range for triple modulation. The new method was applied to the case of an x-ray irradiated fused quartz, finding evidence for an inhomogeneous distribution of the E′ centers. In addition, a new modulation was observed, which was attributed to a noninstrumental source. Moreover, strong evidence was found for the inequivalence of magnetic field sweep and modulation-frequency sweep.
Thermodynamic behavior of the structures and magnetic order of O2 monolayers on graphite
Authors: Duparc O. M. B. , Etters R. D.
Published: July 2002

A Monte Carlo procedure with continuously deformable boundary conditions is used to calculate the thermodynamic behavior of O2 monolayers on graphite. At temperatures 0≤T≤11.9 K, the predicted structural and magnetic properties of the equilibrium high density monolayer is exactly as is observed for ε-O2 and, at T=11.9±0.1 K, a structural and magnetic phase transition into the zeta phase triangular structure with quasihelical magnetic order is predicted. The calculated low density structure is identical to the observed δ phase in the range 0≤T≤14 K, above which orientational disorder occurs, apparently contrary to experimental observations. It is shown that the magnetic character can be understood in terms of a series of nearly uncorrelated, linear, antiferromagnetic chains along the monolayer b axis. A discussion of the success and failures of this calculation and the conclusions that can be drawn from it, is presented.
Electrostatic interactions in three-dimensional solids. Self-consistent Madelung potential (SCMP) approach
Authors: Ángyán János G. , Silvi Bernard
Published: July 2002

A revised formulation of the self-consistent Madelung potential method in terms of a nonlinear Schrödinger equation, analogous to that used in solvent effect theories, is presented. It is shown that the corresponding Hartree–Fock equations can be derived from a description of the crystal wave function by a Hartree product, involving single determinental wave functions of unit motifs, related by symmetry. Earlier calculations using a point charge approximation to the Madelung potential, instead of to the electrostatic interaction energy, lead to variationally incorrect electronic wave functions. An improved method is presented where the Coulomb interactions with the environment are approximated either by Mulliken, or by Löwdin net atomic charges in a consistent manner. The method has been applied to hydrogen fluoride and carbon dioxide molecular crystals.
Bulk properties of two-phase disordered media. IV. Mechanical properties of suspensions of penetrable spheres at nondilute concentrations
Authors: Torquato S. , Lado F. , Smith P. A.
Published: July 2002

We derive rigorous upper and lower bounds on the bulk and shear moduli of suspensions of spheres of variable penetrability distributed throughout a matrix (or fluid), for all possible phase property values, through second order in the sphere volume fraction φ2. The bounds, at the very least, capture the salient qualitative features that come into play when particles overlap, and, in some instances, are shown to be quantitatively very sharp. Among other results, we use these bounds to obtain good estimates of the bulk and expansion viscosities of an incompressible fluid containing spherical air bubbles and thus extend the corresponding results of Taylor in which pair interactions were neglected.
Infrared investigation of hydrogen bonding on the surface of beryllium fluoride glass
Authors: Walrafen G. E. , Klein P. H.
Published: July 2002

Infrared absorbance spectra were obtained from a dry BeF2 glass surface, and from the same surface after exposure to moist air. No absorbance resulted from the dry surface, but an intense, broad, structured contour having maximum absorbance near 3170±20 cm−1 was produced by the wetted surface. Continuous evaporation for 905 days at 15 mTorr and room temperature was then carried out, as the integrated absorbance of the 3170 cm−1 contour was measured relative to the intense, sharp 3690±5 cm−1 absorbance from internal Be–OH groups. The 3170 cm−1 contour is thought to arise from the combined stretching vibrations of surface Be–OH⋅⋅⋅F−⋅⋅⋅H–OH+2(H2O)2(H2O)n units. In these, the primary hydration sphere of H3O+ contains two H2O molecules and one F− ion, all strongly bound, and the second hydration sphere contains up to six H2O molecules, n≤6. Upon evacuation, the second-sphere H2O molecules are removed consecutively, but the two primary-sphere H2O molecules, and the very strong F−⋅⋅⋅H hydrogen bond are unaffected. The relative integrated 3170 cm−1 absorbance AT was observed to decrease at a decreasing rate by a factor of about 2.5 after 50 days of pumping, and then to decline to ∼20% of the t=0 absorbance, upon pumping for 905 days. The temporal behavior of A was found to fit first-order kinetics of the form −(dA/dt)=[0.244 045/(1+t)]A. Here, [0.244 045/(1+t)]=B exp(−∼(ΔH)/RT), where B=9.65×105 d−1 at 298.15 K. ∼(ΔH) is the species-dependent, and therefore time-dependent, enthalpy in cal mol−1, and t is the pumping time in days.
Comment on: ‘‘A recoupled states approximation for molecular scattering theory’’
Authors: Hahne G. E.
Published: July 2002

