bluuebunny/crossref_metadata_2025 huggingface dataset:
Wetting by polymers of a liquid–liquid interface: Effects of short-range interactions and of chain stiffness
Authors: van Eijk Marcel C. P. , Leermakers Frans A. M.
Published: July 2002

The behavior of both flexible and semiflexible polymers near a liquid–liquid interface is investigated with the aid of the self-consistent-field theory as developed by Scheutjens and Fleer. A ternary system (A/BN/C) is studied near the wetting transition. In a symmetric system, i.e., χAB=χBC=χ, a change in the interaction parameter χ introduces a wetting transition. The ratio of the interfacial width ξ of the binary A/C system and the coil size of the polymer determines the order of this transition. Beyond a certain chain length Nc (at fixed ξ) the wetting transition is of first order, whereas it is of second order for N<Nc. The characteristics of the prewetting line, including the prewetting critical point, are discussed in some detail. The nontrivial N-dependence of the position of this critical point is analyzed in terms of a crude thermodynamic model. For a semiflexible polymer an increase of the chain stiffness at a certain value of χ is sufficient to introduce a wetting transition.
Infrared and infrared-visible sum frequency generation spectroscopic response of harmonic monolayer vibrons: Homogeneous profile
Authors: Pouthier V. , Hoang P. N. M. , Girardet C.
Published: July 2002

We determine the profile of the vibrational band of an ordered monolayer adsorbed on a clean surface corresponding to the infrared spectrum and to the resonant infrared-visible sum frequency generation spectrum. The theoretical model is based on the renormalization of the monolayer and substrate Hamiltonians. The harmonic dynamics of the effective vibrons characterizing the collective internal vibrations of the admolecules is written in terms of a complex dynamical matrix whose elements can be expressed as correlation functions of the external libron and phonon modes. The dephasing broadening is obtained by solving a master equation for the time evolution of the vibron modes while the external dynamics of the layer is described by using molecular dynamics simulation. An application to the calculation of the profile of the vibrational band of the low temperature (2×1) CO monolayer adsorbed on NaCl(100) is performed without any adjustable parameter by considering a well established semiempirical potential to describe the molecule-surface and molecule-molecule interactions. The comparison with experimental spectra shows that the homogeneous phase relaxation due to the coupling between the vibrons and the monolayer phonons-librons accounts for the most part of the peak width and interprets the temperature dependence of this width. Extension of the calculations to the interpretation of the orientationally disordered phase obtained for CO at higher temperature is done which corroborates very well the temperature behavior of the monolayer structure and profile.
Quantum calculations of highly excited vibrational spectrum of sulfur dioxide. I. Eigenenergies and assignments up to 15 000 cm−1
Authors: Ma Guobin , Chen Rongqing , Guo Hua
Published: July 2002

The vibrational spectrum of SO2 up to 15 000 cm−1 is calculated using a low-storage filter-diagonalization method based on the Chebyshev propagation. The Hamiltonian in the Radau coordinates is expressed on a direct product of one-dimensional discrete variable representation (DVR) grids. The extended symmetry-adapted discrete variable representation (ESADVR) is implemented to accelerate the calculation of the action of kinetic energy operators, and multiple symmetry-adapted autocorrelation functions are obtained from the propagation of a single wave packet. Approximately 1000 vibrational energy levels are identified and some of them are assigned according to the nodal structure of the eigenstates. Comparison with experimental data indicates reasonably good agreement (<1%). The agreement, however, deteriorates with increasing energy, implicating imperfection in the potential energy surface used in the calculation. Statistical analyses indicate that the system is mostly regular in this energy range. There is some evidence of a normal-to-local mode transition at higher energies.
Classification of organic molecules to obtain electron affinities from half wave reduction potentials: The aromatic hydrocarbons
Authors: Chen Edward S. , Chen Edward C. M. , Sane Neeta , Talley Laura , Kozanecki Nancy , Shulze Shawn
Published: July 2002

Adiabatic absolute electron affinities (EA) of about 80 aromatic hydrocarbons are calculated from literature values of half wave reduction potentials in aprotic solvents. Solution energy differences are estimated by grouping the molecules based on experimental and theoretical values, chemical logic and statistical analysis. The electronegativity values, (IP+EA)/2, calculated using literature data for ionization potentials, are constant for many of the compounds. Others vary in a systematic manner, such as benzene, 4.26±0.05; naphthalene, 4.14±0.02; anthracene, 4.06±0.02; tetracene, 4.03±0.03; pentacene, 3.98±0.03, in eV. Theoretical values, recalculated from the beginning, compare favorably with the literature values. Three independent methods for obtaining absolute EA’s are summarized and verified; the calibration of reduction potentials, the combination of ionization potentials with electronegativities and the use of semiempirical methods.
Infrared spectra of Cl−–(C2H2)n (1⩽n⩽9) anion clusters: Spectroscopic evidence for solvent shell closure
Authors: Weiser P. S. , Wild D. A. , Bieske E. J.
Published: July 2002

