bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Optical Fiber Bundles Combined with Electrochemistry for Chemical Imaging
Authors: Szunerits Sabine , Walt David R.
Published: February 2003

The present Review describes the progress made in using imaging optical fiber bundles for fluorescence and electrochemical‐initiated chemiluminescence imaging. A novel optoelectrochemical micro‐ring array has been fabricated and demonstrated for concurrent electrochemical and optical measurements. The device comprises optical fibers coated with gold via electroless gold deposition and assembled in a random array format. The design yielded an array of approximately 200 micro‐ring electrodes, where interdiffusional problems were minimized. The inner diameter of the ring electrode is fixed by the diameter of the individual optical fibers (25 μm), while the outer radius is determined by the thickness of the deposited gold. While all the fibers are optically addressable, they are not all electrochemically addressable. The resolution of this device is in the tens of micrometers range, determined by the diameter of the optical fiber (25 μm) and by the spacing between each electrically connected fiber. For the purpose of having well‐behaved microelectrode characteristics, this spacing was designed to be larger than 60 μm. The array was characterized using ferrocyanide in aqueous solution as a model electroactive species to demonstrate that this microelectrode array format exhibits steady‐state currents at short response times. This device has potential application to be used as an optoelectronic sensor, especially for the electrolytic generation and transmission of electrochemiluminescence, and was used to demonstrate that electrochemically generated luminescent products can be detected with the fiber assembly.
On the kinetics of the autoxidation of fats: influence of pro‐oxidants, antioxidants and synergists
Authors: Brimberg Ulla I. , Kamal‐Eldin Afaf
Published: February 2003

The influence of minor amounts of pro‐ and anti‐oxidants on the kinetics of the autoxidation of fat has been evaluated. The reaction rates of oxygen with the substrates were found to follow the same basic equation, hitherto established for pure substrates. There is evidence that the surface of the reaction vessel also acts as a reaction catalyst and its effect is proportional to the area of glass in contact with lipids. Oxidation is enhanced by trace metal ions as well as by surface‐active compounds (e.g. hydroperoxides and sterols). Antioxidants such as α‐tocopherol and butylated hydroxyanisole inhibit the oxidation by delaying the start of oxygen consumption (the induction period) while retarders like amino acids only decrease the rate of oxidation. Thus pro‐ and anti‐ oxidants affect either the start or the rate of oxygen consumption. The empirical formula dx/dt = k [O2] (1‐x/n) f′(t) was found applicable to the different stages of oxidation.
Enhancement of Anodic Response for DMSO at Ruthenium Oxide Film Electrodes as a Result of Doping with Iron(III)
Authors: Simpson Brett K. , Johnson Dennis C.
Published: February 2003

The oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone (DMSO2) is representative of numerous anodic oxygen‐transfer reactions of organosulfur compounds that suffer from slow kinetics at noble metal electrodes. Anodic voltammetric data for DMSO are examined at various RuO2‐film electrodes prepared by thermal deposition on titanium substrates. The response for DMSO is slightly larger at RuO2 films prepared in a flame as compared with films prepared in a furnace; however, temperature is more easily controlled in the furnace. Doping of the RuO2 films with Fe(III) further improves the sensitivity of anodic response for DMSO. Optimal response is obtained at an Fe(III)‐doped RuO2‐film electrode prepared using a deposition solution of 50 mM RuCl3 and 10 mM FeCl3 in a 1 : 1 mixture of isopropanol and 12 M HCl at an annealing temperature of 450 °C. The Levich plot (i vs. ω1/2) and Koutecky‐Levich plot (1/i vs. 1/ω1/2) of amperometric data for the oxidation of DMSO at an Fe(III)‐doped RuO2‐film electrode configured as a rotated disk are consistent with an anodic response controlled by mass‐transport processes at low rotational velocities. Flow injection data demonstrate that Fe(III)‐doped RuO2‐film electrodes exhibit detection capability for methionine and cysteine in addition to DMSO. Detection limits for 100‐μL injections of the three compounds are ca. 3.2×10−4 mM, i.e., ca. 32 pmol.
On some nonself mappings
Authors: Ćirić LJ. B. , Ume J. S. , Khan M. S. , Pathak H. K.
Published: February 2003

Let X be a Banach space, let K be a non–empty closed subset of X and let T : K → X be a non–self mapping. The main result of this paper is that if T satisfies the contractive–type condition (1.1) below and maps ∂K (∂K the boundary of K) into K then T has a unique fixed point in K.
A monotone iterative scheme for a nonlinear second order equation based on a generalized anti–maximum principle
Authors: Torres Pedro J. , Zhang Meirong
Published: February 2003

In this paper, a generalized anti–maximum principle for the second order differential operator with potentials is proved. As an application, we will give a monotone iterative scheme for periodic solutions of nonlinear second order equations. Such a scheme involves the Lp norms of the growth, 1 ≤ p ≤ ∞, while the usual one is just the case p = ∞.
The performance of research partnerships
Authors: Caloghirou Yannis , Hondroyiannis George , Vonortas Nicholas S.
Published: February 2003

