bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport in weakly coupled systems
Authors: Dowling Gary R. , Davis H. T.
Published: February 2004

The weak coupling kinetic equation singlet distribution function for both pure and binary mixture systems is solved using the Chapman-Enskog technique. These solutions are used to specifically investigate the effects of spatial and temporal delocalization in the collision operator upon the hydrodynamic equations and kinetic transport coefficients of a fluid. It is shown that both temporal and spatial delocalization must be included in the collision operator if the correct hydrodynamic equations for dense fluids are to be obtained. In addition, the contributions to the kinetic transport coefficients from the different types of delocalization are of the same order of magnitude so these effects should be considered simultaneously in dense fluid kinetic equations.
Orientational properties of the classical one-dimensional multipolar array
Authors: Mandell Myron
Published: February 2004

The static and dynamic properties of a linear array of classical free rotors with nearest-neighbor electric dipole and/or quadrupole interactions are considered. Such static properties as correlation functions and specific heat are calculated. A formalism is presented to treat the moments of the spectral function, and is applied to the pure dipole system, showing the gradual onset of the libronic excitations first treated by Frenkel. Some thoughts are given on the effects of long-range forces, on quantum effects, and on application to such real systems as N2 and HCl.
Hydrogen bonding between neon and water
Authors: Losonczy M. , Moskowitz J. W. , Stillinger F. H.
Published: February 2004

Portions of the neon-water ground-state potential hypersurface have been mapped, using the Hartree-Fock approximation with an extensive Gaussian basis. A weak linear (OH ··· Ne) hydrogen bond appears, with length 3.63 Å, and strength 0.17 kcal/mole. The analogous calculation for the argon-water pair predicts considerably less stabilization, in closer accord with pure electrostatic interaction of a permanent dipole moment (water molecule) and a polarizable particle (noble gas atom).
ENDOR of VF and VOH centers in CaO
Authors: Unruh W. P. , Chen Y. , Abraham M. M.
Published: February 2004

ENDOR (electron-nuclear double resonance) studies on CaO single crystals positively identify the VF center and resolve a discrepancy in the reported g values of the VOH center. Data for the same two centers in MgO were also obtained and compared with previous work. An analysis of the anisotropic hyperfine coupling constants shows that the relative lattice relaxation for both centers is roughly the same in these hosts. As expected, no motional averaging of the anisotropic resonance spectra was observed for either center.
Calculation of the magnetic susceptibility of the ammonia molecule
Authors: Chang Sherry S. , Hameka Hendrik F.
Published: February 2004

We performed an ab initio calculation of the diamagnetic susceptibility of the ammonia molecule by making use of gauge invariant atomic orbitals. The results are χzz = − 14.64 × 10−6 cgs units (along the molecular symmetry axis) and χxx = χyy = − 14.94 × 10−6. The total susceptibility is − 14.84, which differs by 9% from the most recent experimental value − 16.3 ± 0.8.
Electron repulsion integrals and symmetry adapted charge distributions
Authors: Pitzer Russell M.
Published: February 2004

Coupling coefficients with normalization different from that of vector coupling coefficients are defined to express products of symmetry orbitals in terms of symmetry adapted charge distributions of a convenient form. The latter are desired to make a systematic definition of independent electron repulsion integrals such that the integrands are totally symmetric, the optimal form for computation. The integrals arising in simple treatments of several well-known problems are expressed in terms of the newly defined integrals for purposes of illustration. It is shown how similar integrals result from employing irreducible tensor methods. The possibility of using the coefficients for other types of integrals is mentioned briefly.
Quenching cross sections for electronic energy transfer reactions between metastable argon atoms and noble gases and small molecules
Authors: Piper L. G. , Velazco J. E. , Setser D. W.
Published: February 2004

Reaction rate constants for the quenching of electronic energy in metastable argon (3P0,2) by Kr, Xe, and a number of simple molecules have been measured. A hollow, cold-cathode discharge excites the metastables in a flow apparatus. The concentration of metastables was followed by absorption spectroscopy as a function of time and of quenching molecule concentration. Quenching of Ar*(3P2) by Kr, CO, N2, CF4, and H2(D2) proceeds at rates between 0.6 and 7 × 10−11 cm3 molecule −1 · sec−1. Except for Kr, Xe, N2, CO, and CH4, the 3P0 metastable level is quenched slightly more rapidly than the 3P2 level. With the aid of data in the literature, the contribution from the product channels (Penning and associative ionization) are considered for quenching by NO and C2H2. These channels appear not to be of major importance for quenching since the ionization efficiency of these two reactions is low: ∼ 0.2 for NO and ∼ 0.1 for C2H2. The quenching mechanism is discussed in terms of both a curve crossing and a ``golden rule'' rate law; the latter appears to be favored.
Effect of the heavy atom on the nuclear shielding constant. I. The proton chemical shifts in hydrogen halides
Authors: Morishima Isao , Endo Kazunaka , Yonezawa Teijiro
Published: February 2004

The abnormal upfield bias of the proton chemical shift in hydrogen halides, HX, on going from X = F to I is examined theoretically in terms of the third-order perturbation theory including the spin-orbit interaction (λL · S). The expression for the new type of shielding constant σLS is presented in its complete form and in simplified form with the average excitation energy approximation. The numerical calculations using semiempirical SCF wavefunctions predict substantial contribution (51%) of this shielding effect (σLS) to the total shielding of the proton in hydrogen iodide.
Comparative study of accommodation coefficients of helium and neon on clean tungsten under transition, temperature jump, and free molecule conditions
Authors: Roach D. Vincent , Thomas Lloyd B.
Published: February 2004

