bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct partition function of the rigid diatomic rotor
Authors: Kilpatrick John E. , Kayser Richard
Published: February 2003

The direct and exchange partition functions for a rigid diatomic rotor are obtained via the density matrix. An integral representation which is suitable for finding convergent high temperature expansions is formulated by use of the transformation properties of theta functions. The convergent expansion for the direct partition function is shown to consist of the asymptotic Euler–Maclaurin series with each term corrected by a series of nonanalytic terms. The nonanalytic terms are of the form exp(−Nπ2/σ) and the entire expansion is rapidly convergent at high temperature.
Flow–drift tube measurements of H2O2+ reactions with H2O, NH3, NO, and CO and charge transfer of O2+ with H2O2
Authors: Lindinger W. , Albritton D. L. , Howard Carleton J. , Fehsenfeld F. C. , Ferguson E. E.
Published: February 2003

Rate constants have been obtained from thermal energy to about 1 eV mean relative kinetic energy for the exothermic reactions of H2O2+ with H2O, NH3, and NO and the endothermic reaction with CO. In addition, measurements of the charge-transfer reactions of O2+ with H2O2 and N2+ with H2O have been obtained over the same energy range. The proton-transfer reactions of H2O2+ with H2O2 and H3O2+ with H2O are qualitatively observed to be fast. The proton affinity of H2O2 is bracketed by these reactions to be 157±9 kcal/mole.
Study of a central force model for liquid water by molecular dynamics
Authors: Rahman A. , Stillinger F. H. , Lemberg H. L.
Published: February 2003

The simulation technique of molecular dynamics has been used to investigate a central-force model for liquid water at 22 °C and 1 g/cm3. In this model, the same atomic pair potentials are used both for intramolecular and intermolecular interactions. Atomic pair correlation functions and velocity autocorrelation functions have been computed. The results demonstrate that stable, nonlinear, vibrating molecules are present, and that they form a random hydrogen-bond network of the type usually attributed to water. These exploratory calculations suggest that small modifications in the central potentials VHH, VOH, and VOO would produce a more faithful representation of real water.
Quasiclassical trajectory calculations of He–LiF (001) diffraction scattering
Authors: Ray Charles J. , Bowman Joel M.
Published: February 2003

A quasiclassical trajectory method for describing elastic diffraction scattering of an atom from a crystal surface is presented and applied to the He–LiF (001) system. The results for a 20 meV, oriented 4He beam are compared with the recently reported quantum ones of Wolken and the semiclassical ones of Doll. The dependence of the specular scattering intensity on the initial beam orientation is calculated and compared with the quantum results of Wolken. It is concluded that the quasiclassical results are semiquantitatively accurate, only slightly less accurate than the uniform semiclassical results (without inclusion of complex-valued trajectories), but more accurate than the classical and primitive semiclassical results.
The temperature dependence of the NO–O chemiluminous recombination. The RMC mechanism
Authors: Golomb Dan , Brown J. H.
Published: February 2003

The temperature dependence of the NO–O chemiluminous recombination was redetermined in the 188–363 °K temperature and 0.1–1 torr pressure range. Using calibrated photometry, the photon emission rate was obtained absolutely. For 300 °K, and for the 400–800 nm spectral range, Ia0= (3.7±0.4) ×10−17 photons cm3 s−1. Combining the temperature dependence found in this work with previous results, the obtained best fit expression is Ia0(T) = (1.15±0.1) ×10−17(300/T)0.9e xp(350/T) photons cm3 s−1, which is applicable to the 170–1250 °K and 400–800 nm range. The strong negative temperature coefficient is indicative of the radical molecule complex RMC mechanism. It is shown that Ia0(T) has a temperature dependence similar to the equilibrium constant Kc(T) of the intermediary complex.
An empirical chemical shielding function for interacting atoms from direct inversion of NMR data
Authors: Jameson Cynthia J.
Published: February 2003

For two spherically symmetric molecules it is possible to directly determine the chemical shielding function σ (R) from the experimental values of the second virial coefficient of chemical shielding σ1(T) by inversion of the integral equation σ1(T) =4π ℱ∞0 σ (R )exp[−V (R)/kT]R2 dR. Various inversion methods are considered and applied to the xenon system yielding a chemical shielding function which, when integrated over all configurations, yields satisfactory agreement with experimental values of σ1(T).
Vibrational relaxation of the N2O ν1 mode by Ar, N2, H2O, and NO
Authors: Kung R. T. V.
Published: February 2003

The vibrational relaxation of the N2O ν1 symmetric stretch mode and the ν2 bending mode due to collisions with Ar, N2, and H2O were studied at room temperature using a laser fluorescence technique. The V–V equilibration time constants between the ν1 and ν2 modes were measured to be 0.38, 0.26, and 3.0×10−3 μsec⋅atm with Ar, N2, and H2O, respectively, as the collision partner. The ν2 V–T relaxation time constants of 12.1, 1.75, and 9.4×10−3 μsec⋅atm were measured, respectively, for collisions with Ar, N2, and H2O. In both relaxation processes H2O was found to be an extremely efficient relaxer. The effects of N2O–NO collisions were studied. The result suggested a fast V–V equilibration possibly due to the near resonance between the (11 1O) level of N2O and the first excited vibrational level of NO.
Isotopic and nonisotopic thermal diffusion factors from column measurements
Authors: Savirón J. M. , Santamaría C. M. , Carrión J. A. , Yarza J. C.
Published: February 2003

