bluuebunny/crossref_metadata_2025 huggingface dataset:
Survivin is a shared tumor-associated antigen expressed in a broad variety of malignancies and recognized by specific cytotoxic T cells
Authors: Schmidt Susanne M. , Schag Kerstin , Müller Martin R. , Weck Markus M. , Appel Silke , Kanz Lothar , Grünebach Frank , Brossart Peter
Published: February 2003

Survivin, a member of the inhibitor of apoptosis protein family, is expressed in almost all types of malignancies, making this protein a useful tool for the development of broadly applicable vaccination therapies. We used a recently identified HLA-A2 binding peptide and dendritic cells (DCs) from healthy donors to induce survivin-specific cytotoxic T lymphocytes (CTLs) in vitro. These T cells efficiently lysed target cells pulsed with the cognate peptide. Furthermore, survivin-specific CTLs recognized HLA-A2–matched tumor cell lines and primary malignant cells from patients with leukemia in an antigen-specific and HLA-restricted manner as demonstrated with the use of cold target inhibition assays and blocking antibodies. To validate the immunogenicity of survivin we performed the experiments in an autologous setting and used monocyte-derived DCs as targets. Interestingly, we found that DCs up-regulate survivin expression on stimulation with tumor necrosis factor α (TNF-α). However, these mature DCs were not recognized by survivin-specific CTLs, whereas they lysed autologous mature DCs pulsed with the antigenic peptide or transfected with whole tumor RNA purified from a survivin-expressing cell line. To further analyze the possible use of survivin-specific CTLs in cancer therapies, we induced survivin-specific CTLs using peripheral blood mononuclear cells (PBMNCs) and DCs from a patient with chronic lymphocytic leukemia (CLL). The in vitro–generated T cells efficiently recognized autologous malignant CLL cells, whereas they spared autologous-purified nonmalignant B cells or DCs. Our results demonstrate that survivin epitopes are presented on a broad variety of malignancies and can be applied in vaccination therapies.
Human IL-12(p35) gene activation involves selective remodeling of a single nucleosome within a region of the promoter containing critical Sp1-binding sites
Authors: Goriely Stanislas , Demonté Dominique , Nizet Séverine , De Wit Dominique , Willems Fabienne , Goldman Michel , Van Lint Carine
Published: February 2003

To get insight into the regulation of human interleukin-12 (IL-12) synthesis, we determined the chromatin organization of the IL-12(p35) promoter region. First, we determined positioning of nucleosomes within the IL-12(p35) promoter using the indirect end-labeling technique in the THP-1 monocytic cell line. On stimulation with bacterial lipopolysaccharide (LPS) and interferon-γ (IFN-γ), hypersensitivity to digestion with DNase I, micrococcal nuclease, and specific restriction enzymes was detected in the region encompassing nucleotide (nt) –310 to –160, indicating selective inducible chromatin remodeling involving disruption of a single nucleosome (named nuc-2). Using p35 promoter deletion mutants and reporter gene assays, we demonstrated that the –396/–241 region contained critical cis-acting elements. Within this latter region, we characterized physically and functionally 2 Sp1-binding sites, which were acting as key regulatory elements for both basal and LPS/IFN-γ–inducible p35 gene expression: Sp1#1 lies within the remodeled nuc-2 region and Sp1#2 is located in the nucleosome-free region immediately upstream of nuc-2. Finally, we extended the chromatin structure analysis to dendritic cells (DCs) derived from human monocytes and observed the same nucleosomal organization and remodeling as in the THP-1 cell line. Moreover, we found that in DCs, LPS and IFN-γ synergized in the induction of nucleosomal remodeling and that chromatin remodeling at the p35 locus immediately preceded IL-12(p35) mRNA synthesis. Taken together, our results demonstrate that IL-12(p35) gene activation in the course of DC maturation involves selective and rapid remodeling of a single positioned nucleosome within a region of the promoter containing critical Sp1-binding sites.
Noise Impact Assessment in Tisco Mining Complexes in Jharia Coalfield
Authors: Sinha Vinod P. , Pal A. K. , Saxena N. C.
Published: February 2003

This paper highlights the development of value function curves for noise impact assessment based on a literature review and consultation with numerous experts; applying theory to the evaluation of noise impact in the residential complexes of Jamadoba and Sijua coal mining Complexes of the Tata Iron and Steel Company Limited (TISCO), Dhanbad, Jharkhand (India). The ranking and relative weightings of five important effects of noise exposure were established. The relationships between these parameters and Noise Environment Quality (NEQ) value were evaluated through available research findings and accordingly value-function curves for each parameter were developed through Statistical Package for Social Sciences; then, Resultant NEQ [NEQ (R)] was evaluated for all the residential, commercial and other sensitive areas of the Jamadoba and Sijua complexes. This was followed by the validation through a systematic reaction survey of the exposed population on a five-point scale which led to the evaluation of the percentage population which was highly dissatisfied in each of the localities, as well as the noise impact indices of both the residential complexes.
Generation of Reactive Species by One‐Electron Reduction of Fischer‐Type Carbene Complexes of Group 6 Metals and Their Use for Carbon–Carbon Bond Formation
Authors: Fuchibe Kohei , Iwasawa Nobuharu
Published: February 2003

