bluuebunny/crossref_metadata_2025 huggingface dataset:
The lowest triplet states of anthraquinone and chloroanthraquinones: The 1-chloro, 2-chloro, 1,5-dichloro, and 1,8-dichloro compounds
Authors: Hamanoue Kumao , Nakayama Toshihiro , Kajiwara Yōichi , Yamaguchi Tetsuji , Teranishi Hiroshi
Published: July 2002

From the measurements of phosphorescence spectra and triplet–triplet absorptions of the title compounds, it has been proposed that the lowest triplet states (T1) of the α-chloro compounds are of mixed nπ*–ππ* or ππ* character, while the nπ* triplet states are the lowest ones for anthraquinone and 2-chloroanthraquinone (the β-chloro compound). Compared with anthraquinone and the β-chloro compound, much shorter lifetimes of the T1 states and small phosphorescence quantum yields were obtained for the α-chloro compounds. These results have been interpreted in terms of the modification of the geometrical molecular structure by the interaction of the carbonyl group with chlorine atom(s) at the α position(s), causing the T1 states to be of ππ* character with short lifetimes.
The temperature dependence of the EPR spectrum of Cu2+ in ZnTiF6⋅6H2O between 4 and 160 K
Authors: Rubins R. S. , Drumheller John E.
Published: July 2002

The EPR spectrum of Cu2+ in the low temperature monoclinic phase of ZnTiF6⋅6H2O was studied at 9.24 GHz between 4 and 160 K. Assuming the Jahn–Teller spectra to have axial symmetry, g∥ was found to vary from 2.472±0.004 at 4 K to 2.331±0.004 at 158 K, while g⊥ varied from 2.097±0.004 to 2.173±0.004 over this range. From the temperature variations of the g values, the lowering of the energy Δ of one potential well associated with the Jahn–Teller distortion compared to the other two was found to be approximately 143 cm−1. It is shown that an apparent decrease in Δ with increasing temperature above 100 K could be due to the presence of an excited vibronic state about 170 cm−1 above the ground state. The variation of ‖A∥‖ from (107±1)×10−4 cm−1 at 4 K to (53±3)×10−4 cm−1 at 158 K agreed with predictions based on the temperature variation of the g tensor.
Small-signal ac response of supported thin-layer electrochemical cells
Authors: Franceschetti Donald R.
Published: July 2002

Exact impedance expressions are derived for thin layers of supported electrolyte between either identical redox electrodes or nonidentical electrodes of the parent metal type. While the symmetry of the former allows one to treat the system as two identical half-cells in series, the asymmetric concentration perturbation set up in the latter precludes such a separation. The impedance result obtained in the asymmetric case can be represented by an equivalent linear electrical circuit consisting of capacitances, resistances, an inductance, and several lengths of uniform transmission line, one of which exhibits an inductance per unit length. The general impedance result and the corresponding circuit reduce to the expected forms if the electrodes are identical or one electrode is kinetically reversible or ideally polarizable. Representative impedance results are displayed in the complex plane.
Torsional dynamics of molecules on barrierless potentials in liquids. III. Pressure dependent picosecond studies of triphenyl-methane dye solutions in a diamond anvil cell
Authors: Ben-Amotz D. , Jeanloz R. , Harris C. B.
Published: July 2002

Pressure dependent measurements of the nonradiative torsional dynamics of triphenyl-methane dyes are reported. The viscosity dependence of the excited state absorption and fluorescence decays of crystal violet, dissolved in methanol, ethanol, and n-propanol, are studied over a viscosity range of between 0.5 and 500 cP (pressures up to 1.5 GPa ∼15 000 atm). The overall viscosity dependence of the excited state decay time is linear. The nonlinear viscosity dependencies observed in earlier studies may have resulted from the complex nature of the solvents used and, in the case of fluorescence quantum yield measurements, from a pressure dependence of the radiative rate. Differences between the viscosity dependence observed when varying pressure, temperature, or solvent type at low viscosities are tentatively ascribed to pressure and temperature induced conformational changes.
Unitary-group approach (UGA) to the configuration interaction (CI) problems of the many-electron systems: A graphical formula in terms of Young tableaus
Authors: Lin Hai-Lun , Cao Yu-Fang
Published: July 2002

A new direct graphical formula in terms of Young tableaus is derived inductively, which provides a convenient and rapid method of evaluating arbitrary matrix elements of generators and of the products of generators of U(n).
Moment analysis of matrix-enhanced forbidden transitions: Application to Cr atoms isolated in Kr and Xe matrices
Authors: Rivoal Jean-Claude , Vala Martin
Published: July 2002

The band moment analysis of allowed transitions in magnetic circular dichroism/absorption may be complicated by the presence of near-lying forbidden transitions. The rare gas matrix enhances the spin–orbit coupling between the forbidden and allowed states. The theory necessary to extract the spin–orbit constant of the allowed excited state is presented for the case of a matrix-isolated metal atom possessing nP ←nS transitions. Application is made to matrix-embedded Cr atoms which possess two fully allowed states each of which is coupled to a different forbidden state: the orbitally forbidden z 7D state is mixed with the orbitally allowed y 7P state and the spin-forbidden z 5P state is coupled with the spin-allowed z 7P state. The mixing coefficients for both these pairs (in Kr and Xe matrices) have been determined quantitatively. It is shown that both spin and orbital designations of these atomic states in rare gas matrices is meaningless.
Two- and three-particle distribution functions for lattice fluids from Ornstein–Zernike equations
Authors: Johnson Elijah
Published: July 2002

