bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular dynamics study of a single polymer chain in solution. II. Bead–spring model
Authors: Bruns W. , Bansal R.
Published: February 2003

We have simulated the dynamics of a model polymer chain immersed in a solvent. The polymer is represented by a nonamer whose nearest neighbors are linked through a harmonic potential. In addition to this all particles are assumed to interact via a Lennard-Jones potential and the simulations have been performed at a temperature and density which correspond to the triple point of L-J fluids. Equilibrium properties of the chain such as end-to-end distance, radius of gyration, and polymer asphericity are computed. The self-diffusion coefficient and autocorrelation functions of various dynamical variables have also been calculated. All these results have been compared with our previous results obtained on the basis of a bead–rod model for the chain.
An 129I Mössbauer spectroscopic study of iodine doped in poly(vinylpyridines)
Authors: Sakai H. , Matsuyama T. , Maeda Y. , Yamaoka H.
Published: February 2003

The charge densities and the configurations of iodine doped in poly(2- and 4-vinylpyridines) have been studied by using the Mössbauer effect of 129I at 16 K. The ’’outer complex’’ is first formed in the system of poly(2-vinylpyridine) and iodine. The extent of the charge transfer is estimated to be 0.22 in the outer complex, which is nearly the same as pure pyridine. The iodine of the outer complex varies gradually to the tri-iodide anion and then to the iodide anion by accepting electrons from the pyridine ring of the polymer. In the system of poly(4-vinylpyridine) and iodine both the outer complex and the ’’inner complex’’ are first observed, and the iodine species in these complexes vary gradually to the I3− ion and finally to the I− ion in a similar manner as the system of poly(2-vinylpyridine) and iodine. From the values of the Mössbauer parameters the charge or electron populations of the iodine species are calculated, and the arrangements of these species are discussed.
Experimental observations of the effect of an electric field on exciton motion in molecular crystals
Authors: Patel J. S. , Hanson D. M.
Published: February 2003

Phosphorescence measurements of 4,4′-dimethylbenzophenone at 4.2 K are used to obtain information on exciton–photon and exciton–defect interactions. (AIP)
Lattice dynamical calculations on azabenzene crystals: The distributed dipole model
Authors: Gamba Z. , Bonadeo H.
Published: February 2003

Statical and dynamical properties of crystals of benzene and nonpolar azabenzenes have been calculated using a model which includes atom–atom and electrostatic intermolecular interactions. The molecular charge distributions are represented by placing dipoles near the nitrogen atoms and on the C–H bonds; this model reproduces very well the electrical multipoles obtained from ab initio calculations for this series of molecules. The results are in good agreement with experiment, and it is observed that the higher order electrostatic interactions are fundamental for the description of the statics and dynamics of these crystals. The transferability of the intermolecular potential is checked successfully by calculating the properties of crystalline pyrimidine, a polar molecule, not included in the fit.
Dissociative and double photoionization of SF6 in the 75–125 eV region
Authors: Masuoka Toshio , Samson James A. R.
Published: February 2003

Partial cross sections for the singly charged fragments [SFm+(m = 0–5)] and F+ and the doubly charged fragments [SFn2+(n = 0–4)] in SF6 have been measured using a time-of-flight mass spectrometer and synchrotron radiation in the 75–125 eV region. The mass spectrometer collected a constant fraction of all the fragments produced including energetic ones, thus providing true fragmentation yields. The relatively large production rate of double ionization is demonstrated.
Determination of the H–D2 spherically averaged potential and the H–Ne potential from absolute integral cross-section measurements
Authors: Hishinuma Naoshi
Published: February 2003