Mid-infrared vibrational predissociation spectra of mass selected Cl−–(C2H2)n (1⩽n⩽9) complexes have been recorded in the vicinity of the acetylene ν3 vibrational band (2700–3400 cm−1). For clusters containing up to 6 acetylene ligands, the spectra each feature a single dominant band, shifted to lower frequency from the ν3 C–H stretch band of free acetylene, and are consistent with interior solvation structures, whereby roughly equivalent acetylene molecules are bound end-on to a central chloride anion. Spectra of the n=7, 8, and 9 complexes, display multiple peaks and provide evidence for acetylene molecules situated in a second solvation shell and also for the existence of multiple isomeric forms. Depending on the cluster size, the inner solvation shell contains 6–8 acetylene molecules.
Photoinitiated decomposition of HNCO near the H+NCO threshold: Centrifugal barriers and channel competition
Authors: Zyrianov M. , Sanov A. , Droz-Georget Th. , Reisler H.
Published: July 2002

The decomposition of jet-cooled HNCO is investigated near the H+NCO channel threshold [D0(H+NCO)=38 370 cm−1]. Dissociation to H+NCO at energies 17–411 cm−1 above D0(H+NCO) proceeds on the ground potential energy surface (S0), apparently without a barrier. The rotational state distributions of the NCO(X 2Π3/2,0010) fragment are well described by phase space theory (PST), provided that dynamical constraints are included. These constraints are associated with long range (4–7 Å) centrifugal barriers, which are significant even near threshold because of the small reduced mass of H+NCO, and result in a fraction of energy deposited in fragment rotation much smaller than predicted by unconstrained PST. The influence of orientation averaging on the attractive, long-range part of the potential is discussed, and it is argued that angular averaging with respect to the center of mass of the rotating polyatomic fragment results in a shift in the effective potential origin, accompanied by an attenuation of the magnitude of the potential compared to its value for fixed H–N distance. Following initial S1(1A″)←S0(1A′) excitation and internal conversion to S0, HNCO(S0) decays both via unimolecular decomposition of H+NCO and intersystem crossing to the dissociative first triplet state, T1 [yielding NH(X 3Σ−)+CO products]. The competition between the two processes is interrogated by monitoring changes in the relative yields of NCO and NH(X 3Σ−) as a function of excitation energy. It is concluded that near D0(H+NCO), the S0→T1 intersystem crossing rate is several-fold faster than the H+NCO unimolecular decomposition rate.
Rhomboidal SiC3
Authors: McCarthy M. C. , Apponi A. J. , Thaddeus P.
Published: July 2002

During experiments to detect carbon chain molecules in the laboratory, an electrical discharge through a dilute mixture of silane and diacetylene was found to produce a molecule of unusual structure that is composed of only silicon and carbon. On spectroscopic analysis this molecule has been shown to have the elemental formula SiC3, a closed-shell singlet electronic ground state, and a planar rhomboidal geometry that consists of atoms in the shape of a distorted four-membered ring with a transannular carbon–carbon bond. Rhomboidal SiC3 is isovalent with rhombic C4, a long predicted low-lying isomer of C4 of similar structure which has so far eluded spectroscopic detection. Strong lines of SiC3 can be observed under a wide range of experimental conditions, suggesting that this molecule is quite stable, and that kinetic and thermodynamic factors favor its formation. Radio emission lines of SiC3 have now been detected in space in the molecular envelope of the carbon-rich star IRC+10216.
Total and elastic cross-sections for electron and positron scattering from OCS molecule: A comparative study with CO2
Authors: Sueoka O. , Hamada A. , Kimura M. , Tanaka H. , Kitajima M.
Published: July 2002

We have carried out a joint experimental and theoretical study on determination of total and elastic cross-sections for electron and positron impact on OCS molecules. For total cross-section measurements, impact energies are from 0.7 to 600 eV for electron collisions and 0.8 to 600 eV for positron collisions. For elastic scattering, only electron impact has been studied from 1.5 to 100 eV. Our present measurements for total cross-sections for electron impact are found to agree extremely well with the measurements of Dababneh et al. (1982) in the entire energy region studied. The results by Szmytkowski et al. (1994) are consistently larger by 20% above 2 eV, and, in particular, are larger by a factor of two in the 1.2 eV resonance region. The present theory for elastic scattering is in good agreement with the present measurement, and has been employed for understanding the dynamics. The total cross-section recommended here is probably the best in accuracy as of today although further studies would be helpful.
Three-body dispersion contributions to the thermodynamic properties and effective pair interactions in liquid argon
Authors: van der Hoef Martin A. , Madden Paul A.
Published: July 2002

The contributions of three-body triple dipole and dipole-dipole-quadrupole dispersion interactions to the thermodynamic properties of liquid argon are examined, using a recently introduced simulation scheme which contains an explicit, quantum mechanical representation of the underlying electronic structure [Mol. Phys. 94, 417 (1998)]. The experimental pressure and energy at a series of liquid densities are shown to be quite accurately reproduced by a combination of the best available pair potential (Aziz) plus these three-body terms. The extent to which these many-body effects can be encompassed by an effective pair potential is then discussed. The nonuniqueness of such an effective potential is reiterated. It is shown that in the dense liquid, the three-body contribution to the effective pair potential (φ(r)) varies approximately linearly with density and is almost temperature independent. It is shown how the addition of φ(r) to the Aziz pair potential moves the latter toward the widely used Lennard-Jones (12-6) potential.
Interaction of gaseous D atoms with alkyl halides adsorbed on Pt(111), H/Pt(111), and C/Pt(111) surfaces: Hot-atom and Eley–Rideal reactions. I. Methyl bromide
Authors: Wehner S. , Küppers J.
Published: July 2002

