bluuebunny/crossref_metadata_2025 huggingface dataset:
EPR study of polarons in a conducting polymer with nondegenerate ground states: Alkali metal complexes of poly (p-phenylene) and phenylene oligomers
Authors: Kispert L. D. , Joseph J. , Miller G. G. , Baughman R. H.
Published: February 2003

EPR measurements are used to characterize electronic states relevant for carrier transport in alkali metal doped poly(p-phenylene), PPP, fully deuterated poly(p-phenylene), DPPP, and phenylene oligomers. Observed spin concentrations per carbon are at least one decade higher than the Curie spin concentration for Na-doped polyacetylene. The number of these spins, which likely corresponds to polarons (mobile radical anions), is much less than the amount of alkali metal dopant, suggesting that much of the charge on the polymer chains is in bipolarons (spinless dianions). Relevant to the interaction between spins on the polymer chain and the metal cations, the observed g values are close to the free electron value and do not substantially vary with the donor dopant, temperature, or the molecular weight of the phenylene chain. Although the spin-orbit effect on g values is small, room temperature linewidth tends to increase with increasing atomic number of dopant—suggesting some interaction, albeit a smaller magnitude effect than for alkali-metal graphite complexes. The EPR linewidths are exchange narrowed and proton hyperfine broadening is significant. The latter explains the generally broader linewidths for doped PPP than for doped DPPP. The measured susceptibilities have a temperature dependence which suggests equilibrium between separated polaron defects and singlet and triplet spin states formed intermolecularly via polaron pairing. The interaction is antiferromagnetic and the binding energy between polarons is about 2.2 to 3.3 meV. An upper limit estimate of the Fermi-surface density of states for K-doped PPP (0.7 states/eV phenyl) is derived from an upper limit estimate of Pauli susceptibility.
R-matrix theory for molecule–surface scattering: Rotationally inelastic scattering of HD from smooth metal surfaces
Authors: Whaley K. B. , Light J. C.
Published: February 2003

Wigner R-matrix theory is used to treat the rotationally inelastic scattering of HD from smooth metal surfaces. Calculations performed within the assumption of a flat surface show the advantages of this technique relative to propagative R-matrix techniques in the physical interpretation of rotationally mediated selective adsorption resonances. An optical potential is used to describe dissipative scattering at finite surface temperatures and comparison is made to the experimental results of Cowin et al. for HD/Pt(111).
Chemisorbed pyridine on Ni(001): A high resolution electron energy loss study of vibrational and electronic excitations
Authors: DiNardo N. J. , Avouris Ph. , Demuth J. E.
Published: February 2003

High resolution angle-resolved electron energy loss spectroscopy has been applied to the study of the vibrational and electronic losses of pyridine chemisorbed on Ni(001). The evaluation of the contributions of in-plane vs out-of-plane vibrational modes of the chemisorbed molecule in the dipole scattering regime shows that orientational phase transitions occur as a function of coverage and temperature. In particular, the molecular plane is parallel to the surface at low coverages at ∼170 K corresponding to a π-bonded species; at higher coverages the molecular plane tilts vertically with respect to the surface which is indicative of a bonding interaction through the N lone pair. Heating to room temperature or room temperature exposures produce an approximately vertically oriented species with some rotation about the N end. This species might be assigned to a chemisorbed α-pyridyl species. The different types of bonding at the surface are manifested in the characteristics of the electronic loss spectra taken with electron primary energies less than 20 eV. A Ni surface state excitation at ∼0.7 eV observed in the clean spectra is quenched when bonding is through the N-lone pair; this can be related to the localization of the surface electronic state. Intramolecular π→π* excitations are not observed when the molecule is π bonded; this is due to a combination of the broadening of the π levels by interaction with the substrate and the screening of the (parallel) dynamic dipole by the metal surface in the dipole contribution to the loss cross section. Off-specular collection geometries show a broad angular distribution for the inelastically scattered electrons as expected for dipole scattering when the loss energy is a significant fraction of the impact energy. A strong charge transfer excitation centered at ∼3 eV is observed for the n-bonded configurations, and this suggests a Ni d→pyridine 3B1 transition which would be maximized in these cases when the overlap between the respective wave functions is greatest. Electronic loss spectra following the thermal evolution of pyridine initially exposed at room temperature show that the molecular species persists up to ∼220 °C, whereupon characteristic electronic losses for C are observed indicating thermal decomposition.
Picosecond pump–probe and polarization techniques in supersonic molecular beams: Measurement of ultrafast vibrational-rotational dephasing and coherence
Authors: Scherer N. F. , Shepanski J. F. , Zewail A. H.
Published: February 2003

Observation of picosecond transients in supersonic molecular beams of stilbene and aniline is reported. Pump probe and polarization techniques are employed. The pump laser pulse exciting an optically active mode and a delayed pulse probing this population as a function of the delay time. Data on stilbene and aniline at vibrational and rotational temperatures of <10 and <5 K are reported.(AIP)
Measurements of dissociative recombination coefficients of H+3, HCO+, N2H+, and CH+5 at 95 and 300 K using the FALP apparatus
Authors: Adams N. G. , Smith D. , Alge Erich
Published: February 2003

