bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass and size effects on the transport properties of molten salts
Authors: Harada Makoto , Yamanaka Akihiro , Tanigaki Masataka , Tada Yutaka
Published: February 2003

The mass and size dependencies of the ionic transport processes were studied by molecular dynamics calculations on the model fluid interacting through repulsive soft-core and the Coulomb potentials. The mass difference between anion and cation significantly affects the ionic transport processes. On the contrary, the change in the time evolution of the processes due to size difference between unlike ions is comparatively small. A perturbation treatment for the mass effect was developed to describe the velocity autocorrelation function, the electrical current autocorrelation function, and corresponding transport properties.
Spatial correlations in a self-repelling ring polymer
Authors: Prentis J. J.
Published: February 2003

The scattering structure function SN(q) of a large flexible ring polymer with N monomers in a good solvent is calculated as a universal expansion in the variable q2<RG2≳, where <RG2≳ denotes the mean square radius of gyration of the ring. To solve the interacting polymer problem, the methods of renormalized field theory are applied directly to Fixman’s cluster expansion. The results are obtained using the approximation of expanding in ε≡4−(dimension of space) and indicate that the self-repulsion has a greater influence on the large distance behavior of a ring polymer when compared with a linear polymer. In particular, we find that the radius of gyration ratio <RG2≳ring/<RG2≳ line is a universal quantity and to first order in ε is equal to 0.568. For ideal polymers, the ratio is known to be 0.5.
Experimental evidence for vibrational coupling between NO molecules adsorbed on adjacent sites on Pt(111)
Authors: Severson Mark W. , Overend John
Published: February 2003

Infrared spectroscopic experimental evidence has been obtained supporting the idea that NO molecules adsorbed on adjacent sites on a Pt(111) surface are vibrationally coupled. The spectra are inconsistent with a multiple site model or a dimer which have been previously been used to account for the multiple absorption features found in this system.
Single rotational lifetimes of formaldehyde in a hypersonic jet
Authors: Henke W. E. , Selzle H. L. , Hays T. R. , Schlag E. W. , Lin S. H.
Published: February 2003

There has been a question of whether or not rotational effects should generally manifest themselves in a radiationless transition. Lifetimes of single rovibronic levels of formaldehyde in a hypersonic jet are here presented. These show a clear rotational effect, depending both on J and K. This two-dimensionality of the effect obeys general rules derived in the accompanying paper. It is concluded, at least for formaldehyde, that rotational effects are real and explainable in terms of a general theoretical model, and not always a result of the vagaries of particular resonances.
Computational approach to the Green function in reactive scattering
Authors: Shoemaker Curtis L. , Wyatt Robert E.
Published: February 2003

A technique for calculating the reduced multichannel Green function for 3D symmetric atom/diatom reactions is presented. This technique is based on a new method of integrating the close-coupled equations which preserves the Hermitian character of the kinetic energy operator within integration steps. Using this Green function technique, source point boundary conditions for the Green function can be applied for all source points by inverting a single matrix. A series of numerical results for a model reactive system are presented and discussed.
Polyatomic canonical variational theory for chemical reaction rates. Separable-mode formalism with application to OH+H2→H2O+H
Authors: Isaacson Alan D. , Truhlar Donald G.
Published: February 2003

A formalism for the application of variational transition-state theory and semiclassical vibrationally adiabatic transmission coefficients to bimolecular reactions involving an arbitrary number of atoms is presented. This generalizes previous work on atom–diatom reactions. We make applications in this paper to the reactions OH+H2→H2O+H and OH+D2→HDO+D using the Schatz–Elgersma fit to the Walch–Dunning ab initio potential energy surface. For both reactions we find large differences between conventional and variational transition-state theory and large effects of anharmonicity on the calculated rate constants. The effect of reaction-path curvature on the calculated transmission coefficients and rate constants is also large. The final calculated values of the kinetic isotope effects are in good agreement with experiment at high temperature but too large at room temperature.
Measurements of temporal and spatial sequences of events in periodic precipitation processes
Authors: Kai Shoichi , Müller Stefan C. , Ross John
Published: February 2003

A series of new experiments on Liesegang ring (or band) formation is presented which is concerned with the temporal and spatial evolution of the process of structure formation. We have chosen NH4OH and MgSO4 to form rings of Mg(OH)2 precipitate in a gelatin gel, as well as KI and Pb(NO3)2 for periodic precipitation of PbI2 in an agar gel. A temporal sequence of events during the entire period from the start of a Liesegang experiment in a test tube to the completion of the final ring pattern has been determined at many locations in the tube by visual observations and by measurements of transmitted light, of scattered light, of deflection of the transmitted light beam, and of gravity effects. After diffusion of one electrolyte into the gel medium containing the second electrolyte results in an ion product larger than three times the solubility product, at any and all points in space, we observe the onset of homogeneous nucleation of colloidal particles by a steplike increase of the index of refraction. The colloid concentration and the particle number density at the nucleation site are estimated to be 10−2 mol/l and 1015 to 1016 cm−3, respectively. Nucleation is followed by the growth of colloidal particles which gives rise to distinct light scattering (turbidity). Both nucleation and colloid formation take place in space continuously; the fronts of these phenomena move through the system and obey a simple diffusion law. A substantial time interval after their passage, there arises a localized gradient of the index of refraction at the prospective ring positions which indicates onset of structure formation by means of a focusing mechanism. While the localized gradient becomes more pronounced and narrower in space, the turbidity in the regions on either side of the ring location decreases, which indicates a depletion in colloidal material in the neighboring zones. Eventually, a sharp band of visible precipitate appears, which is clearly separated from the preceding ring. We conclude that the ring formation is a postnucleation phenomenon in that structure arises from a spatially continuous region of colloid a long time after nucleation has occurred, and propose that it is associated with the autocatalytic growth of colloidal particles. The location of rings is not determined by the spatial pattern of nucleation and colloid deposition as predicted by the Ostwald–Wagner–Prager theory. Our conclusions are supported by experiments on the influence of gravity on the ring locations, which provide evidence for the existence of colloidal particles of several hundred angstroms in size for a substantial fraction of the time required for the formation of a visible structure.
ESR in quasi-one-dimensional planar ferromagnet TMNB
Authors: Shimizu Masafumi , Ajiro Yoshitami
Published: February 2003

