bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared hole burning of ammonium tartrate: How high a barrier can be overcome?
Authors: Chen Zhan , Strauss Herbert L.
Published: July 2002

The N–D stretching bands of NH3D+ ions doped into ammonium tartrate are studied by spectral hole burning. The crystal structure is known from diffraction studies and the barriers to ammonium-ion rotation from NMR. The N–D bands cover a wide range of hydrogen-bond strengths, and the widths of the bands and the corresponding holes fit the same correlation with frequency as do the N–D stretches in mixed ammonium-alkali sulfates. The energy imparted to the ammonium ion by the excitation of the N–D stretch is about the same as the energy required to surmount the reorientational barrier. However, the bands can be burned and this further defines the possible mechanism for reorientation. The high barriers make it possible to hole burn to high temperatures—up to 90 K. The apparent activation energy for the reorientation of the ions in the dark is about half of the potential barrier, a characteristic of tunneling reactions.
Ab initio spin-free-state-shifted spin-orbit configuration interaction calculations on singly ionized iridium
Authors: Rakowitz Frank , Casarrubios Marcos , Seijo Luis , Marian Christel M.
Published: July 2002

This work presents a systematic test of the performance of a spin-orbit operator founded upon the Wood-Boring-based ab initio model potential method [J. Chem. Phys. 102, 8078 (1995)]. Assuming a separability of the problem into a spin-free correlation treatment and a spin-orbit calculation part, this aim can be reached. We shall show in this publication both the separability and the high level of quality of the spin-orbit operator applying our method to the even spectrum of Ir+. We shall treat the spin-orbit part by means of the above mentioned spin-orbit operator and cope with the spin-free correlation problem through introducing a spin-free-state-shifting operator, shifting the spin-free energies to empirical values obtained from experiment. The quality of the spin-orbit operator is very high, actually better than estimated in previous calculations which were contaminated by an insufficient treatment of correlation. The procedure established is most efficient: Spin-free-state-shifted spin-orbit CI calculations employing a space of the significant reference configurations plus single excitations lead to very reliable spin-orbit splittings provided that the spin-free states are calculated at a high level of quality.
Experimental and ab initio study of the infrared spectra of ionic species derived from PF5, PF3, and F3PO and trapped in solid neon
Authors: Lugez Catherine L. , Irikura Karl K. , Jacox Marilyn E.
Published: July 2002

When a Ne:PF5 or a Ne:PF3 mixture is codeposited at 5 K with a beam of neon atoms that have been excited in a microwave discharge, the infrared spectrum of the resulting solid shows a complicated pattern of new absorptions. Little fragmentation of PF5 into PF3 occurs, but several of the absorptions can be tentatively attributed to PF4. The results of extensive ab initio calculations of the vibrational spectra of the neutral, cation, and anion species of formula PFn are presented, in order to aid in the product identification. Several absorptions of PF4+, PF3+, and PF2+ are identified, with only PF3+ common to both systems. Other prominent absorptions are contributed by PF5−, PF4−, and PF3−. In all of the Ne:PF5 experiments and some of the Ne:PF3 experiments, F3PO was a major contaminant. Therefore, ab initio calculations were also conducted for most of the neutral and charged species that can result from F3PO. There is strong evidence supporting the identification of two of the vibrational fundamentals of F3PO−, and some evidence for a third. Tentative assignments are suggested for neutral and other charged species derived from F3PO.
A nonlocal current density functional for magnetic responses
Authors: Salsbury Freddie R. , Harris Robert A.
Published: July 2002

A nonlocal current density which is a gauge invariant functional of the electron density in the absence of the magnetic field is constructed. Unlike local functionals, which reduce to the Thomas–Fermi current density in the limit of zero gradients, the new functional treats diamagnetism exactly. Additionally, unlike earlier local functionals, the new functional has the capacity to support net paramagnetism. The full magnetic susceptibility and chemical shielding tensor density functionals are also derived.
Precise study of nonlinear optical coefficients and hyperpolarizabilities in cold-drawn and poled ferroelectric Nylon 11 films
Authors: Tsutsumi Naoto , Mizutani Toru , Sakai Wataru , Watanabe Toshiyuki , Miyata Seizo
Published: July 2002

This paper presents a precise study of second-order optical nonlinearity of uniaxially cold-drawn and poled ferroelectric Nylon 11 films. The effects of drawing and poling on refractive indices and second-order nonlinear optical coefficients have been investigated. Drawing caused increase of refractive index (n) parallel to the drawing direction nX, and decrease of n perpendicular to drawing direction in the plane of film nY, as well as decrease of n on the poling direction parallel to film thickness direction nZ. Poling caused significant increase of nZ and decrease of nY. These n results imply that poling aligns the molecular chains so that carbonyl groups in Nylon backbone orient in the poling direction (Z-axis). Cold-drawn and poled Nylon 11 films belong to the mm2 point group. Dependence of second-order harmonic generation (SHG) intensity on incidence angle, i.e., Maker fringe pattern, could be precisely fitted using five independent nonzero tensor components, d33, d32, d31, d15, and d24. However, Kleinman symmetry was not satisfied: d31≠d15 and d32≠d24. The tensor components d33, d31, d15, and d24 increase with increasing remanent polarization, whereas the value of d32 was negligibly small irrespective of the intensity of the remanent polarization. Tensor components of microscopic first-order hyperpolarizability, βzxx, βzyy, βzzz, βxxz, and βyyz were determined. Tensor component βzzz was the largest and βzxx had negative sign. Second-order nonlinearity was largely suppressed in the vicinity of the melting point of Nylon 11.
Calculations of phase transition of polydiacetylenes using localized molecular orbitals by elongation method
Authors: Kurihara Youji , Aoki Yuriko , Imamura Akira
Published: July 2002

