bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron spin resonance study of metallic lithium–ammonia systems
Authors: Glaunsinger W. S. , Sienko M. J.
Published: February 2003

Electron spin resonance (ESR) in metallic lithium−ammonia systems has been investigated in the temperature range 12−296°K. In the liquid solutions and in the cubic phase of Li(NH3)4 the conduction−electron−spin resonance (CESR) line shapes are in excellent agreement with Dyson’s theory. The g shift, which is independent of concentration and temperature, is equal to 7.9±0.3×10−4. The spin−orbit coupling constant derived from the g shift is about 10 cm−1. The diffusion time TD is nearly independent of temperature in the liquid state, but it is strongly dependent on concentration and undergoes a fourfold decrease at the freezing point of Li(NH3)4. The spin−lattice relaxation time T1 is weakly dependent on concentration and temperature in the liquid state and undergoes a twofold increase at the freezing point of Li(NH3)4. The data are consistent with the spin−orbit relaxation mechanism and indicate that to a good approximation the solvated ions are the only spin scatterers in the liquid state. The paramagnetic susceptibility of liquid Li(NH3)4 is independent of temperature and equal to 77×10−6 emu/mole. For metallic concentrations below 18 MPM the cubic phase is found below the solid−solid transition temperature, and the relative amount of the cubic phase present increases with decreasing lithium concentration. An ESR signal is also observed in the hexagonal phase of Li(NH3)4. Paramagnetic susceptibility measurements indicate that the hexagonal−phase ESR signal is due to localized moments which appear near the solid−solid transition temperature. The reciprocal paramagnetic susceptibility varies linearly with temperature down to 30°K, shows a broad minimum between 20 and 30°K, and increases below 20°K. No resonance signal could be detected below 12°K. The paramagnetic susceptibility of hexagonal−phase Li(NH3)4 at 54°K is about 1.5×10−6 emu/mole. The results indicate that the concentration of localized moments is small and they order antiferromagnetically below 20°K. The Fermi surface in the hexagonal phase is re−examined on the basis of the spin−orbit coupling constant determined from g shift measurements.
Reactions of O(1D) with atmospheric molecules
Authors: Tully John C.
Published: February 2003

A statistical model of chemical reaction is applied to collisions of O(1D) atoms with the molecules H2, N2, CO, CO2, N2O, O3, and H2O. Rate constants for reaction and deactivation are computed over the temperature range 100−2100°K. Competition among various product channels is investigated. In most cases quantitative agreement with experiment is achieved.
Semiclassical limit of quantum mechanical transition state theory for nonseparable systems
Authors: Miller William H.
Published: February 2003

The semiclassical limit of quantum mechanical transition state theory is derived by invoking the classical path approximation for the Boltzmann density operator and making use of the stationary phase approximation; separability of motion along a reaction coordinate is not assumed. The resulting expression for the rate constant bears an interesting similarity to that of conventional transition state theory, although all quantities in it refer to the full classical dynamics on the potential energy surface. In place of the vibrational frequencies of the ’’activated complex’’ which appear in the conventional theory, for example, the semiclassical expression contains characteristic frequencies related to the stability properties of a periodic classical trajectory. Conservation of total angular momentum is easily accounted for in a rigorous manner so that the semiclassical model can be applied to three−dimensional dynamical systems.
Theoretical study of inelastic scattering of H2 by Li+ on SCF and CI potential energy surfaces
Authors: Schaefer Joachim , Lester William A.
Published: February 2003

Integral and differential cross sections for pure rotational and simultaneous rotational−vibrational excitation of H2 by Li+ impact have been computed following the coupled−channel formalism using two different SCF potential energy hypersurfaces and a CI hypersurface at 0.6 and 1.2 eV. Sensitivity of integral cross sections to (a) choice of ab initio potential energy surface and (b) expansion length of a Legendre polynomial representation of one of the energy surfaces is examined. It is seen that preparation of H2 in the v = 0, j = 2 state leads to four− and fivefold increases in excitation cross sections to the v′ = 1, j′ = i, i = 0,2,4 states relative to excitation of ground state (v = 0, j = 0) H2. Differential cross sections are reported at 1.2 eV for up to five quantum rotational and for vibrational transitions on one of the energy hypersurfaces. All angular distributions required for determining ratios (inelastic : elastic) of differential cross sections needed for comparison with recent time−of−flight experiments at 0.6 eV are computed using both SCF and CI potential energy surfaces and compared. Further comparisons are made with experiment, beyond those that have appeared to date, which indicate that a significant discrepancy at one of the three angles for which measurements are available is due to experiment.
Analysis of the pitch in binary cholesteric liquid crystal mixtures
Authors: Hanson H. , Dekker A. J. , van der Woude F.
Published: February 2003

The pitch p in the cholesteric liquid crystal phase of mixtures of cholesteryl chloride and p−azoxyanisole has been measured as a function of the composition c. The function p−1 (c) deviates considerably from linearity and shows an inversion of the helical twist sense. The results, as well as those of five other binary cholesteric systems published in the literature, have been analyzed in terms of the molecular theory of Goossens. In the discussion of the results of the analysis, the requirements for a consistent physical interpretation of the interaction parameters that appear in the theory have been emphasized. The results indicate that these requirements are satisfied only in simple systems that do not deviate strongly from linear behavior of p−1 (c). In more complicated systems the specific properties of the individual molecules probably play an important role in determining the cholesteric helix.
Density functional formulation of collisional polarizabilities: Application to homonuclear noble gas diatoms
Authors: Heller Donald F. , Harris Robert A. , Gelbart William M.
Published: February 2003