Measurements of heat conduction by neon and helium between concentric cylinders under free molecule, transition, and temperature jump conditions have been made with particular care to insure that a well defined clean surface state of the inner (tungsten) cylindrical surface was maintained. Several kinetic theoretical treatments applicable to the various regimes have been utilized to calculate the thermal accommodation coefficients of these gases. Comparison of these accommodation coefficient values obtained by analysis of the data in the transition and temperature jump regimes by the Smoluchowski-Kennard temperature jump method, the Langmuir-Wachman mean free path method, and the Lees-Liu moment method with the accommodation coefficient values obtained on the same filament by the well established low pressure Knudsen method has been made, and the values are in remarkable agreement.
Infrared-infrared double resonance experiments using a two-photon technique
Authors: Freund S. M. , Johns J. W. C. , McKellar A. R. W. , Oka T.
Published: February 2004

Infrared-infrared double resonance experiments have been performed using two-level, three-level, and four-level systems in NH3. Use was made of the recently developed technique of microwave infrared two-photon spectroscopy which, in effect, makes infrared gas lasers tunable. Four kinds of experiments were done; (A) monitoring a burnt hole with two-photon spectroscopy, (B) burning a hole with two-photon pumping and monitoring it in the same way, (C) observing the transfer of a burnt hole to other levels due to weak collisions, and (D) observing thermal effects. The experiment (C) revealed a new feature of four-level infrared double resonance which does not exist in four-level microwave double resonance, that is, the velocity change of molecules due to collision can be monitored simultaneously with the state change. Implication of this for the study of collision-induced transitions is discussed.
Crystalline and noncrystalline effects in electron diffraction patterns from small clusters in an argon cluster beam
Authors: Farges J. , Raoult B. , Torchet G.
Published: February 2004

We present an electron diffraction study of extremely small clusters of argon atoms formed by homogeneous nucleation in an expansion nozzle system. The clusters, in general comprising less than 1000 atoms, yielded good quality Debye-Scherrer patterns under conditions essentially free from all substrate interactions. The high precision of the diffraction patterns, even at large angles, makes it possible to assign an effective fcc structure to the particles. However, an anomalously large 111 peak is observed consistently and may be interpreted as resulting from vestiges of noncrystalline structure exhibited by the aggregates in the early stages of their growth.
Transient initial condition effects for Brownian particle motion
Authors: Hynes James T.
Published: February 2004

The effect of a weak local initial deviation from equilibrium on the motion of a Brownian particle is investigated. The resulting initial condition effects, which are excluded in standard projection operator treatments by a special choice of initial condition, are determined by explicit calculation based on the comparison of linear response and linear hydrodynamic predictions. The contribution of the initial condition to the particle equation of motion is found to be long lived, in contrast to previous conjecture.
Symmetry assignments of the lowest CT excited states of ruthenium (II) complexes via a proposed electronic coupling model
Authors: Harrigan R. W. , Crosby G. A.
Published: February 2004

Temperature dependence measurements of the decay times of the observed charge-transfer luminescence of three ruthenium (II) complexes indicate a manifold of decaying excited levels in thermal equilibrium. Relative energies and decay constants for each level have been derived from the data for the tris(2, 2′-bipyridine)ruthenium(II) and tris(4, 4′-diphenyl-2, 2′-bipyridine)ruthenium(II) cations and for cis-dicyanobis(2, 2′-bipyridine) ruthenium(II). An electronic coupling model has been proposed that satisfactorily rationalizes the experimental results and allows the levels to be symmetry labeled.
Effect of pressure on the optical absorption of REF centers in Ce and Tb doped CaF2
Authors: Drotning W. D. , Drickamer H. G.
Published: February 2004

The effect of pressure to 80 kbar has been measured on the absorption peaks associated with REF centers in Ce and Tb doped CaF2. The results are compared with previous data for Gd doped CaF2. The lowest and highest energy excitations [α(1E) and γ(2E)] are associated with an excited state largely of metal 5d(eg) character. The intermediate peak has predominantly color center character. The results are qualitatively similar and consistent with Alig's assignments for all three rare earths. However, the mixing of rare earth and color center orbitals is markedly less for the Ce doped crystal than for the other two. A peak in the spectrum of the Ce doped CaF2 assigned to a 4f → 5d transition in trivalent cerium shifted to lower energy with pressure by an amount essentially identical with the shifts observed for similar transitions on a series of divalent rare earth ions in CaF2.
Possible applications of surface electromagnetic waves to measure absorption coefficients
Authors: Alexander R. W. , Bell R. J. , Ward C. A. , Weaver J. H. , Tyler I. L. , Fischer B.
Published: February 2004

We show that surface electromagnetic waves can probably be used to measure the absorption coefficients of materials overlaying metals. The proposed experimental method is illustrated in the infrared frequency range using water, Teflon, and polyethylene as sample materials.
Angular momentum role in oxygen recombination
Authors: Kivel Bennett
Published: February 2004

The dependence on the atomic oxygen ground state total angular momentum quantum number J of the three body recombination rate to form the ground molecular state X 3Σg- is calculated. An adiabatic approach of the atoms is assumed. For a thermal equilibrium distribution of the atoms in the 3PJ states, a 20% decrease in recombination rate as the temperature increases from 100 to 1000°K is found. The dependence is too small to warrent inclusion in the modified phase-space theory of reaction rates of Keck and co-workers.
On the inhomogeneous model of metal-ammonia solutions
Authors: Lelieur J. P.
Published: February 2004

