bluuebunny/crossref_metadata_2025 huggingface dataset:
Depolarized scattering at a binary liquid critical point
Authors: Petrula John R. , Strauss Herbert L. , Lao Kenneth Q-H , Pecora R.
Published: February 2003

Interferometric and diffraction grating measurements of the depolarized light scattering linewidths in the critical region of a nitroethane-3 methylpentane liquid mixture reveal a relatively weak dependence of the orientational linewidth on ΔT. Plots of the log of the orientational relaxation time vs log ΔT, logτ=−r logΔT+C, yield r=0.031±0.008 while plots of logτ=r′/T+C′ yield r′=1090±292 K. The wide background in the depolarized spectrum exhibits a HWHM of 30 cm−1 which does not change as the critical point is approached. In addition, the HWHM of the completely polarized 875 cm−1 Raman band of nitroethane was found to be 2.1 cm−1 and also to be insensitive to temperature.
A multiple pulse zero crossing NMR technique, and its application to 19F chemical shift measurements in solids
Authors: Burum D. P. , Elleman D. D. , Rhim W.-K.
Published: February 2003

A simple, multiple pulse ’’zero crossing technique’’ for accurately determining the first moment of a solid state NMR spectrum is introduced. This technique was applied to obtain the 19F chemical shift versus pressure curves up to 5 kbar for single crystals of CaF2 (0.29±0.02 ppm/kbar) and BaF2 (0.62±0.05 ppm/kbar). Results at ambient temperature and pressure are also reported for a number of other fluorine compounds. Because of its high data rate, this technique is potentially several orders of magnitude more sensitive than similar cw methods.
Consequences of size dependence of transition probabilities in stochastic equations
Authors: Mukamel Shaul , Procaccia Itamar , Ross John
Published: February 2003

We assume stochastic master equations for the temporal evolution of macroscopic systems with two or more accessible states. Such systems fall into two classes depending on the ratio of transition probabilities between microscopic states of a system, determined by detailed balance, which either scales, or does not, with the size of the system. The two classes have different properties in regard to (1) dependence of rate of transition between macroscopic states on the size of the system; (2) presence of separate time scales; and (3) sharpness of transition between macroscopic states. Thus we show that the stationary distribution function, through the condition of detailed balance, contains information about some properties of the temporal evolution.
Electrically induced variations of Rayleigh scattering: simultaneous monitoring of the intensity and spectral width from macromolecular solutions
Authors: Brownsey G. J. , Jennings B. R.
Published: February 2003

An apparatus has been built with which one can measure the changes in both the spectral characteristics and the intensity of the light scattered from aqueous solutions and suspensions. Illustrative experiments are described on TMV solutions at pH 7.55 and at low ionic strength. The quasielastic scattering experiments led to values of the translational diffusion coefficient and the electrophoretic mobility (u) of the virus particles, while the intensity measurements, indicating the absence of any permanent dipole moment, gave a value for the predominant electrical polarizability (α) and provided the fastest and most reliable determination of the rotational diffusion coefficient. All parameters agree with previous results in the literature. The most promising aspect of this type of apparatus is that the simultaneous evaluation of u and α enables one to study the properties of the electrical double layer and hence the stability of such colloidal particles.
Vibrational deactivation of carbon monoxide by hydrogen from 250 to 2000 °K
Authors: Stricker Josef
Published: February 2003

Vibrational energy transfer probabilities for CO(v=1)+H2→CO(v=0)+H2, CO(v=1)+H2(v=0) →CO(v=0)+H2(v=1), and CO(v=2)+H2(v=0) →CO(v=0) +H2(v=1) are calculated semiclassically, over the temperature range of 250–2000 °K. It is assumed that the molecular interaction potential consists of a superposition of atomic pair potentials represented by Morse function. The potential range was taken as α=2.5 Å−1. The calculations indicate that it is possible to attribute the vibrational relaxation to energy transfer between the vibrations of CO and the vibration rotation as well as translation of H2. Calculated values of V–T and V–V probabilities are in good agreement with experimental data. It is also shown that the V–V probability for CO(v=2)+H2(v=0) →CO(v=0)+H2(v=1) is very large compared with the V–V probability for CO(v=1)+H2(v=0) →CO(v=0)+H2(v=1).
Intensities of binary overtone and combination bands in the ir spectrum of CClF3
Authors: Golden William G. , Horner David A. , Overend John
Published: February 2003

The intensities of the fundamental, binary overtone and binary combination bands in the ir spectrum of CClF3 have been measured. The intensities of the fundamentals have been interpreted in terms of a polar-tensor model; those of the overtone and combination bands have been interpreted in terms of a model which ascribes all the intensity to mechanical anharmonicity and none to higher terms in the dipole–moment expansion in normal coordinates. It appears, from the success of this model, that the contributions from the second derivatives of the dipole moment to the binary overtone and combination bands are relatively unimportant in this molecule.
The photochemistry of formaldehyde: Absolute quantum yields, radical reactions, and NO reactions
Authors: Clark John H. , Moore C. Bradley , Nogar Nicholas S.
Published: February 2003