Absolute integral cross sections for the H–D2 and the H–Ne collisions were measured by means of atomic–hydrogen beam scattering for kinetic energies of the atom of 1.8–330 meV with high accuracy. Realistic potential models which have only two or three adjustable parameters were used for the interpretation of the data in order to remove arbitrariness of interpretation. The best fit potential for H–D2 has a well of depth ε = 2.02 meV at position rm = 3.43 Å, and crosses zero at r0 = 2.99 Å which agrees exactly with r0 obtained by Torello and Dondi from the D–H2 differential cross-section measurements. The best fit potential for H–Ne (ε = 1.46 meV, rm = 3.40 Å, r0 = 2.99 Å) is in good agreement with ab initio potentials calculated by Das et al. The low-energy repulsive part of the best fit H–D2 potential is consistent, in the internuclear distance region of 4a0⩽r⩽5a0, with recent theoretical results of Truhlar and Horowitz for the spherically symmetric term of the H–H2 potential. The best fit H–D2 potential is finally modified in the region of r⩽4.5a0 so that its extrapolation to the short distance region leads to Truhlar and Horowitz’s results for r⩽3.5a0.
Systematic studies on the electrostatic potential at the nucleus and the interelectronic interaction in the atoms and ions
Authors: Teruya Hirohide , Anno Tosinobu
Published: February 2003

Data on the interelectronic interaction energy Vee and the electrostatic potential at the nucleus V0,A, obtained from Clementi’s near Hartree–Fock calculations on various atoms and ions, in the course of our previous work on Politzer’s k for atoms and ions, are systematically examined. It is found that both ΔV0A and ΔVee, the difference in V0A and Vee, respectively, between two successive members on an isoelectronic series of atoms, approach asymptotically to their limits characteristic to the isoelectronic series, when Z →∞. It is shown that this asymptotic behavior can be explained if and only if it is assumed that the screening effect, seen by an outer electron of a given atom, due to inner electrons within that atom, is not constant even for an isoelectronic atoms but depends upon Z or equivalently upon ionic charge.
Linear response theory of the heat of transport of dilute electrolyte solutions
Authors: Kahana Paz Y. , Lin Jeong-long
Published: February 2003

A molecular theory of the heat of transport of dilute electrolyte solutions is developed based on the linear response theory. The calculation is based on the charged square-well (or mound) model of the ionic solution. The effect of the relaxation and electrophoretic forces on the heat of transport is investigated. The limiting slope for the heat of transport obtained in the present theory is discussed in light of the existing theories. Finally, the concentration dependence of the heat of transport predicted by the linear response theory is compared with experimental results of several aqueous 1:1 chloride solutions.
Constant pressure molecular dynamics simulations of the 2D r−12 system: Comparison with isochores and isotherms
Authors: Broughton J. Q. , Gilmer G. H. , Weeks J. D.
Published: February 2003

A simple modification of the microcanonical molecular dynamics simulation permits the calculation of equilibrium and dynamical properties of a system with a predetermined temperature and/or pressure. This method is applied to a two-dimensional array of particles with repulsive r−12 potentials. The scaling property of inverse power potentials provides a direct comparison of data obtained from isochoric, isothermal, and isobaric ensembles. The results are in good agreement, even in the vicinity of the melting transition.
Effect of pressure on molecular conformations. II. T
r
a
n
s–g
a
u
c
h
e equilibrium of 1,2-dichloroethane and 1,2-dibromoethane
Authors: Taniguchi Y. , Takaya H. , Wong P. T. T. , Whalley E.
Published: February 2003

The effect of pressure on the trans–gauche equilibrium of 1,2-dichloroethane in n-hexane solution and of 1,2-dibromoethane in 2-methylbutane and acetonitrile solutions has been measured by the Raman spectrum. The relative integrated intensities of the carbon–halogen stretching vibrations of the two conformers has been taken as a measure of their relative concentrations. The volume change at the trans–gauche transformation for 1,2-dichloroethane is −3.8 ± ∼0.2 and −3.5 ± ∼0.2 cm3 mol−1, respectively, in 20% and 30% v/v solution in n-hexane at 21 °C, and for 1,2-dibromoethane it is −4.5 ± ∼0.7 cm3 mol−1 in 10% and 20% v/v solution in 2-methylbutane and −2.0 and −1.8±∼0.7 cm3 mol−1, respectively, in 10% and 20% solutions in acetonitrile at 21 °C. The contributions to the volume change due to the overlapping of the halogen atoms in the gauche conformation and to the electrostatic effects as represented by the interaction of molecules having dipole and quadrupole moments with a dielectric continuum have been calculated. The calculated and experimental volume changes agree reasonably well.
Effect of pressure on molecular conformations. III. Internal rotation angle in g
a
u
c
h
e-1,2-dichloroethane and g
a
u
c
h
e-1,2-dibromoethane
Authors: Takaya H. , Taniguchi Y. , Wong P. T. T. , Whalley E.
Published: February 2003

