bluuebunny/crossref_metadata_2025 huggingface dataset:
C
60
-propylamine adduct monolayers at the gas/water interface: A Brewster angle microscopy and x-ray scattering study
Authors: Fukuto Masafumi , Penanen Konstantin , Heilmann Ralf K. , Pershan Peter S. , Vaknin David
Published: July 2002

Brewster angle microscopy (BAM), x-ray specular reflectivity and grazing-incidence x-ray diffraction (GID) studies of C60-propylamine adduct monolayers at the gas/water interface as a function of molecular area are reported. At large molecular areas (A>∼150 Å2/molecule), BAM images reveal macroscopic heterogeneity in the film, consisting of the coexistence between regions covered with uniform solidlike monolayer and bare water surface. After compression to a limiting molecular area of 150 Å2/molecule, the film is observed to be homogeneous, with the uniform monolayer covering the entire available surface. Both the x-ray reflectivity results and the GID patterns are consistent with the formation of a uniform monolayer at A∼150 Å2/molecule, while the little dependence that the GID patterns have on the molecular area for A>∼150 Å2/molecule is consistent with the heterogeneity in the film. Upon further compression to higher densities (A<∼120 Å2/molecule), the x-ray reflectivity results suggest the formation of a partial layer either at the molecule/gas interface or at the molecule/water interface. In this high density regime, the shift in the observed GID pattern with molecular area is much smaller than would be expected if the film were to remain a homogeneous monolayer, also consistent with the formation of an inhomogeneous partial layer. The analysis of the broad GID pattern observed from a uniform monolayer in terms of a model 2D radial distribution function, implies a short range positional correlation, extending to only a few molecular distances. The average nearest neighbor distance (d∼13 Å), extracted from the GID analysis, is consistent with the limiting molecular area (A∼150 Å2/molecule) assuming local hexagonal packing. These results together with the sharp facets observed in the BAM images demonstrate that the monolayer when uniform is a two-dimensional amorphous solid.
Guided ion-beam studies of the reactions of Fen+ (n=1–18) with CO2: Iron cluster oxide bond energies
Authors: Griffin James B. , Armentrout P. B.
Published: July 2002

The kinetic energy dependence of the reactions of Fen+ (n=1–18) with CO2 are studied in a guided ion-beam mass spectrometer. The primary product ions are FenO+, which then decompose by sequential loss of iron atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Fen−1+ product ions is also observed. Large cluster ions, n⩾9, form the FenCO2+ adduct at low kinetic energies. The cross section for the primary reaction, Fen++CO2→FenO++CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Fen+–O bond energies are measured and found to compare well with previous measurements obtained from guided ion-beam studies of the Fen++O2 systems. The trends in this thermochemistry are discussed and compared to bulk phase values.
Determination of rate constants for butene isomerization by a temporal inversion method
Authors: Li Genyuan , Rabitz Herschel
Published: July 2002

The determination of rate constants for chemical reaction systems is of considerable practical importance. This paper introduces a temporal inversion method for parameter identification of dynamical systems, and butene isomerization is used to illustrate the method. The rate constants are artificially treated as temporal functions and an explicit equation describing the time evolution of the rate constants is obtained by minimizing the error along the reaction course. With appropriate experimental data the unknown rate constants are guided from arbitrary initial values to their best values for the available experiments at the final time. The method leads to an iterative algorithm. Numerical results show that accurate estimates of all the rate constants can be obtained.
Vibronic analysis of the ion-pair (E0+)←ground state (X0+) transition of BrCl
Authors: Wang P. , Dimov S. S. , Lipson R. H.
Published: July 2002

Vibrationally and rotationally resolved spectra of the first-tier E0+(v′) ion-pair state ←X0+(v′′=0) ground-state transition of jet-cooled BrCl near 145 nm were recorded by exciting the halogen with a tunable vacuum ultraviolet “laser” generated by four-wave difference mixing in Kr gas, and detecting the ions produced by (1+1′) resonance enhanced multiphoton ionization in a linear time-of-flight mass spectrometer. J-numberings for thirty individual isotopic bands were established by ground-state combination differences, and per band rotational constants were derived. Extensive perturbations precluded the determination of an unambiguous absolute v′-numbering for the observed features or equilibrium rotational constants. However, excited-state vibrational isotope shift measurements do indicate that transitions from v′′=0 of the ground-state probe vibrational levels between v′=173 and 205.
Emission spectra of NeRg2+(Rg=Ar,Kr,Xe), ArRg2+(Rg=Kr,Xe), and KrXe2+ heterotrimer ions produced in rare gas flowing afterglows at high stagnation pressures
Authors: Tsuji Masaharu , Tanaka Makoto , Nishimura Yukio
Published: July 2002