ESR measurements at the X band and the Q band were made on a quasi-one-dimensional planar ferromagnet (CH3)4NNiBr3 (TMNB) in both paramagnetic and three-dimensionally ordered phases. A new resonance associated with the spin motions in ferromagnetic chains was found. This resonance is characterized by an isotropic resonance field and a maximum intensity at 5 K. The resonance fields of the other observed signals show a large out-of-plane anisotropy as well as a distinct sixfold in-plane anisotropy with the symmetry axes deviated from the hexagonal axes by 18°. The signals were assigned to the resonance modes in the spin-floplike phase and the ferromagnetic one. These signals were found to be truncated by the magnetic phase transition in the external magnetic field accompanying a prominent hysteresis. The resonance signal of the spin-floplike phase was found to survive even above the three-dimensional antiferromagnetic transition temperature TN. These results are discussed on the basis of a phenomenological model.
An electron impact investigation of the 3p-Rydberg transitions of acetone
Authors: Doering J. P. , McDiarmid Ruth
Published: February 2003

High resolution (15 meV), gas phase, electron impact energy loss spectra of acetone, and acetone-d6 measured as a function of incident energy and scattering angle have been used to study the anomalously weak 7.4 eV 3p-Rydberg transition in acetone. Assignments made on the basis of isotope shifts and differential electron scattering cross sections show that the weak transition observed optically and in the high energy electron impact spectrum is a forbidden transition to the out-of-plane 3p-Rydberg orbital. The band system is built on a vibronically allowed false origin enabled by the ν23 (CO bend) vibration. The analogous transition in the less symmetric molecule methyl ethyl ketone was observed to be optically allowed. All observed bands could be assigned to the one electronic transition to the out-of-plane 3p-Rydberg orbital. The other two 3p-Rydberg transitions do not appear to be active in acetone or methyl ethyl ketone. An unusual feature of this investigation was the experimental investigation of the relative differential scattering cross sections of both true and false vibronic origins within a single electronic transition. The high energy resolution allowed isotopic substitution, a traditional technique of optical spectroscopy, to be used to establish assignments in an electron impact experiment.
Canonical unified statistical model. Classical mechanical theory and applications to collinear reactions
Authors: Garrett Bruce C. , Truhlar Donald G.
Published: February 2003

We present a canonical-ensemble version of the unified statistical model and we apply it to calculate classical-mechanical thermal-rate constants for 11 collinear reactions of the type A+BC→AB+C. The results are compared to accurate classical dynamics. The canonical unified statistical results are always more accurate than variational transition state theory at high enough temperature, but in two cases they significantly overestimate the recrossing corrections at low and medium temperatures.
Resolvent operator approach to many-body perturbation theory. III. Applications
Authors: Banerjee Ajit , Mukherjee Debashis , Simons Jack
Published: February 2003

The resolvent-based closed- and open-shell MBPT developed in the previous papers have been applied for the calculation of ionization potentials (I.P.), electron afinities (E.A.), excitation energies (E.E.), and correlation energies (C.E.) of several prototype atomic and molecular systems. The calculations for I.P., E.A., and C.E. have been performed though third order and the E.E.’s have been calculated through second order. The results presented here are intended to illustrate the utilization of our new MBPT technique and to permit us to compare and check our results with those of other workers who have calculated the above properties using different methods.
Quantum effects on the temperature dependence of surface tension of simple liquids
Authors: Sinha Dipen N. , Semura J. S. , Brodie L. C.
Published: February 2003

An equation of general applicability is proposed to describe the surface tension of simple liquids over an extended temperature range. This equation incorporates the quantum effects on the exponent μ, which characterizes the temperature dependence of surface tension. Far from the critical region, μ decreases with increasing de Boer parameter and appears to reach a constant value μ≃1 for He4 and He3. It is pointed out that for quantum liquids μ crosses over to the nonquantum mechanical value of μ≃1.28 as the critical point is approached. The surface tension and its temperature dependence are predicted for hydrogen isotopes such as T2, DT, D2, HT, and HD.
Quantum beat phenomena in the fluorescence decay of the C̃(1B2) state of SO2
Authors: Sharfin Wayne , Ivanco Michael , Wallace Stephen C.
Published: February 2003