Photoinduced phase transition models between two distinct structures (acetylene and butatriene types) of polydiacetylene were investigated by using an elongation method. The geometries of these oligomers were optimized with ab initio self-consistent field. The wave functions for the calculation of the excitation energies were obtained with complete neglect of differential overlap in spectroscopy (CNDO/S approximation) by the elongation method. The excitation energies were calculated by using the single excitation configuration interaction method on the basis of localized molecular orbitals. The energy diagram for the phase transition is plotted and the structural change associated with the photoinduced excitation is discussed.
Neutral rare-gas containing charge-transfer molecules in solid matrices. III. HXeCN, HXeNC, and HKrCN in Kr and Xe
Authors: Pettersson Mika , Lundell Jan , Khriachtchev Leonid , Räsänen Markku
Published: July 2002

The synthesis of novel rare-gas compounds HXeCN, HXeNC, and HKrCN is reported. HKrCN represents the first stable compound with a Kr–C bond. The novel molecules are formed in solid Xe and Kr by first photolyzing monomeric HCN with a 193 nm ArF laser at 7.5 K. The photolysis produces isolated hydrogen atoms and CN radicals as evidenced by IR spectroscopy and laser induced fluorescence. Annealing of the Kr matrix at ∼30 K and Xe matrix at ∼50 K activates the hydrogen atoms, and they react with rare-gas atoms surrounding the CN radicals producing the rare-gas compounds, which are characterized in this work by means of IR spectroscopy and ab initio calculations. Other products observed are HNC and H2CN. Infrared induced photochemical conversion of HXeNC to HXeCN is accomplished by exciting the Xe–H and C–N stretching fundamentals of HXeNC. The existence of low barrier between these two distinct isomers is confirmed by the ab initio calculations.
Dynamic isotope effect on the product energy partitioning in CH2OH+→CHO++H2
Authors: Rhee Young Min , Kim Myung Soo
Published: July 2002

The deuterium isotope effect on the product energy partitioning in the title reaction was investigated both experimentally and theoretically. The measured kinetic energy release (KER) showed a significant dependence on the position of deuteration. A reliable potential energy surface of the reaction was constructed from ab initio results using the recently developed interpolation algorithm. The classical trajectory calculation on this surface well reproduced the experimental finding. Close inspection of the potential energy surface revealed that the isotope effect on KER and the product rotations arose from the alteration of the symmetry of the reaction path near the transition state induced by the mass change upon isotopic substitution. The product vibrations were found to be affected by the change in the coupling constants which also arose from the mass-dependent change in the reaction path. Possibility of the quantum mechanical tunneling was also considered. Tunneling-corrected classical trajectory results were in excellent agreement with the experimental ones, indicating that the reaction proceeds via barrier penetration below the threshold.
Symmetric Lennard-Jones mixtures in two dimensions
Authors: Vlot Margot J. , van der Eerden Jan P.
Published: July 2002

Two-dimensional NPT Monte Carlo simulations are performed for binary mixtures of Lennard-Jones particles, D and L. The DD-interactions are equal to the LL-interactions. The optimum DL-distance is changed using one parameter in the Lennard-Jones potential by s=σDL/σDD, resulting in nonadditive mixtures. Simulations of the solid phase yields various crystal structures, like triangular, square and hexagonal solid solutions, which are compared with our previous results of analogous three dimensional mixtures [M. J. Vlot et al., J. Chem. Phys. 107, 4345 (1997). In most cases, the 2D crystals are layers from the corresponding 3D compounds. The Gibbs free energy is measured to determine the stability limits. Raising s from s=1 (ideal mixture) to 1.2 a remarkable chainlike order, to which we refer to as spaghetti order, develops continuously in the solid phase. Increasing s further, results in a transition to a liquid, again with clear spaghetti ordering. Topologically these structures show similarities to structures occurring during spinodal decomposition, but our spaghetti solid and liquid are much more stable than the demixed states. We suggest a structure parameter deduced from the partial radial distribution functions (DD and DL), to detect the spaghetti structure.
Mean-field hierarchical equations for some A+BC catalytic reaction models
Authors: Cortés Joaquı́n , Puschmann Heinrich , Valencia Eliana
Published: July 2002

A mean-field study of the (A+BC→AC+12B2) system is developed from hierarchical equations, considering mechanisms that include dissociation, reaction with finite rates, desorption, and diffusion of the adsorbed species. The phase diagrams are compared to Monte Carlo simulations.
Solvent effect on the optical properties of [(NH3)5Ru–pyrazine]+m (m=2,3) complexes by ab initio calculations
Authors: Cacelli Ivo , Ferretti Alessandro
Published: July 2002

