bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of carbamazepine and promethazine in rabbits
Authors: Rukhadze Marina D. , Alexishvili Maka M. , Gonashvili Maya V. , Okujava Nathela V. , Sebiskveradze Maya V.
Published: February 2003

The interaction of carbamazepine and promethazine in rabbits has been investigated. The influence of this interaction on the processes of biotransformation in the liver was revealed. The drugs were administered as single oral doses (100 mg of each drug) as well as simultaneously with an interval of 15 min. The sequence of administration of the drugs was varied. The influence of promethazine on the pharmacokinetics of carbamazepine is expressed by: (a) strong suppression of carbamazepine's level in plasma and appearance of multiple peaks of carbamazepine; (b) suppression of biotransformation of carbamazepine into carbamazepine‐10,11‐epoxide at the initial stages and its increase in the intermediate stages. These data are explained by the active capture of carbamazepine by liver at its primary transferal through the liver and sufficient presystem elimination of carbamazepine in the presence of promethazine. The character of kinetic curves of promethazine varies substantially under the influence of carbamazepine. However, this change is not as strong as in case of carbamazepine. The concentration of promethazine in plasma varies slightly and multiple peaks are not observed. The rate of terminal elimination of promethazine varies and abrupt prolonged segments of elimination appear at the initial and terminal stages of the process in return. These data perhaps indicate the induction of biotransformation of promethazine in the presence of carbamazepine—an inductor of microsomal liver enzymes. The changes of kinetics of promethazine and carbamazepine by simultaneous administration as compared with their administration separately, as well as a comparative consideration of pharmacokinetics of promethazine and carbamazepine by simultaneous administration show the existence of competition in the elimination between these drugs and the periodic saturation of liver for their biotransformation. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of the C4H Bond Dissociation Energies of NADH Models and Their Radical Cations in Acetonitrile
Authors: Zhu Xiao‐Qing , Li Hai‐Rong , Li Qian , Ai Teng , Lu Jin‐Yong , Yang Yuan , Cheng Jin‐Pei
Published: February 2003

Heterolytic and homolytic bond dissociation energies of the C4H bonds in ten NADH models (seven 1,4‐dihydronicotinamide derivatives, two Hantzsch 1,4‐dihydropyridine derivatives, and 9,10‐dihydroacridine) and their radical cations in acetonitrile were evaluated by titration calorimetry and electrochemistry, according to the four thermodynamic cycles constructed from the reactions of the NADH models with N,N,N′,N′‐tetramethyl‐p‐phenylenediamine radical cation perchlorate in acetonitrile (note: C9H bond rather than C4H bond for 9,10‐dihydroacridine; however, unless specified, the C9H bond will be described as a C4H bond for convenience). The results show that the energetic scales of the heterolytic and homolytic bond dissociation energies of the C4H bonds cover ranges of 64.2–81.1 and 67.9–73.7 kcal mol−1 for the neutral NADH models, respectively, and the energetic scales of the heterolytic and homolytic bond dissociation energies of the (C4H).+ bonds cover ranges of 4.1–9.7 and 31.4–43.5 kcal mol−1 for the radical cations of the NADH models, respectively. Detailed comparison of the two sets of C4H bond dissociation energies in 1‐benzyl‐1,4‐dihydronicotinamide (BNAH), Hantzsch 1,4‐dihydropyridine (HEH), and 9,10‐dihydroacridine (AcrH2) (as the three most typical NADH models) shows that for BNAH and AcrH2, the heterolytic C4H bond dissociation energies are smaller (by 3.62 kcal mol−1) and larger (by 7.4 kcal mol−1), respectively, than the corresponding homolytic C4H bond dissociation energy. However, for HEH, the heterolytic C4H bond dissociation energy (69.3 kcal mol−1) is very close to the corresponding homolytic C4H bond dissociation energy (69.4 kcal mol−1). These results suggests that the hydride is released more easily than the corresponding hydrogen atom from BNAH and vice versa for AcrH2, and that there are two almost equal possibilities for the hydride and the hydrogen atom transfers from HEH. Examination of the two sets of the (C4H).+ bond dissociation energies shows that the homolytic (C4H).+ bond dissociation energies are much larger than the corresponding heterolytic (C4H).+ bond dissociation energies for the ten NADH models by 23.3–34.4 kcal mol−1; this suggests that if the hydride transfer from the NADH models is initiated by a one‐electron transfer, the proton transfer should be more likely to take place than the corresponding hydrogen atom transfer in the second step. In addition, some elusive structural information about the reaction intermediates of the NADH models was obtained by using Hammett‐type linear free‐energy analysis.
Fluorogenic Stereochemical Probes for Transaldolases
Authors: González‐García Eva , Helaine Virgil , Klein Gérard , Schuermann Melanie , Sprenger Georg A. , Fessner Wolf‐Dieter , Reymond Jean‐Louis
Published: February 2003

