bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamical and structural aspects of water in potassium ferrocyanide trihydrate
Authors: Savatinova I. , Anachkova E. 
Published: December 2004

AbstractThe present work reviews a systematic spectroscopic investigation of water in the single crystal K4Fe(CN)6 · 3H2O (KFCT) and its isotopic solid solutions. On the basis of precise polarization measurements of Raman spectra and infrared studies, the positions of the OH(OD) oscillators in the ordered crystal state (T < 150 K) are determined. Overtones and combinations of water vibrations in the near infrared region are studied that allow for the evalution of the coupling and anharmonicity constants of the modes. The isotopic dilution technique is used in order to investigate the influence of intra‐ and intermolecular interactions on the OH(OD) vibrations. Information about the distortion of the water molecules, as well as many correlations between spectral parameters of OH(OD) stretchings and structural characteristics of H bonds in KFCT, are derived. As a result, a complete picture of the vibrational dynamics and the structure of the crystallization water in KFCT is obtained.
Dynamic perturbation theory of energy transfer in nonrigid molecular systems: Vibrational predissociation of I2he van der waals molecule
Authors: Tachibana Akitomo , Nagaoka Masataka , Yamabe Tokio 
Published: December 2004

AbstractThe appearance of the maximum linewidth by the vibrational predissociation of I2He van der Waals (vdW) molecule as a function of the initial vibrational quantum number of I2 is predicted by the dynamic perturbation theory. The kinetic energy perturbation is introduced in addition to perturbation potential. The linewidth agrees quite well with experiment.
Theory of half‐collision cross sections
Authors: Girardeau M. D. 
Published: December 2004

AbstractStandard Lippmann–Schwinger theory does not apply to decay of metastable or unstable states due to failure of the adiabatic hypothesis. In the Fock–Tani representation, discrete unstable states can be described by state vectors orthogonal to the asymptotic states representing their decay fragments, and a decay/formation interaction is exhibited explicitly as a portion of the total interaction Hamiltonian. This allows a straightforward derivation of a generalized Lippmann–Schwinger “half‐collision” differential decay cross section without the need of projection operators. It reduces in first order to the product of a resonance line shape by a Golden Rule matrix element squared. In the general case the line shape is non‐Lorentzian and the matrix element factor contains final‐state interaction contributions. The exact expression is expected to be applicable to a variety of processes such as predissociation, autoionization, and Auger effect. The derivation employs the van Hove resolvent formalism to exhibit the dependence of the cross section on the complex self energy of the decaying state.
The electronic structure of 4H‐pyran‐4‐one and its sulfur analogues
Authors: Friedman Paul , Allen Leland C. 
Published: December 2004

AbstractThe electronic structure of 4‐H‐pyran‐4‐one and its sulfur analogues were studied using ab initio wave‐functions. Bond lengths and overlap populations suggest low aromaticity for this group of compounds. Examination of Jorgensen plots of the lowest π orbitals of I‐‐IV leads to the aromaticity order 4H‐thiopyran‐4‐thione (IV) > 4H‐thiopyran‐4‐one (II) > 4H‐pyran‐4‐thione (III) > 4H‐pyran‐4‐one (I). The effects of including d orbitals were studied using the 3‐21G, 3‐21G* (6d), and 3‐21G* (5d) basis sets. Optimized bond lengths, vibrational frequencies, ionization energies, and dipole moments were also obtained, and results for different basis sets were compared.
The theoretical approach to surface chemistry and heterogeneous catalysis
Authors: Simonetta Massimo 
Published: December 2004

AbstractTransition metals are the most interesting items among heavy atoms due to their extensive use in catalysis. Present understanding of heterogeneous catalytic reactions is still very poor, and new experimental and theoretical techniques have been developed in recent years with the aim of elucidating the mechanism of adsorption and reaction of simple molecules over metal surfaces or clusters. Empirical, semiempirical, and ab initio methods of calculations are briefly reviewed: results and perspectives are presented.
Calculated electronic spectra of model ferric cytochrome P450 complexes
Authors: Waleh Ahmad , Collins Jack R. , Loew Gilda H. , Zerner M. C. 
Published: December 2004

