bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution Function of Classical Fluids of Hard Spheres. II
Authors: Ree Francis H. , Lee Yong-Teh , Ree Taikyue
Published: February 2004

The pair- and triplet-correlation functions g12[≡ g(r12)] and g123[≡ g(r12, r13, r23)] are used to make a superposition approximation g123g124g134g234 / (g12g13g14g23g24g34) to the quadruplet correlation function g1234. Introduction of this approximation into the second equation of the Born–Green–Yvon (BGY) hierarchy makes it possible to truncate the hierarchy. The resulting equations are a pair of simultaneous integro-differential equations involving g12 and g123, which hereafter are referred to as the BGY2 equations. The BGY2 theory was further elucidated by the use of the hard-sphere potential to solve the corresponding BGY2 equations at two selected values (10 and 15) of λ, which is used as the independent variable and is equal to 4πρg(σ) (ρ = density, σ = sphere diameter). The densities {ρ = λ / [4πg(σ)]} corresponding to these values of λ can be established from the BGY2 solutions of g(r) at contact distance of two spheres. They are found to be, respectively, 0.298ρ0 and 0.372ρ0 (ρ0 = the close-packed density). At these densities, a separate program, which uses a Monte Carlo (MC) method, was used to evaluate the radial distribution functions for 500 hard spheres. The MC g(r) can be regarded as exact within the observed standard deviations; hence, adequacy of various approximate theories of g(r) can be tested against it. This was done here, not only for the BGY2 g(r) but also for the BGY1 g(r) obtained after truncating the BGY hierarchy by using the Kirkwood superposition approximation for g123 as well as for the Percus–Yevick (PY) g(r). At ρ = 0.298ρ0, the comparison gave values of the g(r) which are vastly improved over values calculated from either the BGY1 g(r) or the PY g(r) and which agree within each other's numerical uncertainties with the MC g(r) at most of the interparticle distances. Nearly perfect agreement (again within numerical uncertainties of the two) of the BGY2 g(r) and the MC g(r) at ρ = 0.372ρ0 was also observed for r < 1.4σ. For r > 1.4σ, the BGY2 g(r) deviates slightly (i.e., 1.6% or less) from the MC g(r) which appears to follow slightly closer to the PY g(r). The discrepancies between the BGY2 and the MC g(r) may be attributable to a large extent to the iterative scheme used in solving BGY2 equations as well as use of the inaccurate density in obtaining the MC g(r). Over-all improvement of the BGY2 g(r) over the BGY1 g(r) is striking. In particular, the pressures calculated from the BGY2 g(r) by the use of the virial theorem agree within statistical uncertainties with the MC pressures at the densities given above.
Nuclear Magnetic Resonance and the Mobility of Water in CsMnCl3·2H2O
Authors: Bug H. , Haas H. , Fleissner M. , Hartmann H.
Published: February 2004

The 1H, 2D, 35Cl, and 133Cs NMR of CsMnCl2·2H2O single crystals have been studied. The proton positions could be determined from the observed shift and dipolar splitting and the deuteron positions from the nuclear quadrupole interaction. Conclusions about the hydrogen bonding network were drawn. The rate of the H2O and D2O reorientation was examined by NMR linewidth measurements at different temperatures and an activation energy of 8.4 kcal/mole computed. Positions and reorientation rate showed no measurable isotope effects. The NMR of the two chlorine sites at room temperature gave νq = 6.106 Mc/sec, η = 0.285 for the bridged chlorine (Mn–Cl–Mn) and νq = 4.192 Mc/sec, η = 0.727 for the single bonded (Mn–Cl). In both cases a hyperfine interaction of As = 1.30 × 10−4cm−1 and Ap = 0.14 × 10−4cm−1 was calculated from the observed paramagnetic shifts. The quadrupole coupling and magnetic shift tensors of 133Cs were measured and from the linewidth and saturation the relaxation times estimated.
Photodissociation of OCCl2 in the Vacuum Ultraviolet: Production and Electronic Energy of Excited Cl2
Authors: Okabe H. , Laufer A. H. , Ball J. J.
Published: February 2004

The photodissociation of OCCl2 in the vacuum ultraviolet yields electronically excited Cl2 producing emission continua in the region 2000–3100 Å. A curve obtained by plotting fluorescence efficiencies as a function of incident wavelength shows diffuse vibrational structure corresponding to the ν1 symmetric stretching mode of OCCl2, indicating that the process is predissociative. Three main continua at 3063, 2565, and 2460 Å were observed by the photolysis of OCCl2 with the Kr 1236-Å line, while only one continuum at 2580 Å was obtained by the Xe 1470-Å line. From threshold energies of the incident photons to produce each continuum it was possible to obtain electronic energies of excited Cl2. Electronic energies thus obtained are 7.21 ± 0.05 eV and 7.93 ± 0.03 eV for the upper states associated with the 2580- and 3063-Å continua, respectively. The electronic energy of the upper state responsible for the 2460-Å continuum lies between 7.33 and 8.93 eV. The effect of inert gas on the emission continua was investigated. A comparison has been made of the emission continua obtained by the photolysis of OCCl2 and those produced by an electric discharge of Cl2. The absorption coefficient of OCCl2 has been measured in the region 1170–1600 Å.
Configuration Interaction Study of the X 3Σ−, a 1Δ, and b 1Σ+ States of NH
Authors: O'Neil Stephen V. , Schaefer Henry F.
Published: February 2004