Emission spectra resulting from clustering reactions of a rare gas ion Rg+(Rg=Ne,Ar,Kr) with a heavier rare gas Rg′(Rg′=Ar,Kr,Xe) have been studied in rare gas flowing afterglows at various stagnation pressures of Rg′. At low stagnation pressures of Rg′, emission spectra of NeRg′+(Rg′=Ar,Kr,Xe), ArRg′+(Rg′=Kr,Xe), and KrXe+ heterodimer ions were found due to radiative association and three-body clustering reactions. At high stagnation pressures of Rg′, new continuous bands were found at the longer-wavelength region of the heterodimer bands in most cases. They were attributed to bound–free transitions of NeRg2′+(Rg′=Ar,Kr,Xe), ArRg2′+(Rg′=Kr,Xe), and KrXe2+ heterotrimer ions. In most cases, the RgRg2′+ bands consisted of two components: the first continuum degraded to the red from near the B 1/2–X 1/2 and C1 3/2–A1 3/2 transitions of the RgRg′+ bands, and the second continuum, a roughly Gaussian feature at longer wavelengths. It was found that the lower Rg+(2P3/2) components were responsible for the formation of RgRg′2+*. The first and the second components were ascribed to the B 1/2–X 1/2 and/or C1 3/2–A1 3/2 transitions and the B 1/2–A2 1/2 transition of RgRg2′+, respectively. The emission intensity of the second continuum increased more rapidly than that of the first one with increasing the stagnation pressure of Rg′ or a foreign gas. It was explained as due to the fact that the first continuum arises from highly vibrationally excited levels near the dissociation limits, while the second one occurs dominantly from low vibrationally excited levels formed by collisional relaxation of the upper vibrationally excited levels.
Dynamics of charge carrier precursor photogeneration in titanyl phthalocyanine
Authors: Gulbinas V. , Jakubenas R. , Pakalnis S. , Undzenas A.
Published: July 2002

The mechanism of the charge carrier photogeneration in Y-form titanyl phthalocyanine was investigated by means of fluorescence and photocurrent measurements. Sample excitation by two time-separated light pulses was applied to obtain information on the time course of the fluorescence and generation processes. Charge carrier precursors—charge pairs—were found to be generated only during the short time interval after the exciton was created. This interval is much shorter than the fluorescence state lifetime.
Vertical and adiabatic electronic excitations in biphenylene: A theoretical study
Authors: Beck M. E. , Rebentisch R. , Hohlneicher G. , Fülscher M. P. , Serrano-Andrés L. , Roos B. O.
Published: July 2002

The low-lying singlet states of biphenylene have been studied using ab initio methods. Vertical excitation energies were calculated by multiconfigurational perturbation theory (CASPT2), starting from a complete active space self-consistent field (CASSCF) reference. The geometries of the most important low-lying excited states were individually optimized at the CASSCF level to study the difference between vertical and adiabatic excitations. Extended atomic natural orbital (ANO)-type basis sets were used to calculate state energies. Geometry optimizations were done with smaller ANO-type basis sets. Excitations from the ground state to the 1 1B3g and 1 1B2u excited singlet states lead to pronounced geometry changes which alter the bond alternation pattern. The theoretical results provide a solid basis for the assignment and interpretation of experimental spectra.
The relativistic Fock-space coupled-cluster method for molecules: CdH and its ions
Authors: Eliav Ephraim , Kaldor Uzi , Hess Bernd A.
Published: July 2002

The relativistic coupled-cluster method starts from the Dirac–Coulomb–Breit Hamiltonian in its low-frequency approximation and includes correlation by Fock-space coupled-cluster with single and double excitations. One- and two-component approximations using the Douglas–Kroll transformation are also tested. Significant relativistic effects are found for CdH, with bond length contracting from 1.820 to 1.778 Å (experimental 1.781 Å) and binding energies decreasing from 0.87 to 0.70 eV (experimental 0.68 eV). The binding energy of the cation increases by 0.1 eV upon inclusion of relativity. The electron affinity of the molecule is 0.44 eV. The Douglas–Kroll values include nearly all the relativistic correction.
Adsorption and desorption dynamics of H2 and D2 on Cu(111): The role of surface temperature and evidence for corrugation of the dissociation barrier
Authors: Murphy M. J. , Hodgson A.
Published: July 2002

We report the effect of surface temperature on the state resolved translational energy distributions for H2 and D2 recombinatively desorbed from Cu(111). Sticking functions S(v,J,E) can be obtained by applying detailed balance arguments and follow the familiar error function form at high energy, consistent with previous permeation measurements [Rettner et al., J. Chem. Phys. 102, 4625 (1995)]. The widths of the sticking functions are identical for both isotopes and are independent of rotational state. S(E) broadens rapidly with increasing surface temperature, with a low energy component which is slightly larger than represented by an error function form. This is similar to the behavior seen on Ag(111) [Murphy et al., Phys. Rev. Lett. 78, 4458 (1997)] but on Cu(111) the low energy component remains a minor desorption channel. The broadening of S(E) can be explained in terms of a change in the distribution of barriers caused by local thermal displacement of the surface atoms, thermal activation of the surface producing sites where molecules can dissociate, or desorb, with a reduced translational activation barrier. At low energy sticking increases rapidly with surface temperature, with an activation energy of 0.54 and 0.60 eV for H2 and D2, respectively. These values are similar to the thermal activation energies calculated for translational excitation of H2/D2 and imply that thermal excitation of the surface is just as efficient as translational energy in promoting dissociation. The influence of surface temperature decreases with increasing translational energy as molecules become able to dissociate even on the static Cu(111) surface. By comparing the energy distributions for desorption with existing angular distributions we determine how the effective energy, Ee=E cosn(E) θ which contributes to adsorption–desorption, scales with translational energy. At translational energies near the threshold for sticking n(E)≈2, sticking scales with the normal component of the translational energy and is not influenced by motion parallel to the surface. At lower energy n(E) drops towards zero, indicating that motion parallel to the surface aids dissociation, consistent with dissociation at a corrugated barrier.
The 5fπ 3Πg←a 3Σu+ and 5fσ 3Σg+←a 3Σu+ systems of Ar2
Authors: Herring C. M. , Eden J. G. , Ginter M. L.
Published: July 2002