The interaction of gaseous D atoms with methyl bromide molecules adsorbed on Pt(111), hydrogen saturated Pt(111), and graphite monolayer covered Pt(111) surfaces was studied in order to elucidate the reaction mechanisms. The reaction kinetics at 85 K surface temperature were measured as a function of the methyl bromide precoverage by monitoring reaction products simultaneously with D atom exposure. On all substrates incoming atoms abstract the methyl group from adsorbed CH3Br via gaseous CH3D formation. In the monolayer regime of CH3Br/Pt(111) pure hot-atom phenomenology was observed in the rates. At multilayer targets the fluence dependence of the kinetics gets Eley–Rideal-like. With coadsorbed H present, the reaction of D with adsorbed methyl bromide revealed in addition to CH3D a CH4 product. This and simultaneous abstraction of adsorbed H via gaseous HD and H2 products clearly demonstrates that hot-atom reactions occur. At CH3Br adsorbed on a graphite monolayer on Pt(111) the abstraction kinetics of methyl was found to agree with the operation of an Eley–Rideal mechanism. These observations are in line with the expectation that hot-atoms do not exist on a C/Pt(111) surface but on Pt(111) and H/Pt(111) surfaces. The methyl abstraction cross-sections in the monolayer regime of methyl bromide were determined as about 0.25 Å2, irrespective of the nature of the substrate. This value is in accordance with direct, Eley–Rideal or hot-atom reactions.
The reaction of O(1D) with H2O, D2O monomers and clusters and the intracomplex reaction in N2O–X2O (X=H,D) photo-initiated at 193 and 212.8 nm
Authors: Imura K. , Veneziani M. , Kasai T. , Naaman R.
Published: July 2002

The reaction of O(1D) with water and water clusters was re-examined. We monitored the nascent product state distributions in the reaction photo-initiated by the dissociation of N2O at 193 and 212.8 nm, and the corresponding photo-initiated intracluster reaction. The study at two different dissociation wavelengths and the use of D2O allowed us to obtain direct information on the effect of initial collision kinetic energy on the energy distribution in the product. Based on the new results obtained we conclude that the reaction of O(1D) with water occurs through abstraction mechanism with a relatively short lived collision complex. In the case of the intracluster reaction, we have indication that more internal energy is deposited in the N2 moiety, compared to the dissociation of an isolated N2O. In addition the results indicate that the reaction between the oxygen atom and the water in the complex involved the formation of a short lived collision complex, with a lifetime of probably only few rotations of OH.
The structure and ground state dynamics of Ar–IH
Authors: McIntosh A. , Wang Z. , Castillo-Chará J. , Lucchese R. R. , Bevan J. W. , Suenram R. D. , Legon A. C.
Published: July 2002

The structure and ground state dynamics of the atom–diatom dimer interaction between Ar and HI has been investigated by microwave and near infrared supersonic jet spectroscopy. Ab initio molecular orbital calculations were used to provide greater insight into the nature of the interaction. The ground state is shown to be in the isomeric form Ar–IH with Rcm=3.9975(1) Å, θ=149.33(1)° for the normal isotopomer and Rcm=3.9483(1) Å, θ=157.11(1)° for Ar–ID. The potential surface from an ab initio molecular orbital calculation was scaled and shifted to yield a nonlinear least-squares fit of the rovibrational state energies to the experimental data. The ground state potential energy surface obtained in this manner has a barrier between the Ar–IH and Ar–HI isomers of 88.5 cm−1 with respect to the global minimum. Such calculations are also used to predict the presence of localized states in the secondary minimum associated with isomers Ar–HI and Ar–DI. Attempts to experimentally identify transitions associated with the latter were unsuccessful. The ground state, Ar–IH isomeric structure, contrasts with the corresponding ground state of the other members of the homologous series Ar–HX (X=F, Cl, and Br) in which the Ar is bound to the proton.
Interaction of H atoms with Cu(111) surfaces: Adsorption, absorption, and abstraction
Authors: Kammler Th. , Küppers J.
Published: July 2002

The interaction of H (D) atoms with clean and D (H) covered Cu(111) surfaces was studied with TDS and direct product detection methods. H (D) atoms exhibit an initial sticking coefficient of 0.22. Due to abstraction, the surface saturation coverage is achieved at Θ=0.34, significantly less than the half monolayer coverage obtained through exposure of energetic H2 molecules to Cu(111) surfaces. Adsorbed H (D) desorbs recombinatively between 250 and 400 K. Desorption of absorbed H (D) via gaseous H2(D2) around 200 (210) K was observed according to a zero-order rate law with an activation energy of 0.40 (0.35) eV. Abstraction of D (H) by H (D) at 80 K lead to gaseous HD and D2(H2) formation. About 1% of the adsorbed species occurred in homonuclear products. Throughout the abstraction reaction the HD rate was found strictly proportional to coverage and flux, in line with a purely quasifirst-order, exponentially decreasing Eley–Rideal-type product rate. However, this phenomenology as well as the occurrence of homonuclear products can be explained by the exclusive action of hot-atom mechanisms, controlled by similar probabilities of reaction and sticking of hot atoms. The abstraction probabilities for adsorbed H or D, extrapolated to unity coverage, are 0.36 per incoming atom, the apparent abstraction cross-sections were obtained as σ=2.0 Å2 for H (ad) and D (ad). Abstraction is independent of temperature. Absorbed species are not extracted by incoming atoms.
An analytical equation of state for chain molecules formed from Yukawa segments
Authors: Davies Lowri A. , Gil-Villegas Alejandro , Jackson George
Published: July 2002

