bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Abundance of Excited O+ Ions in Beams Produced by Electron Impact on O2, CO2, N2O, NO2, and H2O
Authors: Hughes B. M. , Tiernan T. O.
Published: February 2004

The fraction of excited ions present in O+ ion beams produced by impact of 60-eV electrons on various oxygenated molecules has been determined approximately 23 μsec after formation. The technique employed involves the measurement of apparent rate coefficients for charge-transfer reactions of O+ to N2 and CO at very low kinetic energies (∼0.3 eV) in a tandem mass spectrometer. Under these conditions, charge transfer of O+(4S) is endothermic and the formation of N2+ and CO+ products is due solely to excited O+ ions in the reactant beam. By normalizing the rate coefficients for the reactions of O+ from the several sources to that for an O+ beam for which the excited ion abundance is known, the fractional abundance of O+* in each of the respective ion beams is calculated. These fractions for O+ beams from the indicated sources were found to be: CO2, 0.04; N2O, 0.43; NO2, 0.34; H2O, 0.90. The fractional abundance data are utilized for the study of the reactions of both ground-state and excited-state O+with Ar and Kr. Ground-state O+(4S) was found to be completely unreactive with Ar even at ion kinetic energies up to 170 eV. The cross section for charge transfer from excited O+ ions to Ar is quite small at very low kinetic energies but increases sharply at energies above E1ab ∼20 eV. Both O+(4S) and O+(2D) undergo charge transfer to Kr over the energy range investigated and a maximum is observed in the cross section for the O+(4S) reaction. The results are qualitatively consistent with the adiabatic hypothesis for nonresonant charge transfer.
Radial Distribution Functions for a Binary Mixture of Gaussian Molecules
Authors: Carley David D.
Published: February 2004

We assume as an idealized model of a fluid a binary mixture of equal numbers of particles of type a and b such that the Mayer f function for similar particles is given by faa=fbb=0, and for unlike particles it is given by fab=−exp(−r2/α2). That is, the force between similar particles is taken to be zero, while the force between unlike particles is taken to be repulsive. Numerical solutions of the Percus—Yevick and hypernetted-chain integral equations are obtained. These radial distribution function solutions are than represented by Padé approximants.
Contribution to the Theory of Frenkel Excitons in Disordered Molecular Crystals
Authors: Hong Hwei-Kwan , Kopelman Raoul
Published: February 2004

In this paper, we discuss the Frenkel excitons in disordered molecular crystals. Most of our results can be generalized to cover electrons and phonons in other disordered systems as well. In particular, the relationship among the exact Green's function, the CPA (coherent potential approximation) Green's function, and the method of moments is discussed. It is emphasized that, despite its complicated form, the exact Green's function not only yields correct moments for the spectral density function and the overall density-of-states function but also leads to the CPA Green's function if certain terms are modified. Both the exact and the CPA self-energies are expanded with the aid of generating functions. This enables us to demonstrate both systemmatically and analytically how the latter is derived from the former and what exactly the approximations are. A better understanding of the CPA is thus obtained. Specifically, it is shown that the exact self-energy is wave vector and branch independent in the first five terms of its expansion in powers of Z−1 (reciprocal energy). A comparison with a similar expansion of the CPA self-energy indicates that the CPA self-energy is exact to the Z−5 power. Consequently, the spectral density function and the over-all density-of-states functions determined from the CPA method have the correct seven and eight lower moments, respectively. Analytical expressions for these lower moments are also given for future applications.
Studies of OH− and OD− Ions in Magnesium Oxide. II. The Structure of the VOD Center
Authors: Henderson B. , Kolopus J. L. , Unruh W. P.
Published: February 2004

This paper reports EPR, ENDOR, and infrared absorption measurements on the VOD center in MgO. The magnetic properties are well fitted to a spin Hamiltonian which includes terms due to electronic Zeeman, nuclear Zeeman, and hyperfine and nuclear quadrupole interactions. The magnitude of the unpaired electron spin density at the deuterium nucleus is similar to that for the hydrogen nucleus in the VOH center. Infrared absorption due to the fundamental stretching vibration of the O–D− bond in the VOD center occurs at 2464.5 cm−1. The oscillator strength of this vibrational transition is small, being of order 10−2. The analogous stretching frequency of the OH− bond in the VOH center in CaO is observed at 3447 cm−1.
Band Shape of the Circular Dichroism
Authors: Lin S. H.
Published: February 2004

A quantitative theory of the band shape of the circular dichroism for optically active solute molecules dissolved in dense media is presented. Semiempirical equations are derived for the calculation of the circular dichroism. The relations among the band shapes of the circular dichroism, optical rotatory dispersion, and light absorption or emission are discussed.
Dissociation of Cyclobutane Molecule—Ions Formed in Charge Exchange Collisions
Authors: Lifshitz C. , Tiernan T. O.
Published: February 2004

Mass spectra of cyclobutane resulting from charge exchange with slow positive ions have been determined. Product ion intensities were plotted as a function of the energy absorbed by the molecule in the charge exchange collision. Breakdown patterns for cyclobutane have also been calculated using the quasi-equilibrium theory (QET). Good agreement between the computed and experimental ion intensities was obtained for the primary dissociation processes. The relatively large C2H4+ intensity observed experimentally at higher energies is realized in the calculated spectra by assuming that direct cleavage of the C4H8+ ion occurs via a ``loose'' transition state, without prior isomerization. The results suggest that the previously reported differences in the 70-eV mass spectra of the C4H8 isomers are due in part to differences in the breakdown curves of the isomers.
Reactivity of Excited States in Cumene Liquid and Glass at Low Temperatures
Authors: Richards J. T. , Thomas J. K.
Published: February 2004