Transaldolase catalyzes the transfer of dihydroxyacetone from, for example, fructose 6‐phosphate to erythrose 4‐phosphate. As a potential probe for assaying fluorescent transaldolase, 6‐O‐coumarinyl‐fructose (1) was prepared in six steps from D‐fructose. The corresponding 6‐O‐coumarinyl‐5‐deoxy derivative 2 was prepared stereoselectively from acrolein and tert‐butyl acetate by a chemoenzymatic route involving Amano PS lipase for the kinetic resolution of tert‐butyl 3‐hydroxypent‐4‐enoate (7) and E. coli transketolase for assembly of the final product. The corresponding stereoisomer related to D‐tagatose was obtained by a chemical synthesis starting from D‐ribose. Indeed, transaldolases catalyze the retro‐aldolization of substrate 1 to give dihydroxyacetone and 3‐O‐coumarinyl‐glyceraldehyde. The latter primary product undergoes a β‐elimination in the presence of bovine serum albumin (BSA) to give the strongly fluorescent product umbelliferone. A similar reaction is obtained with the 5‐deoxy analogue 2, but there is almost no reaction with its stereoisomer 3. The stereoselectivity of transaldolases can be readily measured by the relative rates of fluorescence development in the presence of the latter pair of diastereomeric substrates.
Hierarchical Self‐Assembly, Coassembly, and Self‐Organization of Novel Liquid Crystalline Lattices and Superlattices from a Twin‐Tapered Dendritic Benzamide and Its Four‐Cylinder‐Bundle Supramolecular Polymer
Authors: Percec Virgil , Bera Tushar K. , Glodde Martin , Fu Qiongying , Balagurusamy Venkatachalapathy S. K. , Heiney Paul A.
Published: February 2003

The synthesis and structural analysis of the twin‐dendritic benzamide 10, based on the first‐generation, self‐assembling, tapered dendrons 3,4,5‐tris(4′‐dodecyloxybenzyloxy)benzoic acid and 3,4,5‐tris(4′‐dodecyloxybenzyloxy)‐1‐aminobenzene, and the polymethacrylate, 20, which contains 10 as side groups, are presented. Benzamide 10 self‐assembles into a supramolecular cylindrical dendrimer that self‐organizes into a columnar hexagonal (Φh) liquid crystalline (LC) phase. Polymer 20 self‐assembles into an imperfect four‐cylinder‐bundle supramolecular dendrimer, and creates a giant vesicular supercylinder that self‐organizes into a columnar nematic (Nc) LC phase which displays short‐range hexagonal order. In mixtures of 20 and 10, 10 acts as a guest and 20 as a host to create a perfect four‐cylinder‐bundle host–guest supramolecular dendrimer that coorganizes with 10. A diversity of Φh, simple rectangular columnar (Φr‐s) and centered rectangular columnar (Φr‐c), superlattices are produced at different ratios between 20 and 10. This diversity of LC lattices and superlattices is facilitated by the architecture of the twin‐dendritic building block, polymethacrylate, the host–guest supramolecular assembly, and by hydrogen bonding along the center of the supramolecular cylinders generated from 10 and 20.
Finite‐Element Analysis of Magnetic Field Driven Transport at Inlaid Platinum Microdisk Electrodes
Authors: Mehta Dipesh , White Henry S.
Published: February 2003

We describe a computer‐assisted analysis of three‐dimensional magnetohydrodynamic (MHD) fluid flow resulting from the passage of electrochemically generated charge through a uniform magnetic field. Magnetic field driven molecular transport in electrochemical systems offers a number of emerging opportunities in research and technology. For instance, electrochemical microfluidic transport1 and molecule trapping2 using magnetic fields and field gradients have been demonstrated in recent reports from this laboratory. A key limitation of these investigations is the difficulty in analyzing magnetic field driven flow and transport, due to the complexity of the governing equations of fluid mechanics, electrochemical molecular transport, and magnetic forces. In general, quantitative expressions describing the distribution and fluxes of electroactive species under the influence of a magnetic field cannot be obtained by a direct analytical solution.
Maxwell's equations in periodic chiral structures
Authors: Ammari Habib , Bao Gang
Published: February 2003

Consider a time–harmonic electromagnetic plane wave incident on a biperiodic structure in ℝ3. The periodic structure separates two homogeneous regions. The medium inside the structure is chiral and heterogeneous. In general, wave propagation in the chiral medium is governed by Maxwell's equations together with the Drude– Born–Fedorov (constitutive) equations. In this paper, the diffraction problem is formulated in a bounded domain by introducing a pair of transparent boundary conditions. It is then shown that for all but possibly a discrete set of parameters, there is a unique quasi–periodic weak solution to the diffraction problem. Our proof is based on the Hodge decomposition, a compact imbedding result, and the Lax–Milgram Lemma. In addition, an energy conservation for the weak solution is also shown.
Solutions with internal jump for an autonomous elliptic system of FitzHugh–Nagumo type
Authors: Reinecke Carolus , Sweers Guido
Published: February 2003

Systems of elliptic partial differential equations which are coupled in a noncooperative way, such as the FitzHugh–Nagumo type studied in this paper, in general do not satisfy order preserving properties. This not only results in technical complications but also yields a richer solution structure. We prove the existence of multiple nontrivial solutions. In particular we show that there exists a solution with boundary layer type behaviour, and we will give evidence that this autonomous system for a certain range of parameters has a solution with both a boundary and an internal layer. The analysis uses results from bifurcation theory, variational methods, as well as some pointwise a priori estimates. The final section contains some numerically obtained results.
Effect of the crosslinking level on the properties of temperature‐sensitive poly(N‐isopropylacrylamide) hydrogels
Authors: Zhang Xian‐Zheng , Wu Da‐Qing , Chu Chih‐Chang
Published: February 2003

