bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation dynamics of thiolactic acid at 193 nm: Detection of the nascent OH product by laser-induced fluorescence
Authors: Pushpa Kumbil K. , Upadhyaya Hari P. , Kumar Awadhesh , Naik Prakash D. , Bajaj Paramanand , Mittal Jai P.
Published: March 2004

Electronically excited thiolactic acid (2-mercaptopropionic acid), H3C–CH(SH)–COOH, undergoes the C–OH bond cleavage on excitation to the S2 state at 193 nm, generating the primary product OH (v,J), which is detected by laser-induced fluorescence technique in a collisionless condition of flow system. The partitioning of the available energy between vibrational, rotational, and translational degrees of freedom of nascent photofragments is obtained from relative intensities of ro-vibronic lines in laser-induced fluorescence spectrum of OH, and their Doppler profiles. The rotational population of OH (v″=0) is characterized by rotational temperature of 408±25 K. OH is produced in a vibrationally cold state, i.e., mostly in v″=0. The average translational energy of OH (v″=0,J″) is found to be 21.5±2.0 kcal/mol, which implies 25.6 kcal/mol of energy in relative translation of photoproducts corresponding to the ft value of ∼0.6. The observed high translational energy is due to the presence of a barrier in the exit channel, implying that the C–OH bond scission takes place on an electronically excited potential energy surface. The observed partitioning of the available energy between various degrees of the photofragments is theoretically modeled, and the hybrid model, with 26.0 kcal/mol of barrier in the exit channel, is found to explain the measured data quite well. The experimental results are also supported with ab initio molecular orbital calculations for both the ground and the excited electronic states. Time-dependent density functional theory is used to understand the nature of various electronic transitions connecting the lower excited states. Potential energy curves as a function of the C–OH bond length of thiolactic acid suggest distinct exit barriers in the S1, T1, and T2 states. But, we could locate the transition state structure for OH formation in the S1 state alone. Thus, although thiolactic acid is excited to the S2 state at 193 nm, it undergoes internal conversion to S1 where it dissociates to yield OH. In addition to the OH channel from excited electronic states, we studied theoretically all probable dissociation channels occurring on the ground electronic state of thiolactic acid.
Is styrene planar in liquid phases?
Authors: Celebre Giorgio , De Luca Giuseppina , Longeri Marcello , Pileio Giuseppe , Emsley James W.
Published: March 2004

The proton NMR spectra of two C13-labeled isotopomers of styrene dissolved in two liquid crystalline solvents have been obtained and analyzed to yield four sets each of 24 dipolar couplings. These couplings were then used to investigate the structure of the ring and the ene fragments of the molecule, and the position of the maximum, φ0, in the ring–ene bond rotational probability distribution. To do this, the effect on the dipolar couplings of small-amplitude vibrational motion was taken into account using vibrational wave functions calculated by molecular orbital and density functional methods. It is concluded that the NMR data are consistent with the ring fragment, averaged over the ring–ene rotation, planar, while the ene fragment is not. The value of φ0 is found to be 18.0°±0.2° for the two solutions, compared with a value of 27° calculated by the molecular method MP2/6-31G*.
A reduced dimensionality quasiclassical and quantum study of the proton transfer reaction H3O++H2O→H2O+H3O+
Authors: Rheinecker Jaime , Xie Tiao , Bowman Joel M.
Published: March 2004

We report quantum and quasiclassical calculations of proton transfer in the reaction H3O++H2O in three degrees of freedom, the two OH+ bond lengths and the OH+O angle. The reduced dimensional potential energy surface is obtained from the full dimensional OSS3(p) energy function of H5O2+ [L. Ojamäe, I. Shavitt, and S. J. Singer, J. Chem. Phys. 109, 5547 (1998)], with an additional long-range correction to reproduce the correct ion–molecule interaction. This surface is used to perform both quasiclassical trajectory and quantum reactive scattering calculations of the zero total angular momentum cumulative reaction probability and cross sections for initial rotational states 0, 1, and 2. Comparison of these quantities are made to assess the importance of quantum effects in this reduced dimensional reaction. Additional quasiclassical cross sections are calculated to obtain the thermal rate constant for the reaction.
Revealing the roles of Hamiltonian coupling in bound-state quantum systems
Authors: Cheong Byeong-Seo , Rabitz Herschel
Published: March 2004

A Hamiltonian coupling identification (HCI) technique is introduced to reveal the independent and cooperative roles of Hamiltonian matrix elements in determining the bound-state energies of quantum systems. The HCI technique operates by encoding each Hamiltonian matrix element with a unique modulation signal, producing a nonlinear signature in the energy eigenvalues that may be decoded to reveal the contributing coupling structure in the Hamiltonian. The HCI technique is capable of exploring the roles of Hamiltonian coupling structure within and beyond the convergence limits of standard perturbation theory expansions. The flexibility residing in the encoding and decoding processes may be exploited to tailor the analysis to meet the desired degree of sought-after information about the Hamiltonian coupling structure. HCI, based on a Fourier encoding and decoding scheme, is illustrated by extracting information on the role of coupling interactions in the potential matrix elements of several simple model systems.
Analytic density-functional self-consistent-field theory of diblock copolymers near patterned surfaces
Authors: Seok Chaok , Freed Karl F. , Szleifer Igal
Published: March 2004