A set of closed and exact equations for the particle distribution functions is used to treat classical fluids which have a pairwise additive potential energy function. The equations involve the two-particle and the three-particle Ornstein–Zernike direct correlation functions. The procedure has been applied to one-, two-, and three-dimensional lattice fluids. Results are presented here for a number of lattice fluids. It is not the main purpose of this article to present a new method for treating lattice fluids. The main purpose is to present a procedure for solving the set of equations mentioned above.
Perturbation treatments of stochastic Verhulst’s equation on the population dynamics under the fluctuating environment
Authors: Morita Akio
Published: July 2002

The stochastic Verhulst equation has been treated analytically in a perturbation method to obtain approximate expressions for the average value of the population with an arbitrary initial values up to the first order of the noise strength, and to calculate moments with an initial value at the saturation value up to the second order of the noise strength. In calculating the latter, we have transformed the Fokker–Planck equation arising from the stochastic Verhulst equation to that corresponding to the Brownian motion of a particle with a nonlinear potential after introducing a variable. Moreover, we have calculated the mean square displacement for the Brownian particle. The analytical results are compared with the numerical ones, and they are in good agreement for small values of the noise strength.
Direct dipole induced energy transfer: A microscopic model for glass relaxation
Authors: Soules Thomas F. , Markovsky Alexander
Published: July 2002

A microscopic model for glass relaxation phenomena is presented based on direct energy transfer from ‘‘tight’’ donor sites to ‘‘loose’’ acceptor sites. The rate of energy transfer, induced by the stress energy field from the donor W, is proportional to 1/R6. Summing over donor sites with different acceptor environments, gives the Williams–Watt form for relaxation vs time with β=0.5. More generally, β is the dimensionality of the structure divided by the order of the donor–acceptor energy transfer mechanism and thermorheological simplicity follows from one relaxation mechanism. Other properties of glass relaxation phenomena including the temperature and fictive temperature dependence of relaxation times are readily understood.
On the circular dichroism of a nonpolar critical binary liquid mixture
Authors: Lee Dong J. , Kim Shoon K.
Published: July 2002

The circular dichroism of a nonpolar binary liquid mixture is discussed in the critical region, where the Ornstein–Zernike approximation does not hold. The correlation function to be used is the Fisher form. We suggest a new experimental method to measure the critical exponent for correlation function by using the present result.
On the stability of H4 in C3v symmetry
Authors: Montgomery J. A. , Michels H. H.
Published: July 2002

The electronic structure of H4 in C3v symmetry has been studied by ab initio calculations. The ground state energy minimum found in these calculations is shown by vibrational analysis to be a saddle point rather than a stable bound state. The path of steepest descent from the C3v saddle point is found to lead monotonically to dissociation into two H2 molecules.
Intraatomic correlation effects for the He–He dispersion and exchange–dispersion energies using explicitly correlated Gaussian geminals
Authors: Rybak Stanislaw , Szalewicz Krzysztof , Jeziorski Bogumil , Jaszunski Michal
Published: July 2002

The coupling of the intermolecular interaction with the intramolecular correlation effects is considered using the coupled cluster (CC) formalism. The CC equations for the dispersion energy are presented and their relation to the double perturbation theory is analyzed. An approximate scheme based on partial decoupling of the CC equations is applied for the He–He interaction. Numerical results are obtained using explicitly correlated Gaussian geminal basis set. They confirm the importance of the intraatomic (apparent) correlation effects and agree very well with the experimentally derived potential.
The distribution of rings of hydrogen-bonded molecules in a model of liquid water
Authors: Belch Alan C. , Rice Stuart A.
Published: July 2002

We report the results of calculations, at five temperatures ranging from 243 to 313 K, of the distributions of non-short-circuited rings of hydrogen-bonded molecules in TIPS-2 water. These data are used to test two hypotheses concerning the use of ring transformations as collective excitations in water. The suggestion by Speedy that it is the concentration of five-membered rings that determines the anomalous properties of water, and the suggestion by Rice, Belch, and Sceats that it is the ‘‘reactions’’ 2(6 ring)⇄(5 ring)+(7 ring) and 8(6 ring)⇄2(4 ring)+4(8 ring) that determines these properties, are both shown to be incomplete. Further verification of the random network model assumption of separation of time scales for network relaxation and local molecular motion is presented.
Susceptibility and Mössbauer study of an antiferromagnetically coupled admixed-intermediate spin state in Fe(TPP) (FSbF5)⋅C6H5F
Authors: Gupta Govind P. , Lang George , Reed Christopher A. , Shelly Kenneth , Scheidt W. Robert
Published: July 2002