In this study, the effect of the level of crosslinking on the properties of poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels was investigated in terms of their lower critical solution temperature (LCST), interior morphology, equilibrium swelling, and deswelling and swelling kinetics. The thermal analysis showed that PNIPAAm hydrogels, having a wide range of crosslinking levels, exhibited almost the same LCSTs, and this was different from what the conventional theory would have predicted. Scanning electron micrographs revealed that the interior network structure of the PNIPAAm matrix became more porous with an increase in the level of crosslinking. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling process and the swelling process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 582–593, 2003
Splitting of energy of dispersive waves in a star‐shaped network
Authors: Mehmeti F. Ali , Régnier V.
Published: February 2003

We study wave and Klein‐Gordon equations in a star‐shaped network. In the wave case we state a d'Alembert‐type solution formula generalizing the formula obtained in Ali Mehmeti [1] and [4] for four branches. In the Klein‐Gordon case (dispersive waves) we solve the problem using the Laplace transform with respect to time. We state a continuity equation linking the energy density and the energy flow for the Klein‐Gordon equation in a star‐shaped network. We observe that the splitting of energy at the central node is the same for propagating waves with and without dispersion.
Shelters for houseless youth: a follow‐up evaluation☆
Authors: Dekel Rachel , Peled Einat , Spiro Shimon E
Published: February 2003

This study followed 345 Israeli youngsters who had been residents of two shelters for runaway and homeless youths, 6–12 weeks after their departure. Telephone interviews were conducted with the youngsters, their parents, and social workers in the community. A majority of the youngsters had either returned to their family homes, or had been placed out of home. Their residential stability was found to be low. Post‐shelter place of residence was related to length of stay at the shelter, amount of contact with their family while at the shelter, and manner of departure. Our findings lead to a typology of shelter uses, and also raise questions about the extent to which shelters achieve their declared goals.
Pressure broadening measurements of the 118.750 GHz oxygen transition
Authors: Setzer Barbara J. , Pickett Herbert M.
Published: February 2003

New low-pressure measurements of the oxygen transition at 118.750 GHz have been made with a magnetically modulated cavity spectrometer at 298 °K. The line broadening parameters for collision with oxygen, nitrogen, water, helium, and argon are 2.131±0.037, 2.20±0.10, 2.30±0.24, 1.605±0.060, and 2.014±0.091 MHz/torr, respectively.
Theory of melting in simple polymers.I.
Authors: Boyle F. P. , Taylor P. L. , Hopfinger A. J.
Published: February 2003

A formalism is described whereby the Helmholtz energy of a polymer crystal or melt is found by solution of a set of self-consistent equations involving functionals of the distribution of torsional angles along a single chain. The interchain interactions are treated in a generalized mean-field framework which starts from a detailed computation of the molecular energetics of a pair of parallel and adjacent chain segments. Intrachain potentials for the cases of polymethylene and polytetrafluoroethylene were obtained from molecular orbital calculations, while interchain potentials were found by in addition using semiclassical techniques. Results are presented to describe the melt transition in these materials.
Dynamics of confined polymer chains
Authors: Brochard F. , de Gennes P. G.
Published: February 2003

We study the motions of a single polymer chain trapped inside a very thin capillary (or slit). We incorporate all excluded volume effects and hydrodynamic interactions through a scaling analysis. We find that the Debye–Bueche approximation, which was qualitatively correct for three-dimensional dilute solutions, becomes completely incorrect for confined chains: the local fluctuations of the monomer concentration which are ignored in the Debye–Bueche picture allow for channels of easy flow of the solvent inside the chain. We obtain scaling formulas (with unknown numerical coefficients) for the diffusion constant and we also analyze the internal mode structure: inside a tube, for wavelengths larger than the diameter, we recover an unexpectedly simple structure of Rouse modes. Finally, we analyze the possibility of ’’sucking in’’ one chain inside a slightly tapered pore, by imposing a certain flow of the solvent. We find that the threshold pressure difference Δpc for aspiration of the chain depends only on the smallest diameter of the pore and is independent of the molecular mass. The magnitude of Δpc is not too large, and the experiment may be feasible.
Theory for the influence of gravity on liquid–vapor interfaces
Authors: Yang Arthur J. M. , Fleming Paul D. , Gibbs Julian H.
Published: February 2003

The van der Waals theory of surface tensions in the presence of gravity is discussed in detail. The physical two-phase solution in the gravitational field is shown to exist and be unique. The relation between the chemical potential and the position of the interface in the gravitational field is elucidated. The solution approaches the solution given previously and the chemical potential approaches its coexistence value as the strength of the gravitational field is diminished. The gravitational effects are seen to be especially enhanced in the neighborhood of the critical point.
The rate of gas absorption at a liquid interface
Authors: Ward C. A.
Published: February 2003