Analytical solutions are derived for the density profiles and the free energies of compressible diblock copolymer melts (or incompressible copolymer solutions) near patterned surfaces. The density-functional self-consistent-field theory is employed along with a Gaussian chain model for bonding constraints and a random mixing approximation for nonbonded interactions. An analytical solution is rendered possible by expanding the chain distribution function around an inhomogeneous reference state with a nontrivial analytical solution, by retaining the linear terms, and by requiring consistency with the homopolymer limit. The density profiles are determined by both real and complex roots of a sixth-degree polynomial that may easily be obtained by solving a generalized eigenvalue problem. This analytical formulation enables one to efficiently explore the large nine-dimensional parameter space and can serve as a first approximation to computationally intensive studies with more detailed models. Illustrative computations are provided for uniform and patterned surfaces above the order–disorder transition. The results are consistent with the previous self-consistent-field calculations in that lamellar ordering appears near the surface above the order–disorder transition and the lamella order perpendicular or parallel to the surface depending on the commensurability between the periods of the surface pattern and the density oscillations.
Sum frequency vibrational spectroscopy of leucine molecules adsorbed at air–water interface
Authors: Ji Na , Shen Yuen-Ron
Published: March 2004

Sum frequency vibrational spectroscopy was used to study adsorption of leucine molecules at air–water interface from solutions with different concentrations and pH values. The surface density and the orientation of the isopropyl head group of the adsorbed leucine molecules could be deduced from the measurements. It was found that the orientation depends on the surface density, but only weakly on bulk pH value at the saturated surface density. The vibrational spectra of the interfacial water molecules appeared to be strongly affected by the charge state of the adsorbed leucine molecules. Enhancement and inversion of polar orientation of interfacial water molecules by surface charges or field controllable by the bulk pH value were observed.
Energy of charged states in the acetanilide crystal: Trapping of charge-transfer states at vacancies as a possible mechanism for optical damage
Authors: Tsiaousis D. , Munn R. W.
Published: March 2004

Calculations for the acetanilide crystal yield the effective polarizability (16.6 Å3), local electric field tensor, effective dipole moment (5.41 D), and dipole–dipole energy (−12.8 kJ/mol). Fourier-transform techniques are used to calculate the polarization energy P for a single charge in the perfect crystal (−1.16 eV); the charge–dipole energy WD is zero if the crystal carries no bulk dipole moment. Polarization energies for charge-transfer (CT) pairs combine with the Coulomb energy EC to give the screened Coulomb energy Escr; screening is nearly isotropic, with Escr≈EC/2.7. For CT pairs WD reduces to a term δWD arising from the interaction of the charge on each ion with the change in dipole moment on the other ion relative to the neutral molecule. The dipole moments calculated by density-functional theory methods with the B3LYP functional at the 6-311++G** level are 3.62 D for the neutral molecule, changing to 7.13 D and 4.38 D for the anion and cation, relative to the center of mass. Because of the large change in the anion, δWD reaches −0.9 eV and modifies the sequence of CT energies markedly from that of Escr, giving the lowest two CT pairs at −1.98 eV and −1.41 eV. The changes in P and WD near a vacancy are calculated; WD changes for the individual charges because the vacancy removes a dipole moment and modifies the crystal dielectric response, but δWD and EC do not change. A vacancy yields a positive change ΔP that scatters a charge or CT pair, but the change ΔWD can be negative and large enough to outweigh ΔP, yielding traps with depths that can exceed 150 meV for single charges and for CT pairs. Divacancies yield traps with depths nearly equal to the sum of those produced by the separate vacancies and so they can exceed 300 meV. These results are consistent with a mechanism of optical damage in which vacancies trap optically generated CT pairs that recombine and release energy; this can disrupt the lattice around the vacancy, thereby favoring trapping and recombination of CT pairs generated by subsequent photon absorption, leading to further lattice disruption. Revisions to previous calculations on trapping of CT pairs in anthracene are reported.
Nanometer-size cluster formation in alkali-metal-doped fullerene layers
Authors: Touzik A. , Hermann H. , Wetzig K.
Published: March 2004

Kinetic Monte Carlo methods have been used to simulate structural transformations in fullerene layers during electrochemical intercalation with alkali-metal ions (A). Special attention is paid to the thermodynamic stability of the AxC60 phases. The calculations point out a phase separation in the doped fullerene layer into alkali-metal-rich and alkali-metal-depleted areas at room temperature. The final state is represented by two phases which coexist as a stable fine mixture of nanoscale particles. The instability of homogeneous layers has potentially critical impact on their electrical properties and can explain the formation of nanostructures (20–50 nm) at the fullerene–electrolyte interface. Rb3C60 clusters are predicted to be larger than K3C60 ones for equal mean alkali-metal concentrations. Experimental data on electrochemical metal deposition on alkali-metal-doped fullerene substrates—in particular, atomic force microscopy measurements—are also consistent with the model proposed.
Ozone adsorption on carbon nanotubes: The role of Stone–Wales defects
Authors: Picozzi S. , Santucci S. , Lozzi L. , Valentini L. , Delley B.
Published: March 2004