Experimental steady state separation data obtained in a concentric tube type Clusius–Dickel column for seven He–Ar mixtures, five Ne–Xe mixtures, and the isotopic natural Ne mixture at ?=340±5 K are presented. The results show that thermogravitational columns are able to furnish correct values for the thermal diffusion factors of the mixtures examined when any one of them is used as a calibration mixture.
ESR linewidth and bonding parameter studies of Cu2+ amino acid complexes
Authors: Misra B. N. , Sharma S. D.
Published: February 2003

Based on the theoretical developments by Roberts and Koski, bonding parameters have been calculated in case of copper (II) complexes of amino acids. Hyperfine linewidth studies of the complexes based on Kivelson’s development have been presented.
Spin projected extended Hartree–Fock calculations by direct minimization of the energy functional
Authors: Rosenberg M. , Martino F.
Published: February 2003

A practicable SEHF scheme for the treatment of electron correlation in systems for which large scale configuration interaction calculations are prohibitive is presented. A study is made of the electronic structures to which the SEHF method may be most profitably applied. In order to illustrate this study and to provide a numerical demonstration of the minimization techniques ab initio SEHF calculations on a number of ten electron systems are reported. These calculations were performed for the singlet ground states of Ne, HF, H2O, NH3, CH4, and cyclic H10.
Ordered spans of unrestricted and self-avoiding random-walk models of polymer chains. I. Space-fixed axes
Authors: Rubin Robert J. , Mazur Jacob
Published: February 2003

An N-step random walk on a cubic lattice is adopted as a model of a random polymer chain. The spans, or extents, of each random walk configuration in the principal lattice directions are arranged in order of magnitude, ξ3?ξ2⩾ξ1. In the case of the unrestricted random walk, the average values of the ordered spans 〈ξi,u〉 and 〈ξ2i,u〉, i=1, 2, and 3, are calculated analytically in the limit of large N. The limiting relative values of the first moments, 〈ξi,u〉 are 1.637 : 1.267 : 1; and the limiting values of the second moments 〈ξ2i,u〉 are 2.710 : 1,600 : 1. In the case of the restricted or self-avoiding walk, the corresponding average spans 〈ξi,r〉 and 〈ξ2i,r〉 are estimated for N?150 by using a Monte Carlo procedure. The same Monte Carlo procedure is used to estimate the values of 〈ξi,u〉 and 〈ξ2i,u〉 for N?1000. On the assumption that the rate of approach of the average ordered spans of the self-avoiding walks to their asymptotic forms is similar to the rate of approach of the average ordered spans of the unrestricted walks to their asymptotic forms, the following estimates are obtained for the ordered spans of the self-avoiding walks: 〈ξi,r(N) 〉=?i,rN0.61 for N≫1 and ?3,r : ?2,r : ?1,r =1.75 : 1.31 : 1. The relative values of the estimates of the second moments of these ordered spans for N≫1 are 〈ξ23,r〉 : 〈ξ22,r〉 : 〈ξ21,r〉 =3.08 : 1.71 : 1. A simple ellipsoidal model is analyzed in order to obtain estimates of the intrinsic spans of the two kinds of random walks. It is assumed that all random walks have the same intrinsic dimensions and form (ellipsoidal), but that their principal axes are oriented at random. The average ordered spans with respect to a set of orthogonal space-fixed axes of this randomly oriented ensemble of ellipsoids depend uniquely on the principal diameters of the ellipsoid (intrinsic spans). A procedure is devised to solve the inversion problem of determining the relative lengths of the principal diameters which correspond to a given set of relative ordered moments with respect to space-fixed axes. The relative values obtained for the principal diameters of the ellipsoid are 2.59 : 1.61 : 1 in the case of the unrestricted random walk and 3.05 : 1.77 : 1 in the case of the self-avoiding walk.
Mössbauer spectroscopy of hemoglobin model compounds: Evidence for conformational excitation
Authors: Spartalian K. , Lang G. , Collman James P. , Gagne Robert R. , Reed Christopher A.
Published: February 2003

Zero-field Mössbauer spectra of a model compound for hemoglobin, capable of undergoing reversible oxygenation, were recorded at various temperatures. A pair of peaks with temperature-dependent quadrupole splitting and linewidth were observed. The results have been interpreted in terms of a model which is consistent with previous x-ray studies and which provides for relaxation effects as the molecule assumes two possible conformational states. In terms of the proposed model, the two conformational states have been characterized by their energy separation and their respective electric field gradient tensors. The relaxation rate at each temperature has also been determined.
The stimulated Raman spectrum of water and its relationship to liquid structure
Authors: Sceats Mark , Rice Stuart A. , Butler J. E.
Published: February 2003

Stimulated Raman spectra (SRS) of H2O, D2O, H2O–D2O mixtures, and aqueous solutions of NaClO4 have been measured using a mode-locked, stabilized Nd glass laser operating in the TEM00 mode. Spectra with relatively narrow peaks were obtained in all cases, as predicted by the first order theory of SRS. Other effects (such as multiple peaks, broadened spectra, and shifted peaks), which have been interpreted as evidence for a mixture model of water, are reconsidered, and it is argued that they are either artifacts arising from modulation by stimulation in the hydrogen bond bending region or arise from disruption of thermal equilibrium in filaments due to the high electric fields present in the focused laser beam.
Three-dimensional natural coordinate asymmetric top theory of reactions: Application to H + H2
Authors: Elkowitz Allan B. , Wyatt Robert E.
Published: February 2003