We apply the general density functional formalism for electron gases in external fields to the specific case of electric susceptibilities of interacting closed shell systems. Computations are presented for the parallel and perpendicular components of the incremental polarizability tensors of He2, Ne2, and Ar2, as functions of internuclear distance. In the case of He2 our results can be compared with recent coupled Hartree−Fock calculations. For all three of the light noble gases we have evaluated the thermal averages of the pair polarizability components which correspond to the second dielectric virial coefficients and low pressure light depolarization ratios: Agreement with experimental data is found to be very good. The dependence of these calculated collision−induced optical properties on interatomic potentials and the long range behavior of the pair polarizability are considered in detail.
On the structure of a free surface of a Lennard-Jones liquid: A Monte Carlo calculation
Authors: Abraham Farid F. , Schreiber Donald E. , Barker J. A.
Published: February 2003

We report a Monte Carlo simulation of the Lennard−Jones liquid−vapor free surface at 84°K and conclude that, contrary to other recent numerical experiments, there exists no layer structure in the liquid region neighboring the free surface.
A new generalized expansion for the potential energy curves of diatomic molecules
Authors: Thakkar Ajit J.
Published: February 2003

A new generalized expansion for the potential energy curves of diatomic molecules is proposed. It is given by where λ (p) = sgn(p) [1 − (Re/R)p], and contains both the Dunham and the Simons−Parr−Finlan (SPF) expansions as special cases corresponding to p = −1 and p = 1, respectively. In order to justify the new expansion, a perturbation theory is developed which yields the Born−Oppenheimer potential as a series identical in form to the new expansion. The perturbation is a purely kinetic−energy perturbation at Re. Prescriptions are given for obtaining both the expansion coefficients and the optimal value of p either from perturbation theory or from spectral data. In terms of spectral data p = −a1 −1. Applications of the new expansion to CO, HF, and 20 alkali halides indicate that it predicts dissociation energies in much closer agreement with experiment than the SPF expansion while maintaining the same quality of agreement with the RKR curve as the SPF expansion provides. A number of possible extensions are discussed including potential energy surfaces for polyatomic molecules, techniques for analytic continuation of the new expansion, and expansions for properties other than the potential energy.
Theory of chemically induced dynamic electron polarization. III. Initial triplet polarizations
Authors: Pedersen J. Boiden , Freed Jack H.
Published: February 2003

An analysis of dynamical aspects of the CIDEP mechanism proposed by Wong et al. is given. This mechanism is based upon the formation of an excited triplet by intersystem crossing that populates the three triplet levels unequally. The subsequent rotational averaging of the initial population distribution coupled with the orientational effects of the zero field splitting is carefully treated in this work utilizing the stochastic Liouville equation in a manner closely analogous to that recently given for ESR line shapes and relaxation of slow−tumbling triplets. It is shown that the predicted CIDEP polarizations can indeed be very substantial, in agreement with Wong et al., but they will depend in general on the relative magnitudes of not only the zero field (D and E) and Zeeman terms (ω0) but also the relevant reaction rates and the rotational tumbling times (τR). A useful perturbation expression valid for D2 ≲ (1/2)[ω02 + τR−2] is obtained which shows these details. Typical complete solutions, obtained numerically, are given for cases when this inequality does not hold.
Study of cross sections, oscillator strengths, generalized oscillator strengths, and atomiclike character of the molecular orbitals of formaldehyde for inelastic transitions to valence and Rydberg states
Authors: Miller Kenneth J.
Published: February 2003

Oscillator strengths, generalized oscillator strengths, and cross sections are calculated using Hartree−Fock wavefunctions for spin allowed electronic transitions from the 2b2(n) and 1b1(π) molecular orbitals to the nb2 (n = 3, 4, and 5), nb1 (n = 2 and 3) and na1 (n = 5,⋅⋅⋅,10) Rydberg series, and for the singlet → triplet 2b2) 2b1) transition. The first Born approximation is utilized in the calculation of f (K), and exchange contributions are included in the calculation of the total cross sections with the Born−Ochkur−Rudge modifications. Contour plots illustrating the radial and angular dependence of the orbitals are presented to substantiate the atomiclike character of the nb2 and nb1 orbitals and to demonstrate the mixture of atomiclike states which contribute to the na1 molecular orbitals. The qualitative shape and trends in the occurence of extrema in the generalized oscillator strengths are discussed for transitions to Rydberg series whose excited molecular orbitals possess a given atomiclike character within the same point group symmetry. The oscillator strengths presented agree well with those determined both by electronic scattering techniques and with ultraviolet measurements in all but the π → π* excitation.
Determination of molecular pair correlation functions and size and shape parameters for diatomic liquids from x-ray and neutron diffraction data
Authors: DasGupta A. , Sandler S. I. , Steele William A.
Published: February 2003