We have carried out a study, by ab initio methods, of the solvent effect on [(NH3)5Ru–pyrazine]m+ (m=2 and 3) complexes, which are of interest as basic units of metallic chains with potential application in molecular electronics and photonics. We have performed multireference configuration interaction (CI) calculations in which solvent effects are included by the Polarizable Continuum Model. A new method for the estimate of the size of the cavities in this approach, which has proven to be suitable for the specific case under study, is also proposed. Our calculations account for the red shift of the metal-to-ligand charge transfer band, observed experimentally for the Ru(II) compound as the solvent donor number increases, and furnish an explanation with a solid theoretical foundation. For the Ru(III) compound we find that the ground state configuration is different in vacuum and in electron donor solvents.
Cross sections for rotational excitations of NH3, PH3, AsH3, and SbH3 by electron impact
Authors: Varella Márcio T. do N. , Bettega Márcio H. F. , da Silva Antônio J. R. , Lima Marco A. P.
Published: July 2002

We report elastic and rotationally inelastic cross sections for e−–XH3 collisions (X: N, P, As, Sb) at the static-exchange level of approximation. The energy range was from 7.5 up to 30 eV. Our fixed-nuclei scattering amplitudes were obtained through the Schwinger multichannel method with pseudopotentials (SMCPP) [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)]. The rotational cross sections were obtained with the help of the adiabatic-nuclei-rotation approximation. There is good agreement with available experimental elastic cross sections. In order to improve rotational cross sections at small scattering angles for the dipole-allowed 00→10 rotational excitation, we have combined the SMCPP and the first Born approximation of the full interaction potential and also of the dipole moment potential. To our knowledge this is the first time that rotational excitation cross sections for these molecules are reported.
Real time monitoring of the evaporative cooling: Application to the dynamics of NaI-(NH3)n clusters
Authors: Grégoire G. , Mons M. , Dimicoli I. , Dedonder-Lardeux C. , Jouvet C. , Martrenchard S. , Solgadi D.
Published: July 2002

The picosecond evaporation dynamics of ammonia molecules from Na(NH3)n clusters produced via the dissociation of NaI within an ammonia cluster is studied experimentally. A time dependence of the mass selected ion signal is observed only for one cluster size and not for larger clusters nor for smaller ones. It will be shown that evaporation in the ionic state is responsible for the absence of an observation of the evaporation in the neutral state. The variation of the ionization cross section with cluster size is the key point for the interpretation of the results.
Infrared laser spectroscopy of CCO: The ν1 band of the ã1Δ electronic state
Authors: Moazzen-Ahmadi N. , Boeré R. T.
Published: July 2002

The rotationally resolved infrared spectrum of the ν1 band of the long-lived ã1Δ electronic state of the CCO radical has been observed between 1918 and 1970 cm−1 using a tunable diode laser spectrometer. Metastable CCO was produced in a discharge through a flowing mixture of carbon suboxide and helium. Fifty eight rovibrational transitions in the P and R branches and the five lowest J lines in the Q branch were measured. The band origin was determined to be 1942.8515(19) cm−1. This is in close agreement to the values determined previously from photoelectron spectroscopy of CCO−.
Time-dependent wave packet study of the one atom cage effect in I2–Ar Van der Waals complexes
Authors: Zamith S. , Meier C. , Halberstadt N. , Beswick J. A.
Published: July 2002

We performed a time-dependent wave packet study to investigate the fragmentation and recombination of the I2–Ar Van der Waals complex following excitation above the B-state dissociation limit. Based on a recently published ab initio potential energy surface of the ground state [C. F. Kunz, I. Burghardt, and B. Hess, J. Chem. Phys. 109, 359 (1998)], we studied the possible kinematic origin of the “one-atom cage effect” by three-dimensional wave packet propagation within the rotational infinite order sudden approximation. We found that final vibrational distributions depend strongly on the ground and excited state equilibrium geometries. Taking uncertainties in the excited state potential into account, we confirm a possible kinematic origin of the one-atom cage effect from a collinear isomer of the I2–Ar complex, initially proposed by Valentini and Cross [J. J. Valentini and J. B. Cross, J. Chem. Phys. 77, 572 (1982)].
Attraction between like-charge polyions in diluted highly asymmetric ionic mixtures
Authors: Schmidt Anatoly B.
Published: July 2002

Using the virial expansion to the Ornstein–Zernike equation, it is shown that an attraction between like-charge polyions can occur, even in diluted ionic mixtures with finite polyion concentration, providing that the polyion Debye parameter proportional to the polyion size is sufficiently high.
The effect of laser bandwidth on the signal detected in two-color, resonant four-wave mixing spectroscopy
Authors: Di Teodoro F. , McCormack E. F.
Published: July 2002

The effect of laser line shape and bandwidth on the signal detected in two-color, resonant four-wave mixing (TC-RFWM) spectroscopy is determined by means of an ab initio calculation of the third-order polarization based on diagrammatic perturbation theory. Modifications to the approach previously used for the case of δ-function laser line shapes are made by introducing a different treatment of the rotating wave approximation and phase-matching conditions. A three-level excitation scheme for double-resonance spectroscopy of bound and quasibound states is analyzed. In the case of Lorentzian laser line shapes, analytic expressions for the signal line profile are obtained for each excitation scheme. Analytic approximations of the signal line profile are also obtained in the case of Gaussian laser line shapes.
Symmetry and structure of rotating H3+
Authors: Kozin I. N. , Roberts R. M. , Tennyson J.
Published: July 2002