Two aspects of the coupled states (CS) and the recoupled states (RCS) formalism of K. McLenithan and D. Secrest [J. Chem. Phys. 80, 2480 (1984)] are discussed. First, there is an inconsistency, in that the Lippmann–Schwinger equation (51) implies, contrary to Eq. (21), that the CS wave function satisfies an inhomogeneous differential equation. This inconsistency is removed, and Eq. (54) is made exact, by the addition of a suitable term to the right-hand side of Eq. (51). Second, the CS-RCS formalism of McLenithan and Secrest defines zeroth- and first-order approximate transition operators; it is argued that the proper functioning of their formalism depends essentially on the use of a physically obscure l-labeling prescription for the determination of S matrices, and lacks uniqueness in that an alternative formalism exists that hews more closely to a strict perturbation theory approach for the zeroth- and first-order approximations to the exact transition operator.
Exact analysis of polycrystalline electron spin echo modulation. II. Model calculations and application to irradiated methanol
Authors: Iwasaki Machio , Toriyama Kazumi , Nunome Keichi
Published: July 2002

To assess the ordinary analysis of polycrystalline electron spin echo modulation (ESEM), in which the mutual nuclear arrangements are completely neglected, a correct angular integration for the polycrystalline samples has been performed including the mutual nuclear arrangements as well as the nuclear quadrupole interaction (nqi) based on the general spin Hamiltonian in an arbitrary coordinate system and the results are compared with those calculated by the spherical approximation. The model calculations by the advanced method indicate that the geometry dependence of the ESEM pattern is considerably enhanced when the nqi term is included, suggesting the necessity of the correct angular integration, especially for the system involving the nqi term. A more reliable local geometry may be expected to be determined by the advanced method. To demonstrate the application of the advanced analysis the radiation damage of irradiated crystalline methanol has been studied by the ESEM method.
An extended theoretical formulation of the circular dichroism band shape of chromophore aggregates by use of the ensemble-averaged resolvent matrix method
Authors: Kamiya Mamoru
Published: July 2002

A new theoretical formulation is given to the circular dichroism band shape of chromophore aggregates by means of the ensemble-averaged resolvent matrix method. This formulation can be used to calculate the circular dichroism band shape of chromophore aggregates having arbitrary strengths of the excited-state interactions between chromophores. Using the resolvent expansion rule, thermal and static effects upon the circular dichroism band shape are incorporated as the mean-frequency shifts of the normalized band shape functions used for ensemble averaging the resolvent matrix of chromophore aggregates. This formulation is applied to derive a generalized band shape expansion formula which gives a theoretical justification to the practical first-order Taylor expansion equation used to calculate the circular dichroism band shape of chromophore aggregates. Basic properties of the generalized band shape expansion formula are investigated by comparing it with the usual perturbation expansion equation for the circular dichroism band shape of chromophore aggregates.
Laser spectroscopic study of defect equilibria in SrCl2
Authors: Wietfeldt John R. , Wright John C.
Published: July 2002

The site distribution of the different charge compensated sites in singly doped samples of SrCl2:Eu3+ and doubly doped samples containing a second rare earth ion has been measured by site selective laser spectroscopy for a range of different dopant concentrations and annealing temperatures. The site distribution exhibits the same anomalous behavior as was observed in alkaline earth halide crystals as long as the dopant levels are not too low. At very low dopant levels, the anomalous behavior is not observed and the dependence follows that expected for simple mass action descriptions of defect equilibria. An association constant is obtained at the low concentrations and it is found that the amount of association is much less than would be expected from theoretical estimates based on Harwell automatic defect evaluation system (HADES) models. Extensive clustering is observed at lower concentrations than in the alkaline earth fluorides. The number of different clusters and the types of clusters do not appear to have a strong dependence on the ionic radius of the dopant ions as would be expected from HADES calculations. The anomalous site distributions at the higher concentrations are attributed to additional interactions between defect structures that result from strain interactions. Since these interactions lead to concentration dependence of the free energy of formation for the different defect sites, it will be necessary to include these effects in models that are used to predict the relative dominance of different sites.
Optical–optical double resonance and double resonance multiphoton ionization in 7Li2 produced by single cw dye laser excitation
Authors: Balz J. G. , Bernheim R. A. , Gold L. P.
Published: July 2002

A comparison of fluorescence detection of optical–optical double resonance transitions with ionization detection of double resonance multiphoton ionization signals was made for Li2 vapor. The spectra in both cases were excited by a single broadband (30 GHz) cw dye laser and exhibited identical features. These arise from ‘‘accidental’’ two-photon double resonance transitions via real intermediate states and consist of hundreds of distinct transitions in the region 565–645 nm studied in this work. Analysis and assignment reveal that multiphoton excitations within the singlet manifold of electronic states of Li2 together with intermediate state rotational relaxation can account for the spectra. A table of vibrational and rotational assignments of the more intense features is available which includes a comparison between calculated and observed intensities for the transitions.
A time-domain EPR study of the SO−3 combination reaction: Radical pair CIDEP without singlet–triplet mixing
Authors: Bartels D. M. , Lawler R. G.
Published: July 2002