This paper investigates partnership performance as perceived by individual partners. It taps into one of the most extensive sources of pertinent empirical information recently constructed in Europe. Partnership success is shown to depend significantly on the closeness of the cooperative research to the in‐house R&D effort of the firm, on the firm's effort to learn from the partnership and its partners, and on the absence of problems of knowledge appropriation between partners. Firms use partnerships as vehicles of risk and uncertainty reduction by collaborating with competitors as well as with suppliers and buyers (but not with universities and public research institutes) when the research is far apart from their in‐house R&D and when the expected outcome is not easily appropriable. Copyright © 2003 John Wiley & Sons, Ltd.
Global existence for the Vlasov–Darwin system in ℝ3 for small initial data
Authors: Benachour Saïd , Filbet Francis , Laurençot Philippe , Sonnendrücker Eric
Published: February 2003

We prove the global existence of weak solutions to the Vlasov–Darwin system in R3 for small initial data. The Vlasov–Darwin system is an approximation of the Vlasov–Maxwell model which is valid when the characteristic speed of the particles is smaller than the light velocity, but not too small. In contrast to the Vlasov–Maxwell system, the total energy conservation does not provide an L2‐bound on the transverse part of the electric field. This difficulty may be overcome by exploiting the underlying elliptic structure of the Darwin equations under a smallness assumption on the initial data. We finally investigate the convergence of the Vlasov–Darwin system towards the Vlasov–Poisson system. Copyright © 2003 John Wiley & Sons, Ltd.
Minimal regularity of the solutions of some transmission problems
Authors: Mercier D.
Published: February 2003

We consider some transmission problems for the Laplace operator in two‐dimensional domains. Our goal is to give minimal regularity of the solutions, better than H1, with or without conditions on the (positive) material constants. Under a monotonicity or quasi‐monotonicity condition on the constants (or on the inverses according to the boundary conditions), we study the behaviour of the solution near vertex and near interior nodes and show in each case that the given regularity is sharp. Without condition we prove that the regularity near a corner is of the form H1+ρ, where ρ is a given bound depending on the material constants. Numerical examples are presented which confirm the sharpness of our lower bounds. Copyright © 2003 John Wiley & Sons, Ltd.
Tracing migration events in man and cattle by stable strontium isotope analysis of appositionally grown mineralized tissue
Authors: Schweissing M. M. , Grupe G.
Published: February 2003

While geologically significant differences of strontium (Sr) isotopic ratios in dental enamel and compact bone from adult human skeletal finds will be basically indicative of an individual residence change between early childhood and adulthood, hardly any information will be available with regard to the approximate individual age at migration. Due to several problems still associated with microsampling techniques, bulk analyses of appositionally grown mineralized tissues were analysed for 87Sr/86Sr ratios in an attempt to mathematically define the ontogenetic stage at individual residence change in historical times. This pilot study presents the results obtained from serial analyses of whole enamel from human permanent dentitions from a Roman fortress site in Germany, and serial sampling of a horn core from a long‐horned ox from an early modern horn core site in Austria. In the first case, more detailed information was expected with regard to population admixture in the Roman provinces, while the horn core analysis was performed in an attempt to shed light on mode and velocity of long distance trade of domestic animals. A mathematical approximation served for the definition of the most likely individual age when Sr with a new isotopic composition first shows up in the course of tissue precipitation. Copyright © 2003 John Wiley & Sons, Ltd.
Training general practitioners in the identification and management of adolescent depression within the consultation: a feasibility study
Authors: Gledhill Julia , Kramer Tami , Iliffe Steven , Garralda M Elena
Published: February 2003

Background

Depressive disorders are common in adolescent general practice attenders.

Method

Adolescent attenders were screened/interviewed for depressive disorders, general practitioners (GPs) completed a checklist indicating recognition of psychopathology prior to and following GP training in the identification/management of adolescent depression.

Results

One hundred and thirty consecutive adolescent attenders were screened before and 184 after training. Ten GPs completed the training. Psychiatric interviews with 38 adolescents with high depressive scores prior to and 44 following training identified 10 (26%) and 21 (48%), respectively, as clinically depressed. Sensitivity of GP identification improved from 2/10 (20%) to 9/21 (43%) without loss of specificity; predictive validity from 2/6 (33%) to 9/12 (75%). Adolescents interviewed appreciated the intervention.

Conclusions

Training GPs is feasible and may improve recognition of adolescent depression.
Primary Mental Health Workers within Youth Offending Teams: a new service model
Authors: Callaghan Jane , Pace Francis , Young Bridget , Vostanis Panos
Published: February 2003

Primary Mental Health Workers (PMHWs) have been deployed to address the mental health needs of young offenders referred to Youth Offending Teams (YOTs) in two UK areas. The mental health characteristics of 60 young people consecutively referred to these PMHWs, the assessment outcome and interventions offered, are described. In addition to the anticipated concerns about oppositional/aggressive behaviour, young people were referred for a range of mental health problems. There were high levels of emotional problems, self‐harm, peer and family relationships difficulties, and school non‐attendance. PMHWs offered a range of direct interventions, as well as consultation to YOT staff. The service findings indicate the usefulness of such an inter‐agency model in strengthening the links between specialist CAMHS and YOTs, and providing an accessible, responsive and effective service to a needy group of young people.
Differences in psychosocial and behavioral profiles between heart failure patients admitted to cardiology and geriatric wards
Authors: De Geest Sabina , Scheurweghs Lieve , Reynders Isabelle , Pelemans Walter , Droogné Walter , Van Cleemput Johan , Leventhal Marcia , Vanhaecke Johan
Published: February 2003

Background:

Heart failure represents a growing epidemic, primarily in the elderly. Development and implementation of management programs designed for use in daily clinical practice remains a major challenge.