We present a global study of how the relative equilibria of the H3+ ion change as the angular momentum J increases. A relative equilibrium is a classical trajectory for which the molecule rotates about a stationary axis without changing its shape. The study confirms previous results which show that the geometry of the minimum energy relative equilibria changes from an equilateral triangle to a symmetric linear configuration at around J=47. The series of bifurcations and stability changes that accompany this transition is presented in detail. New results include the discovery that the rotating equilateral triangle remains linearly stable for a large range of angular momentum values beyond the point where it ceases to be a minimum of the total energy. A third type of relative equilibrium, a rotating isosceles triangle, is also found to be linearly stable in the approximate range J=0–34. Both the equilateral and isosceles triangle configurations lose stability via Hamiltonian–Hopf bifurcations. The frequencies and symmetry species of the normal modes of the stable relative equilibria are computed and harmonic quantization is used to predict how the symmetries of the lowest lying quantum states will change as J increases. Energy level clustering due to tunneling between symmetry-equivalent relative equilibria is described.
Transition probability due to a conical intersection: On the role of the initial conditions and of the geometric setup of the crossing surfaces
Authors: Ferretti Alessandro , Lami Alessandro , Villani Giovanni
Published: July 2002

We have carried out a study of the dynamics in a two-state, two-mode conical intersection with the aim of understanding the role played by the initial position of the wave packet and the slope of potential energy surfaces at the conical intersection point on the transition probability between the two diabatic states. Studying the dynamics for a single period of the tuning oscillator, we find two distinct rules that can be used for a qualitative prediction of the behavior of the transition probability after the first passage through the conical intersection and after a period (two passages). The first quantity is relevant for systems undergoing a rapid, irreversible decay and the second one for understanding in what kinds of conditions one has to expect a periodic fluorescence spectrum.
Tunneling through the potential barrier of the B1Πu state of Li7–Li7
Authors: Bouloufa N. , Cacciani P. , Vetter R. , Yiannopoulou A.
Published: July 2002

A sub-Doppler experiment involving an effusive beam of lithium dimers and a continuous wave (cw) tunable dye laser is used to record the absorption spectrum of the B–X system. Predissociation due to tunneling through the potential barrier of the B state is studied in a small range of energy above the Li(2p)+Li(2s) dissociation limit by analyzing the shape of homogeneously broadened absorption lines and by measuring the fluorescence intensity of Li atoms. Experimental data are interpreted in the frame of a semiclassical dynamical model involving the shape of the potential barrier. Their accuracy should address an improvement of the potential shape through a full quantal dynamical model.
Simplified model for the analysis of interaction types in two-stranded coiled-coils
Authors: Gil María M. , Rubio Ana M. , Rey Antonio
Published: July 2002

We investigate here the adequate balance between hydrophobic and electrostatic interactions in the correct folding of two-stranded, parallel coiled-coils. We have used a very reduced model of rigid straight helices, simulated by means of a Monte Carlo algorithm. The amino acid side chains are reduced to the level of β-carbons, which interact through simple Lennard-Jones-type potentials. The model is able to reproduce the association of only two chains to form dimers, when peptides with a highly regular sequence are studied. For a given value of the parameter controlling the strength of interactions between hydrophobic residues, the electrostatic interactions between charged residues are systematically analyzed. We conclude that the optimum contribution of electrostatic interactions to the global stability of the dimer is about 20%. Weaker interactions provide a substantial population of missfolded antiparallel dimers, while larger electrostatic interactions create associations between dimers. The optimized model has been tested with other simplified sequences, providing results consistent with experimental evidence.
Classical nucleation theory for the nucleation of the solid phase of spherical particles with a short-ranged attraction
Authors: Sear Richard P.
Published: July 2002

Classical nucleation theory is used to estimate the free-energy barrier to nucleation of the solid phase of particles interacting via a potential which has a short-ranged attraction. Due to the high interfacial tension between the fluid and solid phases, this barrier is very large, much larger than in hard spheres. It is divergent in the limit that the range of the attraction tends to zero. We predict an upper limit on nucleation in good agreement with the results of experiments on the crystallization of proteins.
Electronic nonadiabaticity in highly vibrationally excited O2(X 3Σg−): Spin-orbit coupling between X 3Σg− and b 1Σg+
Authors: Jongma Rienk T. , Shi Shiming , Wodtke Alec M.
Published: July 2002

We report full quantum-state-resolved spectra of highly vibrationally excited O2(X 3Σg−,v=26–31). In addition to providing high precision molecular constants for several new vibrational levels, we observe a local spectral perturbation of X 3Σg−(v=28). We present a deperturbation analysis of the observed spectra and assign the perturber to b 1Σg+(v=19). We predict a crossing between the b 1Σg+ and X 3Σg− state at an internuclear separation R=2.45±0.1 Å, somewhat further extended and higher in energy than the outer classical turning point of O2(X 3Σg−,v=28). Using the appropriate vibrational overlap integral, we are able to determine the spin–orbit interaction between these two electronic states, which is 200±20 cm−1 in the vicinity of the crossing. These results suggest that the collision dynamics of highly vibrationally excited O2(X 3Σg−) may involve excited potential surfaces. Furthermore, they imply that present theoretical approaches to the O4 problem, which use a single potential surface, may not be adequate. Possible implications regarding nonequilibrium models of stratospheric ozone formation and the dynamics of the O+O3→2O2 reaction are discussed.
Electrostriction in field-structured composites: Basis for a fast artificial muscle?
Authors: Martin James E. , Anderson Robert A.
Published: July 2002