First-principles calculations within the density functional theory have been performed in order to investigate ozone adsorption on carbon nanotubes. Particular emphasis is placed on the effects of Stone–Wales-like defects on the structural and electronic properties of (i) ideal tubes and (ii) tubes in the presence of ozone. Our results show that structural deformations induced on the pure carbon nanotubes by Stone–Wales defects are similar, as expected, to those induced on graphite; for the (10,0) tube, the semiconducting character is kept, though with a small reduction of the band gap. As for the ozone adsorption, the process on ideal nanotubes is most likely physisorption, though slightly stronger if compared to other previously studied molecules and consistent with the strong oxydizing nature of O3. However, when ozone adsorbs on Stone–Wales defects, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a CO covalent bond; this is consistent with experimental observations of CO functional groups, as well as of the liberation of CO gas phase and of the formation of C vacancies, thus explaining the consumption of the nanotube film upon ozone exposure.
Low-lying electronic states of HBr2+
Authors: Alagia Michele , Brunetti Brunetto G. , Candori Pietro , Falcinelli Stefano , Teixidor Marc Moix , Pirani Fernando , Richter Robert , Stranges Stefano , Vecchiocattivi Franco
Published: March 2004

The present study describes the characterization of energy and structure of HBr2+ in its low-lying electronic states, achieved through an extension of a new empirical method [Chem. Phys. Lett. 379, 139 (2003)] recently introduced to evaluate the interatomic interaction in the HX2+ (X=F,Cl,Br,I) molecular dications. The method is based on identification of the main components of the interaction and their evaluation through some simple correlation formulas. Potential energy curves, given in a simple, natural, and analytical form, made possible the calculations of some important properties, such as double-photoionization energy thresholds, vibrational spacing, average lifetime, and Franck–Condon factors. The predictions, compared with data available in the literature, are of great interest for the analysis and interpretation of some new experimental results.
Fourier transform microwave spectroscopy of the Rg–SH(2Πi) complexes (Rg:Ne, Kr): Determination of the intermolecular potential energy surfaces
Authors: Suma Kohsuke , Sumiyoshi Yoshihiro , Endo Yasuki
Published: March 2004

Pure rotational spectra of Ne–SH and Kr–SH have been studied by Fourier transform microwave spectroscopy. R-branch transitions in the lower-spin component (Ω=3/2) corresponding to a linear Πi2 radical were observed for J″=1.5–4.5 in the region 11–25 GHz for Ne–SH and for J″=1.5–6.5 in the region 5–20 GHz for Kr–SH, respectively, with parity doublings and hyperfine splittings associated with the H nucleus. Although the spectral pattern of Kr–SH is relatively regular, that of Ne–SH is irregular with the J dependence of the parity doublings quite different from other Rg–SH or Ar–OH complexes. Two-dimensional intermolecular potential energy surfaces (IPSs) for both of the species have been determined from the least-squares fittings of the observed rotational transitions utilizing results of high-level ab initio calculations. These IPSs reproduce the observed transition frequencies within the experimental error and provide accurate knowledge on the intermolecular interaction and internal dynamics. Systematic comparisons of Rg–SH complexes have clarified various features of this series of complexes.
Bohmian dynamics on subspaces using linearized quantum force
Authors: Rassolov Vitaly A. , Garashchuk Sophya
Published: March 2004

In the de Broglie–Bohm formulation of quantum mechanics the time-dependent Schrödinger equation is solved in terms of quantum trajectories evolving under the influence of quantum and classical potentials. For a practical implementation that scales favorably with system size and is accurate for semiclassical systems, we use approximate quantum potentials. Recently, we have shown that optimization of the nonclassical component of the momentum operator in terms of fitting functions leads to the energy-conserving approximate quantum potential. In particular, linear fitting functions give the exact time evolution of a Gaussian wave packet in a locally quadratic potential and can describe the dominant quantum-mechanical effects in the semiclassical scattering problems of nuclear dynamics. In this paper we formulate the Bohmian dynamics on subspaces and define the energy-conserving approximate quantum potential in terms of optimized nonclassical momentum, extended to include the domain boundary functions. This generalization allows a better description of the non-Gaussian wave packets and general potentials in terms of simple fitting functions. The optimization is performed independently for each domain and each dimension. For linear fitting functions optimal parameters are expressed in terms of the first and second moments of the trajectory distribution. Examples are given for one-dimensional anharmonic systems and for the collinear hydrogen exchange reaction.
Vacuum ultraviolet pulsed-field ionization-photoelectron study of H2S in the energy range of 10–17 eV
Authors: Hochlaf M. , Weitzel K.-M. , Ng C. Y.
Published: March 2004