Liquid state structure factors calculated from x−ray and neutron diffraction data for liquids made up of homonuclear molecules including N2, O2, Br2, and Cl2 are analyzed. Theoretical calculations of the structure functions were carried out using hard−core diatomic representations of these molecules in conjunction with the blip function calculation of the radial distribution function, extended to deal with nonspherical molecules. The parameters of the hard−core potential were varied to give the best fit between experiment and theory. The results are compared with the intermolecular potential functions used in other studies of these systems. It is concluded that the diatomic Lennard−Jones potential gives satisfactory agreement between theory and a variety of experiments on N2 and O2; ’’best’’ values for the parameters of the potential are suggested for these molecules. It is argued that a satisfactory theoretical treatment of the properties of Cl2 and Br2 should take account of the large quadrupolar interactions as well as the nonspherical shapes of these molecules.
A hydrodynamic effect on chemically induced dynamic spin polarization
Authors: Pedersen J. Boiden , Freed Jack H.
Published: February 2003

Deutch has recently suggested that the effect of the hydrodynamic interaction represented by Oseen’s tensor, on the relative diffusion of radical pairs, should have consequences for CIDNP and CIDEP signals. Detailed solutions to this problem have now been obtained by the finite difference approach of Pedersen and Freed to the stochastic−Liouville equation for the radical−pair mechanism. These solutions show that the hydrodynamic interaction typically leads to polarizations enhanced by factors of the order of 0.9−3 for CIDEP and reduced by factors of (3/4) −2(1/2) for the appropriate CIDNP parameter, and these factors are a function of the nature and magnitudes of the various interactions.
Electronic structure of unidimensional hydrogen fluoride. Molecular and band-structure approaches
Authors: Pietronero L. , Lipari N. O.
Published: February 2003

The electronic properties of a one−dimensional hydrogen fluoride (HF) chain are investigated using both molecular and band−structure methods. In the former approach, two sets of calculations were carried out. First, the Hartree−Fock approximation was used for a chain of up to 5 hydrogen fluoride molecules. Second, semiempirical CNDO calculations were carried out for a chain of up to 10 molecules. Rapid convergence of the bandwidths was attained, resulting in the two highest bands exhibiting widths of 8.8 and 4.3 eV, respectively. In the band−structure approach, the molecular tight−binding method was employed neglecting all three center integrals. Qualitative agreement between the two approaches was obtained although in the latter case, the bandwidths were smaller. This difference derived from the neglect of the three center integrals and, mostly, from the absence of a self−consistency between different molecules in the band−structure approach.
Infrared and Raman spectra of BrF5 and ClF3 in the condensed phase. Evidence of an associated state in liquid ClF3
Authors: Rousson R. , Drifford M.
Published: February 2003

Raman laser spectra of BrF5 and ClF3 have been investigated between 13 and 293 K. Infrared spectra were recorded and analyzed at liquid nitrogen temperature. Vibrational spectra of solid BrF5 agree with the crystallographic data and display the splitting of all transitions into two components, except for ν1, which is only shifted. A type of intermolecular interaction is considered, which accounts for the Raman spectrum. The vibrational study of ClF3 has shown an associated state in the liquid and a solid−solid transition at 192.6 K with an intermediate phase covering 5 K. A dynamical model for association is set up to explain both NMR and Raman spectra. The associated species in the liquid are intimately connected with the structure of the intermediate phase; moreover, the splittings of transitions into doublets allow one to expect molecular interactions similar to those in BrF5.
Molecular beam reaction of the van der Waals clusters (CH3I)n with alkalis
Authors: Ureña A. González , Bernstein R. B. , Phillips G. R.
Published: February 2003

The reactions of K and Rb with van der Waals clusters (n−mers) of methyl iodide, (CH3I)n, have been observed via the crossed molecular beam technique. Under strong expansion conditions, seeded nozzle beams of CH3I contain significant fractions of n−mers: all n ? 6 have been observed directly in the beam by electron bombardment ionization and mass filter detection of the parent ions. Upon heating of the nozzle, the weakly bound ’’polymers’’ revert readily to monomer. Crossing the cluster beam with an alkali beam and using a surface ionization scattering detector of high work function, a sharp peak appears superimposed on the angular distribution of KI (RbI) (that due to the alkali reaction with monomer), which disappears as the CH3I polymers are converted back to monomeric form. From the over−all body of evidence it is inferred that this peak is due to a fairly high molecular weight product (or semistable complex) formed by the reaction of an alkali atom with a methyl iodide cluster molecule (CH3I)n of n? 3.
Laser fluorescence study of AlO formed in the reaction Al + O2: Product state distribution, dissociation energy, and radiative lifetime
Authors: Dagdigian P. J. , Cruse H. W. , Zare R. N.
Published: February 2003