Meaurements are presented of the dissociative recombination coefficients αt for reactions of electrons with H+3 , D+3 , HCO+, DCO+, N2H+, N2D+, and CH+5 ions at 95 and 300 K. The measurements were made under truly thermalized conditions using a flowing afterglow (FALP) apparatus. Contrary to previous stationary afterglow (SA) studies, αt(H+3) was found to be immeasurably small [≲2 (−8) cm3 s−1] at both temperatures which is consistent with recent theoretical predictions. However some evidence was obtained indicating that vibrationally excited H+3 recombined efficiently, which is also in accordance with the recent theory. At 300 K, αt(HCO+)=1.1 (−7) cm3 s−1 and αt(N2H+)=1.7 (−7) cm3 s−1 and both were larger by a factor of three at 95 K. αt(CH+5) =1.1 (−6) cm3 s−1 at 300 K and 1.5 (−6) cm3 s−1 at 95 K. The αt(HCO+) data are compared with previous SA data and the αt(N2H+) and αt(CH+5) data are discussed in relation to the recombination coefficients αe(N2H+) and αe(CH+5) derived from merged beam (MB) cross section data. Stressed throughout the paper is the need to appreciate the chemical and physical processes which can occur in the afterglow and which may distort αt determinations. Tentative explanations are given for the differing values of αt and αe obtained from FALP, SA, and MB experiments.
Jahn–Teller effect in tetrahedral d1 metal complexes
Authors: Agresti A. , Ammeter J. H. , Bacci M.
Published: February 2003

The role of second-order Jahn–Teller effects in influencing absorption and EPR spectra of d1 metal ions in tetrahedral symmetry was analyzed. It is shown that the pseudo-Jahn–Teller effect, which mixes the ground and the first excited state, is effective in some tetrahedral d1 systems, thus providing a plausible explanation for their optical and EPR data.
A
b i
n
i
t
i
o calculation of reaction energies. III. Basis set dependence of relative energies on the FH2 and H2CO potential energy surfaces
Authors: Frisch Michael J. , Binkley J. Stephen , Schaefer Henry F.
Published: February 2003

The relative energies of the stationary points on the FH2 and H2CO nuclear potential energy surfaces relevant to the hydrogen atom abstraction, H2 elimination and 1,2-hydrogen shift reactions have been examined using fourth-order Mo/ller–Plesset perturbation theory and a variety of basis sets. The theoretical absolute zero activation energy for the F+H2→FH+H reaction is in better agreement with experiment than previous theoretical studies, and part of the disagreement between earlier theoretical calculations and experiment is found to result from the use of assumed rather than calculated zero-point vibrational energies. The fourth-order reaction energy for the elimination of hydrogen from formaldehyde is within 2 kcal mol−1 of the experimental value using the largest basis set considered. The qualitative features of the H2CO surface are unchanged by expansion of the basis set beyond the polarized triple-zeta level, but diffuse functions and several sets of polarization functions are found to be necessary for quantitative accuracy in predicted reaction and activation energies. Basis sets and levels of perturbation theory which represent good compromises between computational efficiency and accuracy are recommended.
The role of nonadditive effects in the second hydration shell of Mg2+ and Ca2+. A molecular orbital study of the three-body potential energy surface
Authors: Ortega-Blake I. , Hernández J. , Novaro O.
Published: February 2003

Here we continue [J. Chem. Phys. 76, 5404 (1982)] a quantum mechanical study of the fundamental causes for the different coordination properties of the Mg2+ and Ca2+ ions. We look into the effects of nonadditivity in the second hydration shell, mainly in relation to structure. We also compare our predictions with recent experimental evidence.
Atomic and ionic energy expressions obtained by scaling both the nuclear and electronic charges
Authors: Reif I. , Medina R. , Salazar M. , García-Sucre M.
Published: February 2003

The differential Hellmann–Feynman and virial theorems were used in the scaling of both electronic and nuclear charges of atomic systems. We have obtained expressions for the energy, the inverse electron-nucleus distance, and the inverse electron–electron distance as series expansions in powers of 1/Z. The expansion coefficients depend on the number of electrons and the particular state considered. We show that the first two terms of the energy expansion can be exactly calculated in terms of hydrogen wave functions. Using a three-term-energy expression and fitting the third coefficient we obtain an agreement better than 0.5% with the experimental results of all 190 atomic structures with 2≤Z≤20 and 2≤n≤Z. Based on these calculations we propose a semiempirical energy expression which agrees within 2% with the same experimental results and with the formula of Politzer and Parr for atoms.
Proton spin longitudinal relaxation time in gaseous ammonia and hydrogen chloride
Authors: Lemaire Claude , Armstrong Robin L.
Published: February 2003

New data are presented for the proton spin relaxation time in gaseous ammonia (NH3) at 300 K. The characteristic nonlinear density dependence of the relaxation time at low densities is established. Old data for gaseous hydrogen chloride (HCl) are reanalyzed. The commonly used single relaxation time aproximation for the rotational levels is shown to be inadequate to fit either the NH3 or the HCl data. Excellent fits of both sets of data are obtained using a two parameter, multilevel relaxation time approximation; the parameters deduced are the average rotational level linewidth and the dispersion. An effective intramolecular spin-rotation coupling constant is determined from the NH3 data and it is shown to be consistent with the spin-rotation coupling constants deduced from microwave absorption experiments. Also an angular momentum reorientation cross section is computed from the NMR data and compared to other similar cross sections obtained from microwave, ultrasonic and viscomagnetic experiments. The reorientation process probed by the NMR experiment is shown to be dominated by elastic collisions.
Laser induced bound–bound and bound–continuum emission of the Sr2 A 1Σ+u–X 1Σ+g system
Authors: Gerber G. , Möller R. , Schneider H.
Published: February 2003