Vacuum ultraviolet pulsed-field ionization-photoelectron (PFI-PE) spectra of H2S have been recorded at PFI-PE resolutions of 0.6–1.0 meV in the energy range of 10–17 eV using high-resolution synchrotron radiation. The PFI-PE spectrum, which covers the formation of the valence electronic states H2S+ (X̃ 2B1, Ã 2A1, and B̃ 2B2), is compared to the recent high-resolution He I photoelectron spectra of H2S obtained by Baltzer et al. [Chem. Phys. 195, 403 (1995)]. In addition to the overwhelmingly dominated origin vibrational band, the PFI-PE spectrum for H2S+(X̃ 2B1) is found to exhibit weak vibrational progressions due to excitation of the combination bands in the ν1+ symmetric stretching and ν2+ bending modes. While the ionization energy (IE) for H2S+(X̃ 2B1) obtained here is in accord with values determined in previously laser PFI-PE measurements, the observation of a new PFI-PE band at 12.642±0.001 eV suggests that the IE for H2S+(Ã 2A1) may be 0.12 eV lower than that reported in the He I study. The simulation of rotational structures resolved in PFI-PE bands shows that the formation of H2S+(X̃ 2B1) and H2S+(Ã 2A1) from photoionization of H2S(X̃ 1A1) is dominated by type-C and type-B transitions, respectively. This observation is consistent with predictions of the multichannel quantum defect theory. The small changes in rotational angular momentum observed are consistent with the dominant atomiclike character of the 2b1 and 5a1 molecular orbitals of H2S. The PFI-PE measurement has revealed perturbations of the (0, 6, 0) K+=3 and (0, 6, 0) K+=4 bands of H2S+(Ã 2A1). Interpreting that these perturbations arise from Renner–Teller interactions at energies close to the common barriers to linearity of the H2S+ (X̃ 2B1 and Ã 2A1) states, we have deduced a barrier of 23 209 cm−1 for H2S+(X̃ 2B1) and 5668 cm−1 for H2S+(Ã 2A1). The barrier of 23 209 cm−1 for H2S+(X̃ 2B1) is found to be in excellent agreement with the results of previous studies. The vibrational PFI-PE bands for H2S+(B̃ 2B2) are broad, indicative of the predissociative nature of this state.
Spectroscopy of the OC–HF hydrogen-bonded complex at vHF=3
Authors: Yu Zhenhong , Chuang Cheng-chi , Medley Patrick , Stone Todd A. , Klemperer William
Published: March 2004

The vHF=3 levels of the linear OC–HF complex are observed in the range of 10 800–11 500 cm−1 using intracavity Ti–sapphire laser-induced fluorescence. The vibrational predissociation linewidths of both (30000) and (300110) states exceed 5 GHz; thus, the measured spectra are not rotationally resolvable. Under the assumption that these levels are not strongly perturbed, the rotational constants of the two levels are determined to be 0.1100(1) cm−1 for (30000), 0.1081(1), and 0.1065(1) cm−1 for f and e sublevels of (300110), respectively, through band contour fitting. The (30000)←(00000) band origin is at 10 894.46(1) cm−1, showing a HF wave number redshift of 478.3 cm−1. The 4.07 redshift ratio of vHF=3 to that of vHF=1 indicates a significantly nonlinear increase of the intermolecular interaction energy through HF valence excitation. An ab initio interaction potential surface for HF valence coordinates varying from 0.8 to 1.25 Å is used to examine vibrational dynamics. The HF valence vibration v1 is treated perturbatively, showing that the vibrational redshifts are determined essentially in first order with only a very small second-order contribution. The (300110)←(00000) combination transition is observed with the band origin at 11 432.66(1) cm−1, giving the HF intermolecular bending mode to be 538.2 cm−1. The high frequency of this vibration, compared to that in similar HF complexes, shows the strong angular anisotropy of the intermolecular interaction potential of OC–HF with respect to the HF subunit. The lifetime of the (300110) level increases to 28 ps from 14 ps for (30000).
Excitation energy transfer (EET) between molecules in condensed matter: A novel application of the polarizable continuum model (PCM)
Authors: Iozzi Maria Francesca , Mennucci Benedetta , Tomasi Jacopo , Cammi Roberto
Published: March 2004

We present a quantum-mechanical theory to study excitation energy transfers between molecular systems in solution. The model is developed within the time-dependent (TD) density-functional theory and the solvent effects are introduced in terms of the polarizable continuum model (PCM). Unique characteristic of this model is that both “reaction field” and screening effects are included in a coherent and self-consistent way. This is obtained by introducing proper solvent-specific operators in the Kohn–Sham equations and in the corresponding TD scheme. The solvation model exploits the integral equation formalism (IEF) version of PCM and it defines the solvent operators on a molecular cavity modeled on the real three-dimensional (3D) structure of the solute systems. Applications to EET in dimers of ethylene and naphtalene are presented and discussed.
Photolysis of oxalyl chloride (ClCO)2 at 193 nm: Emission of CO(v⩽6, J⩽60) detected with time-resolved Fourier-transform spectroscopy
Authors: Wu Chia-Yan , Lee Yuan-Pern , Wang Niann S.
Published: March 2004

Upon photolysis of oxalyl chloride at 193 nm, time-resolved and rotationally resolved emission of CO(v⩽6, J⩽60) in the spectral region 1850–2350 cm−1 was detected with a step-scan Fourier-transform spectrometer under nearly collisionless conditions. Boltzmann-type rotational distributions of CO correspond to temperatures 3520±110 (v=1) to 2300±610 K (v=6), with an average rotational energy of 23±2 kJ mol−1. The average vibrational energy of CO is estimated to be 26±4 kJ mol−1 according to observed vibrational populations of v=1–6 and that of v=0 predicted with a surprisal analysis. Combining the average internal energy of CO determined in this work and average translational energies of photofragments Cl and CO determined previously by Hemmi and Suits, we propose a four-body dissociation mechanism producing one pair of translationally rapid and internally excited CO and one pair of translationally rapid Cl, each with similar energies, to account for the energy balance. Formation of translationally slow ClCO, Cl, and CO reported previously by Hemmi and Suits might be rationalized with a second channel involving emission of electronically excited intermediates. We observed no emission of ClCO near 1880 cm−1, indicating that surviving ClCO has little vibrational excitation in the C–O stretching mode.
Reorganization energy associated with small polaron mobility in iron oxide
Authors: Rosso Kevin M. , Dupuis Michel
Published: March 2004