The first observations of quantum beat phenomena in the resonance limit of a sparse density of coupled levels in a triatomic molecule are reported.(AIP)
The free energy of vacancy pairs in the cubic close-packed lattice
Authors: Cook Robert , McGeehan Gerard
Published: February 2003

The configurational free energy change associated with the introduction of pairs of vacancy defects into a cubic close-packed lattice with nearest neighbor harmonic interactions is calculated by lattice dynamics techniques in the classical high temperature limit. A comparison is made with the cell cluster calculations of Garza and Huckaby. (AIP)
Chlorine K x-ray absorption spectra from CrCl3 ⋅ 6H2O and FeCl3 ⋅ 6H2O
Authors: Muramatsu Shinji , Sugiura Chikara
Published: February 2003

Chlorine K x-ray absorption spectra are reported in CrCl3 ⋅ 6H20 and FeCl3 ⋅ 6H20 crystals. A new feature in the Crd3 ⋅ 6H20 spectrum the splitting of 3d levels of Cr3+ ion in the crystal field of CrCl3 ⋅ 6H20. The white lines in the spectra are discussed. (AIP)
Semiempirical e-N2 elastic scattering cross sections from 5 eV to 1 keV
Authors: Ganas P. S. , Green A. E. S.
Published: February 2003

Elastic scattering of electrons from molecular nitrogen has been represented by empirical analytic forms in many calculations of the spatial aspects of electron energy deposition. In this work, elastic scattering of electrons from molecular nitrogen is discussed in terms of phenomenological independent particle potential models which have a few adjustable parameters. Numerical computations are performed for a spheroidal and a spherical potential. By suitable adjustment of the potential parameters, both models accurately reproduce the experimental differential cross sections for incident electron energies in the range 5 eV to 1 keV. The potential parameters are found to be strongly energy-dependent at low energies, and to saturate at higher energies. The integrated cross sections are in reasonable agreement with experiment.
The Raman spectrum of solid hypofluorous acid HOF
Authors: Kim Hyunyong , Appelman Evan H.
Published: February 2003

The Raman spectra of solid HOF, DOF, and an HOF/DOF mixture have been measured. Two of the three internal vibrations (the O–F and O–H stretches) were seen, and they coincide with the bands previously found in the infrared spectrum of the solid. Six low frequency intermolecular bands found in the infrared have been interpreted in terms of a hydrogen-bonded structure consisting of planar zigzag chains, similar to the chains that constitute the structure of solid HF.
Spectroscopic and thermodynamic study of the conformational properties and torsional potential functions of methacryloyl fluoride
Authors: Durig J. R. , Brletic P. A. , Church J. S.
Published: February 2003

The infrared (3500–40 cm−1) and Raman (3500–10 cm−1) spectra have been recorded for the gaseous and solid phases of methacryloyl fluoride. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. The asymmetric potential function for internal rotation of the O = C–F top has been determined from far infrared data, and the following potential constants have been evaluated: V1 = 257±4; V2 = 1582±6; and V3 = 173±3 cm−1. From these data, the s-trans conformer was determined to be the predominant rotamer at ambient temperature with the other conformer being the s-cis; the enthalpy difference between the s-trans and s-cis conformers is 430 cm−1 (1230 cal/mol). This value compares well with the value of 444 cm−1 (1270 cal/mol) obtained for the liquid from a variable temperature study of the Raman spectrum. The methyl torsional barrier was also calculated from the far infrared data to be 1.77 kcal/mol. A vibrational assignment and values for the thermodynamic functions of gaseous methacryloyl fluoride are presented.
Structure-reactivity correlations in state-to-state chemistry
Authors: Agmon Noam
Published: February 2003

The idea that a transiton state is a ’’mixture’’ of reagents and products, previously used in the discussion of thermal structure-reactivity correlations (’’Bro/nsted plots’’), is now utilized to yield a simple, one-parameter analytical expression for the relative rate constants of state-to-state reaction series (i.e., where the initial or final internal state varies). The ’’weights’’ of reactants and products are determined by a maximal entropy or ’’thermodynamic-like’’ procedure. However, instead of using these weights to determine the free energy of activation, they are used directly in a novel statistical model for the reaction probability. The resulting equation is a generalization of the ’’exponential gap’’ law, which obtains when the parameter is very small. We demonstrate the utility of our correlation for both inelastic (energy-transfer) and reactive v to v′ processes.
Stabilization calculations of resonance energies for chemical reactions
Authors: Thompson Todd C. , Truhlar Donald G.
Published: February 2003

Resonance energies for chemically reactive systems are computed from square-integrable wave functions, using both SCF and CI trial functions. We consider three mass combinations (H+FH, H+H2, and H+MuH) and compare to accurate scattering calculations for model potential energy surfaces.
Collisional intramultiplet relaxation of Cd(5s5p 3P0,1,2) by alkane hydrocarbons
Authors: Breckenridge W. H. , Malmin O. Kim
Published: February 2003

