bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared diode laser and microwave spectra and molecular structure of an unstable molecule, FBO
Authors: Kawashima Yoshiyuki , Kawaguchi Kentarou , Endo Yasuki , Hirota Eizi
Published: July 2002

The FBO molecule was generated by a dc discharge in a mixture of BF3, O2, and He and its vibration–rotation and rotation spectra were observed by using infrared diode laser spectroscopy and microwave spectroscopy, respectively. The ν1 B–O stretching mode of F11BO and F10BO and the ν1+ν2−ν2 hot band of F11BO were observed in the region 2050 to 2140 cm−1. Subsequently, the pure rotational spectrum was observed for the following isotopic species: F11BO, F10BO, F11B18O, and F10B18O. The rotational, centrifugal distortion, and l-type doubling constants were determined from the observed spectra, and the partial rs structure of FBO was calculated from rs coordinates and the first moment equation to be r(F–B)=1.2833(7) Å and r(B–O)=1.2072(7) Å.
Theory of size distribution of associating polymer aggregates. I. Spherical aggregates
Authors: Bug A. L. R. , Cates M. E. , Safran S. A. , Witten T. A.
Published: July 2002

We examine the stability of spherical, micellelike aggregates composed of long-chain, polymeric surfactants in dilute solution. The associating polymers consist of long, unbranched hydrophobic chains with one polar end-group per chain and are in a good solvent for the chains. Although the head groups prefer to aggregate in the nonpolar solvent and thus stabilize the spherical structure, the energy associated with the chain repulsions tends to destabilize the aggregates as the chain length increases. For a liquid-drop model of the head interactions, the average aggregation number evolves smoothly towards zero as the chain length increases. An alternate model of the head region, which assumes a preferred head-packing geometry, results in the ultimate destabilization of the spherical aggregate as the chain length is increased beyond a certain threshold. Both models yield a critical micelle concentration (CMC) at low values of the polymer concentration.
Dynamics of SiF4 desorption during etching of silicon by XeF2
Authors: Houle F. A.
Published: July 2002

Time-of-flight distributions have been obtained for SiF4, the principal product of the spontaneous etching reaction between silicon and XeF2. The data were extracted from modulated beam mass spectrometric measurements of SiF+4 intensity as a function of time. Comparison of the velocity and energy distributions derived from the data to the corresponding Maxwell–Boltzmann distributions shows clearly that although the most probable values of the distributions are very close to those expected when the desorbed species are in thermal equilibrium with the surface, the average values are not. The etch product velocity and energy distributions are not characterized by a single temperature, but comprise both hot and cool populations. These results show that the etch product desorption process cannot be described as simple evaporation of weakly bound species in equilibrium with the surface. The nature of the relationship between formation and volatilization is discussed.
Suppressed kinetics of short range ordering at low temperatures
Authors: Fultz B.
Published: July 2002

The kinetics of short range ordering in a binary alloy were studied by Monte Carlo simulation. Unlike the kinetics of ordering by the direct interchange of atoms, at low temperatures there is a marked suppression of the kinetics of ordering when ordering occurs by the vacancy mechanism. Large activation energies are associated with this suppression of kinetics. These activation energies suggest that certain heterogeneities in the atomic arrangements on the lattice behave as traps which the vacancy cannot easily escape at low temperatures. Such traps were observed during simulations of the ordering process.
A comparison of local and global single Gaussian approximations to time dynamics: One-dimensional systems
Authors: Turner Ralph Eric , Snider R. F.
Published: July 2002

The detailed calculation of the dynamics of a chemical system is usually not considered due to the size and cost of the computation. It is thus useful to examine various approximation methods. Such methods first need to be tried out on simple systems, like one-dimensional motion. Here two approaches to approximating the solutions of the Schrödinger and von Neumann equations by single time-dependent Gaussians are explored and contrasted, explicitly for one-dimensional barrier penetration. The first approach, in which no tunneling occurs, is local in nature and characterized by an expansion of the equations of motion to second order about the average position of the Gaussian wave packet or about the average position and momentum of the Gaussian Wigner function. This approach was first introduced by Heller [E. J. Heller, J. Chem. Phys. 62, 1544 (1975)]. Here both Heller’s approach and a more general truncation method are considered. Indeed tunneling can be incorporated if second-order terms in the quantal von Neumann equation are included. However, the resulting dynamics is unstable for kinetic energies where the exact wavepacket (and Wigner function) splits into nonnegligible parts that represent reflection and transmission. In contrast, the second approach is a global method which is obtained by applying appropriate closure approximations to the equations of motion for the first- and second-order position and momentum expectation values. This method allows tunneling and is stable at all kinetic energies. It is also possible to approximate the global equations in such a way that the local equations are obtained.
Fine structure in the [(2Γ3+ν3)←1Γ1] vibronic band in PuF6
Authors: Kim K. C. , Krohn B. J. , Briesmeister R. , Rabideau S.
Published: July 2002

High resolution spectra of the [(2Γ3+ν3)←1Γ1] transition from the absorption band systems near 800 nm in PuF6 have been recorded. Rotational lines and some fine structures have been resolved. The results support a spherical-top configuration despite the possibility of Jahn–Teller distortion.
Large paramagnetic anisotropy of NaMg[Cr(oxalate)3]⋅9H2O
Authors: Merabet K. E. , Carlin Richard L.
Published: July 2002