The inhomogeneous model recently proposed by Jortner and Cohen for metal-ammonia solutions in the intermediate concentration range is used to determine the pressure and temperature coefficient of the electrical conductivity. It is shown that these quantities receive satisfactory interpretation in this model. The pressure coefficient of the electrical conductivity is explained on the basis that the metallic regions are more compressible than the dilute regions. This strongly supports the hypothesis of inhomogeneous conduction in the intermediate concentration range of metal-ammonia solutions.
External heavy-atom spin-orbit coupling—The T1 vibronic activity of naphthalene in p-dihalogenated benzene host crystals
Authors: Gash Bruce W. , Colson Steven D.
Published: February 2004

The phosphorescence of naphthalene in p-dibromobenzene, α-phase p-dichlorobenzene, and γ-phase p-dichlorobenzene host crystals has been studied at high resolution and 4.6°K. The T1 absorption of naphthalene in a p-dibromobenzene host crystal at 4.6°K was recorded by the use of excitation spectroscopy. With the exception of the b3gv17 fundamental (which is nearly degenerate with the agv1 fundamental and probably borrows intensity from it) only vibrations of ag symmetry are active in the naphthalene T1 absorption and emission. This vibronic activity indicates that the external spin-orbit coupling mechanism operative in the heavy-atom-containing chemically mixed crystal is different from the internal spin-orbit coupling mechanism active in the T1 of naphthalene in a deuteronaphthalene crystal. This enhancement of only totally symmetric modes indicates that the external spin-orbit coupling induced by heavy atoms is purely electronic in nature. The internal heavy atom effect is shown to enhance the totally symmetric modes of the parent naphthalene and to vibronically enhance the out-of-plane halogen modes. The external spin-orbit coupling mechanism induced by heavy atoms arises from a mixing of several singlet states with the naphthalene T1. This mixing could involve singlet states of either the naphthalene molecule or the surrounding host molecules.
Electron spin resonance study of γ-irradiated alkyl phosphates: (C2H5O)ṖO2− radical in magnesium diethyl phosphate (MgDEP)
Authors: Ezra F. S. , Bernhard W. A.
Published: February 2004

ESR studies of γ-irradiated [(EtO)2PO2]2Mg at 77°K show the presence of a free radical characterized by a 600–800 G hyperfine coupling to the P31 nucleus and no other resolvable couplings. This free radical arises, with equal probability, from the cleavage of either phosphorous ester oxygen bond. Single crystal data, taken at Q band, give Breit-Rabi corrected principal values of Az = 780, Ax = 615, Ay = 624 (± 5 G), gu = 2.0033, gv = 2.0040, gw = 2.0023 (± 0.0005) for cleavage of one of the ETO–P bonds and Az = 787, Ax = 619, Ay = 629 (± 5 G), gu = 2.0035, gv = 2.0038, gw = 2.0024 (± 0.0005) for the cleavage of the other ETO–P bond. From the hyperfine principal values it is calculated that 70% of the spin density is in an s p3 orbital centered on P31. The symmetry axis of this orbital, the Az direction, is within 10° of the broken EtO–P bond. Arguments are presented which favor the EtOṖO2− free radical over the alternative assignment of ṖO3=.
Electron attachment to cyclic anhydrides and related compounds
Authors: Cooper C. D. , Compton R. N.
Published: February 2004

Negative ion production cross section are sections are tabulated as a function of the bombarding electron energy for dissociative and nondissociative electron attachment to various cyclic anhydrides and related compounds. The unsaturated compounds, maleic anhydride (250 μsec), phthalic anhydride (313 μsec), pyromellitic anydride (8000 μsec), and maleimide (43 μsec) attach thermal electrons to form parent negative ions which are metastable with autodetachment lifetimes that decrease with an increase in the energy of the bombarding electron. The number in parentheses following each compound is the lifetime at peak cross section. Compound negative ion states are reported for the saturated compounds succinic anhydride (1.3 eV), cyclobutane-dicarboxylic anhydride (1.3 eV), glutaric anhydride (0.6 eV), and succinimide (1.1 eV) for electron energies given in the parentheses. In most of the anhydrides the most abundant anions produced by dissociatve electron attachment are metastable RCO2-* ions which result from the ejection of neutral CO from the parent molecules. Experimental evidence shows that the RCO2- dissociates following autodetachment. The metastability of an observed CO2-* ion is attributed to poor Franck-Condon overlap between the potential energy surface of CO2 and CO2-. Negative ion mass spectra are included for acetic anhydride and acetyl peroxide.
Interactions between a mobile adsorbed phase and diffusing gases in porous media—an experimental study
Authors: Bell Weldon K. , Brown Lee F.
Published: February 2004

Experimental data were taken for both nitrogen-helium and propane-helium systems counterdiffusing through a plug of pelleted Graphon. The experimental pressure range was 1–20 atm for the nitrogen-helium and 1–8 atm for the propane-helium system; the temperature range was 299–408°K. The temperature and total pressure gradients were zero in the individual experiments (Wicke-Kallenbach experiments). Because of the uniform nature of the Graphon surface, significant surface transport of the heavier vapor occurred in all experiments. In neither system was the helium diffusion behavior predictable by the dusty-gas diffusion equation, as it should have been if the gas-phase diffusion were unaffected by the moving adsorbed phase. The observed helium flux in the helium-propane experiments also averaged about 20% lower than predicted from the fluxes in the helium-nitrogen system. The first of these observations indicates that the presence of a mobile adsorbed phase significantly affects the diffusion behavior of the gas phase. The second reinforces this conclusion and further indicates that the greater surface flow of propane caused the helium flux to be significantly inhibited. Applications of these observations to catalysis, diffusion within porous materials, and surface diffusion indicate that these phenomena merit further intensive study. In the case of surface diffusion, these results indicate possible major doubts in all previously reported surface fluxes and surface diffusivities in porous materials.
Proton, deuterium, and chlorine-35 nuclear magnetic resonance of solid and liquid t -butyl chloride
Authors: O'Reilly D. E. , Peterson E. M. , Scheie C. E. , Seyfarth Elizabeth
Published: February 2004