Laser-induced emission of the Sr2 molecule consisting of discrete molecular fluorescence series, regularly modulated continuous fluorescence and an unstructured continuum was observed in the gas phase at excitation wavelengths between 600 and 450 nm. The analysis of the molecular line spectra provides Dunham coefficients and RKR potentials for the X 1Σ+g ground state and the excited A 1Σ+u state. The main spectroscopic constants are ωe=40.32 cm−1, Re=4.45 Å and De=1060 cm−1 for the X state and ωe=85.07 cm−1, Re=3.95 Å and De=5400 cm−1 for the A state. The modulated continuum which is due to bound-continuum transitions from a specific exited level v′, j′ to the continuum of the ground state was used to determine the repulsive part of the ground state potential up to 3000 cm−1 above the dissociation limit. Calculated discrete and continuous Franck–Condon factors are in good agreement with the experiment, both depend sensitively on the rotational quantum number J. The unstructured continuum can be interpreted as a quasicontinuous superposition of many fluorescence spectra. Calculations show that laser excitations from levels v″, J″ slightly below the dissociation limit and excitation from continuous states lead to the observed continuum.
The infrared spectra and phase transitions of pure and isotopically impure 2ND3⋅H2O, 2NH3⋅D2O, 2NH3⋅H2O, and 2ND3⋅D2O between 100 and 15 K
Authors: Bertie John E. , Devlin J. Paul
Published: February 2003

Infrared transmission spectra of 2NH3 ⋅ H2O, 2NH3 ⋅ D2O, 2ND3 ⋅ H2O, and 2ND3 ⋅ D2O have been measured between 100 and 15 K. Spectra of NH3, ND3, NH2D, ND2H, H2O, D2O, and HOD as dilute or major impurities in the above crystals have also been measured. Information about the site splitting, multiple-site splitting, and unit-cell-group splitting, has been obtained for many modes. The absorption by the N–D stretching modes of type II ammonia shows that the unit cell group changes from D2h to Ci at the transitions near 52 K. The corresponding absorption by the type I ammonia retains D2h selection rules at 15 K. The distortion to Ci is greater perpendicular to the ac plane of the D2h structure than parallel to it. The two types of ammonia and one type of water molecule under D2h each splits into two types under Ci, yielding six sets of nonequivalent molecules below 52 K. The existence of two nonequivalent sets of type II ammonia molecules below 52 K, each of which is free to reorient above the transitions, is clearly the source of the two lambda transitions at 51.6 and 53.3 K. The shifts with temperature and isotopic substitution indicate varied anharmonic effects on the intramolecular stretching modes. Thus, the higher frequency stretching bands of H2O and D2O shift by 15 and 20 cm−1, respectively, between 90 and 15 K, while the lower frequency bands, at 2975 and 2230 cm−1, barely shift and that of 2ND3 ⋅ D2O sharpens to a doublet split by 10 cm−1 with an overall half-width of 25 cm−1. The bending modes of H2O and D2O have been identified at 1634 and 1200 cm−1. Fermi resonance with 2ν2 affects only the lower frequency O–D stretching mode of the C1 D2O molecules; the Fermi resonance parameter W is 68± 3 cm−1, close to that in D2O ice 1h. The N–D stretching mode of dilute NH2D shows a remarkable rearrangement of intensity between 35 and 15 K, which suggests that the energy of the crystal is of the order of 270 J mol−1 lower when the N–D bond has a particular orientation. The bands due to ν4 of ammonia have been identified for the first time. It was noted earlier that the frequency difference between the ν2 modes of the two types of NH3 and ND3 molecules was much larger than expected from the frequencies of isolated NH2D and ND2H. This work shows this extra splitting to be due to intermolecular coupling between the two types of ammonia molecules. Other interesting indications of intermolecular interactions, including examples of combination bands due to simultaneous transitions of ammonia and water, are evident throughout the spectra.
Measurements of the electric dipole polarizabilities of the alkali halide dimers
Authors: Kremens R. , Bederson B. , Jaduszliwer B. , Stockdale J. , Tino A.
Published: February 2003

We report the first measurements of the average electric dipole polarizabilities of five alkali halide dimers. A combined monomer-dimer molecular beam deflection pattern in an inhomogeneous electric field is subject to an appropriate computational analysis to extract the polarizabilities. A simple combination of bond and effective ionic models to estimate the polarizabilities gives reasonably good agreement with the measured values. The values are, in units of 10−24 cm2, (KF)2:25.3±3.2; (KCl)2:28.6±3.0; (RbCl)2:43.4±4.2; (CsCl)2:36.6±5.0; (CsF)2:21.2±2.6.
Quantum dynamics of the three-dimensional F+H2 reaction. II. Scattering wave function density and flux analysis
Authors: McNutt Joe F. , Wyatt Robert E. , Redmon Michael J.
Published: February 2003