Absolute quantum yields have been measured for the gas phase photolysis of H2CO and D2CO as a function of excitation energy. Over the spectral region examined, 290 nm ?λ?360 nm, formaldehyde can dissociate into either molecular or free radical products: H2CO+hν→H2+CO or H2CO+hν→H+HCO. For H2CO the total photochemical quantum yield was Φtotal=1.0±0.1 for λ?326 nm and 0.68 at λ=353 nm. For D2CO, Φtotal=1.0±0.1 for λ?331 nm and drops to zero near the band origin. The mechanism of formyl radical recombination in pure formaldehyde was shown to be 2HCO→H2CO+CO. Addition of NO to the photolysis mixture allowed determination of the radical/molecule branching ratio by introducing the scavenging reactions: HCO+NO→HNO+CO, and H+NO+M→HNO+M. The threshold for production of radicals was found to be between 339 nm and 330 nm for H2CO, and between 326 nm and 320 nm for D2CO. Radical quantum yields increase steeply at the threshold and remain constant near 0.4 at higher energies.
Molecular electronic Raman transitions and magnetic susceptibility of the chromocene molecule
Authors: Parameswaran T. , Koningstein J. A. , Haley L. V. , Aleksanyan V. T.
Published: February 2003

Raman spectra of solid chromocene have been recorded in the region 10–1200 cm−1 at ambient and low temperatures. Assuming a D5d geometry the bands at 283 cm−1 ν4(a1g), 370 cm−1 ν16(e1g), and 1094 cm−1 ν3(a1g) are assigned to be of vibrational origin, while two electronic Raman bands have been observed with shifts of 35 and 55 cm−1. The series of transitions with the 0′–0 at 35 cm−1 indicate a shift between the ground state and an excited state coupled to the torsional mode ν6(a2g) with frequency 21 cm−1. This mode becomes totally symmetric and hence Raman active if the symmetry is lowered to C5. The electronic Raman data are used to choose a set of parameters and compute the magnetic moment for small distortions from D5d. The magnetic moment <μ (T) ≳ so computed is compared with available experimental data.
On NO−3–H2O interactions in aqueous solutions
Authors: Caminiti R. , Licheri G. , Piccaluga G. , Pinna G.
Published: February 2003

The scattering of x rays from a concentrated NH4NO3 aqueous solution has been measured and analyzed at 25°C. It is shown that the sample may be considered as a solution of nitrate ions in water. In this way the existence of discrete NO−3–H2O interactions is demonstrated unequivocally. Good agreement with experimental data is achieved through a model in which each O atom in the nitrate ion gives rise to three weak hydrogen bonds with water molecules.
EPR study of free radicals produced in pyrrole by x-irradiation and tritium atom decay
Authors: Lloyd Roger V. , DiGregorio Silvio , Wood David E.
Published: February 2003

The formation of free radicals from pyrrole has been studied by EPR spectroscopy. Radicals were prepared by the radioactive decay of pyrrole-1-t and pyrrole-d4-1-t in matrices of pyrrole and pyrrole-d5, respectively, and by the x irradiation of pyrrole in a matrix of adamantane. In each case the radical formed by the addition of a hydrogen atom to C2 was obtained. The EPR parameters for the radical in adamantane were A (H2) =38.4 G (two protons), A (H3) =A (H5) =11.1 G, A(H4) =1.7 G, (A (N) =3.64 G, g=2.0030. INDO calculations suggest that the radical is best described as an allylic system strongly conjugated with the nitrogen atom.
NMR line shapes of tunneling methyl groups in enclathrated molecules
Authors: Ripmeester John A.
Published: February 2003

1H NMR line shapes, obtained at low temperatures (T<5 K), are reported for CH3Br, CH3CD2Cl, and CH3CD2Br molecules enclathrated in the heavy water clathrate hydrates, and for CH3CD2I and CH3CCl3 molecules enclathrated together with D2S, in the heavy water double clathrate hydrates. Line shapes for CH3Br and CH3CCl3 are characteristic of very fast and slow tunneling, respectively. Those obtained for the ethyl halides indicated intermediate tunneling rates. To account for the latter line shapes it is necessary to include a distribution in tunneling frequencies in the Apaydin and Clough line shape calculation. Satisfactory simulated spectra are given by a log-normal distribution. The methyl group rotational barrier heights derived from the tunneling frequencies for a threefold sinusoidal barrier can be correlated with the guest molecule dimensions relative to the size of the clathrate hydrate cage.
Time-of-flight determination of radiative decay rates for high Rydberg states in atomic nitrogen
Authors: Kocher C. A. , Fairchild C. E.
Published: February 2003

State selection by electric field ionization is employed in an atomic beam time-of-flight determination of radiative decay rates for high Ryberg nitrogen atoms, produced by electron impact dissociative excitation of N2. The highest-lying Rydberg states are field ionized; populations of the remaining excited states are modified by in-flight radiative decay. From studies of the atomic beam transit-time distribution at electric fields up to 4.5 kV/cm, radiative decay rates Γn have been inferred for states having principal quantum numbers n in the range 19≲n≲35. The data are consistent with an initial population P (n) ∝1/n3 and with Γn = (8.8±0.7) ×108 sec−1/n3. Evidence is given that the observed states are p states and that l-changing collisions do not significantly affect the measurements.
Rotationally and vibrationally inelastic scattering in the rotational IOS approximation. Ultrasimple calculation of total (differential, integral, and transport) cross sections for nonspherical molecules
Authors: Parker Gregory A. , Pack Russell T
Published: February 2003