Excited singlet and triplet states of cumene (isopropylbenzene) have been produced in cumene liquid at 23 and −78°C, and in cumene glass at 77°K, by short 12-nsec pulses of 3-MeV electrons. In the presence of added solutes such as anthracene and naphthalene, singlet and triplet states of these compounds are also observed. The spectra of the short-lived species have been recorded by the pulse radiolysis technique and these are discussed. The rates of energy transfer from both cumene singlet and triplet states to added solutes at 77°K have been investigated. The rate of singlet energy transfer from cumene to naphthalene was found to be k3〉3×10−12M−1· sec−1 while the rate of triplet energy transfer to naphthalene was much slower, k2=5.7× 108M−1· sec−1. The lifetime of the triplet state of cumene at 77°K under the pulse conditions used was 2.8 μsec. The nature of the processes leading to the excited states is briefly discussed.
Vibrational Excitons and Polaritons in Molecular Crystals
Authors: Barentzen H.
Published: February 2004

A classical microscopic theory is presented for vibrational excitons interacting with the electromagnetic radiation field in uniaxial and biaxial molecular crystals. The coupled exciton—photon field leads to an eigenvalue equation, the solutions of which are polariton modes. It is shown how their frequencies ω(k) can be calculated, if the oscillator strengths are known. It is further shown, that there is a close connection between factor-group splitting and LO/TO splitting. That part of the effective field, whose range is bounded by the surface of the Lorentz sphere, produces factor-group splitting, while LO/TO splitting is caused by the long-range part of the effective field, which is produced by the matter outside the Lorentz sphere.
Enskog Theory and the Relationship between the Transport Coefficients of Fluids
Authors: Frisch H. L. , McLaughlin E.
Published: February 2004

A direct test of the dense fluid of hard spheres transport theory of Enskog is proposed utilizing certain ratios of the coefficients of self-diffusion, shear viscosity, and thermal conductivity. Application of the simple test to computer generated molecular dynamics of hard spheres transport data and available experimental data on dense fluids composed of roughly spherical molecules show that: (1) Enskog theory describes both the molecular dynamics data and the experimental data up to densities V0/V=0.5 and (2) departs from both significantly above that density value, while (3) molecular dynamics on hard spheres transport data with temperature dependent diameter appears to account adequately for the available experimental data.
Analytical Evaluation of Multicenter Molecular Integrals. I. Two-Center Overlap and Two-Center Coulombic Integrals over Hydrogenic Orbitals of Integral Principal Quantum Number
Authors: Alper Joseph S.
Published: February 2004

A new method for evaluating multicenter molecular integrals is presented. This approach makes use of the group-theoretic properties of the four-dimensional spherical harmonics which are related to the Fourier transforms of hydrogenic wavefunctions. The method is applied to the case of two-center overlap and two-center Coulombic integrals whose orbitals have integral principal quantum numbers.
Rederivation and Analysis of Fixman's Theory of Excess Sound Absorption near Fluid Critical Points
Authors: Gutschick Vincent P. , Pings C. J.
Published: February 2004

We retrace the thermodynamic and hydrodynamic analysis used by M. Fixman [J. Chem. Phys. 36, 1961 (1962)] in the first quantitative explanation of the anomalously large sound absorption near fluid critical points. With some oversights and ambiguities corrected, the basis theory is seen to be firmly based in classical thermodynamics and hydrodynamics. The use of the Ornstein—Zernike, Debye, and Flory—Huggins models for reduction of key quantities appears necessary for thermodynamic consistency. For analysis of experimental data, Fixman's theory is preferred over alternative theories, though no one theory is truly satisfactory. With a view toward interpreting our data presented in the following paper [V. P. Gutschick and C. J. Pings, J. Chem. Phys. 55, 3845 (1971)], we argue the applicability of Fixman theory in systems having a strong background of additional (thermal) relaxation.
Ultrasonic Investigation of the Lower Consolute Point of the 2,6-Lutidine: Water System
Authors: Gutschick Vincent P. , Pings C. J.
Published: February 2004

Sound absorption coefficients and velocities have been measured over ranges in frequency, temperature, and composition for 2, 6-lutidine/water near its critical mixing point. Large excess absorption coupled to critical fluctuation dynamics is found, as in other binary mixtures. A strong background of ordinary thermal relaxation is also apparent. Interpretation of the details of the absorption and velocity, as well as of auxiliary data on the shear viscosity and density, in terms of the Fixman mechanism of critical region absorption combined with a chemical association model cannot be attempted quantitatively. The reason lies in defects in Fixman theory for the composition dependence of the critical absorption and in the inherent inability of the chemical association model to account for phase separation behavior. Nevertheless, Fixman's form for the absorption as a function of frequency and temperature at the critical composition is satisfactory, and some important qualitative aspects of binary fluid structure come to light, including inherent differences of upper and lower consolute points.
Soft Modes in Molecular Crystals
Authors: Raich J. C. , Etters R. D.
Published: February 2004