The magnetic susceptibilities of single crystals of NaMg[Cr(oxalate)3]⋅9H2O are reported over the temperature interval 40 mK–4.2 K. Large anisotropy is observed due to the large zero-field splitting of the 4A2 ground state; the parameters that fit the data are 2D/k =−2.45(3) K, g∥=1.985(5), g⊥=2.035(10), and an exchange correction of zJ/k =0.006(1) K.
Calculations of electric field effects on persistent spectral holes in amorphous host–guest systems
Authors: Schätz P. , Maier Max
Published: July 2002

The dependence of spectral holes of dye molecules in amorphous solids on the following parameters has been calculated: the electric field strength, the angles between the hole-burning and probing laser light fields and the external electric field, the electric dipole moment difference Δμm between the excited and ground state of the guest molecule, the contribution Δμ* of the host matrix to the electric dipole moment difference, and the angle γ, between Δμm and the transition dipole moment μge. When the molecular dipole moment difference Δμm dominates the spectral hole broadens or splits into two holes by the application of the electric field, depending on the angle γ and the directions of the laser light fields and the external field. With increasing values of the host-induced electric dipole moment difference Δμ* the spectral hole shape in the electric field changes significantly if appropriate directions of the light fields and the external field are chosen. The material parameters γ, Δμm, and Δμ* can be determined unequivocally by comparing the calculated holes both in the frequency dimension and the electric field dimension with experimental results.
Lattice disorder in small crystals
Authors: Allegra Giuseppe , Brückner Sergio
Published: July 2002

Disorder resulting in a Gaussian distribution of lattice points around their average positions is investigated according to a bead-and-spring harmonic model of thermal fluctuations, which may also be approximately extended to defective lattices with structural inhomogeneities. Using both the monoatomic simple-cubic lattice model and a more sophisticated model with crossing bonds, exact results are obtained in both cases for the infinite crystal. Conversely, finite crystals are exactly treated within the first model only, whereas the second one is investigated through Monte Carlo simulations in the phase space of the phonon modes. The less accurate Monte Carlo results appear to support the analytical ones. Unlike Hosemann’s model of the paracrystal, fluctuations of the lattice points cannot be described according to the convolution rule. In qualitative agreement with Hosemann’s suggestions, disorder increases with decreasing crystal size. The half-peak width δS(S=2 sin θ/λ) of the diffraction lines varies as A/N+(BS)2/α, where A and B are suitable constants and N is the number of lattice points per cubic crystal edge. In the most significant S range comprised between two limits Smin and Smax, α=1 and B∝N−1, whereas α>1 and α<1 for SSmax, respectively. While Smin vanishes for large N, Smax is slowly increasing with N.
Effect of adsorbate proximity on surface reactions: Synthesis and decomposition of the formate intermediate in UHV from coadsorbed CO, H2O, and O on Rh(100)
Authors: Gurney Bruce A. , Ho W.
Published: July 2002

The coadsorption of CO, H2O, and O on the Rh(100) surface has been studied using temperature programmed electron energy loss spectroscopy (TP-EELS), temperature programmed reaction spectroscopy (TPRS), and low energy electron diffraction (LEED). Following exposure at 90 K both H2O and CO are adsorbed without decomposition on the O-covered surface. As the temperature is increased to between 150 and 200 K, TP-EELS reveals that hydroxyl (OH) is formed (with bending mode at 114 meV and stretching mode at 394 meV) and disappears as gas phase water is evolved at 260 K. Beginning at 220 K and continuing to 260 K, two new modes develop at 94 and 164 meV which we identify as the scissor [δ(OCO)] and symmetric stretch [νs(OCO)] modes of bidentate formate (HCOO). TP-EELS and TPRS establish that the formate decomposes near 290 K with gas phase CO2 and H2O as products. Based on EELS intensity vs temperature, the kinetics of formate production (activation energy E=8±2 kcal⋅mol−1, and preexponential ν=103±2 cm2⋅s−1) and decomposition (E=26±3 kcal⋅mol−1, ν=1017±2 s−1) were determined. The effect of varying the initial reactant concentrations on the rate of formate production indicates that adsorbate concentrations high enough to force CO and OH into adjacent sites are required for the reaction to proceed. The role of preadsorbed O is both to facilitate production of OH through reaction with coadsorbed H2O and to help provide the crucial crowding of the surface necessary for HCOO formation.
Semiclassical wave packet treatment of the rigid asymmetric rotor
Authors: Huber Daniel , Heller Eric J. , Harter William G.
Published: July 2002

We discuss a semiclassical treatment of the rigid asymmetric rotor that delivers eigenenergies as well as eigenstates. We give possibilities to improve the semiclassical wave functions to any accuracy required. The method is devised so that inclusion of vibrations is possible. As no information about energetically lower states is included in the procedure, the calculation of highly excited states is easier than with conventional quantum methods. Calculation of quantum splitting from semiclassical eigenstates is treated. We give numerical examples for every procedure developed, so that the performance of the theory can be judged.
Accurate third order energy of the H(1s)–H(1s) van der Waals interaction
Authors: Koga Toshikatsu , Uji-ie Mitsuru
Published: July 2002

We report an accurate coefficient of the leading third order energy (proportional to R−11) of the H(1s)–H(1s) van der Waals interaction based on the very accurate first order perturbation wave function obtained recently by using the momentum space technique.
Method for calculating the electronic structures of large molecules; helical polymers
Authors: Springborg Michael , Andersen Ole Krogh
Published: July 2002