Proton spin-lattice (T1) and rotating frame (T1ρ) relaxations have been measured in (CH3)3CCl from 90°K to the melting point (249°K). In Solid III (below 183°K) there is a minimum in T1 which is due to rotation of the methyl groups about an axis perpendicular to the plane containing the three protons. In this phase T1ρ exhibits an inflection which is assigned to a motion of the molecule about the C–Cl bond direction. In Solid II (from 183 to 223°K) T1 has a minimum due to the motion around the C–Cl bond direction. In the fcc Solid I the molecules are tumbling isotropically and translational diffusion is relatively fast. Chlorine-35 nuclear quadrupole resonance (NQR) is observed in Solids III and II. The observed NQR frequency depends on temperature as predicted by the Baver theory except in the immediate vicinity of the phase transitions where the apparent torsional frequencies decrease significantly. Coefficients of self-diffusion (D) were measured in the liquid from the melting point to the gas-liquid critical point (490°K). D is represented by D = (12.8 ± 0.7)10−3 exp[−(3.69 ± 0.03)/RT] to within 40° of the critical point whereupon D gradually begins to increase very rapidly with further increase in temperature to a value of 1.2 × 10−3 cm2 sec−1 in the gas. Rotational correlation times τ2 have been measured for deuterium, protons, and chlorine-35 in the liquid from 223 to 300°K. Values of τ2 for D, H, and Cl are unchanged at the freezing transition between the liquid and Solid I, but are discontinuous at the Solid I and Solid II transition. Rotational correlation times for molecular tumbling and methyl group rotation are calculated from the values of τ2 for H, D, and Cl.
Nuclear relaxation and spin exchange in ammonium hexafluorophosphate (NH4PF6)
Authors: Albert Shmuel , Gutowsky H. S.
Published: February 2004

The three phases of solid ammonium hexafluorophosphate (NH4PF6) have been studied by cw and pulsed NMR methods between 298° and 77°K. The proton and fluorine second moments of 1.8 and 1.9 G2, respectively, at 298°K are consistent with rapid, randomized reorientations of NH4+ and PF6- ions, while the larger values at 77°K require that there be little or no motional narrowing by reorientations of the PF6− ions even though the narrowing by NH4+ reorientations is still present. For both nuclear species the spin-lattice relaxation time (T1) studies of the two low-temperature phases reveal three distinct regions: (1) Between 109° and 110°K their relaxation is exponential with time. (2) Between 105° and 87°K the relaxation is nonexponential, but may be expressed as the sum of two exponential terms. At each temperature the same pair of time constants applies to both nuclear species. (3) At 77°K the relaxation is again exponential, with different T1's for protons and fluorine. The nonexponential behavior in region (2) is attributed to spin exchange between protons and fluorine nuclei. It results from modulation of the H–F dipole-dipole interactions by relatively slow reorientations of the PF6− ions. This interpretation was confirmed by a study of the fluorine T1 of ND4PF6, for which only exponential decays were observed. Activation parameters for the PF6- reorientation were determined from the fluorine T1 in ND4PF6. The parameters depend somewhat upon temperature, being 4.1 ± 0.2 kcal/mole and (3.7 ± 0.5) × 10−16 sec above 130°K and 4.4 ± 0.3 and (5.2 ± 1.5) × 10−17 below. A discontinuity occurs in the T1's at the 192°K phase transition, and in the high temperature NaCl phase the T1's are almost independent of temperature and probably are governed by spin-rotation interactions. DTA experiments indicate that no additional phase transitions occur in NH4PF6 between 300° and 473°K.
Electric field spectra and dipole moments of 1,3-diazaazulene
Authors: Braun James R. , Lin Tien-Sung , Burke Francis P. , Small Gerald J.
Published: February 2004

Nitrogen heterocycles of azulene have currently been under study to examine the effects of nitrogen substitution in the azulene system. We have determined the dipole moments of three different electronic states of 1,3-diazaazulene: the ground state, the first excited singlet state (1ππ*, B1), and the phosphorescent state (3ππ*). Measurements have been performed on the origin band and several prominent vibronic bands of the 1B1 ← 1A1 transition. The dipole moment of the ground state was determined from dielectric constant measurements, and the change in dipole moments upon excitation to higher electronic states was measured from the pseudo-Stark effect of molecular crystals on diazaazulene in a naphthalene host. The measured values are μ(GS) = 2.98 ± 0.01 D, |Δμ(GS−S1)| = 1.80 ± 0.05 D, and |Δμ(GS—T1)| = 1.10 ± 0.07 D. The measurements enable us to examine the role of nitrogen atoms participating the charge distribution of the σ core and the π-electron cloud in the 1B1 ← 1A1 transition in comparison with the known dipole moment of the corresponding first excited singlet state of azulene. Discussion on the direction of the change in dipole moment and the relative magnitude of the dipole moments of the origin bands of S1 and T1 states as well as the vibronic bands 264, 539, and 575 cm−1 are presented.
Anisotropy in nuclear quadrupole shielding
Authors: Stout E. W. , Garrett B. B.
Published: February 2004