The self-consistent phonon approximation is applied to study the temperature dependence of the libron and phonon modes for simple molecular crystals. Several linear chain models are studied to illustrate the soft mode behavior of these excitations near the orientational order—disorder transitions that occur in many molecular crystals. It is shown that both libron and phonon frequencies are strongly temperature dependent in the neighborhood of the transition in qualitative agreement with experimental observations. Both the cases of strong and weak orientational coupling are considered. The effects of the cubic anharmonic terms are also discussed.
Network Alteration in Thallium Aluminogermanate Glasses
Authors: Riebling E. F.
Published: February 2004

Ternary thallium aluminogermanate glasses were prepared with Al/Tl ratios of 0.444 and 1.00 and Tl2O contents as high as 26 mole %. Measured densities and refractive indices of these glasses, some of them were highly colored, were converted to molar volumes and molar refractivities. The partial molar volume results suggest that GeO6 octahedra stability is more or less independent of univalent cation type (rare-gas-vs-pseudo-rare-gas types) and that GeO6 octahedra cease to exist for Al/Tl ratios greater than 0.5. Volume and visual viscosity evidence for network retention with Al2O3/M2O=1.00 glasses is presented. There appears to be a direct relationship between the refractive index and the Tl–O packing efficiency. The onset of color at about 15 mole % Tl2O appears to be related to the greater polarizing power of Tl+ compared to K+. Molar refractivity calculations agree with this model for the environmental changes encountered by Ge4+ and Tl+.
Large Angle Elastic Scattering of Ar+ by He
Authors: Chiang M. H. , Gislason E. A. , Mahan B. H. , Tsao C. W. , Werner A. S.
Published: February 2004

Measurement of accurate differential cross sections for systems of the type ``heavy projectile light target'' are shown to be practical, provided measurements are restricted to large center-of-mass scattering angles θ. As an example, cross sections for the system Ar+−He have been measured from θ=60–180° in the energy range 2.7–9.1 eV. Using two-parameter repulsive potentials the results are inverted to yield a potential which reproduces the scattering at all energies. Dramatic evidence is given that potentials of the form V(r)=K/r3 are unsatisfactory for fitting the intermolecular potential in the region of 1–10 eV. The potential derived from these experiments is an average of two molecular potentials, since both the X 2Σand A 2Π states of Ar+−He correlate to ground state atoms. Comparisons are made with theoretical estimates of the two molecular potentials and with the Ar−He+ and Ar−He potentials.
Effect of Chemical Exchange between D2 and HBr on the Thermal Diffusion Separation of D and H in a Trennschaukel
Authors: Mathur B. P.
Published: February 2004

The effect of chemical exchange on the thermal diffusion separation of isotopes is investigated by use of a ``trennschaukel'' and the results of the limited investigation of the D2-HBr system are reported. Although the system has some advantages for investigating the magnitude of the various effects that occur, it turned out to be a rather complicated system because of the number of species present (D2, HD, H2, HBr, DBr) and the corrosive nature of HBr. The D2–HBr system was studied first without catalysis of the exchange reaction, and then with a platinum catalyst present. Without a catalyst considerable concentration of deuterium occurs in the hot region. With a catalyst the isotopic equilibria are established among the species with D being transferred preferentially to the bromide molecules which then concentrate in the cold region. However, this effect and the thermal diffusion effect for D2 and HD relative to H2, which also tend to concentrate D in the cold region, were not sufficiently large to make the over-all ratio (D/H)hot/(D/H)cold less than 1. This ratio without catalysis was between 1.4 to 1.1 depending on the mole fraction of D in the D2–HBr mixture. With catalysis of the exchange reaction, the ratio was reduced to between 1.2 and 1.05 without significant dependence on the concentration of deuterium in the mixture.
Intramolecular Proton Transfer in the Excited Singlet State of 3-Hydroxy-2-naphthoic Acid
Authors: Ware W. R. , Shukla P. R. , Sullivan P. J. , Bremphis R. V.
Published: February 2004

Studies of fluorescence quenching via intramolecular proton transfer are described for the systems 3-hydroxy-2-naphthoic acid in several solvents. It has been found that bases which promote the proton transfer in nonpolar solvents function by parallel static and dynamic mechanisms and that the mechanism proposed by Hirota, which assumes rapid establishment of the proton transfer equilibrium during the lifetime of the excited state, is inadequate. The mechanisms of both the static and the dynamic processes have been investigated by using fluorescence lifetime techniques and by making steady-state fluorescence quenching measurements. The results for various solvents and various temperatures are reported for the acid, its methyl ester, and the corresponding methoxy derivative.
Use of the Nonsymmetrical Wavefunction. II. Dynamic Polarizability of Molecular Hydrogen
Authors: Ando Toshihiko , Saika A.
Published: February 2004

The nonsymmetrical (NS) wavefunction is employed to calculate the real- and imaginary-frequency dynamic polarizabilities of the hydrogen molecule, and double perturbation theory allows one to calculate them through first order in electron correlation within the same theoretical framework. From the imaginary-frequency polarizability, the London coefficients for the dispersion interactions of H2–H2 and H–H2 are also obtained. The results in the shielding and geometric approximations are compared with other theoretical and experimental values, and it is found that the use of the NS wavefunction can be extended to time-dependent problems with reasonable accuracy and much ease of computation.
Angular Variation of Intensities of Forbidden Lines in CaCO3:Mn2+ in Parallel and Perpendicular Configurations
Authors: Narayana P. A.
Published: February 2004