The electrostriction of composites consisting of dielectric particles embedded in a gel or elastomer is discussed. It is shown that when these particles are organized by a uniaxial field before gelation, the resulting field-structured composites are expected to exhibit enhanced electrostriction in a uniform field applied along the same axis as the structuring field. The associated stresses might be large enough to form the basis of a polymer-based fast artificial muscle.
Proton polarization transfer in a ring system
Authors: Khitrin A. K. , Fung B. M.
Published: July 2002

The transfer of homonuclear spin polarization in a small ring system of protons which are coupled with dipole–dipole interaction has been explored experimentally. The approach was to follow the magnetization transfer from one initially polarized proton to other protons in a benzene molecule dissolved in a liquid crystal matrix. The results show that, at times up to about 100 ms, the magnetization of the initially polarized spin oscillates around a value higher than 1/6 of its initial magnetization, and the system does not approach a state close to thermodynamic equilibrium on this time scale.
Development and experimental verification of a theory for high-field, ultralow-temperature magnetic linear dichroism of glasses containing molecular chromophores with spin doublet ground states
Authors: Bominaar Emile L. , Peterson Jim
Published: July 2002

The first observation of magnetic linear dichroism in a metalloprotein Kramers system is reported, namely, that exhibited by the porphyrin moiety in ferricytochrome c (spin S=12). The measurements were conducted at low temperatures and in strong magnetic fields to maximize the signal intensity, which is intrinsicly weak in this case. The theory used in the interpretation of the wavelength dependence of this magneto-optical effect is based on the rigid-shift approximation in which the dichroic spectra are expressed as a sum of zeroth, first, and second derivatives of the underlying electronic absorption band. Similar to the case for magnetic circular dichroism, magnetic linear dichroism is caused by the Zeeman interactions of the molecular-chromophore electrons with an applied magnetic field. Two kinds of Zeeman interaction are considered, termed “inner state” and “outer state” depending on, respectively, whether or not they act between the components of a single Kramers doublet of the chromophore. It is formally demonstrated that the zeroth-derivative term for an electric-dipole transition between Kramers doublets arising from inner-state Zeeman interactions (nominally the strongest effect) completely cancels in the powder average over a randomly oriented ensemble of chromophores for all values of temperature and field. This cancellation has a profound effect on the magnetic linear dichroism of molecular chromophores suspended in glasses, as the effect now entirely relies on a set of weaker residual terms, each one having its own spectroscopic characteristics. The residual contributions have been estimated on the basis of electronic-term-energy differences and bandwidths in ferricytochrome c, resulting in the identification of the inner- and outer-state terms C1 and F0 as the dominant signatures. This prediction is in agreement with the experimental data for the shape and dependence on applied field and temperature of the magneto-dichroic spectrum for this chromophore. The magnetic linear dichroisms arising from inner- and outer-state Zeeman interactions in a system with S=12, like the one considered here, are of comparable magnitude, which makes the information content of magnetic linear dichroism distinctly different from that obtainable from magnetic circular dichroism, where the inner-state contributions dominate. From this analysis, magnetic linear dichroism emerges as the preferred magneto-optical spectroscopy for assessing outer-state Zeeman interactions under cryogenic conditions and is, in this respect, complementary to magnetic circular dichroism.
Large two-photon absorption cross sections in two-dimensional, charge-transfer, cumulene-containing aromatic molecules
Authors: Norman Patrick , Luo Yi , Ågren Hans
Published: July 2002

Ab initio simulations of two-photon absorption in donor–acceptor substituted cumulene-containing aromatic molecules have been carried out. The results reveal that these two-dimensional, charge-transfer species possess particularly large two-photon absorption in the visible region with possible applications for optical limiting.
Core ionization energies of carbon–nitrogen molecules and solids
Authors: Snis A. , Matar S. F. , Plashkevych O. , Ågren H.
Published: July 2002

Core ionization energies have been calculated for various carbon–nitrogen molecules and solids. The systems investigated contain many of the bonding possibilities which presumably arise in carbon nitride thin films prepared under varying conditions. The molecular core ionization energies are calculated by the ΔSCF self-consistent field method. Several singly, doubly, and triply bonded CxNyHz species have been considered. Core ionization energies of two C11N4 C sp2 and C sp3solids have been calculated with the full-potential linearized augmented plane wave method. Molecular C 1s binding energies increase with approximately 1 eV for each singly or doubly bonded nitrogen atom attached. The trend is similar in the solids although variations and saturation effects are obtained due to hybridization and nitrogen content. The 1s binding energies of two-coordinated nitrogen atoms in C sp2 molecules and of pyramidal three-coordinated nitrogen atoms in C sp3 molecules are close to each other. The differences depend on the size of the systems and the number of CH3 groups attached. In the solid state compounds, where no CH3 groups are present, the energies of two-coordinated nitrogen in a C sp2 environment are always lower than the energy of pyramidal three-coordinated nitrogen in the C sp3 solid, by more than 1 eV. Concerning the micro structure in thin CNx films, comparisons of the computational results with experiment indicate that at low nitrogen concentrations the atomic configuration close to the N atoms are mostly of sp3 character. At higher N contents more two-coordinated nitrogen atoms are incorporated. The N 1s binding energy shifts observed at high substrate temperatures could be explained by either a gradual formation of three-coordinated N atoms in a graphitic-like C sp2 environment or by local domains containing high N concentrations.
Ground state and vertical electron detachment energies of icosahedral and D5h Al13−
Authors: Dolgounitcheva O. , Zakrzewski V. G. , Ortiz J. V.
Published: July 2002