The reaction Al + O2 → AlO + O has been investigated by the method of laser−induced fluorescence. Excitation spectra are reported for AlO products formed under single−collision conditions in a ’’beam−gas’’ arrangement. The relative vibrational populations (proportional to total cross sections for formation), as well as the relative rotational populations for the v = 0 and v = 1 vibrational levels, are derived. The rotational distributions are found to differ significantly, with v = 0 having more rotational excitation than v = 1. The vibrational distribution is non−Boltzmann, the falloff with v ≳ 1 exceeding v = 1 compared to v = 0. The observed internal state distributions are compared with those calculated from phase space theory. It is concluded tentatively that the partitioning of the Al + O2 reaction energy among the product modes is not governed solely by statistical considerations. The dynamics of the Al + O2 reaction are compared with those of the exothermic Ba + O2 and endothermic K + O2 reactions. From a knowledge of the AlO internal states populated by the Al + O2 reaction and from an estimate of the thermal reactant energies, a lower bound for the ground state dissociation energy of AlO is derived. By combining the present lower bound with the upper bound previously derived from observation of the onset of an AlO absorption continuum, the value D00(AlO) = 121.5±1 kcal/mole is recommended for aluminum monoxide. Direct measurement of the fluorescence decay of the AlO B 2Σ+ state as a function of time after excitation by the short (∼5 nsec) laser pulse has allowed the determination of the radiative lifetimes τ (v′ = 0) = 100±7 nsec, τ (v′ = 1) = 102±7 nsec, and τ (v′ = 2) = 102±4 nsec, where the error estimates represent three standard deviations.
Conformational contribution to the entropy of melting. I. Linear chain hydrocarbons
Authors: Turturro A. , Bianchi U.
Published: February 2003

An experimental method is proposed and used to measure the thermal pressure coefficient γ as a function of volume at the melting temperature of crystalline substances. This method was applied to linear hydrocarbons with 11, 13, 15, 17, and 19 carbon atoms; values of the entropy increase due to volume expansion (ΔSv) and to conformational disorder on melting (ΔSc) were obtained.
Self-diffusion in a binary critical fluid
Authors: Keyes T.
Published: February 2003

The self−diffusion coefficient of a large tagged particle in a binary critical fluid ’’bath’’ is calculated. The validity of the Stokes−Einstein law in the critical system, and the possibility of determining the critical behavior of η, the shear viscosity, from measurements of D via the Stokes−Einstein law are discussed. It is concluded that η cannot be directly deduced from D if the critical correlation length exceeds the tagged particle radius.
The sulfur Kβ emission and K-absorption spectra from gaseous H2S. III
Authors: LaVilla Robert E.
Published: February 2003

The sulfur Kβ emission in fluorescence and K absorption from gaseous H2S were measured on a double crystal spectrometer. The sulfur Kβ spectrum consists of four peaks. The three strongest peaks are shown to be single vacancy transitions of electrons from the three outer MO’s to fill the single K shell vacancy. The weak fourth peak on the high energy side of the three line structure is identified as a double vacancy transition. The sulfur K−absorption spectrum consists of three peaks of decreasing intensity with increasing photon energy. The unusual breadth (FWHM of 1.50 eV) and asymmetry on the high energy side of the first peak is ascribed to the Frank−Condon factors of the transitions to the unoccupied antibonding MO’s 3b2 and 6a1. The other two peaks, which are narrow, are identified as transitions to Rydberg levels. In addition, the binding energy of the sulfur K shell electron was estimated to be 2478.3 eV. The sulfur L2,3 absorption of H2S is also discussed briefly.
Microwave spectrum, structure, and dipole moment of 1,1-difluorocyclopropane
Authors: Perretta Armond T. , Laurie Victor W.
Published: February 2003

The microwave spectra of five isotopic species of 1,1−diffluorocyclopropane have been studied in the region 18−40 GHz. Structural parameters were obtained: r (C1C2) = 1.464±0.002 Å, r (C2C2′) = 1.553±0.001 Å, r (CF) = 1.355±0.002 Å, r (CH) = 1.082±0.002 Å, &FCF = 108.4±0.2°, &C2C1C2′ = 64.1±0.1°, &HCH = 116.9±0.2°. The dipole moment has been determined to be 2.32±0.02 D. Rotational transitions belonging to a vibrational state of A symmetry at about 327 cm−1 and to a vibrational state of B symmetry at about 351 cm−1 have also been observed.
An application of Gordon’s M- and J-diffusion models to the calculation of the correlation functions of infrared perpendicular transitions in linear molecules
Authors: Dreyfus C. , Tai Nguyen Tan
Published: February 2003

The M− and J−diffusion models, which are proposed by Gordon to describe the reorientation of molecules, and which were applied to parallel vibrations only, are extended to the particular case of the perpendicular vibration of a linear molecule. In the case of the M−diffusion model, the method presented here yields a simple analytical form for the correlation function of the perpendicular vibration. In the case of the J−diffusion model, the spectral intensity is also obtained in a simple analytical form. Previously published experimental data on compressed gases are compared with the theoretical results.
Quantum mechanical reactive scattering: An accurate three-dimensional calculation
Authors: Kuppermann Aron , Schatz George C.
Published: February 2003

Accurate three−dimensional (3−D) quantum−mechanical calculations of differential and total cross sections for the H + H2 exchange reaction on the Porter and Karplus potential energy surface have been performed. These are the first such calculations which are vibrationally and rotationally converged, and the results are believed to be accurate to 5% or better. They can serve as a comparison standard against which approximate methods can be tested.
Quantum mechanical reaction cross sections for the three-dimensional hydrogen exchange reaction
Authors: Elkowitz Allan B. , Wyatt Robert E.
Published: February 2003