AbstractRestricted open‐shell ground state properties and electronic spectra of two closely related low‐spin, ferric, 6‐coordinate, model cytochrome P450 complexes, one with a methyl mercaptide and the other a mercaptan as the second axial ligands, have been calculated with a newly modified, semiempirical INDO‐SCF‐CI method. The sensitivity of the calculated spectra to protonation of the sixth axial ligand, and the ability of the method to predict characteristic spectral features for the complexes investigated, are determined. Assignment of transitions, including xy‐ and z‐polarized transitions, are made and compared with experimental observations where available. In particular, the origin of the anomalous split Soret spectrum observed in low‐spin ferric complexes with mercaptide but not a mercaptan is investigated. Finally, a two part hypothesis is presented which provides a general explanation for the origin of both the observed split Soret and the red‐shifted normal Soret in various ferrous and ferric P450 complexes in terms of the ground state orbital characters and simple symmetry considerations.
The proton affinity and the structure of protonated species of methylsilane
Authors: Kohda‐Sudoh S. , Katagiri S. 
Published: December 2004

AbstractAn ab initio LCAO‐MO‐SCF calculation was made on the proton affinity (PA) of methylsilane (CH3SiH3) by using STO‐3G, MIDI‐1, and MIDI‐1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH3SiH3 is 160.5 kcal/mol, which exceeds that of SiH4 by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ‐complex between CH4 and SiH. Other two species are also σ‐complexes between H2 molecule and SiH3CH or CH3SiH, and similar to CH, SiH, GeH, and C2H.
Molecular theory and cooperative mechanism of shock waves‐induced detonations in energetic molecular crystals
Authors: Odiot S. , Peyrard M. , Schnur J. , Oran E. 
Published: December 2004

AbstractAt a microscopic level, two molecular models, respectively one‐ and two‐dimensional, for describing the shock‐induced detonationmechanism of an energetic crystal have been previously successively presented (after initiation).We put together, here, their characteristic features, and we discuss their respective contributions inorder to define the molecular and crystalline conditions that a crystal fulfills to sustain a shock induced wave detonation. The two‐dimensional model which allows longitunal but also transversal atomic motions, has enabled us to elicit the crystalline structure in relation with the existence of a wave detonation propagation in the crystal or not. By comparison to detonation experiments the coherence of the models is performed. It may thus be possible to form an idea as to why a molecular compound can detonate through a shock wave.
A DFT study of the ground state of the N3 radical
Authors: Słupski Romauld B. , Wasilewski Jan 
Published: December 2004

AbstractThe X2 Πg ground state of the N3 radical has been studied by means of the DFT approach with inclusion of nonlocal (gradient) terms. Many different Gaussian basis sets of increasing quality, from small split‐shell type up to the TZPP class, have been used. For each of the basis sets, the experimentally known linear symmetric conformation has been optimized using the analytical gradient technique and the vibrational fundamentals have been calculated in the harmonic approximation using the numerical Hessian. For comparison, the standard UHF‐type calculations have also been performed. Despite the fact that the Kohn‐Sham equations have been resolved in the spin‐ and symmetryunrestricted manner, the nonlocal version of DFT is able to describe correctly the geometric properties and vibrational spectrum of this open‐shell degenerate state, provided that a good quality polarized basis set is used. © 1995 John Wiley & Sons, Inc.
Self consistent reaction field theory of solvent effects in the framework of Gaussian density functional method
Authors: Mineva Tzonka , Russo Nino , Toscano Marirosa 
Published: December 2004

AbstractElectrostatic and dispersion contributions of solute‐solvent interactions have been considered in the self‐consistent reaction field scheme and implemented in the LCGTO‐DF (linear combination of Gaussian‐type orbitals‐density functional) method. Results for the tautomeric equilibrium of formamide‐formamidic acid, for the cis‐trans energy difference in dichlorodiammineplatinum(II), and for H2OHF hydrogen‐bond systems are in agreement with the available experimental and previous high‐level ab initio data. The role of the dispersion energy is discussed for the different studied systems. © 1995 John Wiley & Sons, Inc.
Time‐dependent quantum fluid dynamics of the photoionization of the He atom under an intense laser field
Authors: Dey Bijoy Kr. , Deb B. M. 
Published: December 2004