Further analysis of the quantum dynamics of the three-dimensional F+H2→FH+H reaction for total angular momentum J=0 focuses on the properties of the total scattering wave function. After assembling the scattering wave function (as outlined in the previous paper), we study throughout the interaction region the wave function probability density and flux. In order to present 3D figures, two different 2D projections of the wave function are utilized—constant s planes and constant m planes. Salient topological features are noted and compared at system energies below, on, and above the 0.36 eV resonance. Quantum whirlpools (which are quite sensitive to the total energy) are located in the reactant and product valleys.
VV-VT intermode coupling in vibrational energy transfer
Authors: Shin H. K.
Published: February 2003

The coupling of VV and VT energy transfer modes in molecular collisions is studied with an exponential-operator solution of the Schrödinger equation of motion. The effects of VT mode on a nominally VV process and VV mode on a nominally VT process have been calculated for the specified initial state of ‖60〉. The evolution of all VV channels from ‖60〉 and the transformation of these channels to the final VV-VT state are discussed in detail. At collision energies of several times vibrational quantum, the VV-VT intermode coupling is so strong that energy transfer processes cannot be represented by the VV or VT mechanism alone.
Coupled fluctuations in temperature and heat flux from a nonequilibrium state
Authors: Nettleton R. E.
Published: February 2003

By a projection operator technique, originally proposed by Zwanzig, one can calculate from the solution of the Liouville equation a distribution function g for local fluctuations in the kinetic energy and heat flux. The system is a small subvolume immersed in an infinite fluid, and the fluctuations are from nonequilibrium states characterised by mass density, temperature, and heat flow. A Fokker–Planck equation is derived for g which is consistent with the hydrodynamic and Cattaneo–Vernotte equations. This is solved by an expansion in orthogonal polynomials in the fluctuations, and the solution is used to determine cross correlations in the energy and heat flux. These correlations are not given by the Einstein approximation to g and differ between steady and nonsteady nonequilibrium states.
Wetting phenomena with long-range forces
Authors: Privman V.
Published: February 2003

We study the effect of long-range, power-law forces on a critical continuous wetting transition within classical mean-field theory. Repulsive forces destroy the transition; attractive, long-range forces drive the transition first order and we locate the resulting prewetting line and associated prewetting critical point.
Transient electron mobility in pulse-irradiated gaseous argon under a steady field
Authors: Tembe B. L. , Mozumder A.
Published: February 2003

Change in the dc electron mobility with time due to energy moderation has been calculated in gaseous argon using the displaced pseudo-Maxwellian (DPM) approximation. This method for the evolution of electron thermalization in the presence of an external electric field is convergent for small fields and adequate up to the second order in drift velocity. For Ramsauer gases it predicts a short time maximum in the transient mobility curve which has been observed by Sowada and Warman in gaseous argon. The calculation is in good qualitative and semiquantitative agreement with experiment. After discussing the possible factors accounting for the remaining difference, the plausible one appears to be the inherent error in the assumed velocity distribution.
N2 W 3Δu–A 3Σ+u emission in the near-infrared luminescence spectrum of N2-doped solid argon and krypton
Authors: Zumofen G. , Sedlacek J. , Taubenberger R. , Pan S. L. , Oehler O. , Dressler K.
Published: February 2003

The near-infrared emission spectrum of N2 diluted in rare-gas matrices exhibits a variety of new emission lines featuring different linewidths and decay times. One vibrational v″ progression of lines characterized by widths of 25 cm−1 and by decay times of 70 μs in Ar and of 60 μs in Kr is assigned to the forbidden electronic transition W 3Δu (v′)–A 3∑+u (v″=0–4). Selectively unrelaxed initial states v′=4 in 14N2 and v′=3 in 15N2 are observed, and the resistance of these particular levels against radiationless relaxation is attributed to bottlenecks in the cascade of internal conversion processes among the vibrational levels of the A, B, B′, and W electronic states. The assignments are based on isotope shift measurements and on quantitative estimates of allowed and induced vibrational and electronic radiative transition probabilities. The relative efficiency of multiphonon relaxation in different rare-gas matrices is discussed in the light of these and of other comparable measurements.
Jet spectroscopy of anthracene and deuterated anthracenes
Authors: Lambert W. R. , Felker P. M. , Syage J. A. , Zewail A. H.
Published: February 2003

Fluorescence excitation and SVL fluorescence spectra of jet-cooled h10-, 9d1-, 9,10d2-, and d10- anthracene are reported. Ground state vibrational assignments are presented for all these species and are compared with literature values. In addition, assignments for the first excited singlet state of h10- anthracene are made using SVL spectra and rotational band contours as guides. The work presented herein serves as an essential reference for other work from this research group concerning the dynamics of excited anthracene (see accompanying papers), and completes the spectroscopy of the polyacene series.
Dynamics of t
r
a
n
s–c
i
s photoisomerization of large molecules in supersonic jets
Authors: Majors Truett J. , Even Uzi , Jortner Joshua
Published: February 2003

In this paper we report on the time-resolved fluorescence decay lifetimes from photoselected vibrational states in the S1 manifold of trans-stilbene, 4-Cl trans-stilbene and 4-methyl trans-stilbene cooled in supersonic jets and excited by a mode-locked dye laser. Decay lifetimes as short as 100±30 ps were recorded, using a fast single photon counting system. The energy dependence of the nonradiative decay rates, knr, of trans-stilbene is invariant with respect to the para-substitution of Cl, whereupon the intersystem crossing to the triplet in 4-Cl trans-stilbene dose not provide the main route for photoisomerization and constitutes a distinct, energy dependent, decay channel. The invariance of knr with respect to para-methyl substitution indicates that intrastate vibrational energy redistribution (IVR) does not involve all accessible molecular modes. The experimental data are consistent with a nonadiabatic trans–cis isomerization in the isolated molecule, which involves S1–S2 internal conversion in conjunction with IVR.
Molecular dynamics study of collision induced absorption in rare gas liquid mixtures
Authors: Birnbaum George , Mountain Raymond D.
Published: February 2003