The reorganization energy is an important quantity controlling electron transfer rates. The internal contribution arising from the energy to reorganize donor/acceptor bonds can be evaluated by the “direct” and “4-point” methods. We examine how spatial separation leading to the noninteracting character of the donor and acceptor affects the reorganization energy. We show that the direct method captures contributions from interaction of the donor and acceptor while the 4-point method does not, and the two methods converge at large separation. Comparing reorganization energies determined by the two methods yields a measure of the degree of interaction between the initial and final states. The analysis is illustrated in the characterization of small polarons in iron oxides.
Ab initio based force field and molecular dynamics simulations of crystalline TATB
Authors: Gee Richard H. , Roszak Szczepan , Balasubramanian Krishnan , Fried Laurence E.
Published: March 2004

An all-atom force field for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is presented. The classical intermolecular interaction potential for TATB is based on single-point energies determined from high-level ab initio calculations of TATB dimers. The newly developed potential function is used to examine bulk crystalline TATB via molecular dynamics simulations. The isobaric thermal expansion and isothermal compression under hydrostatic pressures obtained from the molecular dynamics simulations are in good agreement with experiment. The calculated volume-temperature expansion is almost one dimensional along the c crystallographic axis, whereas under compression, all three unit cell axes participate, albeit unequally.
Density-functional theory of spherical electric double layers and ζ potentials of colloidal particles in restricted-primitive-model electrolyte solutions
Authors: Yu Yang-Xin , Wu Jianzhong , Gao Guang-Hua
Published: March 2004

A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the ζ potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson–Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.
van der Waals–Tonks-type equations of state for hard-hypersphere fluids in four and five dimensions
Authors: Wang Xian-Zhi
Published: March 2004

Recently, we developed accurate van der Waals–Tonks-type equations of state for hard-disk and hard-sphere fluids by using the known virial coefficients. In this paper, we derive the van der Waals–Tonks-type equations of state. We further apply these equations of state to hard-hypersphere fluids in four and five dimensions. In the low-density fluid regime, these equations of state are in good agreement with the simulation results and existing equations of state.
Periodic change of viscosity and density in an oscillating chemical reaction
Authors: Yoshimoto Minoru , Shirahama Hiroyuki , Kurosawa Shigeru , Naito Masayoshi
Published: March 2004

It was found that the periodic change of the solution viscosity and density was generated in the Belousov–Zhabotinsky (BZ) reaction. This rhythmic phenomenon was observed in both the iron catalyst {[Fe(Phen)3]2+–[Fe(Phen)3]3+} and the cerium catalyst [Ce(III)–Ce(IV)] system, where the solution viscosity and density were synchronized with the redox potential in the in-phase mode. However, the time delay existed between the redox potential and the solution viscosity and density. The behavior of the BZ reaction was also monitored in the presence of the nonionic surfactant. This experiment revealed that, beyond the critical micelle concentration, the phase between the redox potential and the solution viscosity and density was synchronized into the antiphase mode. We suggested that the variation of the catalyst drove the oscillation of the solution viscosity and density in the BZ reaction.
Reflectivity and anisotropic optical functions of quaterthiophene single crystals
Authors: Tavazzi S. , Borghesi A. , Campione M. , Laicini M. , Trabattoni S. , Spearman P.
Published: March 2004

Polarized reflectance spectra of quaterthiophene single crystals are reported with different angles and planes of incidence. The strong dependence of the spectral features on the experimental configuration is described by an orthorhombic model and the components of the complex diagonal dielectric tensor are given.
Photodissociation of benzene under collision-free conditions: An ab initio/Rice–Ramsperger–Kassel–Marcus study
Authors: Kislov V. V. , Nguyen T. L. , Mebel A. M. , Lin S. H. , Smith S. C.
Published: March 2004

The ab initio/Rice–Ramsperger–Kassel–Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of benzene at various wavelengths upon absorption of one or two UV photons followed by internal conversion into the ground electronic state. Reaction pathways leading to various decomposition products have been mapped out at the G2M level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for C6H5+H, C6H4+H2, C4H4+C2H2, C4H2+C2H4, C3H3+C3H3, C5H3+CH3, and C4H3+C2H3 have been calculated subsequently using both numerical integration of kinetic master equations and the steady-state approach. The results show that upon absorption of a 248 nm photon dissociation is too slow to be observable in molecular beam experiments. In photodissociation at 193 nm, the dominant dissociation channel is H atom elimination (99.6%) and the minor reaction channel is H2 elimination, with the branching ratio of only 0.4%. The calculated lifetime of benzene at 193 nm is about 11 μs, in excellent agreement with the experimental value of 10 μs. At 157 nm, the H loss remains the dominant channel but its branching ratio decreases to 97.5%, while that for H2 elimination increases to 2.1%. The other channels leading to C3H3+C3H3, C5H3+CH3, C4H4+C2H2, and C4H3+C2H3 play insignificant role but might be observed. For photodissociation upon absorption of two UV photons occurring through the neutral “hot” benzene mechanism excluding dissociative ionization, we predict that the C6H5+H channel should be less dominant, while the contribution of C6H4+H2 and the C3H3+C3H3, CH3+C5H3, and C4H3+C2H3 radical channels should significantly increase.
Vibrational relaxation of CH3I in the gas phase and in solution
Authors: Elles Christopher G. , Cox M. Jocelyn , Crim F. Fleming
Published: March 2004