We present an analysis of the thermodynamic properties of chain molecules formed from Yukawa segments using the statistical associating fluid theory with interactions of variable range (SAFT-VR) and the high-temperature expansion of the mean-spherical solution (MSA-HTE) to the Ornstein–Zernike equation for a simple Yukawa fluid. The SAFT-VR expressions derived previously for this system allow the MSA-HTE equation of state to be reformulated in terms of first-order perturbation quantities, thus improving its accuracy. Furthermore, the MSA-HTE solution provides a full theoretical derivation of the perturbation theory used in SAFT-VR, together with a completely analytical equation of state for chain molecules composed of segments which interact via the Yukawa potential.
New intermolecular potential models for benzene and cyclohexane
Authors: Errington Jeffrey R. , Panagiotopoulos Athanassios Z.
Published: July 2002

New intermolecular potential models for benzene and cyclohexane have been developed, parameterized to the vapor–liquid coexistence properties. The models utilize the Buckingham exponential-6 potential to describe nonbonded interactions. Histograms reweighting grand canonical Monte Carlo methods were used to obtain the model parameters. A new algorithm for insertion of molecules with complex molecular architectures or stiff intramolecular constraints has been developed. The algorithm is based on the creation of a reservoir of ideal chains from which structures are selected for insertion during a simulation run. The new potential models reproduce the experimental saturated liquid densities and vapor pressures to within average absolute deviations of 0.3% and 2.2%, respectively. Critical parameters are also in good agreement with experiment. The infinite dilution behavior of these two cyclic molecules in water was studied. A combination of Widom insertion and expanded ensemble techniques were used to determine the Henry’s law constant of benzene and cyclohexane in water. The results obtained have qualitatively correct temperature dependence. However, the Henry’s constant of benzene in water is overestimated and that of cyclohexane is underestimated at all temperatures by approximately a factor of 3.
Stochastic Schrödinger equation. II. A study of the coherence seen in pump-probe experiments that use a strong pump laser
Authors: Makarov Dmitrii E. , Metiu Horia
Published: July 2002

We use the stochastic Schrödinger equation approach to examine an experiment performed by Scherer, Jonas, and Fleming [J. Chem. Phys. 99, 153 (1993)]. They have excited I2 molecules dissolved in n-hexane with a strong, ultrashort pump pulse. This creates moving wave packets on both the excited and the ground electronic states. The coherent motion of these packets is studied by measuring the absorption of a weak probe pulse, as a function of the delay time between the pulses. We show how the oscillations in the signal are connected to different excitation mechanisms and to the interference between various packets created by the lasers. Our purpose is to clarify the dynamics of the packets and to show that the stochastic Schrödinger equation approach can be used to study their decoherence. We did not intend to try to develop a realistic model for the I2 dynamics and its interaction with the solvent and do not perform a detailed comparison with the experiment. Nevertheless, the calculations reproduce, semiquantitatively, the observations.
Lattice model of living polymerization. II. Interplay between polymerization and phase stability
Authors: Dudowicz Jacek , Freed Karl F. , Douglas Jack F.
Published: July 2002

Representative spinodal curves and polymerization lines for the equilibrium polymerization of linear polymers in a solvent have been calculated using a Flory–Huggins-type mean-field theory. The calculations are primarily restricted to systems that polymerize upon cooling, but examples are also given for systems that polymerize upon heating. In the former case, we find that an increase in the magnitude of enthalpy of propagation |Δh| (“sticking energy”) leads to an elevation of the critical temperature Tc and to a decrease of the critical composition φc when |Δh| exceeds a critical value |Δhc|. The shifts in the critical temperature and composition, ΔTc≡Tc(Δh)−Tc(Δh=0) and Δφc≡φc(Δh)−φc(Δh=0), vary linearly with Δh for |Δh|>|Δhc| over a large range of sticking energies |Δh|, so that ΔTc is proportional to Δφc for a sufficiently large sticking energy. Variations in the phase boundaries with Δh are also evaluated for systems that polymerize upon heating, but the presence of multiple critical points in this case renders a general description of these changes difficult. The polymerization line is found to be independent of solvent quality (χ interaction parameter) within the simple Flory–Huggins model, but the phase stability is strongly influenced by the magnitude of both χ and Δh. Similarities between living polymers and other types of associating polymers (thermally reversible gels, micelles) suggest that some of the thermodynamic consequences of particle association in these self-assembling systems are insensitive to the detailed nature of the clustering process. Thus, our results may have a much broader range of applicability than living polymer solutions (e.g., gelation in clay and other colloidal suspensions, polyelectrolyte solutions, cell aggregation, and self-organization of biologically significant structures that exist at equilibrium).
Almost temperature independent charge carrier mobilities in liquid crystals
Authors: Palenberg M. A. , Silbey R. J. , Malagoli M. , Brédas J.-L.
Published: July 2002