Rotationally resolved transitions of the 5fπ 3Πg←4sσ a 3Σu+ and 5fσ 3Σg+←4sσ a 3Σu+ systems of Ar2 have been observed by laser excitation spectroscopy in a pulsed corona discharge. These systems were previously observed at lower resolution [D. J. Kane et al., J. Chem. Phys. 96, 6407 (1992)] with the system tentatively labeled nlλΠg–a and subsequently assigned as 5fπ 3Πg–a on the basis of theoretical considerations [P. Duplàa and F. Spiegelmann, J. Chem. Phys. 105, 1500 (1996)]. Rotational analyses for the (0–0) and (0–1) bands of both systems are presented and the upper states characterized. The (0–2) bands of the 5fπ–a and 5fσ–a transitions are observed also, as are the (0–0) band of 4fδ 3Δg–a 3Σu+ and the (1–0) and (2–0) bands of 5fπ–a, but with rotational structures insufficiently developed to permit analysis. The linewidths of the rotational lines of the above bands are much broader than are the lines of the 7pσ 3Σu+–a system previously analyzed [C. M. Herring et al., J. Chem. Phys. 101, 4561 (1994)], presumably because of increased lifetime broadening. Several spectral features observed in the 5fπ 3Πg←4sσ a 3Σu+ band structures that are not apparently compatible with this upper state assignment are discussed.
Master equation analysis of deterministic chemical chaos
Authors: Wang Hongli , Li Qianshu
Published: July 2002

The underlying microscopic dynamics of deterministic chemical chaos was investigated in this paper. We analyzed the master equation for the Williamowski–Rössler model by direct stochastic simulation as well as in the generating function representation. Simulation within an ensemble revealed that in the chaotic regime the deterministic mass action kinetics is related neither to the ensemble mean nor to the most probable value within the ensemble. Cumulant expansion analysis of the master equation also showed that the molecular fluctuations do not admit bounded values but increase linearly in time infinitely, indicating the meaninglessness of the chaotic trajectories predicted by the phenomenological equations. These results proposed that the macroscopic description is no longer useful in the chaotic regime and a more microscopic description is necessary in this circumstance.
The steric effect in a full dimensional quantum dynamics simulation for the dissociative adsorption of H2 on Cu(111)
Authors: Dai Jiqiong , Light John C.
Published: July 2002

The rotational alignment of the dissociative adsorption of H2 on the Cu(111) surface has been studied by a six-dimensional quantum dynamics simulation. The theoretical rotational alignment is in excellent agreement with the experimental measurement of Hou et al. [Science 277, 80 (1997)]. The translational energy threshold of the dissociation is found to increase with increase of rotational quantum number j then to decrease after j=4 or 5. No substantial difference in the dependence of rotational alignment on the excess translational energy has been found between the dissociation of H2 and D2 on the Cu(111) surface. The variation of rotational alignment as a function of excess translational energy is almost independent of the rovibrational level (v,j) of the initial state. The theoretical study further predicts that the rotational alignment curve (a function of translational energy) would first shift toward high translational energy with increasing j, then shift back toward low translational energy after j=5.
Study of a model polyelectrolyte solution with directional attractive forces between the macroions
Authors: Kalyuzhnyi Yu. V. , Vlachy V.
Published: July 2002

A modification of the primitive model of a polyelectrolyte solution, containing macroions and counterions, is presented. The macroions are assumed to carry 20 (or in some calculations 10) negative charges and the counterions are monovalent. Asymmetry in size between the two species is 15:2. In addition to the Coulombic forces, the macroions also interact via a short-range directional attractive force. The parameters of this attraction are chosen to result in the formation of dimers, but no trimers or higher clusters can be formed. This model of a polyelectrolyte solution is studied for a range of concentrations and for several values of the depth of the potential well, using the statistical-mechanical theory based on the two-density formalism for associating fluids. The results indicate that the short-range attraction between macroions and consequently the formation of dimers, yields a significant decrease of the osmotic coefficient for the model polyelectrolyte solution. Part of the effect is due to the strong attraction between the doubly charged aggregates and counterions in the solution. The effect of dimerization is also reflected in the excess internal energies and in all three pair distribution functions.
Anomalous hydrogen adsorption sites found for the c(2×2)-3H phases formed on the Re(101̄0) and Ru(101̄0) surfaces
Authors: Döll R. , Hammer L. , Heinz K. , Bedürftig K. , Muschiol U. , Christmann K. , Seitsonen A. P. , Bludau H. , Over H.
Published: July 2002

Hydrogen adsorption on the (101̄0) surfaces of Ru and Re leads to the formation of c(2×2)-3H phases. As determined by quantitative low-energy electron diffraction (LEED) and density functional theory calculations, hydrogen atoms, as expected, occupy threefold coordinated hcp sites along the densely packed rows and the unexpected short-bridge sites along the ridges in both c(2×2) phases. The Ru and Re substrates reconstruct only weakly and in a very similar fashion under hydrogen chemisorption. Most notably, there is a buckling in the third substrate layer of about 0.06 Å. Probably (though not outside the limits of error), there are also slightly lateral displacements (0.02 Å) of top-layer substrate atoms which are bridge-coordinated to hydrogen. The metal–hydrogen bond lengths determined for both surfaces correspond to hydrogen radii in the expected range of 0.4–0.7 Å.
Anharmonicity in the ring stretching modes of diborane
Authors: Stanton John F. , Gauss Jürgen
Published: July 2002