Very rapid collisional intramultiplet relaxation of the intial distribution of Cd(3P0,1,2) quantum states produced in the process Cd(1P1)+ RH → Cd(3P0,1,2) + RH, where RH are the alkane hydrocarbons, has been observed. This relaxation has been characterized by pulsed laser excitation of Cd(1P1) and determination of Cd(3P2,1,0) relative populations at short time delays using laser-induced fluorescence. The population of the Cd(3P1) state was also monitored by time-resolved fluorescence at 3261 Å. It was shown that not only are the cross sections for collisional conversion of Cd(3P2) to Cd(3P1) or Cd(3P0) quite large, but that the Cd(3PJ) states are produced with substantial amounts of translation energy in the Cd (1P1)-alkane deactivation process, thus increasing the effective Cd (3P0,1,2) collision frequency at short times. Using kinetic simulation techniques, lower limits were estimated for the cross sections for intramultiplet relaxation of Cd (3P2) by several alkane hydrocarbons. Analysis of Cd(3P1) fluorescence data at longer delay times, where translational equilibrium had been established, allowed the determination of cross sections for intramultiplet relaxation of Cd(3P1) to Cd(3P0) by the alkanes studied. The magnitudes of the cross sections are discussed within the framework of the Baylis–Krause theory of electronic-to-rotational energy transfer originally developed to explain the intramultiplet relaxation of Cs(2P3/2) by the isotopic methanes.
The measurement of tunnel states in solid CH3NO2 and CD3NO2
Authors: Alefeld B. , Anderson I. S. , Heidemann A. , Magerl A. , Trevino S. F.
Published: February 2003

Inelstic neutron scattering is used to measure the tunnel splitting of the ground state of CH3NO2 and CD3NO2. (AIP)
Brillouin scattering near the low-temperature glass transitions of polymethyl methacrylate
Authors: Kato E.
Published: February 2003

The temperature dependence of the Brillouin shift of polymethyl methacrylate is reported. The low-temperature glass transitions, the β,γ and δ, transitions seem to alter the slope of the curve of Brittouin shift plotted against the temperature gradient. (AIP)
17O NMR in liquid O2
Authors: Dundon Jeffrey M.
Published: February 2003

The NMR signal of 17O was found in liquid oxygen. The shift in field due to the paramagnetism of O2 was measured as a function of temperature between 55 and 80 K. A value for the hyperfine splitting is derived. Measured T2 is compared with theory.
The scavenger problem in diffusion-controlled recombination
Authors: Raaen S. , Hemmer P. C.
Published: February 2003

A systematic and analytic treatment of the recombination probability for a pair of ions in the presence of a homogeneously distributed scavenger is presented. Results for both low and high scavenger concentrations are given for different ranges of the initial separations of the two ions. The low-density expansion corrects some previously published results, while the recombination probability for large scavenger densities is derived for the first time. Approximations, uniformly valid for all initial distances, are constructed and shown to be in excellent agreement with numerical results.
Magnetic measurements on ytterbium selenate octahydrate and the nature of its ligand field
Authors: Neogy D. , Nandi J.
Published: February 2003

The principal magnetic susceptibilities of the single crystal of ytterbium selenate octahydrate have been measured in the temperature range 90–300 K. A least squares fit of the Curie–Weiss law to χ̄ yields a negative paramagnetic Curie temperature, similar to an antiferromagnetic material. The site symmetry of the RE3+ ions in sulfates and selenates is discussed. A fairly good explanation of the observed data is obtained through an analysis with a crystal field (CF) of tetragonal symmetry. Some interesting thermal and hyperfine properties are also predicted. From the structural and magnetic studies of RE sulfates and selenates it is concluded that the CF in these salts is of tetragonal symmetry at least to the first approximation.
Phase behavior near the critical point of a binary liquid mixture in the presence of isotopic exchange
Authors: Knobler Charles M. , Scott Robert L.
Published: February 2003

The measurements by Gulari, Chu, and Woermann [J. Chem. Phys. 73, 2480 (1980)] of phase-separation temperatures and the intensity and angular dependence of scattered light for mixtures of isobutyric acid, D2O, and H2O are discussed in terms of a square-prism phase diagram appropriate for mixtures that can undergo metathesis. In this representation, tie lines are straight lines nearly parallel to one of the axes and experimental paths are easily visualized. The conditions required for exponent renormalization are reviewed and it is argued that the extent of renormalization observed by Gulari et al. in the two-phase region is suprisingly large.
Existence of the dielectric constant in fluids of classical deformable molecules
Authors: Ramshaw John D.
Published: February 2003

The existence of the dielectric constant ε is investigated for fluids composed of classical deformable (polarizable) molecules. The development is based upon generalized functional-derivative relations which involve joint distributions in molecular positions rk and dipole moments μk. Sufficient conditions for the existence of ε are expressed in terms of the generalized direct correlation function c(12) = c(r1, μ1; r2, μ2). It is found that ε exists if −kTc(12) depends only on relative positions and dipole moment directions (in addition to ‖μ1‖ and ‖μ2‖), and becomes asymptotic to the dipole–dipole potential at long range. An expression for ε in terms of a short-ranged total correlation function h0(12) emerges automatically from the development. An expression for ε in terms of c(12) is also derived. The latter expression involves an inverse kernel in (‖μ1‖, ‖μ2‖) space. The case of rigid polar molecules is reconsidered as a special case of the present formulation.
Thermochemical properties of the gaseous lower valent fluorides of uranium
Authors: Lau K. H. , Hildenbrand D. L.
Published: February 2003