A particular partitioning of the Hamiltonian in natural collision coordinates is shown to lead to the use of hindered asymmetric top basis functions to represent all rotational motion (triangle tumbling plus internal bending) during reaction. These functions (along with perturbed Morse oscillator functions) are used as an adiabatic basis for expansion of the scattering wavefunction. The theory is discussed for both one and two reaction path potentials. The close coupled equations for the translational wavefunctions are then solved for the H + H2 reaction at total angular momentum J = 0. Wavefunction bifurcation and matching at the reactant–product boundary surface is considered in detail. Finally, numerical results (reaction probabilities, probability conservation, detailed balance, energy dependence of reactive S-matrix elements, probability density, wavefunction real part, and flux) are presented and comparisons are made with other quantum mechanical, semiclassical, and statistical reaction studies.
Correlation function formula for the intrinsic viscosity of dilute polymer solutions
Authors: Felderhof B. U. , Deutch J. M. , Titulaer U. M.
Published: February 2003

The correlation function formalism for the intrinsic viscosity of polymers is studied. A controversy concerning the correct force to use in the momentum flux is resolved. It is shown that when the diffusion equation is used in the full configuration space of polymer segments the forces entering the momentum flux are purely mechanical and there is no entropic contribution. A comparison is made with Kirkwood’s theory of viscoelastic behavior. The correlation function expression we advocate is shown to yield the correct high frequency limiting behavior for the case of elastic dumbbells.
Dynamics of the reaction of F+ with D2
Authors: Wendell K. , Jones C. A. , Kaufman Joyce J. , Koski W. S.
Published: February 2003

The energy and angular distribution of the ionic products from the reaction F+(D2,D)FD+ were measured as a function of primary ion energy ranging from 0.7 to 12.5 eV in the laboratory system. At the low energies the distribution showed a high degree of symmetry although some forward peaking was detectable. At the higher energies the distribution was asymmetric relative to ±90° indicating that the reaction was proceeding by an impulsive direct mechanism. A study of the exoergicity as a function of projectile energy shows that the bulk of the exothermicity of the reaction is converted into vibrational energy in the product ion. Failure to observe the reaction F+(D2,FD)D+ was attributed to a violation of the spin and symmetry conservation rules.
Experimental and calculated electronic structure of gaseous CrO2F2 and CrO2Cl2
Authors: Jasinski Jerry P. , Holt Smith L. , Wood J. H. , Asprey Larned B.
Published: February 2003

The gas phase electronic absorption spectra of CrO2F2 and CrO2Cl2 have been measured in the visible, near ultraviolet regions. Interpretation has been made by comparison with a molecular orbital calculation for each molecule by the SCF-Xα-SW method. The calculated ground and excited states and observed electronic transitions correlate directly with those for the parent isoelectronic CrO2−4 and MnO−4 species.
Self-avoiding walks terminally attached to an interface
Authors: Whittington Stuart G.
Published: February 2003

We present some rigorous results on the asymptotic behavior of the numbers of self-avoiding walks terminally attached to an interface. In particular we show that the value of a particular limit for ’’tails’’ is the same as the value of the corresponding limit for ’’loops.’’ We also derive some rigorous bounds on the limiting behavior, for long walks, of the partition function of the system. Exact enumeration results for several lattices are interpreted as suggesting that a phase transition may occur from three dimensional behavior to two dimensional behavior and that the mean square length exponent may change discontinuously from 1.2 to 1.5 at this point.
Pseudorotational local mode participation in OH and OD(A 2Σ+) vibrational relaxation in a Ne lattice
Authors: Brus L. E. , Bondybey V. E.
Published: February 2003

Radiationless transitions within the A 2Σ+ state of OH and OD in a Ne lattice at 4.2 °K are observed. The radicals are substitutional impurities undergoing slightly perturbed free rotation [D. S. Tinti, J. Chem. Phys. 48, 1459 (1968)]. The local phonon relaxation time is ?10 nsec. Emission spectra show an intermediate strong coupling (or resonant mixing) occurring between rotational levels and lattice phonon levels. The v′=0 lifetimes are 582±10 and 565±10 nsec on OH and OD, respectively, with fluorescence quantum yields ≳0.90. The Lorentz–Lorenz dielectric model overestimates the vacuum to solid radiative rate increase by a factor of two. At high radical concentrations Förster transfer from OD(v′=0) to OH(v′=0) occurs. The vibrational relaxation rates are fast (4×104–4×105 sec−1), with higher rates in OH despite the larger vibrational energy gaps in OH. The rates are extremely sensitive to lattice defects and/or additional impurities causing small (?0.3 Å) red or blue shifts from the principal site spectra. The principal accepting modes appear to be pseudorotational localized modes. Defects appear to enhance relaxation by creating additional localized modes.
Analysis of pitch–concentration dependences in some binary and ternary liquid crystal mixtures
Authors: Bak C. S. , Labes M. M.
Published: February 2003

Utilizing a general equation in which pitch in a mixture of liquid crystals is a quadratic function of the number densities of component molecules of given molecular twisting powers, we treat two special cases: binary cholesteric mixtures and a ternary mixture of two cholesteric and one nematic compounds. Experimental data are shown to be adequately described by the equation over the entire concentration range.
Photodissociation of molecular beams of methylene iodide and iodoform
Authors: Kawasaki M. , Lee S. J. , Bersohn R.
Published: February 2003