Carbon–carbon bond‐forming reactions mediated by one‐electron reduction of Fischer‐type carbene complexes of Group 6 metals were investigated. In the case of aryl‐ or silylcarbene complexes of tungsten, the anion radical species generated by one‐electron reduction smoothly underwent addition reaction to ethyl acrylate. One‐electron reduction of α,β‐unsaturated carbene complexes afforded biscarbene complexes by dimerization of the corresponding anion radical species at the position γ to the metal center. In contrast, one‐electron reduction of chromium phenyl‐ or alkylcarbene complexes gave, via carbonyl insertion, α‐methoxyacylchromate complexes, which further underwent conjugate addition to various electron‐poor olefins to give the corresponding α‐methoxyketones.
Surviving in an environment of financial indiscipline: a case study from a transition country
Authors: Pejic‐Bach Mirjana
Published: February 2003

Financial indiscipline combined with restricted access to financial markets is a big problem for small businesses in transition countries. In such an environment, small businesses find it hard to collect accounts receivable from their customers, which causes liquidity crises and, in the worst case, bankruptcy. This article describes the development of a system dynamics model to explain the financial indiscipline problem in small businesses. Various policy options are evaluated using this model: (1) retaining profit; (2) borrowing money from the bank; (3) tightening the accounts receivable policy; and (4) delaying payment to suppliers. Tightening the accounts receivable policy in combination with delaying payment to suppliers is found to be the most successful option. However, in most of the transition countries, the legal system is inefficient and such measures would lead to an illiquid economy with a weak small‐business sector. Copyright © 2003 John Wiley & Sons, Ltd.
Vibrational relaxation studies of matrix isolated C−2
Authors: Allamandola L. J. , Rojhantalab H. M. , Nibler J. W. , Chappell T.
Published: February 2003

Absorption studies of C−2 formed by 1216 Å photolysis of C2H2 in Ar at 14 °K indicate that the C−2 concentration approaches a limit of ∼1 ppm, possibly due to electron return tunneling to the unknown cation counterpart X+ for separations closer than ∼175 Å. A dual pulsed laser method was used to produce vibrationally excited C−2 and to monitor the v″=1 nonradiative decay. Lifetime values were strongly dependent on C2H2 concentration and increased to 147 msec at an Ar:C2H2=20 000 ratio. This value was reduced to 93 msec for a Ar:C2D2 matrix, presumably because of near resonance of the C−2 energy (1779 cm−1) with the C≡C stretch (1762 cm−1). Decay times were longer in Kr and Xe than in Ar. The absence of any temperature effect over the range 14 to 30 °K indicates that few lattice phonons are involved in the rate determining step, the transfer to C2H2. The rate constant for this transfer decreases as the third to fifth power of an average C−2–C2H2 distance, a much slower drop than the tenth power dependence predicted for the first applicable electrostatic coupling term, a quadrupole–quadrupole interaction. A more direct coupling through the intermediate argon atoms is implied but 13C studies show that this coupling does not extend so far as to permit ’’resonant’’ transfer of vibrational energy from one C−2 to the next. Direct decay to lattice phonons is slow, with a lower lifetime limit of ∼160 msec in Ar.
Observation of the set of three sublevel phosphorescence spectra of quinoxaline. Analysis of radiative mechanisms
Authors: Yamauchi Seigo , Azumi Tohru
Published: February 2003

A method to observe phosphorescence spectra for the three triplet sublevels is proposed, and is applied to quinoxaline in a single crystal of naphthalene-d8. The method consists of measurements of the time resolved phosphorescence spectra at temperatures where spin polarization is achieved and under the influence of the microwave field to saturate the magnetic transition between the spin sublevels. The method is best applied to the cases where total decay rate constants are small for two sublevels. The Tz spectrum is identical to the known thermally averaged spectra observed at 4 K, whereas the Tx and Ty spectra are markedly different from the Tz spectrum in the spectral distributions. The relative radiative rate constants as well as the total decay rate constants are obtained by the method of microwave induced delayed phosphorescence for some selected vibronic bands. On the basis of the observed spectra and the kinetic data, mechanisms in which vibronic bands gain intensity are discussed. Finally, from the qualitative analysis of the experimental results in conjunction with theoretical considerations, the magnitudes of the matrix elements with respect to spin–orbit coupling are estimated. In the matrix element over molecular orbitals the contribution of one center terms dominates. The sum of two center and three center terms contributes about 10%, and the sum of three center terms contributes about 3% of the matrix element.
An investigation of the electrostatic energy in the formic acid crystal, using multipole and point-charge lattice sums
Authors: Smit P. H. , Derissen J. L. , van Duijneveldt F. B.
Published: February 2003

The electrostatic part of the lattice energy of the formic acid crystal is calculated using multipole moments up to the sixth moment and point charges obtained from ab initio wavefunctions for formic acid monomers. The calculations are carried out as a function of the molecular orientation in the crystallographic unit cell. It is found that the electrostatic lattice energy of formic acid is both large in magnitude (−17.8 kcal/mole) and varies strongly with the molecular orientation. Several orientations, including the one observed experimentally, minimize the electrostatic energy and the location of these minima is dictated by nearest-neighbor interactions. The nonobserved minima can be excluded for geometrical reasons. The electrostatic component of the lattice energy is found to act as a driving force for molecular distortion upon crystallization. Qualitative but not quantitative agreement is obtained between the multipole lattice energy and the point-charge energy based on Mulliken populations.
Cyclotron resonance and carrier scattering processes in anthracene crystals
Authors: Burland D. M. , Konzelmann U.
Published: February 2003