High temperature gaseous equilibria involving the lower-valent uranium fluorides UF, UF2, UF3, and UF4 were studied by mass spectrometry, and reaction enthalpies and entropies with estimated uncertainties of ±2 kcal/mol and ± 2 cal/deg mol were derived solely from the temperature coefficients of reaction equilibrium constants. These results yield the following bond dissociation energies at 298 K in kcal/mol: D°(F3U–F) = 148.2; D° (F2U–F) = 149.0; D° (FU–F) = 136.5; and D° (U–F) = 157.5. The sum of these values is compatible with the heat of atomization of UF4(g) evaluated from independent sources. A value of D°(F3U–F) derived from electron impact measurements agrees well with the equilibrium data. The reaction entropy data indicate that the electronic entropies of UF, UF2, and UF3 are comparable to that of atomic uranium in the same temperature range, and provide a basis for estimating the total thermodynamic functions of these species. Experimental entropies obtained for UF4 indicate the likelihood of a distorted tetrahedral structure of effective C2v symmetry. The results provide sufficient information for predicting the equilibrium composition of the gaseous U–F system over a wide temperature range.
Electron motion in high-pressure polar gases: NH3
Authors: Christophorou L. G. , Carter J. G. , Maxey D. V.
Published: February 2003

Drift velocities w for slow electrons in NH3 vapor have been measured and are reported as a function of the density-reduced electric field E/N (⩽24×10−17 V cm2), density N (2.43–292×1018 molecule cm−3), and temperature T (300–650 K). The w decreases with increasing N considerably and this decrease varies with T; for a fixed N it is higher the lower the T. Use is made of the T- and N-dependence of w to assess the role of the various processes which delay the electron drift. The density range above ∼2.5×1019  molecules cm−3 seems to represent the transition from the free (or quasifree) to the localized (anionic) electron state. The number density NL at which complete electron localization occurs, has been estimated at various T. At T=300 K, NL≃3.3×1020 molecule cm−3 or ∼0.01 g cm3. Estimates have also been made of the binding energy of the electron to the trapping species (possibly NH3 clusters) which, depending on T, range from 0.11 to 0.15 eV.
Electrodynamics at a metal surface. II. Fresnel formulas for the electromagnetic field at the interface for a jellium model within the random phase approximation
Authors: Maniv Tsofar , Metiu Horia
Published: February 2003

We compute the electromagnetic fields generated at a vacuum–metal interface by incident radiation. We use a jellium model and the random phase approximation. The validity of the Fresnel equations at small distances from the surface is discussed. Numerical values for the continuous variation of the electric field vector through the interface are presented. Our main concern here is to illustrate the effects of the nonlocality of the dielectric response and of the continuous variation of the response function across the interface on the electrodynamic properties of the system.
Effects of polydispersity on fluorescence quenching in micelles
Authors: Almgren M. , Löfroth J. -E.
Published: February 2003

The effects of polydispersity on fluorescence quenching in micelle systems are discussed theoretically. Predictions are tested on computer generated fluorescence decay data for quenching in polydisperse micelle systems. It is shown that the estimated parameters, i.e, aggregation numbers and rate constants, are highly dependent on the micelle size distribution, and on the dynamic properties of the solubilizate–micelle system. Two extreme cases are considered: a static one, where no size changes of the micelles occur during the residence time, and a dynamic one where very large size variations take place. In the static case, the estimated aggregation number will decrease with quencher concentration from the weight average aggregation number in the limit of zero quencher concentration. In the dynamic case, the number average aggregation number is obtained, independent of quencher concentration. The initial decay constant contains information about the aggregation numbers, and in the generated data, this could be used to indicate the presence of polydispersity. Data from a number of experiments with the single photon counting technique are presented and analyzed according to the presented theory.
NMR observation of the swelling process of polydimethylsiloxane networks. Average orientational order of monomeric units
Authors: Cohen-Addad J. P. , Domard M. , Herz J.
Published: February 2003

The swelling process of several polydimethylsiloxane gels was observed from the relaxation process of the magnetization transverse component of protons bound to elementary chains. Polymeric gels were studied in equilibrium with solvent vapor, using chloroform. A model of progressive swelling process from the dry gel to the equilibrium with pure solvent liquid is proposed from observed elementary chain properties. At small swelling degrees, gels behave like strongly entangled chains in concentrated solutions; then, elementary chains are desinterspersed and a packing condition may be applied from a characteristic swelling degree to equilibrium swelling. In this concentration range, gels swollen by different solvents behave the same way at a given swelling degree. Trapped entanglements are perceived. All these properties are derived from residual dipolar interactions associated with average orientational order of monomeric units induced by chain elongation. This residual energy is shown to be proportional to (r/N)2, with r the end-to-end vector and N the number of links of a chain. The C theorem proposed by De Gennes is extended to NMR properties. It is clearly shown that NMR observed on a chain segment may be sensitive to both its overall dimensions (30 Å) and its internal isomerization properties.
Single collision gas-surface vibrational energy transfer in reactive systems. Variation of initial energy distribution
Authors: Arakawa R. , Kelley D. F. , Rabinovitch B. S.
Published: February 2003