It is shown that the internal rotation angle in gauche-1,2-dichloroethane and gauche-1,2-dibromoethane can be determined from the ratio of the integrated anisotropic Raman, or integrated infrared, intensities of the two carbon–halogen stretching vibrations. This theory has been used to determine, from the Raman spectrum, the value of the angles of 1,2-dichloroethane in solution in n-hexane and of 1,2-dibromoethane in solution in 2-methylbutane and acetonitrile, and how they vary with pressure. For 1,2-dichloroethane, the angle decreases at the rate of ∼2° kbar−1, and so the cis conformation should become stable at ∼15 kbar. For 1,2-dibromoethane, overlapping bands restrict the accuracy, but the spectrum is consistent with about the same rate of decrease. For trans- 1,2-dibromoethane, the asymmetric carbon–bromine stretching vibration has a measurable Raman intensity, which can only occur if the molecule is distorted from the exact trans conformation. If all the distortion is attributed to the departure of the internal rotation angle from the ideal value, the root-mean-square deviation is ∼10° and ∼15° in 2-methylbutane and in acetonitrile solution, respectively. The mean-square torque causing the distortion is ∼1.5 and ∼3.4 × 10−3 mdyn2 Å2, respectively. About 1.5 × 10−3 mdyn2 Å2 is presumably due to repulsive forces in both solutions, and ∼1.9 × 10−3 mdyn2 Å2 is due to the electrostatic field of the acetonitrile molecules. The rms electrostatic field at the center of a dibromoethane molecule is ∼0.1 V Å−1. A simple model assuming randomly oriented spherical dipolar molecules predicts a field of about one third of this value.
Direct absorption spectra of higher excited states of jet-cooled monosubstituted benzenes: Phenylacetylene, styrene, benzaldehyde, and acetophenone
Authors: Leopold D. G. , Hemley R. J. , Vaida V. , Roebber J. L.
Published: February 2003

The second π→π* absorption bands of phenylacetylene, styrene, benzaldehyde, and acetophenone cooled in supersonic molecular jets are investigated by direct ultraviolet absorption spectroscopy. New vibronic structure is observed and vibrational assignments are discussed. The most prominent vibronic bands arise from motions centered in the substituent and from substituent-sensitive benzene modes. This contrasts with the spectra of the first π→π* transitions of these molecules, which exhibit structure involving ring-localized motions primarily. The spectra presented here demonstrate the utility of the direct absorption technique in the investigation of higher electronic transitions of jet-cooled molecules.
Optical absorptions and photochemical conversions of paramagnetic defects in KClO3 and KClO4 at 26 K
Authors: Bjerre Nis , Byberg J. R.
Published: February 2003