Using a (3s, 2p, 1d / 2s, 1p) basis set of contracted Slater-type functions and an iterative natural orbital scheme, ab initio valence configuration interaction studies have been done on the lowest three states of the imidogen radical at eight internuclear separations. Included in the CI were those configurations differing by zero, one, or two space orbitals from the Hartree–Fock configuration, except that the 1σ orbital was held doubly occupied. The size of the CI varied from 259 (1Δ) to 418 (3Σ−). For the ground state the computed total energy lies below that reported in any previous calculation except the 3379 configuration wavefunction of Bender and Davidson. From the potential curves thus obtained, the spectroscopic constants re, ωe, ωexe, Be, and αe are calculated, and compare well with the available experimental constants. The molecular splittings are calculated to be 2.00 eV (X 3Σ− − a 1Δ) and 0.79 (a 1Δ − b 1Σ+), but when the discrepancy between calculated and experimental atomic limits is taken into account these splittings are estimated as 1.47 eV and 1.02 eV, the latter being close to the experimental value of 1.05 eV. Dissociation energies (De) for the X 3Σ−, a 1Δ, and b 1Σ+, states are calculated as 3.06 eV, 3.97 eV, and 4.13 eV, respectively. For comparison, the Hartree–Fock dissociation energy for the X 3Σ− state is 2.10 eV and Gaydon's experimental value os 3.41 ± 0.16 eV. The occupation numbers and most important configurations are given at several internuclear distances for each state.
Electron Spin Resonance and Relaxation Studies of Internal Motion in CH2CO2− Radicals Trapped in γ-Irradiated Sodium Acetate Crystals
Authors: Fujimoto M. , Janecka J.
Published: February 2004

CH2CO2− radicals are stable in γ-irradiated sodium acetate crystals. The ESR spectra of CH2CO2− and carbon-13 labeled radicals, CH213CO2− and 13CH2CO2−, were studied in detail in the temperature range of 77°K to room temperature. It was found that the CH2 group executes an internal motion which is characterized by proton exchange in the oriented radicals. The motion is slowed on lowering the temperature, giving rise to an electron spin relaxation time of the order of microseconds at 77°K. The correlation time for the motion was found to be temperature dependent, varying as exp (V / kT) with an activation energy V of the order of 3 kcal mole−1.
Collision Dynamics and the Statistical Theories of Chemical Reactions. II. Comparison of Reaction Probabilities
Authors: Morokuma Keiji , Karplus M.
Published: February 2004

The reaction probability obtained as a function of total energy from transition-state theory for classical collinear atom, diatomic-molecule exchange reactions is compared with the results of trajectory calculations for the same potential surface. For a well-defined barrier in the symmetric H, H2 reaction, there is excellent agreement up to rather high energies. Other reactions (e.g., H2+Br⇄HBr+H) yield considerably larger deviations; these can be shown to result from a transmission coefficient that is less than unity, from a nonequilibrium distribution in the transition region, or from both effects.
Vibrational Frequencies and Force Constants for Tetrahedral MgX4−2 (X=Cl, Br, and I) in MgX2–KX Melts
Authors: Maroni Victor A.
Published: February 2004

Raman spectra are reported for the species present in MgX2–KX melts (X=Cl, Br, and I) with X−1/Mg+2 mole ratios near 4.0. The observation of one polarized band and three depolarized bands for each halide melt is consistent with the existence of the tetrahedral complexes MgCl4−2, MgBr4−2, and MgI4−2. All the observed frequencies are calculated within 1 cm−1 using a Urey—Bradley force field which consists of an Mg–X stretching constant, an X–Mg–X bending constant, and an X ··· X repulsion constant.
Energy-Transfer Processes in Monochromatically Excited Iodine Molecules. V. Rotational Energy Transfer in Argon-Excited I2
Authors: Kurzel R. B. , Steinfeld J. I. , Hatzenbuhler D. A. , Leroi G. E.
Published: February 2004

Rotationally resolved energy-transfer rates have been measured for I2 excited to J′=11 and 15 of v′ = 43 of the B 3Π0u+ state by the argon laser line at 5145 Å, for accompanying changes in v′ of 0, ± 1, ± 2, and ± 3, in collisions with ground-state I2, H2, He, and Ne. In all of these collisions, there is a persistence of rotational state, | Δ J′  | ≤ 14 being favored; however, broader distributions are found, as expected, for collisions with larger |Δ v|'s or with heavier collision partners. The microscopic rate constants are asymmetric to Δ J′>0, as expected for (T/B)1/2 ≈ 80.
Symmetry Adapted Perturbation Theories: Application to a Generalized Eigenvalue Equation for the Hydrogen Molecular Ion
Authors: Laughlin C. , Amos A. T.
Published: February 2004

Analogues of the Murrell—Shaw, Musher—Amos, and van der Avoid—Hirschfelder symmetry adapted perturbation theories are devised for the case of a generalized eigenvalue equation. The new procedures are applied to the hydrogen molecule ion and perturbation energies through second order are calculated at various internuclear distances.
Zero-Point Vibrational Corrections to One-Electron Properties of the Water Molecule in the Near-Hartree—Fock Limit
Authors: Ermler W. C. , Kern C. W.
Published: February 2004