The results of extensive multi−channel quantum mechanical studies of the three dimensional hydrogen exchange reaction are reported. Reaction cross sections were obtained for both the Porter−Karplus potential surface (collinear barrier height 0.396 eV) and the Yates−Lester−Liu surface (collinear barrier 0.424 eV).
Comparison of the combined phase-space/trajectory and quasiclassical trajectory methods in the study of reaction dynamics: H + I2 and H + Br2
Authors: Porter R. N. , Thompson D. L. , Raff L. M. , White J. M.
Published: February 2003

Results for the combined phase−space/classical trajectory (CPST) and standard quasiclassical trajectory (SQCT) procedures for investigating the dynamics of homogeneous gas−phase reactions are compared in the case of H + X2 → HX + X (X = Br or I). The relative absence of dynamical effects for these systems permits SQCT calculations with low statistical error and would seem to enhance the validity of the basic assumptions of CPST. The high reduced mass of X2 also reduces differences between CPST and SQCT that arise from quantization of internal X2 states in the latter method. When the critical phase−space surface is chosen so that its configuration−space projection traverses only regions of low three−body interaction (< 2 kcal/mole), the CPST computed rate coefficients and angular distributions are in qualitative accord with SQCT results. When phase−space points on the critical surface are integrated back into the reactant phase space, nonequilibrium distributions are obtained for the distribution of relative translational energies and for the initial H−I2 angular orientation. If the critical surface is altered so that its configuration−space projection traverses regions of larger three−body interaction, differences between the CPST and SQCT results are found to increase if the probability density is not weighted by the square of the BC distance. Finally, it is demonstrated that the combined method may require more computation time than for a standard trajectory calculation of the same accuracy.
Electron loss cross sections for O−, O−2, NO−2, and NO−3 in several gases
Authors: Bennett R. A. , Moseley J. T. , Peterson J. R.
Published: February 2003

The cross sections for electron loss for O−, O−2, NO−2, and NO−3 on He, N2, and Ar, for O− on O2, and NO−3 on NO2 have been measured using a beam attenuation technique. The measured cross sections are the sum of collisional detachment and electron transfer cross sections. Except for O− + O2, the cross sections are nearly constant for ion energies in the range 1 to 4 keV and generally increase with target mass.
A determination of the stabilities of H+5, H+7, H+9, and H+11 from measurement of the gas phase ion equilibria H+n + H2 = H+n+2 (n = 3,5,7,9)
Authors: Hiraoka K. , Kebarle P.
Published: February 2003

The ion equilibria H+n + H2 = H+n+2 for n = 3,5,7,9 were determined in a pulsed electron beam high ion source pressure mass spectrometer. Van’t Hoff plots of the temperature dependence of the equilibrium constants Kn,n+2 lead to the corresponding ΔH°, ΔS°, and ΔG° changes. The ΔH values obtained were ΔH3,5 = −9.6, ΔH5,7 = −4.1, ΔH7,5 = −3.8 ΔH9,11 = −2.4 kcal/mole; ΔS°3,5 = −24.6, ΔS°5,7 = −19.8, ΔS°7,9 = −20.2, ΔS°9,11 = −19.3 e.u. (standard state 1 atm). These results are compatible with predictions from theoretical calculations in which the protonated hydrogen clusters are represented by a three center bonded H+3 to which H2 molecules are weakly attached. The first three H2 molecules go to the three corners of the H+3 triangle and the fourth goes to an outer position.
Rotational excitation in H2–H2 collisions: Close-coupling calculations
Authors: Green Sheldon
Published: February 2003

Rotational excitation in molecule−molecule collisions has been treated for the first time by accurate quantum close−coupling scattering calculations, employing an expansion basis set of two to three rotational levels for each molecule and correctly accounting for exchange of identical particles. Elastic and inelastic cross sections have been computed for collisions of para−para, ortho−ortho, and para−ortho hydrogen molecules assuming an intermolecular potential suggested previously. The accuracy of recent ’’effective potential’’ calculations is demonstrated by comparison with the exact quantum results.
Molecular rotation in some simple fluids
Authors: van Konynenburg P. , Steele William A.
Published: February 2003

Experimental studies of the rotational dynamics in liquid nitrogen, ethane, ethylene, and carbon dioxide are reported for a number of temperatures and densities along the saturated vapor lines. The intensity of depolarized light scattering was measured as a function of frequency shift; after attempting to correct for collision−induced contributions to the total intensity, the spectra were Fourier transformed to yield orientational correlation functions [C2(t*)] and cross angular momentum−orientation correlation functions [𝒢2(t*)]. It is argued that the collision−induced part may be too large relative to the scattering from permanent polarizability anisotropy to allow one to extract reliable rotational correlation functions for ethane, and possibly for ethylene as well. Data for the remaining systems (nitrogen and carbon dioxide) were compared to theoretical curves calculated from the J−diffusion model for random walk in angular momentum space. Values for the frequency of the randomization of angular momentum were derived for the experimental systems studied. The results are compared with calculations of the collision frequency in dense fluids of nonspherical hard−core molecules.
Dielectric properties of fluids composed of spheres of constant polarizability
Authors: Alder B. J. , Strauss Herbert L. , Weis J. J.
Published: February 2003