Al 13 − clusters are studied with ab initio, many-body methods. Coupled-cluster theory places the icosahedral structure 0.54 eV lower than the D5h isomer. Electron propagator predictions on the photoelectron spectrum of Al13− are in close agreement with the observed bands and attribute shakeup character to features at higher energy.
Lateral instabilities of cubic autocatalytic reaction fronts in a constant electric field
Authors: Tóth Ágota , Horváth Dezső , van Saarloos Wim
Published: July 2002

The region of instability for planar reaction fronts of cubic autocatalysis between ionic species under constant electric field has been determined accurately. The ratio of diffusion coefficients at the onset of instability δcr is substantially varied by the component-dependent drift and directly proportional to the concentration of the autocatalyst behind the front βs as δcr=2.3002βs. This opens the possibility to use electric field as a control parameter for reaction-front instabilities. The dispersion relation calculated from the linear stability analysis of the full system is in good agreement with the initial evolution of the Fourier modes associated with the slightly perturbed planar reaction front obtained by the direct integration of the governing equations in two spatial dimensions.
Comment on “Ab initio dynamic dipole polarizabilities for O2, its photoabsorption spectrum in the Schumann–Runge region, and long-range interaction coefficients for its dimer” [J. Chem. Phys. 109, 9802 (1998)]
Authors: Lewis B. R. , Gibson S. T. , Yoshino K.
Published: July 2002

The oscillator-strength density calculated ab initio for the Schumann–Runge transition of O2 by Spelsberg and Meyer [J. Chem. Phys. 109, 9802 (1998)] is assessed against an up-to-date experimental database.
Ab initio study of the gas-phase structure and electronic properties of M–CH3 (M=Li, Na) and M–CCH (M=Li, Na, K): A combined post-Hartree–Fock and density functional theory study
Authors: Scalmani G. , Brédas J. L. , Barone V.
Published: July 2002

The structure of isolated, monomeric M–CH3 (M=Li, Na) and M–CCH (M=Li, Na, K) has been recently determined by millimeter/submillimeter rotational spectroscopy. These accurate experimental results offer the opportunity for an extensive ab initio study of these molecules in order to assess the accuracy of the latest developments in density functional theory (DFT). As a general trend, DFT results from hybrid functionals (B1LYP, mPW1PW91, and PBE0) are in very good agreement with experiment while conventional functionals (BLYP) show slightly larger errors. In addition, DFT methods show rapid basis set convergence, whereas post-HF techniques [MP2, QCISD, and CCSD(T)] give comparably good results only using large basis sets. The properties derived from the electron density are computed to a fairly similar accuracy by all methods, provided a large basis set is used. The importance of a proper treatment of electron correlation in the description of the bond between the carbon and the alkali metal atom is emphasized.
Charge-transfer effects in the gas-phase protonation of ozone: Locating the conical intersections
Authors: Ceotto M. , Gianturco F. A.
Published: July 2002

We have performed fully correlated calculations using as a basis set the cc-pV5Z expansion with geometry optimization for the O3H+ moiety and have then calculated the partial cuts of the potential energy surfaces (PESs) for the first two roots using the cc-pDZP basis set expansion. Two electronically induced conical intersections (CIs) were found in the Cs-plane subspaces and one of them was accurately located by calculating the geometric phases for different path integrals. We also discuss the adiabatic versus nonadiabatic effects and suggest a kinetic mechanism for the dynamics of the gas-phase protonation of ozone which includes the role played by the present conical intersections. We also try to provide useful suggestions for the practical search of conical intersections based on a physically guided subspace factorization.
Orientation and symmetry of ethylene on Pd(110): A combined HREELS and NEXAFS study
Authors: Okuyama H. , Ichihara S. , Ogasawara H. , Kato Hiroyuki , Komeda T. , Kawai Maki , Yoshinobu J.
Published: July 2002

The orientation and symmetry of low-coverage ethylene adsorbed on Pd(110) at 150 K were studied by high-resolution electron energy-loss spectroscopy (HREELS) and near-edge x-ray absorption fine structure (NEXAFS) analysis. HREELS measurements unambiguously revealed that ethylene is π-bonded with the C–C axis preferentially aligned along the [11̄0] row; this finding was also confirmed by NEXAFS. The molecular symmetry of this species was found to be C1 and thus, we proposed that the C–C axis is tilted against the surface. The effect of coadsorption with hydrogen was examined, and a flat-lying species with C2 symmetry was found to dominate on H-covered Pd(110). Furthermore, the coadsorbed hydrogen induced the C–C axis rotated about the surface normal, possibly reflecting the zigzag phase formation of adsorbed hydrogen atoms.
Energy disposal in collisions of nitric oxide with molecular adlayers on transition metal single crystal surfaces: Translational energy disposal
Authors: Ainsworth M. K. , McCombie J. , McCoustra M. R. S. , Chesters M. A.
Published: July 2002