Molecular beams of CH2I2 and CHI3 have been dissociated by polarized ultraviolet light and the angular distribution of the fragments has been measured. The photofragment mass spectra show that the lower lying excited states of CH2I2 and CHI3 dissociate to give an iodine atom and the corresponding radical. The angular distribution fitted the form 1+βP2(ϑ), where ϑ is the angle between the detection and polarization directions. β was 0.90±0.16 for CH2I2 and 0.46±0.16 for CHI3. These values prove that the molecule dissociates in a time short compared to its period of rotation. Moreover, the first two absorption bands in CH2I2 are shown to be of A1→B1 type polarized along the I–I vector, and in CHI3 they are of A1→E type polarized perpendicular to the threefold axis. A crude exciton model amounts for the number and symmetries of the energy states.
Dielectric fluctuations, orientational fluctuations, and depolarized scattering
Authors: Keyes T.
Published: February 2003

Linear response theory and Kirkwood–Yvon theory are combined to calculate the dielectric tensor in the presence of a weak molecular orientational order. The results for the dielectric tensor are then used to calculate depolarized scattering intensities via the ’’phenomenological’’ theory.
Electron-impact excitation of H2O and D2O at various scattering angles and impact energies in the energy-loss range 4.2–12 eV
Authors: Chutjian A. , Hall R. I. , Trajmar S.
Published: February 2003

The electron-impact excitation of H2O and D2O has been studied at electron energies close to threshold and at large scattering angles in order to enhance spin and/or symmetry forbidden electronic transitions; and at energies far from threshold and at small scattering angles to enhance optically allowed transitions. The energy-loss range covered is 4.2–12 eV. From a comparison of the present measurements and recent, accurate ab initio calculations, several new assignments of electronic transitions in both H2O and D2O have been made or suggested. Also suggested are future works which could be carried out in order to unravel the complex Rydberg spectra above 11 eV.
Microwave spectrum, barrier to hindered internal rotation, molecular structure, and electric dipole moment of silyl phosphine
Authors: Varma Ravi , Ramaprasad K. R. , Nelson J. F.
Published: February 2003

The microwave spectrum of silyl phosphine, SiH3PH2, has been observed and assigned. A set of structural parameters, consistent with the observed moments of inertia, has been calculated. The barrier to hindered internal rotation of the silyl top is 1535±40 cal/mole. The dipole moment has been determined to be 0.59±0.05 D (‖μa‖ = 0.236±0.005 D; ‖μc‖ = 0.54±0.04 D) from measurements of the Stark effect. The study seems to discount possibility of partial double bonding of type (p → d)π between the phosphorous and the silicon atoms in silyl phosphine molecule.
Evidence for ion pairing and solvation from Raman spectra of solutions of ammonium, silver, potassium, sodium, and calcium nitrates in liquid ammonia
Authors: Lundeen J. W. , Tobias R. S.
Published: February 2003

Digital Raman spectra of solutions of NH4NO3 (6.4, 8.7m), AgNO3 (1–4m), NaNO3 (1–5.5m), KNO3 (1–3m), and Ca(NO3)2 (1–2.6m) in liquid ammonia have been analyzed by least squares curve fitting. Perturbations of the nitrate ion spectra, particularly splitting of ν3, clearly indicate the presence of ion pairs in all of the solutions. The effects are similar to those observed for concentrated aqueous solutions, although the spectra generally are simpler, indicating only one environment for nitrate is important in all except Ca(NO3)2 solutions. The ion pairs appear to involve direct cation–anion contact, and the splitting of the nitrate ν4 correlates well with the ionic potential of the cations. The failure to observe a splitting of ν4 for potassium, ammonium, and silver cations is attributed to their low polarizing power, suggesting that the ν4-splitting criterion for inner-sphere complex formation fails with weakly polarizing cations. The splitting of nitrate ν3 by ion pairing in liquid ammonia is considerably less than that observed for aqueous solutions, and the same effect has been reported for alkali metal nitrates in glassy water and ammonia matrices at 12 °K. The ν3 splittings of univalent nitrates show an inverse correlation with the heats of ammoniation of the cations except in the case of the small lithium ion, suggesting that charge transfer from ammonia to metal ion decreases the cation polarizing power. Two weak, broad low frequency features (296, 329 cm−1) are assigned as silver–ammonia stretching modes, and this is the only system which exhibits vibrations for the first coordination sphere. This is compared with the behavior of aqueous solutions containing Ag(NH3)2+, and a fluxional first coordination sphere is suggested for Ag(I) in liquid ammonia. A band at 260 cm−1 is assigned to a calcium nitrate quasilattice mode, and this is the only system for which such a vibration is observed. The general features of the Raman spectra of electrolyte solutions in water and liquid ammonia are compared.
Dynamics of stiff polymer chains. III. Reduced distribution functions and the Gaussian correlated model
Authors: Kovac Jeffrey , Fixman Marshall
Published: February 2003

Diffusion equations are formulated for the reduced distribution functions of one and two bond vectors in a chain polymer. Closure of the singlet equation is examined on the basis of a Gaussian approximation for the pair distribution function, and the complex intrinsic viscosity is calculated for a freely jointed chain. The results at all frequencies agree well with previous exact and approximate treatments of this model. The approximate closure method seems particularly suitable for application to realistic models in which small sections of the chain would be treated numerically, and coupled together analytically.
A 14N nuclear relaxation study of hydrogen bonding in diethylamine–alcohol solutions
Authors: Rowland T. J.
Published: February 2003