The dipole−dipole autocorrelation functions for systems of particles interacting with a Lennard−Jones potential are calculated in order to determine the variation of the dielectric properties with density and temperature. Comparison with static dielectric data shows that the observed deviation from the Clausius−Mossotti relation is primarily due to the dependence of the atomic polarizability on density. A new contribution to the dielectric dispersion is found to be of the order of 10−4 of the polarizability, at liquid densities and at visible frequencies, and should be observable.
A more complete kinetic theory of DNA renaturation
Authors: Rau Donald C. , Klotz Lynn C.
Published: February 2003

We develop here a more complete theory of DNA renaturation kinetics which differs from the Wetmur and Davidson theory mainly in the assumption that nucleation is not necessarily the rate−limiting step. Thus, the theory includes the several first order zipping steps. Our assumption that zipping is much slower than previously thought appears to be due to the presence of secondary structure in reacting single strands. The theory explains several anomalies seen in renaturation kinetic experiments followed by optical density. Specifically, it explains quantitatively (1) the deviations from linearity in reciprocal−second−order (RSO) plots, (2) the variation with concentration of rate constants obtained from the early−time linear region of an RSO plot, and (3) the high values of complexity calculated for viral DNAs using bacterial DNAs as the known standard. Renaturation kinetic experiments followed by hydroxypatite chromatography do not show these anomalies, since hydroxyapatite presumably ’’sees’’ only nucleation. In this paper the theory is derived and compared with experiments on bacterial and bacteriophage DNA. The implications of the theory for other biologically oriented experiments will be explained elsewhere.
The vapor pressure of high-purity solid and liquid curium
Authors: Ward J. W. , Ohse R. W. , Reul R.
Published: February 2003

The vapor pressure of triply−distilled curium−244 metal has been measured in the temperature range 1300−2000 K, using Knudsen effusion target−collection techniques. Precise geometrical conditions were chosen to insure that the intercepted molecular beam came entirely from the curium sample surface within the cell. Second−law equations are Log10P (atm) = (6.082±0.129) − (19618±193)/T (K) (solid, 1327−1639 (K), Log10P (atm) = (5.586±0.157) − (18894±275)/T (K) (liquid, 1640−1972 (K). From these data, the heat and entropy of fusion/transition are calculated to be 3.31 kcal and 2.19 cal/deg, respectively. The average second−law entropy is 25.56±0.72 cal/deg. Similarities noted in other work between the chemical and physical properties of curium and gadolinium were clearly evident. Free−energy functions for gadolinium were used directly to give ΔH298K (3rd−law) = 92128±76 cal for the heat of sublimation from the solid phase, and 92482±112 cal for the liquid. Difficulties encountered in high−temperature effusion studies with reactive materials are discussed in the light of these and earlier results.
Frictional properties of dilute polymer solutions. II. The effect of preaveraging
Authors: Deutch J. M. , Felderhof B. U.
Published: February 2003

Our development of the Debye−Bueche theory for the frictional properties of dilute polymer solutions is continued. A simplified version of the mean field theory is introduced that involves a preangular average (PAA) of the hydrodynamic interaction. A comparison is made between the exact mean field theory and the simplified PAA theory for the case of a uniform sphere and of an infinitesimal shell segment distribution.
Model calculation of vibronic sidebands in Cs2UBr6
Authors: Chodos Steven L. , Satten R. A.
Published: February 2003

A simple seven parameter lattice dynamics model for Cs2UBr6, employing a Urey−Bradley valence force field for the short range interactions and standard long range Coulomb terms, was used to calculate the shape of vibronic side bands accompanying a Γ1g → Γ1g and a Γ1g → Γ2g electronic transition. Simplifying assumptions concerning the vibronic interaction were made. The results were fairly good and instructuve for the sideband accompanying the Γ2g electronic transition partly because the vibronic effective Hamiltonian was more realistic in that case.
Optical spectra of orientationally disordered crystal. V. Raman spectrum of ice Ih in the range 4000–350 cm−1
Authors: Wong P. T. T. , Whalley E.
Published: February 2003

The Raman spectrum of polycrystalline ice Ih has been investigated using laser excitation in the frequency range 4000−350 cm−1. The relative intensities have been discussed in a semiquantitative way that takes explicit account of the intermolecular coupling of the molecular vibrations in the crystal. The principal conclusions from the work are summarized at the end of the paper.
Phase equilibrium isotope effects in molecular solids and liquids. Vapor pressures of the isotopic carbon dioxide molecules
Authors: Bilkadi Zayn , Lee Myung W. , Bigeleisen Jacob
Published: February 2003

The vapor pressures of samples of CO2 enriched in C13 and O18 have been compared with normal CO2 over the temperature range 154−217°K. Over the entire temperature range the order of the vapor pressures is P13CO2 > P12CO2 > PC18O2. The results are explained by the small shift in the internal vibrations, which dominate the carbon isotope effect, and hindered rotation in the solid and liquid. While the isotope effect on melting is small for carbon substitution, it is found to be large for oxygen substitution. Hindered rotation is the major contribution to the oxygen isotope effect in the solid, while the hindered translation is the most important contribution to the oxygen isotope effect in the liquid. Model calculations of the logarithm of the reduced partition function ratios of the solid and liquid, ln(fc/fg), are made in an anharmonic version of the Stern−Van Hook−Wolfsberg cell model. These calculations give good agreement with the experimentally determined ln(fc/fg) values for the solid, liquid−vapor isotope fractionation measurements of Grootes, Mook, and Vogel, and lattice dynamic calculations.
Semiclassical calculation of bound states in a multidimensional system. Use of Poincaré’s surface of section
Authors: Noid D. W. , Marcus R. A.
Published: February 2003