AbstractA time‐dependent (TD), nonperturbative quantum fluid density functional equation of motion, developed in our laboratory, is numerically solved for studying the photoionization dynamics of the He atom under an intense, ultrasharp, ultrashort laser pulse. The generalized nonlinear Schrödinger equation is obtained through a hydrodynamical continuity equation and an Euler‐type equation of motion. It yields the electron density, effective potential surface, and other density‐based quantities from start to finish. Starting from the ground‐state Hartree–Fock density for He at t = 0, various singlet and triplet states of singly and doubly excited (autoionizing) He as well as several states of He+ have been identified in the time‐evolved electron density, by a Fourier transformation of the time variable of the complex autocorrelation function. Computer visualizations of the TD difference density and difference potential show distinctly nonlinear and extremely interesting geometrical features of the oscillating atom. Detailed mechanistic routes for multiphoton, sequential, and above‐threshold ionization have been obtained, each route involving many states. The present, comprehensive method reveals the important physical features of the atom–laser interaction and the calculated results are consistent with current experimental and theoretical results. This emphasizes the validity of the hydrodynamical approach for studying TD quantum mechanical phenomena. © 1995 John Wiley & Sons, Inc.
A density functional study of chemical reactions
Authors: Andzelm Jan , Baker Jon , Scheiner Andrew , Wrinn Michael 
Published: December 2004

AbstractDensity functional theory (DFT) was used to study reactions involving small molecules. Relative energies of isomers and transition structures of diazene, formaldehyde, and methylenimine were determined using various DFT functionals and results were compared with MP2 and MP4 calculations. DFT reaction barriers were found to be consistently lower. For some reactions, such as OH + H2→ H2O + H, gradient‐corrected functionals predict very low or nonexistent barriers. The hybrid Hartree–Fock–DFT adiabatic connection method (ACM) often provides much better results in such cases. The performance of several density functionals, including ACM, was tested in calculations on over 100 atomization, hydrogenation, bond dissociation, and isodesmic reactions. The ACM functional provides consistently better geometries and reaction energetics than does any other functional studied. In cases where both HF and gradient‐corrected DFT methods underestimate bond distances, the ACM geometries may be inferior to those predicted by gradient‐corrected DFT methods. © 1995 John Wiley & Sons, Inc.
Maximum‐entropy analysis of atomic compton profiles
Authors: Angulo J. C. , Yáñez R. J. , Antolín J. , Zarzo A. 
Published: December 2004

AbstractThe maximum‐entropy formalism is used to obtain approximations to the atomic Compton profile, 𝚥(q), in terms of the first few radial expectation values 〈Pn〉 of the momentum density γ(p). This method leads to the least‐biased results by the information not used. In particular, analytical and numerical approximations to the kinetic energy T and to the height of the peak 𝚥(O) and the half‐width q0.5 of the Compton profile are obtained. Our results generalize and improve some approximations to 𝚥(q) previously obtained by other authors. For illustration, the accuracy of these approximations are studied by means of near‐Hartree–Fock wave functions. © 1995 John Wiley & Sons, Inc.
Direct calculations of charge densities of solids: Applications to the alkali‐earth sulfides
Authors: Cortona P. , Monteleone A. Villafiorita , Becker P. 
Published: December 2004

AbstractWe performed ab initio self‐consistent calculations for the five alkali–earth sulfides—BeS, MgS, CaS, SrS, and BaS—by a method which allows the direct calculation of the ground‐state electron density without a preliminar determination of the wave functions and of the energy eigenvalues of the system. We report the results for the standard cohesive properties (equilibrium lattice parameters, dissociation energies, bulk moduli), a study of the relative stability of the 131 (NaCl), B2 (CsCl), and B3 (ZnS) phases, and of the behavior under pressure of these compounds (equation of state; pressure and change of volume associated to the structural phase transition B1 → B2 or B3 → B1). © 1995 John Wiley & Sons, Inc.
Density functional theory of the collective electronic excitations in NanKn clusters
Authors: Bol A. , Alonso J. A. , López J. M. 
Published: December 2004