A perturbation approach to the calculation of induced field gradients shows that Sternheimer shielding contains a significant amount of anisotropic character and that conventional treatment of the shielding as a scalar effect may be inadequate in the prediction of nuclear quadrupole observables. An order of magnitude estimate indicates that inclusion of anisotropy in shielding can result in discrepancies of the order of 25% from values predicted with isotropic shielding for both asymmetry parameters and coupling constants.
Geometry of the LiO2 radical
Authors: O'Neil Stephen V. , Schaefer Henry F. , Bender Charles F.
Published: February 2004

Ab initio quantum mechanical calculations have been carried out for the two lowest electronic doublet states of the lithium dioxide molecule. The results are pertinent to possible crossed molecular beam experiments and to matrix isolation spectroscopy. A qualitative discussion of the electronic structure changes accompanying the Li + O2 and LiO + O reactions is given. For the quantitative calculations, a contracted Gaussian basis set was used, designated Li (9s 4p/4s 2p), O (9s 5p/4s 3p). For isosceles triangle configurations, the 2A2 state is the electronic ground state, with equilibrium geometry r(LiO) = 1.82 Å and θ(O–Li–O) = 44.5°. The 2B2 state is predicted to lie 14 kcal/mole higher with r(LiO) = 1.76 Å and θ(O–Li–O) = 46.5°. For C∞v geometry the 2Π state bond distances were predicted, R(Li–O) = 1.62 Å and R(O–O) = 1.35 Å. There appears to be little or no barrier between the C2v and C∞v forms.
Competition between charge exchange and chemical reaction: The D2+ + H system
Authors: Preston Richard K. , Cross R. James
Published: February 2004

The trajectory surface hopping (TSH) model was used to study the competition between chemical reaction and charge exchange for the reactions D2+ + H → D2 + H+, DH + D+, D + H + D+, D + D + H+. The three adiabatic surfaces, one triplet and two singlet, which are needed to describe this system are computed using the diatomics-in-molecules-zero-overlap approximation. Cross sections and the reaction dependence on impact parameter are obtained as a function of initial vibrational quantum number at the relative energy of 2 eV. The chemical reaction is found to depend in part on surface crossings and the charge exchange on chemical interactions. The results are discussed as a prototype of this sort of competition.
Viscosity of the binary gas mixtures argon-methane and argon-ammonia
Authors: Rakshit A. B. , Roy C. S. , Barua A. K.
Published: February 2004

Viscosities of the binary gas mixtures argon-methane and argon-ammonia have been measured by an oscillating-disc viscometer as functions of composition in the temperature range from −35 to 35°C. For the nonpolar-nonpolar system argon-methane, the agreement between the experimental and calculated values of mixture viscosity is fairly satisfactory. For the nonpolar-polar system argon-ammonia, the calculated values from the combination rules are lower than the experimental data. Attempts have been made to derive information on the unlike interactions from mixture viscosity data.
High-temperature flow behavior of glass-forming liquids: A free-volume interpretation
Authors: Cukierman M. , Lane J. W. , Uhlmann D. R.
Published: February 2004

High-temperature viscous flow data are reported for three relatively simple organic liquids: o-terphenyl, salol, and α-phenyl-o-cresol. The results are combined with previous flow data on the same liquids to obtain viscosity-temperature relations over some 15 orders of magnitude. For each liquid, as well as for tri-α-naphthylbenzene, the free-volume theory of Turnbull and Cohen is found to provide a close representation of the data for viscosities between 10−2 P (the high-temperature limit of the data) and about 104 P. Over this range, even the pre-exponential factors derived from fitting the experimental results are in close agreement with those predicted by the theory. At lower temperatures, the free-volume expression overestimates the difficulty of flow. For all four organic liquids, the fractional free volumes at the points of departure, TB, of the experimental data from the free volume predictions are close to 0.015. An empirical high-temperature flow relation of the free-volume form is suggested as η ≈ [(MkT)1/2/a02] exp {0.25/[0.015 + Δ α (T - TB)]}, where M is the mass of the molecule, a0 is its diameter, and Δα is the difference in thermal expansion coefficient between liquid and glass. It is suggested again that free-volume theories be used to represent flow behavior in the fluid range rather than in the high-viscosity region as the glass transition is approached.
PES of high-temperature vapors. IV. The cesium halides. Effect of spin-orbit interaction on the photoelectron and mass spectra of the alkali halides
Authors: Berkowitz J. , Dehmer J. L. , Walker T. E. H.
Published: February 2004

The He(I) photoelectron spectra of the cesium halides are presented. They exhibit two well-separated sets of peaks, one deriving from orbitals formed from halogen p -type orbitals and the other from the cesium p orbitals. Each set of bands is analyzed by taking into account spin-orbit interaction within the degenerate ∏ states and subsequently between the ∏(1/2) and ∑(1/2) states. This analysis is a prototype for all alkali halides and has been used in conjunction with ab initio calculations to construct potential energy curves for LiCl, LiBr, LiI, and KF. These cases suffice to characterize the variations in the photoelectron spectra and mass spectra for all the alkali halides.
Free energy of nearly close packed strips of hard squares in a ``brickwall'' configuration
Authors: Beyerlein Adolph , Stafford Michael
Published: February 2004