We present a self-consistent one-electron scheme for calculating ground-state properties of large systems with complex boundaries. It is based on linear muffin-tin orbitals (LMTO’s) and the density functional formalism in its local approximation. A multiple-κ LMTO basis set is used. No shape approximations, neither for the potential nor for the charge density, are made. Outside the spheres the charge density is fitted to a series of atom-centered Hankel functions and the two- and three-center integrals used for the overlap and Hamiltonian matrices, as well as for the charge density fit, are performed analytically. Inside the spheres the non-muffin-tin part of the charge density is treated by spherical-harmonics expansions. It is shown how the method can be applied to helical polymers. Test calculations on the N2 molecule are reported.
A time-dependent wave packet analysis of the dynamics of transition state spectroscopy in one dimension
Authors: Jiang Jun , Hutchinson John S.
Published: July 2002

The transition state absorption spectrum and the dynamics of the excited state are calculated for a one-dimensional reactive system with the basic features of the reaction K+NaCl→KCl+Na. We have propagated a Gaussian minimum wave packet on two Eckart potential curves coupled by an intense laser field, where the bound states supported by the upper potential well are exactly solved. By applying time-dependent perturbation theory, the continuum–bound transitions are calculated, and a bound excited state is obtained when the wave packet reaches the interactive region. The transition probabilities show a strong dependence on laser frequency which is well explained by Franck–Condon calculations. By contrast, a Landau–Zener model is quantitatively incorrect. By studying the excited wave packet dynamics and the transition probability spectra at different times, we conclude that the excitation to the upper potential surface is not localized to crossings of the dressed potential curves.
Structure-property predictions for new planar forms of carbon: Layered phases containing s
p2 and s
p atoms
Authors: Baughman R. H. , Eckhardt H. , Kertesz M.
Published: July 2002

Structure, thermodynamics, and electronic properties are predicted for a new low energy phase of carbon which contains planar sheets equally occupied by sp2 and sp carbon atoms. The isolated planar sheets have the same planar symmetry as do the layers in graphite (p6m) and can be formally viewed as resulting from the replacement of one-third of the carbon–carbon bonds in graphite by –C 3/4 C– linkages. This material, called graphyne, is predicted to have a crystalline state formation energy of 12.4 kcal/mol carbon, which appears to be much lower than for any carbon phase which contains acetylenic groups as a major structural component. Based on the major structural reorganization required for graphitization and the observed high temperature stability of known model compounds, high temperature stability is predicted for graphyne. While graphyne will have similar mechanical properties as graphite, it is predicted to be a large bandgap semiconductor (Eg=1.2 eV) rather than a metal or semimetal. Based on this bandgap and the known behavior of related conjugated polymers having linear structures, interesting nonlinear optical properties (including a large third-order susceptibility) are expected. Property aspects are also predicted for other previously uninvestigated carbon phases which are structurally related to graphyne. Finally, structural features of alkali metal charge–transfer complexes of graphyne, which are expected to be metallic, and of related carbon phases are predicted.
Magnetic birefringence study of isotropic suspensions of tobacco mosaic virus
Authors: Photinos P. , Rosenblatt C. , Schuster T. M. , Saupe A.
Published: July 2002

The magnetic field induced birefringence in isotropic aqueous suspensions of tobacco mosaic virus (TMV) was measured as a function of temperature and concentration in high magnetic fields (100 kG). The temperature range was between 15 and 50 °C and the concentration range was between 4 and 20 mg/cm3. We find that the Cotton–Mouton constant (C) increases with decreasing temperature by 15%–20% over the entire range and extrapolates to infinity at a finite temperature of 110 to 150 K. At constant temperature, the measured ρ/C(ρ=number of TMV particles per cm3 of suspension) can be expanded in a power series of ρ, where the coefficients are expressed by the irreducible cluster integrals. At 20 °C the experimental values can be fitted to the linear form: ρ/λC=(2.09×1030–1.35×1015ρ)G2/cm3. For rigid cylindrical particles with l=3000 Å and d=180 Å, and using the rigid hard particle interaction model, we find for the first order coefficient 0.62×1015, i.e., a significant deviation for the rigid hard-rod model. This deviation is also indicated by the variation of C with temperature. We discuss the results on TMV and of similar measurements on phage fd in terms of the interparticle interaction and rigidity of the particles.
Reaction–diffusion dynamics in inhomogeneous systems
Authors: Ohtsuki Toshiya , Keyes Thomas
Published: July 2002

The macroscopic behavior of reaction–diffusion systems in inhomogeneous media is investigated theoretically. The phenomenological reaction–diffusion equation describing spatial and temporal evolution of the coarse-grained density is derived for systems where reactions take place only on the surface or in the inside of spherical static catalysts immersed dilutely. General cases of one-component reactions and two examples, X+Y→products and X⇄Y, Y+Y→ products, of multi(two)-component systems are considered. It becomes evident that in general, the phenomenological reaction–diffusion equation has a different functional form from that of the microscopic reaction–diffusion equation. In addition, it should be emphasized that accordingly as D→∞ or D→0, where D is a diffusion coefficient of reactants, the process exhibits two asymptotic behaviors, the reaction-controlled behavior and the diffusion-controlled behavior. In the reaction-controlled region, the system is homogenous on a macroscopic scale and the density dependence of the phenomenological equation is identical to that of the microscopic equation. In