Conspicuous differences between ab initio harmonic frequencies for the ν6 and ν17 hydrogen bridge stretching modes of diborane and those calculated from an empirical harmonic force field have remained unexplained for nearly 20 years. This work conclusively demonstrates that an unexpectedly large anharmonicity effect is responsible for the discrepancy. Cubic and semidiagonal quartic force constants obtained with coupled-cluster theory and a reasonably large basis set are used to calculate fundamental frequencies. For the bridge BH stretching (BHb) modes, all theoretical values are within 15 cm−1 of the actual fundamental frequencies, while corresponding harmonic frequencies are well above the empirical values. It thus appears that BHb-stretching anharmonicity is considerably greater than previously supposed, being roughly three times that (as measured by the magnitude of 1−ν/ω) for terminal BH bonds. This is likely to be a general feature of electron-deficient compounds.
Theory of microphase separation in multiple segment-type statistical multiblock copolymers with arbitrary block molecular weight distributions
Authors: Slot J. J. M. , Angerman H. J. , ten Brinke G.
Published: July 2002

A Landau free energy is derived for the weak segregation regime (WSR) of melts belonging to a very general class of statistical multiblock copolymers, referred to as “multiple segment-type statistical multiblock copolymers.” Copolymer chains in this class consist of sequences of up to M⩾2 chemically different types of segments, organized into sequences of blocks of varying lengths (molecular weights). The possible sequences of blocks that are encountered in the copolymer chains, as far as their type is concerned, are described by a first-order Markov process, while the block molecular weight distributions of these M types of blocks are completely arbitrary. The number of blocks per chain is assumed to be large. This class of copolymers is sufficiently general to encompass all industrial relevant bulk statistical multiblock copolymers, such as all known thermoplastic elastomers. The particular free energy considered is just one realization of an even more general Landau free energy which is applicable to the WSR of melts of all conceivable copolymers, including homopolymers and all possible blends. The derivation of this Landau free energy is given in Appendix A.
Kinetics of crystallization in conducting polymers observed from electron spin resonance
Authors: Nascimento O. R. , Correa A. A. , Bulhões L. O. S. , Pereira E. C. , Pawlicka A. , Walmsley L.
Published: July 2002

Electron spin resonance (ESR) spectra of pressed pellets of ClO4− doped poly(3-methylthiophene) (P3MT) were recorded as a function of time for samples quenched to 110 K and rapidly heated to 223 K. For a thin sample, fitting the ESR spectra with two Lorentzian absorption lines we were able to follow the decrease of the narrow line associated with the amorphous fraction of the polymer and the increase of the broad line, corresponding to the crystalline fraction. The crystallization process is discussed in terms of Avrami’s equation and confirmed from differential scanning calorimetry (DSC) data.
Neutron spin echo investigation of the concentration fluctuation dynamics in melts of diblock copolymers
Authors: Montes H. , Monkenbusch M. , Willner L. , Rathgeber S. , Fetters L. , Richter D.
Published: July 2002

Diblock copolymers in the melt exhibit order–disorder phase transitions (ODT), which are accompanied by strong concentration fluctuations. These transitions are generally described in terms of the random phase approximation (RPA) of Leibler and Fredrickson, which is able to explain small angle scattering results in the neighborhood of the ODT, in particular around the correlation peak at q*. The RPA theory has been extended to include dynamical phenomena, predicting the short time relaxation of the dynamic structure factor in polymeric multicomponent systems. We report small angle neutron scattering and neutron spin echo experiments on polyethylene–block-polyethylethylene (PE-PEE) and poly(ethylene-propylene)–block-polyethylethylene (PEP-PEE) copolymers with molecular weights of 16.500 and 68.000 g/mol, which explore the structure and dynamics of these block copolymers. Studying melts with different hydrogen/deuterium labeling it was possible to observe experimentally the different relaxation modes of such systems separately. In particular the collective relaxation behavior as well as the single chain motion were accessed. The experimental results were quantitatively compared with the RPA predictions, which were based solely on the dynamical properties of the corresponding homopolymers and the static structure factors. The collective dynamics exhibits an unanticipated fast relaxation mode. This mode is most visible at low wave numbers (q⩾q*) but extends to length scales considerably shorter than the radius of gyration. Furthermore, the dynamical RPA yields expressions for the mobilities of chain segments in the block copolymer melt. These combination rules are at variance with the experimental findings for the single chain dynamics, while they hold for the collective response.
Observation of the molten globule state in a Monte Carlo simulation of the coil-to-globule transition of a homopolymer chain
Authors: Liang Haojun
Published: July 2002

In a two dimensional Monte Carlo simulation of the coil-to-globule transition of a homopolymer chain, we observed a state between the coil and globule states, in which the center of the chain has a higher density than the periphery. The existence of this special state indicates that the melting of the globule is not an all-or-none process, i.e., the periphery melts prior to the center. This state resembles the molten globule state of a protein chain and confirms the previous experimental results.
Diffusion on fractals with interacting internal boundaries
Authors: Aarão Reis F. D. A.
Published: July 2002