The exact Helmholtz free energy FN of strips of m rows and an infinite number of columns of hard squares in a nearly close packed ``brickwall'' configuration is calculated through m = 4. These results are used to estimate a more accurate value of the free energy parameter C in the expansion, FN/NkT = 2 ln(λ/σ) −2 ln(τ −1) + C + D(τ −1) + E(τ −1)2 +..., for an infinite two dimensional system of hard squares in a ``brickwall'' configuration. The quantity σ is the particle diameter, λ is the mean thermal de Broglie wavelength, and τ is the ratio of the system area to the close packed system area. The estimate for C is −0.1787, which is greater than −0.2604 [J. Chem. Phys. 53, 1532 (1970)] or −0.268 [J. Chem. Phys. 56, 5434, (1972)], the estimated values of C for the square lattice configuration by the modified cell cluster and Monte Carlo methods, respectively. This supports earlier conclusions [J. Chem. Phys. 56, 5434 (1972); J. Comput. Phys. 7,403 (1971)] that the square lattice configuration is more stable. The previous modified cell cluster estimate of C for the ``brickwall'' configuration, −0.0239, deviates considerably from the new estimate because the cell cluster expansion converges slowly for this configuration.
Multiple rotors and electron scattering by gases
Authors: Karle J.
Published: February 2004

The theory for the treatment of restricted and free rotation for a single rotor in electron diffraction by gases has been developed previously. An extension of the theory is presented for the case that a molecule possesses more than one rotational axis. The general case of multiple rotors is treated by developing a theory for the double rotor, since the contributions to the electron scattering arise from pairs of atoms and therefore only two different rotors, at most, would be involved in any individual contribution to the scattering. The theoretical formulas which have been developed for the double rotor include the effects of both the frame vibrations and the torsional motions. Both restricted internal rotation and free rotation of the rotors have been considered. There are two cases for the double rotor which are distinguished by the intersection or the nonintersection of the rotational axes. Formulas have been developed describing both the radial distribution and molecular intensity functions for the double rotor. In addition, new expressions have been obtained for the case of the single rotor which arise from alternative approximation techniques.
Reaction between atomic fluorine and CF3Br: Evidence for a pseudotrihalogen radical intermediate
Authors: Bozzelli Joseph W. , Kolb C. E. , Kaufman M.
Published: February 2004

The kinetics of the reaction between atomic fluorine and CF3Br has been investigated in the temperature range 188–373 °K using molecular beam analysis in conjunction with an H2 titration to measure the concentration of atomic fluorine in a flow reactor. The effective second order rate constant for this reaction varies from 2.5 × 108 cm3/mole · sec at 373 °K to 8 × 109 cm3/mole · sec at 188 °K. This unusual temperature dependence, as well as the pressure dependence of the effective rate constant, is explained by a mechanism involving the formation of a stable pseudotrihalogen radical CF3BrF. The radical reacts with atomic fluorine by competing pathways that result in either net recombination of atomic fluorine or net consumption of CF3Br. In agreement with the proposed mechanism, CF3Br is found to be at least 12 times more efficient than CF4 as a catalyst for the recombination of fluorine atoms.
Coupled channel study of rotational excitation of H2 by Li+ collisions
Authors: Lester William A. , Schaefer Joachim
Published: February 2004

Integral cross sections for rotational excitation of H2 by Li+ impact have been computed in a coupled channel formalism for the energy range 0.05–0.5 eV. Computational results are reported for the rigid rotator, ``energy corrected'' rigid rotator, and vibrating rotator models (the latter using accurate numerical vibrational functions of the Kolos-Wolniewicz potential including adiabatic correction). The ``energy corrected'' model, which adjusts the energy levels of the rigid rotator to agree closely with the experimental levels of the diatomic molecule by inclusion of the centrifugal distortion term, affords a noticeable improvement over the usual rigid rotator approximation for H2 with no increase in computational effort. Comparison with the classical rigid rotator results of LaBudde and Bernstein [J. Chem. Phys. 59, 3687 (1973)] show reasonable agreement with the present rigid rotator cross sections retaining open channels only. Peaks are obtained in the partial integral cross section in the threshold region for the (a) 0 → 2 transition (0.05 eV), (b) 0 → 4 transition (0.15 eV), and (c) 0 → 6 transition (0.3 eV). For 0 → 4,6 excitations, indirect transitions make the dominate contribution to the cross sections.
Statistics of a random coil chain in the presence of a point (two-dimensional case) or line (three-dimensional case) obstacle
Authors: Saito Nobuhiko , Chen Yi-der
Published: February 2004

Exact expressions are given for the distribution function of the end-to-end vector of a random coil chain under the restriction that the chain makes a definite number of turns around a fixed point (two-dimensional case) or a fixed straight line (three-dimensional case). The ring-closure probability and the mean square end-to-end distance are also calculated. The final results are given in graphs.
Low frequency vibrations in polyvinylidene fluoride (form II)
Authors: Rabolt J. F. , Johnson K. W.
Published: February 2004

The far-infrared spectra of crystalline polyvinylidene fluoride (form II) has been obtained at temperatures ranging from 13 to 373 °K. The results show four lines at 53, 85, 102, and 175 cm−1. The latter three lines are assigned to intramolecular vibrations of a single TGTG′ chain. The 53 cm−1 line is attributed to a rotatory lattice mode predicted by a factor group analysis of space group P21/c and substantiated by both crystallinity studies and by the investigation of frequency shifts and intensity changes with decreasing temperature. The latter is consistent with a contraction of the unit cell at low temperatures and an increasing intermolecular interaction between the two chains in the unit cell.
Collisional deactivation of vibrationally excited singlet molecular oxygen
Authors: Parker J. G. , Ritke D. N.
Published: February 2004