Aims:

This study aimed at profiling a hospitalized heart failure population in view of medical, behavioral, educational, psychosocial and health resources utilization parameters stratified by admission to cardiology and geriatric wards.

Methods and results:

Using a descriptive comparative design, 109 European heart failure patients admitted to cardiology (42%) and geriatric wards (58%) were included. Significant differences (all P<0.0001) were identified between the two groups. Patients admitted to cardiology had a mean age of 68.5, 33% were women, and the mean ejection fraction was 38%. Patients admitted to geriatrics had a mean age of 85, 68% were women, and the mean ejection fraction was 56%. Sixty‐six percent were admitted for cardiac reasons. Medical, educational, behavioral, psychosocial and health resources utilization data were retrieved from medical files as well as by patient and family interviews. Results showed significant differences between groups. Patients admitted to geriatric wards received significantly less ACE inhibition and β‐blockers. Moreover, these patients were significantly less knowledgeable, showed poorer self‐management, poorer hearing, more cognitive impairment, a higher degree of depressive symptomatology, more problems with ADL and IADL, and used significantly more home health care services compared to patients admitted to cardiology wards.

Conclusion:

The characteristics of the heart failure population at large are quite different from those of populations included in large‐scale therapeutic trials. Findings from this study provide options for tailored management strategies for both profiled subgroups.
Mechanical collapse vs ideal glass formation in slowly vitrified solutions: A plausibility test
Authors: Angell C. A. , Donnella J.
Published: February 2003

Homogeneous nucleation temperatures TH for binary solutions have been measured using the emulsion technique. From their composition dependence it is argued that the excess entropy paradox (Kauzmann paradox) for supercooling liquids cannot reasonably be resolved by postulating the intercession of a first order phase change (homogeneous nucleation anticipating mechanical instability) prior to the exhaustion of the excess entropy reservoir at T0. There are evidently composition ranges in which TH lies below T0. This observation implies that in certain ’’clean’’ solutions the ’’ideal glass’’ state can in principle be approached.
Use of a stable free radical as a NMR spin probe for studying intermolecular interactions. XIV. A proton relaxation study of the hydrogen bond involving a stable free radical
Authors: Endo Kazunaka , Morishima Isao , Yonezawa Teijiro
Published: February 2003

Pulsed NMR methods have been used to investigate the proton spin relaxation for the solutions containing a DTBN radical. The present study on frequency and temperature dependences of proton relaxation times affords the information on the distance between solvent molecules and the DTBN radical, and on the dynamical aspects of the solvent–radical interaction. The observed 1H relaxation rates were analyzed on the basis of the Hubbard and Solomon–Bloembergen theories. The 1H relaxation of aprotic solvent molecules [CH3OD, C6H6 and (CH3)2CO] in the presence of DTBN is explained by a pure dipole–dipole interaction governed by translational random motions, while the proton relaxation of proton–donor molecules (CD3OH and CHCl3) in the presence of DTBN radical is dominated by the dipolar correlation time for the hydrogen bonding. The correlation times, the activation energies, and the intermolecular distances were evaluated. The closest distance between the proton and the paramagnetic center of the radical in the aprotic solvent was found to be close to the distance estimated from van der Waals radii. The hydrogen bond lengths for CD3OH– and CHCl3–DTBN bimolecular interaction systems were evaluated as rOH⋅⋅⋅O?1.9 Å and rCH⋅⋅⋅O ?2.1 Å from the effective separation between the proton and the odd electron center. The lifetime of the hydrogen bond complex was also obtained.
Molecular dynamics of the rough sphere fluid. III. The dependence of translational and rotational motion on particle roughness
Authors: Pangali Charanjit S. , Berne Bruce J.
Published: February 2003

Molecular dynamics studies of two generalized forms of the rough sphere model are reported. The generalization permits us to vary the coupling between rotational and translational motion through a stick parameter λ. The autocorrelation functions show deviations from the Enskog theory for all values of λ studied—indicating that collective effects are involved. It appears that the angular velocity correlation function is the sum of two exponentials. A simulation of a mixture of disparate sized rough spheres was also performed. It is found that the rotational motion of the small particle is not significantly altered upon introduction of the large particles, but the linear velocity correlation function of the small particle differes considerably from that of the neat fluid (in the time regime from 5–15 mean collision time units).
Calculation of strain and polarization fields at the surface of MgO crystals. Breathing shell model
Authors: Barnett R. N. , Bass Ronald
Published: February 2003

The strain and polarization fields associated with an (001) surface of MgO have been calculated within the lattice statics approximation. A central force shell model was used to describe the interionic potential, and isotropic shell deformation effects are included to account for the Cauchy breakdown in MgO. This breathing shell model has already excelled in describing the phonon spectrum of MgO. It is found that there are strong distortions in the first ten layers of the slab in addition to a small bulk contraction. The bulk contraction, a consequence of the shell breathing, contributes a term to the surface energy which is independent of the slab thickness.
Orientation isotope effect in ion–molecule reactions
Authors: Hierl Peter M.
Published: February 2003