Molecular dynamics simulation of a rare gas liquid mixture has been used to investigate the connections of the collision induced absorption spectrum and the forces acting between liquid particles. We find that the force law and induced dipole moments determined for low density gases are incapable of producing collision induced absorption spectra which are in qualitative agreement with the experimentally observed low frequency part of the spectra for Ar–Ne mixtures. Qualitative agreement is obtained if the gas phase dipole is modified so that the zero of the dipole moment roughly matches the zero of the force between unlike species. This represents a substantial change in the gas phase dipole. The implications of these results are briefly discussed.
Product branching ratios in the reaction of Xe*(3P2,0) with IBr. Role of excited potential surface
Authors: de Vries Mattanjah S. , Tyndall George W. , Martin Richard M.
Published: February 2003

The reaction of Xe*(3P2,0) with IBr to form the XeI* and XeBr* excimers was studied using two crossed molecular beam techniques. Emission spectra were obtained between 200 and 400 nm, and relative cross sections and branching ratios were measured as a function of collision energy over the range 15–420 meV. The observed effects are discussed in terms of a curve crossing model, involving the neutral potential surface and both ground and excited Xe++IBr− potential surfaces. In this model, XeBr* is formed from the ground state ionic potential and XeI* is formed from the excited potential.
Spin-orbit effects in chemical reactions: The reaction of spin-orbit state-selected Ca(3P
J) with Cl2, Br2, and CH3Cl
Authors: Yuh Huoy-Jen , Dagdigian Paul J.
Published: February 2003

An optical pumping state selection technique is employed to investigate the effect of atomic spin-orbit state on chemical reactivity for the Ca(3P0) level, for which the spin-orbit splitting is small. The spin-orbit dependence of the chemiluminescence and chemi-ionization cross sections has been determined for the reactions of Ca(3P0) with Cl2, Br2, and CH3Cl. For the CaCl A–X and B–X chemiluminescence channels of the Cl2 and Br2 reactions, the spin-orbit dependence is substantial, and the order of reactivity is J=2>J=1>J=0. The differences in reactivity of the spin-orbit states for these channels in the CH3Cl reaction are much smaller, as is true also for the chemi-ionization channels of all three reactions. No significant differences in reactivity were found for the C–X chemiluminescence channel in the Cl2 and Br2 reactions. The nonreactive intramultiplet mixing cross sections were estimated by modeling the dependence of the Ca(3P0→1S) emission intensity vs scattering pressure. These experimental results are interpreted in terms of the expected dynamics of these reactions. The spin-orbit selectivity is related to how the asymptotic spin-orbit states evolve into the different electrostatic covalent surfaces at smaller separations.
Semiempirical valence bond model of hyperfine interactions and bonding in RbO and CsO
Authors: Adrian Frank J. , Jette A. Norman
Published: February 2003

The alkali hyperfine structure (hfs) splittings in the 2Σ radicals RbO and CsO are analyzed using a semiempirical valence bond (VB) wave function similar to that used previously for the noble gas monohalides. For the alkali monoxides this wave function is ψ=N(2Σ)[χ𝒜Φ(M+ ⋅ ⋅ ⋅ O−) +(1−χ2)1/2𝒜Φ(M++ ⋅ ⋅ ⋅ O=)], where M and O denote the alkali and oxygen, respectively, and 𝒜 is the antisymmetrization operator. This antisymmetrization and the effects of interatomic electron correlation in the Φ(M++ ⋅ ⋅ ⋅ O=) VB structure are the principal contributors to the hfs. At the bond distances RRbO=4.30 and RCsO=4.67a0 the parameters χ=0.9996 and 0.9967 for RbO and CsO, respectively, give good agreement between theory and experiment for both the isotropic and anisotropic hfs. The admixture of the doubly ionized Φ(M++ ⋅ ⋅ ⋅ O=) VB structure, which produces covalent bonding involving the alkali cation core orbitals and the oxygen anion valence orbitals, is small as expected from the high energy of this structure.
Semiempirical model of the exchange polarization mechanism of transferred hyperfine interactions in ionic radicals
Authors: Adrian Frank J. , Jette A. Norman
Published: February 2003

This paper presents a semiempirical method for calculating metal hyperfine interaction constants in ionic radicals whose zero-order wave function places the unpaired electron completely on the anion with zero overlap between it and the relevant cation orbitals. The mechanistic basis of the calculation is spin polarization of closed-shell anion orbitals by their exchange interaction with the unpaired electron, followed by partial transfer of the resulting unpaired electron density in these anion orbitals to the cation orbitals via overlap. The exchange polarization is described by a perturbation theory expansion in anion excited states, which expansion is summed by introducing semiempirical average excitation energies. The contribution of direct exchange polarization of the cation orbitals to the cation hyperfine interactions is found to be negligible, due primarily to the very large excitation energies of the cation core orbitals. Calculated results are compared with experiment for the ionic radicals Na(C=CH2) and NaO2.
A variational approach to static correlations in dilute colloidal suspensions
Authors: Ronis David
Published: February 2003