We present a theoretical description of the almost temperature independent mobilities of photoinjected electrons or holes in discotic liquid crystals. Using data from band structure calculations on triphenylene-based systems, we calculate the electron and hole mobility using the framework of the stochastic Haken–Strobl–Reineker model. We show how almost temperature independent mobilities can be explained in two ways, either by assuming the fluctuations of the tunneling matrix element to be small or by combining the different temperature dependences of the different modes of molecular thermal motion.
Control of photofragment velocity anisotropy by optical alignment of CH3I
Authors: Sugita Akihiro , Mashino Michio , Kawasaki Masahiro , Matsumi Yutaka , Gordon Robert J. , Bersohn Richard
Published: July 2002

A molecule placed in an electric field can be aligned because of the anisotropy of its polarizability tensor. As an alternative to high static electric fields, the electric field of a pulsed laser can be used for alignment. The alignment can be demonstrated by measurement of the control of the anisotropy of photodissociated fragments generated by polarized light. Sakai et al. have recently reported such an experiment on aligned iodine molecules [J. Chem. Phys. 110, 10235 (1999)]. This paper reports an independent finding of the same phenomenon with CH3I. General equations are presented for the degree of alignment and its control of the photodissociation amplitude. The control parameter for a symmetric top or linear molecule is −(α−αzz)(E2/2kT)P2(cos χ), where α is the mean polarizability, αzz is the element of the polarizability tensor along the symmetry axis, and χ is the angle between the E vectors of the aligning and dissociating lasers. The fragment velocity anisotropy can be increased or decreased by varying this control parameter.
Spin–orbit effects on the transactinide p-block element monohydrides MH (M=element 113–118)
Authors: Han Young-Kyu , Bae Cheolbeom , Son Sang-Kil , Lee Yoon Sup
Published: July 2002

Spin–orbit effects on the bond lengths and dissociation energies of sixth- and seventh-row p-block element monohydrides MH(M=Tl–Rn and element 113–118) are evaluated using relativistic effective core potentials at the coupled-cluster level of theory. Spin–orbit effects play a dominant role in the determination of molecular properties for the seventh-row hydrides. Spin–orbit effects on the bond lengths and dissociation energies of seventh-row hydrides are qualitatively similar to, but substantially larger than those of the sixth-row homologs due to the enormous spin–orbit splitting of 7p orbitals. Spin–orbit interactions change the bond lengths of sixth- and seventh-row hydrides by −0.02∼+0.03 Å and −0.21∼+0.21 Å , respectively. Spin–orbit interactions usually elongate the bond lengths except for the molecules of the (p1/2)1-valence atoms, i.e., TlH and (113)H. The maximum elongation is predicted for (115)H, where the element 115(eka-bismuth) has the (7p3/2)1 configuration outside the inner (7p1/2)2 closed-shell. The spin–orbit coupling weakens the bondings between the heavy element and the hydrogen except for BiH and changes the dissociation energies by −0.71∼+0.08 eV and −2.18∼−0.23 eV for sixth- and seventh-row hydrides, respectively. The dissociation energy of the (114)H molecule is merely 0.39 eV, because the element 114(eka-lead) has a closed-shell electronic structure in the jj-coupling scheme. The bonding between the element 118(eka-radon), which is another closed-shell atom, and hydrogen is very weak and can be regarded as a pure van der Waals bond. But with highly electronegative elements the element 118 seems to form more stable compounds than other closed-shell atoms such as the element 112(eka-mercury) or the element 114.
Exact long-time asymptotics for reversible binding in three dimensions
Authors: Agmon Noam , Gopich Irina V.
Published: July 2002

Using an iterative solution in Laplace–Fourier space, we obtain a rigorous mathematical proof for the long-time asymptotics of reversible trapping in three dimensions with distance-dependent reactivities obeying detailed balancing.
Solid-state deuterium nuclear magnetic resonance of the methyl dynamics of poly(α-methylstyrene) and polymethylphenylsilane
Authors: O’Connor Robert D. , Ginsburg Eric J. , Blum Frank D.
Published: July 2002

The methyl-d3 dynamics of two relatively similar polymers, poly(α-methylstyrene) (PAMS-d3) and polymethylphenylsilane (PMPS-d3), are investigated via deuterium NMR relaxation experiments. Our analysis of the relaxation data uses the entire solid-echo spectra to maximize the precision of the experiments with regard to the information available on the methyl dynamics. The analysis is novel in that it does not use M∞ or M0 to fit the relaxation data. Additionally, the three-site symmetric jump model is shown to not have an observable azimuthal angular dependence for T1 relaxation. The methyl dynamics are quantified with τm, σ, and f which are the log-average correlation time, half-height full-width (base 10) of a log-normal distribution of reorientation rates, and the anisotropy of the relaxation, respectively. The anisotropy parameter, f, is based on a serial combination of the rotational diffusion and symmetric three-site jump reorientation of a methyl deuteron. This serial model coupled with a distribution of τc’s has a minimal number of parameters that have physical meaning and quantify the observations of our relaxation data. Generally, at similar temperatures the methyl reorientation in PAMS-d3 is at least 100 times slower than that of PMPS-d3. For both polymers, both τm and σ decrease with increasing temperature, resulting in activation energies of 12 and 5 kJ/mol for PAMS-d3 and PMPS-d3, respectively. Also, with increasing temperature a mechanistic change from three-site jump to rotational diffusion is observed and quantified. This information, along with that of other studies, suggests that the PAMS-d3 methyls have highly restrictive environments that may be closely coupled to phenyl-ring reorientation.
The triplet wave function of C60 from W-band electron nuclear double resonance spectroscopy
Authors: Dauw X. L. R. , van den Berg G. J. B. , van den Heuvel D. J. , Poluektov O. G. , Groenen E. J. J.
Published: July 2002