We studied random walks interacting with the internal boundaries (borders of lacunas) of Sierpinski carpets (SC), which are infinitely ramified fractals with fractal dimensions DF between 1 and 2. The probability of steps along the borders is u=exp(−E/kBT) times the probability of steps in the bulk, where E<0 represents attraction and E>0 represents repulsion. The mean-square displacement 〈RN2〉 and the mean fraction of adsorbed steps 〈mN〉 of N-step walks were calculated using numerical simulations and extrapolations to the fractal limit considering the expected forms of finite-size corrections. The asymptotic fraction of adsorbed steps m (N→∞) is exactly calculated and confirms the accuracy of the simulations’ results. m varies continuously with u, and then there is no adsorption-desorption transition. As N→∞, 〈RN2〉≈AN2ν, thus we estimated the diffusion exponents νA and νR and the coefficients A(A) and A(R) in the attractive and in the repulsive cases, respectively, and the noninteracting exponent ν0. νR is universal and smaller than ν0, and A(R) decreases with the temperature. ν(A) is universal and larger than ν0 because the attraction helps the diffusing particles to contour the obstacles of the disordered substrate. In a SC with DF≈1.9, A(A) decreases with the temperature T, for all T; in a SC with DF≈1.7, A(A) is maximum for T∼|E|/kB, which consequently provides a condition for fastest diffusion. We suggest the investigation of these features in real systems.
Learning to interpolate molecular potential energy surfaces with confidence: A Bayesian approach
Authors: Bettens Ryan P. A. , Collins Michael A.
Published: July 2002

A modified form of Shepard interpolation of ab initio molecular potential energy surfaces is presented. This approach yields significant improvement in accuracy over previous related schemes. Here each Taylor expansion used in the interpolation formula is assigned a confidence volume which controls the relative weight assigned to that expansion. The parameters determining this confidence volume are derived automatically from a simple Bayesian analysis of the interpolation data. As the iterative scheme expands the data set, the confidence volumes are also iteratively refined. The potential energy surfaces for nine reactions are used to illustrate the accuracy obtained.
Structures, thermochemistry, and electron affinities of the germanium fluorides, GeFn/GeFn−(n=1–5)
Authors: Li Qianshu , Li Guoliang , Xu Wenguo , Xie Yaoming , Schaefer Henry F.
Published: July 2002

Four different density functional methods have been employed to study the molecular structures, electron affinities, and first dissociation energies of the GeFn/GeFn−(n=1–5) molecules. The three types of electron affinities reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The first Ge–F dissociation energies De(Fn−1Ge–F), De(Fn−1Ge−–F), and De(Fn−1Ge–F−) of the GeFn/GeFn− species are also reported. The basis set used in this work is of double-ζ plus polarization quality with additional s- and p-type diffuse functions, labeled as DZP++. Among the four density functionals used in this work, the BHLYP (which includes 50% exact exchange) method determines the molecular structures in best agreement with experiment, while other methods generally overestimated bond lengths. The theoretical Ge–F bond distances for the GeFn−(n=1–4) anions are predicted about 0.1 Å longer than their corresponding neutral counterparts. No significantly bound minimum was found for the neutral GeF5 molecule, while a D3h structure was confirmed to be a genuine minimum for ionic GeF5−. Based on the precise experimental result of EAad(GeF), the adiabatic electron affinities obtained at the DZP++ BHLYP level of theory are again most reliable, with the BLYP method being next. The DZP++ BHLYP adiabatic electron affinities are 1.02, 0.85, 3.72, and 1.46 eV for GeF, GeF2, GeF3, and GeF4, respectively. The vertical detachment energy of GeF5− is predicted to be very large. The substantial value (1.46 eV) of the EA for GeF4 is especially interesting, in that the valence isoelectronic species SiF4 does not bind an electron. A number of experimental electron affinities and experimental thermochemical quantities appear to be error.
A thermophysical study of the melting process in alkyl chain metal n-alkanoates: The thallium (I) series
Authors: Cheda J. A. R. , Redondo M. I. , Garcı́a M. V. , López de la Fuente F. L. , Fernández-Martı́n F. , Westrum E. F.
Published: July 2002

The peculiar thermal behavior of the thallium(I) n-alkanoates series (consisting in several transitions between polymorphic and mesomorphic phases) in comparison with other metallic n-alkanoates series is stated. The allowance of highly accurate adiabatic heat capacity data permits a study of the CH2 contributions to the lattice heat capacity curve at low temperature. Moreover, in this series an anomalous gradual enhancement of the lattice heat capacity has been interpreted from vibrational spectroscopy results as a noncooperative effect due to the internal hindered rotation of the alkyl chain (formation of gauche defects, even in the solid state). The thermodynamics of the “stepwise melting process” from the totally ordered solid at low temperature to the isotropic liquid is based on a revised lattice heat-capacity curve. This was used to evaluate the energy and entropy not only of the clear first order transitions present in the series but also of the described noncooperative effect. The CH2 enthalpy and entropy contribution for this series is estimated and a comparison with the published values for other series is carried out. Moreover, the texture of the mesophases is revealed by polarized light microscopy.
Infrared photofragmentation of “hot” and “cold” nitric oxide cluster ions
Authors: Mouhandes A. , Stace A. J.
Published: July 2002