The Gibbs–Bogoliubov inequality is used to determine the best hard core diameters to represent a suspension containing highly charged colloidal particles in which the counter ions are considered explicitly. The hard core reference system is analyzed in terms of the Percus–Yevick approximation for mixtures with additive diameters. In addition, an analytic solution to the Percus–Yevick equations for the nonadditive case, in which one of the species has zero radius is given, and effective colloid diameters are computed. The results of this procedure are discussed in light of light scattering experiments.
Theory of non-Newtonian viscosity and normal stress coefficients of fluids
Authors: Eu Byung Chan , Ohr Young Gie
Published: February 2003

The evolution equation for the traceless symmetric part P̂ of the stress tensor derived previously for dense simple fluids is further investigated of its applicability to non-Newtonian fluid behaviors and normal stress effects. Nonlinear differential equations for three independent components of the stress tensor are obtained in the case of a unidirectional flow in an incompressible fluid. The asymptotic stability of the steady state (equilibrium) is studied with linearized equations and the stability conditions are derived. Approximate steady state solutions are calculated from the evolution equations for the three components and viscometric functions are obtained therefrom. By taking the evolution equations as a set of phenomenological evolution equations, we show that it is possible to apply them even to nonsimple fluids such as polymer solutions, by analyzing experimental data on the shear rate dependencies of the viscometric functions of some polymer solutions. We also show that the approximate viscometric functions used for analysis can be reduced to a set of corresponding-state viscometric functions to a good accuracy. Relations of the evolution equations for P̂ to some of the existing rheological equations of state are discussed. It is shown that suitable linearizations of the present nonlinear evolution equation for P̂ yield the same forms as those for the existing rheological equations of state.
Hartree–Fock study of polysulphur-nitride. I. The isolated infinite chain
Authors: Dovesi R. , Pisani C. , Roetti C. , Saunders V. R.
Published: February 2003

The electronic structure of the infinite chain of polysulphur-nitride (SN)x has been investigated at an ab initio Hartree–Fock level, using two basis sets previously employed to study molecular precursors and molecular subchains. The use of d orbitals turns out to be essential for stabilizing the polymer and reducing its ionicity. Nonmetallic broken-symmetry solutions are considered also, the stabilization energy in this case is quite small (0.2 eV/cell).
Observation of glass-like behavior in conjugated polymer molecules
Authors: Ha Jung-Mi Y. , Stratt Richard M. , Risen William M.
Published: February 2003

Soluble substituted polydiacetylenes (a class of conjugated polymers) undergo a variety of phase transitions signaled by color changes. The particular example we studied, poly-3BCMU in chloroform/hexane solutions, exhibits a low temperature blue phase and a high temperature yellow phase. The visible and resonance Raman spectra of both the blue and yellow forms dispaly coexisting conjugation length regimes of 6, 10, and >20 monomers. However, we find that the relative proportions of these regimes indicates that that are three, rather than two, different phases: an equilibrium blue phase, an equilibrium yellow phase, and a metastable blue phase containing short conjugation lengths quenched in. It is this last phase which we characterize as glass-like.
The rotational spectrum, internal rotation, and structure of NH3–CO2
Authors: Fraser G. T. , Leopold K. R. , Klemperer W.
Published: February 2003

The radio frequency and microwave spectra of NH3–CO2 have been measured using the molecular beam electric resonance technique. The spectrum is characteristic of an asymmetric top in which the NH3 subunit exhibits effectively free internal rotation. The spectroscopic constants obtained for the ground internal rotor state are presented below: (B+C/2) (MHz)  3756.178(3),  (B−C/2) (MHz)  597.4(2), A−(B+C/2) (MHz)  8035.(8),  ΔJ (MHz)  0.0240(4), δK (MHz)  0.20(2),  ΔJK  (MHz)  0.23(5), δJ (MHz)  0.007(1),  eQqaa (MHz)  −3.175(4), eQqbb (MHz)  1.557(9),  eQqcc (MHz)  1.617(11),  μ(D)  1.7684(14). The N–CO2 framework of the complex has C2v symmetry with a N–C weak bond length of 2.9875(4) Å. The average bending angle of the NH3 subunit is 22.71(5)° with a difference in amplitude of 1.0(4)° between the in plane and out of plane excursions. The weak bond stretching force constant is 0.070(1) mdyn/Å and the induced dipole moment is 0.411(2) D. (B+C)/2 for the first excited internal rotor state (‖m‖=1) is 3753.008(4) MHz and the quadrupole coupling constant eQq‖m‖=1aa=−3.176(9) MHz is identical with that measured for the ground internal rotor state.
Electronic spectra of van der Waals molecules HgNe, HgAr, and HgKr in a supersonic jet
Authors: Fuke Kiyokazu , Saito Takayuki , Kaya Koji
Published: February 2003

The van der Waals molecules HgNe, HgAr, and HgKr were prepared in a supersonic jet. The fluorescence excitation spectra of A 30+–X 10+ and B 31–X 10+ optical transitions for these molecules which arise from the Hg 3P1–1S0 atomic transition were analyzed and the spectroscopic constants were determined from these analyses. The potential curves were constructed by assuming a Morse function. These results were compared with the results of Rydberg–Klein–Rees calculations of the well width vs well depth.
Multiple scattering effects in EXAFS: Comparison between theory and experiment for Pt metal
Authors: Biebesheimer V. A. , Marques E. C. , Sandstrom D. R. , Lytle F. W. , Greegor R. B.
Published: February 2003