The rotational correlation time τq of 14N in diethylamine has been measured in a number of solutions containing normal alcohols as solute. Using the nuclear absorption linewidth of 14N to follow changes in τq, contributions associated with hydrogen bonding and with alcohol chain hindrance were identified. Solution viscosities are also reported and correlation times derived from them are compared with the corresponding τq in order to contrast their responses to solute additions of this type.
Magnetic circular dichroism in hemoglobin
Authors: Treu J. I. , Hopfield J. J.
Published: February 2003

Magnetic circular dichroism (MCD) and absorption have been measured in various derivatives of hemoglobin in an applied field of 16 kG at temperatures ranging from 77 to 294 °K. The visible and Soret bands have been studied. We develop a spin–orbit coupling model to help explain the sign, magnitude, and 1/T temperature dependence of the MCD of deoxyhemoglobin. The results for deoxyhemoglobin are compared with those for unligated separated alpha and beta chains. Differences in spectra occur which can only be attributed to the different temperature dependent heme environments for chains and for tetramers. Cyanomethemoglobin and oxyhemoglobin are also discussed.
Generalization of Slater’s transition state concept
Authors: Williams Arthur R. , deGroot Robert A. , Sommers Charles B.
Published: February 2003

We present a generalization of the transition state technique introduced by Slater for the calculation of many-electron relaxation effects accompanying electronic excitations in molecules and molecular simulations of solids. By making use of ground state information (which is generally available but not used in the Slater formulation) and transition states which are computationally cheaper (due to being closer to the ground state), the generalization permits the evaluation of excitation energies to be improved in any of three ways: (1) comparable accuracy for less computation; (2) improved accuracy for comparable computation; and (3) full Δ-SCF accuracy can be approximated with arbitrary precision with additional computation. In particular, we show that excitation energies of somewhat greater accuracy are obtained from self-consistent calculations performed for transition states corresponding to 2/3 of the transition rather than 1/2 of the transition as in the original formulation by Slater.
Energy dependence and isotope effect for the total reaction rate of Cl+HI and Cl+HBr
Authors: Bergmann K. , Moore C. Bradley
Published: February 2003

A laser initiated chemical reaction method has been used to determine the total reaction rates for Cl+HI and Cl+HBr and the dependence of the rates on collision energy and H–D isotopic substitution. The rate constants are k=1.64×10−10 cm3 molecule−1⋅sec−1 (σ=33.5 Å2) for Cl+HI and k=7.4×10−12 cm3 molecule−1⋅sec−1 (σ=1.44 Å2) for Cl+HBr. Measurements were all done at 295 °K in slowly flowing gases. Substituting H by D decreases the rate constant by a factor of 1.84 in the case of HI and by 1.5 in the case of HBr. The isotope effect may be a result of tunneling on corner cutting trajectories. The cross section decreases with increasing collision energy. This, together with the large reaction cross section, indicates the importance of an attractive potential in these systems.
Statistical mechanical theory of polymers. II. Thermodynamic functions of a single ring polymer
Authors: Naghizadeh Jamshid , Ailawadi Narinder K.
Published: February 2003

Statistical thermodynamics of a single ring polymer with an intersegmental interaction is developed. Volume in this system is defined in terms of the mean-square radius of gyration. The concept of compressed and expanded states of the polymer is developed by introducing a coefficient-of-expansion σ. In this way, the volume of the single polymer can be varied and change of free energy with this variation in volume can be studied. Tension is now defined as the infinitesimal change in free energy due to an infinitesimal change of volume, i.e., infinitesimal expansion of the system. The chemical potential is the change in free energy due to charging (or severing of) one of the segments of the polymer chain. Using these definitions and methods analogous to statistical mechanical theory of fluids, explicit expressions are derived for the equation of state as well as other thermodynamic properties in terms of the binary intersegmental correlation function g(2)(R) and the intersegmental interaction u (R). The techniques developed here are applicable to the study of gas–liquid type phase transitions observed in polymer solutions and Monte Carlo simulation experiments.
Statistical mechanical theory of polymers. III. Equation of state for the hard sphere model of a single ring polymer
Authors: Naghizadeh Jamshid , Ailawadi Narinder K.
Published: February 2003

Thermodynamic functions for a single ring polymer with hard-sphere binary intersegmental interactions are studied. The integral equation of the binary intersegmental correlation function g(2)(R) developed earlier is expressed in terms of a parameter λ in a manner analogous to Kirkwood, Maun, and Alder for the case of fluids. The parameter λ is related to the coefficient of expansion σ (and therefore density) by a thermodynamic identity. The binary intersegmental correlation function g(2)(R) is now computed numerically by an iterative procedure. Numerical values of various thermodynamic functions are computed. The data are in qualitative agreement with Monte Carlo calculations of Mazur and McCrackin at high temperatures.
Weibull distribution and kinetics of heterogeneous processes
Authors: Kolar-Anić Lj. , Veljković S. , Kapor S. , Dubljević B.
Published: February 2003

The rate equation Qt/Q∞ = 1 − e−btn, where Qt/Q∞ is the fractional yield of an interface reaction at time t, was shown to be formally analogous to the Weibull distribution functions. Further correlation between the Weibull and the normal distributions did allow for a direct statistical interpretation of surface processes. Rates are thus defined by the well known parameters μ and σ. Geometrically incompatible processes were standardized on the basis of the exponent n and the shape parameter β of the Weibull distribution. For 3<n<4, processes obeyed the normal distribution, and for n<0.7, they obeyed the log normal distribution. By using the linearized probability plots, ambiguities imposed by the multiple logarithming of the above rate equation are avoided.
Statistical foundations of heterogeneous kinetics
Authors: Kolar-Anić Lj. , Veljković S.
Published: February 2003