Transient electronic absorption measurements reveal the vibrational relaxation dynamics of CH3I following excitation of the C–H stretch overtone in the gas phase and in liquid solutions. The isolated molecule relaxes through two stages of intramolecular vibrational relaxation (IVR), a fast component that occurs in a few picoseconds and a slow component that takes place in about 400 ps. In contrast, a single 5–7 ps component of IVR precedes intermolecular energy transfer (IET) to the solvent, which dissipates energy from the molecule in 50 ps, 44 ps, and 16 ps for 1 M solutions of CH3I in CCl4, CDCl3, and (CD3)2CO, respectively. The vibrational state structure suggests a model for the relaxation dynamics in which a fast component of IVR populates the states that are most strongly coupled to the initially excited C–H stretch overtone, regardless of the environment, and the remaining, weakly coupled states result in a secondary relaxation only in the absence of IET.
Experimental verification of the Smoluchowski theory for a bimolecular diffusion-controlled reaction in liquid phase
Authors: Arita Toshihiko , Kajimoto Okitsugu , Terazima Masahide , Kimura Yoshifumi
Published: March 2004

We report experimental verification of the Smoluchowski theory for diffusion-controlled reactions in solution at the steady-state limit. We have determined both the diffusion coefficients and the self-termination reaction rates of the diphenylmethyl radical simultaneously. Smoluchowski theory is insufficient to discuss the reaction rate for the self-termination reaction of the diphenylmethyl radical, so the reaction rate of an encounter complex based on the Collins–Kimball treatment is estimated.
Influence of strain on transport in dense Lennard-Jones systems
Authors: Petravic Janka
Published: March 2004

We study the shear stress relaxation and temperature dependence of the diffusion coefficient, viscosity, and thermal conductivity along a high-density Lennard-Jones isochore of the reduced density of 1.0, as it crosses the freezing and melting lines, in equilibrium and under constant strain.
Localization and freezing of a Gaussian chain in a quenched random potential
Authors: Rostiashvili Vakhtang G. , Vilgis Thomas A.
Published: March 2004

The Gaussian chain in a quenched random potential (which is characterized by the disorder strength Δ) is investigated in the d-dimensional space by the replicated variational method. The general expression for the free energy within so-called one-step-replica symmetry breaking (1-RSB) scenario has been systematically derived. We have shown that the replica symmetrical (RS) limit of this expression can describe the chain center-of-mass localization and collapse. The critical disorder when the chain becomes localized scales as Δc≃bdN−2+d/2 (where b is the length of the Kuhn segment length and N is the chain length) whereas the chain gyration radius Rg≃b(bd/Δ)1/(4−d). The freezing of the internal degrees of freedom follows to the 1-RSB-scenario and is characterized by the beads localization length D2¯. It was demonstrated that the solution for D2¯ appears as a metastable state at Δ=ΔA and behaves similarly to the corresponding frozen states in heteropolymers or in p-spin random spherical model.
Electron attachment and detachment and the electron affinity of cyclo-C4F8
Authors: Miller Thomas M. , Friedman Jeffrey F. , Viggiano A. A.
Published: March 2004

New measurements have been made of rate constants for electron attachment to c-C4F8 (octafluorocyclobutane) and thermal electron detachment from the parent anion, c-C4F8−, over the temperature range 298–400 K in 133 Pa of He gas in a flowing-afterglow Langmuir-probe apparatus. From these data the electron affinity for c-C4F8 was determined, EA(c-C4F8)=0.63±0.05 eV. The motivation was to resolve a discrepancy between our earlier EA estimate and a higher value (EA=1.05±0.10 eV) reported from a recent experiment of Hiraoka et al. [J. Chem. Phys. 116, 7574 (2002)]. The electron attachment rate constant is 9.3±3.0×10−9 cm3 s−1 at 298 K. The electron detachment rate constant is negligible at room temperature but climbs to 1945±680 s−1 at 400 K. G3(MP2) calculations were carried out for the neutral (D2d, 1A1) and anion (D4h, 2A2u) and yielded EA(c-C4F8−)=0.595 eV. Bond energies were also calculated for loss of F from c-C4F8 and loss of F or F− from c-C4F8−. From these, dissociative electron attachment is found to be endothermic by at least 1.55 eV.
A complete nearest-neighbor force field model for C60
Authors: Hands Ian D. , Dunn Janette L. , Bates Colin A.
Published: March 2004