Extended x-ray absorption fine structure (EXAFS) model functions have been calculated for the LIII edge in Pt metal. All single, double, and triple scattering contributions were taken into account, using a recently developed multiple scattering formalism. Theoretical values for the scattering amplitude, phase, and Debye–Waller factor and the ‘‘universal curve’’ for the electron mean free path have been used. Comparison to experimental data gives an estimate of the limitations in the current formalism, and shows that multiple scattering effects are important in Pt only at radial distances corresponding to fourth shell nearest neighbors.
Rotationally inelastic transitions between the fine-structure levels of the 3Σ−g electronic ground state of O2
Authors: Corey Gregory C.
Published: February 2003

Infinite-order sudden calculations, including the effects due to the coupling of the rotational and the electronic spin angular momenta, are reported for the inelastic differential and integral cross sections of O2 in its 3Σ−g electronic ground state, scattering against He and Ar. These calculations demonstrate that measurements of differential cross sections that fully resolve the dependence on the O2 fine-structure levels can in fact provide detailed information about the anisotropy of the van der Waals interaction potential much more readily than measurements of the total or unresolved j state inelastic differential cross sections. Several propensity rules for transfer of rotational energy in 3Σ electronic states, which were derived recently by Alexander and Dagdigian [J. Chem. Phys. 79, 302 (1983)] in the large-j limit, are found to be valid for O2 for all values of j.
Rotational energy transfer in H+H2(v) inelastic collisions
Authors: Mayne Howard R.
Published: February 2003

Quasiclassical trajectory calculations have been carried out at translational energies between 0.2 and 0.8 eV on H+H2(v), v=1, 2, 3, using the accurate SLTH potential surface. Integral and differential cross sections are given for the lowest rotationally inelastic collision Δj=2. The mean polarization angle as a function of impact parameter for this same transition is also studied. It is found that the integral cross section reflects the shape of the repulsive part of the potential. The differential cross sections display rotational rainbows. In most cases these are of the ‘‘repulsive’’ type. However, for the v=3 at high T, the rainbows are of the ‘‘attractive’’ type. The polarization data is found not to be a good probe of the attractive well.
EPR studies of some f n and d n electronic impurities in KTaO3 single crystals
Authors: Abraham M. M. , Boatner L. A. , Olson D. N. , Höchli U. T.
Published: February 2003

Single crystals of the cubic perovskite host, potassium tantalate (KTaO3), doped with iron group, lanthanide, and actinide impurities have been investigated using the technique of electron paramagnetic resonance (EPR). The EPR spectra of Yb3+ and U5+ have been observed for the first time in potassium tantalate by employing crystals co-doped with both impurities. Multiple doping of the material during the crystal growth process avoided the production of semiconducting KTaO3 and resulted in the incorporation of adequate concentrations of the trivalent lanthanide ion Yb3+. The EPR results indicate that Yb3+ occupies a site in which the local symmetry is axial as a result of nearby charge compensation. Pentavalent uranium is found to occupy a substitutional cubic symmetry site. EPR investigations of Cu2+, Co2+, Mn2+, Ni3+, and Fe3+ were also carried out.
Variation of nuclear magnetic shielding with intermolecular interactions and rovibrational motion. IX. 19F in F2C=CH2 and F2C=CF2
Authors: Jameson Cynthia J. , Jameson A. Keith , Oppusunggu D.
Published: February 2003

The effects of intermolecular interactions on 19F nuclear magnetic shielding in CF2=CF2 and CH2=CF2 have been measured in the pure gas at modest densities (7–35 amagat). For CH2=CF2 other measurements by Wisman in 50–150 amagat gas samples agree with our results, and the slopes of the shielding vs density plots are identical within experimental error. The entire set of data for the gas phase and including 170–380 amagat in the liquid phase show a nonlinear behavior, deshielding with increasing density by -0.0152 ppm amagat−1 for the low density gas and somewhat less deshielding for the liquid. The temperature dependence in the limit of zero pressure is also reported here: σ0(T)−σ0(300)=-4.066×10−3(T-300)-1.69×10−5(T-300)2 ppm for F in CH2=CF2 (which is very similar to that previously reported for O=CF2) and −8.127×10−3(T−300)–2.09×10−5(T−3002)ppm in CF2=CF2.
Cu and Ag as one-valence-electron atoms: CI results and quadrupole corrections for Cu2, Ag2, CuH, and AgH
Authors: Stoll H. , Fuentealba P. , Schwerdtfeger P. , Flad J. , Szentpály L. v. , Preuss H.
Published: February 2003

Our recent pseudopotential results for Cu2, Ag2, CuH, and AgH [J. Chem. Phys. 79, 5532 (1983)] are refined in two ways: (i) the density-functional approximation for valence correlation is replaced by a CI treatment, and (ii) the dipole polarization potential describing core-valence correlation is supplemented by a quadrupole correction term.
The use of an independent boson model to study the dynamic effects of electron excitations by a particle colliding with a metal surface
Authors: Leung K. M. , Schön G. , Rudolph P. , Metiu Horia
Published: February 2003