Cyclotron resonance experiments on holes orbiting in the ab plane of an anthracene crystal are described in detail. We were unable to reduce the cyclotron resonance experiment to a routine procedure and consequently are able to report useful cyclotron resonance measurements on only a few (six) anthracene crystals. Nevertheless we have been able to obtain useful information on the valence band structure and hole scattering properties in anthracene from these measurements. The measured effective mass of 11 me, where me is the free electron mass, is shown to be in qualitative agreement with calculations of the effective mass tensor. From the shape of the cyclotron resonance line at 2 K, we have obtained experimental hole scattering times ranging from 4×10−10 sec down to 10−12 sec and below depending on sample quality. By a detailed examination of the possible low temperature scattering mechanisms, we have concluded that, at 2 K, holes in anthracene are most efficiently scattered by charges trapped at point defects, either chemical impurities or local lattice defects.
Penning ionization of H2 by He*: Calculation of anomalous structure in the singlet interaction potential
Authors: Isaacson A. D. , Hickman A. P. , Miller W. H.
Published: February 2003

Calculations are reported for the singlet He*−H2 potential energy surface. Anomalous structure in the interaction potential is discussed. (AIP)
The dynamical structure factor S (Q,ω) of solid β-N2
Authors: Klein Michael L. , Weis Jean-Jacques
Published: February 2003

A classical computer simulation study of the dynamical structure factor S (Q,ω) for a simple model of solid β-N2 is reported. We utilized a hexagonal system composed of 288 molecules interacting via a (12–6) atom–atom potential. Periodic boundary conditions were used to simulate the infinite crystal. The molecular half-bond length d was assumed to be given by d=0.1646σ, where σ is the zero of the atom–atom potential. The molecular density ρ=Nσ3/V=0.836 and the temperature T=1.27 ε/kB (ε is the potential well depth) were such that using recently proposed potential parameters our thermodynamic state corresponded to V=26.1 cm3/mole, T=47.4 K. When compared with real β-N2 under these conditions our calculated pressure is a little too high, and the transverse optic, Raman active frequency too low. For small wave vectors Q≲2 Å−1, the full dynamical structure factor shows phonon peaks which are virtually indistinguishable from those due to the center of mass motion, while at larger Q (between 4.8 and 6.4 Å−1) the spectra are dominated by the reorientational motion of the molecules. The computer simulation phonon energies are compared with lattice dynamical calculations employing an intermolecular potential derived from the spherical average of the atom–atom potential. There is particularly poor agreement for long wavelength shear modes, probably due to the neglect (in the lattice dynamical calculations) of the coupling of these modes to molecular reorientational motion.
Rate measurements of reactions of helium metastable species at atmospheric pressures. I. He (2 3S) in pure afterglows
Authors: Myers Gary , Cunningham A. J.
Published: February 2003

Using resonance absorption spectrometry the rates of the reactions He(2 3S)+He(2 3S) Kaa→products and He(2 3S) +2HeKc→products have been measured in the afterglow period of electron beam excited discharges in helium at atmospheric pressures. Lorentz broadened absorber linewidths calculated using a simple classical interruption theory allowed absolute metastable concentrations to be determined. Reported rates for these reactions are in excellent agreement with literature values measured at lower pressures.
Thermodynamic study of gaseous ternary europium–tungsten–oxygen molecules
Authors: Balducci G. , Gigli G. , Guido M.
Published: February 2003

In the course of a mass spectrometric Knudsen cell study of the vaporization of europium orthophosphate and mixtures of it with europium sesquioxide the molecules EuWO3, EuWO4, Eu2WO5, and EuW2O7 were observed in the vapors. From the study of a number of pressure independent equilibrium reactions the atomization energies of these ternary molecules have been determined. In addition, the dissociation energy of EuO was determined and compared with previous results. The results obtained are D°0(EuO) =111.6±1.7; D°0,at(EuWO3) =569.6±6.9; D°0,at(EuWO4) =714.6±6.5; D°0,at(Eu2WO5) =960.0±10.9; D°0,at(EuW2O7) =1276.3±9.0 kcal mol−1.
Quantum corrections to the second virial coefficient of a gas using hard sphere basis functions
Authors: Singh B. P. , Sinha S. K. , Singh Y.
Published: February 2003

The quantum corrections to the second virial coefficient for a gas at high temperature are calculated using the modified Wigner–Kirkwood expansion method, developed by Derderian and Steele. We find that the higher corrections depend both on the shape of the well and the value of the potential at the core. The general expression for the second virial coefficient of a gas at high temperature is given as Bdir=Bdirc + (2πa3/3) e−βup(a) [(3/2√2) (λ/a) + (BII/π)(λ/a)2 + BIII/16√2π) (λ/a)3 + ...], where BII and BIII are constants depending upon the shape and nature of the perturbation potential and equal to unity in the limit of hard sphere [i.e., up(r) →0].
Toward a theory of the Perrin matrix for light scattering from dilute polymer solutions
Authors: Harris Robert A. , McClain Wm. Martin
Published: February 2003

We present a treatment of the polarization of light scattered by dilute polymer solutions. The treatment is complete in the sense that it gives a theoretical expression for every quantity that can be measured by the use of polarized light, at a given scattering angle and given optical frequency. The monomer units of the polymer are assumed to be small with respect to wavelength, but no such assumption is made for the polymer as a whole. The final closed expressions should be very accurate for bodies in the size range of enzyme molecules, and should permit calculations of light scattering properties as a function of polymer geometry.
Far infrared absorption of diatomic polar molecules in simple liquids and statistical properties of the interactions. I. Spectral theory
Authors: Bonamy L. , Hoang P. Nguyen Minh
Published: February 2003