the diffusion-controlled region, the coarse-grained density follows the Smoluchowski-type linear reaction–diffusion equation and decays exponentially for all cases regardless of the type of reactions. At intermediate regimes, the phenomenological equation is generally a nonanalytic function of the density and the system shows a complex space and time dependence. In case of the bimolecular reaction, X+X→products, for instance, the crossover from the expontential to the algebraic decay is observed. The existence of more than two limiting behaviors in multicomponent reactions is also elucidated but their essential features are same as those of one-component systems. It is argued that asymptotic properties clarified here are universal phemomena found in a wide variety of real inhomogeneous systems.
On the molecular weight dependence of the thermodynamic and of the hydrodynamic pair interaction between chain molecules. IV. Second virial coefficients revisited
Authors: Gundert F. , Wolf B. A.
Published: July 2002

In the preceding papers of this series, it has been shown theoretically and experimentally how the Flory–Huggins interaction parameter χ and the Huggins coefficient kH for polymers differing in molecular weight are built up from the contributions of inter- and intramolecular contacts between polymer segments. In the present work, new experimental material concerning solutions of well-fractionated polyisobutene (PIB) and polystyrene (PS) is presented which, for the first time, includes worse than theta conditions. Its evaluation corroborates the above concept and reveals two features not observed so far. As the solvent quality becomes very unfavorable, the parameters measuring the intermolecular contacts between segments increase as one would expect from the data obtained for good solvent conditions. In contrast to that, the intramolecular parameters no longer decrease smoothly below theta conditions, but show a drastic reduction. This behavior is attributed to coil-collapse phenomena. The second feature concerns the following observation: If the inter- and intramolecular parameters are plotted as a function of the Kuhn–Mark–Houwink exponent, differences in the behavior of PIB and PS become noticeable under certain conditions. These observations are explained by the influence of the particular architecture of the polymer chain.
A study of generalized potential surfaces
Authors: Jug Karl , Krüger Thomas
Published: July 2002

The previously developed concept of generalized potential surfaces is applied to a three-state model system with a single nuclear coordinate. For polyatomic systems the method is reformulated in internal coordinates. On the basis of SINDO1 calculations a qualitative explanation of the nuclear coupling between the ground and first excited state of azulene is given.
Vibrational spacings for H+3
Authors: Hamilton Ian
Published: July 2002

Vibrational spacings for H+3 are calculated for two different fits to the potential energy surface of Dykstra and Swope. We use a variational calculation with a distributed Gaussian basis (DGB); the calculation is shown to be simple and efficient.
A coupled cluster study of the stability of lithium clusters
Authors: Förner Wolfgang , Seel Max
Published: July 2002

Coupled cluster studies on Li2, on the Li6 ring and on other Li6 clusters are reported. In its linear approximation the coupled cluster method gives a larger fraction of the correlation energy for Li2 than the nonlinear version, although other physical properties like force constant and bond length are described unsatisfactory. The planar Li6 ring is predicted to be stable in the equidistant form. Larger rings tend to have a Peierl’s distorted alternant geometry on the Hartree–Fock level. Thus Li behaves somewhat similar to (CH)n, while for Hn also the n=6 ring is distorted. The stability of equidistant six-membered rings is therefore attributed to the existence of rather delocalized 2s electrons. The comparison of the results for Li6 clusters of different symmetry (D6h,Oh,C5v) with similar calculations reported in the literature indicates that the inclusion of p-functions is essential, whereas the size of the s function subspace is not very important.
The role of 〈r2μ2〉 in the response of the mean square dipole moment to the expansion of a family of model chains
Authors: Mattice Wayne L.
Published: July 2002

The response of the mean square dipole moment 〈μ2〉 to chain expansion has been studied in a family of chains for which 〈r ⋅ μ〉0=0. Here r and μ are the end-to-end and dipole moment vectors, respectively, angle brackets denote the statistical mechanical average, and zero as a subscript denotes the ensemble unperturbed by long range interaction. For some of these chains, 〈μ2〉 increases upon chain expansion, while for other chains 〈μ2〉 decreases when the chain expands. At small expansion, the behavior is described by n0.43 (〈r2μ2〉0/〈r2〉0〈μ2〉0−1), where n denotes the number of bonds.
A thermodynamic perturbation theory for multicomponent and polydisperse mixtures
Authors: Kincaid John M. , MacDonald Rosemary A. , Morrison Graham
Published: July 2002

We describe a general perturbation method that can be used to solve the equilibrium and critical-point conditions for model systems described by an analytic Helmholtz free energy. The general technique is developed within the framework of continuous or polydisperse systems; it may be applied to systems with discrete components, as well as to systems described by a continuous distribution of components. The expansion is based on the assumption that the microscopic parameters characterizing the system may be expressed as those of a reference system plus a series of ‘‘small’’ corrections. Explicit formulas for the first- and second-order solutions to the equilibrium and critical-point conditions are given. The low-order perturbation solutions will be useful when the phase boundaries of the system are close to those of the reference system.
Spin fluctuations of paramagnetic iron centers in proteins and model complexes: Mössbauer and EPR results
Authors: Schulz C. E. , Nyman P. , Debrunner P. G.
Published: July 2002