A force field model is developed for C60 that features 13 force constants representing all interactions between nearest-neighboring atoms. The model is compared with, and tested against, other force field models in the literature. Force constants for C60 are then deduced by fitting the model to the 14 known optically accessible vibrational frequencies of the molecule. Finally, the model is fitted to two existing theoretical calculations of the complete vibrational spectrum of C60. Fair agreement is obtained with the theoretical calculations, implying that interactions with atoms other than nearest neighbors are small.
Lagrange multiplier based transport theory for quantum wires
Authors: Kosov D. S.
Published: March 2004

We discuss how the Lagrange multiplier method of nonequilibrium steady state statistical mechanics can be applied to describe the electronic transport in a quantum wire. We describe the theoretical scheme using a tight-binding model. The Hamiltonian of the wire is extended via a Lagrange multiplier to “open” the quantum system and to drive current through it. The diagonalization of the extended Hamiltonian yields the transport properties of wire. We show that the Lagrange multiplier method is equivalent to the Landauer approach within the considered model.
Properties of branched confined polymers
Authors: Sikorski Andrzej , Romiszowski Piotr
Published: March 2004

A model of star-branched polymer chains confined in a slit formed by two parallel surfaces was studied. The chains were embedded to a simple cubic lattice and consisted of f=3 branches of equal length. The macromolecules had the excluded volume and the confining surfaces were impenetrable for polymer segments. No attractive interactions between polymer segments and then between polymer segments and the surfaces were assumed and therefore the system was a thermal. Monte Carlo simulations were carried out employing the sampling algorithm based on chain’s local changes of conformation. Lateral diffusion of star-branched chains was studied. Dynamic properties of star-branched chains between the walls with impenetrable rod-like obstacles were also studied and compared to the previous case. The density profiles of polymer segments on the slit were determined. The analysis of contacts between the polymer chain and the surfaces was also carried out.
The importance of three-body terms in the fragment molecular orbital method
Authors: Fedorov Dmitri G. , Kitaura Kazuo
Published: March 2004

A previously proposed two-body fragment molecular orbital method based on the restricted Hartree–Fock (RHF) method was extended to include explicit three-body terms. The accuracy of the method was tested on a set of representative molecules: (H2O)n, n=16, 32, and 64, as well as α and β n-mers of alanine, n=10, 20, and 40, using STO-3G, 3-21G, 6-31G, and 6-31++G** basis sets. Two- and three-body results are presented separately for assigning one and two molecules (or residues) per fragment. Total energies are found to differ from the regular RHF method by at most ΔE2/1=0.06, ΔE2/2=0.04, ΔE3/1=0.02, and ΔE3/2=0.003 (a.u.); rms energy gradients differ by at most ΔG2/1=0.0015, ΔG2/2=0.000 75, ΔG3/1=0.000 20, and ΔG3/2=0.000 10 (a.u./bohr), and rms dipole moments are reproduced with at most δD2/1=3.7, δD2/2=3.4, δD3/1=2.6, and δD3/2=3.1 (%) relative error, where the subscript notation n/m refers to the n-body method based on m molecules (residues) per fragment. A few of the largest three-body calculations were performed with a separated trimer approximation, which presumably somewhat lowered the accuracy of mostly dipole moments which are very sensitive to slight variations in the density distribution. The proposed method is capable of providing sufficient chemical accuracy while providing detailed information on many-body interactions.
High-level ab initio studies of the electronic excited states of the hydroxyl radical and water–hydroxyl complex
Authors: Schofield Daniel P. , Kjaergaard Henrik G.
Published: March 2004

The lowest-energy electronic transitions in the hydroxyl radical and the hydrogen bound complex H2O⋅HO have been studied using ab initio methods. We have used the complete active-space self-consistent field and multireference configuration interaction (MRCI) methods to calculate vertical excitation energies and oscillator strengths. At the MRCI level the lowest-lying Σ+2←2Π electronic transition is redshifted by about 2500 cm−1 upon formation of the H2O⋅HO complex. We propose that this transition could be used to identify the complex in the gas phase, which in turn could be used to examine the role of H2O⋅HO in atmospheric reactions.
1.4 μ
m
band electroluminescence from organic light-emitting diodes based on thulium complexes
Authors: Zang F. X. , Hong Z. R. , Li W. L. , Li M. T. , Sun X. Y.
Published: April 2004

Near-infrared (NIR) electroluminescence (EL) devices have been fabricated employing thulium complexes as emitting materials. The EL emissions at 1.4 and 0.8 μm were observed from the devices of tris-(dibenzoylmethanato)-mono-(bathophenanthroline or 1,10-phenonthroline) thulium [Tm(DBM)3bath or Tm(DBM)3phen] at room temperature and assigned to F34→H34 and F34→H36 transitions of Tm3+ ions, respectively. By comparison with the NIR emissions of four Tm complexes with different ligands, it was found that the first ligand played a more important role for the Tm3+ ion emissions rather than the second one. In order to meet the requirement of optical communication, both Tm(DBM)3bath and erbium [Er] (DBM)3bath were incorporated into EL devices so that a broadened EL emission band ranging from 1.4 to 1.6 μm was obtained, showing the potential application of Tm complexes for optical communication systems.
Remote hydrogen plasma doping of single crystal ZnO
Authors: Strzhemechny Yuri M. , Mosbacker Howard L. , Look David C. , Reynolds Donald C. , Litton Cole W. , Garces Nelson Y. , Giles Nancy C. , Halliburton Larry E. , Niki Shigeru , Brillson Leonard J.
Published: April 2004