The radical ion ⋅SO−3 was studied by in situ pulsed radiolysis of aqueous alkaline sodium sulfite solutions in a pulsed EPR spectrometer. Initial radical concentrations on the order of 5×10−4 M were generated, and detailed measurements of the decay of ⋅SO−3 magnetization were performed on the microsecond time scale. It was found that the second order decay of both longitudinal and transverse magnetization lags behind the second order decay of radical population when the reaction rate approaches the relaxation rates 1/T1,2. The observations may be explained in terms of the spin-pairing requirements for formation of a singlet reaction product. The spin pairing gives rise to a ‘‘passive’’ form of radical pair mechanism (RPM) chemically induced dynamic electron polarization (CIDEP) which has previously gone unrecognized. RPM polarization therefore occurs in ⋅SO−3 encounters despite the lack of hyperfine dependent singlet–triplet mixing between radical reencounters, which is necessary for the accepted RPM mechanism. The implications of these observations for the interpretation of time-resolved EPR experiments are discussed.
A theoretical electron density study of potassium hydrogen diformate KH(HCOO)2
Authors: Taurian O. E. , Lunell S. , Tellgren R.
Published: July 2002

The deformation electron density of KH(HCOO)2 has been studied from quantum mechanical ab initio MO-LCAO-SCF calculations and compared with X–N maps obtained at 120 K. The two formate groups are connected with a short noncentered hydrogen bond (2.437 Å). The deformation density in the covalent bonds and in the hydrogen bond is discussed and compared to results obtained from similar molecules. The nature of the hydrogen bond is found to be best described as a proton shared between two acceptors. The effect of the crystal field has been calculated and illustrated in double difference maps. The relation between the observed charge flow and the noncentered nature of the hydrogen bond is discussed.
Comment on ‘‘Accurate analytic model potentials for D2 and H2 based on the perturbed-Morse-oscillator model’’
Authors: Wright James S.
Published: July 2002

Huffaker and Cohen (ref.1) claim that the perturbed−Morse−oscillator (PMO) model, for the potential energy function for hydrogen, gives very high accuracy results; surpassing that of the RKR potential. A more efficient approach to formulating analytical functions based on the PMO model is given, and some defects of the PMO model are discussed.(AIP)
Flow induced transitions in smectic liquid crystals
Authors: Condat C. A. , Thirumalai D.
Published: July 2002

The effects of an elongational flow field on the liquid crystalline A–C and N–A phase transitions are investigated using a mean field approximation. The presence of the flow is shown to make the A–C transition sharper; it becomes first order at high strain rates. The N–A transition is weakened because the flow makes the nematic range effectively wider. It is also shown that the theory presented here can be used to analyze the effects of constant external electric field gradients on a system of molecules which do not have permanent dipole moments.
Molecular hyperfine interactions in Ag(CO)3
Authors: Arratia-Perez Ramiro , Marynick Dennis S.
Published: July 2002

Relativistic molecular orbital calculations in the multiple scattering approximation are reported for silver tricarbonyl, and comparisons are made to optical absorption and electron spin resonance spectra. Spin–orbit effects are modelled through the Dirac scattered-wave (DSW) formalism. Spin–polarization effects are estimated from quasirelativistic spin-unrestricted calculations. The influence of different local density potentials on the spin distributions and hyperfine tensors are examined. The calculations show good agreement with optical spectral data and with the observed 107Ag and 13C hyperfine tensors. The use of relativistic exchange–correlation potentials in calculating spin-dependent properties leads to a slightly better agreement with experiment. The calculations predict that the unpaired electron in Ag(CO)3 has about 40% silver 5pz character.
Theoretical determination of the radiative lifetime of the A 2Σ+ state of OH
Authors: Bauschlicher Charles W. , Langhoff Stephen R.
Published: July 2002

The radiative lifetime of the A 2Σ+(v′=0, N′=1) state of OH has been computed, using the theoretical potentials and transition moment, to be 673 ns, in excellent agreement with two of the experimental values (686±14 and 693±10 ns) determined by laser excitation fluorescence. The electron correlation treatment has been calibrated using full CI (FCI) calculations in a [4s3p2d/2s1p] Gaussian basis set. When a δ orbital is included in the CASSCF/MRCI treatment, the transition moment is within 0.2% of the FCI value. A basis set study shows that the [6s5p4d2f1g/4s3p2d] ANO basis set employed in our study is probably within 1% of the basis set limit for the transition moment. The theoretical radiative lifetimes, which are expected to be lower bounds and accurate to 2%, are sufficiently accurate to rule out the slightly lower value determined by Hanle effect studies, and the higher values determined for the v′=0 N′=1 level by the high frequency deflection technique (HFD). The HFD lifetimes for higher N′ values, however, are in relatively good agreement with theory.
The nuclear quadrupole moment of 14N. A theoretical prediction from full valence shell and full configuration interaction atomic wave functions
Authors: Scuseria Gustavo E. , Schaefer Henry F.
Published: July 2002

Full configuration interaction ab initio studies of the 2p 3p 1P1 state of N+ are carried out in order to obtain the molecular electric field gradient at the nitrogen nucleus. A careful calibration of the basis set leads to a q value (−0.94 a.u.) obtained using a 〈13s9p5d2f/10s7p5d2f〉 basis set with an estimated accuracy of ±0.01 a.u. Combined with the experimental nuclear quadrupole coupling constant for this system, we predict the nuclear quadrupole moment of 14N to be Q(14N)=(20.7±0.4) mb.
Close packing of spheres
Authors: Williams D. E. G.
Published: July 2002