The zero-point vibrational motion of the water molecule in its ground electronic state is analyzed with a near-Hartree—Fock potential energy surface constructed from a (9s5p2d/4s1p) /[4s3p2d/2s1p] basis set of contracted Gaussian orbitals. The harmonic and cubic force constants relative to the computed minimum are obtained, and a normal coordinate analysis is carried out for several isotopic variants. A set of one-electron properties including molecular moments, field gradients, forces, and densities is computed at each point on the potential surface, and then averaged over the zero-point motion with a vibrational wavefunction which contains anharmonicity terms through the cubic constants. The vibrational corrections are typically about 1% of the equilibrium values, but are as large as 20% in cases such as the 17O quadrupole coupling constant along the C2 axis. The theoretical isotope shifts for the quadrupole moments of H2O and D2O are in good agreement with experiment. Predictions are made for isotope shifts in other properties. A b initio values of the bond and angle displacement coordinates and their root-meansquare amplitudes are also determined.
Trajectory Studies of Halogen Atom—Molecule Exchange Reactions
Authors: Borne Thomas B. , Bunker Don L.
Published: February 2004

We studied the reactions X+Y2 →XY+Y, usually with X=Br, Y=I but with a few calculations for other choices (X=Cl or Y=Br). We used empirical potential surfaces having minima 0–10 kcal deep. In addition we could control all aspects of the shape and position of this potential well. Comparison with recent experimental results reveals that no reasonable potential well for collinear reactant approach will explain the observed scattering. The calculated behavior of the reaction is relatively insensitive to well properties, though it continues to depend on other potential shape parameters in the usual way. We suggest that the characteristic features of X+Y2 reactive scattering may arise from the predominant effect of some feature of the interaction potential at fairly large reactant separation. Comparison of our results with those of trajectory studies for D++H2 indicates that formation of a long-lived intermediate complex in the neighborhood of a potential well will in practice depend sensitively on the particle masses and initial energies.
Intermolecular Potentials and Infrared Spectra
Authors: Gordon Roy G. , McGinnis Richard P.
Published: February 2004

In an effort to learn more about the angle dependence of intermolecular potentials, pressure broadened infrared spectra have been compared with calculations from a trial potential. Infrared spectra of the CO fundamental absorption band were measured at densities of helium gas perturber from 10 to 100 amagats at room temperature. The same spectra were calculated from the potential using a semiclassical impact theory of overlapping lines. The comparisons show that the potential accounts quite well for the spectra except at low pressures, suggesting that the long-range part of the potential was too strong. Satisfactory agreement was obtained even at pressures which were so high that the impact theory is not rigorously applicable. The success of these calculations should encourage the use of this technique for, on the one hand, testing intermolecular potentials and, on the other, predicting pressure broadened spectra of molecular gases over a wide range of pressures.
Angular Distribution of the Photoelectron Spectra for Ar, Kr, Xe, H2, N2, and CO
Authors: Carlson Thomas A. , Jonas A. E.
Published: February 2004

The distribution of photoelectrons as a function of the angle Θ between the direction of the incoming photon and outgoing photoelectron has been measured for Ar, Kr, Xe, H2, N2, and CO. The experiments have been carried out with a double focusing electrostatic electron spectrometer to which has been attached a chamber containing a gas discharge lamp that can be freely rotated. The HeI (584 Å) and NeI (736, 744 Å) resonance lines were used as photon sources. For each of the photoionization bands studied the angular distribution could be fitted to the general shape predicted from theory: 1+β/2 (3/2 sin2θ −1). In addition, the values of the parameter β experimentally determined were in good agreement with theoretically determined values for H2 and for the rare gases but only partially satisfactory agreement for the first ionization potential of N2. The II states of N2+ and CO+ give lower values of β than the Σ state according to expectations. In general the vibrational structure for a given band was independent of Θ, but several exceptions were found for both N2 and CO, which have been discussed in terms of the presence of autoionization states and possible breakdown in the Born—Oppenheimer approximation.
Theory of Atomic Recombination on Surfaces
Authors: Gelb A. , Kim Shoon K.
Published: February 2004

A simple kinetic theory for atomic recombination on solid surfaces employing the Rideal mechanism is presented. The temperature dependence of the reaction rate is discussed in terms of ``transition temperature'' which characterizes change in the kinetic order of the recombination reaction with respect to the gas-phase atom concentration. The transition temperatures are shown to correspond to the maxima and the minima of the reaction rate. The experimental data of Wood and Wise and others for hydrogen recombination on glass surfaces are satisfactorily reproduced with the assumption of two types of adsorption sites on glass surfaces having the binding energies of 42 and 2.1 kcal/mole, respectively. Qualitative agreement is also found with the limited experimental data for hydrogen recombination on metals. A comparison of the present theory with the steady state theory of De Boer and Van Steenis is given in the Appendix with a refined definition of the partition function for the activated complex in the reaction on surface.
Diffusion of Tl+ in Single-Crystal KCl
Authors: Tiernan R. J. , Wuensch B. J.
Published: February 2004

Diffusion coefficients for Tl+ in single-crystal KCl have been determined in air over a temperature range of 233 to 727°C from concentration gradients measured with the aid of electron microbeam probe spectroscopy. The variation of the diffusion coefficients with temperature provides D0 of 5.81 10−11 and 1.34 10−3 cm2/sec, and activation energies of 0.24 and 1.30 eV in temperature ranges of 233–457 and 457–727°C, respectively. The enthalpy of Schottky pair formation is thus 2.12 eV.
On the Collisional Transfer of Rovibronic and Translational Energy between Differently Excited Like Molecules
Authors: Chiu Ying-Nan
Published: February 2004