A mathematical analysis of the correlation between Weibull and gamma distributions is presented. On this basis, processes obeying the relation Qt/Q∞ = 1 − e−btn (Qt/Q∞ being the fractional yield of an interface reaction at time t) can be explained better. Selected values of n, found experimentally, reflect the specific rate dependence of the distribution of the surface potential on active sites. By using the corresponding gamma distribution functions we show that most of these processes obey either directly or indirectly the normal distribution of the activity of reacting sites.
Exact quantum, quasiclassical, and semiclassical reaction probabilities for the collinear F+D2 → FD+D reaction
Authors: Schatz George C. , Bowman Joel M. , Kuppermann Aron
Published: February 2003

Exact quantum, quasiclassical, and semiclassical reaction probabilities and rate constants for the collinear reaction F+D2 → FD+D are presented. In all calculations, a high degree of population inversion is predicted with PR03 and PR04 being the dominant reaction probabilities. In analogy with the F+H2 reaction (preceding paper), the exact quantum 0→3 and 0→4 probabilities show markedly different energy dependence with PR03 having a much smaller effective threshold energy (ET=0.014 eV) than PR04 (0.055 eV). The corresponding quasiclassical forward probabilities PR03 and PR04 are in poor agreement with the exact quantum ones, while their quasiclassical reverse and semiclassical counterparts provide much better approximations to the exact results. Similar comparisons are also made in the analysis of the corresponding EQ, QCF, QCR, and USC rate constants. An information theoretic analysis of the EQ and QCF reaction probabilities indicates nonlinear surprisal behavior as well as a significant isotope dependence. Additional quantum results at higher energies are presented and discussed in terms of threshold behavior and resonances. Exact quantum reaction probabilities for the related F+HD → FH+D and F+DH → FD+H reactions are given and an attempt to explain the observed isotope effects is made.
The use of discontinuous trial functions in the computation of the electronic structure of molecules: Calculation of the ESCA spectrum of tetrathiofulvalene (TTF)
Authors: Antoci Salvatore
Published: February 2003

It is shown that discontinuous trial functions can be easily adopted in the computation of the electronic structure of molecules; in fact, when used in conjunction with a model of the molecule based on intersecting spheres, they permit very fast and accurate calculations to be performed. As an example, the computation of the ESCA spectrum of a large organic molecule (TTF) is presented.
Temperature dependence of the rate constants for the reactions O(3P) + 2,3-dimethyl-2-butene and O(3P) + NO + M determined by a phase shift technique
Authors: Singleton D. L. , Furuyama S. , Cvetanović R. J. , Irwin R. S.
Published: February 2003

Absolute values of the rate constant k2 for the reaction of O(3P) atoms with 2,3-dimethyl-2-butene are determined over the temperature range 298–481 °K using modulated photosensitized decomposition of N2O to generate O(3P) atoms. The rate constants obtained from the phase shift measurements fit the Arrhenius expression, k2 = (1.24±0.12) ×1010 exp(774±76 cal mole−1/RT) in units of l mole−1⋅sec−1. The indicated uncertainties are least squares standard deviations. Possible explanations for the negative Arrhenius activation energy are reviewed. Also, the rate constant k3 for the reaction O(3P) + NO + M is redetermined for M=N2O. Over the temperature range 298–473 °K, the results fit the Arrhenius expression, k3 = (6.12±0.45) ×109 exp(1230±55 cal mole−1/RT), where the units are l2 mole−2⋅sec−1 and the uncertainties are the least squares standard deviations.
Reactive and nonreactive modes of electronic excitation and molecular dissociation in hyperthermal collisions of alkali atoms with alkali halides
Authors: Neoh S. K. , Herschbach D. R.
Published: February 2003

A molecular beam study of translational-to-electronic energy transfer in collisions of hyperthermal K or Rb atoms with thermal alkali halide molecules is reported. Data are presented for the chemiluminescence cross sections for the Tb–NaI system. (AIP)
Are elements 112, 114, and 118 relatively inert gases?
Authors: Pitzer Kenneth S.
Published: February 2003

Initial results of the application of relativistic Hartree–Fock (DHF) orbitals to the covalent ponding of elements 112, 114, and 118 lead to the conclusion that these elements are volatile and relatively inept. (AIP)
The velocity dependence of the excitation transfer reaction Ar(3P2,0) + N2(X 1Σ+g) → Ar(1S) + N2(C 3Πu)
Authors: Lee Wellington , Martin Richard M.
Published: February 2003

The velocity dependence of the title reaction was determined using crossed effusive molecular beams with one beam time-of-flight velocity selected. The basis of the method is discussed, and the resolution is derived in terms of the experimental parameters. The velocity dependence was determined over the range 390–1630 m/s, corresponding to 0.013–0.226 eV relative energy. The cross section rises rapidly to 0.10 eV above which it is nearly constant to 0.226 eV. The thermal rate constant temperature dependence is calculated from the cross section energy dependence and normalized to the literature value for the rate constant at 300 °K. The cross section function over the energy range studied accounts for ≳ 90% of the rate constant over the temperature range 78–600 °K. The activation energy is calculated over the range 50–700 °K from the cross section function and compared with the threshold energy E0. Comparison of the present work with previous studies of the total quenching of Ar(3P2,0) by N2 indicates that the cross sections for formation of N2(B 3Πg) and N2(C 3Πu) have a similar energy dependence below 0.05 eV. If these two states are formed via a common complex as previously proposed, this similarity suggests that the dependence on energy is primarily that for complex formation rather than for the subsequent partitioning into N2(B) and N2(C) +Ar(1S) products.
Deuteron relaxation in liquid crystals: Di-n-alkoxyazoxybenzenes, n=1,7
Authors: Orwoll Richard D. , Wade Chas. G. , Fung B. M.
Published: February 2003