Electron-nuclear double resonance spectra at 95 GHz and electron-spin-echo envelope-modulation spectra at 9.5 GHz are reported for a frozen solution of fully C13 enriched C60 molecules in their photoexcited triplet state. Analysis of these data reveals that the triplet wave function is largely localized on a part of the molecule. Upon excitation, the C60 molecule adopts a structure of D5d symmetry with four symmetry inequivalent carbon atoms. The equator atoms each carry 3.8% of the spin density and the atoms next to the equator 1.1%, together accounting for 98% of the total spin density. These π-spin densities make the hyperfine interaction mainly anisotropic. A slight s-spin density on the equator atoms adds a sizable isotropic hyperfine coupling. The triplet wave function is calculated quantum-chemically and compared with the observed spin-density distribution.
Full-dimensional quantum dynamics study on the mode-specific unimolecular dissociation reaction of HFCO
Authors: Yamamoto Takeshi , Kato Shigeki
Published: July 2002

The mode specificity of the unimolecular reaction of HFCO is studied by six-dimensional quantum dynamics calculations. The energy and mode dependency of the dissociation rate is examined by propagating a number of wave packets with a small energy dispersion representing highly excited states with respect to a specific vibrational mode. The wave packets are generated by applying a set of filter operators onto a source vibrational state. All the information necessary for propagating the wave packets is obtained from a single propagation of the source state, thus allowing a significant decrease of computational effort. The relevant spectral peaks are assigned using the three-dimensional CH chromophore Hamiltonian. The resulting dissociation rate of the CH stretching excited state is in agreement with that obtained from a statistical theory, while the rates of the out-of-plane bending excited states are about one order of magnitude smaller than the statistical rates. A local-mode analysis also shows that the relaxation of the out-of-plane excitation proceeds very slowly within 3 ps. These results clearly indicate weak couplings of the out-of-plane bending excited states with other in-plane vibrational states, which is in qualitative agreement with experimental findings. From a computational point of view, a parallel supercomputer is utilized efficiently to handle an ultra large basis set of an order of 108, and 200 Gflops rate on average is achieved in the dynamics calculations.
Interfacial structure of a mixed dipolar liquid in contact with a charged solid surface
Authors: Senapati Sanjib , Chandra Amalendu
Published: July 2002

We develop a nonlinear theory for the calculation of interfacial structural properties of a dipolar mixture in contact with a charged solid surface. Both the molecular sizes and the dipole moments of various species can be unequal. Explicit numerical results are obtained for the interfacial structure of a binary dipolar liquid in contact with a charged surface of varying surface charge density. The dipole moments of the two species are also varied. The density profiles of both the species are found to be highly inhomogeneous and oscillatory near the solid surface. The more polar species is found to exhibit a positive electrostriction at the surface with an increasing surface electrostatic field. An opposite behavior is observed for the less polar species. The polarization profiles reveal pronounced orientational order of the solvent molecules of both the species near the charged surface. The contact polarizations of the more polar and the less polar species show, respectively, a more than linear and a less than linear increase with increasing surface charge density. The predictions of the present theory for a given set of parameter values are compared with the results of Monte Carlo simulation of the same system and a good agreement is found for the inhomogneous density and polarization profiles of both the species.
Time-dependent density functional calculations of molecular photoionization cross sections: N2 and PH3
Authors: Stener M. , Decleva P.
Published: July 2002

A method based on the time-dependent density functional theory (TD-DFT) is proposed to calculate the photoionization cross section employing the explicit continuum wave-function, within a One Center Expansion and B-Splines radial basis set. The LB94 exchange-correlation potential with correct asymptotic behavior is employed. The results obtained for N2 and PH3 are in excellent agreement with the experimental data and are of comparable accuracy of ab initio methods. A deterioration is still present in the inner valence. For PH3 the effect of TD-DFT is dramatic and recovers completely the Kohn–Sham deficiency. The method has proven efficient for both valence and core ionization.
Strong amplification of sidebands in a strongly driven three-level atomic system
Authors: Mavroyannis Constantine
Published: July 2002