A line-tunable CO laser has been used to record infrared absorption profiles for (NO)n+ and (NO)n+.Ar clusters for n in the range 2–19 and at wavelengths between 1600 and 1900 cm−1. The presence of an argon atom is shown to have the effect of reducing the internal energy content of the ions, and for the case of (NO)2+. Ar is the only circumstance under which infrared absorption can be detected for the dimer ion. The trimer ion, (NO)3+, is found to have a very strong absorption feature at ∼1700 cm−1, which remains both static and comparatively narrow in subsequent cluster ions containing up to 19 nitric oxide molecules. It is concluded that (NO)3+ forms a stable core in larger clusters and that there is very little additional charge delocalization.
A combined analysis of the ν9 band and the far-infrared torsional spectra of ethane
Authors: Moazzen-Ahmadi N. , Schroderus J. , McKellar A. R. W.
Published: July 2002

Fourier transform measurements of the lowest frequency degenerate fundamental band of CH3CH3 (v9=1←0) in the 12-μm region together with far-infrared torsional spectra have been analyzed to investigate vibration–torsion–rotation effects in a symmetric top molecule. Several spectra of the ν9 band were recorded under different experimental conditions with apodized slit functions of about 0.002 cm−1. Although the intrinsic tunneling splitting in each (J′←J″) doublet in the ν9 band is predicted to be of the order of 0.002 cm−1, in some cases the observed splitting for an intermediate J″ of 20 is several times this value. In extreme cases, splittings of the order of 0.25 cm−1 have been observed. These splittings are caused primarily by the Coriolis interaction between the torsional stack of levels v4=0,1,2,…, for v9=1 and the corresponding stack for the ground vibrational state. Because of a near-degeneracy between the upper level in the ν9 band and its interacting partner (v9=0, v4=3), the (l=−1;K=17,σ=0) torsion–rotation series is resonantly perturbed. For this case, perturbation-allowed v4=3←0 torsional transitions have been identified. Here σ=0, 1, 2, or 3 labels the torsional sublevels. Measurements from the ν9 and 3ν4 bands, frequencies from the far-infrared torsional spectra in the ground vibrational state, and lower state combination differences from ν9+ν4−ν4 band were fitted to within experimental uncertainty using a symmetry adapted effective Hamiltonian which has been used for analyses of similar spectra in methyl silane and CH3CD3. Two Coriolis parameters were determined: the experimental value of ζ̃9z=0.2610(12) is in good agreement with the calculated value of 0.25, whereas the experimental value of ζ̃4,9x=0.2267(20) is about 3 times smaller than the calculated value of 0.60. The theoretical treatment presented here makes use of standard symmetric top formalism and the G36† double-group formalism.
Hydrodynamic effects in photoinduced electron transfer
Authors: Mikhelashvili M. S.
Published: July 2002

The role of molecular motion in reversible charge transfer kinetics, which takes into account the hydrodynamic effect of molecular repulsion, has been considered in this work. The radial dependence of the diffusion coefficient, D(r), which accounts for disorder structure, is used. The hydrodynamic effect in infinite space is an essential factor. It decreases with the decrease of the acceptor concentration and of the forward charge transfer rate constant. It increases with the decrease of the viscosity of the solutions, in the case of high rate constants of the charge transfer. A comparison of this effect on the basis of two different theories has been made. The geometry of the molecular spectra influences the charge transfer process and the hydrodynamic effect. There exists a “false” hyperhydrodynamic effect as a result of the joint influence of the geometry of molecular spectra and of the r dependence of D(r).
A theoretical framework for the experimental determination of host–guest interaction energies in solid inclusion compounds
Authors: Harris Kenneth D. M. , Jupp Peter E. , Lee Sang-Ok
Published: July 2002

A mathematical model is developed to provide the framework of an experimental approach for determining host–guest interaction energies in solid inclusion compounds with one-dimensional tunnel host structures. The approach considers the competitive inclusion of two different types of potential guest molecules X(S)qX and X(S)rX (q≠r) within the tunnel host structure, where X represents a given type of end group (e.g., CH3, halogen, etc.) and S represents an appropriate spacer unit (e.g., CH2, CH, etc.). Sequential and simultaneous models for the growth of the guest substructure within the host tunnel are considered. The relative proportions (m and 1−m) of the two types of guest molecule included within the host tunnel depend on the relative proportions (γ and 1−γ) of the two types of guest molecule in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel structure for including the two different types of guest molecule. Expressions linking χ, m, and γ are developed, and can be applied to determine χ directly from experimental measurements of m for a series of inclusion compounds prepared for different (known) values of γ. Fundamentally, the value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two different types of guest molecule, and χ may be expressed in terms of the host–guest interaction energies for the spacer units S and the end groups X, and the guest–guest (X⋯X) interaction energy. The mathematical model provides a framework for assessing these different energy contributions from experimental measurements of m for sets of inclusion compounds prepared for different values of the parameters q, r, and γ, and with the same host tunnel structure.
Comparison of numerical methods for the calculation of cold atom collisions
Authors: Rawitscher G. H. , Esry B. D. , Tiesinga E. , Burke J. P. , Koltracht I.
Published: July 2002