In line with the principle of the first Born approximation, we give a simple treatment of the comprehensive transfer of rotation, vibration, and electronic and translational (rovibronic-translational) energy in the collisions between (electronically) differently excited like molecules. It is shown that the electronic exchange degeneracy between the collision partners gives rise to first-order (long-range) dispersion forces which may result in large energy transfer cross sections. The formalism is for diatomic or linear molecules, with or without electronic angular momentum, and may be easily adapted to symmetric-top molecules. A first-order, general (electronic) multipole-multipole interaction is used as the scattering potential, which is written as a contraction of tensors. The transition matrix elements are evaluated by Racah's method, showing the explicit dependence on the conserved total angular momentum as well as on the angular momenta of the individual molecules and the angular momentum of the relative orbital motion. The relative motion is treated as a plane wave. Coupled representations with definite total angular momentum and alternatively uncoupled representations of the wavefunction (in the Appendix) are used to derive the matrix elements and cross-sections. The general case of small vibronic energy discrepancies is considered. Differential cross sections as well as total cross sections are given explicitly. Under the assumption of long-range electronic interaction and fast electronic transition, the cross sections are shown to be proportional to Franck-Condon overlap integrals, multipole rotational transition line strengths, and Bessel function integrals for the relative motion. The necessary reduced matrix elements for the multipole transition and for the relative motion are computed and discussed. Assuming the validity of the Born-Oppenheimer approximation, i.e., no vibronic interaction and no rotation-electronic interaction, etc., the effect of permuting the nuclei of like molecules of the same nuclear spin is shown to be unimportant if the permanent dipoles of the states are small. This treatment of energy transfer should be applicable to differently excited states (of like molecules) between which there are large multipole transition moments, which interact in the first order because of the exchange degeneracy.
Dipole Correlations in Molten Alkali Metal Nitrates and Sodium Nitrite
Authors: Wegdam G. H. , te Beek J. B. , van der Linden H. , van der Elsken J.
Published: February 2004

The far infrared spectra of some solid and molten alkali metal nitrates and sodium nitrite have been measured at various temperatures. The dipole moment correlation functions obtained from these spectra by Fourier transformation are presented and are connected with a solid state formalism. These dipole correlation functions give a measure of the lifetime of the correlated motions in the liquid phase. The lifetimes for the molten salts are of the order of 10−12−10−13 sec. High anharmonicity and large fluctuations characterize the liquid phase.
Matrix Infrared Spectrum and Bonding in the Monobromomethyl Radical
Authors: Smith David W. , Andrews Lester
Published: February 2004

The simultaneous deposition of atomic beams of lithium (6Li or 7Li) with CH2BrX (X=F, Cl, Br, I) at high dilution in argon on a CsI cold window at 15°K produces infrared absorptions identified as the monobromomethyl radical and the corresponding lithium halide. The identity of the radical is confirmed by comparing the spectra of the reactions of CH2BrX (X=Br, I) with Na and K. The reactions of CHDBr2 and CD2Br2 with Li and Na support assignments to v2, the symmetric H–C–H valence angle bend, v3, the C–Br stretch, and v6, the out-of-plane hydrogen bend, of the monobromomethyl radical. Bromine isotopic splittings are observed for the first time in an argon matrix. The high C–Br stretching force constant (3.42 ± 0.02 mdyn/ Å) indicates considerable electronic stabilization in the CH2Br radical and suggests (p–p) π and some (p–d) π bonding between carbon and bromine. The large positive quartic term in the out-of-plane bending potential function is consistent with a planar radical.
Study of the Potential Surfaces of the Ground and First Excited Singlet States of H2O
Authors: Gangi R. A. , Bader R. F. W.
Published: February 2004

The lowest 1A′ and 1B1 potential surfaces of the water molecule are calculated and are discussed together with the results of previous investigations concerning the reactions of O(1D) and O(3P) with H2(1Σ g+). It is found that the insertion of O(1D) into an H2 molecule to yield H2O and the abstraction of hydrogen to yield OH and H both occur preferentially for an acute angle approach of the oxygen atom with respect to the H–H bond. The activation energy of abstraction is found to be small enough to account for the formation of OH radicals which are also found as products during O(1D) insertion reactions. It is illustrated that the symmetry rules based on second-order perturbation theory may serve as a useful guide in the initial mapping of a potential energy surface. Finally, the electronic charge and spin density distributions of the lowest 1B1, 3B1, and 1A1 states are compared and discussed.
Geminate Recombination of X-Ray Excited Electron—Hole Pairs in Anthracene
Authors: Hughes R. C.
Published: February 2004

A recent controversy is discussed concerning the relative importance of geminate and track recombination of charge carriers excited by ionizing radiation in single crystals of anthracene. Data is presented which strongly supports the geminate recombination hypothesis for bulk excitation by x rays in the 50–500−keV range. In agreement with the earlier work of Kepler and Coppage, it is found that it requires about 2700 eV to create a pair of charge carriers in anthracene at an applied field of 10 kV/cm.
Experimental Determination of the P—T Melting Curves of Kr, Ne, and He
Authors: Crawford R. K. , Daniels W. B.
Published: February 2004