Measurements of the collisional deactivation time of the ν′ = 1 vibrational level of the 1Δg electronic state have been made using a high pressure gas cell equipped with an acoustic detector. To separate relaxation effects from effects due to viscosity, thermal conductivity, cell geometry, and nonuniform irradiation by the laser beam a detailed theoretical treatment of the acoustical behavior of the cell was required. Application of these results to the existing system was carried out and used to determine the appropriate relaxation times from the experimental data. Accordingly it was determined that for pure oxygen p τ = 0.05 sec · atm. Addition of increasingly large amounts of He caused this value to fall steadily to a limiting value p τ = 0.016 sec · atm which agrees well with the data obtained by previous investigators for the ν′ = 0 vibrational level.
Electronic structure calculations for large planar molecules by SCF-scattered wave method
Authors: Liberman D. A. , Batra I. P.
Published: February 2004

Electronic structure calculations using the SCF-scattered wave program of Johnson and Smith for the molecules carbazole, fluorenone, dinitrofluorenone, and trinitrofluorenone are reported. A qualitative description of the lowest excited states of these molecules is presented and a brief review of the theory underlying the calculations is given. Our calculations predict that the lowest excitation in carbazole should be polarized along the short molecular axis and in fluorenone along the long molecular axis. Polarized light absorption experiments should then provide an excellent check on the validity of these calculations. It is also shown that the lowest excitation in carbazole, fluorenone, and dinitrofluorenone should be a π→π* transition whereas in trinitrofluorenone it is suspected to be an n →π* transition. Comparison with minimal basis LCAO Hartree-Fock calculations and experiments is made where possible.
13C chemical shift anisotorpy and the H–C–H bond angle of 13CH3 OH in a nematic liquid crystal solvent
Authors: Bhattacharyya Pranab K. , Dailey Benjamin P.
Published: February 2004

A pulsed FT NMR spectrometer is used to determine the anisotropy in the carbon-13 chemical shift tensor and the H–C–H bond angle in methyl alcohol from studies in a nematic liquid crystal solvent. The H–C–H bond angle measured by proton magnetic resonance is 109 ° 20′ ± 4′. The signs of the coupling constants D13CH, DHH, and J13CH and the ordering parameter S33 are established to be all positive. The value of Δσ (13C) obtained from temperature studies of the nematic phase chemical shift is 69 ± 5 ppm. The anisotropy obtained from the nematic—isotropic phase chemical shift difference (at 77 °C) is 63 ± 6 ppm.
Analysis of multiple pulse NMR in solids
Authors: Rhim W-K. , Elleman D. D. , Vaughan R. W.
Published: February 2004

The general problems associated with the removal of the effects of dipolar broadening from solid state NMR spectra are analyzed. The effects of finite pulse width and H1 inhomogeneity are shown to have limited the resolution of previous pulse cycles and a new eight pulse cycle designed to minimize these problems is discussed. Spectra for F19 in CaF2 taken with this cycle are presented showing residual linewidth near 10 Hz. The feasibility of measuring proton chemical shift tensors is discussed.
Electric quadrupole moment of CO and molecular torque in liquid Ar and N2 from ir spectra
Authors: Buontempo U. , Cunsolo S. , Jacucci G.
Published: February 2004

The far ir absorption spectra of CO in Ar in the gas and liquid phases and the rotovibrational spectrum of CO in Ar and N2 in the liquid phase have been measured; the value of the electric quadrupole moment is obtained. A moment analysis is done of the dipolar part of the spectrum, obtaining the value of the torque in the different cases. A long time exponential decay of the dipolar correlation function extracted from the rotovibrational spectrum of CO in liquid Ar is observed.
Electric and magnetic properties of BrCN from microwave Zeeman measurements
Authors: Blackman G. L. , Brown R. D. , Burden F. R.
Published: February 2004

The high field Zeeman effect of the microwave spectrum of BrCN has been analyzed to obtain molecular g values, molecular susceptibilities, and the molecular quadrupole moment.
Thermal expansion and low temperature phase transition of thallous azide
Authors: Mauer F. A. , Hubbard C. R. , Hahn T. A.
Published: February 2004

Thallous azide, TIN3, is tetragonal at room temperature. It transforms at 248 ± 5 °K to a phase that can be indexed on the basis of an orthorhombic cell. Lattice parameters of the tetragonal phase have been determined by the Bond single crystal method at intervals of approximately 25 °K from 248 to 498 °K. Single crystals do not survive the transition, so the parameters of the orthorhombic phase were measured by powder diffraction at intervals of 25 °K down to 133 °K. Representative parameters, after corrections for the effects of radiation damage, are a = 6.2094 Å, c = 7.3583 Å at 298.2 °K for the tetragonal phase, and a = 8.718 Å, b = 8.766 Å, c = 7.395 Å at 238.2 °K for the orthorhombic. Thermal expansion parameters show anomalies that are believed to be the result of changes in the orientation of azide ions. The linear expansion coefficients, αa and αc, for the tetragonal phase are both approximately 5.2 × 10−5 °K−1 at the transition. By 486 °K, αc has increased to 21 × 10−5 °K−1 and αa has decreased to −1.2 × 10−5 °K−1. For the orthorhombic phase αb remains constant at 5.2 × 10−5 °K−1 while αa increases from 10 × 10−5 °K−1 to 22 × 10−5 °K−1 and αc decreases from −1.5 × 10−5 °K−1 to −11 × 10−5 °K−1 in the temperature range 150 to 225 °K. There does not appear to be a discontinuity in the volume at the transition. The volume expansion coefficient is approximately 17 × 10−5 °K−1 for the orthorhombic phase and 15 × 10−5 °K−1 for the tetragonal.
Reinvestigation of the molecular structure of gaseous beryllium borohydride BeB2H8 by electron diffraction
Authors: Gundersen Grete , Hedberg Lise , Hedberg Kenneth
Published: February 2004