Comparison between three different numerical techniques for solving a coupled channel Schrödinger equation is presented. The benchmark equation, which describes the collision between two ultracold atoms, consists of two channels, each containing the same diagonal Lennard-Jones potential, one of positive and the other of negative energy. The coupling potential is of an exponential form. The methods are (i) a recently developed spectral type integral equation method based on Chebyshev expansions, (ii) a finite element expansion, and (iii) a combination of an improved Numerov finite difference method and a Gordon method. The computing time and the accuracy of the resulting phase shift is found to be comparable for methods (i) and (ii), achieving an accuracy of ten significant figures with a double precision calculation. Method (iii) achieves seven significant figures. The scattering length and effective range are also obtained.
An efficient approach for calculating vibrational wave functions and zero-point vibrational corrections to molecular properties of polyatomic molecules
Authors: Ruud Kenneth , Åstrand Per-Olof , Taylor Peter R.
Published: July 2002

We have recently presented a formalism for calculating zero-point vibrational corrections to molecular properties of polyatomic molecules in which the contribution to the zero-point vibrational correction from the anharmonicity of the potential is included in the calculations by performing a perturbation expansion of the vibrational wave function around an effective geometry. In this paper we describe an implementation of this approach, focusing on computational aspects such as the definition of normal coordinates at a nonequilibrium geometry and the use of the Eckart frame in order to obtain accurate nonisotropic molecular properties. The formalism allows for a black-box evaluation of zero-point vibrational corrections, completed in two successive steps, requiring a total of two molecular Hessians, 6K–11 molecular gradients, and 6K–11 property evaluations, K being the number of atoms. We apply the approach to the study of a number of electric and magnetic properties—the dipole and quadrupole moments, the static and frequency-dependent polarizability, the magnetizability, the rotational g tensor and the nuclear shieldings—of the molecules hydrogen fluoride, water, ammonia, and methane. Particular attention is paid to the importance of electron correlation and of the importance of the zero-point vibrational corrections for obtaining accurate estimates of molecular properties for a direct comparison with experiment.
Electronic excitation and oscillator strength of ethyl bromide by vacuum ultraviolet photoabsorption and electron energy loss spectroscopy
Authors: Giuliani A. , Motte-Tollet F. , Delwiche J. , Mason N. J. , Jones N. C. , Gingell J. M. , Walker I. C. , Hubin-Franskin M.-J.
Published: July 2002

The high resolution vacuum ultraviolet photoabsorption spectrum of ethyl bromide has been recorded between 5 and 10.15 eV (248–122 nm) using synchrotron radiation. It exhibits a broad structureless valence band centred at 6.1 eV of low cross section followed by a region dominated by excitation of Rydberg states. A high resolution photoelectron spectrum (PES) of the lowest energy ionization band has been obtained and provides ionization energies necessary for identification of related Rydberg-excited states. Also, analysis of the vibrational fine structure in the PES has allowed identification of the normal vibrational modes excited and their wave numbers in the ion. These data, in turn, have been used in the assignment of the lowest energy photoabsorption bands arising from electron excitation into the 5s Rydberg orbital. The electron energy loss spectrum, recorded from 6.5 to 14.1 eV, under electric-dipole conditions, confirms the magnitude of the photoabsorption cross-section values obtained using the synchrotron radiation and extends the differential and optical oscillator strength values up to 14.004 eV.
Representation of the 6D potential energy surface for a diatomic molecule near a solid surface
Authors: Busnengo H. F. , Salin A. , Dong W.
Published: July 2002

An efficient method is proposed to construct the six-dimensional Potential Energy Surface (PES) for diatomic molecule-surface interactions from low dimensional cuts obtained in ab initio calculations. The efficiency of our method results from a corrugation-reducing procedure based on the observation that most of the corrugation in a molecule-surface PES is already embedded in the atom-surface interactions. Hence, substraction of the latter leads to a much smoother function which makes accurate interpolations possible. The proposed method is a general one and can be implemented in a systematic way for any system. Its efficiency is illustrated for the case of H2/Pd(111) by using recent ab initio data. We report also the results of very stringent checks against ab initio calculations not used in the interpolation. These checks show the high accuracy of our method.
Two-dimensional hard dumbbells. II. Pressure in terms of free volumes and surfaces
Authors: Gay Shawn C. , Rainwater James C. , Beale Paul D.
Published: July 2002

For systems of fused-hard-sphere molecules, we relate cavity distributions to free-volume distributions and derive new statistical geometry relations between thermodynamic and cavity properties. From these results, we formulate two different approaches for calculating the pressure of systems of two-dimensional homonuclear hard dumbbells in terms of the geometry of the free volume of a molecule observed over the course of a simulation. We find a simple linear relationship to exist between the compressibility and the average of the ratio of the surface area and volume of the angle-averaged free volumes of the dumbbells. We find excellent agreement between the pressure as calculated via both approaches and the pressure as calculated from simulations.
Can surface-enhanced Raman scattering serve as a channel for strong optical pumping?
Authors: Haslett T. L. , Tay L. , Moskovits M.
Published: July 2002