The local environment of an ‘‘origin’’ sphere in an assembly of spheres may be represented by a Voronoi polyhedron or by a polyhedron of simplicial lines. These figures may be projected on to a spherical surface of contacts1 and this representation is used here to examine the number of spheres of one diameter which can be packed regularly in contact with an origin sphere of the same or other diameters. The restriction that in the packings the spheres contacting the origin sphere also make contact with all their neighbor spheres in the contacting shell allows only 15 configurations in the range of radius K (radius of origin sphere/radius of contacting sphere), 0.225<K<8.8. The relationship of two of these configurations and the possible structure of the C60 molecule is examined. The reason why a previous model of random close packing produced answers which agreed well with experimental values only for some values of K is revealed.
Hydrophobic effects in the water network structure of aqueous solutions of a semiclathrate molecule
Authors: Green J. L. , Sceats M. G. , Lacey A. R.
Published: July 2002

In-phase collective small amplitude proton motions are observed in the OH stretching Raman spectrum of the semiclathrate crystalline hydrate of tetra-n-butyl ammonium hydroxide, its melt and aqueous solutions. These are quantified and used in dilute solutions as a probe of the network structure of water surrounding the molecule. Clear evidence of structural enhancement of the network is obtained in dilute solutions as well as the destruction of the network by hydrophobic interactions as the concentration is increased. Evidence for change of molecular conformation, suggesting intramolecular hydrophobic interactions, is obtained from the CH stretching spectra.
Effect of zero-point motion on μ+–19F dipole coupling in the FμF− ion in fluoride insulators
Authors: Noakes D. R.
Published: July 2002

A simple harmonic-potential argument is used to provide a first estimate of the ground state muon zero-point motion in the FμF− ion on the basis of the FHF− and FDF− ions in solids. A cutoff-dependent estimate of the ground state μ+–19F dipole coupling indicates that the motion causes a small increase in coupling over the fixed point-dipole value. The smallest observed F–F separation through μ+, deduced from muon spin relaxation (μSR) in CaF2, is then slightly larger than expected.
Comment on ‘‘Molecular overlap integrals with exponential-type orbitals’’
Authors: Weniger E. Joachim , Steinborn E. Otto
Published: July 2002

A recent article by A. K. Bhattacharya and S. C. Dhabal [J. Chem. Phys. 84, 1598 (1986)], dealing with the fast and accurate evaluation of molecular overlap integrals with exponentially declining atomic orbitals, is analyzed critically. It is shown that some of their analytical results can be improved, and that some others are already known in the literature. Concerning their numerical investigations, it is shown that Gauss–Jacobi and not Gauss–Legendre quadrature should be used for the evaluation of the one-dimensional integral representation for overlap integrals with different scaling parameters.
Dynamical analysis of lattice mode frequencies, specific heats, sound velocities, and Debye temperature of δ and ε-phase O2 monolayers on graphite
Authors: Kirin D. , Kuchta B. , Etters R. D.
Published: July 2002

Based upon structural and magnetic properties determined in a previous work, a lattice dynamics calculation of the lattice mode frequencies, dispersion curves, specific heats, sound velocities, and Debye temperature of δ and ε-phase O2 monolayers on graphite is conducted. The calculated lattice specific heat of the δ phase is in good agreement with experiment but, for ε-O2, the predicted results fall between two independently measured sets of data with differences that cannot be presently explained. The predicted sound velocities for different propagation vectors show that both δ and ε-O2 are nearly isotropic, elastically.
Higher-order adiabatic separation of strongly coupled systems. II. Generalized Hénon–Heiles Hamiltonian
Authors: Tung Nguyen-Dang T.
Published: July 2002

The phase corrected adiabatic approximation [Y. Maréchal, J. Chem. Phys. 83, 247 (1985); T. T. Nguyen-Dang and A. D. Bandrauk, J. Chem. Phys. 85, 7224 (1986)], is applied to obtain a second-order adiabatic representation for the generalized Hénon–Heiles system. This representation provides a formal link between nonintegrable Hénon–Heiles systems and the integrable anti-Hénon–Heiles system, for which the representation denotes exact separability in terms of normal coordinates q1=(1/√2)(x+y), q2=(1/√2)(x−y). In the nonintegrable cases, the representation denotes a higher-order adiabatic separability of the two coupled modes of the Hénon–Heiles systems, as its basis states are unitarily equivalent to Born–Oppenheimer-type product states, and are coupled only by residual couplings that are of second-order in the original coupling constant λ.
A computational study of the x-ray satellite spectrum of NH3
Authors: Brammer Ronald
Published: July 2002

Calculations of total energies of neutral and of singly and doubly ionized ammonia have been performed using restricted Hartree–Fock and complete active space multiconfiguration self-consistent field formalisms. Transition energies and ionization potentials based on energy differences of these calculations are presented and compared with existing experimental and theoretical results. Satellite structure unexplained in the previously published x-ray emission spectra is here explained, based on the new calculations.
The statistical mechanical theory of concentration fluctuations in mixtures
Authors: Debenedetti Pablo G.
Published: July 2002