The angular variation of intensities of electronic forbidden (Δ M=2, Δ m=0) and nuclear forbidden (Δ M=1, Δ m=−1) transitions in Mn2+:CaCo3 in parallel and perpendicular configurations was investigated. The intensity expressions for these transitions, assuming that the direction of the rf magnetic field makes an arbitrary angle with the direction of the static magnetic field, were derived. It is found that there is a good agreement between the theoretical and experimental results. From the comparison of the spectra in the parallel and perpendicular configurations for θ=0 and 12 π, it is concluded that D, A, and B have the same sign.
Low-Magnitude, Pure-Primary, Hydrogen Kinetic Isotope Effects
Authors: Stern Marvin J. , Schneider Mary E. , Vogel P. Christian
Published: February 2004

It is shown theoretically that low-magnitude, primary, hydrogen kinetic isotope effects may be characterized by the same types of temperature-dependence irregularities that have been previously shown to be expected fairly commonly for secondary hydrogen isotope effects and primary heavy-atom isotope effects. Upper limits are given for the magnitudes of pure-primary and mixed-primary—secondary hydrogen kinetic isotope effects possibly associated with such temperature-dependence ``anomalies.''
Instabilities in Coupled Chemical Reactions with Pressure-Dependent Rate Coefficients
Authors: Ortoleva Peter J. , Ross John
Published: February 2004

Instabilities are investigated in a model system consisting of several coupled chemical reactions; one reaction step is autocatalytic, and in another partial molar volume changes and pressure dependent rate coefficients are considered. The hydrodynamic equations of motion (for density, mass velocity, and concentration of chemical species) for this system are linearized in small deviations from steady state. The behavior of the system is analyzed by means of a set of hydrodynamic mode coordinates and their corresponding eigenvalues; the system is shown to be unstable under certain conditions not only to perturbations in concentrations but also to other hydrodynamic variables. For spatially homogeneous modes (k=0) the stable, marginally stable, unstable, oscillatory, and nonoscillatory regions of the eigenvalue spectrum are calculated for several limiting cases of the various experimental parameters. The normal modes are also calculated in the same limiting cases. A phase diagram is constructed for the stability of the system to homogeneous perturbations in terms of reduced parameters. For k≠0 there appear the expected acoustic modes but their form is altered by the presence of the reactions. Some of the reaction modes at k≠0 become unstable closer to chemical equilibrium than the corresponding modes in the homogeneous case (k=0). This result holds even in the limit of no diffusion. In that limit there exists a new mechanism of symmetry breaking which establishes inhomogeneous reaction modes due to the dynamical coupling of scalar equations of reaction (with pressure-dependent rate coefficients) and the vector equation of conservation of momentum. Possible biological applications of the theory are mentioned.
Low Temperature Infrared and Raman Spectra of the Ammonium Halides
Authors: Harvey K. B. , McQuaker N. R.
Published: February 2004

Using infrared and laser Raman techniques the vibrational spectra of seven of the eight low temperature phases of the ammonium and deuteroammonium halides (halide ion=Cl−, Br−, and I−) have been recorded. More complete assignments than previously available have been made for the vibrations of crystalline NH4+ and ND4+ ions of Td and D2d symmetries. These include assignments for longitudinal components of infrared active vibrations. Frequencies of acoustical translations are inferred by assigning combinations involving the ν1(A1) ammonium ion lattice vibrations and acoustical translations.
Polarized Optical Absorption Spectrum of Ho3+ in HoCl3· 6H2O
Authors: Stöhr Joachim , Gruber John B.
Published: February 2004

The optical absorption spectrum of Ho3+ in single crystals of HoCl3· 6H2O has been investigated at 4.2°K between 2500 and 9000 Å. Polarization studies have been carried out on most spectroscopic groups in the region between 3200 and 9000 Å. The far-infrared spectrum, reported between 30 and 400 cm−1 at room temperature, made it possible to distinguish between the optically observed vibronic and electronic (zero-phonon) spectra. The observed centers of gravity of the 4f10[SL]-J levels of Ho3+ are compared to those calculated previously for Ho3+ in LaCl3.
Model for the Trapped Electron in 3-Methylpentane Glass—An Electron in a Linear Random Lattice
Authors: Funabashi Koichi , Maruyama Yusei
Published: February 2004

A set of 22 randomly spaced molecules and an excess electron was studied by the method of tight-binding approximation. Optical transition probabilities between the lowest (ground) state and all the other states were computed approximately and plotted against transition energies. It was found that when fluctuation in transfer energy is large the optical transitions can be grouped into two bands. The first band consists of the transitions between the lowest state (localized) and the ``conduction band,'' and the other one involves the ground state and the localized excited states which lie above the conduction band. As the energy fluctuation is diminished, those two bands merge together. A possible relationship of this model to the absorption spectrum of the trapped electron in glassy 3-methylpentane is discussed.
Alignment of Nematic Liquid Crystals
Authors: Lee James D. , Eringen A. Cemal
Published: February 2004