We have analyzed the Mössbauer spectra of several iron proteins in the regime of intermediate fluctuation rates of the magnetic hyperfine interaction using the dynamic line shape model of Clauser and Blume. All Mössbauer data were recorded in applied fields so that the electron Zeeman interaction is much larger than the hyperfine splittings. We modeled the transitions between the eigenstates of the electronic spin Hamiltonian by an effective spin–phonon coupling V(1)=V0∑′i,j=x,y,zSi Sj and described the phonons in the Debye approximation. With V0 as the only adjustable parameter the model reproduced the major temperature dependence of the spectral shapes for spins from S=1 to S=5/2. We found V0 to lie in the narrow range 3 K ≤V0/k≤19 K, which is of the order of the zero-field splittings, but does not correlate with it. The smallest values of V0 were observed in the four-coordinate iron–sulfur proteins. Refinements and implications of the model are discussed.
Molecular structural changes at the phase transitions in thermotropic liquid crystals: A spectroscopic study of 4-dodecyloxy-4′-cyano biphenyl
Authors: Galbiati Elisabetta , Zerbi Giuseppe
Published: July 2002

The analysis of the vibrational infrared and Raman spectra of 4-dodecyloxy-4′-cyano biphenyl (12-OCB) reveals characteristic structural markers which describe the evolution of the molecular structure through K–SA and SA–I phase transition. The conformational collapse of the dodecyloxy residue into a ‘‘liquid-like’’ structure unquestionably occurs at K–SA transition. A rearrangement of the conformation of the biphenyl residue is also observed.
An analytical approximation to the HNC pair correlation functions: The case of 2:2 electrolytes
Authors: Corti H. R. , Fernández Prini R. , Blum L.
Published: July 2002

An analytical form of the HNC pair correlation function for the primitive ionic solution is proposed. This form interpolates between the EXP and MSA approximations. For 2:2 electrolytes it gives very good agreement to the thermodynamics and pair correlation function of the HNC.
The coadsorption of oxygen and potassium on Ru(001): Evidence for the formation of K–O compounds
Authors: de Paola R. A. , Hoffmann F. M. , Heskett D. , Plummer E. W.
Published: July 2002

In order to study an adsorption system where bond formation between coadsorbates competes with the adsorbate–metal substrate bond, we have investigated the interaction between oxygen and a potassium monolayer on Ru(001). At low exposures of oxygen (0.4 L), vibrational, photoemission, Auger, and workfunction data indicate the formation of a KO2 species. EELS spectra are characterized by an intense K–O stretch at 240 cm−1 and the absence of Ru–O stretching modes. Auger spectra indicate a K:O stoichiometry of 1:2 and photoemission spectra contain features indicative of O–O bond formation. Subsequent exposure of oxygen results in the adsorption of atomic oxygen with a characteristic Ru–O stretching vibration at 615 cm−1. Annealing of the K–O layer results in the decomposition of KO2 to Kad+Oad, both being bonded more strongly to the metal substrate than the individually adsorbed species and thus indicating through-metal interactions between atomic oxygen and potassium.
Synthesis and structure–property aspects of poly(carbon diselenide)
Authors: Iqbal Z. , Correale S. T. , Reidinger F. , Baughman R. H. , Okamoto Y.
Published: July 2002

Poly(carbon diselenide), (CSe2)x, is obtained as a black powder either by thermal polymerization of CSe2 solutions at high pressure, slow thermal polymerization under ambient conditions of neat CSe2, or photopolymerization of CSe2 solutions. X-ray diffraction measurements indicate that the as-prepared polymer is highly disordered and does not contain free crystalline or amorphous selenium. This result contrasts with the extensive formation of free selenium in the high pressure, high temperature polymerization of neat CSe2. The electrical conductivity is below 10−6 S cm−1, which is consistent with a band gap of ∼2 eV obtained by diffuse reflection spectroscopy. Details of the thermal properties, and the optical absorption, electron spin resonance, infrared absorption, Raman scattering, and extended x-ray absorption fine structure (EXAFS) spectra of the polymer are discussed. The EXAFS data clearly indicate that Se–Se bonds (but not Se chains) are present. The resonance-enhanced Raman and infrared absorption spectra are consistent with the presence of conjugated carbon–carbon and C=Se bonds, respectively. Based on these results, the structure indicated for (CSe2)x is the head-to-head polymer Se ∥ [–Se–Se–C–C–]n, ∥ Se rather than the head-to-tail polymer Se Se ∥  ∥ [–C–Se–C–Se–]n, proposed by previous workers. This polymer thermally decomposes above about 130 °C to form trigonal selenium as a by-product.
Electronic structure of polyisothianaphthene
Authors: Lazzaroni R. , Riga J. , Verbist J. , Brédas J. L. , Wudl F.
Published: July 2002

We investigate the electronic structure of polyisothianaphthene, comparing the experimental data obtained by x-ray photoelectron spectroscopy (XPS) with the results of valence effective Hamiltonian calculations. In the neutral form, the theoretical density of valence states is in very good agreement with the experimental measurements. The shifts observed for the core and valence levels upon doping confirm the very low value of the band gap in this system. Several models explaining the evolution of the line shapes in the oxidized polymer are discussed.
Harmonic autocorrelation function: Application to diatomic photoelectron spectra
Authors: Lee Soo-Y. , Lim Swee-Kim
Published: July 2002