Pressure—temperature melting data have been obtained at pressures of 0–8 kbar for Kr, 0–10 kbar for Ne, and 1–10 kbar for He. The estimated accuracy of the data is ± 1 bar and ± 0.002 to ± 0.011oK. Use of a modified Simon melting equation of the form P=A(T+D)c+B to represent the data removes nearly all of the systematic deviations which are observed when the usual Simon melting equation P=ATc+B is applied. The modified form of the equation also provides much better high pressure extrapolations from the melting curve data.
Magnetic Circular Dichroism of the α Bands of Some Polycyclic Aromatic Hydrocarbons
Authors: Larkindale J. P. , Simkin D. J.
Published: February 2004

The magnetic circular dichroism (MCD) of six polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, 1,2-benzanthracene, picene, and 1,2–3, 4-dibenzanthracene) has been measured in the α (1Lb) absorption region. A band in the MCD spectrum of anthracene which does not correspond to any reported absorption band has been assigned to the hitherto unobserved α band. The sign and magnitude of the MCD's observed are in good agreement with those calculated using CNDO wave-functions.
Photochemistry of Trifluoromethyl Benzenes. I. (Trifluoromethyl)benzene
Authors: Gray David , Phillips David
Published: February 2004

Fluorescence and intersystem crossing quantum yields of (trifluoromethyl)benzene have been measured at different exciting wavelengths. At 265.3 nm the fluorescence yield decreases with increase in pressure of aromatic or of chemically inert quenching gas. At 253.7 nm the yield is independent of pressure of aromatic or inert gas, while at 248.2 nm the fluorescence yield increases with increase in chemically inert gas pressure. Buta-1, 3-diene and oxygen were found to strongly quench the fluorescence of (trifluoromethyl)benzene and the but-2-enes did so slightly. Other olefins were found to act mainly as vibrational relaxers.
Chemistry of Nuclear Recoil 18F Atoms. V. Mechanism and Systematics in CH3CF3
Authors: Krohn Kenneth A. , Parks Norris J. , Root John W.
Published: February 2004

Nuclear recoil 18F atoms undergo hot F-for-F and F-for-H atomic substitution and hot F-for-CH3 and F-for-CF3 alkyl replacement reactions in CH3CF3. The primary absolute yields corresponding to these processes are 3.56 ± 0.07, 8.22 ± 0.09, 5.79 ± 0.31, and 8.5 ± 2.5 % (estimated value), respectively. The total primary hot yield for organic products is 26.1 ± 2.5 %, and that for all hot reactions including F-to-HF and F-to-F2 abstraction is 83 ± 3 %. There is no evidence in favor of hot F-for-2F or F-for-2H double substitution reactions in CH3CF3. Recoil 18F exhibits approximately a sixfold systematics preference for alkyl replacement reactions at the carbon—carbon bond in CH3CF3 relative to the average of substitution reactivities at carbon—fluorine and carbon—hydrogen bonds. The per-bond preference for primary substitution reactions at carbon—hydrogen relative to carbon—fluorine bonds is 2.30 ± 0.06. The sums of primary hot yields for organic products are comparable for recoil 18F in CH3CF3 vs recoil 3H in alkanes, so that these two recoil systems differ principally in that 18F exhibits a preference for alkyl replacement reactions, whereas recoil 3H exhibits a preference for T-for-H substitution. All the organic products from primary 18F hot reactions exhibit extensive unimolecular decomposition.
Polarized Vibrational Spectra of Potassium Chlorate
Authors: Bates John B.
Published: February 2004

The Raman spectra of single crystal KClO3 were measured in the region above 30 cm−1 at 298 and 77°K. Single crystal infrared spectra in the internal mode region were measured by reflection at 298°K. Infrared spectra of the polycrystalline material also were measured at 77°K. Assignments for all of the crystal vibrations that are derived from correlation field splitting of the (internal) ClO3− vibrations were made from the results of the polarization measurements. Longitudinal optical mode frequencies for the ν3(Bu) and ν3(Au) components obtained from polarized (infrared) specular reflection measurements on polycrystalline KClO3 are also reported. The bands due to the Raman active lattice modes were observed in the region below 200 cm−1 and were tentatively assigned to librational or to translatory-type motions. The 2-cm−1 splitting observed for the ν1 mode of the 35Cl18O16O2 and 37Cl18O16O2 isotopes in the low-temperature Raman spectra was assigned to an orientational effect in the lattice.
Reptation of a Polymer Chain in the Presence of Fixed Obstacles
Authors: de Gennes P. G.
Published: February 2004

We discuss possible motions for one polymer molecule P (of mass M) performing wormlike displacements inside a strongly cross-linked polymeric gel G. The topological requirement that P cannot intersect any of the chains of G is taken into account by a rigorous procedure: The only motions allowed for the chain are associated with the displacement of certain “defects” along the chain. The main conclusions derived from this model are the following:

(a) There are two characteristic times for the chain motion: One of them (Td) is the equilibration time for the defect concentration, and is proportional to M2. The other time (Tr) is the time required for complete renewal of the chain conformation, and is proportional to M3.

(b) The over-all mobility and diffusion coefficients of the chain P are proportional to M−2.

(c) At times t < Tr the mean square displacement of one monomer of P increases only like 〈(rt − r0)2〉 = const t1/4.