The initial vibrational energy distribution of molecules that collide with a hot surface has been varied. The effect of the variation on the collisional reaction probability (Pc) has been studied under single collision conditions. These experiments provide a more sensitive test of the relative suitability of various analytical forms for the collisional transition probability matrix P than has been achieved previously in earlier VEM experiments. The reaction system is the isomerization of cyclobutene to 1, 3-butadiene. A seasoned fused quartz surface was used over the temperature range Tr = 600–900 K. Variation of the initial vibrational energy population vector of cyclobutene molecules was made by change of their initial temperature Tc in the range 273–620 K. The experimental collisional efficiency β1 declined from 0.31 to 0.013 over the combination temperature ranges Tr, Tc = 600,500 to 900,273. Stochastic models of the vibrational transition probability were fitted to the data and provided values for the average amount of energy (<ΔE′≳E0) transferred from the hot molecules in a down transition from the threshold energy level E0; Gaussian or Boltzmann exponential forms of P prove to be the most suitable to fit the data. Calculated values, <ΔE′≳E0 on the basis of a Gaussian function model for P declined from 5600 to 3700 cm−1 with increase in the surface temperature from 600 to 900 K.
Effect of intensity on fragment internal state distributions in the infrared multiphoton dissociation of vinyl cyanide
Authors: Miller Charles M. , McKillop John S. , Zare Richard N.
Published: February 2003

The technique of laser induced fluorescence has been used to observe the C2 and CN fragments produced in the infrared multiphoton dissociation of vinyl cyanide CH2 = CHCN in a low pressure flowing gas. The rotational distributions of the lowest vibrational level of the C2 fragment were found to be well characterized by temperatures. As was previously observed for the CN fragment of this parent molecule, a distinct decrease in the values of these temperatures is seen to occur during the photolysis laser pulse. This is interpreted as the result of an intensity effect in the later stages of the infrared pumping process. Additional information is also presented on the behavior of the CN radical. Modeling calculations within the framework of the energy-grained master equation support this interpretation.
Quenching of metastable Ar, Kr, and Xe atoms by oxygen-containing compounds: A resonance fluorescence study of reaction products
Authors: Balamuta John , Golde Michael F.
Published: February 2003

Quenching of electronically excited Ar, Kr, and Xe(3P0,2) atoms by diatomic and triatomic oxygen-containing compounds has been studied by atomic resonance fluorescence in a discharge-flow system at room temperature. Absolute branching ratios for molecular fragmentation in the quenching reactions have been obtained, showing that this channel is dominant in many cases. While single R–O bond cleavage is usually the favored process, cleavage of both bonds of H2O occurs in nearly 50% of quenching collisions with Ar*, and evidence is obtained for analogous atomization of NO2 and SO2 by Ar*. Emission by electronically excited fragment species has been found to be mostly weak; thus, dissociative excitation is a minor channel except for the reactions of Ar* with N2O and H2O.
The vibrational relaxation of NO(v = 1–7) by O2
Authors: Green B. D. , Caledonia G. E. , Murphy R. E. , Robert F. X.
Published: February 2003

Highly vibrationally excited NO(v = 1–10) has been created by irradiation of N2/trace O2 mixtures with 36 keV electrons. The resulting spectrally-resolved time histories of the NO fundamental vibration/rotation band have been analyzed to determine the room temperature rate constants for the processes NO(v)+O2→NO(v−1)+O2, v = 1–7. The rate constants increase monotonically with v.
Reaction of Cr+, Mn+, Fe+, Co+, and Ni+ with O2 and N2O. Examination of the translational energy dependence of the cross sections of endothermic reactions
Authors: Armentrout P. B. , Halle L. F. , Beauchamp J. L.
Published: February 2003

Reactions of Cr+, Mn+, Fe+, Co+, and Ni+ with O2 and N2O to yield metal oxide ions are examined using an ion beam apparatus. Reaction cross sections σ as a function of ion translational energy E are reported. With one exception, Fe++N2O, the cross sections exhibit an energy threshold Eo. Several models are used to interpret the excitation functions for the O2 reactions and it is concluded that the classical line-of-centers form σ α (1–Eo/E) is most useful. Bond energies derived in this manner are D°(CrO+) = 3.45±0.1 eV, D°(MnO+) = 2.48±0.1 eV, D°(FeO+) = 3.01±0.1 eV, D°(CoO+) = 2.76±0.1 eV, and D°(NiO+) = 1.95±0.1 eV. Since these bond energies are all greater than D°(N2–O) = 1.7 eV, the observation of energy thresholds for the reactions with N2O are surprising. These results are explained in terms of a qualitative view of the electronic potential energy surfaces involved.
A perturbative variational approach to a multireference CI
Authors: Bendazzoli G. L. , Fano G. , Ortolani F. , Palmieri P.
Published: February 2003

A previously proposed perturbative variational CI method has been extended to the case of a many-dimensional reference space, where all the configurations have a common core plus two valence electrons. Compared to ordinary CI, the Hamiltonian and overlap matrices are extremely reduced in dimension. All matrix elements have been obtained by means of diagrammatic techniques, and a Fortran program adapted to medium–large orbital bases has been implemented. The method has been applied to ethylene in the ground state equilibrium geometry (D2h), giving about 97% of the total correlation energy of a SDCI calculation with the same AO basis. It has also been applied to 90° twisted ethylene (D2d), where a two-dimensional reference space is needed; the computed value of the ground state rotational barrier is about 67 kcal mol−1.
The use of model potentials in molecular calculations. I
Authors: Sakai Y. , Huzinaga S.
Published: February 2003