To determine the diffusion coefficient of a gas in a liquid the usual procedure is to expose the liquid interface for a period of time, measure the amount of gas absorption, and from this infer the diffusion coefficient. The usual assumption to make at the liquid–gas interface is that equilibrium is established immediately upon exposure of the liquid to the gas. This assumption has led to the illogical consequence of the inferred diffusion coefficient depending upon the period of time for which the liquid interface is exposed to the gas. We use the Einstein expression for the probability of a transition in a system to derive an expression for the rate of gas absorption. When this derived rate is used to infer the diffusion coefficient, the same value is found from experimental techniques with extreme values of the exposure time. The accuracy of the predicted gas absorption rate supports the view that the Einstein relation is not limited to predicting fluctuations about an equilibrium state.
High resolution millimeter-wave spectrum of methyl bromide. Spin–rotation and nuclear shielding tensors of bromine
Authors: Demaison J. , Dubrulle A. , Boucher D. , Burie J.
Published: February 2003

The ground state rotational spectrum of CH3 Br has been observed using a molecular beam-absorption spectrometer. The B rotational constant and the quartic and sextic centrifugal distortion constants are determined with great accuracy. From the hyperfine splitting the quadrupole coupling constant and the spin–rotation constants of the two isotopic species 79Br and 81Br can also be deduced. These data are used to determine the elements of the bromine nuclear magnetic shielding tensor.
Simulation of the bound-free KrF* emission spectra from reactive quenching of Kr(5s[3/2]2) and Kr(5s[3/2]1) atoms
Authors: Tamagake K. , Setser D. W.
Published: February 2003

The low pressure KrF emission spectra, which includes the KrF(III,1/2−I,1/2 or B–X) and the KrF(II,3/2−I,3/2 or C–A) transitions arising from the reaction of metastable or resonance states of Kr with F2, NF3, and CF3OF, have been simulated by computer. Since a broad distribution of very high v′ levels is produced by the chemical reactions, the dependence of the spectrum upon various properties of the upper and lower states was first investigated. A general discussion of the types of emission spectra that can be expected from bound-free transitions from high v levels is first presented. As a starting point for fitting the KrF spectra, the ab initio potential curves and the dependence of the transition moments upon internuclear separation calculated by Hay and Dunning for KrF were used. The I,1/2 and III,1/2 curves are generally satisfactory but some modification of the I,3/2 potential curve was necessary in order to fit the observed spectra. As the final step, KrF* vibrational distributions from the Kr*+F2, CF3OF, and NF3 reactions were assigned that gave simulated spectra in agreement with the low pressure spectra. The fraction of the available energy released as KrF* vibrational energy was ≳50%. The assignment of the initial vibrational distribution as well as 〈fV〉, and to the dependence of the transition moment upon internuclear separation. Within some general limitation, this spectrum is not very sensitive to the I,1/2 or III,1/2 potential curves.
Infrared intensities: A comprehensive quantitative analysis for transition metal carbonyls M(CO)6 (M=Cr, Mo, and W) and Ni(CO)4
Authors: Prasad P. L. , Singh Surjit
Published: February 2003

A comprehensive analysis of infrared intensities has been made for Cr(CO)6, Mo(CO)6, W(CO)6, and Ni(CO)4 molecules. Making use of the isotopic frequencies reported by Jones, McDowell, and Goldblatt, α matrices have been evaluated. The atomic polar tensors and dipole moment derivatives δμg/δSj for all possible sign combinations have been reported. The correct sign combination has been determined from the criterion of maximum ξ2 value as reported earlier. The bond moment parameters and atomic charges have been determined using the modified first order approach. The atomic charges obtained for Cr, Mo, W, and Ni, respectively, are 0.55, 0.64, 0.65, and 0.11e. The atomic polar tensors are found to show systematic trends in the molecules considered and indicate that they may be predicted qualitatively for other similar molecules. The analysis of bond moment parameters and polar tensors have led to the support of general ideas about the nature of bonding between metal and CO ligands.
Dynamics of three-body half collisions. I. Secondary product decomposition in the photodissociation of acetyl iodide
Authors: Kroger Peter M. , Riley Stephen J.
Published: February 2003

Photofragment spectroscopy of acetyl iodide (CH3COI) at 266 nm shows evidence of a two-step dissociation into three products. Initial photodissociation yields an iodine atom and a highly internally excited acetyl radical containing on average 80% of the energy available in the dissociation process. The transition dipole moment of the initial absorption lies in the C–C–O plane near the C–I bond axis, and breakup of the photoexcited acetyl iodide is rapid, on the order of 10−13 sec. The acetyl fragment is found to live for several rotational periods, ∼10−11 sec. Its subsequent decomposition to CO and CH3 can be modeled by statistical theories of unimolecular decay. It is found that an average 30% of the energy residing in the acetyl radical ultimately appears as relative translational energy of the CO and CH3 fragments.
Primary free radicals formed in x-irradiated inositol
Authors: Box Harold C. , Budzinski Edwin E.
Published: February 2003

Single crystals of myo-inositol were x-irradiated at 4.2 °K and the free radical products identified by means of ESR–ENDOR spectroscopy. All of the identified products result from loss of hydrogen. One of the products is an alkoxy-type radical. Two other products are of the type –HCOH–ĊOH–HCOH–. In order to account for these radicals, it is postulated that a hydrogen transfer process occurs following the initial radiation-induced oxidation–reduction process.
The dynamics of the reaction H+2+H2→H+3+H, with isotopic variations
Authors: Douglass Charles H. , McClure Donald J. , Gentry W. Ronald
Published: February 2003