We have considered the excitation spectra for a three-level atom interacting simultaneously with a strong pump field and a weak signal field. The atom consists of an upper excited state ‖2〉 and two lower states ‖1〉 and ‖3〉 where the transition ‖1〉↔‖3〉 is electric-dipole forbidden from parity considerations. The pump field, whose frequency mode ωb is initially populated, operates near resonance between the states ‖2〉 and ‖3〉, ‖2〉↔‖3〉, while the signal field describes the radiative decays ‖2〉→‖3〉 and ‖2〉→‖1〉, respectively. Using the Green function method, the spectral functions for the signal field have been calculated in the limit of high photon densities of the pump field describing the following processes: (i) one-photon process; the spectra consist of a main peak at the signal frequency ω=ω21 and a pair of sidebands at ω=ω21±Ω−(ω23−ωb)/2, where Ω2=Ω2b/2+(ω23−ωb)2/4 with Ωb and (ω23−ωb) being the Rabi frequency and the detuning of the pump field, respectively. The intensity of the main peak at ω=ω21 is positive indicating signal-field absorption while those of the sidebands are always negative implying amplification (stimulated emission) of the signal field. The sum of the intensities (in absolute value) of the sidebands is twice that of the main peak at resonance while in the off-resonance case it depends on the value of the ratio (ω23−ωb)/2Ω. (ii) Stimulated three-photon process; the spectra consists of a pair of sidebands peaked at ω=ω21−2ωb±Ω−(ω23−ωb)/2 whose intensity is negative indicating amplification. At resonance the sidebands have equal intensities but at finite detuning asymmetry arises enhancing one peak while diminishing the intensity of the other. (iii) Stimulated two-photon process; the stimulated Raman spectra consist of a peak at ω=ω31, which has a delta function distribution, and a pair of strongly amplified sidebands at ω=ω31±Ω+(ω23−ωb)/2. The computed spectra for the three processes are presented graphically for different values of Rabi frequencies and detunings.
Gravitational radiation from dust
Authors: Isaacson R. A. , Welling J. S. , Winicour J.
Published: July 2002

A dust cloud is examined within the framework of the general relativistic characteristic initial value problem. Unique gravitational initial data are obtained by requiring that the space-time be quasi-Newtonian. Explicit calculations of metric and matter fields are presented, which include all post-Newtonian corrections necessary to discuss the major physical properties of null infinity. These results establish a curved space version of the Einstein quadrupole formula, in the form ‘‘news function equals third time derivative of transverse quadrupole moment,’’ for this system. However, these results imply that some weakened notion of asymptotic flatness is necessary for the description of quasi-Newtonian systems.
On the scalar-tetradic theory A—The Birkhoff theorem: Horizons and singularities
Authors: Sáez D. , Arnau J. V.
Published: July 2002

In a recent paper a unique solution of the field equations of theory A, describing the outer field of the sun, has been obtained for each value of the coupling constant W. Here, this solution is studied in detail for any possible value of W (horizons, singularities,. . .) and the Birkhoff theorem is proved in the framework of theory A.
Mathematical aspects of quantum fluids. I. Generalized two-cycles of 4He type
Authors: Kupershmidt B. A.
Published: July 2002

It is shown that the two-cocycle involved in the Hamiltonian description of the superfluid 4He, both nonrotating and rotating, is a particular case of generalized symplectic two-cocycles on semidirect product Lie algebras.
Magnetic generalization of the Kerr–Newman metric
Authors: García Díaz Alberto
Published: July 2002

The exact expression of the magnetized Kerr–Newman metric is presented. The obtained solution possesses five continuous arbitrary parameters; mass, angular momentum, electric charge, and electric and magnetic field parameters.
Relativistic, stationary, axisymmetric perfect fluids. II. Solutions with vanishing magnetic Weyl tensor
Authors: Sklavenites D.
Published: July 2002

The formalism of the previous article is used to obtain solutions of Einstein’s field equations for the interior of a rigidly rotating perfect fluid, with zero magnetic Weyl tensor. It is found that these solutions cannot represent isolated rotating masses.
Generating relations for reducing matrices. II. Corepresentations
Authors: Aroyo M. I. , Kotzev J. N. , Angelova-Tjurkedjieva M. N. , Dirl R. , Kasperkovitz P.
Published: July 2002

The auxiliary group approach developed in Paper 1 [R. Dirl, P. Kasperkovitz, M. I. Aroyo, J. N. Kotzev, and M. Angelova-Tjurkedjieva, J. Math. Phys. 27, 37 (1986)] is generalized for the case of corepresentations of antiunitary groups. It allows us to reduce the multiplicity problem and to derive consistent generating relations for the elements of the reducing matrices for coreps. Two examples are worked out to illustrate the general scheme.
The basis for the symmetric irreducible representations of SO(9)
Authors: Yu Z. R. , Scholten O. , Sun H. Z.
Published: July 2002

An explicit basis is constructed for the symmetric irreducible representation (irrep) of SU(9)⊇SO(9)⊇SO(5)×SU1(2)×SU2(2). It is also indicated how good angular momentum states can be constructed. The techniques used are based on the well-known tensor algebra for the infinitesimal generators of simple Lie groups.
Central-limit theorems on groups
Authors: Mello P. A.
Published: July 2002

The probability density pN of the product of N statistically independent (and identically distributed, each with probability density p1) elements of a group is studied in the limit N→∞. It is shown, for the compact groups R(2) and R(3), that pN→1 as N→∞, independently of p1. It is made plausible that a similar behavior is to be expected for other compact groups. For noncompact groups, the case of SU(1,1)which is of interest to the physics of disordered conductors, is studied. The case in which p1 is isotropic, i.e., independent of the phases, is analyzed in detail. When p1 is fixed and N≫1, a Gaussian distribution in the appropriate variable is found. When the original variables are rescaled by 1/N and the limit N→∞ is taken, keeping the ratio of the length of the conductor to the localization length fixed, an explicit integral representation for the resulting probability density is found. It is also exhibited that the latter satisfies a ‘‘diffusion’’ equation on the group manifold.
Hydrodynamics of a topologically nontrivial metric
Authors: Harriott Tina A. , Williams J. G.
Published: July 2002