The optical absorption of KClO3 crystals irradiated with x-rays at 26 K are assigned to paramagnetic defects by correlating the changes in the optical absorption and ESR spectrum observed during annealing and selective bleaching. The polarization of the absorption bands and structure of the defects derived earlier by ESR indicate that three transitions involve charge transfer within the electron-excess defects: [O−,ClO3−]→[O(lD),C1O32−] (∼255nm), [O−,ClO−2]→[O(1D),ClO2−2] (∼ 385 nm), and [O−,ClO2−]→[O2−,ClO2] (∼ 295 nm), whereas transitions at 560 and 360 nm are assigned to charge transfer between ClO3 and an adjacent ClO−3 and to ClO2, respectively. The optical absorption of KClO4 similarly contains a strong band at 252 nm assigned to charge transfer within the electron-excess defects: [O−,ClO−3]→[O(1D),ClO32−]. Bands at 660 and 345 nm are assigned to charge transfer between the hole defect (ClO4)−2 and adjacent ClO−4 and to an internal transition in the ClO2 component of the hole defect [ClO2,O2], respectively. Bands at 430 and 530 nm probably belong to defects with integral electron spin. The charge transfer model is consistent with the observed migration of ClO3 and (ClO4)−2 during bleaching. Moreover, the model allows interpretation of photochemical conversions of the configuration of O− defects in terms of ’’substitution’’ reactions of the type A ’’selection rule’’ observed in the conversions of [ClO3−,O−] defects in KClO4 suggests that the oxygen atom to become O− after the excitation may be determined during the excitation process by the symmetry of the initial configuration. The interpretation of the spectra of O− defects leads to estimates of the electron affinities of ClO−2 and ClO−3: 0.2 and −1.5 eV, respectively.
The effects of symmetry within the local mode picture: A reanalysis of the overtone spectra of the dihalomethanes
Authors: Mortensen O. Sonnich , Henry Bryan R. , Mohammadi M. Ali
Published: February 2003

The overtone spectra of dichloromethane, dibromomethane, and di-iodomethane are measured in the spectral region from 1770 to 850 mμ. The spectra in this region, and the CH stretching fundamentals, are analyzed in terms of a local mode picture. The spectra display the splittings predicted between the symmetrized combinations of local mode states arising from coupling of the two CH oscillators. We calculate the coupling matrix elements directly using a ’’ladder’’ approximation based on the properties of harmonic oscillator wave functions. The validity of this approximation is demonstrated by a comparison to matrix elements of Morse oscillators. Through a direct calculation of the kinetic energy coupling in dichloromethane from the observed bond angle, we show that kinetic energy provides the principal source of coupling in all of these molecules. Differences in overtone spectral structure between the three molecules are attributed to a Fermi resonance involving two quanta of HCH bending. Adiabatic changes in this bending frequency with increased local CH stretching excitation are discussed.
Infrared spectra of anhydrous and hydrated barium nitrite
Authors: Wood D. L.
Published: February 2003

The infrared spectra of crystalline barium nitrite monohydrate and of the deuterium substituted or anhydrous counterparts were investigated at various temperatures up to the melting piont of the anhydride 516 K (243 °C). Samples were prepared as mineral oil mulls, single crystal plates, and oriented polycrystalline sheets and were measured in polarized or unpolarized radiation. In addition to observations of the dehydration occurring near 430 K (167 °C) as temperature is increased and transitions among the three forms of anhydride (I, II, and III) known from x-ray and thermal measurements, a new transition near 348 K (75 °C) in the monohydrate was investigated, and a new, room temperature form of anhydride (IV) was discovered.
ESR study of ṖCl2 radicals produced in a single crystal of PCl3
Authors: Bonazzola L. , Michaut J. P. , Roncin J.
Published: February 2003

ESR spectra of ṖCl2 radicals were studied in single crystals of PCl3 made at low temperature and irradiated with γ rays. The principal values and the direction cosines of the hyperfine and g tensors were determined in the temperature range 25–75 K. The relative signs of the couplings, the modes of motion of the radical, and its location in the matrix were determined from the temperature dependence of the hyperfine tensors.
XeF2 photodissociation studies. I. Quantum yields and kinetics of XeF(B) and XeF(C)
Authors: Black G. , Sharpless R. L. , Lorents D. C. , Huestis D. L. , Gutcheck R. A. , Bonifield T. D. , Helms D. A. , Walters G. K.
Published: February 2003

Photodissociation of XeF2 with synchrotron light pulses (0.3 ns duration) has been used as the source of the XeF(B, C, and D) excited states. The time-resolved profiles of the intensity of the resulting fluorescence have been recorded and partially analyzed. Most of the measurements were made in the strong XeF2 absorption band between 145 and 175 nm. The absorption cross section was redetermined out to 210 nm, with a maximum value of (5.9±0.5)×10−17 cm2 at 158 nm. By comparison with O(1S) signals from N2O photodissociation, quantum yields for XeF B, C, and D state production were determined. Radiative lifetimes of (14±1) and (100±10) ns were found for the B and C states. Rate coefficients for quenching by XeF2 are reported as are those for converting B to C by collision with Ne, Ar, and N2, along with upper limits for quenching of the C state by these gases.
Comment on ‘‘Theory of vibrational overtone line shapes of polyatomic molecules’’
Authors: Deguchi K. , Sado A. , Nishikawa K. , Aono S.
Published: February 2003