A method utilizing integration along invariant curves on Poincaré’s surfaces of section is described for semiclassical calculation of eigenvalues. The systems treated are dynamically nonseparable and are quasiperiodic. Use is also made of procedures developed in the previous paper of this series. The calculated eigenvalues for an anharmonically coupled pair of oscillators agree well with the exact quantum values. They also agree with the previous semiclassical calculations in this laboratory, which instead used integrations along the caustics. The present paper increases the number of systems capable of being treated. Using numerical counter examples for nondegenerate systems, it is also shown that an alternative view in the literature, which assumes that periodic trajectories alone suffice, leads to wrong results for the individual eigenvalues.
On the two state model for electrons in nonpolar liquid hydrocarbons
Authors: Tachiya M. , Mozumder A.
Published: February 2003

Assuming that electrons are partially free and partially trapped in nonpolar liquid hydrocarbons, we have treated theoretically the scavenging and neutralization processes in these systems. The square root law in scavenging at low cencentrations and the t−1/2 law in the decay of the survival probability at long times which are experimentally observed and theoretically derived for the one state model, can also be derived for the two state model in these respective limits. However, the Laplace transform relation between the probability of scavenging and that of survival against neutralization, which obtains for the one state model, is no longer strictly valid in the two state model.
Photovoltaic effects of metal–chlorophyll-a–metal sandwich cells
Authors: Tang C. W. , Albrecht A. C.
Published: February 2003

The microcrystalline chlorophyll−a film prepared by the method of electrodeposition is shown to have strong photovoltaic effects. The photovoltaic cell (M1‖Chl‖M2) has lamellar arrangement with the Chl−a film sandwiched between two metal electrodes. With dissimilar electrodes of different work functions, φM, the cell usually exhibits a dark rectification behavior. A large forward bias current is seen when the metal with a lower φM is the negative electrode. The rectification is small when the same metal is used as both electrodes. A blocking contact or Schottky barrier is evidently present at the Chl−a‖metal junction particularly fo the metal having a low φM. A p−type semiconduction in Chl−a is implicated. In the photovoltaic mode, cells such as (Al‖Chl‖Hg) and (Al‖Chl‖Au) have an open circuit voltage ranging from 200−500 mV. The power conversion efficiency for these cells is on the order of 10−3% which is among the highest in photovoltaic cells using organic materials. The direction of the photovoltaic current and the shape of its action spectrum are strongly dependent on the electrode materials. The blocking contact at the Chl−a‖metal junction is primarily responsible for the photovoltaic activity of the cell. When this blocking contact is established at the directly illuminated electrode the action spectrum closely matches the absorption spectrum of the Chl−a film. An inverse type response is found when the blocking contact is at the indirectly illuminated electrode with the Chl−a layer essentially acting as an inner filter. The photocurrent is shown to increase when the cell is reverse biased. A minimum quantum yield for charge generation of about 0.03 is found in (Al‖Chl‖Hg) and (Al‖Chl‖Au) cells.
Resonance vibrational energy transfer in liquids in the repulsive potential region
Authors: Tokuhiro Tadashi , Rothschild Walter G.
Published: February 2003

It was found that the resonance vibrational energy transfer caused by the short−range repulsive part of the intermolecular (perturbing) potential may play an important role as mechanism to produce broadening of vibrational band contours of molecules in the liquid state. The value of the full bandwidth at the half peak height (Δν1/2) for the ν4 (C−H deformation) fundamental of neat chloroform (8.2 cm−1) was reduced to 6.2 cm−1 at infinite dilution with deuterochloroform. This difference in Δν1/2 can be reproduced by either the above repulsive mechanism or by resonance energy transfer caused by the long−range transition dipole−transition dipole interactions. Physical aspects of these mechanisms are discussed and compared with those of NMR relaxation. The significance of the repulsive resonance transfer process with respect to transition state theory is indicated.
The enthalpies of the solutions of liquid metals in the liquid chalcogens—the structure and the chemical bond around solute metals
Authors: Maekawa Takashi , Yokokawa Toshio
Published: February 2003

The enthalpies of the solutions of several B metals in the liquid chalcogen can be calculated by using a cluster model around the solute metal. For a given coordination number and numbers of the valence electrons of the solute metal, the ionicity of the metal−chalcogen bond was also estimated. The calculated enthalpies coincide fairly well with those of the experimental ones.
High temperature vibrational relaxation of H2O by H2O, He, Ar, and N2
Authors: Kung R. T. V. , Center R. E.
Published: February 2003