The curvature and Einstein tensor are computed for a metric having one or more kinks (solitons) present. It is pointed out that the components of the fluid velocity four-vector can be identified in a natural way with certain parameters present in the metric. Making this identification, a number of hydrodynamical quantities are computed.
Generating relations for reducing matrices. I. Ordinary representations
Authors: Dirl R. , Kasperkovitz P. , Aroyo M. I. , Kotzev J. N. , Angelova-Tjurkedjieva M.
Published: July 2002

Auxiliary groups are constructed that make it possible to reduce the multiplicity problem and to derive consistent generating relations for the elements of reducing matrices. Three examples are worked out to illustrate the general scheme.
The Schücking problem
Authors: Ozsváth István , Sapiro Leland
Published: July 2002

The embedding problem for a three-parametric family of homogeneous three-spaces into a higher-dimensional Euclidean space is considered. These three-spaces occur as space sections in cosmological models. After general consideration a certain two-parametric family is embedded into a five-dimensional Euclidean space, deferring the solution of the general case to later papers.
The global Utiyama theorem in Einstein–Cartan theory
Authors: Bruzzo Ugo
Published: July 2002

A global formulation of Utiyama’s theorem for Einstein–Cartan-type gravitational theories regarded as gauge theories of the group of space-time diffeomorphisms is given. The local conditions for the Lagrangian to be gauge invariant coincide with those found by other authors [A. Pérez-Rendón Collantes, ‘‘Utiyama type theorems,’’ in Poincaré Gauge Approach to Gravity. I, Proceedings Journées Relativistes 1984; A. Pérez-Rendón and J. J. Seisdedos, ‘‘Utiyama type theorems in Poincaré gauge approach to gravity. II, ’’ Preprints de Mathematicas, Universidad de Salamanca, 1986] in Kibble’s and Hehl’s approaches.
The physical basis of an n g-boson system
Authors: Sen Xiao-yan , Yu Z. R.
Published: July 2002

The mathematical group chain of an n g-boson system is SU(9)⊃SO(9)⊃ SO(5)×SU1(2)×SU2(2)∪SUa(2)×SUb(2). In this paper, the mathematical basis of this group chain is obtained by using the briefer method and then constructing the states of n g-bosons with good angular momentum.
Generating relations for reducing matrices. III. Kronecker products
Authors: Dirl R. , Kasperkovitz P. , Aroyo M. I. , Kotzev J. N. , Davies B. L.
Published: July 2002

In the first two of this series of papers [R. Dirl et al., J. Math. Phys. 27, 37 (1986); M. I. Aroyo et al., ibid. 27, 2236 (1986)] a systematic method to calculate the elements of reducing matrices has been developed. In this paper this ‘‘auxiliary group approach’’ is adapted to multiple Kronecker products. Three examples are worked out to illustrate the efficiency of generating relations and the proposed reduction of the multiplicity problem.
Berry phases and unitary transformations
Authors: Jordan Thomas F.
Published: July 2002

Berry phases for spin are defined for any closed loop made by a vector changing direction in three-dimensional space. A sequence of rotations moves the vector along the loop. Each rotation is around the axis perpendicular to the moving vector. The Berry phases come from the eigenvalues of the unitary operator for the product of these rotations. The angle of the product rotation is shown to be the solid angle enclosed by the loop. The proof uses the ordinary language of quantum mechanics. The product is calculated from the commutation relations for spin. A general framework is set up to define Berry phases for other transformations and states like those for rotations and spin. The integral formula is derived. Alternatives for dynamics are shown to provide different applications and interpretations of the same mathematics. An example is used to show how one Hamiltonian may be simpler than others. Adiabatic evolution is obtained in the limit as a coupling constant goes to zero, so the adiabatic changes are made by a weak perturbation that acts over a long time. The Berry phase is the same whether the coupling constant is large or small. A rationale for the definition of Berry phases is obtained from any of the alternatives for dynamics. It is particularly clear in both the limit of adiabatic evolution, where the Hamiltonian does not contain the operator that generates Berry phases, and the opposite extreme where the Hamiltonian is the operator that generates Berry phases. The latter is illustrated with an example for spin. The general definition of Berry phases and the method of calculating them are illustrated by obtaining Berry phases from Lorentz transformations. They are similar to those obtained from rotations. A vector traces a loop on a unit hyperboloid instead of the unit sphere. In place of the solid angle, the Berry phases contain the analogous measure of the area enclosed by the loop on the hyperboloid.

The sign is opposite what it is for rotations. The general definition is shown to fit any unitary representation of a semisimple Lie group. The complete set of commuting operators is chosen to contain a basis for a Cartan subalgebra of the Lie algebra of generators. If a sequence of transformations by unitary operators in the group representation takes each operator in the Cartan subalgebra around a loop in the Lie algebra back to the same operator, it can be made by unitary operators in the group representation that have all the properties required for the definition of Berry phases. The loops are made by vectors moving in a real space, the Lie algebra. The motion of the vectors must maintain the lengths and angles defined by the Cartan metric of the Lie algebra. The Berry phases are determined by one loop made by one suitably chosen operator from the Cartan subalgebra.