A simple kinematic model is proposed to account for the kinetic isotope effect (KIE) upon the reactions of simple ions X+ with HD. This model is based upon (1) the fact that the displacement of the center of polarizability from the center of mass in the HD molecule will affect the alignment of the reactants, (2) the fact that, for many ions X+, reaction must occur by a surface crossing mechanism, and (3) the assumption that the ratio XH+/(XH++XD+) equals the fraction of intimate collisions in which the H end of HD is oriented towards the ion at the moment the reactants pass over the centrifugal barrier in the effective radial potential (or cross over to the X–HD+ surface if the crossing occurs before the centrifugal barrier is reached). Use of the ion–induced dipole potential for the reactants permits the derivation of an analytic expression for the KIE. With no adjustable parameters, this model accounts quantitatively for the very different KIE’s observed in the reactions of Ar+ and Kr+ with HD at low collision energies.
Role of three-body interactions in trimer binding
Authors: Bruch L. W. , Blaisten-Barojas E. , Novaro O.
Published: February 2003

A semiclassical perturbation expansion is developed for the ground state energy of three identical particles interacting via pair and three-body potentials. The result is applied for the ground state energy of three neon atoms, where the non-pair-additive terms make a small contribution, and for three beryllium atoms where such terms make a large contribution. Models are constructed for the pair and three-body potentials of beryllium, using the results of self-consistent field and dispersion energy calculations. The beryllium dimer and trimer are self-bound.
Deactivation of vibrationally excited SO2 by O(3P) atoms
Authors: West Gary A. , Weston Ralph E. , Flynn George W.
Published: February 2003

Laser-induced infrared fluorescence has been used to measure collisional energy transfer rates of SO2 in the presence of O(3P) atoms. Deactivation of the ν1 and ν3 stretching modes is found to be rapid, with efficiencies 30–40 times the corresponding rare gas rates. Energy transfer between the ν1 and ν3 modes induced by O atoms is relatively inefficient compared to deactivation, in contrast to the effect observed for rare gas atoms.
Inversion of the Kirkwood–Buff theory of solutions: Application to the water–ethanol system
Authors: Ben-Naim A.
Published: February 2003

A general procedure is outlined whereby experimental data such as partial molar volumes, isothermal compressibilities, and partial vapor pressures may be processed to obtain information on the extent of the affinity between two species in a mixture of two (or more) components. A particular example of the water–ethanol system is processed in this manner to obtain the quantities Gαβ which are integrals over the pair correlation functions between two species α and β. This information is relevant to several topics of interest in the field of aqueous solutions, such as the solvation of solutes, hydrophobic interactions, and structural changes in the solvent brought by the addition of solutes to water. More generally it may be used to characterize the properties of various mixtures on a molecular level.
Vibrational spectra and structure of H+(H2O)nβ- alumina
Authors: Colomban Ph. , Lucazeau G. , Mercier R. , Novak A.
Published: February 2003

Single crystals and polycrystalline samples of β-alumina containing hydrated proton H+(H2O)n have been studied by infrared and, to some extent, by Raman spectroscopy. The spectra of fully hydrated and more of less deyhdrated samples and their deuterated derivatives have been compared to those of Na+ β-alumina and of mixed crystals with different M+/H+ ratios (M=Na, K, Ag). It can be shown that the samples heated above 400 °C contain H3O+ ions occupying Beevers–Ross sites as dominant species; midoxygen sites with single and double occupancy are less populated. The spectroscopic data are consistent with nearly nonhydrogen-bonded H3O+ ions having a slightly distorted C3v pyramidal structure. The fully hydrated β-alumina, on the other hand, appears to contain also higher species such as H5O2+ and H7O3+. The former is believed to have an unsymmetrical structure, H3O+H2O, with terminal groups hydrogen bonded to the oxygen atoms of spinel blocks. The latter is characterized by OH stretching bands similar to those of H7O3+ClO4−.
On three-dimensional rotational averages
Authors: Andrews D. L. , Thirunamachandran T.
Published: February 2003

In theories which describe the response of freely rotating molecules to externally imposed stimuli it is frequently necessary to average rotationally a product of direction cosines relating space-fixed and molecular coordinate frames. In this paper a systematic method for deriving the required tensor averages is presented, and results up to the seventh rank are explicitly shown. Where appropriate both reducible and irreducible expressions are given and their equivalence is demonstrated. Finally, some useful identities relating rotational averages of different ranks are noted.
Photoionization mass spectrometry of HI and DI at high resolution
Authors: Eland J. H. D. , Berkowitz J.
Published: February 2003