We demonstrate that remote plasma hydrogenation can increase electron concentrations in ZnO single crystals by more than an order of magnitude. We investigated the effects of this treatment on Hall concentration and mobility as well as on the bound exciton emission peak I4 for a variety of ZnO single crystals–bulk air annealed, Li doped, and epitaxially grown on sapphire. Hydrogen increases I4 intensity in conducting samples annealed at 500 and 600 °C and partially restores emission in the I4 range for Li-diffused ZnO. Hydrogenation increases carrier concentration significantly for the semi-insulating Li doped and epitaxial thin film samples. These results indicate a strong link between the incorporation of hydrogen, increased donor-bound exciton PL emission, and increased n-type conductivity.
The Huggins band of ozone: Unambiguous electronic and vibrational assignment
Authors: Qu Zheng-Wang , Zhu Hui , Tashiro Motomichi , Schinke Reinhard , Farantos Stavros C.
Published: March 2004

The Huggins band of ozone is investigated by means of exact dynamics calculations using a new (diabatic) potential energy surface for the B21 state. The remarkable agreement with the measured spectrum strongly suggests that the Huggins band is due to the two Cs potential wells of the B21 state. The vibrational assignment, based on the nodal structure of wave functions, supports the most recent experimental assignment.
Biocatalysis for Sustainable Organic Synthesis
Authors: Sheldon Roger A. , Rantwijk Fred van
Published: April 2004

Biocatalysis offers mild reaction conditions, an environmentally attractive catalyst–solvent system, high activities, and chemo-, regio-, and stereoselectivities, while the use of enzymes generally circumvents the need for functional group activation and avoids protection/deprotection steps required in traditional organic syntheses. This review, using β-lactam antibiotics as an example, discusses recent advances in biocatalysis research towards the goal of ‘green’ methodologies for the manufacture of (fine) chemicals and the emulation of a cell's enzymatic cascade processes.
Induction of oral tolerance to prevent diabetes with transgenic plants requires glutamic acid decarboxylase (GAD) and IL-4
Authors: Ma Shengwu , Huang Yan , Yin ZiQin , Menassa Rima , Brandle James E. , Jevnikar Anthony M.
Published: April 2004

Induction of specific immunological unresponsiveness by feeding protein antigens is termed oral tolerance and may be a potential therapy for autoimmune diseases. Whereas oral tolerance therapy may be both simple and effective, the requirement for large amounts of protein will limit clinical testing of autoantigens, which are difficult to produce. We have previously demonstrated transgenic plant production and direct oral delivery of a β cell autoantigen murine GAD67 to prevent autoimmune diabetes in nonobese diabetic mice. Mucosal adjuvants such as cholera toxin B subunit may lower the level of autoantigen required, but the development of neutralizing mucosal antibody responses may limit usefulness in enhancing long-term oral tolerance. IL-4, being an endogenous protein, would avoid this result and possibly enhance oral tolerance but has not been tested as a mucosal adjuvant. In this study, human GAD65 (hGAD65), as well as murine IL-4, was expressed in transgenic plants for feeding trials. Both IL-4 and hGAD65 plant tissue were required to protect nonobese diabetic mice from diabetes, and no benefit was found if either was used alone. Combined therapy enhanced levels of IgG1 anti-GAD antibodies, increased splenocyte IL-4/IFN-γ cytokine responses, and produced protective regulatory T cells. These results demonstrate that orally administered plant IL-4 remains biologically active and is synergistic when given with hGAD65 in inducing robust oral immune tolerance. Using transgenic plants expressing IL-4 and GAD65 may be a novel clinical approach to the prevention of human type 1 diabetes by oral tolerance.
The p75NTR-interacting protein SC1 inhibits cell cycle progression by transcriptional repression of cyclin E
Authors: Chittka Alexandra , Arevalo Juan Carlos , Rodriguez-Guzman Maria , Pérez Pilar , Chao Moses V. , Sendtner Michael
Published: March 2004

Schwann cell factor 1 (SC1), a p75 neurotrophin receptor–interacting protein, is a member of the positive regulatory/suppressor of variegation, enhancer of zeste, trithorax (PR/SET) domain-containing zinc finger protein family, and it has been shown to be regulated by serum and neurotrophins. SC1 shows a differential cytoplasmic and nuclear distribution, and its presence in the nucleus correlates strongly with the absence of bromodeoxyuridine (BrdU) in these nuclei. Here, we investigated potential transcriptional activities of SC1 and analyzed the function of its various domains. We show that SC1 acts as a transcriptional repressor when it is tethered to Gal4 DNA-binding domain. The repressive activity requires a trichostatin A–sensitive histone deacetylase (HDAC) activity, and SC1 is found in a complex with HDACs 1, 2, and 3. Transcriptional repression exerted by SC1 requires the presence of its zinc finger domains and the PR domain. Additionally, these two domains are involved in the efficient block of BrdU incorporation by SC1. The zinc finger domains are also necessary to direct SC1's nuclear localization. Lastly, SC1 represses the promoter of a promitotic gene, cyclin E, suggesting a mechanism for how growth arrest is regulated by SC1.