The time-dependent formulation of photoabsorption or photoionization is used to derive an analytical expression for the autocorrelation function of a Gaussian wave packet moving in an excited state harmonic potential. The short time limit of the harmonic autocorrelation function is used to analyze the experimental autocorrelation functions, obtained by the Fourier transformation of diatomic photoelectron spectra without the need for any corrections, to give information about the excited state surfaces of the ionic species. It yields both the frequency and the displacement in the equilibrium geometry of the local harmonic fit to the anharmonic excited state surface taken about the equilibrium geometry of the ground electronic state. The method can be viewed as the quantum mechanical analog to the classical analysis of the Franck–Condon picture of photoabsorption or photoionization of diatomic molecules in the harmonic approximation. It is (a) easy to use, (b) provides one bound for the displacement in the equilibrium geometry between excited and ground electronic states, (c) gives the displacement to within 10% of results obtained by rotational analysis, and (d) attaches a definite sign to the displacement which the conventional harmonic Franck–Condon analysis cannot do. The reflection autocorrelation function and the information that it carries about the excited state potential is also discussed.
Photochemical reactions of ClF and BrF with hydrogen in solid argon. Infrared spectra of mixed hydracid dimers
Authors: Hunt Rodney D. , Andrews Lester
Published: July 2002

Argon diluted samples of H2 and ClF were codeposited at 10 K, and no reaction was observed. Photolysis produced a sharp 2834.5, 2832.5 cm−1 doublet, in agreement with (HF)(HCl) dimer from HF and HCl codeposition experiments. Irradiation at 14–16 K markedly increased the mixed dimer and produced weak monomer and dimer bands of HCl and HF, mixed trimer absorptions, and a sharp band at 3857.9 cm−1 for the Cl--HF radical complex. In similar experiments with HD, two mixed dimers, (HF)(DCl) and (HCl)(DF), were formed; likewise, photolyzing D2 with ClF produced two mixed dimers of the form (DF)(DCl) and (DCl)(DF). In the H2 and BrF system, photolysis produced a sharp absorption at 3814.6 cm−1, in agreement with (HBr)(HF) dimer from HBr and HF codeposition experiments, and a new 3830.5 cm−1 band due to the Br--HF radical complex. In a parallel study with HD, two mixed dimers, (HBr)(DF) and (DBr)(HF), were observed while only one mixed dimer, (DBr)(DF), was formed by BrF and D2. In complementary experiments with H2 and Cl2, (HCl)2 was observed at 2818.1 and 2816.2 cm−1.
van der Waals induced polarization: The influence of the magnetic dipolar interaction
Authors: Van Labeke D. , Grossel Ph. , Vigoureux J. M.
Published: July 2002

Usual studies of van der Waals interactions between two systems only take into account electrical interactions. However we show that, when calculating the induced dipole, two sorts of terms must appear: the first ones (characterized by the presence of a quadrupolar transition) are well known. The others (which characterize magnetic interactions) have never been considered. We study and compare these two kinds of terms. As in previous papers, we use quantum electrodynamics and retardation effects are taken into account. In the near zone limit, the magnetic terms varying as 1/R5 are generally negligible when compared to the quadrupolar terms which vary in 1/R7. In the Casimir zone, the new magnetic terms are of the same order as the quadrupolar ones, and show a 1/R8 dependence.
Comments on a model influence functional for quantum systems
Authors: Wu David , Carmeli Benny , Chandler David
Published: July 2002

We continue the study of a model non-Gaussian influence functional proposed by Allinger, Carmeli, and Chandler [J. Chem. Phys. 84, 1724 (1986)] to approximate the exact influence functional resulting from integrating out all quantum states but those of primary interest. The premise of this work is that the influence of many secondary states on a single primary state can be closely approximated by the influence of a degenerate level of states with equal coupling to the primary state. The degeneracy reflects the fluctuations possible among the secondary states and in fact can be associated with the partition function of the exact secondary states. The new calculations presented herein emphasize the importance of entropic-like effects properly described by this degeneracy, and for the models we examine, our basic premise is shown to be correct.
Pair correlation functions and density profiles in the primitive model of the electric double layer
Authors: Plischke Michael , Henderson Douglas
Published: July 2002

In the primitive model of the electric double layer an electrolyte near a charged surface is modeled by an assembly of charged hard spheres in a medium of dielectric constant ε. We solve numerically the inhomogeneous Ornstein–Zernike equation for the pair correlation functions in the hypernetted chain and mean spherical approximations together with the Lovett–Mou–Buff–Wertheim equation for the density of the ions near a charged surface. For highly charged surfaces the profiles display layering and charge reversal. The density profiles and diffuse layer potential are generally in excellent agreement with Monte Carlo data. The pair correlation functions at small separation are significantly different from correlation functions in the bulk and at larger separation have the well-known power law decay (r−3) as function of separation when both hard spheres are kept at constant distance from the surface.
High-resolution laser spectroscopy of strontium isocyanate, SrNCO
Authors: O’Brien L. C. , Bernath P. F.
Published: July 2002

The 0–0 band of the Ã 2Π–X̃ 2Σ+ transition of the linear free radical strontium monoisocyanate, SrNCO, was recorded at high resolution. By comparing the molecular constants of SrNCO with related molecules, the NCO− ligand was found to be nitrogen bonding to the strontium atom. The spectrum is extremely dense because of the small rotational constant, B″=0.0426 cm−1, and overlapping sequence structure. The Sr–N bond length was estimated to be 2.26 Å in the ground X̃ 2Σ+ state.
The effect of an unusual type of quenched disorder on phase transitions: Illustration in a mixed-valence system
Authors: Adachi Steven H. , Panson Andrew E. , Stratt Richard M.
Published: July 2002