A simple, direct derivation of the rotational infinite order sudden (IOS) approximation in molecular scattering theory is given. Connections between simple scattering amplitude formulas, choice of average partial wave parameter, and magnetic transitions are reviewed. Simple procedures for calculating cross sections for specific transitions are discussed and many older model formulas are given clear derivations. Total (summed over rotation) differential, integral, and transport cross sections, useful in the analysis of many experiments involving nonspherical molecules, are shown to be exceedingly simple: They are just averages over the potential angle of cross sections calculated using simple structureless spherical particle formulas and programs. In the case of vibrationally inelastic scattering, the IOSA, without further approximation, provides a well-defined way to get fully three dimensional cross sections from calculations no more difficult than collinear calculations. Integral, differential, viscosity, and diffusion cross sections for He–CO2 obtained from the IOSA and a realistic intermolecular potential are calculated as an example and compared with experiment. Agreement is good for the complete potential but poor when only its spherical part is used, so that one should never attempt to treat this system with a spherical model. The simplicity and accuracy of the IOSA make it a viable method for routine analysis of experiments involving collisions of nonspherical molecules.
Temporal coherence in multiphoton absorption. Far off-resonance intermediate states
Authors: Milonni P. W. , Eberly J. H.
Published: February 2003

We develop a consistent formalism for the treatment of temporal atomic or molecular coherence in multiphoton absorption. The formalism is fully quantum mechanical under the assumption that the exciting laser fields are well described by coherent states. We make use of the language and methodology of resonance physics to the extent possible, but deliberately avoid the rotating-wave approximation, and do not restrict the allowed atomic states to be finite in number or the electric field strengths to be small in magnitude. For compactness in the presentation only electric dipole transitions are considered. As all of the transitions, both stimulated and spontaneous, are due to the activation of quantum mechanical dipoles, it is most efficient to construct the formalism so that it emphasizes the role of dipole operators, and we do this. The one strong restriction imposed here, but avoided in a following paper, is to consider only multiphoton transitions that have one resonance between initial and final states and no intermediate resonance. We describe, in effect, the time dependences associated with the early multiphoton absorption calculations of Bebb and Gold.
Reflection of light from monomolecular layers on metal surfaces
Authors: Sherman P. G. , Philpott M. R.
Published: February 2003

A theory is presented of the electronic spectra, at optical frequencies, of a monolayer of dye molecules a fixed distance from a metal surface. The coupling of the exciton polariton states of the dye layer to the plasmon surface polariton modes of the metal leads to a large enhancement in the absorption of the dyes as measured by attenuated total internal reflection. This technique uses a prism to couple out the polariton modes of the monolayer–metal system. Model calculations that explore the type of phenomena expected are described for a cyanine dye monolayer close to a plane surface of silver.
Structural and optical properties of Cu- and Fe-doped PVC films
Authors: Rao T. V. , Chopra K. L.
Published: February 2003

Thin films of polyvinylchloride (PVC) with different concentrations of Cu and Fe have been prepared using a solution growth technique. Spectrophotometric methods were employed for the estimation of the metal concentration. The metal doped PVC films were characterized using electronic spectra, infrared spectra, and electron microscopy. In Cu-PVC films, copper exists as colloidal, Cu+, and Cu2+ states. In Fe-PVC films, only Fe3+ is present. Incorporation of metal in PVC results in a reduction in the degree of crystallinity of the films. The presence of the metal dampens considerably the C–Cl and C–H vibrations. The introduction of Fe in the films produces a new vibration at 1050 cm−1 which is explained in terms of interaction between Fe3+ and C+–Cl−.
The contributions of zero point energy effects and tunneling to ’’normal’’ deuterium kinetic isotope effects
Authors: Kaldor Sheena B. , Saunders William H.
Published: February 2003

Deuterium kinetic isotope effect and the contributions of zero point energy and tunneling to it has been discussed.(AIP)
Production of the excited OH radical in collisions of 50–250 keV He+, O+, N2+, O2+, and Ar+ ions with H2O molecules in water vapor
Authors: Nussbaum Gilbert H. , Cathers Arthur R.
Published: February 2003

Results are reported for collisions experiments using Hc+, O+, N+, O+2, and Ar+ ion projectiles with water vapor molecules in a ’thin’ water vapor target.(AIP)
Center of mass description of polymer flow: Friction approximation for the pressure tensor with antisymmetric stress
Authors: Olmsted R. D. , Snider R. F.
Published: February 2003

A statistical mechanical derivation of the equations of continuity and motion appropriate for the fluid dynamical description of dilute polymeric liquids is presented. This provides a molecular interpretation for the fluid densities of mass and momentum and their corresponding fluxes, which is different from that obtained by Curtiss, Bird, and Hassager [Adv. Chem. Phys. 35, 31 (1976)]. Comparisons are made with that theory. In particular, the pressure tensor appropriate to the present description has an antisymmetric component. For a dilute solution of dumbbells the symmetric part of the polymer contribution to the pressure tensor is reduced (with two approximations standard in polymer theory) to the familiar Giesekus result. Within the context of the same approximations the antisymmetric part is evaluated and found to be of comparable size.
Rate constants for the reactions of O2+, NO2+, NO+, H3O+, CO3−, NO2−, and halide ions with N2O5 at 300 K
Authors: Davidson J. A. , Viggiano A. A. , Howard Carleton J. , Dotan I. , Fehsenfeld F. C. , Albritton D. L. , Ferguson E. E.
Published: February 2003