We performed a merged-beam study of the reactions HD++D2→HD+2+D, D+3+H, D+2+HD→HD+2+D, D+3+H, in which we measured the absolute reaction cross sections, branching ratios, and product energy distributions over the range of relative kinetic energy from ∼0.002 to 8 eV. Within the experimental uncertainty all three types of data are identical for the two reactant charge states at initial kinetic energies less than 0.5 eV, leading us to believe that adiabatic charge equilibration between the reactants occurs prior to reaction at these low energies. Diabatic behavior becomes increasingly dominanant at higher energies. The reaction mechanism is direct and products are formed with a broad distribution of translational energies. In low energy collisions, on the average, a small fraction of the reaction exothermicity and the reactant excitation energy is converted into translational energy of the products. At higher energies there is a net conversion of translational into internal energy. The reaction energetics are not in agreement with stripping model predictions.
Adsorption and oxidation of rhodamine B at ZnO electrodes
Authors: Spitler Mark , Calvin Melvin
Published: February 2003

The adsorption of Rhodamine B on the (0001) face of ZnO single crystals from an aqueous solution was monitored through measurement of the absorbance of the adsorbed dye. Analysis of these spectra yielded a Langmuir-type adsorption isotherm with a plateau surface concentration of 1.1×10−7 mmoles/cm2. A comparison was made between the absorbance of the adsorbed dye and that of the dye in solution. These data were correlated with electrochemical measurements of the photo-oxidation of this dye at ZnO crystals used as electrodes. The quantum efficiency of photo-oxidation was 0.027, which was approximately constant as a function of surface coverage. A kinetic model was formulated for the time decay of the photocurrent.
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o configuration interaction study of the valence states of O2
Authors: Saxon Roberta P. , Liu B.
Published: February 2003

Configuration interaction calculations have been performed for the 62 electronic states of O2 arising from O atoms in the lowest 3P, 1D, and 1S states. The calculations used an extended one-particle basis set, and included internal and semi-internal electron correlation effects. Numerical values for potential curves are reported for all states. Detailed comparison with experiment and other calculations is made for the seven lowest bound states: X 3Σg−, a 1Δg, b 2Σg+, c 1Σu−, C 3Δu, A 3Σu+, and B 3Σu−. For these seven states the maximum error in the calculated spectroscopic constants Re, De, Te, and ωe are 0.04 Å, 0.4 eV, 0.2 eV, and 120 cm−1, respectively.
13C–13C dipolar spectra in solids
Authors: van Willigen H. , Griffin R. G. , Haberkorn R. A.
Published: February 2003

A single crystal NMR study has been made of the 13C–13C dipolar interaction in oxalic acid dihydrate (HOX) and diammonium oxalate monohydrate (DAOX). The results show that indirect contributions to the interaction are negligibly small so that the dipolar tensor provides information on the C–C bond length and orientation in the crystal lattice. In HOX the relative orientations of the principal components of the chemical shift and dipolar tensors confirm the unusual orientation of the shift tensor components with respect to the molecular coordinate system. Because of the nonplanar structure of the oxalate ion in DAOX, the ratio between the chemical shift difference of the two 13C atoms in one molecule and the dipolar splitting can be varied by a suitable choice of crystal orientation. As a consequence, the 13C–13C spectra exhibit A2 and AB patterns.
van der Waals–Lifshitz forces in lyotropic polypeptide liquid crystals
Authors: Samulski Thaddeus V. , Samulski Edward T.
Published: February 2003

The McLachlan susceptibility theory is used to calculate the van der Waals–Lifshitz forces betwen two chiral, rodlike dielectric particles embedded in an isotropic dielectric medium. The resulting interparticle potential contains an asymmetric term in φ, the mutual dihedral angle between the major axes of the particles. The variations of the free energy of interaction with respect to the mutual orientation of the particles and the relative magnitudes of the medium and particle dielectric permittivities can explain the origin and unusual solvent dependence of the cholesteric twist exhibited by lyotropic polypeptide liquid crystals.
cw saturation of infrared absorption in CH3F
Authors: Devir Adam D. , Oppenheim Uri P.
Published: February 2003

The CH3F molecule has a simple energy level structure and all the energy transfer processes in it are known. A simple set of rate equations may therefore be used for the analysis of cw saturation of the absorption of the P (20) –9.4 μ CO2 laser line by CH3F. After measuring and calculating all the parameters which appear in the rate equations, the experimental results are compared to the theoretical model. Good agreement between theory and experiment is obtained. It is shown that diffusion of excited absorber molecules out of the laser beam cross section plays an important role in understanding the cw saturation of infrared absorption.
Dynamical orientation correlations in solution
Authors: Wolynes Peter G. , Deutch J. M.
Published: February 2003

A many particle coupled translation–rotation diffusion model is analyzed in regard to single particle and collective orientational correlation functions. This model contains a hydrodynamic mechanism which gives rise to dynamical orientation correlations in solution. An approximate expression for the dynamical correlation factor ? is derived in terms of the static pair distribution function. In contradiction to recent arguments, ? does not vanish for this model. We also show that in the case where the pair potential of the solute particles is spherically symmetric, the Debye relaxation law is unmodified by the long-range hydrodynamic interaction.
The computation of nuclear motion and mass polarization adiabatic energy corrections for several states of the hydrogen molecule
Authors: Ford A. Lewis , Greenawalt E. M. , Browne J. C.
Published: February 2003