Two problems in the theory of nematic liquid crystals are formulated. One is concerned with the change of orientation due to magnetic field and the other with shear flow. The solutions of the governing differential equations explain the physical phenomena which have been observed experimentally, namely the alignment of nematic liquid crystals with the magnetic field and with shear flow. In fact, it is shown that these two phenomena are closely related to each other.
Mass-Spectrometric and Vapor Pressure Studies on the Sublimation of Realgar (As4S4)
Authors: Munir Zuhair A. , Street G. Bryan , Winters Harold F.
Published: February 2004

The nature of the sublimation process for the molecular solid realgar (As4S4) has been investigated using mass spectrometric and vapor pressure techniques. Vapor originating from the congruent sublimation of this compound is composed predominantly of As4S4(g) molecules, with smaller concentrations of other species. Of these latter species, those of As4S3, As4, and As2 are believed to originate from partial decomposition of solid As4S4. The amount of these decomposition products relative to As4S4(g) in the vapor phase was found to decrease with increasing temperature. The mass spectra of the vapors resulting from the sublimation of synthetic and natural samples of realgar were essentially the same. The expression for the equilibrium sublimation of realgar in the temperature range 452–534°K is log P(atm)= (8.021±0.200) − (0.619±0.010)104/T. On the assumption that realgar sublimes primarily to As4S4(g) molecules, the second law heat and entropy for sublimation at 493°K were calculated to be 28.3±0.5 kcal/mole and 36.7±0.9 eu, respectively. From free surface sublimation studies the sublimation coefficient at 455°K was found to be 0.47.
Cluster Expansion and Autocorrelation Functions: Self-Diffusion Coefficient
Authors: Eu Byung Chan
Published: February 2004

A density series of the autocorrelation function for the self-diffusion coefficient of an isotropic fluid is obtained by means of a cluster expansion (different from that used by Ernst, Haines, and Dorfman) of the resolvent operator corresponding to the Liouville operator for the system. Nonsingular potentials are assumed for the interaction potential between pairs of the particles. It is shown that the self-diffusion coefficient, and thus transport coefficients in general, can be put into a form similar to that of equilibrium statistical mechanics, when the resolvent operator is expanded in terms of clusters just as the configuration integral is expanded in terms of the cluster integrals in equilibrium statistical mechanics. The cluster functions may also be expanded into irreducible cluster functions. This decomposition of the clusters into the irreducible clusters is derived from the integral equations for the collision operators corresponding to the clusters, and makes it possible to establish formally, to an arbitrary order of density, Zwanzig's procedure of inverting the resolvent operator, GN (ε). The density coefficients of the inverted operator, Bm+1 (ε), are given in terms of the irreducible cluster functions and would exist as ε→ 0, provided that the collision operators fulfill certain analytic properties. On the assumption of an exponential potential for a two-dimensional gas, B3 (ε) is estimated to be finite in the very weak interaction limit as ε→ 0.
Exponential Hamiltonian: Convergence in an iterated product representation for a linear harmonic oscillator
Authors: Handler George S.
Published: February 2004

Using an iterated product representation of an exponential Hamiltonian, the density matrix for the potential V(x) = 1/2Kx2 is derived in nth-order approximation. The density matrix so found is shown to converge to the exact quantum mechanical result in the limit of n → ∞.
On the theory of Brownian motion. VI. Asymptotic solution of a retarded Fokker-Planck equation
Authors: Mazo Robert M.
Published: February 2004

The solution of a retarded one-dimensional Fokker-Planck equation is expressed in terms of a contour integral. This integral is evaluated asymptotically for two forms of the force correlation function: (a) a delta function (classical case-no retardation) and (b) a t−3/2 fall off for long times. Solutions are expressed in terms of known functions. It is indicated how this technique can be extended to the three-dimensional case, and the appropriate Green's functions are displayed.
Transition probabilities for the Meinel band system of N2+
Authors: Cartwright David C.
Published: February 2004

Newly measured natural lifetimes for vibrational levels 1–8 and 10 of the A 2Πu state of N2+ have been analyzed by a weighted, nonlinear, least squares technique to extract the absolute transition moment and its dependence on internuclear distance. Both are considerably different from previous results and lead to different transition probabilities and oscillator strengths. Transition probabilities for both v′=0 and 9 are obtained by interpolation of the ``electronic'' portion of the band strength and result in predicted values for the lifetimes of the v′=0 and 9 levels.
Deuteron relaxation in paramagnetic solutions
Authors: Fung B. M.
Published: February 2004

A previous suggestion by several authors that the ratios of relaxation times of deuteron and proton in paramagnetic solutions should be equal to (γH/γD)2, or 42.4, has not been substantiated by experimental data. Several factors that cause the deviation are discussed. These factors are: (1) chemical exchange, (2) isotope effect on internal rotation, (3) cross correlation between dipolar and quadrupolar interactions, and (4) time dependence of the electric field gradient due to spin-orbit coupling. Of these factors, only (3) can be neglected in all cases.
Infrared spectra and vibrational assignments of trans–CH3N–NH, CH3N–ND, CD3N–NH, and CD3N–ND
Authors: Ackermann Martin N. , Burdge Jeremy J. , Craig Norman C.
Published: February 2004