Heller and Mukamel’s theory of the line shapes of overtone vibrations in polyatomic molecules is further explored. Local mode interactions are discussed. (AIP)
Piezoelectric K3Ta3B2O12: Crystal structure at room temperature and crystal growth
Authors: Abrahams S. C. , Zyontz L. E. , Bernstein J. L. , Remeika J. P. , Cooper A. S.
Published: February 2003

K3Ta3B2O12 is a new piezoelectric material that crystallizes in the hexagonal system with space group P6̄2m and one formula unit in the unit cell. The lattice constants are a = 8.781 58±0.000 04 and c = 3.899 02±0.000 02 Å at 298 K (λCuKα = 1.540 598 Å). The integrated intensities of a full sphere of reciprocal space, with radius (sin ϑ)/λ?1.15 Å−1, were measured with a CAD-4 diffractometer and resulted in 1050 independent reliable structure factors. The crystal structure was solved by means of Patterson and Fourier series and was refined by the method of least squares, with final agreement factor R = 0.0133. Corner-sharing triads of TaO6 octahedra are stacked along the c axis and are connected by planar BO3 groups. The resulting large trigonally girdled pentagonal prismatic interstices are occupied by the K+ ions. The average Ta–O distance is 1.973 Å in a strongly distorted octahedron. The B–O distance is 1.364±0.004 Å and the average K–O distance is 2.992 Å. The absolute sense of each polar axis has been determined and the piezoelectric d22 coefficient measured as 1.6±0.1 pC N−1. Piezoelectricity has not been detected in the related material K3Nb3B2O12, neither has evidence been found for a quadrupling in the a axis of K3Ta3B2O12 such as is readily observed in K3Nb3B2O12.
Compatibility of the Enskog kinetic theory with hydrodynamics
Authors: Grmela Miroslav , Rosen Robert , Garcia-Colin Leopoldo S.
Published: February 2003

It is proved in this paper that the condition that guarantees the compatibility of the Enskog kinetic theory with equilibrium thermodynamics guarantees also that the hydrodynamic transport coefficients calculated from the linearized Enskog kinetic theory possess the Onsager–Casimir symmetry.
A corresponding states correlation of the homogeneous nucleation thresholds of supercooled vapors
Authors: McGraw Robert
Published: February 2003

The homogeneous nucleation thresholds for a number of vapors are examined in dimensionless corresponding states form. Strong correlations in behavior are observed which are independent of specific nucleation models. In particular, the influence of molecular structure and degree of intermolecular association on nucleation is addressed. Five classes of vapors are included as part of an extensive survey of reported critical supersaturation ratio measurements: simple atomic and molecular vapors of high rotational symmetry, alkane and alkylbenzene vapors, associated vapors (e.g., organic acids), and vapors condensing to associated hydrogen-bonded liquids (e.g., the lower molecular weight alcohols and water). The classical Becker–Döring–Zeldovich nucleation theory is recase in dimensionless form based on empirical relations for the surface tension and density of a simple fluid. Pitzer’s acentric parameter is used to correlate departures from simple behavior for some of the more complex vapors included in the survey. Only those vapors which condense to form strongly associated liquids show a pattern of nucleating at supersaturations less than those of the corresponding simple fluid.
Vibrational dynamics of a simple polymer
Authors: Scherer C. , Naghizadeh J.
Published: February 2003