This paper reports the computation of the diagonal matrix elements of the nuclear motion and mass polarization operators (often referred to as adiabatic corrections) for several electronic states of the hydrogen molecule. It is observed that reasonably simple wavefunctions will yield accurate expectation values for the nuclear motion operators. The present calculation covers a greater range of R for the X 1Σ+g and B 1Σ+u states than is covered in the very accurate work of Kolos and Wolniewicz, and includes computations for the C 1Πu and D 1Πu states for which no theoretical results have been previously reported. For the latter states the present diagonal corrections have been used in conjunction with the very recent Born–Oppenheimer potential energy curves of Kolos and Rychlewski [J. Mol. Spectrosc. 62, 109 (1976)] to compute vibrational level energies for both H2 and D2. The diagonal corrections largely remove the mass-dependent part of the discrepancy between theory and experiment for these vibrational level energies.
Chlorine nitrate: Kinetics of formation by ClO+NO2+M and of reaction with OH
Authors: Zahniser M. S. , Chang J. S. , Kaufman F.
Published: February 2003

Kinetic studies by the discharge–flow technique are reported. For ClONO2 formation from T=250–365 K, ClO decays in excess NO2 are monitored by conversion of ClO to Cl followed by resonance fluorescence detection at 134.7 nm. For OH reaction over T=246–387 K, pseudo-first-order OH decays are observed directly by OH-resonance fluorescence. The recombination reaction (1) is near its low pressure, third-order limit with k1= (0.83±0.12) ×10−31 cm6 s−1 at 300 K for M=He and (1.52±0.23) ×10−31 cm6 s−1 at 297 K for M=N2. The k1,He temperature dependence corresponds to T−3.15. These results are in good agreement with those of other studies. A temperature- and pressure-dependent, empirical rate constant expression for stratospheric modeling calculations is proposed. The rate constant k2 for the OH reaction is found to be (1.19±0.10) ×10−12 exp[(−333 ±22)/T] cm3 s−1, i.e., (3.93±0.11) ×10−13 at 295 K. The results are compared with other measurements and their significance for stratospheric processes is discussed.
Vibrational relaxation of uranium hexafluoride: Ultrasonic measurements
Authors: Bass H. E. , Shields F. Douglas , Breshears W. D. , Asprey L. B.
Published: February 2003

Ultrasonic attenuation has been measured in UF6 at room temperature over an f/P range of 20 kHz/atm to 70 MHz/atm. A single relaxation process was inferred with an isothermal relaxation time of 5.7×10−9 sec-atm. Assuming the three higher energy modes are coupled by fast transfer processes to the three lower energy modes and that the three lower energy modes relax together in parallel, it was found that the rate of de-excitation of the first excited level of the lower energy modes is 4.2×10−8 sec−1⋅atm−1. This corresponds to an average of 17 collisions to transfer a quantum of vibrational energy to translation.
Energy distribution in selected fragment vibrations in dissociation processes in polyatomic molecules
Authors: Band Yehuda B. , Freed Karl F.
Published: February 2003

The full quantum theory of dissociation processes in polyatomic molecules is converted to a form enabling the isolation of a selected fragment vibration. This form enables the easy evaluation of the probability distribution for energy partitioning between this vibration and all other degrees of freedom that results from the sudden Franck–Condon rearrangement process. The resultant Franck–Condon factors involve the square of the one-dimensional overlap integral between effective oscillator wavefunctions and the wavefunctions for the selected fragment vibration, a form that resembles the simple golden rule model for polyatomic dissociation and reaction processes. The full quantum theory can, therefore, be viewed as providing both a rigorous justification for certain generic aspects of the simple golden rule model as well as providing a number of important generalizations thereof. Some of these involve dealing with initial bound state vibrational excitation, explicit molecule, fragment and energy dependence of the effective oscillator, and the incorporation of all isotopic dependence. In certain limiting situations the full quantum theory yields simple, readily usable analytic expressions for the frequency and equilibrium position of the effective oscillator. Specific applications are presented for the direct photodissociation of HCN, DCN, and CO2 where comparisons between the full theory and the simple golden rule are presented. We also discuss the generalizations of the previous theory to enable the incorporation of effects of distortion in the normal modes as a function of the reaction coordinate on the repulsive potential energy surface.
Viscous liquids and the glass transition. VII. Molecular mechanisms for a thermodynamic second order transition
Authors: Goldstein Martin
Published: February 2003

It has been previously shown that the ’’configurational’’ specific heat ΔCp of a liquid above Tg contains significant contributions from nonconfigurational sources such as changes with structural state (fictive temperature) of (1) lattice vibrational frequencies, (2) anharmonicity, and (3) numbers of molecular groups participating in secondary relaxations. Using the potential energy U of the structural state as an order parameter, we calculate the behavior of the liquid specific heat for simple models based on the first two mechanisms, and show that either gives a second order transition of the type generally conjectured as necessary to account for the entropy–temperature relation of the equilibrium supercooled liquid. We give qualitative arguments for believing that the third mechanism acts similarly. We show also that all three mechanisms if acting simultaneously give a single transition. Direct experimental evidence that anharmonicity, the most plausible mechanism on the basis of present scanty evidence, depends on structural state is lacking, but an order-of-magnitude calculation shows that only a small dependence on structural state is necessary to account quantitatively for observed ΔCp’s at the glass transition.
A librational model for molecular reorientation in condensed phases
Authors: Kushick Joseph N.
Published: February 2003