The structure of beryllium borohydride has been reinvestigated by gaseous electron diffraction at a nozzle temperature of 40 °C. The experiments were characterized by unusual photographic problems which were overcome with difficulty. The structure analysis led to the unexpected result that the molecule, or at least the major part of the free molecules, has a linear heavy-atom structure, in agreement with conclusions based on an early electron-diffraction investigation but in disagreement with those from more recent electron-diffraction and spectroscopic studies which have generally favored triangular configurations. Our diffraction data were satisfactorily interpreted in terms both of molecules with configuration B–Be–B and with configuration Be–B–B. The data require the peripheral atoms of the molecule, or the principal species of the molecule, to be bonded to the central one through three hydrogen bridges giving the central atom sixfold coordination; the successful models have molecular symmetries D3d and C3v for the B–Be–B configuration and C3v symmetry for the Be–B–B. The discovered Be–B–B models seem rather unlikely on several grounds, but it cannot be ruled out that more plausible ones exist. The B–Be–B models appear to fall in one broad region of parameter space roughly defined by the following values of the principal geometric parameters chosen as averages and differences of bond distances and bond angles: r̄(Be–B) = 1.790 Å(0.015), 0 ≤ Δr(Be–B) ≤ 0.10 Å, r̄(B–Hb) = 1.303 Å(0.012), 0 ≤ Δr̄ (B–Hb) ≤ 0.12 Å, r̄(B–Ht) = 1.16 Å (0.04), ∠HbBHt = 117.5° (1.2), and 0 ≤ ∠HbBHt ≤ 10°; the parenthesized quantities are estimates of 2σ. The possibility that gaseous beryllium borohydride may comprise more than one species is discussed.
Electronic structure of ferricenium ion from absorption, MCD, and ESR studies
Authors: Rowe M. D. , McCaffery A. J.
Published: February 2004

The absorption and MCD spectra of the ferricenium ion have been measured at 290 and 9 °K. The data have been used, together with 20 °K ESR spectra to obtain quantitative information about the ground state of this molecule. The ground state emerges as a E‴(2Eg) state into which is mixed the E″(2Eg) state via a low symmetry perturbation. Evaluation of this from ESR and MCD data yield the values δ = 1043 cm−1 at 20 °K and δ = 263 cm−1 at 290 °K. The MCD strongly confirms the assignment of the electronic absorption band at 16 200 cm−1 as 2E2g → 2E1u.
Spin correlations and cumulants of Ising chains with applications to helix-coil transitions
Authors: Tanaka Toyoichi , Suzuki Masuo
Published: February 2004

Many-spin correlations and cumulants are obtained explicitly for Ising chains with arbitrary boundary conditions. Applications of these expressions to helix-coil transitions are discussed.
Statistical mechanics of wormlike chains: Path integral and diagram methods
Authors: Yamakawa Hiromi
Published: February 2004

The statistical mechanics of a continuous wormlike chain is developed in analogy with the quantum mechanics of a particle in a potential field. An integral equation for the characteristic function is derived from the path integral formulation and its solution is obtained by operational and diagram techniques. It provides a useful method of calculating the moments. A modified Daniels-type expansion of the distribution function is also derived to give correctly any number of first moments.
Effect of excluded volume on the dipole moments of chain molecules
Authors: Liao S. C. , Mark J. E.
Published: February 2004

Dielectric constants have been determined for dimethylsiloxane chains (CH3)3Si[OSi(CH3)2]x OSi(CH3)3 in the thermodynamically good solvent cyclohexane and in the undiluted state, for degrees of polymerization x + 1 ranging from 102 to 103, at a number of temperatures in the range 10–60 °C. These data indicate that at constant temperature the dipole moment ratio 〈μ2〉/nm2 (where 〈μ2〉 is the mean-square dipole moment of a chain consisting of n = 2x + 2 bond dipoles of magnitude m) is independent of chain length, as has been predicted for chains of such structural symmetry. Unfortunately, comparison of the experimental values of the dipole moment ratio with those predicted from rotational isomeric state theory is complicated by pronounced specific solvent effects and comparison of experimental and theoretical values of d ln 〈μ2〉/dT is also difficult because of the very small magnitude of this coefficient.
Variation of diamagnetic properties of the hydrogen molecule with internuclear separation
Authors: Zeroka Daniel
Published: February 2004

The diamagnetic susceptibility χ and the magnetic shielding constant for the hydrogen molecule are investigated in the range of internuclear separations R = 1.0–12 a.u. using a previously reported technique and the reported wavefunction of Fraga and Ransil. The values at Re = 1.4 a.u. are χ = −3.8837 × 10−6 cgs units and σ = 27.095 ppm. For normal H2, the averages over nuclear motion, where zero-point vibration and centrifugal distortion are taken into account, are 〈χ〉=-3.9761× 10-6 cgs units and 〈σ〉=26.760 ppm at 300 °K; these averages are approximately 2.38% and 1.24%, respectively, smaller than the equilibrium values. The variation of 〈χ〉 and 〈σ〉 over the temperature interval 20–300 °K is considered, on the basis that intermolecular force contributions are zero, and is found to be quite small. Furthermore, a useful table of some integrals that frequently arise in magnetic shielding studies is included as an Appendix.