Magnetic properties of the synthetic hexafluoroantimonate complex of iron (III) tetraphenylporphyrin, Fe(TPP) (FSbF5)⋅C6H5F, were studied by susceptibility and Mössbauer techniques. The measured effective magnetic moment varies from 1.7 β at 1.5 K to 4.14 β at 300 K. The data were analyzed with the ‘‘Maltempo model’’ combined with a mean field antiferromagnetic treatment. This analysis shows that the system is predominantly in the S=3/2 spin state (98%) with an unusually small spin–orbit coupling constant ζ=79 cm−1. The net interaction of a given spin with the thermal average of all the spins is (1.39 cm−1)S⋅〈S〉T. Mössbauer spectra were recorded from 4.2 to 64 K in fields 0 to 6 T. The chemical shift δ=0.39 (Fe) mm/s and quadrupole splitting ΔE=4.29 mm/s are temperature independent and typical of ferric ions in the admixed–intermediate spin state. Mössbauer analysis confirms that the exchange interaction must couple many spins rather than forming spin pairs as seen in earlier work. The analysis also provides the rather low hyperfine coupling constant P/gNβN=28 T/unit spin, and contact constant κ=0.25. The spectra imply slow relaxation in fields greater than 4 T at 4.2 K, the rate increasing with increasing T and decreasing H. All Mössbauer and susceptibility data were fitted with a common parameter set; only the relaxation parameter was varied from one spectrum to another.
A correlation between NMR chemical shifts and Mössbauer quadrupole splittings for 119Sn and 125Te in organotin and organotellurium compounds
Authors: Jones C. H. W. , Sharma R. D.
Published: July 2002

A correlation has been observed between solution NMR chemical shifts δNMR and Mössbauer quadrupole splittings Δ for 119Sn and 125Te in a number of organotin and organotellurium compounds. These correlations are discussed in terms of the effects on δNMR and Δ of the valence p-orbital populations and the inverse cube of the radii of the 5p electrons.
3
1P NMR chemical shielding tensor of 2-aminoethylphosphonic acid
Authors: Van Calsteren Marie-Rose , Birnbaum George I. , Smith Ian C. P.
Published: July 2002

The symmetric part of the 31P NMR chemical shielding tensor was determined in a single crystal of 2-aminoethylphosphonic acid (AEP). The principal values, relative to 85% H3PO4, are σ11=87.1, σ22=15.6, and σ33=−47.5 ppm. Four orientations of the chemical shielding tensor on the molecule are possible, but only one of them shows correlation with the bond directions. The two most shielded components of the tensor lie almost in the plane containing the two P=O bonds, with σ22 approximately bisecting the O–P–O angle and σ33 roughly along the O–O connecting vector, leaving the phosphorus relatively deshielded in the perpendicular σ11 direction. The results can be correlated with the electron density distribution around the phosphorus atom, as determined by the bonding pattern of the phosphonate. A comparison is made with 31P NMR chemical shielding tensors in analogous phosphorus-containing compounds.
Electron correlation calibrated at the large dimension limit
Authors: Goodson D. Z. , Herschbach D. R.
Published: July 2002

Correlation energies (CEs) for two-electron atom ground states have recently been obtained to good approximation from a simple perturbation treatment using 1/D as the expansion parameter, with D the dimensionality of space. In hydrogenic units, the CE varies almost linearly with 1/D between limits at D→1 and D→∞ which are exactly calculable. However, for D→∞ the CE is only about 35% smaller than the ‘‘true-world’’ value at D=3. This is in striking contrast to the analogous error in the mean field approximation of statistical mechanics, which vanishes for sufficiently large D. Here we show that the CE for D→∞ can be made to vanish by modifying the Hartree–Fock (HF) variational wave function. A separable form is retained but a factor Θ(θ) is included, with θ the angle between the electron–nucleus radii r1 and r2. Likewise, the error in the HF value for the first derivative of the energy with respect to 1/D can be made to vanish by employing a suitable choice of coordinates in separate factors of the wave function. The choice is determined by the vibrational normal modes of the electrons about the rigid configuration attained in the D→∞ limit. We estimate that these improvements in the HF wave function at large D will reduce the CE for D=3 by about a factor of 10 or more for any two-electron atom. We also relate our results to those obtained with hyperspherical coordinates and show that the large-D limit accounts for the success enjoyed by the hyperspherical approximation at D=3. These findings offer prospects for reducing CEs for multielectron systems by exploiting dimensional calibration of the HF wave function.
Reply to ‘‘Comment on ‘Accurate analytic model potentials for D2 and H2 based on the perturbed-Morse-oscillator model’ ’’
Authors: Huffaker J. N.
Published: July 2002

Wright’s comments (ref.1),on the perturbed−Morse−oscillator model for the potential energy function for hydrogen and deuterium are answered. (AIP).
Cross sections for rotationally inelastic scattering of H2CO. II. Collisions with CO2, N2, O2, and H2
Authors: van Hulst Niko F. , ter Meulen J. J. , Dymanus A.
Published: July 2002

Cross sections for ΔJ=0, ±1, and ±2 transitions in the K−1=1 ladder of formaldehyde (H2CO) in collision with CO2, N2, O2, and H2 are measured in a double-resonance beam maser. The dependence of the cross sections on detection angle, relative velocity, and H2 temperature is investigated. The experimental cross sections are confronted with calculations in modified Anderson theory and adiabatically corrected sudden approximation. For CO2 and N2 scattering dipole–quadrupole interaction dominates, a large fraction of the integral cross section is probed and agreement with theory is good. For O2 and H2 scattering also induction and dispersion forces are important; agreement with theory is less satisfactory indicating that the full potential, including the repulsive part, should be taken into account.
Intensity cancellation effects in the hyperfine structure of molecules with large nuclear spins: The 6500 Å system of NbO
Authors: Merer A. J. , Sassenberg U. , Féménias J.-L. , Cheval G.
Published: July 2002