The reactions of N2O5 with CO3−, NO2−, and the halide ions, F−, Cl−, Br−, and I−, have been found to be very fast (k∼10−9 cm3 s−1) at 300 K and to produce the NO3− ion. It is inferred from the thermochemistry of the halide reactions that the neutral products must be XNO2. The positive ions O2+ and NO+ react with N2O5 to produce NO2+, while H3O+ reacts with N2O5 to form NO2+ and H2NO3+. NO2+ was observed not to react readily with N2O5.
Statistical mechanics of helical wormlike chains. VI. Approximations
Authors: Yamakawa Hiromi , Shimada Jiro , Fujii Motoharu
Published: February 2003

Two methods of evaluating approximately the distribution functions and related averages for the helical wormlike chain are presented. One, called the weighting function method, is a modification of the Laguerre series approximations developed in Paper V and also a generalization of the procedure of Fixman and Skolnick. The other, called the ε method, is a simple one leading to expansions in terms of the relative deviation of the squared end-to-end distance near the rod limit. After an examination of the convergence of the two methods, they are applied to a derivation of approximate expressions for the mean reciprocal distance required in the calculation of the transport coefficients of helical wormlike cylinders, and also to a re-evaluation of the scattering functions at large magnitudes of the scattering vector. Relations between the characteristics of the average chain configuration and the model parameters are also examined to serve as criteria for the selection of test codes.
Static semiclassical response of a bounded electron gas. I.
Authors: Lert Peter W. , Weare John H.
Published: February 2003

A semiclassical theory of the self-consistent linear response of a metal surface to a one-dimensional perturbation is presented. The response is developed using JWKB wavefunctions and approaches the Thomas–Fermi form asymptotically in the bulk. The accuracy of the approach is investigated by comparison with the exact quantum mechanical response using the infinite barrier model. Agreement within 5%–10% is found at metallic densities except for high wavenumber (≳kF) perturbations. The semiclassical response in the surface region is no worse than in the bulk. The computational expense of using this method with a finite square-well model of the surface barrier is the same as that of quantum mechanical linear response theory for an infinite square-well model. Overconfinement of the electron gas due to the model infinite barrier causes the image plane to be located inside the equivalent jellium edge in both treatments.
The fourth virial coefficient for a Lennard-Jones fluid in two dimensions
Authors: Glandt E. D.
Published: February 2003

The fourth virial and its temperature derivative are reported for a two-dimensional Lennard-Jones fluid. The elementary diagram is obtained by a Fourier series procedure analogous to the method proposed by Barker and Monaghan for the three dimensional case. The density expansion of the radial distribution function is also considered, and values of the first- and second-order coefficients are reported. Various approximations given by the Percus–Yevick (PY) and hypernetted-chain theories are tested and it is found that the PY–energy-equation values are very good, especially at high temperatures. Rowlinson’s inverse-steepness expansion is also applied and it is found that it would be reliable at reduced temperatures kT/ε greater than about 30. The critical properties are estimated. The value for the critical temperature, kTc/ε=0.492, is in agreement with a previous estimate from the PY theory but lower than the computer simulation results.
Laplace transformation of the Schrödinger equation: Application to scattering
Authors: Leasure Steven , Bowman Joel M.
Published: February 2003

The single channel radial Schrödinger equation for the l=0 partial wave and an exponential potential is Laplace transformed. We investigate the analytic properties of the transform wavefunction and perform the inverse transformation to obtain the radial scattering wavefunction and scattering matrix. This Laplace transform approach is generalized to any potential which can be represented as a finite summation of exponentials. A particularly tractable solution is obtained for range parameters which are integral multiples of each other. The single channel results of the Laplace transform approach are then extended to multichannel scattering for an exponential potential for the l=0 partial wave.
Phase transition in barium chlorate monohydrate
Authors: Cancella L. S. G. , Gualberto G. M. , Lima C. A. S. , Vargas H. , Pelzl J.
Published: February 2003

The dehydration of barium chlorate monohydrate is investigated as the monoclinic fully hydrated Ba(ClO3)2⋅H2O modification is transformed into the orthorhombic face centered (ofc) fully anhydrous Ba(ClO3)2. The underlying structural changes were followed, both on single crystal and powdered samples, as a function of their degree of dehydration using a combination of several experimental techniques which included Raman and infrared spectroscopy, x-ray diffraction, thermogravimetry, and thermodifferential analysis. The dehydration process gets thermally activated at T∼85 °C and the transition seems to proceed through intermediate steps, where the two phases coexist with a gradual dominance of the ofc phase as the temperature increases. The role of the loss of the water of crystallization in the process is clarified and the experimental results are interpreted by invoking a two-step mechanism for the accomplishment of the structural changes within the crystal. This comprises random nucleation and growth of clusters of vacancies, left by the exit of H2O molecules, which up to a certain critical size can retain the original crystal structure, followed by a sudden onset of the phase transition within each of the overcritically sized clusters. As this process goes on, the concentration of clusters increases and the transition gets further enhanced by cluster–cluster interactions.
Collisional deactivation studies of the XeF* (B) state by He, Xe, NF3, and F2
Authors: Eden J. G. , Waynant R. W.
Published: February 2003

Measurements of the rates of quenching of XeF* (B) by He, Xe, NF3, and F2 are reported in this paper. Photolyzing XeF2 in the presence of the desired diluent gas resulted in the single-step, collisionless formation of XeF* (B), allowing exponential decay studies of the B state population to be made. The large three body quenching rate measured for xenon (∼2.4×10−29 cm6 sec−1) supports the existence of the trimer Xe2F*. Also, for a given pressure, NF3 quenches XeF(B) ∼13 times slower than does F2.
Charge transfer reactions of ground C+(2P) and excited C+(4P) state ions with neutral molecules
Authors: Moran T. F. , Wilcox J. B.
Published: February 2003