The ionization potentials of HI and DI to the 2Π3/2 and 2Π1/2 states are redetermined by extrapolation of Rydberg series seen in photoionization, as: I.P.(HI), 2Π3/2=10.386±0.001 eV, 2Π1/2 =11.0495±0.001 eV; I.P.(DI), 2Π3/2=10.387±0.001 eV, 2Π1/2 =11.0505±0.001 eV The spin-orbit parameter A(HI) =−0.664±0.002 eV. Several new Rydberg series have been identified and the first vibrationally excited levels have been located in three of the 2Π states. The spectra of HI and DI are discussed and are contrasted with the photoionization spectrum of atomic Xe. Changes in the relative shapes and intensities of Rydberg peaks as functions of n* are ascribed to changes in angular momentum coupling schemes.
Rotational states of the NH+4 ion in (NH4)2SnCl6 by inelastic neutron scattering
Authors: Prager M. , Press W. , Alefeld B. , Hüller A.
Published: February 2003

The tunnel splitting of the librational ground state of a NH+4 ion in (NH4)2 SnCl6 has been analyzed by ’’incoherent’’ inelastic neutron scattering. Ground state splittings of 2.96±0.04 and 1.51±0.03 μeV have been observed at T=6 K and are interpreted as transitions between A?T and T?E spin symmetry states, respectively. With increasing temperature the observed tunnel splitting shifts towards smaller energies but fails to show significant lifetime broadening. The first excited librational state is observed at 13.4±0.5 meV. An excitation with E?30 meV probably corresponds to the second excited librational state. Above 70 K classical reorientational motion gives rise to quasielastic scattering. From the temperature dependence of the quasielastic linewidth an activation energy EA=590±30 K is obtained. A three dimensional rotational potential is discussed in view of the above data. The temperature dependence of the tunneling states is compared with current theories.
Gas phase infrared spectra of oxonium hydrate ions from 2 to 5 μ
Authors: Schwarz Harold A.
Published: February 2003

Infrared spectra of oxonium hydrate ions, generated by pulse radiolysis of argon containing small amounts of water vapor, have been measured using a signal averaging technique. The symmetric and antisymmetric OH stretch frequencies of the H3O+ part of H9O4+ are found at 3000 and 2660 cm−1. H11O5+ frequencies are found at 2180, 2860, and 3200 cm−1. In addition, bands at 3620 and 3710 cm−1, due to the outer water molecules are observed. Bands found during the growth of H9O4+ at low water pressures are at 3490, 3290, 3170, 2850, and 2700 cm−1. The 3490 cm−1 frequency is attributed to H3O+.
Molecular motions and lattice stability of a disordered organic alloy: Binary solid solutions of 1,4-dihalonaphthalenes
Authors: Bellows James C. , Prasad Paras N.
Published: February 2003

Molecular motions of 1,4-dihalonaphthalenes and their binary solid solutions are studied by Raman spectroscopy to understand the effect of chemical perturbation of the lattice stability. In the 1,4-dihalonaphthalene series, 1,4-dichloronaphthalene and 1-bromo-4-chloronaphthalene are isomorphous but the additional chemical perturbation by another bromine atom creates a lattice instability which results in a different crystal structure for 1,4-dibromonaphthalene. Not only is the binary organic alloy (solid solution) of 1,4-dichloronaphthalene with 1-bromo-4-chloronaphthalene stable for all composition, but 1-bromo-4-chloronaphthalene shows large solubility with 1,4-dibromonaphthalene as well. In both alloys, all phonons are amalgamated and so are some internal vibrations which are predominantly nonhalogen modes. In the 1-bromo-4-chloronaphthalene alloy with 1,4-dibromonaphthalene, the lattice is unstable in the critical concentration region with mole fraction of 1,4-dibromonaphthalene between 0.24 and 0.44. In this region, the lattice can be driven from the 1-bromo-4-chloronaphthalene crystal form to that of 1,4-dibromonaphthalene by additional chemical perturbation. Certain features of the phonon motions and exciton splittings are retained across this critical concentration region, indicating that the lattice instability encountered is not along all molecular degrees of freedom and that certain intermolecular interactions do not change in going from 1-bromo-4-chloronaphthalene crystal form to that of 1,4-dibromonaphthalene. A close inspection of their crystal structures shows that in each case the molecules stack to form linear chains and that some of the relationships between two stacks remain unchanged. The structural similarity suggests that the one dimensional triplet exciton transport found in 1,4-dibromonaphthalene may also be present in the other two compounds.
The Rayleigh depolarization ratio and rotational Raman spectrum of water vapor and the polarizability components for the water molecule
Authors: Murphy William F.
Published: February 2003

This paper describes the observation and computer simulation of the rotational Raman spectrum of water vapor and the measurement of the depolarization ratio for Rayleigh scattering from water vapor, which was found to be (3.0±1.4) ×10−4. These results were combined with the value of the mean polarizability to calculate the principal polarizability components of the water molecule. At 514.5 nm, they are (in units of 10−24 cm3): αxx=1.468±0.003, αyy =1.415±0.013, and αzz=1.528±0.013, where the x axis is the dipole axis and the y axis is perpendicular to the molecular plane.
Anomalous thermoelastic behavior and molecular reorientations in crystals
Authors: Michel K. H. , Naudts J.
Published: February 2003