The magnetic hyperfine structure of certain low-JQ lines in the optical spectrum of NbO shows an unusual intensity cancellation effect. In contrast to the normal pattern that ΔF=ΔJ hyperfine components are the strongest, the intensities of the ΔF=ΔJ components are found to pass through zero near the center of the range of F values. Although this effect is implicit in the intensity formulas for the quadrupole hyperfine structure of microwave lines, it seems not to have been noted in published spectra because of the unusual circumstances required for its appearance: a nuclear spin of at least I=5/2 is needed, and only Q lines show it. A classical vector model is presented for its interpretation.
Gas phase dynamics and spectroscopy probed with picosecond transient grating experiments
Authors: Rose Todd S. , Wilson William L. , Wäckerle G. , Fayer M. D.
Published: July 2002

Picosecond transient grating experiments in sodium and iodine vapors, involving the 3S→3P and X→B transitions, respectively, are discussed in detail. Population gratings in sodium demonstrate that the technique can be used to measure velocity distributions in the gas phase. It is shown that the time dependent transient grating signal is related to the Fourier transform of the velocity distribution. Similar experiments on iodine illustrate the effect of state changing collisions on the grating signal. Theoretical calculations for a model in which the change of state is caused by a single collision are given. Close agreement with the data is observed for the situation in which the collision takes the initial velocity into a random velocity distribution. From this model a collision cross section is determined. The results demonstrate that information on collision dynamics can be obtained from grating experiments. In addition, the sodium experiments are used to illustrate a new type of time domain high resolution spectroscopy. When the grating excitation pulses have perpendicular polarizations, a polarization grating, rather than the usual population grating, is formed. Diffraction from the sodium polarization grating shows larger time dependent oscillations in the diffraction efficiency. These oscillations yield the ground state and excited state hyperfine frequencies (1.77 GHz and 189 MHz, respectively). A detailed theoretical description of the origin of the oscillations is presented. The results suggest that polarization grating spectroscopy can have applications in other areas, such as molecular rotational dynamics.
Estimation of the amount of nonadjacent reentry in polymer crystallization. II. Application to once folded n-paraffins
Authors: Passaglia E. , DiMarzio E. A.
Published: July 2002

The methods described in the preceding paper have been used to calculate the composition of a strip of once folded molecules of n-C294H590. The fraction of cilia and of stems participating in adjacent and nonadjacent reentry were calculated as a function of undercooling in regime I. Two cases corresponding to crystallization from the melt and one corresponding to dilute solution were considered. The results are strongly dependent on the relative rates of deposition of a stem from the liquid phase and the folding and reentry of the dangling half of an already attached molecule. The rate constants for adjacent and nonadjacent reentry were taken to be the same except that nonadjacent reentry leaves a hole in the strip. The undercooling below the melting point of the extended chain crystal at which the growing strip is in equilibrium with its environment is shown to be determined by all the imperfections in the strip, and particularly by the free energy of mixing. In all cases, the fractions of adjacent and nonadjacent reentry at this equilibrium undercooling are approximately equal and the fraction of cilia is a maximum. At higher undcoolings, the fraction of adjcent reentry rises, while the fractions of cilia and nonadjacent reentry fall, the exact behavior depending on the solution concentration and hence the relative rates of stem deposition from the liquid phase and of folding. This behavior is correlated with the free energy of mixing.
Second-order correction to the arbitrary trajectory method of semiclassical quantization
Authors: De Leon N.
Published: July 2002

In this paper we extend the arbitrary trajectory approach to semiclassical quantization developed in an earlier paper. A numerical method is developed and tested that uses a second-order correction to extrapolate several energy eigenvalues from a single trajectory. The method is based upon finding the second-order action derivatives of the Hamiltonian. We test the scheme on a Hamiltonian previously analyzed by Swimm and Delos. We find that about 100 energy eigenvalues can be fairly accurately obtained with three reference trajectories (24 total trajectories). Strengths, weaknesses, and future applications of the method are discussed.
Energetic consideration of the vibrational potential function in the effective nuclear charge model. VII
Authors: Ohwada Ken
Published: July 2002

The homogeneity characteristics of the molecular energy with respect to the atomic number are discussed in detail on the basis of the local and nonlocal homogeneity hypothesis which has been proposed in a previous report [J. Chem. Phys. 85, 5882 (1986)]. It is first shown that the homogeneity hypothesis is convenient for describing the local and nonlocal properties of molecules. Inhomogeneous linear second-, third-, fourth-, and nth-order differential equations are constructed from the constrianed linear first-order differential equation and solved for understanding general potential forms of molecules. The results obtained give the theoretical basis to various models so far presented. The approximate potential function obtained by solving the constrained linear third-order differential equation is successfully applied to the calculations of higher-order potential constants as well as molecular energy components. Lastly, all the expressions of molecular energy components with the homogeneity constraint are given by making use of the general solution derived from the constrained linear nth-order differential equation.
Structural aspects of the effect of pressure on the Raman and infrared spectra of n-hexadecane
Authors: Wong P. T. T. , Chagwedera T. E. , Mantsch H. H.
Published: July 2002