The vibrational relaxation of H2O by H2O, He, Ar, and N2 has been studied behind incident shock waves at temperatures between 1800 and 4100°K. The relaxation processes were monitored by the observation of the infrared emission of the water vapor at 6.3 μ (the bending mode) and 2.7 μ (the asymmetric mode). The relaxation times for the two modes were found to be essentially the same with little temperature dependence. This implies rapid intramolecular energy transfer between the various modes. Measured values of pτ are 7.6×10−3, 0.23, 0.49, and 0.69 μsec⋅atm, respectively, for H2O−H2O, H2O−He, H2O−Ar, and H2O−N2 collisions.
Study of the structure of molecular complexes. XII. Structure of liquid water obtained by Monte Carlo simulation with the Hartree–Fock potential corrected by inclusion of dispersion forces
Authors: Lie G. C. , Clementi E.
Published: February 2003

The two−body Hartree−Fock potential for water−water interaction has been partially corrected by addition of the water−water dispersion interaction recently computed by the Quantum Chemistry Group at the University of Warsaw (Professor W. Kol/os) using a perturbation technique. The new potential has been used in a Monte Carlo simulation of liquid water, where 343 water molecules per unit cell have been considered. The main part of the simulation has been performed at T = 25°C; however, some work is presented for T = 4°C and for T = 75°C. The computed pair correlation functions gO−O, gO−H, and gH−H are in good agreement with the experimental data; agreement is found not only for the main peak of gO−O at ∼2.9 Å, but also for the second peak at ∼4.5 Å and the third peak at ∼7.0 Å. To further verify the agreement between simulated result and experimental data, we have computed the neutron scattering and the x−ray scattering intensities at different scattering angles. Again the agreement between simulation and experiment is good, thus providing a strong indication that the potential obtained on a quantum−mechanical basis is a realistic one.
Nitrogen and proton hyperfine interactions in the triplet state of azanaphthalenes at zero field
Authors: Dennis L. W. , Tinti D. S.
Published: February 2003

The zero field optically detected ESR and ENDOR spectra of the triplet state of 1,8−diazanaphthalene are presented and completely interpreted in terms of a spin Hamiltonian which includes proton hyperfine interactions. The latter are shown to be of considerable importance at zero field even in systems containing quadrupolar nitrogen nuclei. The previously unassigned features in the zero field spectra of diazanaphthalenes are explained and some new assignments are proposed in quinoline.
Paramagnetic hexafluoride anions of Group VI
Authors: Morton J. R. , Preston K. F. , Tait J. C.
Published: February 2003

Certain isotropic ESR spectra observed in γ−irradiated SF6 and in γ−irradiated solid solutions of SeF6 and TeF6 in SF6 are attributed to the hexafluoride anions of the Group VI elements. Hyperfine interaction measurements for the species 33SF6−, 77SeF6−, and 125TeF6−, observed in natural abundance, show that the central atom outer s orbital makes a very large contribution to the (totally symmetric) semioccupied orbital in these radicals. INDO MO calculations for SF6− gratifyingly predict a half−filled orbital which has the representation A1g in Oh symmetry and which is primarily composed of S 3s and F 2pσ atomic orbitals. An additional isotropic spectrum present in γ−irradiated 1% SeF6 in SF6 is believed to be that of SeF5 in which hyperfine interaction with the unique (apical) F nucleus is not detectable.
Detailed echo-shape fitting in NMR spin-echo experiments
Authors: Chan S. O.
Published: February 2003

In NMR pulse experiments performed on liquids, the desired information has usually been obtained either from the echo maxima or from the Fourier transform of the free induction signal trailing a (1/2) π pulse or half of the last spin echo in a Carr−Purcell train. The present work explores the feasibility of extracting information directly from the echo shape by a fitting procedure. In principle, this technique can regain the selectivity and resolution lacking in the conventional high−power spin−echo methods. Possible applications to the studies of selective spin−spin relaxation, nuclear transfer processes, and molecular diffusion in multicomponent systems are discussed.
Dynamics of critical fluctuations of a macromolecular solution
Authors: Lao Q. H. , Chu B. , Kuwahara N.
Published: February 2003

The angular and the spectral distribution of scattered light intensity and the hydrodynamic shear viscosity from polystyrene (Mn = 1.96×105, Mw/Mn < 1.02) in cyclohexane were measured at the critical solution concentration above the critical consolute temperature in the one phase region. In comparing the linewidth, correlation length, and shear viscosity data with the modified mode−mode coupling theory of Kawasaki, we note that the magnitude of a ’’scaled linewidth’’ Γ+ (≡6πη*pΓ/kBTK3) as a function of Kξ is a factor of 1.5−3 higher than the single universal curve of Kawasaki and Lo, where η*p, Γ, kB, T, K, and ξ are, respectively, the shear viscosity, the linewidth, the Boltzmann constant, the absolute temperature, the magnitude of the momentum transfer vector, and the correlation length. Since the theory describes only the critical part of the linewidth Γc, we separate the decay rate due to critical fluctuations and the finite molecular size of the polymer. The resultant scaled linewidth Γ* (≡6πη*pΓc/ kBTK3) as a function of Kξ can then be brought down to the universal curve. Our comparison between existing polymer data and theory represents a first attempt to take into account the finite molecular dimension of the system in decay rate of order parameter fluctuations. The data exhibit considerable scatter after the background correction. Consequently, there seems to be a need to consider more carefully the manner in which the backgrounds are subtracted before more crucial comparisons between experiments and theory can be made.