The dynamics of the scattering of nitric oxide (NO) from well-characterized and ordered layers of carbon monoxide (CO) and ethylidyne (CCH3) adsorbed on a Pt(111) substrate have been investigated by time-of-flight methods. Time-of-flight profiles for scattered NO are reported for a range of incident NO translational energies between 10 and 50 kJ mol−1 from scattering substrates at 108 and 300 K. The measurements reveal that scattering occurs both into a trapping-desorption channel and a direct inelastic channel. The latter is accompanied by a significant (>60%) loss in the NO translational energy. This is true for both substrates and contrasts markedly with the many observations made of atomic and molecular scattering from clean metal single crystal planes. Hard cube model calculations are presented as a basis for the interpretation of the direct inelastic behavior that point toward a surface collision partner mass of the same magnitude as the incident molecule and toward differences in the strength of the NO-adlayer attractive interaction as the origin of subtle changes in the scattering behavior from the low temperature substrates as a function of the incident translational energy.
On the triplet–singlet energy gap of acetylene
Authors: Le Hung Thanh , Flock Michaela , Nguyen Minh Tho
Published: July 2002

The triplet–singlet energy gap of acetylene, Te(3B2–1Σg+), was calculated using the coupler-cluster theory including all single and double excitations plus perturbative corrections for the triples, and multiconfigurational second-order perturbation theory methods with large basis sets. The cis-bent triplet state (ã 3B2) is calculated to lie 30 500±500 cm−1 above the ground singlet state (1Σg+); the latter value differs somewhat from the most recent evaluation of T0=28 900 cm−1 [Amed et al., J. Chem. Phys. 110, 4248 (1999)] but agrees well with an earlier theoretical estimate of 30 270 cm−1 [Yamaguchi et al., Theor. Chim. Acta 86, 97 (1993)]. Thus the discrepancy of 1000 cm−1 may well arise from an interpretation of experimental results rather than a shortcoming of theoretical calculations.
Fractional power dependence of the mean lifetime of a first order reaction on the time scale of environment relaxation in the slow diffusion limit
Authors: Okada Akira
Published: July 2002

We investigated the fractional power dependence of the mean lifetime on a time scale of environment relaxation for first order reactions described in terms of the reaction–diffusion equation with bounded diffusion. Modifying the static (nondiffusing) approximation so that the decay rate at long times becomes correct, we calculated the values of the powers in the slow diffusion limit. As a result, they were found to be fractional, depending on the sink term and the initial condition. The values of the powers obtained by the theory are in agreement with those found by direct numerical calculations for slow diffusion. In the case of the harmonic sink, we proved that the theory gives the correct values of the powers in the slow diffusion limit.
Local dynamics of isotactic and syndiotactic polypropylene in solution
Authors: Destrée M. , Lauprêtre F. , Lyulin A. , Ryckaert J.-P.
Published: July 2002

The local dynamics of polypropylene (PP) in solution is studied by C13 NMR relaxation and by molecular dynamics (MD) simulation via the orientational autocorrelation function (OACF) of C-H bonds. The interpretation protocol of this function proposed by Dejean de la Bâtie, Lauprêtre and Monnerie (DLM) [R. Dejean de la Bâtie, F. Lauprêtre, and L. Monnerie, Macromolecules 21, 2045(1988)] is applied and tested on new NMR measurements of the various microstructures of polypropylene. This interpretation scheme of the OACF is supported by a detailed study employing simulated PP trajectories in an atomistic heat bath. MD simulations indicate that, quite generally, the correlation time for segmental motions, τ1, extracted from the DLM motional model is closely linked with the mean time between conformational jumps. Both experiments and simulations suggest a slightly higher mobility of meso sequences by comparison with racemic sequences. Our analysis of the microscopic aspects of the segmental dynamics and its manifestation in motional models allows us to trace the microscopic origin of the larger mobility of meso sequences.
Influence of cross-linking on the segmental dynamics in model polymer networks
Authors: Kramarenko V. Yu , Ezquerra T. A. , Šics I. , Baltá-Calleja F. J. , Privalko V. P.
Published: July 2002

In an attempt to study the specific influence of cross-linking on the α relaxation in polymer networks, a series of model heterocyclic polymer networks (HPN) with well-defined cross-link densities and constant concentration of dipolar units were studied. Model HPN systems were prepared by simultaneous trimerization of 1,6-hexamethylene diisocyanate (HMDI) and hexyl isocyanate (HI). These HPN systems were characterized by dielectric relaxation spectroscopy in the 10−1 Hz<F<105 Hz frequency range and in the 123 K<T<493 K temperature interval. The α relaxation in these systems depends on network density and shifts toward higher temperatures as the cross-link density increases for high HMDI/HI ratios. Discussion of the α-relaxation shape in light of recent models indicates that segmental motions above the glass transition systematically experience a growing hindrance with increasing degree of cross-linking. Description of the temperature dependence of relaxation times according to the strong–fragile scheme clearly shows that fragility increases as polymer network develops.
Temperature dependent relaxation and recombination dynamics of the hydrated electron
Authors: Madsen D. , Thomsen C. L. , Thøgersen J. , Keiding S. R.
Published: July 2002