Raman and infrared spectra of neat n-hexadecane were measured as a function of hydrostatic pressure up to 54 and 83 kbar, respectively. The application of high pressure leads to anomalous frequency shifts and band splittings, and induces drastic changes in the band shapes and in the distribution of intensities within the spectra. The pressure-induced changes in the vibrational spectra of n-hexadecane are discussed in terms of phase transitions, molecular distortions, interchain interactions, frequency dispersions, and Fermi resonance interactions. The effect of pressure on the Raman and infrared spectra of n-hexadecane is used to test conclusions drawn from theoretical Fermi resonance calculations concerning the origin of several features in the Raman spectra of n-alkanes. Evidence is given to show that some assumptions made in these calculations are incorrect and that the model used is too simple to account for the intensity distribution in the CH stretching region of the Raman spectra of n-alkanes. It is also shown that the peak heights of the 2930 and 2850 cm−1 Raman bands can be affected by such factors as the magnitude of interchain interactions which renders questionable the use of the peak height ratio between these bands for the quantitative estimation of the gauche/trans population in biomembranes and polymers. While hydrostatic pressure initially causes a conformational ordering of the chains in n-hexadecane, at high pressures the compression along the chain direction is predominant over the lateral compression, leading to a distortion of the methyl end groups and a conformational disordering of the methylene chains.
Osmotic pressure of ring-polymer solutions
Authors: Tanaka Fumihiko
Published: July 2002

For a pair of ring polymers in a solution, the number of mutual entanglements is invariant and, hence, a frozen variable. Such restriction on thermally accessible configurations causes a new type of intermolecular interaction. This paper theoretically studies the nature of molecular interaction caused by topological constraints. Observed depression of the theta temperature by 6 °C in the solution of ring polystyrene compared with that of linear polymer is explained by the existence of repulsive force, which acts between disjoint rings and originates in topological constraints. By the use of Gauss’ linking number for the topological invariant, the second and third virial coefficients are calculated as a function of molecular weight and compared with the experimental observation on ring polystyrene in cyclohexane.
A crossed beam study of the competition between rotational and vibrational energy transfer in H2+glyoxal (S1) collisions
Authors: Butz Kirk W. , Du Hong , Krajnovich Douglas J. , Parmenter Charles S.
Published: July 2002

A crossed beam study of the rotational and vibrational energy transfer hydrogen and glyoxal collisions is reported. A laser pumped rotational states in the absorption spectrum of glyoxal and the resulting emission was monitored.(AIP)
A unified approach to local force laws in quantum chemistry
Authors: Ghosh Swapan K.
Published: July 2002

The local (nonintegrated) versions of the Hellmann–Feynman, virial and the hypervirial theorems are derived through a unified approach. The quantum fluid dynamical equations of motion as well as explicit expressions for the hidden force and stress terms, which are otherwise absent in the global forms of the theorems, are thereby obtained. Results are presented for the microscopic local pressure for a simple atomic system.
Adsorbate islanding in surface reactions: A combined Monte Carlo-lattice gas approach
Authors: Silverberg M. , Ben-Shaul A.
Published: July 2002

The effects of reactant aggregation and lateral interactions on bimolecular surface reactions A+B→AB are studied using a theoretical model combining Monte Carlo simulations with (modified) lattice gas approximations, with special reference to temperature programmed reactions. A and B are chemisorbed species yielding a rapidly desorbing product AB. We are particularly interested in systems where one reactant (A) tends to organize in ordered domains, as a result of strong A–A attractive forces. Our modeling scheme consists of two stages. First, A is randomly adsorbed at a temperature lower than the critical temperature of the gas–solid transition, and phase separation (i.e., A aggregation) starts taking place. This process is modeled by (conserved) Monte Carlo dynamics. As in previous studies, we find that after a while the A atoms form finite, metastable, often highly ramified islands, whose further growth is a very slow process. At this stage, or earlier, B is adsorbed on the A-free lattice sites, T is raised (linearly) and reaction begins. It is assumed that A is stationary while B is highly mobile and that B diffusion is much faster than A+B reaction. Thus, the distribution of B on A-free sites is always in equilibrium, but it depends on A–B and B–B interactions, as well as on coverage, temperature, and, in particular, the given distribution of A atoms. To calculate the B distribution we formulate and employ two lattice gas models, which are appropriately modified versions of the mean-field and the quasichemical approximations. To follow the time-space evolution of the system we use Monte Carlo methods to simulate the slow processes, A aggregation and AB formation, and (one of the) lattice gas models for B distribution. Calculations of thermal desorption spectra are performed for A and B adsorbed on a 500×500 square lattice (with periodic boundary conditions) assuming nearest-neighbor

lateral interactions wAA, wBB, and wAB. The results reveal nontrivial kinetic behaviors, which depend strongly on initial conditions (coverages, dosing sequence) and interaction parameters. These are reflected in the temperature programmed spectra and the apparent (coverage dependent) activation energies derived from them. It is shown, for example, that the major effect of A–B interactions on the rate is via their influence on local concentration of B’s near A’s. B–B interactions affect directly the reaction activation barrier. A–A interactions show both ‘‘topological’’ and ‘‘energetic’’ effects.
Quantum close-coupled studies of collisions of NO(X 2Π) with a Ag(111) surface
Authors: Smedley Jane E. , Corey Gregory C. , Alexander Millard H.
Published: July 2002