Deuteron spin lattice relaxation T1Q has been measured in the liquid crystal and liquid phases of di-methoxyazoxybenzene deuterated at the aromatic positions (PAA-d8) and di-n-heptyloxyazoxybenzene similarly deuterated (HOAB-d8). T1Q of PAA-d8 was measured at 4.5 and 10.5 MHz over the entire liquid crystal range and also at 15.35 MHz at 133 °C, just below the clearing point. No frequency dependence was observed. In contrast to proton relaxation, T1Q is strongly temperature dependent in the mesophases of both compounds. The results indicate that relaxation in this frequency range is more strongly influenced by rapid molecular reorientation and internal rotations than by collective mode mechanisms.
Semiclassical quantization of nonseparable systems: A new look at periodic orbit theory
Authors: Miller William H.
Published: February 2003

A modified version of Gutzwiller’s periodic orbit theory of semiclassical eigenvalues is presented which eliminates some of the principal shortcomings of the original result. In particular, for a nonseparable system with N degrees of freedom the new quantum condition characterizes the eigenvalues by N quantum numbers (rather than just one), and it also reduces to the correct result in the limit that the system is a separable set of harmonic oscillators (whereas the original quantum condition does not). This new periodic orbit quantum condition is seen to bear an interesting relation to Marcus’ recent theory of semiclassical eigenvalues which involves manifolds of quasiperiodic trajectories.
Approximation of TFD molecular densities by the sum of separated atom TFD densities
Authors: Junker B. R. , Menendez M. G.
Published: February 2003

It is shown analytically that the ’’bounds’’ on the approximate TFD potential obtained when the molecular TFD density is approximated by the sum of the separated atom densities must cross. This is in agreement with the result of Gunther that the lower ’’bound’’ is not a true bound.
Excitation of the C 3Πu state of N2 by electron impact
Authors: Chen S. T. , Anderson Richard J.
Published: February 2003

The λ=3371 Å spectral band of the C 3Πu→B 3Πg (v′=0, v″=0) second positive system is investigated using time-resolved spectroscopy with electron beam pulse widths of 100 nsec, 260 nsec, and 5 μsec. Lifetime data for the v′=0 vibrational level of the C 3Πu electronic state are obtained for incident electron energies and N2 gas pressures in the range 25–200 eV and 2–380 mtorr, respectively. In the case of the 260 nsec electron pulse, a single radiative decay component is observed which exhibits a dependence upon electron impact energy. However, in the case of a 5 μsec excitation pulse the resulting radiative decay is observed to consist of two decay components. The short-lived component is identified as the primary C 3Πu state excitation, while the long-lived component is identified as the radiative cascade contribution from higher electronic states, including possibly the metastable E 3Σ+g state. When the long-lived cascade contribution is subtracted from the total C 3Πu population, the C state natural radiative lifetime becomes independent of energy. In addition, the lifetime is observed to be independent of N2 gas pressure over the pressure range ∼2–380 mtorr.
Chain model theory of lipid monolayer transitions
Authors: Nagle John F.
Published: February 2003

The extensive surface area A and the conjugate surface pressure Π are introduced into a cooperatively interacting hydrocarbon chain model. The exact statistical mechanical method of solution is extended to accommodate the new variables. The previously discussed 3/2 order transition becomes a critical point in phase diagrams involving Π and A. The values of the usual critical exponents are β=1, δ=2, γ=γ′=1, and α=0, and the 3/2 order exponents appear on the critical isobar, Π=Πc. The model shows Π-A phase behavior which is strikingly different from the P–V behavior, in agreement with the difference between the experimental Π-A monolayer behavior and the P–V bilayer behavior. This supports the theory that the bilayer is two weakly coupled monolayers.
13C chemical shielding in oxalic acid, oxalic acid dihydrate, and diammonium oxalate
Authors: Griffin R. G. , Pines A. , Pausak S. , Waugh J. S.
Published: February 2003

13C chemical shielding tensors in three oxalates were investigated in order to determine the effects of protonation and conformation changes on the tensor elements and their orientations. The experimental results, together with those in the accompanying paper [R. G. Griffin and D. J. Ruben, J. Chem. Phys. elding) of σ22 and in one case a concurrent rotation of the tensor about σ33, the element which is perpendicular to the COO plane. On the other hand, the simple conformational change of the twisting of carboxyl groups relative to one another, which occurs in diammonium oxalate monohydrate, results in small rotation of the tensor around σ11 and also may contribute to a decrease in the shielding of the σ22 component in this molecule. The orientation of the 13C tensor in oxalic acid dihydrate is different from that observed in other oxalate ions and carboxyl groups. The influence of a change in hydrogen bonding strength on tensor elements is discussed.
Carbon-13 chemical shielding in ammonium hydrogen oxalate hemihydrate
Authors: Griffin R. G. , Ruben D. J.
Published: February 2003