AbstractThe collective electronic response of NanKn clusters has been studied for some model structures. In their low‐temperature lowest‐energy structure, those clusters have all the K atoms on the surface. The collective oscillation frequencies for clusters with the K atoms segregated to the surface are red‐shifted with respect to the corresponding frequencies for isomers with a very similar underlying skeleton but with the Na atoms segregated to the surface. The collective frequency varies smoothly with respect to the degree of relative segregation. These results may be useful in the analysis of the collective response of large alloy clusters and microcrystals. © 1995 John Wiley & Sons, Inc.
Beam brightness modulation (BBM) method as applied to Auger electron spectroscopy
Authors: Mogami A. 
Published: December 2004

AbstractThe principle of the beam brightness modulation (BBM) method, as well as such advanced characteristics as high speed response, wide dynamic range of primary beam currents, selective signal detection, and signal‐to‐noise superiority in N(E) spectra, are reported by comparing with both the conventional analyzer energy modulation and the pulse counting methods. Some device‐related technologies for the BBM method are also described as well as advantages of Auger electron spectroscopy (AES) using N(E) spectra obtained by the BBM method.
AES and HRTEM study of an a‐SiNx: H/W/WSix/a‐SiNx: H multilayer structure realized by PEVCD
Authors: Monteil C. , Durand J. , Berjoan R. , Cros B. , Martinez J. P. 
Published: December 2004

AbstractA multilayer insulator–metal–insulator capacitive structure was realized by plasma‐enhanced chemical vapour deposition for a discharge frequency of 35 kHz. The chosen materials were amorphous hydrogenated silicon nitride as the insulator and tungsten as the metal. An interlayer of tungsten silicide used as an adhesion layer is deposited between W and a‐SiNx:H. An AES depth profiling study coupled with high‐resolution transmission electron microscopy observation showed the presence of interphases: the interfacial zone between a‐SiNx:H and W is constituted by a WNx interphase ∼10 nm deep. Small crystallites are observed in tungsten‐based materials. The presence of a mixed phase containing tungsten, silicon, nitrogen and a small amount of oxygen is obvious and noticed on the AES spectra at the WSix/a‐SiNx:H interface: its thickness appears to be ∼7 nm.
Numerical methods for quantification of Auger sputter depth profiles from oxide films on stainless steels
Authors: Olsson Claes‐Olof A. 
Published: December 2004

AbstractAccurate quantification of Auger sputter depth profiles from oxide films on stainless steels is complicated by two spectral overlaps: O/Cr and Cl/Mo. The chlorine/molybdenum overlap is readily resolved using target factor analysis or any other related method, assuming that there is no molybdenum on the surface. The O/Cr overlap is more difficult to resolve, because the oxide films on stainless steels usually contain large amounts of chromium. It is shown that by using a Cr base spectrum acquired from a sputter‐cleaned surface and an oxide spectrum acquired from Mo oxide, it is possible to resolve the O/Cr overlap for passive films as well as annealing oxides. This gives less noise and higher accuracy, because the operator‐dependent definition of a background at the higher binding energy side of the Cr 529 eV peak is avoided.
New technique for the simultaneous correction of topographical and backscattering artefacts in electron‐excited Auger spectroscopy and microscopy
Authors: Crone M. , Barkshire I. R. , Prutton M. 
Published: December 2004

AbstractIn order to relate an Auger signal to the atomic concentration in the surface of a solid, it is well known that corrections have to be made for matrix effects. Also, corrections may be needed to compensate for the effects of artefacts caused by properties of the sample other than the concentration of different elements. Large artefacts can be caused by the surface topography and subsurface composition variations often present in ‘real’ samples. This paper reports a new correction scheme that enables the quantitative analysis of samples with a structure for which no prior knowledge exists. The scheme uses the ratio of the Auger peak height to a background count rate above the energy of all significant Auger features, combined with a linear correction invoving the atomic number of the substrate and the Auger backscattering factor. Inhomogeneous samples with angle of incidence variations from 0° to 45° and an arbitrary atomic number can be analysed with an accuracy of ∼5 at.% using this method. Limitations exist for thin unsupported films.
Formation of barium carbide during AES depth profiling of thin BaF2 films
Authors: Kashin G. N. , Makhnjuk V. I. 
Published: December 2004