A general theory of concentration fluctuations in mixtures is derived. The resulting expressions, which include the Kirkwood–Buff theory as a particular case, relate different partial molar properties to a single combination of molecule number fluctuations within differently defined subsystems. The formalism, therefore, gives rise to a common definition for partial molar energies, volumes, enthalpies, and entropies in terms of molecule number fluctuations exclusively. Likewise, a second function of molecule number fluctuations describes both the mixture’s isobaric specific heat as well as its isothermal compressibility. The partial molar energy and enthalpy definitions, moreover, suggest new methods for the study of mixture properties via computer simulations.
A self-consistent theory of laboratory frame cross correlation functions
Authors: Evans M. W.
Published: July 2002

A theory is developed for laboratory frame cross correlation functions detected recently by computer simulation. It is based on the concept of itinerant oscillation as developed by Coffey et al., and for the first time provides a self-consistent analytical description of numerically observed laboratory frame time cross correlation functions in molecular matter.
Analytic representation of secondary-electron spectra
Authors: Inokuti Mitio , Dillon Michael A. , Miller John H. , Omidvar Kazem
Published: July 2002

The secondary-electron spectrum, or the energy distribution of the ejected electrons resulting from charged-particle impact, is a crucial input to the microscopic modeling of radiation actions. The present article shows a general method for systematizing a bulk of data on the secondary-electron spectrum into a small number of indices. Our method is based on firm theoretical grounds, i.e., on thorough examination of the mathematical physics that governs the secondary-electron spectrum. We present several examples of the analysis of recent experimental data for proton impact.
A new family of Langmuir–Blodgett films of tetracyanoquinodimethane charge transfer salts: Pristine and iodine doped conducting films
Authors: Vandevyer M. , Richard J. , Barraud A. , Ruaudel-Teixier A. , Lequan M. , Lequan R. M.
Published: July 2002

A new family of semiamphiphilic tetracyanoquinodimethane (TCNQ) ionic salts of nonconjugated cations, namely octadecyl-dimethylsulfonium, octadecyl-methyl-ethyl-sulfonium, and octadecyl-trimethylphosphonium labeled a, b, and c, respectively, has been synthetized. Langmuir–Blodgett (LB) films are built up from these three compounds, which are mixed with octadecylurea in a molar ratio 1/1, in order to improve the stability of the film at the water surface. The structural properties of the transferred films are thoroughly investigated by linear dichroism in the IR and UV–visible ranges, together with ESR spectroscopy. In the films of the three compounds, the polar sheets contain (TCNQ− • )2 dimers, which are the largely prevalent species. The molecular planes of these dimers are found to be roughly parallel to the substrate. Moreover, a strong in-plane orientation of the dimers is found in films of compound c. This phenomenon is thought to be related to an overall flow orientation of rod-shaped crystallites in the floating film, during the high speed downstroke of the substrate across the film. Advantage is taken from the high and well-controlled thinness of LB films to make iodine vapor diffuse into the films and convert the precursor films into conducting ones. The iodination process leads for the three salts to a stable ternary conducting compound located in the polar planes of the LB assembly. Correlatively, it induces a strong molecular reorganization in the films: the TCNQ molecules stand on edge with their long molecular axis perpendicular to the substrate. In spite of this considerable rearrangement arising from iodination, we notice that the strong in-plane anisotropy observed in pristine films of c is retained in conducting films of the iodinated c compound. Beside these structural results,

the IR spectra of conducting films are reminiscent of these of highly conducting, but not metallic-like, organic conductors. The conductivity of the films is estimated from their IR spectra and found to be 20–50 Ω−1 cm−1. However, dc conductivity measurements provide a value at least ten times lower than the one estimated from IR spectra. This behavior is likely related to the polycrystalline nature of the films whose macroscopic inhomogeneities are evidenced by scanning electron microscopy.
Electric dipole moment of molecules of ellipsoidal shape determined from dielectric measurements
Authors: Makosz J. J.
Published: July 2002

An equation was derived for calculating dipole moments from dielectric measurements in dilute solutions of dipole molecules in nonpolar solvents. For this purpose the Onsager formula, as generalized by Scholte, was applied for molecules of ellipsoidal shape. The expression obtained was verified using experimental data from earlier studies and also from literature data. In each case good agreement was found between values of dipole moments calculated from dielectric measurements and those measured for molecules in the vapor phase.
Computer modeling of molecular liquid mixtures. II. The excess properties of a diatomic Lennard-Jones model mixture for CO2/C2H6
Authors: Fincham D. , Quirke N. , Tildesley D. J.
Published: July 2002

A recent study of the CO2/C2H6 liquid mixtures has been extended to calculate the excess volume, excess enthalpy, and excess Gibbs free energy. An additional 60 molecular dynamics simulations were performed to calculate the excess properties accurately. Although the model gives accurate densities for the coexisting liquid mixtures at 269.25 K, the agreement with experimental excess properties is poor. The excess properties have the correct sign, but are too large (by a factor of 4 in the case of the excess volume). These differences are attributed to the model for CO2 which gives a coexisting pressure ∼1.2 MPa below its experimental value.
SANS studies of concentrated protein solutions: Determination of the charge, hydration, and H/D exchange in cytochrome C
Authors: Wu Chuan-Fu , Chen Sow-Hsin
Published: July 2002