Total charge transfer cross sections have been measured for the reactions of 0.7–2.5 keV C+(2P) and C+(4P) ions with Ar, H2, N2, CO, CO2, and O2. Time-of-flight techniques have been used to measure the fast neutral C0 products from charge transfer reactions. These reactions have been examined as a function of the electron energy used to produce the reactant ions and reaction cross sections determined for ground C+(2P) and excited C+(4P) state ions. Reactant C+ beams have been produced by controlled electron impact ionization of carbon monoxide. The cross sections for charge transfer reactions involving the excited C+(4P) ions are significantly larger than the corresponding reactions of ground state ions.
Chemiluminescent matrix reactions of atomic oxygen, sulfur, and O(3P)+H2S
Authors: Smardzewski Richard R.
Published: February 2003

Optical multichannel techniques have been used to analyzed the visible chemiluminescence generated by diffusion-controlled warmup (8→20 °K) of separate, uv-photolyzed inert gas matrices containing O3, H2S, H2S+O2, and O3+H2S molecules. Oxygen atoms were observed to diffuse and recombine in solid argon at ∼17 °K to produce the intense Herzberg I band system of molecular O2 (A→X) which was also observed in krypton though not in xenon matrices. The lack of any detectable emission in xenon was attributed to premature diffusion and depletion of atomic oxygen prior to diffusion-controlled warmup. Matrix diffusion and recombination of sulfur atoms produced intense S2 emission (B→X) in all three matrices (Ar, Kr, Xe). Long, structured vibrational progressions (0,ν″) were observed in argon and krypton, while a broad, relatively structureless emission was observed in xenon. Suggested mechanisms for this latter effect include such processes as vibrationally unrelaxed fluorescence and/or S2*–Xe van der Waals ’’complex’’ formation. Diffusion of sulfur atoms in matrices containing traces of molecular O2 produced the phosphorescent emissions of SO2 (a→X) which appeared to be orders of magnitude more intense than the S2 emissions. Oxygen atoms were observed to diffuse and react with H2S molecules in dilute argon matrices at ∼14 °K, thereby generating SO2 phosphorescence (a→X) as well as two emission systems of lesser intensity (520–675 nm), each with an approximate vibrational spacing of ∼1040 cm−1. Suggested emitter(s) responsible for these latter chemiluminescent systems are presented.
Effect of surface processes on hydrogen and nitrogen permeation. I. Adsorption
Authors: Shupe Dean S.
Published: February 2003

The permeation of hydrogen and nitrogen through a metal wall is analyzed for the case where surface adsorption is rate limiting in addition to volume diffusion. By applying equilibrium thermodynamics plus a minimum of kinetic theory, an expression is derived for steady state permeation. The expression reduces to the familiar Richardson equation in the limit of negligible surface resistance. In addition, unsteady permeation with slow adsorption is examined by solving appropriate finite difference equations. The results accurately predict anomalies commonly encountered in permeation and diffusion data at low temperatures and pressures, e.g., the pn anomaly where n≳1/2, curvature or droop in Arrhenius plots, and anomalously low diffusivities. The analysis is useful not only in understanding the influence of surface effects on permeation, but also in applying permeation membranes to the study of surface phenomena.
Equation of state of fluid n-D2 from P–V–T and ultrasonic velocity measurements to 20 kbar
Authors: Mills R. L. , Liebenberg D. H. , Bronson J. C.
Published: February 2003

The molar volume V and ultrasonic velocity u of fluid n-D2 were measured simultaneously in a piston-cylinder apparatus over the range 75<T<300 K and 2<P<20 kbar. The data were fitted to an equation of state of the Benedict type which reproduced the 1404 experimental data sets of V and u within an average deviation of 0.4%. Values of the thermodynamic properties of n-D2 were calculated and compared with those from a parallel study of n-H2 in an attempt to treat isotopic effects.
Surface-induced NMR line splittings and augmented relaxation rates in water
Authors: Walmsley Roger H. , Shporer Mordechai
Published: February 2003

Nuclei in liquid water adsorbed onto substrates in layered silicates or ordered macromolecules have been shown to exhibit nuclear magnetic resonance line splittings. In aqueous protein solutions they also exhibit a dispersion in their longitudinal relaxation rate at low frequencies. Furthermore, the reduced line splittings and relaxation rates have been found to be the same for 1H, 2H, and 17O and independent of the nature of the substrate. We show that these results are consistent with a surface-induced anisotropy in the orientational probability distribution of the water molecules. Agreement between this theory and the experimental results is possible only if the values of the H–O–H angle and the coefficients for the field gradient anisotropies at the 2H and 17O nuclei are close to those found in the solid phase. The theory is consistent with a model for the water surface in which all of the molecules are statistically equivalent and rotationally mobile under a weak anisotropic constraint.
Hindered rotational energy levels of a linear ion in octahedral and tetrahedral cystalline fields
Authors: Smith David
Published: February 2003