Based on infrared spectra (4000–200 cm−1) of the gas phase, condensed phase (77°K), and nitrogen matrices (20°K) vibrational assignments for trans-CH3N–NH, CH3N–ND,  CD3N–NH, and CD3N–ND have been obtained. The assignments of the fifteen fundamentals of each molecule are well founded in experiment except for the provisional values for the torsional mode. For trans-CH3N–NH the fundamentals are: (a′) 3127, 2992, 2925, 1559, 1457, 1435, 1382, 1120, 920, and 557 cm−1, (a″) 2988, 1430, 1140, 844, and ∼ 170 cm−1. Normal coordinate calculations are presented in support of these assignments and as a basis for further analysis of the published infrared spectra of the parent molecule, trans-N2H2. It is shown that the spectra for N2H2, N2HD, and N2D2 can now be interpreted in a unified way.
Theory of biomembrane phase transitions
Authors: Nagle J. F.
Published: February 2004

Experiments on the chain melting thermal transition in simple biological membranes are briefly reviewed and shown to indicate that a microscopic order-disorder model may be appropriate to describe the thermodynamics of the transition. To test this conclusion further a pair of two dimensional lattice models (A and B) are introduced and the statistical mechanics is solved exactly using dimer techniques. The phenomenological parameters required by the models are evaluated from experiments on other systems. The more realistic of the two models (model A) has a second order transition at a temperature of 353°K compared to 315°K for dipalmitoyl-L-α-lecithin membranes. However, the specific heat peaks do not have the same shape and the transition is broader for model A than for the experiment. In comparison, the less realistic model B has a first order transition at 925°K, considerably higher than the experimental transition temperature. From these results it seems likely that the points of disagreement between model A and experiment may be due to the simplified features of model A. It is concluded that the basic order-disorder model is likely to be correct for the main transition. There is also a smaller transition at a lower temperature which is also discussed in terms of an order-disorder model involving the phospholipid head groups. In this case the calculation shows that the simple model is either wrong or that some additional features must be added.
Towards an understanding of the form of correlated wavefunctions for atoms
Authors: Handy N. C.
Published: February 2004

The transcorrelated method enables energies and properties to be found from correlated wavefunctions CΦ. The purpose here was to give some rules, for small atoms, to write down correlation functions C=Πi>jf(rij) which when multiplied into Φ, a suitable linear combination of Slater determinants, give an accurate correlated wavefunction CΦ. For the He isoelectronic series a form can be found for f(rij) in which the only correlation parameter is Z, the nuclear charge, such that CΦSCF gives transcorrelated energies within 0.003 a.u. of the exact energy (Z = 1,2,3,10). This form of f(rij) is extended to atoms with two shells, so that f depends upon parameters Z1 if ri and rj are in the first shell, and Z2 if they are in the second shell. Through independent assessments of the accuracy of these wavefunctions for Be, C, O and Ne, rules can be given for Z1 and Z2. Using these rules, the predicted correlation energies of eight such atoms were calculated and found to be reasonably accurate.
Vibrational spectrum of chlorine heptoxide
Authors: Witt J. D. , Hammaker R. M.
Published: February 2004

The infrared and Raman spectra of chlorine heptoxide, Cl2O7, have been recorded in the vapor, liquid, and solid phases. The fundamental vibrations, with the exception of the two torsional modes, have been assigned under C2 symmetry. The resulting assignment leads to a near degeneracy of the skeletal stretches near 700 cm−1, and places the skeletal bending mode at 154 cm−1. A normal coordinate analysis has been carried out for Cl2O7 and related ClO3 group-containing molecules. Similarities in the skeletal stretching force constants (KR≃ 3 mdyn/ Å) and in the Cl–O bond lengths of Cl2O and Cl2O7 suggest that bonding is substantially the same in both molecules, thus implying a Cl–O single bond in the skeleton of Cl2O7. Thermodynamic properties of Cl2O7 have been calculated using torsional frequencies estimated from mean amplitudes of vibration.
Condensation on a spherical droplet
Authors: Loyalka S. K.
Published: February 2004

The problem of condensation on a spherical droplet situated in an infinite expanse of an isothermal vapor diffusing through a heavy background gas is studied. The BGK model is used and the condensation rate is calculated by following the work of Marshak (1947) on Milne's problem in neutron transport.
Correlation functions of classical fluids. II. The direct correlation functions of mixtures of Kihara molecules in the Percus-Yevick theory and the integral compressibility equation of state
Authors: Lee Lloyd L. , Hulburt Hugh M.
Published: February 2004

We have determined the direct correlation functions Cij(r) for binary mixtures from the Percus-Yevick integral equation assuming the Kihara potential. The variations of Cij(r) with temperature, density, and composition are examined. The characteristics of the correlations functions are found to be complex functions of the thermodynamic state that obey no simple rules. For most part, the theoretical results are confirmed by experimental information. The resulting Cij(r) are used in an ``integral'' compressibility equation of state, newly proposed by Baxter, for mixtures to produce the P-V-T information on the argon-nitrogen system. Comparison with the virial equation of state and experiments shows that the predictions from Baxter's formula are superior at low densities, while the virial pressures are better at high densities. We also investigated the direct correlation functions of some pure substances, including argon, krypton, and xenon. For the case of argon, the use of a numerical potential advanced by Dymond and Alder proves to sustain a better comparison with experimental x-ray diffraction data.
Free energy near the critical point of fluids according to the scaling hypothesis
Authors: Lentini E. , Vicentini-Missoni M.
Published: February 2004