A theory of the far infrared spectra of diatomic polar molecules dissolved in simple liquids is presented. The starting point is a basic spectrum of additive Lorentzian lines, whose widths and shifts are expressed up to second order with respect to the interaction. This basic spectrum is distorted by the finite correlation time of the interaction, by the correlation between initial states, and by the overlap between the lines which are not completely resolved for the liquid state. All these deviations, including the overlap correction, which leads to a nonadditivity effect of the lines, are also treated up to second order with respect to the interaction.
Far infrared absorption of diatomic polar molecules in simple liquids and statistical properties of the interactions. II. Statistical theory and spectral application
Authors: Hoang P. Nguyen Minh , Bonamy L.
Published: February 2003

The statistical properties of the directing intermolecular field, which describes the anisotropic action to which polar molecules are submitted when immersed in a simple liquid, are expressed in terms of equilibrium averages. These averages are obtained by means of a convenient cell model for the liquid structure. This statistical information is inserted in the spectral theory of Paper I. The different spectral effects are numerically analyzed. It is shown that only the overlapping line effect must be retained in the far-infrared absorption of such a liquid solution. When using this (nonadditivity) overlapping line effect the theoretical and experimental band profiles are in agreement.
Diagrammatic perturbation theory. The ground state of the carbon monosulfide molecule
Authors: Wilson Stephen
Published: February 2003

Diagrammatic many-body perturbation theory is employed in a study of the ground state of the carbon monosulfide molecule for bond lengths close to the equilibrium value. The calculations are complete through third order in the energy within the algebraic approximation. Two different zero-order Hamiltonians are considered and all two-, three-, and four- body terms are determined for the corresponding perturbation expansions. Many-body effects are found to be very important. Padé approximants to the energy expansion are constructed and upper bounds are evaluated. Almost 53% of the estimated correlation energy is recovered. The variation of components of the correlation energy with nuclear separation is investigated. Spectroscopic constants are also calculated.
On the coupled states and infinite order sudden approximations to the body frame wavefunction
Authors: Kouri Donald J. , Goldflam Rudolf , Shimoni Yair
Published: February 2003

New CS and IOS approximations to the total angular momentum body frame radial wavefunction ψJ(jλ‖j0m0‖R) are derived. The new expressions for ψCSJ(jλ‖j0m0‖ R) and ψIOSJ(jλ‖j0m0‖R) are not diagonal in λ, m0 and they lead to the proper exact solution when the potential is set equal to zero. In addition, since ψJCS and ψJIOS are linear combinations of ψlm0(j‖j0‖R) and ψIOSlm0(j‖j0‖R) for all l satisfying ‖J−j‖⩽l⩽J+j, one expects improved behavior for larger J (especially for elastic elements where j=j0). It is explicitly shown that the present nondiagonal expressions for ψJCS(jλ‖j0m0‖R) are consistent with the Shimoni–Kouri expressions for the bodyframe T matrix TJCS(jλ‖j0m0), which is also not diagonal in λ, m0. The present results are expected to provide the basis of an improved CS and IOS theory of reactive scattering.
Multiple-photon isotope separation in SF6: Effect of laser pulse shape and energy, pressure, and irradiation geometry
Authors: Lyman J. L. , Rockwood S. D. , Freund S. M.
Published: February 2003

The isotopically selective dissociation of SF6 induced by intense CO2 laser radiation has been experimentally investigated. These experiments demonstrate that the reaction yield can be greatly enhanced by designing the reaction cells for better photon utilization. It was found that although the probability of reaction increases with laser energy fluence, the reaction probability is almost independent of the pulse shape or the instantaneous laser intensity. Experiments over a range of pressures showed that collisions decrease the probability of reaction.
Infrared spectrum of D2O vibrationally decoupled in glassy H2O
Authors: Ritzhaupt Gary , Devlin J. Paul
Published: February 2003

The infrared spectrum of a glassy sample containing approximately 5% D2O in H2O is presented. The decoupled D2O band complex is prominently displayed in the stretching frequency region of the spectrum. (AIP)
Linear and nonlinear susceptibilities of rare earth ferroic molybdates
Authors: Bonneville R. , Auzel F.
Published: February 2003

We have measured the linear and nonlinear susceptibilities of several mixed rare earth molybdates Ln2xGd2(1−x)(MoO4)3, where Ln is Nd, Sm, Gd, Tb, Ho, Yb. We conclude that the major part of the nonlinear optical properties is due to the MoO4 tetrahedra orientation and to the Mo–O bond hyperpolarizability. Extrapolated linear and nonlinear polarizabilities of pure compounds Ln2(MoO4)3 agree with the instability of Yb, Tm, and Er ferroic molybdates.
Application of the scaled particle theory to the problem of hydrophobic interaction. II. Mixtures of water and ethanol
Authors: Tenne R. , Ben-Naim A.
Published: February 2003

Following part I of this series, we have considered the process in which m simple solute molecules are brought from fixed positions at infinite separation from each other to a close-packed configuration, where they are confined to a spherical region of a suitable diameter. This process is carried out at a fixed temperature and pressure, and within the solvent, the latter being a mixture of water and ethanol at various compositions. We have used a combination of theoretical (based on the scaled-particle theory) and experimental information to compute the free energy, entropy, and enthalpy changes associated with this process. The results obtained by this procedure are all consistent with similar trends that have been obtained previously by a different method.
Nonadiabatic interaction in unimolecular decay. III. Selection and propensity rules for polyatomic molecules
Authors: Galloy C. , Lorquet J. C.
Published: February 2003