The hindered rotational energy levels of a linear ion or molecule are computed in both octahedral and tetrahedral crystalline fields. Symmetry-adapted wavefunctions up to J=27 are used for the computation of the energy levels. The tunneling frequencies are determined from the energy levels.
The effect of magnetic field on the heat conductivity of O2–N2 and O2–H2 gas mixtures
Authors: De Udayan , Bhanja S. , Barua A. K.
Published: February 2003

The fractional change of the longitudinal coefficient of heat conductivity, (Δλ⊥/λ) due to a magnetic field applied normal to the temperature gradient in a hot-wire thermal conductivity cell has been studied for the O2–N2 and O2–H2 gas mixtures at different concentrations. A small Senftleben–Beenakker effect for N2 has been observed at the higher values of H/p (H being the magnetic field and p the pressure). Neglecting this feature the results can be interpreted fairly well by applying the extension of Köhler and Raum’s theory to the case of O2–inert-gas mixtures. From the experimental data several inelastic cross sections have been derived.
Carbon-13 chemical shielding tensors in p
a
r
a-xylene
Authors: Torman J. van Dongen , Veeman W. S.
Published: February 2003

The 13C chemical shielding tensors in a single crystal of para-xylene have been determined with high resolution double resonance NMR techniques. The eigenvectors of the tensors are found to coincide with the local symmetry of the various nuclei. A comparison is made with the tensors of similar compounds that have been reported earlier.
EPR of electron irradiated K4OsII(CN)6 in KCl single crystals
Authors: Vugman N. V. , Rossi A. M. , Danon J.
Published: February 2003

Electron irradiation of the diamagnetic OsII(CN)64− ion in a KCl host lattice at 77 °K produces three paramagnetic species. Annealing experiments reveal that these species decay into at least four other species. EPR studies indicate that each species can be assigned to a pentacoordinated OsI(CN)5 complex, with 5d7 low spin configuration arising from the trapping of an electron in a dz2 orbital, associated with a charge compensating vacancy located at different lattice sites. The EPR spectra show a strong quadrupolar interaction. The g values, the magnetic hyperfine interaction, and a minimum value for the quadrupolar interaction with the 189Os nucleus are presented and discussed. Ligand hyperfine structure with four equivalent and one nonequivalent nitrogens is measured and the ligand fs and fp spin densities are calculated and discussed. The relative contribution of 5d and 6p electrons to the electric field gradient is discussed and compared with Mössbauer spectroscopy results.
Electron drift and diffusion in polyatomic gases: Calculations for CH4, CD4, and related models
Authors: Kleban Peter , Davis H. Ted
Published: February 2003

We present the results of direct numerical calculations of electron drift velocities and diffusion coefficients in polyatomic gases as a function of applied electric field E. Model scattering cross sections appropriate to CH4 and CD4 and others of related form are used. The kinetic theory ideas presented in previous work are more extensively tested. We find good agreement with available experimental results for CH4 and CD4. The diffusion is found to be strongly anisotropic, consistent with the anisotropy of the (space-independent) velocity distribution calculated previously. The diffusion parallel to the field has a strong maximum as a function of E, in a region where apparently no experimental work has been done. Drift and diffusion results for some CH4 cross sections derived by comparison of experiment with approximate analytical treatments of the Boltzmann equation are discussed. We demonstrate that these treatments depend on parameters inadequate to specify the problem completely. The effects on drift velocity of angle dependence in the elastic scattering cross section are tested as are those of a resonance in the inelastic scattering. By comparison of our results for drift and diffusion with a proposed generalization of the Nernst–Einstein relation to large E, we show that this generalization is quantitatively invalid for gases with electron–molecule cross sections similar to those of CH4 and CD4.
Photoconduction in monolayer assemblies with functional units of sensitizing and conducting molecular components
Authors: Polymeropoulos E. E. , Möbius D. , Kuhn H.
Published: February 2003

Vectorial charge separation is studied in assemblies where a mixed monolayer of a cyanine dye with the chromophores in the layer plane and a chainlike π-electron system oriented perpendicular to the layer plane are sandwiched between fatty acid monolayers and metal electrodes. The cyanine dye is excited by light and the excited electrons move through the π-electron system which acts as the conducting element. Conduction takes place according to different mechanisms depending on the temperature. In the low temperature mode the logarithm of the photocurrent decreases linearly with (1/temperature)1/2, while in the high temperature mode it decreases linearly with (1/temperature); in both modes the photocurrent is proportional to the light intensity and its logarithm increases linearly with the bias voltage. If the conducting π-electron system is absent, the photocurrent is about an order of magnitude smaller but again proportional to the light intensity. Its logarithm increases linearly with the square root of the bias voltage. The results in the complex assembly can be interpreted by assuming that the excited electron is transfered from the cyanine dye to the π-electron system by tunneling or by thermal activation over a barrier of 0.25 eV; from there it tunnels through the next fatty acid layer to an interface state, and then hops to the positively biased electrode. This model can be checked by specifically altering the thickness of the tunneling barrier (by exchanging arachidic acid for fatty acids with shorter chain lengths). In the arrangment where the conducting element is absent the results are interpreted by assuming that the excited electron either tunnels through or is thermally activated over the potential barrier of the hydrocarbon matrix (1 eV). The different voltage dependence in the two arrangements with and without conducting π-electron system can be quantitatively explained as being due to the fact that the chromophore of the cyanine dye is perpendicular to the applied field, while the chain of the π-electron system is parallel to this field.
Elasticity of a real polymer chain for different modes of motion
Authors: Allegra G.
Published: February 2003