Small angle neutron scattering (SANS) was used to study a series of concentrated protein solutions containing horse heart cytochrome C ranging from 0.6 to 24 g/dL at two ionic strengths. Since the solutions were manifestly nonideal throughout the whole concentration range, a contrast variation method applicable at finite Q (magnitude of the scattering vector) was applied to extract three basic properties of the protein in mixed D2O/H2O solutions at a concentration of 12 g/dL. These properties are the dry volume, the hydration, and the amount of H/D exchange of the protein in D2O-containing solvents. These three basic parameters were then used as an input to extract the protein charge at all other concentrations. A generalized one-component macroion theory (GOCM) was used to compute the interparticle structure factor for a given protein charge, Zp. The Zp ’s so obtained are in good agreement with a separate titration experiment which determines the surface charge of the protein in the solutions. We show that Zp is a constant at a given pH value (pH=6.8) independent of the concentration of protein.
Constant electronic energy trajectories in abstract nuclear charge space and level set topology
Authors: Arteca Gustavo A. , Mezey Paul G.
Published: July 2002

The boundaries defining the electronic energy level set topologies in abstract nuclear charge space NZ of molecular systems are analyzed. Several rigorous properties are derived, from which new results on geometry-independent constraints of electronic energy hypersurfaces are obtained. The asymptotic behavior of the boundaries at atomic pairwise–infinite separation is approximated making use of density functional theory. The relationships obtained for such a boundary allow one to evaluate very simply (just with a pocket calculator) upper and lower bounds to the electronic energy which are of interest in the study of chemical reactions and conformations. The procedure is also applied to discuss the feasibility of certain molecular ionization processes, as well as to derive some inequalities concerning atomic ionization potentials.
Solvent structure effects in the macroscopic theory of van der Waals forces
Authors: Podgornik Rudi , Cevc Gregor , Žekš Boštjan
Published: July 2002

The theory of van der Waals forces is generalized in order to include the effects of solvent structure by explicitly dealing with the spatial correlations between the solvent molecules. This is achieved within the framework of nonlocal dielectric response theory, with the specular reflection approximation to apply the nonlocal response of the structured solvent in the bulk to give the response of such solvent intercalated between the interacting macroscopic surfaces. A closed form expression for the zero-order contribution to the van der Waals free energy is derived for two semi-infinite dielectric regions (characterized by a standard, local dielectric response and fixed dielectric constant), interacting across a layer of a structured solvent described by a nonlocal dielectric response function. The nonlocal character of the latter gives rise to several quantitatively and qualitatively new features of the dispersion interaction; the most important ones are similar in consequences to the effects of spatial variation of the Hamaker coefficient, as seen from the particular case of solvents with an exponentially decaying spatial intersolvent correlations.
Polydispersity probed by light scattering of secondary particles in controlled growth experiments of silica spheres
Authors: Philipse A. P. , Vrij A.
Published: July 2002

From dynamic light scattering measurements of diluted silica dispersions formed in controlled growth experiments we obtained effective diffusion coefficients De(K) which exhibit a pronounced maximum as a function of the scattering vector K. The maximum is due to the presence of particles much smaller than the grown particles and which are formed in a secondary nucleation. It appears that De(K) is a sensitive probe for the presence of the small particles. From both theory and experiment we conclude the following. (1) The maximum is a consequence of small particle scattering at a K value where the scattering of the large particles is at a minimum. (2) The magnitude of the maximum is a sensitive measure of polydispersity in size of the large particles. Similar conclusions are drawn from measurements of the second cumulant Q(K). This function provides a measure of the width of the distribution of diffusion coefficients. Its K dependence curve shows a very peculiar shape, due to the presence of the small particles. This shape is also predicted theoretically.
Liquid GeBr4. I. A test of the anomalous x-ray scattering method as applied to disordered materials
Authors: Ludwig K. F. , Warburton W. K. , Wilson Lane , Bienenstock A. I.
Published: July 2002

This study tested the accuracy of the anomalous x-ray scattering technique as part of an investigation of the molecular liquid GeBr4. The differential anomalous scattering technique proved to be quite accurate, giving nearest-neighbor coordination distances and numbers correct to 0.02 Å and 4%, respectively, as compared with known values. The high accuracy of the approach evidently depends on a cancellation of systematic errors when subtracting data sets at two nearby photon energies. The straightforward three-wavelength approach to determining the partial-distribution functions is quite ill conditioned and small experimental errors cause large errors in the resulting partial distribution functions. An alternate procedure, suggested by Munro, uses differences to determine the partial distribution functions (PDF’s) and hence takes advantage of the cancellation of systematic errors. This approach yields Br–Br, Ge–Br, and Ge–Ge PDF’s with error levels of approximately 5%–10%, 30%, and 100%, respectively. Singular value decomposition of the weighting matrix can be used to predict the relative accuracies of the three PDF’s before experimentation.
Ellipsometric study of critical adsorption at the surface of a polymer solution: Evidence for a slowly decaying interfacial profile
Authors: Heidel Barbara , Findenegg Gerhard H.
Published: July 2002