Consideration of the form of the classical-trajectory equations applied to the predissociation of a polyatomic molecule leads to the following possible sources of simplification: (i) Internal coordinates which remain unchanged during the course of a nonadiabatic reaction can be ignored in the calculation of the transition probability; (ii) Symmetry considerations play a role in the value of the couplings and lead to propensity rules; (iii) Certain nuclear trajectories are unable to bring about a nonadiabatic transfer of population between two electronic states. Methods to determine these inefficient trajectories are indicated. A method of calculating the coupling matrix elements of the ε/εq operator is presented. Finally, it is shown that once these coupling matrix elements are calculated, the diabatic states can be easily obtained. They exhibit all the properties which are expected from them, but they do not, in general, correspond to pure electronic configurations. As an example, the previous considerations are applied to the case of the nonadiabatic interaction between two 4A2 states of the CH2+ ion.
On the contribution of nonhydrodynamic interactions to the concentration dependence of the drag coefficient of rigid macromolecules
Authors: Phillies George D. J.
Published: February 2003

The Stokes’ law drag coefficient for a rigid macromolecule in solution has long been known to depend on the macromolecule concentration. This concentration dependence has generally been interpreted entirely in terms of hydrodynamic interactions between the macromolecules. It is argued here from a fluctuation–dissipation relation that direct (e.g., hard sphere, electrostatic) interactions between macromolecules also contribute to the drag coefficient. An approximate calculation indicates that the contribution of direct intermacromolecular interactions to the drag coefficient can be as important as the contribution of hydrodynamic intermacromolecular interactions.
Inverse isotope effect for electron transfer reactions in ethanol
Authors: Ražem Dušan , Hamill William H. , Funabashi Koichi
Published: February 2003

The rate constants of solvated electrons reading with scavengers in O2 H5O H and C2 H5 OD are reported. Inverse isotope effect is found to be closely related to the electron affinities of the scavengers.(AIP)
Laser-induced electronic transitions in a molecular beam: The dipole moment of d 3Δi
i v=4 carbon monoxide
Authors: Hemminger John C. , Cavanagh Richard , Lisy James M. , Klemperer William
Published: February 2003

Measurement of the Stark effect in the CO transition a 3Πv=0→d 3Δiv=4 is made using a tunable dye laser as resonance radiation in a Rabi-type molecular beam electric resonance spectrometer. The observed spectral linewidths are 4 MHz (FWHM). The electric dipole moment of CO d3Δiv=4 is 0.42±0.02 D. The sign of the moment is determined to be C−O+.
Explicit representation of lone-pair orbitals in molecular orbital calculations for NH3, H2O, N2H4, and H2O2
Authors: Ryan P. Barry , Todd H. David
Published: February 2003

Single Gaussian basis functions have been used to represent lone-pair orbitals in contracted-Gaussian basis calculations on NH3, N2H2, H2O, and H2O2. Both Pople’s STO-4G and Dunning’s [4s3p/2s]← (9s5p/4s) contracted basis sets were used. The lone-pair functions are located near the N and O nuclei, and their optimum positions and exponents are shown to be relatively insensitive to molecular environment. This indicates that lone-pair functions may be explicitly included as part of a contracted basis set to represent polarization effects. This augmented, contracted-Gaussian basis set is shown to yield significant improvements in computed values of rotational barriers and molecular geometries at relatively small cost in additional computation time.
High pressure studies of fluorenone emission in plastic media
Authors: Mitchell D. J. , Schuster G. B. , Drickamer H. G.
Published: February 2003

The energy and the quantum efficiency for fluorenone fluorescence in the crystalline state and in polymeric matrices was measured as a function of external pressure over the range 0–140 kbar. The application of high pressure induces changes in the quantum yield, which ranges from 0.001 at low pressure to a maximum of ∼0.1 at high pressure in hydrocarbon plastics. These results are interpreted as arising from the decrease in the energy of the lowest ππ excited singlet state relative to other relevant states as the external pressure is increased.
Remarks on anisotropic rotational diffusion effects in the ESR spectra of radical cations generated on an acidic surface
Authors: Muha G. M.
Published: February 2003

The linewidth variations in the ESR hyperfine spectra of the radical cations of anthracene, perylene, and tetracene generated by adsorption on an acidic surface (silica–alumina) are analyzed in terms of the Freed–Fraenkel theory as modified to include anisotropic diffusion effects. The analysis is based on computer simulation of the observed experimental spectra. In the case of anthracene and perylene quite acceptable agreement is obtained if the diffusion tensor is chosen to have axial and near-axial symmetry, respectively, although a small amount of modulation of the isotropic hyperfine interactions may also be present in each case. The results are reviewed in terms of current theories of the nature of the adsorbent–adsorbate interaction on this type of surface. Similar calculations applied to tetracene failed to produce agreement between the simulated and experimental spectra and an additional spin relaxation mechanism involving electron transfer was included in the calculation. Although agreement was somewhat improved thereby, discrepancies remained. The tetracene results are reviewed in terms of the known redox behavior of the system.
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o SCF and CI studies of three states of NH2
Authors: Bell Stephen , Schaefer Henry F.
Published: February 2003