Close-coupled calculations of transition probabilities for rotationally inelastic scattering of NO(X 2Π) by a rigid, uncorrugated Ag(111) surface are presented. These calculations explicitly include the two adiabatic potential energy surfaces of V+ and V− symmetry, which are required in a fully quantum mechanical treatment of the collision dynamics. This enables us to provide the first theoretical description of the dependence of the transition probabilities on the spin–orbit and Λ-doublet states of the scattered molecules, which are a direct manifestation of the open-shell character of the 2Π electronic ground state of NO. A comparison is made with the results of experiments by Luntz, Kleyn, and Auerbach at IBM, and Zare and co-workers at Stanford.
Viscosity measurement of a photopolymerized monolayer of a linear–chain polymer
Authors: Miyano K. , Veyssié M.
Published: July 2002

The shear mechanical relaxation has been studied of a monomolecular film at the air/water interface while it was being polymerized by irradiating UV light. The mixture of monomer and linear-chain polymer thus formed showed a diverging shear relaxation time τ which varies as τ∼t2.6ir as a function of the irradiation time tir.
Polydisperse systems: Interference effects in small angle scattering
Authors: Mengoni A.
Published: July 2002

The effect of interference between the various components of a system of spheres in the scattering function at small angles has been investigated in the framework of the Born–Green kinetic theory of fluids. Calculations have been made for close-packed systems of spheres with Schultz distribution of radii and two types of interactions: the simple hard-sphere (excluded-volume) interaction and the hard sphere with a permeable shell.
Hopping-to-band transitions in disordered electronic systems
Authors: Zhang Qing , Phillips Phillip
Published: July 2002

We investigate the effect polaron formation has on the transport of an electron among a band of tight binding sites interacting with a thermal bath of phonons. At T=0 we show that interactions with phonons stabilize Anderson localized states by the formation of self-trapped species. A localization criterion is then derived which defines the strength of the transfer matrix element needed for given values of the site energy disorder and the phonon coupling to destroy the stability of the self-trapped states. The Anderson upper limit criterion is recovered in the limit that the phonon coupling vanishes. The conductivity is then calculated as a function of the site energy disorder W using small polaron theory. A hopping-to-band transition is shown to exist for small values of W at a temperature ∼1/9 θD (the Debye temperature). Thermally activated Arrenhius behavior and variable range hopping obtain in the hopping regime. The conductivity in the metallic or low temperature regime vanishes as W−1. The relation to Mooij correlations is discussed.
Kinetic study of the reaction of HO2 with ozone
Authors: Sinha Amitabha , Lovejoy Edward R. , Howard Carleton J.
Published: July 2002

The reaction HO2+O3→OH+2O2 has been studied using a discharge-flow system with laser magnetic resonance detection. The rate constant for the reaction was determined directly by monitoring the first-order decay of isotopically labeled H18O2 in excess 16O3. The data give a curved Arrhenius plot over the temperature range 243<T<413 K: k(T)=(3.8±2.4) ×10−14 exp[−(820±190/T)] cm3 s−1. A more representative fit is obtained with a three parameter expression: k(T)=(3.2±5.8)×10−13 exp[−(1730±740)/T] + (1.2±0.5)×10−15 cm3 s1. The error limits are the 95% confidence limits on the coefficients while the accuracy of the measurements is estimated to be about ±20% at each temperature. An analysis of the OH radical product indicates that 16OH is formed predominately (75±10)%. The scrambling reactions H18O2+16O3→H16O2+18O18O16O (1c) and H18O2+16O2→H16O2+18O2 (8) were also examined and found to be slow. Their rate constants are k1c<2×10−17 cm3 s−1 at 297 and 333 K and k8<3×10−17 cm3 s−1 at 297 and 413 K.
Molecular dynamics of hard spheres. II. Hard spheres in a spherical cavity
Authors: Macpherson A. K. , Carignan Yvon P. , Vladimiroff T.
Published: July 2002

The equation of state for hard spheres in a spherical cavity is calculated and compared with the results previously found when the containing boundary was a channel. It was found that the spherical surface provides a focusing effect on both the pressure and the compressibility factor. An examination of the results suggested that the density and compressibility factors could be expanded in a series of Maxwellian functions. It was found that a six-term series which was modified in the immediate vicinity of the wall was sufficient. This has an advantage over the usual Fourier series expansion in that less terms are required. In addition, an argument can be made that such a series has a foundation in the physics of the problem.
Bonding and adsorption structure of CO on W(100)-(5×1)–C
Authors: Friend C. M. , Serafin J. G. , Baldwin E. K. , Stevens P. A. , Madix R. J.
Published: July 2002

The adsorption structure of carbon monoxide on W(100)-(5×1)–C has been characterized using high-resolution electron energy loss spectroscopy and near edge x-ray absorption fine structure measurements. A single C–O stretch of 2100 cm−1 is observed at a surface temperature of 130 K. The C–O bond vector is determined to be normal to the surface on the basis of near edge x-ray absorption fine structure measurements. The position in energy of the C(1s)→σ* resonance in CO was measured to be 304.2 eV. The empirical relation between the σ* resonance energy and bond length yields a bond length of 1.12 Å. All spectroscopic results are consistent with CO bound atop a single tungsten atom, normal to the surface plane with minimal C–O bond weakening. These results correlate with the known difference in the reactivity of the W(100)-(5×1)–C surface compared to clean W(100). The increased barrier for CO dissociation on the W(100)-(5×1)–C surface is explained on the basis of reduced backdonation of electron density from the tungsten d band to the CO 2π* orbitals. Tight-binding slab calculations for CO on W(100) and W(100)-(5×1)–C which support this contention are discussed.
Third harmonic generation from a monolayer film of a polydiacetylene, poly-4-BCMU
Authors: Berkovic G. , Shen Y. R. , Prasad P. N.
Published: July 2002