A model is suggested to describe molecular reorientation in phases where rotation is strongly hindered. The model is based on simple librational motion of each molecule within an effective potential energy well. The relaxation of orientational correlation is related to distribution functions for angular velocity and librational frequency, and it is found that this decay can be simply related to the angular velocity correlation function. The model is then applied to molecular dynamics simulations of reorientation in dense media. The role of librational motion in reorientation is discussed.
The potential surface for planar cyclopropenyl radical and anion
Authors: Davidson Ernest R. , Borden Weston Thatcher
Published: February 2003

The potential surfaces for the 2E″ state of planar cyclopropenyl and the 1E′ state of planar cyclopropenyl anion are examined using full pi-space configuration interaction within an STO-3G basis. Both states are subject to first order Jahn–Teller distortions of the bond lengths. Small second order effects slightly favor the ethylenic form of the radical. Much larger second order effects strongly favor the allylic form of the anion.
On entropy production in a stochastic model of open systems
Authors: McAdory R. T. , Schieve W. C.
Published: February 2003

Two expressions for the entropy production of a system arbitrarily far from equilibrium are considered for a stochastic model. The two expressions result from the consideration of two different definitions of the nonequilibrium entropy: the Gibbs form and the generalized form suggested by the Brussels–Austin group. The entropy principle is established briefly for isolated and then, in detail, for open systems, and the origin and form of the entropy flow is discussed.
Van der Waals interaction between linear molecules
Authors: Schröder Harald
Published: February 2003

First a standard expansion in spherical harmonics for the interaction of elongated axial-symmetric molecules obeying the law r−2n is derived, where an integral representation for the coefficients is given. In the second step we will show how the integrals can be evaluated and present the coefficients as analytical functions of the distance between two molecules and their dimensions as well. This is carried out explicitly in the case of the London–van der Waals interaction (r−6) for linear centrosymmetric molecules up to the fourth order term.
Molecular Rydberg states. VII. Water
Authors: Wang H. -t. , Felps W. S. , McGlynn S. P.
Published: February 2003

The optical absorption spectra of H2O and D2O are reported at various pressures for 2000?λ?950 Å. The 1670 Å band is vibrationally structured (ν2 bend) and the excited 1B1 state contains a considerable intravalence 4a1 component. The 1280 Å state 3sa1; 1A1 is linear and dominantly Rydberg. A Renner–Teller analysis of the 1280 Å band leads to detection of a perturbing state at 1365 Å which may be assigned as a bent, heavily Rydberg 3sa1; 1B1 state. A reanalysis of K-shell excitation spectra bolsters this 3sa1; 1B1 assignment. Isotope shift studies in the 1130–980 Å region lead to some vibronic reassignments. The terminal state of the 968 Å absorption band is a linear 5sa1; 1A1 state. In sum, a total of 21 electronic states, comprising fragments of six Rydberg series, have been assigned.
The relationship between the Mulliken electronegativities of the elements and the work functions of metals and nonmetals
Authors: Chen Edward C. M. , Wentworth W. E. , Ayala J. A.
Published: February 2003

The relationship between the Mulliken electronegativities of the elements and the work functions of metals has been investigated, and it has been found that these two are equal. This investigation has been extended to binary nonmetals using a relationship proposed by Nethercot with good success so that a general procedure for the experimental determination of Mulliken electronegativities for the elements has been established. In addition, values of valence state promotion energies and electron affinities for several elements have been calculated.
The 1B2u excited state of benzene: Force field and normal coordinates
Authors: Robey M. J. , Schlag E. W.
Published: February 2003

A complete valence force field is presented for the 1B2u excited state of benzene. Perprotonated and perdeuterated isotopes were used in the refinement which matches known frequencies to within one half percent. New excited state vibrational frequencies from two-photon spectroscopy enable reliable planar and out-of-plane force fields to be calculated. The frequencies of experimentally unobserved vibrational modes are given with the forms of the normal coordinates in the electronic excited state. These coordinates, for modes which strongly coupled the ground and excited states, are found to be mixtures of the ground state modes in accordance with the theory of vibronic coupling. The force field predicts an isotope shift upon electronic excitation which is in close agreement with experiment.
Molecular dynamics simulation of a fluid of hard spherocylinders
Authors: Rebertus D. W. , Sando K. M.
Published: February 2003

Using the molecular dynamics method we have computed the compressibility factor, orientational order parameter, velocity autocorrelation function, and diffusion constants for a system of 256 hard spherocylinders at two densities in the liquid region. The equation of state is in agreement with that found by the Monte Carlo method and that predicted by the scaled particle theory. The calculated orientational order parameter was near the expected value of (1/N)1/2 for an isotropic system.
Potential constants and structure of the UF5 monomer
Authors: Jones Llewellyn H. , Ekberg Scott
Published: February 2003