Theoretical calculations have been made for the ? 2B1, ? 2A1,, ? 2B2 states of the NH2 radical using a double-zeta and double-zeta-plus- polarization basis sets. With the most extensive basis set and configuration interaction the optimum geometry for the 2B1 state is r=1.029 Å, ϑ=103.1°, while the experimental geometry is r=1.024 Å, ϑ=103.3°. Similarly, the CI geometry for the 2A1 state is r=1.000 Å, ϑ=143.4° while the experimental geometry is r=1.004±0.03 Å, ϑ=144°±5°. The CI excitation energy between these states is Te=11 830 cm−1 compared with the origin of the ?–? transition of 11 122 cm−1 and the barrier to linearity in the 2A1 state by CI is 974 cm−1 compared with the experimental barrier of 777±100 cm−1. The ? 2B2 state is predicted to have the geometry r=1.162 Å, ϑ=47.5° with an excitation energy from the ? 2B1 state of 38640 cm−1.
Phosphorescence emission and polarization of hydroxypyridines
Authors: Hotchandani S. , Testa A. C.
Published: February 2003

Phosphorescence quantum yields and lifetimes of 2-, 3-, and 4- hydroxypyridine and 2-methoxypyridine have been measured at 77 ° K in EPA and alkaline EPA using 285 and 254 nm excitation. The phosphorescence polarization is negative with the exception of 4-hydroxypyridine in alkaline EPA, and lowest triplet state is in all cases π,π*. The lack of phosphorescence for 2-, 3-, and 4-hydroxypyridine in a methylcyclohexane glass is attributed to a solvent dependent intersystem crossing process. The O–O band for the lowest triplet of 4-hydroxypyridine and 2-methoxypyridine in EPA appears at 29.9 and 26.7×103 cm−1, respectively. The primary spin–orbit coupling process 1n,π* 3 π,π*; however, in 4-hydroxypyridine there is evidence of second order vibronic spin–orbit coupling which involves an out of plane vibration (∼828 cm−1). In the latter case the mixing scheme appears to be 3π,π* 3n,π* 1π,π*. The negative phosphorescence polarization observed for 3-hydroxypyridine in alkaline EPA when excited into S1 and S2 indicates that its transition moment is out of plane polarized.
NaCl polymers
Authors: Martin T. P.
Published: February 2003

The equilibrium configurations of NaCl polymers containing from one to seven molecules were determined by numerically minimizing the total energy. A rigid ion model was used to describe the two particle interactions. The binding energy per molecule and the interatomic distances were found to increase monotonically as molecules were added to the polymer, even though the pentamer and heptamer possess permanent dipole moments. Once the equilibrium configuration was established, the second derivatives of the total enery with respect to atomic displacements were evaluated numerically and the dynamical matrix diagonalized to give the vibration frequencies of each polymer. The eigenvectors were also evaluated and used to calculate the strength of the infrared absorption for each mode of vibration. Experimental far infrared absorption spectra of NaCl in various stages of aggregation are also reported. The samples were prepared at liquid helium temperature by the simultaneous condensation of argon and NaCl vapor onto a transparent substrate. Although NaCl vapor contains only monomers and dimers, larger polymers could be formed by using a relatively high concentration of NaCl in the argon matrix. An assignment of absorption lines to specific polymers is made by comparing the experimental and calculated absorption spectra.
Molecular dynamics calculation of the liquid structure up to a solid surface
Authors: Toxvaerd So/ren , Praestgaard Eigil
Published: February 2003

The technique of molecular dynamics is used to calculate the properties of a liquid phase in contact with a fcc crystal phase. A system of 1680 particles which interact through a Lennard-Jones potential is divided into two closed subsystems by imposing artificial boundaries across which the particles can interact, but not pass. One of the subsystems is melted and a state corresponding to coexisting liquid–solid bulk states is obtained. The constraint is removed and it is observed that the state is maintained, which suggests that the system is in thermodynamic equilibrium. The interface shows a gradual decline of order, and the structure in the middle of the fluid system cannot be distinguished from that of a pure liquid with the same temperature and density. The density profile is also calculated for a fluid up to a solid surface without lattice structure where the layering in the interface is seen to be more pronounced.
Infrared and Raman spectra of the lattice vibrations of cyclopropane
Authors: Bertie John E. , Jacobs Stephen M.
Published: February 2003

Following the paper by Shurvell et al. [J. Mol. Spectrosc. 53, 77 (1974)], the Raman and infrared spectra of the lattice vibrations of cyclopropane between 78 and 4 °K have been recorded. The infrared frequencies coincide with Raman frequencies, indicating that the crystal class is C2v rather than D2h. This conclusion is supported by the number of vibrations observed, which is more consistent with the two-molecule cell of the C2v crystal class than the four-molecule cell of the D2h crystal class.
Kerr constants, depolarization ratios, and hyperpolarizabilities of substituted methanes
Authors: Burnham A. K. , Buxton L. W. , Flygare W. H.
Published: February 2003

The static Kerr constants of eight substituted methanes in the gas phase have been measured by a low-frequency null technique. Combining these results with gas phase depolarization ratio measurements we show that the hyperpolarizability contributions to the Kerr constant are small except for CH3F. The magnitudes of the hyperpolarizabilities obtained are in good agreement with the values obtained from second harmonic generation measurments. In the case of nitromethane the electric birefringence and depolarization ratio measurements are combined to obtain the three principal values of the polarizability tensor.
Modified Hartmann–Hahn double NMR in solids for high resolution at low gyromagnetic ratio: CaF2 and quadrupole interaction in MgF2
Authors: Bleich Hermann E. , Redfield Alfred G.
Published: February 2003