The ultrafast solvation and recombination dynamics of the hydrated electron generated by two-photon ionization of water at 4.65 eV is studied by transient absorption spectroscopy as a function of temperature in the range from 277 K to 355 K. The part of the spectral blue shift which is observed in the absorption spectrum of the hydrated electron after 1 ps is purely continuous and is accurately described by the well known analytical expression for the temperature dependent absorption spectrum of the ground state hydrated electron. This indicates that thermal relaxation or more likely solvation of the hydrated electron predominantly causes the blue shift. The survival probability of the hydrated electron shows a strong temperature dependence, which is satisfactory explained by the temperature dependent mobility and reaction rates of the species involved in the recombination. This implies that the average initial separation between the hydrated electron and the ionization site of 〈r0〉=1.0±0.1 nm does not depend significantly on the bulk water temperature.
Effects of pressure on radiation processes in solid hydrogen: An ESR study
Authors: Kumada Takayuki , Shevtsov Valeri , Aratono Yasuyuki , Miyazaki Tetsuo
Published: July 2002

The effect of pressure on yields of H atoms produced by X-irradiation of solid hydrogen has been studied using electron spin resonance (ESR) spectroscopy at around 4 K. The yields of H atoms have been found to decrease with an increase in pressure. We have concluded that the above finding is due to cage effects on the reaction producing H atoms, H2→2H, H3++e−→3H, and so on, which should occur during X-irradiation of H2 molecules in solid hydrogen. The pressure dependence of the yields of H atoms can be explained by a large compressibility of solid hydrogen. This also indicates that the compressibility is one of the important parameters in radiation-chemical processes in the solid phase.
Exact calculation of the lineshape and the scattering operator for a model of a two-level atom interacting with a continuous spectrum of radiation
Authors: Davidson Russell , Kozak John J.
Published: July 2002

In this paper we calculate exactly the lineshape for a model of an excited two-level atom in interaction with a continuous spectrum of radiation for the problem of spontaneous emission. Specifically, for the case of a d=1 radiation field, we use the exact results reported in our earlier work [J. Math. Phys. 14, 414, 423 (1973)] for the probability ρ(τ) of the atom’s being in the excited state at time τ to obtain an analytic expression for the lineshape of the emitted radiation (i.e., the photon). We also calculate the lineshape using two Wigner–Weisskopf style approximations and the results, for a given choice of coupling function, are compared numerically with the profile generated using the exact solution. These comparisons show convincingly the success with which these two approximations can be expected to reproduce the qualitative and quantitative features of the exact lineshape for values of the coupling constant α ranging between 0.01 and 0.3. Finally, we calculate explicitly the scattering operator corresponding to the above spontaneous emission problem and work out exactly the probability of forward and backward scattering of a photon by the atom at and away from resonance.
The anti-self-dual Coulomb field in Minkowski space-time
Authors: Porter John R.
Published: July 2002

The twistor encoding of the anti-self-dual Coulomb field is given in terms of the space-time connections pulled back to I+ and to I−. This description differs considerably from that of the twistor encoding of transverse or radiation fields, which have been the only fields studied in this fashion to date. A twisted structure results on I+ and a topologically incomputable one on I− and these are identified modulo the null lines intersecting the source world-line.
Nonequilibrium statistical thermodynamics of second-order stochastic processes in the limit of large resistance
Authors: Lavenda B. H. , Serra R.
Published: July 2002

The phase-space generalization of the kinetic analog of Boltzmann’s principle is derived. A kinetic criterion for the contraction of a second-order (Ornstein–Uhlenbeck) to a first-order (Einstein–Smoluchowski) stochastic process is advanced on the basis of an asymptotic expansion of the joint entropy in the limit of large resistance. The kinetic criterion is shown to be the stationary solution to the first velocity moment of the phase-space Fokker–Planck equation. The Stratonovich criterion for the validity of the Einstein–Smoluchowski description is corroborated from the asymptotic expansion of the joint entropy. Second-order Gaussian processes are used for illustration where it is shown that (i) the principles of least dissipation of energy and maximum joint entropy are equivalent, and (ii) the observed, local velocity arises from an exact balance between rates of growth and decay of velocity fluctuations.
Glauber’s coherent states and the semiclassical propagator
Authors: Solari H. G.
Published: July 2002

This paper studies the classical propagator on Glauber’s coherent states in a generalized P-form. A full class of equivalent expressions labeled by a complex number is found through a direct WKB expansion. The study of matrix elements of the propagator between coherent states shows that they match Klauder’s classical expression but are in some disagreement in the semiclassical order with expression derived through path integral procedures. Arguments are given that favor the present results. The properties of the time propagator with respect to symmetry operations are stated. Possible extensions are briefly discussed.
Low-energy scattering for medium-range potentials
Authors: Newton Roger G.
Published: July 2002

The low-energy behavior of the transmission coefficient in one dimension and of the phase shifts in two and three dimensions is studied for the Schrödinger equation with central potentials that have finite absolute moments of order between 1 and 2. Resulting modifications of Levinson’s theorem are also derived.