These results may also turn out to be useful for the (more difficult) problem of entanglement effects in unlinked molten polymers.
Vibrational Investigations of Several Alkali Metal Haloxenates
Authors: LaBonville P. , Ferraro J. R. , Spittler T. M.
Published: February 2004

Several alkali metal haloxenates of the type MXeO3F, where M=K, Rb, Cs, and MXeO3Cl·MCl, where M=Rb, Cs were synthesized. The infrared and Raman data for these salts were obtained at room temperature and at liquid nitrogen temperature. Vibrational assignments were made, and a normal coordinate treatment using the generalized valence force field was attempted for KXeO3F.
Cation Diffusion and Conductivity in Solid Electrolytes. I
Authors: Sato Hiroshi , Kikuchi Ryoichi
Published: February 2004

The characteristics of cation diffusion and ionic conductivity in solid electrolytes are discussed using β- and β″-alumina as examples. The problem is characterized by a cation migration by the vacancy mechanism in a “cation-disordered phase,” a system in which the number of available vacant sites is of the same order of magnitude as the number of diffusing cations. The path probability method is used to derive both the tracer diffusion and the ionic conductivity; this method avoids the difficulties connected with the application of the ordinary random walk approach to such systems. β″-Alumina is regarded as an example of the “cation-disordered phases” in which all available cation sites are equivalent, while β-alumina represents those in which available cation sites are divided into several nonequivalent sublattice sites. When the derived diffusion coefficient is interpreted using the language of the conventional random walk approach, the jump frequency of cations is found to include two factors, the vacancy availability factor V and the effective jump frequency factor W, both of which take into account the effect of surroundings of the migrating ion and characterize the cooperative mode of the cation motion. Both of these factors, as well as the correlation factor f, depend strongly on composition of cations and on temperature. The Nernst–Einstein relation which relates the tracer diffusion and the charge diffusion is found to include characteristic correlation factors. Even in ionic conductivity, a correlation factor fI is found to appear in the β-alumina-type electrolytes. Although both f and fI vary drastically depending on the cation concentration, the ratio of the two remains within limits determined by the geometry of the crystal lattice. The value of the ratio indicates the predominant mechanism of diffusion.
Electronic Structure and Electronic Spectrum of Nitrogen Dioxide. II. Configuration Interaction and Oscillator Strengths
Authors: Gangi R. A. , Burnelle L.
Published: February 2004

The ground state and the five lowest excited states of NO2 which were investigated in an earlier work are studied further. It is found that, of various methods of including configuration interaction, better results are obtained when configurations of each symmetry and spin species are formed from the self-consistent field orbitals of the lowest state of that species. With a basis set of 33 Gaussian-type orbitals, up to 180 configurations are included at three values of the bond angle to obtain potential-energy curves of the six states. The calculations are then repeated at the equilibrium geometry of the gound state using 72 Gaussian-type orbitals contracted to 39 basis functions. Oscillator strengths of the allowed and forbidden transitions are obtained.
Intensity and Linewidth Studies of the System Polystyrene–Cyclohexane in the Critical Region
Authors: Kuwahara N. , Fenby D. V. , Tamsky M. , Chu B.
Published: February 2004

The cloud-point curve and critical opalescence of the system polystyrene (Mn = 392 000)–cyclohexane have been investigated. The critical point, as determined by the phase-volume ratio method, is at a higher concentration than the maximum in the cloud-point curve. Experiments are reported on the angular and the spectral distribution of scattered light for a solution of composition corresponding to the maximum in the cloud-point curve and on the spectral distribution for a solution of critical concentration. The temperature dependence of the extrapolated zero-angle scattered intensity obeys a relation lim K→0 IC−1∝(T − Tsp)γ with γ = 1.26 ± 0.08. The long-range correlation length ξs obeys a relation ξs∝(T − Tsp)−νs with νs = 0.62. The extrapolated linewidth obeys a relation lim K→0 (Γ / K2)∝(T − Tsp)γ* with γ* ≈ 1 at the concentration exhibiting the maximum phase separation temperature (Tp,max), and γ* ≈ 0.77 at the critical solution concentration (Tsp = Tc). The long-range correlation length of the critical concentration solution obeys a relation ξΓ∝(T − Tc)−νΓ with νΓ ≈ 0.58. Various exponents as compared with the corresponding values for one- and two-component systems show that the critical exponent concept and the spinodal generalization are equally applicable to multicomponent (polymer) systems.
On the Elastic and Inelastic Scattering of Neon Atoms by a (100) Surface of Lithium Fluoride at 150°K
Authors: Williams Brian R.
Published: February 2004

Results are presented for the scattering of neon atoms (obtained from a nozzle source) from a cleaved surface of lithium fluoride maintained at 150°K. The scattering patterns reveal well-defined peaks resulting from coherent scattering. Inelastic scattering is also observed: (1) scattering due to the thermal motions of surface atoms giving streaks extending in the 〈100〉 direction from the elastic peaks; (2) incoherent or cosine scattering. A brief comparison with the scattering of argon atoms is made.
Infrared Spectra and Vapor Pressure Isotope Effect of Crystallized Ammonia and Its Deuterium Derivatives
Authors: Wolff H. , Rollar H.-G. , Wolff E.
Published: February 2004