Third harmonic generation has been observed for the first time from a monolayer film on water subphase. This study, conducted for a polydiacetylene, poly-4-BCMU, reveals a conformational transition in the monolayer film whereby the effective π-electron conjugation is reduced. From the study, the orientation of the polymer at the water subphase and the value of the second hyperpolarizability γ along the polymer chain is also determined. The corresponding bulk susceptibility χ(3) is found to be in agreement with those reported by earlier studies.
Is there a zeroth order time-step error in diffusion quantum Monte Carlo?
Authors: Reynolds P. J. , Owen R. K. , Lester W. A.
Published: July 2002

It is demonstrated that the short-time Green’s function often used in diffusion quantum Monte Carlo simulations of the Schrödinger equation generates an unbiased probability distribution in the limit of vanishing time step τ. For finite τ, an error is introduced into the potential which is of O(τ). An expression for this term is derived.
Theoretical and experimental studies of the system Ca+(H2O)n for n=1 to 10
Authors: Kochanski Elise , Constantin Emilia
Published: July 2002

Monte Carlo calculations and gas phase mass spectrometry studies have been carried out on the system Ca+(H2O)n. The parameters used in the calculations to describe the interaction energy between Ca+ and a water molecule are deduced from quantum mechanical ab initio determinations. The clusters formation energies through the reaction Ca+(H2O)n−1+H2O ⇄ Ca+(H2O)n have been calculated for n=1 to 10 and determined from gas phase mass spectrometry for n=1 to 5. For n=6 to 10, theoretical work shows that, though the most stable structures have six water molecules in a first shell surrounding Ca+, the statistical distribution increases from 5.28 to 5.63, due to the presence of many stable configurations with five water molecules in the first shell. A comparison is done with the system H3O+(H2O)n.
Angular aspects of electron correlation and the Coulomb hole. II. The 2 1S and the 2 3S excited states of helium
Authors: Ugalde J. M. , Boyd Russell J. , Perkyns John S.
Published: July 2002

The K–L intershell correlation effects for both singlet and triplet states arising from the 1s2s electronic configuration of the helium atom are analyzed in detail with the aid of the complete (nonreduced) interelectronic probability density and the local Coulomb hole functions. The calculations for both singlet and triplet states suggest the existence of nuclear Coulomb well channels similar to those recently described for the intrashell case of Berry and Krause. When the reference electron is close to the nucleus, the 2 1S Coulomb hole resembles the ground state Coulomb hole, whereas this feature is lost in the 2 3S state due to the effect of exchange correlation. Electron correlation is shown to reduce the nuclear shielding provided by the K-shell distribution and, as a consequence, to lead to a relative shrinking of the outer shell density. Other differences between the ground state and excited state correlation effects are described.
Translational component of the interaction-induced dipole correlation functions in dense fluids
Authors: Gburski Z. , Samios J. , Dorfmüller T.
Published: July 2002

The correlation functions associated with the translational motion of a dipole induced by the permanent multipoles of an order l=1,2,3,... in dense media have been calculated analytically assuming the isotropic diffusion mechanism. The reflecting wall boundary condition at the distance of the closest approach of two molecules has been taken into account. The translational correlation functions obtained from this model have been compared with the results of molecular dynamics simulations in liquids N2 and CS2, and good agreement has been obtained.
A unified approach to spin polarization (CIDEP) and relaxation by Heisenberg spin exchange. I. Generalized equations for reactive radicals
Authors: Syage Jack A.
Published: July 2002

A theory of Heisenberg spin exchange (HSE) has been formulated in this and the following paper to consider the processes of chemically induced dynamic electron polarization (CIDEP) and relaxation. The framework, which includes all the spin states of a radical pair (RP), relies on an exact transient solution of the encounter RP density matrix. To aid in interpreting time-resolved ESR studies of these effects, a nonphenomenological formulation of Bloch-type equations is explicitly derived for the ⋅RH and ⋅RH2 radical spin systems as well as for general radical systems in terms of their n-line ESR spectra. The longitudinal and transverse relaxation rates and the frequency shifts are calculated for conditions spanning the weak to the strong exchange limit under a wide range of viscosities. The normally slight frequency shifts are shown to be strongly enhanced by CIDEP although not to an extent that is easily observable. Aside from the usual degeneracy effects, a curious HSE relaxation behavior is predicted for ESR lines that exhibit multiplet CIDEP, wherein the observed longitudinal relaxation rate can appear faster than the transverse rate by an amount that depends on the degeneracy of the line vs the total number of transitions of the radical. The present theory is formulated to be descriptive of time-resolved ESR experiments. Implications to reactive radicals are discussed and the solutions of the modified Bloch equations are presented to consider (i) instantaneous, geminate, and diffusive RP CIDEP, (ii) coupled and time dependent relaxation by HSE, and (iii) second-order chemical decay.
Algebraic symmetry in chemical reaction systems at stationary states arbitrarily far from thermodynamic equilibrium
Authors: Shiner J. S.
Published: July 2002