The model potential method proposed by Bonifacic and Huzinaga in 1974 is unique among various effective core potential methods in that it is capable of producing the pseudovalence orbitals with the proper nodal structure. This unique feature of the method has now been fully exploited and implemented by improving the process of determination of the model potential parameters and the valence orbital basis functions. The present article includes a general exposition of the method and the application to a number of atoms: Li–Ne, Na–Ar, K, Ca, Ni, Cu, Br, and Pd.
The use of model potentials in molecular calculations. II
Authors: Sakai Y. , Huzinaga S.
Published: February 2003

The model potential method is applied to CO, HCl, P2, Cl2, SH2, Cu2, Br2, Ni(CO)4, and Pd(CO)4. The results are generally very satisfactory. Reduction of computing cost is substantial for molecules containing heavy atoms.
The hydrogenic limit of many-electron atoms
Authors: Tal Yoram , Bartolotti Libero J.
Published: February 2003

The properties of many-electron atoms in the limit of infinite nuclear charge Z and a constant degree of ionization 1−N/Z (N being the total number of electrons) are investigated. The hydrogenic limit of such atoms, defined as a system of N noninteracting electrons moving about a nucleus of charge Z, is studied in detail. In addition to the well-known formulas for the energy components we derive closed form expressions for all the moments of the charge density ∫dτrkρ(r) where k⩾−1. These results serve as a starting point for the comparison of two density functional theories: the Thomas–Fermi (TF) theory and the local density functional (LDF) theory. It is shown that in both cases the energy components, as well as the moments of the charge density, converge to the hydrogenic limit as N/Z→ 0. We further compare the TF and LDF predictions for the total energy E over the whole range 0⩽N/Z⩽1. It is shown that LDF may closely approach the TF theory for an appropriate choice of the electronic repulsion parameter.
Low-temperature thermoluminescent behavior of 5′dCMP single crystals
Authors: Cooke D. Wayne , Close David M.
Published: February 2003

Thermoluminescence (TL) and emission spectra studies of x-irradiated single crystals of deoxycytidine-5′-phosphate monohydrate (5′ dCMP) were conducted in the interval 10–300 K. Two intense glow peaks were observed at 42 and 74 K with additional weaker peaks at 112, 140, and 200 K. By applying the Randall–Wilkins theory of glow curves to our data we obtained thermal activation energies (E) and frequency factors (s) characterizing each of the glow peaks, except the one at 200 K—it was of insufficient intensity. The parameters are: 42 K (E = 0.032±0.009 eV, s = 316 s−1); 74 K (E = 0.095±0.035 eV, s = 105 s−1); 112 K (E = 0.080±0.02 eV, s = 20 s−1); and 140 K (E = 0.12±0.04 eV, s = 56 s−1). As a check on the validity of the Randall–Wilkins theory we generated theoretical glow curves using the experimental parameters of the 42 K peak. Excellent agreement between the two glow curves was found. Typical spectral emission from each glow peak consists of band emission exhibiting maxima at 428 and 463 nm. We attribute these peaks to radiative electronic transitions from the first excited singlet and triplet states to the ground state (S1→S0+hν and T1→S0+hν). Based upon our experimental results we present an energy-level diagram depicting the TL process in single crystal 5′dCMP in the interval 10–300 K. Finally, we discuss possible correlations between the appearance of TL glow peaks and the thermal decay of radiation-induced radicals as observed by ESR and ENDOR.
Collisional quenching of Pb 6p2 3P1 and 6p2 3P2 metastables by ground state Pb atoms
Authors: Reiser C. , Djeu N. , Burnham R.
Published: February 2003

Collisional quenching of the two lowest Pb atom metastable levels, 6p2 3P1 and 6p2 3P2, has been studied at Pb vapor densities of (1–20)×1016 cm−3. The metastable atoms were created in a heat pipe oven by stimulated Raman scattering using an XeCl laser pump. Their subsequent decay was then probed with tunable, single-frequency UV on the 266.3 and 261.4 nm Pb resonance lines. The observed rate constants are 2.0×10−13 cm3 sec−1 for 3P1 and 3.2×10−13 cm3 sec−1 for 3P2.
The infrared laser spectrum of the CN radical in its ground state
Authors: Davies P. B. , Hamilton P. A.
Published: February 2003

Ten vibration–rotation transitions in the fundamental band of the CN radical in its ground 2𝒥+ electronic state have been measured in absorption using a tunable infrared diode laser. The observed frequencies are in good agreement with the values derived from optical emission spectroscopy. Splittings arising from electron spin–rotational fine structure are resolved in some of the transitions and agree with values calculated from the spin–rotation constants measured in laboratory microwave studies.
Green’s functions and optical line shapes of a general two-level system in the strong electronic coupling limit
Authors: Friesner Richard
Published: February 2003

An approximate analytic form for the time-dependent one-exciton Green’s function of a system with two excited electronic states coupled to a single harmonic vibrational mode is derived. The Fourier transform of this is used to calculate optical line shapes; these are compared with results obtained from exact numerical methods and give excellent agreement. A discussion of the basic ideas of the formalism is given, and possible extensions of this work to more complicated systems (e.g., multimode vibronic coupling problems) are mentioned.
Resonance Raman spectra of some radiolytically prepared halogen derivatives of p
a
r
a-benzosemiquinone radical anion
Authors: Tripathi G. N. R. , Schuler R. H.
Published: February 2003