We derive, an algorithm which permits the calculation of our independent boson Hamiltonian for a jellium with a surface, which gives, when solved exactly, the same results as the random phase approximation. Applications to films and spheres are discussed in detail. The independent boson scheme is applied to the computation of the influence of the electron-hole pair excitations on the trajectory of a charged particle scattered by the metal surface. We show that the classical equation of motion of the particle, coupled to the quantized boson fields, is stochastic and must contain a peculiar force which depends on the final state of the quantum fields and on the past and the future of the trajectory. If the bosons are held at constant temperature, the motion of the particle is given by a quantum Langevin equation, which is derived here. The equation of motion derived here can be applied to both phonon-or electron-hole pair excitations.
Vibrational spectroscopic study on partly hydrogenated t
r
a
n
s-polyacetylenes
Authors: Furukawa Yukio , Arakawa Tsutomu , Takeuchi Hideo , Harada Issei , Shirakawa Hideki
Published: February 2003

Raman and infrared spectra have been studied on variously hydrogenated trans-polyacetylenes which are prepared by exposing Na-doped trans-polyacetylene films to ethanol. Raman spectra have been analyzed by reference to the relations between the number of trans-conjugated double bonds (NC=C) and the ν1 and ν3 frequencies. NC=C’s of increased short segments are correlated with the distribution of dopants. Information on (CH2)k groups and very short (CH=CH)n groups including isolated (CH=CH) is obtained from infrared spectra and hydrogenation processes are proposed. Upon iodine doping the hydrogenated films exhibit three infrared bands which are similar to the well-known three-band pattern of doped polyacetylene, while they give poor electrical conductivities at the maximum iodine doping. Hence, the three bands of doped polyacetylene do not straightforwardly correlate with the overall conductivity. The infrared results strongly indicate that a relatively short conjugated segment with methylene groups at both terminals can be doped as well as a long polyene and the structure including the force field of the doped part in the segment is similar to that in the long polyene. Importance of intermolecular packing of the doped parts in realizing a high electrical conductivity is pointed out.
Cross sections and angular distributions for individual fragment fine structure levels produced in one- and two-photon photodissociation of NaH
Authors: Singer Sherwin J. , Freed Karl F. , Band Yehuda B.
Published: February 2003

Close coupled calculations are presented for photodissociation of NaH to the first excited atomic limit NaH+hν→Na(2P1/2,3/2)+H(2S). The calculations employ ab initio potential curves and dipole matrix elements. Resonances are predicted in the low energy photodissociation cross section to each of the sodium fine structure levels, and some are shown to arise from nonadiabatic interactions. The calculated ratio of the Na (2P3/2) to the Na(2P1/2) cross section does not approach the predicted high energy limit of 2:1 until the excess dissociation energy is more than an order of magnitude larger than the atomic spin-orbit splitting. Anisotropy parameters, that describe the angular distribution of photofragments and polarized sodium D-line fluorescence, exhibit dramatic energy variation near threshold, including some resonance structure. In general, these anisotropy parameters are different for fragments produced in each of the sodium fine structure levels. These NaH calculations delineate some of the qualitative features to be anticipated in wide classes of diatomic photodissociation involving fragments with fine structure.
Monte Carlo random walk calculations of unimolecular dissociation of methane
Authors: Viswanathan R. , Raff L. M. , Thompson Donald L.
Published: February 2003

Microcanonical rate coefficients and product energy distributions are computed for the CH3+H and CH2+H2 dissociation channels of CH4 by a random walk procedure. The formulation is based on Slater theory, but uses Metropolis Monte Carlo procedures to average over the reactant phase space. We find that the convergence rates of the calculations for the CH4 system are less rapid than that obtained in previous studies on more simple systems involving the dissociation of argon clusters. The convergence rate is found to decrease as the complexity of the process increases. Thus, convergence of the rate calculations for the simple two-center elimination reaction to form CH3+H is found to be at least an order of magnitude faster than that for the three-center channel leading to CH2+H2. When convergence is obtained, the computed rates and product translational energy distributions are in good accord with previously obtained quasiclassical trajectory results. The computer time required to obtain converged results for the two-center reaction is substantially less than that needed for the corresponding trajectory calculations. It is likely that the calculations for the three-center channel will likewise be more efficient than trajectory calculations provided importance sampling is included in the Metropolis procedure.
New Monte Carlo method to compute the free energy of arbitrary solids. Application to the fcc and hcp phases of hard spheres
Authors: Frenkel Daan , Ladd Anthony J. C.
Published: February 2003

We present a new method to compute the absolute free energy of arbitrary solid phases by Monte Carlo simulation. The method is based on the construction of a reversible path from the solid phase under consideration to an Einstein crystal with the same crystallographic structure. As an application of the method we have recomputed the free energy of the fcc hard-sphere solid at melting. Our results agree well with the single occupancy cell results of Hoover and Ree. The major source of error is the nature of the extrapolation procedure to the thermodynamic limit. We have also computed the free energy difference between hcp and fcc hard-sphere solids at densities close to melting. We find that this free energy difference is not significantly different from zero: −0.001<ΔF<0.002.
Kerr effect. I. Field effect on correlation in polarizable fluids
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

We make a systematic study of the distortion induced by a strong electric field on the orientationally averaged particle–particle correlations in a fluid. Such distortion occurs even for nonpolar particles with linear scalar polarizability and gives rise to the Kerr effect (which in general has other contributions as well). After obtaining our general result we consider explicitly its low-density contribution to the Kerr constant and its behavior in the critical region.