A theory is given to evaluate the elastic constant of the force acting on the general atom of an (–A–)N polymer chain for any normal mode of motion allowed by skeletal rotations; recourse to the classical description in terms of beads and springs should thus be rendered unnecessary. The results are obtained after evaluation of the configurational free energy stored in the chain by the action of a general set of constant forces; according to the usual assumptions, the average displacements produced by the forces are assumed not to be too large compared with the statistical fluctuations. An algorithm to calculate the general force constant on the basis of the classical configurational statistics of polymer chains is given, and numerical results are reported for high molecular weight polyethylene. All other parameters being the same, the short relaxation times in the vicinity of the limit of the classical bead–spring theory (i.e., a sinusoidal wave comprising about 20 methylene units within each wavelength) are an order of magnitude smaller than calculated according to that theory. The whole spectrum of both the force constants and of the relaxation times (neglecting at present the internal viscosity as well as the hydrodynamic interactions) down to the shortest wavelength comprising two skeletal atoms is given.
Two- and three-photon resonances in the four-photon ionization spectrum of nitric oxide at low temperature
Authors: Zakheim David , Johnson Philip
Published: February 2003

The multiphoton ionization spectrum of nitric oxide cooled by a supersonic expansion has been recorded in the region 400–490 nm. The cooling of rotational degrees of freedom has allowed analysis of the two- and three-photon resonances observed in this region, and it is found that the simple extension of one-photon intensity relationships to the three-photon spectrum is unwarranted. The relative intensities of the two- and three-photon resonances support the notion that a kinetic rate equation description provides a basic framework for the interpretation of multiphoton ionization spectra initiated by a pulsed, multimode dye laser. The role of predissociation in the observed spectra is discussed.
Dynamics of ferromagnets: Langevin approach to the mean spherical model
Authors: Ronca G.
Published: February 2003

Formal similarities between the Hamiltonian of a chain of harmonic oscillators and the effective Hamiltonian of the mean spherical model are exploited by introducing a ’’white noise’’ Langevin equation which reproduces the equilibrium properties of the 3D mean spherical model. Application to the dynamics with no magnetic field is made in three steps: (a) determination of the space–time correlation function at equilibrium; (b) spin relaxation calculations at different constant temperatures; (c) prediction of thermodynamic behavior after sudden coolings from T0?Tc to T?Tc. Dynamic transitions with a final equilibrium state below Tc have a common feature: The approach to global equilibrium requires a time proportional to νγ, where ν is the total number of lattice sites; γ=2/3 for cooling to T?Tc and spin relaxation at T=Tc, whereas γ=1 for spin relaxation at T<Tc. An actually infinite system does not recover symmetry after spin relaxation below Tc, and forms expanding ’’islands’’ of correlated spins after cooling to T?Tc.
Calculation of the vibron band and of the vibron–phonon combination bands in the ir and Raman spectra of solid α-CO
Authors: Zumofen Gert
Published: February 2003

The observed gas-to-solid shift, splitting, and intensity ratio of the vibrational band in solid α-CO and the shifts of CO isotopes suspended in solid 12C16O and in N2 matrices have been studied by calculations based on known gas-phase and matrix properties. Equations and numerical results for the crystal sums of the various intermolecular interactions are tabulated. It has been shown that the random distribution of the two possible orientations of the CO molecules modifies the dipole–dipole interaction in such a way that the ir spectrum is not affected whereas the Raman spectrum is spread over the entire vibron band. The splitting in the ir spectrum reported by Dubost is interpreted as LO–TO splitting which becomes visible because of nonnormal incidence. The vibron–phonon combination bands have been calculated using electrical anharmonicities, i.e., the bilinear dependence of the polarizability and of the dipole moment on internal and external coordinates. An ellipsoidal cavity has been assumed to compute the influence of the local field on the Raman intensity of the split vibron bands and on the intensity ratio of the vibron and the sideband in solid α-CO and α-N2.
Detection and assignment of the far infrared LMR spectrum of SeH (X 2Π3/2)
Authors: Davies P. B. , Handy B. J. , Lloyd E. K. Murray , Russell D. K.
Published: February 2003

Laser magnetic resonance spectra of SeH(X 2Π3/2) have been detected at 184 μm. Transitions in 76,77,78,80,82SeH have been identified, and assigned to Zeeman components of the J =5/2→7/2 transition.
Energy relaxation of a system of harmonic oscillators
Authors: Jolicard Georges
Published: February 2003

The evolution of the vibrational energy of gas mixture under nonequilibrium conditions is studied using the evolution operator formalism. For a mixture of different harmonic gases we obtain a result that partially corrects the defects introduced by the linearization of differential equations.
Vibrational Raman spectra and intramolecular potential function of solid solutions of dimethyl ether-d and dimethyl ether-d6
Authors: Levin Ira W. , Pearce Robert A. R. , Spiker Robert C.
Published: February 2003

Vibrational Raman spectra of dilute solid solutions of dimethyl ether-d0 and dimethyl ether-d6 were recorded at liquid nitrogen temperatures. These data were used to develop a variety of modified internal valence force fields for specifically reflecting intermethyl potential energy coupling terms. A final 18 parameter force field was generated by applying a backward elimination statistical procedure to the least-squares refinement computation for the force constants. This force field emphasizes the importance of a methyl–methyl interaction term between out-of-plane H–C–O bending displacement coordinates. Vibrational assignments for the dimethyl ether-d0, -d3, and -d6 isotopic species were determined from the potential energy distributions calculated from the 18 parameter force field. The effects of both the tilt of the methyl group and inequivalence of the Hin-plane–C–O and Hout-of-plane–C–O angles upon the normal coordinate analysis frequency fits were assessed.
Diatomic molecule vibrational potentials: Accuracy of representations
Authors: Engelke Ray
Published: February 2003