We have reinvestigated the infrared spectra of crystalline NH3, NH2D, ND2H, and NH3, which were throughly studied by Reding and Hornig in 1951 and 1955. The antisymmetric stretching bands of NH3 and ND3 are found to be split. Their shifts relative to the values for the gas phase found to be approximately equal by the previous measurements have now been shown to be distinctly different. The antisymmetric stretching vibrations of NH2D and ND2H are observed separately from those of NH3 and ND3. The ND stretching vibration of NH2D consists of a triplet composed of the unperturbed vibrational center band and of two satellite bands due to correlation field splitting. It has been derived from this splitting that intermolecular coupling between the ammonia molecules is weak. The equality of the NH and ND stretching force constants in NH2D and ND2H as well as in NH3 and ND3 follows from two facts: (1) The NH stretching vibration of ND2H lies in the middle of the NH2 stretching vibrations of NH2D, also the ND stretching vibration of NH2D lies in the middle of the ND2 stretching vibrations of ND2H; (2) only single NH and ND stretching bands are observed. Therefore, the unequal shifts of the symmetric and of the antisymmetric stretching vibrations of NH3 and ND3 relative to the values observed in the gas phase cannot be explained by an asymmetric change of stretching force constants during crystallization. They must be explained by Fermi resonance of the symmetric stretching vibration with the parallel component of the overtone of the deformational vibration. The calculation of the vapor pressure isotope effect of crystalline NH3 and ND3 by using the corrected vibrational frequencies shows further evidence in support of these explanations.
On the Equation of State of Small Systems
Authors: Hubbard Joe
Published: February 2004

Lebowitz and Percus recently described a method by which a thermodynamic function F in a canonical ensemble could be expressed in terms of a differential operation on F as described in a grand canonical ensemble. The result of such a transformation was to derive an explicit expression for the dependence of the virial coefficients in the expansion of the canonical pressure on the number of molecules in the periodic system. The purpose of this article is to elucidate the methods and assumptions used in this transformation and to derive the expression for the canonical pressure by applying this method to the (N–P–T) ensemble → (N–V–T) ensemble transformation.
Shape of the Coexistence Curve near a Plait Point in a Three-Component System
Authors: Zollweg John A.
Published: February 2004

The degree, d, of the coexistence curve near the plait point in the system ethanol–water–chloroform has been determined from measurements of the volumes of coexisting phases in sealed samples. The result, d = 2.67 ± 0.12, shows the deviation from the mean-field d = 2 and shows also the renormalization d = (1 − α′) / β that is predicted by current theories. (1 / β is the degree of the temperature-density coexistence curve in a pure fluid and α′ is the index of its constant-volume specific heat singularity.)
Numerical Calculation of Vibrational Relaxation and Dissociation for a Quantum Anharmonic Oscillator
Authors: Dove J. E. , Jones D. G.
Published: February 2004

The vibrational relaxation and dissociation of gaseous H2 highly diluted in an argon heat bath have been studied numerically at temperatures between 2500 and 15 000°K. Collisional transition probabilities between the vibrational levels of H2 were calculated by the method of Schwartz, Slawsky, and Herzfeld in a form modified for a Morse oscillator. The master equation was solved by numerical integration to give the time dependence of the vibrational level populations and of dissociated molecules in a simulated shock-wave experiment. The absolute values of the calculated rate coefficients for dissociation are in good agreement with experiment, but the predicted vibrational relaxation times are about a factor of 35 shorter than those determined experimentally. At all temperatures, the upper vibrational levels in the dissociating gas are substantially depleted below their equilibrium populations. The Arrhenius activation energy for dissociation is 102.5 kcal mole−1, slightly lower than the dissociation energy of 103.2 kcal but higher than the experimentally determined activation energies by about 10 kcal. An incubation period of about 1 to 1.5 vibrational relaxation times precedes the establishment of approximately steady dissociation. The computed incubation behavior is compared with that predicted from the diffusion theory model of Brau, Keck, and Carrier. The vibrational relaxation behavior of this anharmonic oscillator molecule has been examined. In the absence of dissociation, the relaxation time as defined by the Bethe–Teller equation differs from its SHO value by less than 10%, and is found to show variations of less than 10% with time. The present results are also used to examine some approximations made in theories of coupled vibration and dissociation.
Highly Conducting Ion-Radical Salts of Tetrathiotetracene
Authors: Perez-Albuerne E. A. , Johnson H. , Trevoy D. J.
Published: February 2004

The electrical resistivity and thermoelectric power of the organic semiconductor tetrathiotetracene (TTT) and its chloride, bromide, iodide, and thiocyanate salts are reported as a function of temperature. The ion–radical salts, of nearly 1:1 stoichiometry, were discovered to be highly conducting organic semiconductors and have resistivity values at room temperature ranging from 2.3 × 103 Ω·cm for TTT–chloride to 0.71 Ω·cm for TTT–iodide. The sign of the Seebeck coefficient of TTT–chloride corresponds to an n-type semiconductor, while for TTT and the other salts it indicates p-type behavior. Infrared absorption spectra of the solids, uv–visible spectra of solutions, preliminary x-ray powder patterns and density measurements are correlated with electrical properties. The influence of constitution of the ion–radical salts on the electrical resistivity and possible mechanisms of conduction are discussed.
Time Correlation Functions for a Molecular Gas: Magnetic Field Effects
Authors: Kapral Raymond , Desai Rashmi C.
Published: February 2004