Although quenched disorder can modify the Hamiltonian of a solid in a variety of ways, a relatively small number of microscopic models have been employed to study the effects of disorder. It is becoming clear, however, that the phase diagrams of disordered systems can be extremely sensitive to the precise form of the disorder. A case in point is provided by a disordered version of the mixed valence compound FeIIFeIII2O(OAc)6(py)3(py). We suggest that when some fraction of the FeIIFeIII2 complexes are replaced with CoIIFeIII2 complexes, the effect is analogous to putting magnetic impurities into a spin model (rather than to either the more conventional nonmagnetic impurities or to random fields). We note that the mixed valence example can be analyzed in terms of two simpler models which illustrate this novel form of disorder: an Ising ferromagnet with some fraction of spins randomly quenched into either ‘‘up’’ or ‘‘down’’ states, and an Ising antiferromagnet with a finite fraction of quenched up spins. The models are studied with a cluster mean field theory and via simulation. For these models (and by extension, for the mixed valence system), we predict that there should be anomalously long relaxation times and a zero temperature critical impurity concentration which is not determined by ordinary percolation.
Photochemical hole burning of 1,4-dihydroxyanthraquinone in polymer glasses: Poly(ethylene), poly(methacrylic acid), and their copolymer systems
Authors: Tani Toshiro , Itani Akira , Iino Yasuhiro , Sakuda Makoto
Published: July 2002

Photochemical hole spectra of 1,4-dihydroxyanthraquinone in polymer matrices at liquid helium temperatures were investigated by changing the main chain structure of polymer molecules systematically. Polymer molecules adopted here were poly(ethylene-co-methacrylic acid) (EMA) and its homopolymers poly(ethylene) (PE) and poly(methacrylic acid) (PMAA). Polarity of matrices or the number density of the electric dipoles mainly localized around the methacrylic acid units are decreased in the sequence of PMAA, EMA, and PE. Remarkable matrix effects on the hole-growth profiles were observed: The holewidth in the saturated regime decreased with decreasing the polarity of the polymer matrices from 1.4 cm−1 in PMAA through 0.15 cm−1 in EMA to 0.05 cm−1 in PE. The model of the photoinduced hole broadening is proposed in relation to the nature of two-level systems of the polymer glasses which exert influence on the holewidth. Dipole–dipole coupling is possibly a dominant interaction in the present systems. The results on the annealing properties of holewidth are also discussed.
Collision-induced intramolecular energy flow and fragmentation in van der Waals complexes: Atom+tetramer collisions
Authors: Shin H. K.
Published: July 2002

Intramolecular energy flow and fragmentation processes in a linear van der Waals complex consisting of four molecular units undergoing collision with an incident atom are studied by solving Hamilton’s equations of motion for positions and momenta of all molecular units and van der Waals bonds. Numerical results are obtained for an O2 tetramer, which is in interaction with an argon atom: Ar+(1–2⋅⋅⋅3–4⋅⋅⋅5–6⋅⋅⋅7–8). Energy flow is found to be very efficient, and above the fragmentation threshold most of the energy transferred to the complex through the collision of the first unit (1–2) of the complex with Ar is found to become localized at the terminal van der Waals bond 5–6⋅⋅⋅7–8, the dissociating mode, thus causing the end molecular unit (7–8) to break off. Short-time dynamics of energy buildup in each molecular unit and van der Waals bond is analyzed in detail.
Structure of the correlation energy in 3d1 systems
Authors: Jankowski Karol , Rutkowski Andrzej
Published: July 2002

Third-order pair energies and the total third-order energy are obtained for the first time for an atomic system containing 3d electrons. The variational–perturbation method is applied within the framework of the Rayleigh–Schrödinger perturbation theory with H0=HHF. The N-electron first-order wave function is defined in terms of orbital configurations of one-electron functions and symmetry-adapted pair functions in the form of partial-wave (PW) expansions. Extensive basis sets including all PW up to l,l′≤9 are used. For Zn2+ the total third-order energy amounts to about 9% of the second-order energy obtained in the same basis set, which is considerably more than for closed-shell ten-electron systems. Values of the energy functional for the function ψ0+λψ1 are also reported. The latter represent the most accurate variational results obtained so far for atomic systems containing 3d electrons.
The microwave spectrum of CO in the a 3Π state. II. The submillimeter wave transitions in the normal isotope
Authors: Carballo Norbert , Warner Hugh E. , Gudeman Christopher S. , Woods R. Claude
Published: July 2002

Precise measurements of the frequencies of a number of new rotational transitions of a 3Π CO (v=0–4) in the range 250–500 GHz are reported. In addition earlier measurements of the J=0–1 frequencies near 90 GHz have been repeated at higher precision and extended to include the v=6 lines. The nonlinear least-squares analysis of this microwave data combined with the lambda doublet transition frequencies of Klemperer and co-workers was carried out for v=0–4 by direct diagonalization of a Hamiltonian matrix that included the relevant v subblock of the a 3Π state along with the subblocks for v′=0–10 of the a′ 3Σ+ state. The new frequencies make possible the determination from the rf-microwave data set of several parameters that previously had to be assumed, and the method of treating most of the a–a′ perturbations directly in the large matrix yields parameters, especially lambda doubling constants, which vary less, but more smoothly, with J than before. The later smoothness is found to be enhanced by inclusion of an off-diagonal, spin–spin interaction in the a–a′ perturbation Hamiltonian, as was done in published fits of FTIR spectra of the a′ 3Σ+–a 3Π system. We also discuss the theory of the perturbed Zeeman effect of a 3Π CO, along with some preliminary measurements, and report a value of the pressure broadening parameter for a typical rotational transition in this state.
Zero-field and high-field electron paramagnetic resonance (EPR) of Cr3+ in some cage complexes
Authors: Strach Steven J. , Bramley Richard
Published: July 2002