Starting from a repulsive overlap potential, we derive a microscopic Hamiltonian that takes into account single particle orientational potential effects and rotational–translational coupling in molecular crystals. This coupling leads to an effective orientational interaction between nonspherical molecules. Theoretical expressions for the elastic constants in the presence of this interaction are derived. The anomalous thermoelastic behavior which was discovered by Haussühl for c44 and c11 in KCN and NaCN, and found by Rowe et al. in neutron measurements of TA phonons, is explained. The qualitative and quantitative agreement between theory and experiment is convincing.
Determination of diffusion coefficients by submicron droplet evaporation
Authors: Davis E. James , Ray Asit K.
Published: February 2003

Lennard-Jones potential function constants, diffusion coefficients, and vapor pressures for relatively nonvolatile organics in gaseous media have been determined by measuring the evaporation rates of submicron droplets suspended in an electric field in a laser beam. A light-scattering method was used to obtain the droplet size as a function of time for diffusion-controlled evaporation.
Statistical mechanical theory for nonuniform fluids: Properties of the hard-sphere system and a perturbation theory for nonuniform simple fluids
Authors: Singh Y. , Abraham Farid F.
Published: February 2003

We present a formal theory for the statistical mechanics of a nonuniform classical fluid and apply it to the hard-sphere fluid using the Wertheim–Thiele solution for the direct correlation function in the Percus–Yevick approximation. With a knowledge of the nonuniform hard-sphere fluid results, we develop a perturbation theory of nonuniform simple fluids motivated by the Weeks, Chandler, Andersen perturbation theory of uniform fluids. Using our perturbation theory, the properties of a Lennard-Jones liquid–vapor interface are calculated and compared with recent numerical experiments near the triple point. We find excellent agreement. Comparisons with other formulations are made, and the agreement is not so good.
Photoelectron spectroscopic study of hydroxylamine (NH2OH) and o-methylhydroxylamine (NH2OCH3)
Authors: Kimura Katsumi , Katsumata Shunji
Published: February 2003

Hei photoelectron spectra of hydroxylamine and o-methylhydroxylamine in the gaseous phase have been measured below 20 eV, and have been resolved into five and seven ionization bands, respectively, corresponding to p-type molecular orbitals. On the basis of available ab initio MO calculations by Fink et al., the p-type photoelectron bands of hydroxylamine have well been interpreted in terms of a trans staggered form already known as the most stable conformation in the gaseous phase. Orbital assignments on the p-type bands of o-methylhydroxylamine have been made on the basis of CNDO/2 calculations which were also carried out in the present work, except for the first two bands whose assignments were based on orbital-interaction considerations. An ionization-energy sum rule proposed previously has also been tested for the compounds studied here.
Mössbauer spectroscopic determination of the electronic structure of highly oxidized iron in hemoproteins
Authors: Harami T. , Maeda Y. , Morita Y. , Trautwein A. , Gonser U.
Published: February 2003

Mössbauer spectra have been obtained from the hydrogen peroxide compounds of peroxidase and met-myoglobin, in the presence of an applied magnetic field. The magnetically perturbed spectra and the temperature dependence of the quadrupole splittings have been analyzed with a low symmetry ligand field approximation and spin–orbit coupling. The electronic structure of heme-iron in peroxidase Compound II and met-myoglobin H2O2 compound is ascribed to a low-spin (t2g)4 S=1 paramagnetic configuration. The axial and rhombic field parameters are determined to be 624 and ?312 cm−1, respectively. The lowest state is characterized by a spin-singlet Sz=0 in a 3A2 multiplet. The covalency parameter indicates the large expansion of radial charge-distribution of the t2g orbitals in these compounds.
The dynamics of the reaction D+2+O(3P) →OD++D, and the influence of the atomic quadrupole moment on the cross section at very low kinetic energies
Authors: McClure Donald J. , Douglass Charles H. , Gentry W. Ronald
Published: February 2003

We report the results of a merged-beam study of the reaction D+2+O(3P) →OD++D over the range of relative kinetic energy from 0.002 to 27 eV. The data include accurate absolute values of the total reaction cross section and also high-resolution measurements of the product ion laboratory energy distributions, which are deconvoluted to obtain estimates of the product energy and angle distributions in c.m. coordinates. The reaction mechanism is direct, with the OD+ product scattered preferentially in the direction of the incident O atom, and with large average internal excitation. The fact that O(3P) possesses an electrostatic quadrupole moment has important consequences for the interpretation of the low-energy data in terms of the adiabatic state correlations of reactants, intermediates, and products. Our major conclusions are (1) that the average probabilities of reaction for low-energy capture collisions are about 87% for approaches on Σ−–A2 potential energy surfaces and about 53% for approaches on Π–B1, B2 surfaces and (2) that the data are not consistent with the assumption of electronic adiabaticity.
Optical oscillator strengths and excitation energies in solids, liquids, and molecules
Authors: Wemple S. H.
Published: February 2003