A phenomenological equation of state which obeys the scaling hypothesis and gives a good representation of data in the critical region of fluids has been used to calculate the free energy per unit volume. An interpolation formula for the scaled free energy function a(x), which is useful for analytic calculations of thermodynamic functions, is proposed and compared with experimental specific heat and pressure data.
Uranium-fluorine lattice vibrations of β1-dipotassium uranium fluoride
Authors: Ohwada Ken
Published: February 2004

The infrared spectrum of β1-dipotassium uranium fluoride, β1-K2UF6, has been measured in the frequency region from 4000 cm−1 down to 30 cm−1. A normal coordinate analysis of the optically active U–F lattice vibrations has been made on the basis of a chain model of infinite (UF6)∞2− neglecting the potassium atoms. Some of the observed bands have been assigned to the U–F lattice vibrations on the basis of the results of this analysis. The stretching and repulsion force constants have been obtained and discussed with respect to the uranium-fluorine bond distances. Furthermore, to explain the lower vibration frequencies below 100 cm−1, the interactions between the potassium ions and the infinite (UF6)∞2− chains have also been investigated.
Measurement of the thermal conductivity of helium up to 2100°K by the column method
Authors: Faubert Francis M. , Springer George S.
Published: February 2004

The thermal conductivity of helium was measured at atmospheric pressure in the range 800–2100°K by the column method. The data could be correlated by the polynomial λ = 0.635 × 10−1 + 0.310 × 10−3T−0.244 × 10−7T2, where λ is in watts per meters degrees Kelvin and T is in degrees Kelvin. The results obtained were compared with previous thermal conductivity measurements. The data of Desmond and Saxena and Saxena agree closely with the present results; the data of Timrot and Umanskii appear to be too low and those of Blais and Mann too high. Values for f=λ/ηCv, computed using measured thermal conductivities and available viscosity data, were found to agree well with classical results from kinetic theory.
Exponential or scaled SCF orbitals in correlated wavefunctions for two-electron atoms
Authors: Carlton Terry S. , Morrell James A. , Arnow David M.
Published: February 2004

Wavefunctions for the ground state of H−, He, Li+, and Be2+ are approximated by the product of orbitals with a correlation function. Use of optimally scaled SCF orbitals in place of fully optimized orbitals causes an additional energy error of at least 0.001 hartree. Exponential orbitals are superior to scaled SCF orbitals in open-shell cases or if the correlation function increases with (r1 − r2)2; otherwise SCF orbitals are superior. Application of correlation functions to open-shell wavefunctions causes the outer orbital to contract more than the inner orbital, which actually expands slightly except at low atomic numbers. If the correlation factor depends on (r1 − r2)2 as well as r12, the inner and outer exponential orbitals can become identical when Z is greater than 2. Several three-parameter wavefunctions have errors of 0.0010–0.0018 hartree. Good approximations to completely flexible correlation functions of r12 alone are 1 − A exp(− B r12) and (1 + A r12)C. In the latter function and [1+Ar12+B(r1−r2)2]C the optimum C can be predicted accurately by extrapolation.
Excitation of forbidden transition in helium by electron impact at kinetic energies of 300–500 eV. Singlet-triplet transitions at high kinetic energy
Authors: Skerbele Ausma , Harshbarger William R. , Lassettre Edwin N.
Published: February 2004

The transition 23S← 11S in helium has been studied by electron impact over the kinetic energy range 300–500 eV. The ratio σT/σS of scattered current for this transition to that for 21S← 11S is a maximum at scattering angle θ of 0°. The intensity ratio decreases with increasing θ to a minimum (which is below background) and then increases again to barely observable levels at θ ≥ 12°. At θ = 0° the ratio exceeds all presently developed theories by at least two orders of magnitude. At θ ≥ 12° the ratio agrees approximately with the Born-Oppenheimer formula for exchange scattering. The ratio of cross sections for the transitions 21S← 11S and 21P← 11S has been determined over the range θ = 5° to 20°. Up to 15°, agreement with the Born approximation is good. Agreement is poor (25%) at θ = 20°.
Dipole moment and hyperfine constants of OD A2Σ+ from ab initio calculations
Authors: Green Sheldon
Published: February 2004

The dipole moment and hyperfine constants of OD (and OH) A2Σ+ have been obtained from ab initio calculations, using self-consistent field and configuration interaction techniques. Special attention has been given to the effects of basis set quality and vibrational motion. For OD A2Σ+ in the ground vibrational level, a value of μ = 1.84±0.06 D is obtained. This is consistent with a recent measurement by Weinstock and Zare but not with an earlier determination of Scarl and Dalby.
Intensity correlation of light scattered from hydrodynamic fluctuations
Authors: Tartaglia P. , Chen S. H.
Published: February 2004

We investigate conditions under which measurement of intensity correlation function of scattered light gives correlation functions of hydrodynamic fluctuations. We show that for a normal fluid the validy of the fluctuating hydrodynamic equations guarantees that the measured intensity correlation function is simply related to the hydrodynamic correlation functions. Even for the fluid near the critical point we show that this is true under the usual experimental condition, the so called non-Gaussian terms being too small to be observed. We then extend the same consideration to the case of clipped intensity correlation function.
Photoelectron emission by solvated electrons in liquid ammonia
Authors: Aulich H. , Baron B. , Delahay P. , Lugo R.
Published: February 2004