The resonance Raman spectra have been obtained on radiolytically and chemically prepared halogen derivatives (chloro-, bromo-, 2.5 dichloro-, tetra chloro-, and tetra bromo-) of p-benzosemiquinone radical anion. Excitation is in the moderately intense absorption band at 430–460 nm. All Raman spectra show a strongly resonance enhanced and polarized line corresponding to a vibrational frequency of 1590–1620 cm−1 which is assigned to the Wilson phenyl mode 8a (CC stretch). A number of weaker lines are also observed and their assignment discussed. The electronic transitions in resonance are identified as 2B3g–2B1u (in D2h point group) in view of the resonance Raman band intensities. This supports the assignment by Harada based on ASMO CI calculations which has recently been in dispute.
Single crystal ESR study of x-irradiated thiophosphate O,O,O-triester of methyl β-D-ribopyranoside: Electron capture by the thiophosphate moiety
Authors: Hamerlinck J. H. H. , Schipper P. , Buck H. M.
Published: February 2003

X-irradiation of a single crystal of thiophosphate O,O,O-triester of methyl β-D-ribopyranoside at 77 K produces a σ phosphoranyl radical anion (2) by electron capture among secondary radicals resulting from bond scission. The ESR parameters of (2) in correlation with the x-ray analysis of its precursor establish a TBP structure with the unpaired electron in apical position. The results suggest that in irradiated nucleic acid polymers, electrons can be trapped by phosphorus giving rise to a phosphorus-centered radical which subsequently induces bond break by α or β scission generating thermodynamically more stable sugar and base radicals.
Laser excitation spectra and lifetimes of Pb2 and Sn2 produced by YAG laser vaporization
Authors: Bondybey V. E. , English J. H.
Published: February 2003

A new and very general technique, combining pulsed laser vaporization with laser induced fluorescence is described. The gas phase electronic spectra of Pb2 cooled to near 77 °K by liquid N2 are very simple and yield the vibrational constants for the ground state and two low lying electronic states. Some lifetime information is also obtained and preliminary observations of Sn2 spectra are reported.
A thermodynamics for a system under shear
Authors: Hanley H. J. M. , Evans Denis J.
Published: February 2003

A thermodynamics is introduced for fluids subjected to a constant shear. The theory is based primarily on the results of computer simulations using the technique of homogeneous shear nonequilibrium molecular dynamics applied to a system of 108 Lennard-Jones particles. It is supported qualitatively by the results of several authors for other systems. The shear rate γ enters explicitly into the description of the fluid: the equation of state is p = p(V,T,γ) and thermodynamic equation is dE = TdS −pdV+ζdγ, where ζ is a state function. Using the relations found previously to be valid for a wide range of γ: p = p0+p1γ3/2 and E = E0+E1γ3/2, the thermodynamics can be checked numerically for consistency and several consequences, such as stability criteria criteria, can be verified. The criteria indicate that phase changes are influenced by the shear rate when the system is subjected to the shear.
A numerical method for finding the concentrations of chemicals in equilibrium
Authors: Avery Leon
Published: February 2003

A new numerical method for solving the chemical equilibrium problem is described. It works by alternating projections of an estimate onto the set of all points representing systems at equilibrium and the set of all points consistent with conservation condtions. It is convenient to use and can handle large ill-conditioned systems quickly and accurately. It generalizes to nonideal solutions; however, it has only been tested for the ideal solution case as yet.
Computer studies of Brownian motion in a Lennard-Jones fluid: The Stokes law
Authors: Brey J. J. , Ordóñez J. Gómez
Published: February 2003

Molecular dynamics calculations have been carried out on a system of identical particles interacting through a Lennard-Jones potential containing a heavy test particle. It is shown that the autocorrelation function of the total force can be used to compute the friction constant, if an appropriate cutoff is introduced. In the limit of large mass and density, the test particle behaves as a Brownian particle, with a friction constant that is mass independent and obeys the Stokes law.
Theory of nematic systems of semiflexible polymers. I. High molecular weight limit
Authors: Ronca G. , Yoon D. Y.
Published: February 2003

A statistical theory of nematic systems has been developed for semiflexible polymers on the basis of a new wormlike model of chain statistics. This wormlike chain model closely represents the short-range statistics of real chains and allows the evaluation of the orientation-dependent configurational partition function, which replaces the rotational partition function employed in the classical treatments of nematic systems of rodlike particles. This theory has been applied to polyethylene (PE) and polytetrafluoroethylene (PTFE) chains in the bulk, and leads to the conclusion that PE chains form a stable isotropic melt (with its first order isotropic-nematic transition expected to occur around ∼75 K), whereas PTFE forms a stable nematic phase in the melt. Furthermore, the entropy changes accompanying the isotropic-nematic transitions of semiflexible polymers are predicted to be quite small, and the predicted order parameters at the transitions are not very high, falling in the range 0.4–0.7.
Short-distance monomer correlations in a self-repelling polymer chain
Authors: Witten T. A.
Published: February 2003

We calculate the amplitude of the large-wave vector scattering structure function S(q) of a long random coil in a good solvent, using field theory renormalization and expanding to first order in ε≡4- (dimension of space). This amplitude is some 35% smaller than that of a swollen Gaussian chain. This is consistent with nonrenormalization group theories and with experiment.