An examination of average dipole coordinate matrix elements and electronic excitation energies in over 140 solids, liquids, and molecules reveals simple trends related to polarity, metallicity, ionicity, anion–anion ’’contact’’, cation core hybridization, and disorder. These results point to the key roles played by metallicity and polarity in crystalline solids as expressed by the empirical relationship ?2=fdZa/30.16, where 30.16 eV Å is a fundamental constant given by e/6ε0, ? is the dimensionless coordinate matrix element introduced by Harrison and Pantelides, d is the bond length in Å, Za is the formal chemical valency of the anion, and f is a coefficient associated with first-neighbor and second-neighbor delocalization, i.e., f=4.8±0.3 eV in ’’covalent’’ crystals, f=3.0±0.2 eV in ’’ionic’’ crystals, and f=3.8±0.2 eV in ’’anion-contact’’ crystals. The latter classification includes a variety of materials with close-spaced anions such as LiF, MgS, several rutile-structure compounds, and CdI2. Wurtzite-structure chalcogenides form a transitional group between large ’’ionic’’ and ’’covalent’’ classes. Direct contributions to ?2 from valencelike d10 and s2 ’’cores’’ are evident in some cases (e.g., CuCl, TlBr, PbTe, BiI3) and can be accounted for simply by including these ’’cores’’ in the valence electron count. Such direct effects are not observed, for example, in the Zn or Cd salts. Metallicity trends (described by d) and polarity trends (described by Za) are absent in liquids and molecules, and oscillator strengths (f) are considerably larger than observed in solids although matrix elements are comparable. The primary excitation energy results relate both to an approximate power law dependence on bond length of the form E0∼d−s, where 2<s<3 and to a substantial reduction in E0 for materials with valencelike d10 or s2 cation ’’cores’’. In most molecules the average excitation energy E0 falls close to the first ionization potential. Finally, the implications of these results on the dielectric models of Phillips and Harrison and on the nature of the chemical bond are discussed.
A model for unimolecular reaction of sulfur hexafluoride
Authors: Lyman John L.
Published: February 2003

The thermal dissociation data for SF6 has been re-evaluated using RRKM unimolecular reaction rate theory and was found to be consistent with a higher value for the sulfur–fluorine bond strength (92 kcal/mole). A model based on a rate equation formalism has been developed that includes unimolecular dissociation, collisional energy transfer (V–T processes), and absorption and emission of laser radiation. The model was designed to test theories of absorption of laser radiation for laser-induced chemical reaction in SF6 that are amenable to a rate equation formalism. It was found that the thermal reaction and vibrational relaxation data could be adequately reproduced. Sample calculations of laser-induced chemical reactions are performed.
Exciton scattering processes in (1,4)-dibromonaphthalene
Authors: Burland D. M. , Konzelmann U. , Macfarlane R. M.
Published: February 2003

The dephasing of optically prepared k?0 triplet excitons in crystalline (1,4) -dibromonaphthalene (DBN) has been investigated by measurement of the temperature dependence of the absorption line shape. At temperatures below 10 K the dephasing is due to scattering of the exciton by impurities or lattice defects. We show that the naturally occurring 13C containing DBN molecules can make a significant contribution to this linewidth. Above 10 K the excitons are scattered by optical phonons. The most likely exciton–phonon scattering process is shown to involve a single phonon scattering of the exciton between the two crystallographically inequivalent sites.
Laser fluorescence detection of nascent product state distributions in reactions of Sc and Y with O2, NO, and SO2
Authors: Liu K. , Parson J. M.
Published: February 2003

The reactions of Y and Sc with O2, NO, and SO2 have been investigated by the laser-induced fluorescence method. The excitation spectra are reported for metal oxide products formed under single-collision conditions in a beam–gas arrangement. Possible systematic errors which arise in deducing the internal state distributions from the spectra are discussed. The relative vibrational populations of metal oxides for all reactions are close to unbiased statistical distributions (in the sense of the information theoretic approach). Although the rotational distributions from the reactions with NO and SO2 also follow statistical behavior, those from the reactions with O2 peak significantly lower than the statistical ones. Radiative lifetimes are reported for the A and B states of YO and ScO, and the B and C states of LaO.
Theoretical determination of bound–free absorption cross sections in Ar+2
Authors: Stevens Walter J. , Gardner Maureen , Karo Arnold , Julienne Paul
Published: February 2003

A b initio calculations have been carried out for the potential energy curves and transition moments of the 2Σ+u, 2Πg, 2Πu, and 2Σ+g states of Ar+2 which arise from the 2P+1S ion–atom asymptote. These data have been used in a theoretical calculation of the dissociative absorption cross sections from the bound 2Σ+u state to the repulsive 2Πg and 2Σ+g states. The 2Σ+u→2Πg transition, which is dominated by spin–orbit effects, has a maximum absorption cross section of 2.6×10−19 cm2 centered at 716 nm with a full width at half-maximum of 185 nm at room temperature. The 2Σ+u→2Σ+g transition is found to be much stronger with a maximum cross section of 0.5×10−16 cm2 centered at 300 nm with a full width at half-maximum of 75 nm at room temperature.
Kinematics of charge transfer: Ar++H2
Authors: Hierl P. M. , Pac?k V. , Herman Z.
Published: February 2003

Product angular and velocity vector distributions have been measured in a crossed beam experiment for the charge transfer process Ar++H2→Ar+H2+ at relative collision energies of 0.13, 0.48, and 3.44 eV. Charge transfer was found to occur by two distinct mechanisms: (1) a simple electron-jump mechanism which preserves the quasirectilinear trajectories of the colliding species and which selectively produces H2+ in the vibrational state most nearly resonant with the reactant ion, and (2) an intimate-collision mechanism which results in large-angle scattering and which produces H2+ in a broad range of vibrational states.
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o calculations for the X 2Σ, A 2Π, and B 2Σ states of NaAr: Emission spectra and cross sections for fine-structure transitions in Na–Ar collisions
Authors: Saxon Roberta P. , Olson R.E. , Liu B.
Published: February 2003