Photoelectron emission (PEE) by potassium (0.002–3 mole liter−1) and sodium (0.013–0.21 and 7.2 mole liter−1) in liquid ammonia at −60°C was studied from 1.55 to 5.4 eV. The PEE spectrum is composed of the previously reported band with its maximum about 3.2 eV and a new band peaking about 4.6 eV. The highly asymmetric low-energy band is assigned to PEE by solvated electrons. Its interpretation by a recent model for PEE by solutions results in a linear dependence of the range of quasifree electrons in solution on photon energy. The quantum yield appears to be proportional to the square root of the analytical metal concentration up to 0.1 mole liter−1. The 4.6 eV symmetric PEE band is interpreted as the result of bound-bound transitions (similar to β band for F centers) followed by autoionization. Experimental methods are outlined, and their details are available in an unpublished report.
High pressure optical studies of rare earth ions in CaF2 and other fluorides
Authors: Wang P. J. , Drickamer H. G.
Published: February 2004

High pressure optical absorption studies have been performed on a series of rare-earth ions Sm2+, Dy2+, Sm2+, and Tm2+ in CaF2, Tm2+ in SrF2, EuF2, and Gd3+ in CaF2. For the first five substances the transitions from the 4fn ground state to the 4fn − 1 5d configuration shift to lower energy with increasing pressure. This is consistent with the 4f→ 5d electronic transitions observed or postulated in a number of rare-earth metals at high pressure. The impurity center introduced by gadolinium in CaF2 has been shown to be a Gd3+ ion associated with a neighboring anion vacancy containing two trapped electrons. The shifts of the three peaks observed are consistent with the assignments of Alig. Two new absorptions are induced irreversibly by pressure. These behave very much like pressure-induced peaks in x-irradiated CaF2 which have been attributed to electrons trapped at lattice imperfections.
On the share of vacuum modes in van der Waals' attraction
Authors: Langbein D.
Published: February 2004

The interrelations between the different investigations into the the van der Waals' energy between macroscopic bodies reported by Lifshitz, van Kampen et al., and Langbein are considered. It is shown that the surface mode hypothesis, which causes several branch points and Riemann surfaces rather than a single frequency plane, can be avoided by using finite boundary conditions. The resulting symmetric treatment of all vacuum modes, in addition, yields a more symmetric final energy expression. The frequency integral over the dispersion function extends from −i∞ to + i∞ rather than twice from 0 to +i∞. The use of the latter integral means an unnecessary neglect of terms of sixth order in the electron-photon coupling parameter.
Trajectory study of reactions in HBr–Br2 systems
Authors: White John M.
Published: February 2004

A large number of trajectories have been calculated employing a semiempirical potential energy surface for H2Br2. Primary attention has focussed on reactions of H with HBr and Br2 and the isotopically substituted analogs. Cross sections have been determined for a large number of different relative velocities and initial vibration-rotation states of the diatomic reactant. Center-of-mass angular scattering distributions and energy partitioning distributions were determined and compared with experimental data from molecular beam and infrared chemiluminescence data. Good agreement is found in the case of energy partitioning with about 80% of the available energy appearing as internal energy. Agreement is excellent in the case of angular scattering—the trajectory calculations predict a small amount of forward scattering, which increases and becomes fairly uniform in the backward hemisphere. Rate constants were computed from cross sections for both thermal and hot atom experiments. Absolute thermal rate coefficients for H + Br2 and H + HBr are generally to high. The ratio of these rates compares favorably with experimental results. The thermal rate of abstraction (D+HBr → DH+Br) versus exchange (D+HBr → DBr+H) has been computed and is in poor agreement with experimental results. For hot atom reactions occuring in the HBr–Br2 and DBr–Br2 systems, agreement is satisfactory.
Theory of vibronic intensity borrowing. Comparison of Herzberg-Teller and Born-Oppenheimer coupling
Authors: Orlandi G. , Siebrand W.
Published: February 2004

The Herzberg-Teller theory of vibronic intensity borrowing is reinvestigated. A potentially serious deficiency is found in the conventional approximation scheme based on neglecting vibronic perturbation of the ground state relative to that of the excited state. Simple theoretical models are studied and show systematic cancellation of the lowest-order induced transition dipole moment if both vibronic perturbations are included. As a result the vibronic coupling between Born-Oppenheimer states via nuclear momenta, for which such a cancellation does not occur, tends to contribute measurably to the induced transition moment, contrary to what usually is assumed. Two methods to distinguish between Herzberg-Teller-type (HT) and Born-Oppenheimer-type (BO) contributions are discussed, namely the absorption-emission asymmetry and the isotope effect. The former results from interference between HT and BO terms, which is usually constructive in absorption and destructive in emission; the latter is due to the fact that BO coupling is much more sensitive to isotopic substitution than HT coupling. The induced components of S0−S1 transitions in benzene, pyrazine, and pyrene are shown to exhibit anomalous isotope effects and/or absorption-emission asymmetries which indicate substantial BO contributions, even when normal-coordinate rotation upon deuteration or excitation is taken into account. It is concluded that a quantitative calculation scheme for vibronically induced intensities must include vibronic perturbation of the ground state and both HT and BO couplings.