We have measured the coefficient of ellipticity ρ̄ of light reflected at the free liquid surface of solutions of polystyrene (M̄w=110 000) in cyclohexane near the upper critical solution point of the system. At the critical composition φc it is observed upon approaching the critical solution temperature Tc from above that the ellipticity exhibits a finite maximum (ρ̄max) about 0.4 K above Tc. This behavior can be explained semiquantitatively in terms of the increasing width of the interface, which is proportional to the correlation length ξ of composition fluctuations in the bulk liquid and diverges with ξ on approaching Tc. The calculation of ρ̄ starts from a dielectric profile function ε(z) which models the short-ranged number density profile of the surface and the superimposed slowly decaying composition profile from the surface into the bulk solution. The ellipticity is obtained by a numerical algorithm originally developed for calculating the reflection properties of stratified dielectric media. The temperature dependence of ρ̄ for samples of concentrations higher and lower than φc, above and below the phase separation temperature, is also discussed in the light of these calculations.
Interaction potentials and mobility calculations for the HeO+ system
Authors: Simpson R. W. , Maclagan R. G. A. R. , Harland P. W.
Published: July 2002

Valence bond, SCF, and MP4SDQ calculations are reported for three low lying states of the HeO+ molecular ion; 4Σ(4S), 2Π(2D), and 2Π(2P). Together with the two-temperature theory of ion transport, these interaction potentials have been used to calculate the drift velocity and reduced mobility of O+ in helium as a function of the electric field to gas number density ratio. The calculated HeO+(4Σ) interaction potentials adequately describe the mobility of ground state O+ in helium, however, the O+(2D) mobility calculated using the 2Π(2D) interaction potential does not match the experimental mobility measurements for the metastable O+* ion which have been reported as the O+(2D) state. An interaction potential is reported for HeO+[2Π(2P)] which will reproduce the experimental mobility of O+*.
Near threshold ionization effects in the Ge L2M2,3M4,5 and L2M4,5M4,5 Auger spectra of volatile germanium compounds
Authors: Venezia Anna Maria , Vayrynen I. Juhani , Cavell Ronald G.
Published: July 2002

The proximity of the L2 (2p1/2) ionization potential in germanium compounds to the MgKα radiation energy introduces threshold ionization effects in the Ge LMM Auger spectra derived from this level. The spectra of GeH4, Ge(CH3)4, Ge(C2H5)4, GeF4, and GeCl4 excited with MgKα radiation are compared with those excited with AlKα radiation and post-collision interaction (PCI) and spectator satellite effects induced are analyzed. Comparison of L2,3M2,3M4,5 and L2,3M4,5M4,5 spectra reveal a final state dependence of the satellite shifts.
Critical properties of the uniaxial–biaxial transition in micellar nematic phases
Authors: Melnik G. , Photinos P. , Saupe A.
Published: July 2002

The critical properties of the second order uniaxial–biaxial nematic transition (NL–Nbx) of the potassium laurate/1-decanol/D2O system were studied on surface and magnetic field aligned films of 0.1 and 0.5 mm thickness. The biaxial order was measured as a function of temperature and field. We find deviations from mean field behavior in a 20 mK range below the transition NL and in a temperature range of at least the same extent above the transition Nbx. The values obtained for the critical exponents of order parameter (β) and susceptibility (γ) in the uniaxial range are in good agreement with the values calculated for the xy model. A reliable value for the susceptibility exponent in the biaxial phase could not be obtained because the field range for which the effect is proportional to H2 is very small and the low field limit of the susceptibility could not be determined. From high field measurements we obtain a value of 4.0 as the lower limit for the exponent of the critical isotherm (δ). The result confirms that the transition follows the xy model. Drifts of the transition temperatures complicated the experiments. They are probably due to a partial esterification of potassium laurate.
Screening of hydrodynamics in a solution of crumpled manifolds
Authors: Muthukumar M.
Published: July 2002

Considering a collection of crumpled manifolds of dimension D in a hydrodynamic continuum of space dimension d, the concentration dependence of the hydrodynamic screening length is derived. The frequency, molecular mass, and concentration dependencies of the viscosity of the solution are obtained in both the unscreened and screened regimes for arbitrary D and d and the conditions of validity are specified.
Comparison between Borel resummation and renormalization group descriptions of polymer expansion
Authors: Freed Karl F. , Douglas Jack F.
Published: July 2002

Borel summations on the sixth-order perturbation series for the polymer mean square end-vector expansion factor α2 by Muthukumar and Nickel are compared with the computationally simpler second order in ε renormalization group crossover description of the excluded volume dependence of α2. An essential feature of the comparison is the use of the same cross over variables and the same definitions of α2 in both treatments. The agreement is found to be very good.
Dependence of the N2 vibrational potential on density
Authors: Engelke Ray
Published: July 2002

Recently, part of the vibrational spectrum of the ground electronic (X 1∑+g) state of condensed phase N2, shocked to high density, has been measured by Schmidt, Moore, and Shaw. Densities (ρ) of nearly three times the ambient liquid value were obtained in the shock wave experiments. Due to the high temperatures achieved behind the shock waves, up to six vibrational levels of N2 were observed. These vibrational spectra show clear frequency shifts from their ambient condition values. Here, these experimental spectra are used to infer changes in the vibrational potential of N2 due to the high density environment. The vibrational portion of the Rydberg–Klein–Rees (RKR) method is used to do this. We find that, in the range of densities studied, the energies [E(n;ρ)] of the first five vibrational transitions of N2 can be accurately represented by E(n;ρ)=ωe(ρ)(n+ 1/2 )−ωexe(n+ 1/2 )2, where ωe(ρ)=ω0e+A[1−(ρ0/ρ)1/3] and ωexe is a constant which is independent of the thermodynamic state of the environment; here, ω0e and A are fitting constants and ρ0 and ρ are the ambient (liquid) and shocked densities of N2. Given E(n;ρ), one can obtain the classical turning point difference, r12, of the N2 potential as a function of n and ρ by using the RKR procedure. It is found that at the highest shock density observed (2.13 g/cm3), the relative change in r12 from the ambient condition values is about −1% for the first six vibrational levels.
Note on the relation between total electronic energy and the sum of orbital energies
Authors: Cioslowski J.
Published: July 2002