Moderately high resolution NMR of rare spins in solids is described, using a modified Hartmann–Hahn double resonance experiment. Resolution is achieved by high power resonant decoupling of abundant spins, and the Hartmann–Hahn condition is achieved by irradiation of the rare spins off resonance, which preserves their chemical shift in the rotating frame. The rare spins are saturated with an additional weak variable frequency rf field. Following this cross-polarization period is a period when strong gated rf is applied off resonance to the abundant spins. This permits time-shared observation of the abundant spin magnetization, which reflects saturation of the rare system during the previous cycle. At the same time it serves to replenish the rare spin magnetization because it is off resonance. Transition between the two modes is adiabatic. This method distorts the rare-spin line shape, but a related model experiment is also described which would not do so. This method is expected to be more useful than that of Pines, Gibby, and Waugh for studies of rare low gyromagnetic ratio species (lower than 13C) of spin 1/2 nuclei. The sensitivity limit is estimated to be in the millimolar range and is expected to be independent of gyromagnetic ratio. In CaF2 the 43Ca gyromagnetic ratio is measured to be 286.545±0.01 Hz/G. In MgF2 the 25Mg quadrupolar interaction is inferred to be e2qQ/h=3.2±0.3 MHz, η=0.36±0.04, with the uncertainty arising from lack of a fourth order theory.
On the use of total cross sections for obtaining the anisotropic interaction potential in atom–diatom system
Authors: Eccles Joseph , Secrest Don
Published: February 2003

A study is made of the ’’conservation of the total cross section’’ and the ’’equivalence of the total cross section’’ rules for scattering from H2. It is shown that these rules are a better approximation than the random phase approximation would indicate. Cross section formulas are given for scattering atoms from mj state selected molecules and it is shown that total cross sections for state selected molecules depend on the anisotropic part of the interaction potential, while the spin-averaged total cross section often depends only on the spherically symmetric part of the interaction potential. The total spin-averaged cross section is thus independent of the initial rotation state of the molecule and depends only on the relative collision energy. It is further demonstrated that isotopic substitution, which shifts the center of mass changing the symmetric part of the interaction potential, has too small an effect on the total cross section to be useful as a means of determining the anisotropy of the potential.
A study of the Bonham series representation of the Born–Oppenheimer exchange amplitude and the derivation of a local exchange potential
Authors: Huo Winifred M.
Published: February 2003

The convergence and range of applicability of the Bonham series representation of the Born–Oppenheimer exchange amplitude is investigated. Numerical calculations on 1 1S→2 3S and 1 1S→2 3P of He by electron impact demonstrate that the first three terms of the Bonham series can provide an adequate representation of the Born–Oppenheimer amplitude from high energies down to near threshold. The three-term Bonham series is then used to represent the Hartree–Fock exchange kernel in momentum space, which has been shown by Lassettre to be proportional to the Born–Oppenheimer amplitude. Inverse Fourier transform, plus an additional approximation of replacing the momentum which appears as an expansion parameter in the Bonham series by its averge value, gives us a local exchange potential. If the averge momentum in the Thomas–Fermi model is used, the first term of the local exchange potential is just the electron gas exchange potential. A second term corresponding to a correction for the inhomogeneity in the electron gas density, is also obtained. No adjustable parameter is involved. Exchange energies of He, Be, and Ne calculated using the local exchange potential agree much better with the Hartree–Fock results than the electron gas model.
Pressure dependence of the lattice parameters of naphthalene up to 5.5 kbar and a re-evaluation of the elastic constantssa)
Authors: El Hamamsyb) M. , Elnahwy S. , Damask A. C. , Taub H. , Daniels W. B.
Published: February 2003

The pressure dependence, up to 5.5 kbar, of the lattice parameters of naphthalene was determined, using neutron diffraction techniques. The variations were fitted to straight lines, the slopes of which are the linear compressibilities. The volume compressibility at 5 kbar was found to be in good agreement with the values obtained by Bridgman and by Vaidya and Kennedy. A set of elastic constants for naphthalene was calculated using the experimental values of the linear compressibilities. This set is found to be in close agreement (except for C11) with a set calculated by Pawley, who used the general intermolecular potential of Kitaigorodskii.
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o studies of the hydrated H3O+ ion. II. The energetics of proton motion in higher hydrates (n=3–5)
Authors: Newton Marshall D.
Published: February 2003