Three infrared-active UF stretching modes have been observed for UF5 isolated in argon and neon matrices. From the frequencies and their relative intensities the structure and UF force constants have been estimated. It is quite clear that the molecule has C4v symmetry, the axial bond has the same strength as the UF bonds in UF6, the radial bonds are somewhat weaker, and the axial–radial UF, UF′ angle is about 101°.
Vaporization kinetics of sodium chloride
Authors: Wagoner R. H. , Hirth J. P.
Published: February 2003

The vaporization rates of pure and calcium doped sodium chloride single crystals have been measured in vacuum (<3×10−7 torr) and oxygen (10−5 torr). In initial vacuum sublimation, calcium doping was found to increase vaporization rates and decrease the activation energy of free sublimation with respect to pure sodium chloride. Introduction of oxygen into the system was found to decrease vaporization rates and increase activation energies with calcium doped specimens whereas the kinetics of pure sodium chloride vaporization remained unchanged. The effect of oxygen could also be produced by long vacuum sublimation times. These results could be explained in terms of kinetic rate control at the desorption step of sublimation.
Zero-phonon lines in the singlet spectrum of the charge transfer crystal anthracene-PMDA: Experimental evidence and model calculations
Authors: Haarer D.
Published: February 2003

The absorption, fluorescence, and reflectivity spectra of anthracene-PMDA (pyromellitic acid dianhydride) single crystals are investigated at 2 °K. From the intensity of the zero-phonon transition and from the width of the phonon sidebands, one obtains information about the strength of the electron–phonon coupling. Within the framework of a configuration coordinate model one can show that about six phonons of frequency 62 cm−1 are emitted after a vertical Franck–Condon excitation from the ground state to the lowest excited charge transfer state. This rather strong electron–phonon coupling is supported by a model calculation on a localized charge transfer complex which assumes that the excited state relaxation arises primarily from the Coulombic attraction of the ionic donor–acceptor states.
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o computation of force constants. V. The theoretical anharmonic force fields and vibrational frequencies of methyl fluoride and methyl chloride
Authors: Schlegel H. Bernhard , Wolfe Saul , Bernardi Fernando
Published: February 2003

The anharmonic force fields of methyl fluoride and methyl chloride have been calculated ab initio. The theoretical and experimental harmonic force fields agree fairly well, but certain small discrepancies are found for CH3F. Agreement between calculated and observed anharmonic frequencies is good. It is suggested that application of the theoretical anharmonicity corrections to the observed frequencies can lead to better estimates of the experimental harmonic frequencies and force constants.
Nitrogen-14 nuclear quadrupole resonance study of substituted nitrobenzenes
Authors: Subbarao S. N. , Bray P. J.
Published: February 2003

Nitrogen-14 nuclear quadrupole resonance (NQR) spectra of 26 C–nitro compounds are reported and analyzed in the framework of the Townes and Dailey theory. Six different possibilities for the principal axis system of the electric field gradient (efg) tensor at the nitrogen of the NO2 group are considered. The results lead to the conclusion that the z direction of the principal axes is in the plane of the molecule and perpendicular to the C–N bond, whereas the x direction is along the C–N bond. The variations of the π electron density are in very good agreement with the ideas of classical chemistry. Satisfactory correlations of NQR data with the Hammett σ and σR constants have been found. σp and σR for the cholesteryl group are determined which suggest that the cholesteryl group, COOC27H45, is an electron attracting group. The nitrogen-14 quadrupole coupling constant in the solid phase of nitromethane (1695 kHz) is found to be substantially larger than that found in the gaseous phase (1187 kHz) by microwave measurements. This result cannot be explained by invoking the presence of hydrogen bonds in the solid phase of nitromethane.
Membrane Targeting of Rab GTPases Is Influenced by the Prenylation Motif
Authors: Gomes Anita Q. , Ali Bassam R. , Ramalho José S. , Godfrey Richard F. , Barral Duarte C. , Hume Alistair N. , Seabra Miguel C.
Published: February 2003

Rab GTPases are regulators of membrane traffic. Rabs specifically associate with target membranes via the attachment of (usually) two geranylgeranyl groups in a reaction involving Rab escort protein and Rab geranylgeranyl transferase. In contrast, related GTPases are singly prenylated by CAAX prenyl transferases. We report that di-geranylgeranyl modification is important for targeting of Rab5a and Rab27a to endosomes and melanosomes, respectively. Transient expression of EGFP-Rab5 mutants containing two prenylatable cysteines (CGC, CC, CCQNI, and CCA) in HeLa cells did not affect endosomal targeting or function, whereas mono-cysteine mutants (CSLG, CVLL, or CVIM) were mistargeted to the endoplasmic reticulum (ER) and were nonfunctional. Similarly, Rab27aCVLL mutant is also mistargeted to the ER and transgenic expression on a Rab27a null background (Rab27aash) did not rescue the coat color phenotype, suggesting that Rab27aCVLL is not functional in vivo. CAAX prenyl transferase inhibition and temperature-shift experiments further suggest that Rabs, singly or doubly modified are recruited to membranes via a Rab escort protein/Rab geranylgeranyl transferase-dependent mechanism that is distinct from the insertion of CAAX-containing GTPases. Finally, we show that both singly and doubly modified Rabs are extracted from membranes by RabGDIα and propose that the mistargeting of Rabs to the ER results from loss of targeting information.