Configuration interaction (CI) calculations were performed for the X 2Σ, A 2Π, and B 2Σ states of NaAr. The A 2Π state is calculated to have a well depth of 492 cm−1 at an internuclear separation of 3.04 Å. Small wells of 55 and 32 cm−1 were found for the X 2Σ and B 2Σ states located at 5.01 and 6.80 Å, respectively. The spectra for A 2Π–X 2Σ emission in the limits of zero and infinite Ar pressure were calculated and compared with the experiment of York, Scheps, and Gallagher and the predictions using the pseudopotential curves of Pascale and Vandeplanque. The potentials from this work give spectra in much better agreement with experiment than the pseudopotential predictions. Total and differential cross sections for fine-structure changing transitions Na(2P1/2) +Ar→Na(2P3/2)+Ar−17.2 cm−1 were calculated by a quantum mechanical technique. The total cross sections are in excellent agreement with experimental results. The excited state differential cross sections exhibit prominent rainbow structure centered at τR=EΘR=5.5–6.0 eV deg.
Exciton–lattice interaction and the line shape of exciton absorption in molecular crystals
Authors: Sumi H.
Published: February 2003

The exciton–lattice interaction cannot be treated adiabatically in many molecular crystals where the exciton bandwidth is at most comparable to lattice-vibration energies. It cannot also be treated perturbationally at about room temperatures where the absorption line width of excitons is comparable to the larger of the exciton bandwidth and lattice-vibration energies in most molecular crystals. A simple model which describes excitons in molecular crystals from a unified viewpoint is proposed. The model has three characteristic energies: the half-width B of the exciton band, the average amplitude of the scattering potential for excitons produced by lattice vibrations D, and the inverse of the correlation time of the potential fluctuation γ on the order of lattice-vibration energies in units of C=1. It describes singlet excitons when B≳γ and triplet excitons when B≪γ. The dynamical-coherent-potential approximation applied to this model bridges reasonably the following two limits: the strong-scattering limit for D≫B and D≫γ in which the exciton absorption has a Gaussian line shape, and the weak-scattering limit for D≪B or D≪γ in which the exciton absorption has a motionally narrowed Lorentzian line shape. The exponentially decreasing low-energy absorption tail, obeying the Urbach–Martienssen rule, grows up as B/γ increases towards the adiabatic limit of B/γ ≫1. The model is consistently applied to observed exciton spectra in various molecular crystals.
Nonadiabatic effects in the collision of F(2P) with H2(1Σg+). III. Scattering theory and coupled-channel computations
Authors: Rebentrost Frank , Lester William A.
Published: February 2003

The theory of nonreactive atom–diatom collisions in the presence of multiple electronic surfaces is developed in both space-fixed and body-fixed coordinate frames. The formalism is applied to the scattering of fluorine atoms by para- and ortho-hydrogen molecules. Coupled-channel computations of integral cross sections for fine structure and rotational transitions are carried out in the rigid rotor approximation using ab initio self-consistent-field potential energy surfaces and are facilitated by the use of a diabatic representation of the molecular channel states. The magnitudes of the cross sections at a specific translational energy are found in general to decrease with increasing energy defect. For F(2P1/2)+p-H2 the cross section for a near resonant electronic-to-rotational energy transfer process dominates other inelastic transitions by at least an order of magnitude.
Molecular structure of the methyl anion CH−3. An investigation of the effects of electron correlation using the theory of self-consistent electron pairs (SCEP)
Authors: Dykstra Clifford E. , Hereld Mark , Lucchese Robert R. , Schaefer Henry F. , Meyer Wilfried
Published: February 2003

Since Hartree–Fock theory often predicts stable negative ions to lie above the analogous neutral +e−, there have been legitimate concerns that structural predictions at this level of theory may be of dubious value. To investigate this question, ab initio electronic structure theory has been applied to the methyl anion using the large and flexible basis of Duke. Electron correlation was taken into account explicitly using the recently developed theory of self-consistent electron pairs (SCEP). The geometrical structure of CH3− is found to be essentially unchanged by electron correlation. The near Hartree–Fock inversion barrier for CH3− is 1.72 kcal/mole, and this is reduced to 1.50 kcal/mole by correlation effects.
On the accuracy of ionization potentials calculated by Green’s functions
Authors: von Niessen W. , Diercksen G. H. F. , Cederbaum L. S.
Published: February 2003

A many-body Green’s function method is used to calculate vertical valence ionization potentials to high accuracy for the atoms and molecules Ne, N2, F2, CO2, P2, H2O, and H2S. Large basis sets including several sets of polarization functions are used in the calculations to reach the limit of the presently achievable accuracy for molecular systems. The maximum errors in the computed ionization potentials are 0.1 to 0.25 eV depending on the molecule and the basis set. The results are extremely stable, when large basis sets are used. Comparison with other methods is made.