A method is presented for increasing the radius of convergence of certain representations of diatomic molecule vibrational potentials. The method relies on using knowledge of the analytic structure of such potentials to the maximum when attempting to approximate them. The known singular point (due to the centrifugal and/or Coulomb potentials) at zero internuclear separation should be included in its exact form in an approximate representation. The efficacy of this idea is tested [using Peek’s ’’exact’’ numerical Born–Oppenheimer potential for the (1sσg)2Σ+g state of H+2 as a test problem] when the representational form is the series of (1) Dunham, (2) Simons, Parr, and Finlan, (3) Thakkar, and (4) Ogilvie–Tipping, and also (5) when the form is a [2, 2] or a [3, 3] Padé approximant. Significant improvements in accuracy are obtained in some of these cases, particularly on the inner wall of the potential. A comparison of the effectiveness of the five methods is made both with and without the origin behavior being included exactly. This is useful in itself as no comprehensive accuracy comparison of the standard representations seems to have appeared in the literature. The Ogilvie–Tipping series, corrected at the origin for singular behavior, is the best representation presently available for states analogous to the (1sσg)2Σ+g state of H+2.
Lateral charge drift observed with split electrodes: Off-diagonal mobility components and lateral spread of space charge in anthracene
Authors: Walker E. Irene P. , Marchetti Alfred P. , Young Ralph H.
Published: February 2003

By adaptation of the time-of-flight experiment for photoconducting insulators, one can observe charge motion perpendicular to the applied electric field. Off-diagonal mobility components for electrons in anthracene have been measured: μac′=−0.11±0.04, μc′a=−0.2±0.1 cm2/V sec. Space-charge spreading perpendicular to the applied field has been observed.
Electron transfer in collisions of doubly charged atomic ions with rare-gas atoms for primary-ion energies below 100 eV
Authors: Maier William B. , Stewart Bruce
Published: February 2003

Cross sections are measured for several electron-transfer processes of the form An++B→A(n−1)++⋅⋅⋅, where A and B are atoms. Cross sections for most of these reactions are moderately large (∼0.5 Å2) somewhere in the energy range examined, but cross sections for He2++He, Ne2++He, Ne2++Ne, and Ar2++Ar are quite small. Examination of the potential-energy curves of the reactants and products seems qualitatively to account for many of the observations.
The role of a catalyst in the isotopically excited laser photochemistry
Authors: Lin C. T. , Atvars T. D. Z.
Published: February 2003

Laser photochemistry of Bcl3/H2 using catalysis was carried out experimentally. The 10.55 μm radiation from a high power (G W/cm2) TEA CO2 pulse laser was used to selectively excite the 11Bcl3 molecules. Using Ti catalyst the reaction products analyzed were 10B11BH2Cl4, 11B11BH2Cl4, and HCl, whereas those were 10B11Bcl4, 11B11Bcl4, and HCl when Pb metal powder was employed, i.e., 10B10BH2Cl4 and 10B10Bcl4 molecules were not generated in our experiment. Moreover, it was found that the 10Bcl3 concentration in the unreacted Bcl3 gas increased from 20% to 37% after 360 laser pulses, but the isotopic enrichment was not obtained for the reaction products. The mechanisms for the observed catalytic laser photochemistry are proposed.
Accurate a
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o potential curves for the X 2Πg, A 2Πu, a 4Σ−u, and 2Σ−u states of the 0−2 ion
Authors: Das G. , Wahl A. C. , Zemke W.T. , Stwalley W. C.
Published: February 2003

A b initio potential energy curves and spectrocopic constants of the X 2Πg, A 2Πu, a 4Σ−u and 2Σ−u of the negative ion of molecular oxygen (0−2), of major interest in the upper atmosphere, are presented in a sequence of increasing computational sophistication. The unique features of the correlation problem for homonuclear ions are analyzed in detail. The most accurate 76-configuration MCSCF ground X 2Πg state results are examined and found (as expected) to be in excellent agreement with experiment. The most accurate A 2Πu excited state results (also involving a 76-configuration MCSCF wavefunction) are expected to be of comparable accuracy, while somewhat less accuracy is expected for the best calculations of the 4Σ−u and 2Σ−u states (64 and 65 configurations used, respectively).
Dynamic effects of pair correlation functions on spin relaxation by translational diffusion in liquids. II. Finite jumps and independent T1 processes
Authors: Freed Jack H.
Published: February 2003

Hwang and Freed have previously given solutions for the relative diffusion of molecules that include the proper boundary condition (i.e., an excluded volume due to a distance of minimum approach) which has usually been neglected in spin relaxation theories. In this work their results are extended to include effects of (1) one type of spin that is rapidly relaxing, (2) diffusion by jumps of finite size, and (3) frequency-dependent diffusion coefficients in the theory of spin relaxation by intermolecular dipolar interactions. These results are mathematically simpler and sounder than those commonly employed. In particular, it is shown that for case (2) measurements of J (O), the zero-frequency spectral density cannot solely be used to determine the jump size, in constrast to the Torrey theory, which did not consider the boundary-value problem.