Time correlation functions appropriate for the study of thermal conduction and viscous dissipation are considered for a molecular gas in the presence of a static magnetic field (Senftleben–Beenakker effect). The classical Boltzmann equation is used in the formulation although the generalization to the quantum mechanical case is straightforward. The results are illustrated by an explicit calculation for diamagnetic molecules within the framework of a simple model used by Kagan and Maksimov. The time correlation functions which correspond to the nondiagonal components of the thermal conductivity and viscosity tensors show the most interesting structure. The results are discussed and further extensions of the present calculations are outlined.
Catastrophe in the Random-Phase Approximation: Critique of a Theory of Phase Transitions
Authors: Wheeler John C. , Chandler David
Published: February 2004

A detailed investigation is presented of the theory of phase transitions afforded by the random phase approximation (RPA) and Gaussian fluctuation theory. Arguments are given which indicate that these two theories are equivalent. A rigorous analysis is carried out on the RPA for a simple binary model that should exhibit a phase transition. It is found that when the RPA free energy is used to calculate the thermodynamics for the model a catastrophe region exists in which the system collapses to negatively infinite free energy and thermodynamic stability breaks down before (at lower densities and higher temperature) the region is reached. The catastrophe surface which surrounds the region has been identified in the previous literature as the limit of stability for the model, and the singularities associated with the catastrophe have been incorrectly identified as true critical singularities. The incorrect identification leads to results which contradict the second law of thermodynamics. It is shown that there is no sensible solution to the equations obtained from a Maxwell construction to bridge the catastrophe. The RPA for the binary model is also discussed within the context of the compressibility theorem. When this route to the thermodynamics is taken, it is found that the behavior predicted by the RPA is purely classical. Arguments are presented which indicate that the results found with the binary model are general features of the RPA; the application of the approximation to more general one- and two-component systems yield the same results. Finally, a tentative explanation for the catastrophe is given. The explanation suggests a modified RPA which does not violate the second law of thermodynamics; however, the patched up theory is classical.
Rotational Diffusion of Tobacco Mosaic Virus
Authors: Wada A. , Ford N. C. , Karasz F. E.
Published: February 2004

The line shape of the Rayleigh component of light scattered from dilute tobacco mosaic virus solutions has been examined as a function of scattering angle using a homodyne technique and an autocorrelation function computer. By these means two Lorentzian components corresponding to the translational and rotational diffusional coefficients of the anisotropic molecule were separated. It is concluded that this experimental technique permits the resolution of the observed line more readily than the alternative wave analyzer method. The agreement between theory and experiment is good for the time constants and for the fractional amplitudes as a function of scattering angle except for a deviation of the calculated and observed amplitude at high angles.
Anisotropic Photodissociation of Cadmium Dimethyl
Authors: Jonah C. , Chandra P. , Bersohn R.
Published: February 2004

Cadmium dimethyl has been photolyzed at very low pressures with polarized light. The cadmium atoms are deposited perpendicular to the ε vector of the light. The methyl radicals also move perpendicularly to the ε vector. The interpretation of these results is that the transition movement is perpendicular to the axis of the molecule and the three (or two) fragments separate along the molecular axis. The cadmium atoms were detected by the apprearance of a black film and the methyl radicals were detected by the bluing of a white film of MoO3.
Theory of the Coupling of Electronic and Vibrational Excitations in Molecular Crystals and Helical Polymers
Authors: Philpott Michael R.
Published: February 2004

The effect of the internal vibrations of monomers (or molecules) on the electronic absorption spectra of aggregates with either helical or three dimensional translational symmetry is considered using molecular exciton theory. In this treatment the single-particle excitations (vibronic excitons) are coupled to all those two-particle manifolds in which vibronic and ground vibrational excitons occupy different lattice sites. This allows for collective coupling among single-particle levels overlapped by two-particle continua. The main approximations invoked are (a) the crude Born—Oppenheimer approximation to factorize the wavefunctions of isolated monomers, (b) neglect of electron exchange between monomer wavefunctions (tight binding), and (c) the neglect of any mixing of different electronic states by intermonomer forces. Wave sums of exciton resonance interactions are eliminated in favor of a density of sums function. To test the range of coupling strengths for which the theory is valid calculations are performed for a one-dimensional polymer model with only nearest-neighbor interactions and a three-dimensional crystal model with a simple density function. For intermediate coupling the influence of three- and higher-particle states becomes important and these states are included in the energy calculations by an extended fraction type of technique. Other calculations explore the effect of (a) a change in the vibrational frequency of the monomer after electronic excitation, (b) changes in the energy of the optical k=0 levels with direction of the exciting radiation, and (c) changes in the transition intensity of the isolated monomer.
Evidence for a Low-Lying Triplet State of the Hydroxide Ion
Authors: Merkel Paul B. , Hamill William H.
Published: February 2004

Phosphorescence with a λmax at ∼400 mm has been observed from aqueous hydroxide solutions at room temperature and at 77°K and from crystalline barium hydroxide at 77°K. Although the intrinsic absorption of the hydroxide ion appears to onset at a shorter wavelength, the phosphorescence can be excited at a photon energy as low as 350 nm which on energetic grounds eliminates the possible involvement of a quartet state of the hydroxyl radical produced by photoionization of OH−. On the basis of this observation, quenching experiments, and theoretical prediction, the phosphorescence is more plausibly assigned to emission from the lowest triplet state of the hydroxide ion.