High-field and zero-field electron paramagnetic resonance spectra of polycrystalline [Cr diamsar]Cl3⋅H2O, [Cr diamsar H2]Cl5⋅xH2O, and 1% Cr/rac[Co diamsar H2]Cl5⋅1.5H2O were recorded (diamsar≡1,8-diamino-3,6,10,13,16,19-hexaazabicyclo [6.6.6] eicosane). Combining the high- and zero-field spectra made determination of the spin-Hamiltonian parameters from powder spectra an easy matter, even with two sites in the cobalt host case. Full matrix refined parameters are given, but an iterative perturbation method was used with the actual field B rather than the central field, B0=hν/gμB, to get accurate parameters. Corrected perturbation formulas are given. For a rigid cage ligand like diamsar, there is considerable variation in the spin-Hamiltonian parameter D and evidence that the principal axis of the corresponding interactions does not necessarily lie close to the ligand’s threefold axis.
Analysis of the stability of the nematic phase consisting of semiflexible surfaces
Authors: Odijk Theo
Published: July 2002

The stability of the nem atic phase composed of structureless semiflexible surfaces interacting via their mutual excluded volume is analyzed. A highly oriented state would be unfeasible in the second virial approximation. It is argued that higher-order virial terms could stabilize the nematic state.
Differential force law and related integral theorems for a system of N identical interacting particles. II. Spherical symmetry
Authors: Baltin R.
Published: July 2002

The differential force law (DFL) and related integral theorems, derived in a previous paper for general geometries, are applied to spherical systems of identical interacting particles, e.g., electrons. From the special functional form of the first-order density matrix, induced solely by symmetry, the DFL occurs as a scalar, pointwise equation relating radial and rotational parts, trad and trot, of the kinetic energy density t to the force density f and to derivatives of the particle density n. Furthermore, an exact connection between the pressure p, trad, and n is established. Finally some theorems are derived which relate integrals, extending over an arbitrary concentric part of the system and involving t, p, and f, to values of p, n, and n′ at the surface of the sphere with radius R. One of these theorems is a generalized virial theorem tending to the usual well-known virial theorem in the limit R→∞.
Calculation of the nuclear spin–spin coupling constants. V. Configuration interaction calculation of σ- and π-electron contributions
Authors: Fukui H. , Miura K. , Sakurai T.
Published: July 2002

Configuration interaction calculation for σ- and π-electron contributions to the nuclear spin–spin coupling constants in acetylene and ethylene molecules is presented. The calculation is performed by the sum-over-states configuration interaction (SOS-CI) method with the two kinds of electron correlation approximations, which use the singly and doubly excited configuration interaction (SD-CI) calculation for the ground state and use the S-CI or SD-CI calculation for the excited triplet states. Quantitative agreement between the calculated and experimental coupling constants is not good, but the π-electron contribution Jπ shows the same trends for all the used basis sets and two approximations of electron correlation. Jπ contributes negligibly to the one-bond coupling constants 1JCC and 1JCH, but it makes important contributions to the two-bond coupling constants 2JHH and 2JCH.
Morphology, linear and nonlinear optical studies of poly[1,6-di(N-carbazolyl)-2,4 hexadiyne] thin films (pDCH)
Authors: Le Moigne J. , Thierry A. , Chollet P. A. , Kajzar F. , Messier J.
Published: July 2002

A joint work on morphology, structure, and nonlinear optical properties of vacuum evaporated thin films of pDCH on different amorphous or monocrystalline substrates is presented. The thin film evaporation of some diacetylene monomers on the alkali-halide single crystals leads to epitaxy with particularly good biorientation of the polymer chains, the b repetitive distance of the monomer matches well with two equivalent [110] and [1̄10] directions of the cubic KBr cystal. Polymerization is thermally induced. The resulting pDCH films are polycrystalline with low optical defects. Crystal sizes are in the range of 0.1 to 0.3 μm with some long needles of 2–3 μm length. Third harmonic generation (THG) and electric field induced second harmonic generation (EFISHG) measurements on disordered thin films show the two-photon resonances at 1.35–1.45 μm wavelength range, similarly as in other polydiacetylenes, with resonant values 〈χ(3) (−3ω; ω,ω,ω)〉=(1±0.1)×10−10 esu (THG) and 〈χ(3) (−2ω, ω,ω,0)〉=(6.4±0.4)×10−11 esu (EFISHG). The biorientational order of the pDCH chains observed by electron microscopy on various alkali-halide single crystals is confirmed on a macroscopical scale by third harmonic generation. As expected for a bioriented film, the angular dependence of THG intensity follows the theoretical law. So, for the first time, both morphological and optical techniques have been used in combination to characterize thin films and have shown a nearly perfect biorientation of the polymer crystals.