The Robinson–Schaad approximate formula relating the total electronic energy and the sum of orbital energies of a scaled system is rederived and generalized using a Radau-type quadrature.
A study of the Fourier-series representation for internal rotation
Authors: Chung-Phillips Alice
Published: July 2002

A systematic procedure for developing a satisfactory Fourier-series representation of the potential energy function for internal rotation is presented. The procedure involves the selection of energy values at equally spaced dihedral angles of rotation and the use of an interpolating scheme to determine the expansion coefficients. As numerical examples, STO-3G potential energies arising from rigid rotations about the central carbon–carbon bonds in ethane, propane, chloroethane, butane, 1-chloropropane, 1,2-dichloroethane, and the meso and dl isomers of 2,3-dichlorobutane are used as input values. The resulting potential energy functions are evaluated on the basis of calculated potential energies and conformational properties as compared with the reference STO-3G values. Variations in the rate of convergence of the series expansion for different types of substituted ethanes are noted and discussed.
Study of He–H2CO collisions at interstellar temperatures using the L2 R-matrix method
Authors: Bocchetta C. J. , Gerratt J. , Guthrie G.
Published: July 2002

Total cross sections for collisions of He(1S) atoms with H2CO molecules at interstellar temperatures (18–120 K) have been calculated using the L2 R-matrix method developed previously. Using 13 slightly nonorthogonal radial basis functions, excellent agreement has generally been obtained with an earlier close-coupled study. However, in two crucial regions (32.7 and 47.7 K) where strong resonances had been reported, we find that the cross sections are smooth. The accuracy of the present calculations were checked at intervals using the de Vogelaere method with parameters set very tightly. Strong resonances in the 20.2 K region were however found and characterized as being of Feshbach (compound state) type, with the He atom lying in the potential well near the O atom of formaldehyde. Similar resonances in the 127 K region are also predicted. Consequently the state-to-state rate constants, upon which the collision pump mechanism for the cooling of the k doublets of formaldehyde depends, now need to be recomputed using the new values for the cross sections. This series of studies shows that the use of slightly nonorthogonal radial basis functions—and which as a result possess arbitrary derivatives at the R-matrix boundary—is the key to the reliable application of this very stable and versatile method to molecular collision problems.
Temperature dependence of the g value of Ni2+ in ZnSiF6⋅6H2O
Authors: Shrivastava Keshav N. , Rubins R. S. , Hutton Stuart , Drumheller John E.
Published: July 2002

The measured increase in g∥ between 4 and 100 K for Ni2+ in ZnSiF6⋅H2O has been explained as a consequence of the dynamical phonon coupling between the spins and the lattice. The Debye temperature of θ=130 K previously determined from the zero-field splitting has been found to agree with that obtained from the temperature dependence of the g value. The zero-point vibrational correction to the g value has been deduced.
A complete basis set model chemistry. I. The total energies of closed-shell atoms and hydrides of the first-row elements
Authors: Petersson G. A. , Bennett Andrew , Tensfeldt Thomas G. , Al-Laham Mohammad A. , Shirley William A. , Mantzaris John
Published: July 2002

The major source of errror in most ab initio calculations of molecular energies is the truncation of the one-electron basis set. A complete basis set model chemistry is defined to include corrections for basis set truncation errors. This model uses double zeta plus polarization level atomic pair natural orbital basis sets to calculate molecular self-consistent-field (SCF) energies and correlation energies. The small corrections to give the complete basis set SCF energies are then estimated using the l−6 asymptotic convergence of the multicenter angular momentum expansion. The calculated correlation energies of the atoms He, Be, and Ne, and of the hydrides LiH, BH3, CH4, NH3, H2O, and HF, using the double zeta plus polarization basis sets vary from 83.0% to 91.2% of the experimental correlation energies. However, extrapolation of each of the pair energies and pair-coupling terms to the complete basis set values using the asymptotic convergence of pair natural orbital expansions retrieves from 99.5±0.7% to 101.1±0.6% of the experimental correlation energies for these atoms and molecules. With the exception of ammonia which gave 101.1%, the calculated correlation energies agree with the experimental values to within the error limits of the experiments for all these atoms and molecules with more than four electrons. The total extrapolated energies (ESCF+ECorrelation) are then in agreement with experiment to within ±0.0014 hartree (root mean square deviation) and represent the most accurate total energy calculations yet reported for the molecules. The largest discrepancies with experiment occur for methane, where we obtain ETotal =−40.5112 hartree compared to EExpt =−40.514±0.002 hartree, and ammonia, where we obtain ETotal =−56.5659 hartree compared to EExpt =−56.563±0.002 hartree.