For systems of chemical reactions the phenomenological equations of nonequilibrium thermodynamics display the differential symmetry of Onsager reciprocity in general only for stationary states in the vicinity of thermodynamic equilibrium, as is well known. It will be shown here, however, that systems of chemical reactions, on the macroscopic, phenomenological level of chemical kinetics, do show a less stringent symmetry at all stationary states arbitrarily far from equilibrium. The key is a reformulation of the kinetic equations for single chemical reactions as resistive laws relating the force driving a reaction to the rate of the reaction through a (nonlinear) generalized chemical resistance; these laws are analogous to the ‘‘voltage=current times resistance’’ laws for resistive elements in electrical networks. The resistive laws for single reactions then lead naturally to stationary state relations for systems of coupled chemical reactions of the form of the phenomenological equations of nonequilibrium thermodynamics, and these relations display algebraic symmetry at stationary states arbitrarily far from equilibrium, although the differential symmetry of Onsager reciprocity is in general not valid. An example illustrates the relation of the symmetry property for chemical reactions to that displayed by RC electrical networks and how the chemical symmetry follows from analogs of Kirchhoff’s laws obeyed by systems of chemical reactions.
Many-body crystal field calculations. II. Results for the system Pr3+–Cl−
Authors: Ng Betty , Newman D. J.
Published: July 2002

Contributions to the Slater parameters, crystal field and correlation crystal field parameters for the two-ion system Pr3+–Cl− are calculated using the many-body diagrammatic expansion technique. Both ligand polarization and covalency are shown not to provide significant contributions to the Slater parameters. Ligand polarization is also eliminated as a major contributor to the correlation crystal field, but this mechanism does produce significant crystal field contributions. New, important, contributions to all three sets of parameters are identified and the overall results are related to experimental data.
Fluctuating hydrodynamics approach to dilute polymer solutions. I. Solvent velocity correlations and weak flow
Authors: Friedman B. , Rabin Y.
Published: July 2002

We study solvent dynamics in a solution consisting of polymers and solvent. Our starting point is a system of Langevin equations where the solvent velocity field and solvent velocity fluctuations are explicitly included. We calculate the Fourier transform of the solvent velocity autocorrelation function in the dilute regime. From this correlation function we calculate the dynamic viscosity of the solution and obtain an effective equation of motion of the solvent which turns out to be the generalized Maxwell model of a linear viscoelastic fluid.
Diode laser spectroscopy of the ν3 and ν2 bands of FHF− in 1300 cm−1 region
Authors: Kawaguchi Kentarou , Hirota Eizi
Published: July 2002

The ν3, ν2, and ν1+ν3−ν1 bands of a linear molecular anion FHF− have been detected by diode laser spectroscopy in 1300 cm−1 region. The previously reported 1848 cm−1 band [K. Kawaguchi and E. Hirota, J. Chem. Phys. 84, 2953 (1986)] was reassigned to the ν1+ν3 combination band. Analysis of the observed spectra gave the fundamental frequencies ν1=583.0539(13), ν2=1286.0284(22), and ν3=1331.1502(7) cm−1 with three standard deviations in parentheses. From the rotational constants obtained, the equilibrium F–F internuclear distance was calculated to be 2.277 71(7) Å.
The viscosity of colloidal spheres in deionized suspensions
Authors: Okubo Tsuneo
Published: July 2002

Viscosities of colloidal spheres, i.e., colloidal silica (diameter 8 and 45 nm) and monodisperse polystyrene latices (diameter 85 to 780 nm), are measured in deionized (‘‘salt-free’’) suspensions and in the presence of a small amount of NaCl. The reduced viscosities (specific viscosity divided by concentration) of deionized silica (diameter 8 nm) are much higher than would be expected by Einstein’s prediction and decrease sharply with increasing concentration. A sharp peak is observed in the reduced viscosity vs concentration curves of deionized colloidal silica of 45 nm diameter and the deionized latex spheres. The peak corresponds to the transition between ‘‘liquid-like’’ and ‘‘crystal-like’’ structures. These results show that electrostatic intersphere repulsion and the elongated Debye-screening length around the colloidal spheres are essential to explain the extraordinary properties.
Nascent rotational distributions of N+2(X 2Σ+g) produced by electron-impact ionization of N2 in a supersonic beam
Authors: Nagata Takashi , Nakajima Atsushi , Kondow Tamotsu , Kuchitsu Kozo
Published: July 2002

Laser-induced fluorescence from nascent N+2(X 2Σ+g) ions produced by electron impact on a N2 supersonic beam was observed. An analysis of the B 2Σ+u−X 2Σ+g (0,0) band shows that the rotational state distributions cannot be represented by a single Boltzmann function, higher N″ levels being overpopulated. Experimental and analytical efforts were made to minimize the influence of cascading and relaxation on the rotational distributions. The rotational energy of N+2(X) thus estimated increases with decreasing electron energy from 2.26±0.16 meV at 300 eV to 4.24±0.27 meV at 25 eV. This trend is explained qualitatively in terms of angular momentum transfer through multipole electron–molecule interactions.