A b initio molecular orbital calculations on the higher hydrates of H3O+, using a split valence level basis set (4–31G), have led to the following results. (1) Energies for successive hydration are in good accord with gas-phase thermochemical data. (2) Hydrogen-bonded OH and O⋅⋅⋅O distances in H9O4+ are in excellent agreement with condensed phase diffraction data. (3) Large variations in OH (≲0.08 Å) and O⋅⋅⋅O (∼0.25 Å) distances caused by strong hydrogen bonding are monotonically correlated with OH stretching force constants and frequencies, which cover a range of 1500 cm−1. (4) Excellent quantitative correlation is obtained between calculated and observed infrared gas-phase frequencies for six intense OH stretching bands, as represented by the least-squares fit, νexp=−704+1440 (FSGS)1/2±15 cm−1. This least squares relationship is used to assign some of the other experimental absorption bands from the gas phase. The only major uncertainty is in the case of the symmetric H3O+ mode in H3O+(H2O)3. (5) The relative magnitudes of frequencies for symmetric (ν1) and antisymmetric (ν3) stretching modes are found to switch upon passing from H3O+ (ν1<ν3) to H3O+(H2O)3 (ν1≳ν3). (6) The isoelectronic species H3O+(H2O)3 and OH−(H2O)3 are predicted have very similar frequencies for symmetric stretching of hydrogen-bonded OH groups, in accord with Raman data for aqueous acid. (7) Addition of a fourth water molecule to the first solvation shell of H3O+ does not lead to any significant stabilization, a result consistent with x-ray and neutron diffraction results from aqueous HCl. (8) The most stable isomer of H13O6+ is found to be an H9O4+ moiety, somewhat perturbed from three-fold symmetry by two second shell water molecules. (9) The tetrahydrate of the diaquahydrogen ion yields an H13O6+ structure 2.2 kcal/mole higher in energy and provides a possible model for the symmetric intermediate in aqueous proton transfer (observed activation energy, 2.4 kcal/mole). This model emphasizes the importance of concerted reorganization of OH and O⋅⋅⋅O bond lengths in the vicinity of the excess proton, with proton tunneling not expected to be a major factor, since the postulated intermediate offers a symmetric single-well potential for the excess proton.
Host spin–lattice relaxation narrowing in the EPR of Mn2+ in CoSO4⋅7H2O single crystals
Authors: Saraswat R. S. , Upreti G. C.
Published: February 2003

Electron paramagnetic resonance (EPR) of Mn2+ doped in CoSO4⋅7H2O single crystals has been studied from 300 to 77 K and at ∼9.3 GHz. Two different types of crystals of CoSO4⋅7H2O have been obtained, which grow in two different temperature ranges about 298 K. The two forms exhibit different types of spectra: one form [to be referred to as CoSH(I)] shows two 30 line Mn2+ spectra with D=459×10−4 cm−1, ‖E‖=134×10−4 cm−1 and the other form [to be referred to as CoSH(II)] shows only a single 30 line spectrum with D=234×10−4 cm−1, ‖E‖=19 ×10−4 cm−1. The observation of resolved Mn2+ spectra at 300 K and its broadening on lowering the temperature in CoSO4⋅7H2O:Mn2+ crystals has been discussed in terms of ’’host spin–lattice relaxation narrowing.’’ The observed shift in the Mn2+ gz value from that in diamagnetic hosts is probably due to the Co2+ ions, which produce a local static magnetic field at the site of Mn2+ ions. From the observed linewidth in the EPR spectrum of Mn2+ in single crystals of CoSO4⋅7H2O the T1 of Co2+ in CoSO4⋅7H2O has been estimated to be ∼1.1×10−11 s.
Polyatomic force constants from charge densities and field gradients
Authors: Bartlett Rodney J. , Parr Robert G.
Published: February 2003

Cartesian-coordinate expressions for polyatomic molecule force constants are considered to investigate the relationship between these quantities and field gradients, ’’atomic force constants’’ or Laplacian terms as ∇2αW, and ’’perfectly following densities.’’ It is shown that for hydride molecules, AHN, the Laplacian quantities obey the approximate relationship ∇2AW?N∇2HW. For triatomic molecules (A–C–B), a ’’diatomics in molecules’’ argument is successful in predicting the quantities ∇2AW and ∇2BW, which are combinations of the stretching and bending force constants. This lends credence to the approximate universality of a relationship for diatomic molecules suggested by Anderson and Parr. Furthermore, it is shown that while only diagonal Cartesian constants are needed to completely describe the general quadratic valence force field (GQVFF) for linear triatomic molecules, nonlinear triatomics require Cartesian constants of the form ∂2W/∂XA∂YC to specify the GQVFF constants. However, the latter may be related to the field gradient tensor and perfectly following densities through the Eckart conditions imposed on Cartesian constants. Possiblities for further applications of the formulas are discussed.
A comparison of exact classical and quantum mechanical calculations of vibrational energy transfer. II. The effect of long-lived collision complexes
Authors: Gordon Robert J.
Published: February 2003

Exact classical and quantum mechanical calculations of V–T relaxation were carried out for the model system He+O2(v=1). The diatomic molecule was treated as a harmonic oscillator, and a spherically symmetric Lennard-Jones intermolecular potential was assumed. The bin and two-moment methods were used to quantize the classical energy transfer. For a deep well both classical and quantal calculations showed evidence of complex formation. In this case inelastic transitions were classically allowed even at low collision energies. The classical transition probabilities generally agreed within a factor of 2 with the quantal results. The final energy distribution of the complex trajectories was not completely random, as compared with the information-theoretic prior expectation.
Statistical mechanical theory for nonuniform fluids. II. Hard-sphere fluid in the presence of an external field
Authors: Singh Y. , Abraham Farid F.
Published: February 2003

In Part I of this study, we extended a formal theory for the statistical mechanics of a nonuniform classical fluid to the hard-sphere fluid system and developed a perturbation theory of nonuniform simple fluids. In this paper, we apply our theory to the problem of the soft-wall/hard-sphere fluid interface by solving for the external potential required to yield the known hard-sphere fluid density in contact with a structureless 9–3 soft repulsive wall potential. We find excellent agreement between the solution for the external potential and the 9–3 wall potential. Using the ’’local density approximation,’’ the comparison shows poor agreement.