We have measured the two 13C chemical shift tensors in single crystals of ammonium hydrogen oxalate hemihydrate, NH4HC2O4⋅ (1/2)H2O, using solid state double resonance techniques. One of the two types of tensors in the unit cell, the one belonging to the ionic carboxyl group, is oriented with its least shield component σ11 within 6° of the C–C bond, while the other tensor, belonging to the protonated carboxyl group, has its σ11 twisted 24° off this bond. Both tensors have σ33 perpendicular to the oxalate plane. Protonation of the carboxyl group does not affect the shifts of the σ11 and σ33 tensor elements, but it does move the σ22 component in the direction of increased shielding. Implications of the orientation of these tensors to crystal and molecular structure determination are discussed.
Rational orbitals for 3S states of two-electron systems
Authors: Birss Fraser W. , Choi Jong H.
Published: February 2003

The concept of rational orbitals for 3S states of two-electron systems is introduced, based upon finding that pair of orbitals which yield that single configuration function which maximally overlaps with a configuration interaction wavefunction. Methods for obtaining these orbitals are discussed and applied to a number of 3S states of helium.
On the temperature dependence of the recombination fluorescence of photoionized tryptophan in aqueous glasses: Consequences of electron tunneling
Authors: Moan Johan , Ho Ken K. , Kevan Larry
Published: February 2003

The recombination fluorescence seen when tryptophan in ethylene glycol/water and 9M LiCl frozen aqueous glasses is photoionized has been investigated. It is found that the intensity as well as the initial decay rate of this recombination fluorescence decreases as the uv irradiation temperature increases from 77 K. This is interpreted in terms of a tunneling process in which the electron trap depth increases slightly with increasing irradiation temperature. This causes the tunneling rate constant to decrease, and as the trap depth drops below the lowest singlet level of tryptophan, an increasing fraction of the recombination events will lack the energy necessary to generate recombination fluorescence.
On the theory of time resolved near-resonance light scattering
Authors: Metiu Horia , Ross John , Nitzan Abraham
Published: February 2003

Time resolved resonance and near-resonance light scattering is analyzed by means of Green’s operator formalism. We study the process of a photon wavepacket colliding with and scattered from a given molecule. Two decay components similar to those observed by Williams, Rousseau, and Dworetsky are obtained under appropriate conditions. Unlike other recent treatments of this problem, the light pulse is not treated as a pure quantum state (minimum uncertainty wavepacket) but rather as a mixture having characteristic time and energy profiles. It is shown that the nature of the light pulse may strongly influence the ratio of the short time to the long time decay intensities.
Magnetothermodynamics of ferroelectric, ferroelastic, antiferromagnetic β-terbium molybdate. I. Heat capacity, entropy, magnetic moment of the electrically polarized form from 0.4 to 4.2 °K with fields to 90 kG along the c crystal axis
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2003

The magnetic moment and heat capacity of a 1.170 cm diam spherical single crystal of electrically polarized β-Tb2(MoO4)3 have been measured at stabilized fields of 500, 1000, 1500, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G, along the c crystal axis, and over the range 0.4–4.2 °K. The heat capacity at zero field was also measured over the same temperature range. The temperature dependent magnetic moment reached saturation at fields of 65 and 90 kG. Its value, 43 050 G cm3/mole Tb3+, corresponds to a splitting factor of gc= 15.41. The small temperature independent magnetic susceptibility χTind = 0.0070 cm3/mole Tb3+ indicates that the upper levels of the 7F6 multiplet are well above the ground doublet. As expected, any effect of reversing the magnetic field with respect to the electrical polarization was too small to be detected. The T3 lattice heat capacity was evaluated at saturating fields of 65 and 90 kG since the electronic heat capacity vanished at these high fields owing to the high g value. This also enabled evaluation of the zero entropy of the electron–lattice systems, and the effective hyperfine field which causes nuclear spin polarization. It is known from x-ray data that Tb3+ has two equally divided environments in β-Tb2(MoO4)3. The magnetocalorimetric data indicate two largely independent electronic systems. The data have been separated into the two electronic, the nuclear, and lattice components of the heat capacity. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.5–4.2 °K. Several magnetic moment measurements were obtained over the range 0.5–1.4 °K with fields to 25 kG along the a crystal axis.
Ion pair production by electron impact on H2 and CO: Kinetic energy distributions and threshold behavior
Authors: Köllmann K.
Published: February 2003

Kinetic energy distributions and ion efficiency curves are obtained for ion pair production by electron impact on H2 and CO. The results are used to test the hypothesis that, if the threshold behavior of the cross section can be described by a step function, the first derivative of the ion efficiency curve should reflect the total kinetic energy distribution of the ion pairs. (AIP)
Molecular beam electric deflection of the tetrahalides CF4, CCl4, SiF4, SiCl4, GeCl4, TiF4, TiCl4, VF4, and VCl4
Authors: Muenter Annabel A. , Dyke T. R. , Falconer W. E. , Klemperer W.
Published: February 2003

Using molecular beam electric deflection, the temperature dependence of polar behavior has been studied for the molecules CF4, CCl4, SiF4, SiCl4, GeCl4, TiF4 TiCl4, VF4, VF4, and VCl4. A number of these molecules show polar behavior consistent with a vibrationally induced dipole moment for states with one or both of the triply degenerate vibrations excited. In four of the tetrachloride species, the presence of a vibrationally induced dipole moment was confirmed by the change in polar behavior with isotopic substituion of the Cl atoms. The deflection behavior of the transition metal tetrahalides varied from nonpolar in VCl4 to very polar in TiF4.