AbstractInvestigations of barium fluoride thin films by AES were performed. During AES depth profiling we observed the transformation of surface carbon from graphite to carbide form. The role of ion and electron bombardment in such a transformation has been investigated. We suggest that under Ar+ bombardment the surface barium carbide is formed due to recoil implantation of surface carbon atoms into the barium fluoride film and subsequent chemical reaction with barium.
Electrophysiological responses of serotoninergic dorsal raphe neurons to 5‐HT1A and 5‐HT1B agonists
Authors: Sprouse Jeffrey S. , Aghajanian George K. 
Published: December 2004

AbstractA direct comparison was made of the effects of serotonin 5‐HT1A and 5‐HT1B selective compounds on the spontaneous firing rate of dorsal raphe serotoninergic neurons in chloral‐hydrate‐anesthetized rats. Following intravenous administration, the 5‐HT1A selective compounds ipsapirone (TVX Q 7821) and LY 165163 potently inhibited single‐unit activity in a dose‐dependent manner whereas the 5‐HT1B selective compounds, m‐chlorophenylpiperazine (mCPP) and trifluoromethylphenylpiperazine (TFMPP), displayed only weak or irregular actions. Low microiontophoretic currents of ipsapirone and LY 165163 were also effective in suppressing spontaneous firing; dose‐response relationships for the 5‐HT1A compounds were indistinguishable from that of 5‐HT itself. In contrast, dorsal raphe neurons were only weakly responsive to microiontophoretic application of mCPP and TFMPP; dose‐response relationships for the 5‐HT1B compounds were significantly displaced from that of 5‐HT. In intracellular studies, ipsapirone and LY 165163, when added to the media bathing brain slices, mimicked the actions of 5‐HT in hyperpolarizing dorsal raphe cell membranes and decreasing input resistance; however, the maximal effects of the 5‐HT1A compounds on these membrane properties exceeded those of 5‐HT. In summary, dorsal raphe 5‐HT neurons appear highly responsive to 5‐HT1A, but not to 5‐HT1B compounds; these findings are discussed with regard to the 5‐HT receptor subtypes as candidates for the somatodendritic autoreceptor of dorsal raphe neurons.
Development of presynaptic specializations induced by basic polypeptide‐coated latex beads in spinal cord cultures
Authors: Peng H. Benjamin , Markey Donald R. , Muhlach William L. , Pollack Emanuel D. 
Published: December 2004

AbstractThe development of the neuromuscular synapse in initiated by an interaction between the motoneuron processes and the skeletal muscle. Previously we showed that basic polypeptide‐coated latex beads can mimic the nerve in effecting a postsynaptic differentiation (Peng, H.B. and Cheng, P. ‐ C.: J. Neurosci., 2:1760–1774, 1982). In this study, we examined whether these beads can also induce a presynaptic differentiation along the nerve processes. Explant cultures were prepared from the spinal cords of Xenopus larvae and polyornithine‐coated latex beads (0.45–4.5 μm in diameter) were applied. After 1–2 days, the cultures were processed for light and electron microscopy. For light microscopy, the cells were permeabilized and labeled with a monoclonal antibody against a 65‐KD antigen on synaptic vesicles. Indirect immunofluorescence revealed that this antigen was concentrated at 60% of the bead‐neurite contacts, therefore suggesting the clustering of synaptic versicles at these sites. This phenomenon was not observed at the contacts between neurites and negatively charged (polycarboxylate) beads. However, a concentration of this antigen was also observed at the varicosities along the neurites cultured on polylysine substrate. Thin‐section electron microscopy showed the following features: (1) The neurites formed terminal‐like varicosities on the bead. (2) Within these varicosities, clusters of 50–60‐nm clear vesicles were prominent at the bead‐neurite contact. (3) Large (80–100 nm) dense‐cored vesicles were also present in the varicosity, but they did not form clusters. (4) Basement membrane did not form at the bead‐neurite interface, in contrast to its appearance at the bead‐muscle contact from our previous study. (5) Coated pits were occasionally observed at the contact area. Thus, our results show that the beads can induce a differentiation characteristic of the presynaptic nerve terminal along the spinal cord neurites.