The surface-enhanced Raman scattering spectra of a number of dye and colorless molecules adsorbed on deposited coloidal silver films were systematically studied as a function of power and position using a Raman microscope. The anti-Stokes portions of the spectra of the dyes reproducibly show line intensities much greater than what is expected on the basis of the equilibrium population of the excited vibrational states, even at the lowest incident light intensities used. This behavior was observed previously and attributed to optical pumping of vibrationally excited states of the molecules by unusually intense surface-enhanced Raman transitions, [Phys. Rev. Lett. 76, 2444 (1996)] suggesting either uncommonly large Raman cross-sections or very intense local field strengths exceeding those encountered in the most powerful currently available lasers. Based on this work, however, we ascribe the apparently large anti-Stokes intensities primarily to a difference in the Stokes and anti-Stokes Raman cross-sections resulting from resonance or pre-resonance Raman processes in the adsorbate–surface complex rather than to strongly nonequilibrium populations in the molecular vibrational states. Finally, we observed no significant inhomogeneity in the Raman enhancement in the images of the deposited silver coloid samples down to spatial resolutions of ∼1 μm.
Spinor group and its restrictions
Authors: Sarma C. R. , Paldus J.
Published: July 2002

A realization of the spinor algebra of the rotation group SO(N),  N=2n or 2n+1, in the covering algebra of U(2n) is exploited to obtain explicit representation matrices for the SO(N) generators in the basis adapted to the subgroup chain SO(N)⊃U(n)⊇U(n−1)⊃⋅⋅⋅⊃U(1). As a special case the computation of matrices of U(n) representations characterized by a k-column Young tableau is reduced to the evaluation of at most k-box totally symmetric representations of U(2n).
Irreducible representations of the exceptional Lie superalgebras D(2,1;α)
Authors: Van der Jeugt J.
Published: July 2002

The shift operator technique is used to give a complete analysis of all finite- and infinite-dimensional irreducible representations of the exceptional Lie superalgebras D(2,1;α). For all cases, the star or grade star conditions for the algebra are investigated. Among the finite-dimensional representations there are no star and only a few grade star representations, but an infinite class of infinite-dimensional star representations is found. Explicit expressions are given for the ‘‘doublet’’ representation of D(2,1;α). The one missing label problem D(2,1;α)→su(2)+su(2)+su(2) is discussed in detail and solved explicitly.
SU(m/n) weight systems and superprojection matrices
Authors: Kim Chang-Ho , Kim Kee Yong , l’Yi W. S. , Kim Yongduk , Park Young-Jai
Published: July 2002

Representations of the SU(m/n) superalgebra are studied in terms of the Kac–Dynkin weight systems. Superprojection matrices are introduced for the possible branching patterns.
Reeh–Schlieder-type density results in one- and n-body Schrödinger theory and the ‘‘unique continuation problem’’
Authors: Requardt Manfred
Published: July 2002

A couple of Reeh–Schlieder-type density results are proved to hold in one- and n-body Schrödinger theory, that is, it is proved that states localized at time zero in an arbitrarily small open set of Rn are already total after an arbitrarily small time (which implies much more than the well-known acausal behavior of nonrelativistic theories). It is shown that there exists a close connection to the so-called ‘‘unique continuation property’’ of elliptic partial differential operators. Furthermore, a certain machinery of analytic continuation is developed and the notion of generalized propagation kernels is introduced, which also might be of use elsewhere (e.g., in scattering theory).
Superfield and irreducible superfield structure
Authors: Villasante M.
Published: July 2002

Field contents for scalar superfields in different numbers of dimensions are tabulated. Tables of field contents for some irreducible superfields included in the scalar superfield in 11 dimensions are also given.
Relativistic charged bosons in a magnetic field. I. Wave functions and matrix elements
Authors: Witte Nicholas S. , Dawe Ross L. , Hines Kenneth C.
Published: July 2002

A system of charged zero-spin bosons in the presence of a uniform magnetic field is studied using a relativistic spinor formalism. Equations of motion for the relevant operators are developed. The eigenfunctions of two different sets of commuting operators are obtained by the use of ladder operators and also by direct solution of the Klein–Gordon equation in both coordinate and momentum representations. Matrix elements are calculated which will be required in later consideration of the collisionless conductivity and dielectric tensors for the boson–antiboson plasma in a strong magnetic field (see papers II and III in this series).
Ideal-preserving Lorentzian connections
Authors: Al Saad A. , Benn I. M.
Published: July 2002

Fibers of the exterior bundle over a Lorentzian manifold can be given the structure of a Clifford algebra. The minimal left ideals of this Clifford algebra may be interpreted as spinors. In order to better understand spinorial properties of the Kähler equation in a curved space-time, conditions for the Lorentzian connection to preserve these ideals are examined.
KdV-invariant polynomial functionals
Authors: Tsujishita Toru
Published: July 2002

It is proved that the algebra of the KdV-invariant polynomial functionals on the space of C∞ functions on the one-dimensional torus is isomorphic to the polynomial algebra of the infinite number of the conserved quantities found by Miura, Gardner, and Kruskal [J. Math. Phys. 9, 1204 (1968)]. As a corollary, it is shown that the algebra of the isospectral polynomial functionals of the Hill’s operator also coincides with this algebra.
Generalized complex superspace—Involutions of superfields
Authors: Kobayashi Yuji , Nagamachi Shigeaki
Published: July 2002

Distinguished involutions called transposition and conjugation in the algebra of complex supernumbers are introduced. On the base of these involutions an analysis is developed over complex superspaces. Consistency of integration under supertransformations between two complex superspaces is shown.