Equations of motion of a representative polymer (polyethylene) are developed. The chain constraints are implicitly incorporated into the equations through the use of transformation matrices. The final equation has a simple form with a configuration dependent mass tensor. As an example, the low temperature torsional modes of polymers of various lengths are solved and the contribution of these modes to the specific heat is calculated. The theory is suitable for extension for the calculation of dynamical properties such as the torsional diffusion.
Monolayer and multilayer adsorption of water on Ru(001)
Authors: Thiel P. A. , Hoffmann F. M. , Weinberg W. H.
Published: February 2003

The properties of H2O adsorbed on Ru(001) at 95 K have been studied using a variety of techniques. The geometrical properties of the overlayer, deduced from low-energy electron diffraction and electron stimulated desorption ion angular distributions, indicate that layered, hydrogen-bonded clusters of H2O molecules form which have specific orientation with respect to the hexagonal metallic substrate. The vibrational, electronic, and thermodynamic properties of the first two layers of H2O admolecules are distinct from the properties of ice multilayers. At an adsorption temperature of 165 K, only the first two layers adsorb, and the H2O lattice is more ordered than at 95 K, which is an effect analogous to the irreversible vitreous-to-cubic phase transition which occurs at approximately this temperature in bulk ice. Off-specular scattering measurements have resolved overlapping vibrational features with different angular distributions of intensity.
Photoemission study of matrix isolated Cu atoms and clusters
Authors: Schmeißer D. , Jacobi K. , Kolb D. M.
Published: February 2003

Ultraviolet photoemission spectra of Cu atoms and clusters isolated at 7 K in Ar, Kr, and Xe matrices have been measured using He I and He II radiation. For single matrix-isolated Cu atoms, d-level emission around 5.1 eV below EF (9.3 eV below Evac) has been observed in all three matrices. Comparison with respective gas phase data yields a relaxation shift (for the 3d94s1 final state) of about 1.3 eV. For matrix-isolated Cu clusters the emission peak due to d-band emission is independent of the matrix gas, indicating that the relaxation is solely determined by the cluster itself, rather than by the surrounding matrix. In the matrices doped with clusters the emission from the np levels of the noble gas atoms is markedly modified by the dopant. It is shown that the relaxation of the np levels is dominated by the Cu clusters, yielding emission spectra similar to those from physisorbed noble gases.
Kinetics of the Cl–H2 system. I. Detailed balance in the Cl+H2 reaction
Authors: Miller John C. , Gordon Robert J.
Published: February 2003

A well-known problem in chemical kinetics is the observation that the ratio of the measured rate constants for the reactions Cl+H2 and H+HCl apparently does not equal the known equilibrium constant. Previous work has indicated that the difficulty exists in the H+HCl measurements, which were complicated by wall effects and secondary reactions of H. We have measured both rate constants over the temperature range 200–500 K, using a resonance fluorescence–flash photolysis apparatus in which wall effects were insignificant. The ratio of our measured rate constants is in excellent agreement with detailed balance.
Optical detection of photoproducts using a pulsed supersonic molecular beam: Application to intramolecular V ⇄ E coupling in IR laser excited polyatomics
Authors: Watson T. A. , Mangir M. , Wittig C. , Levy Martin R.
Published: February 2003

It is well established that electronic emission often accompanies the IR multiple photon excitation of polyatomic species in the presence of a strong electromagnetic field. We have used a pulsed supersonic molecular beam arrangement to study this phenomenon for the case when propenenitrile is irradiated with the focused output from a TEA CO2 laser. Electronically excited species prepared in this way have long spontaneous emission lifetimes and can therefore be detected, via their emission, downstream from the intersection of the laser and molecular beam axes. By measuring time of flight and angular distributions, we can obtain the center-of-mass recoil velocity distribution of the emitting species. For the case of propenenitrile, the recoil velocity distribution is peaked at 250 m s−1 with a width of approximately 200 m s−1. Details of the multistep dissociation process are discussed, and we conclude that H2 molecular elimination precedes formation of the emitting species, which is either C2HCN or C2CN.
Data correlation analysis applied to electron diffraction
Authors: Holder C. H. , Gregory D. , Fink M.
Published: February 2003

A method of data evaluation is proposed for electron diffraction data whereby nonreproducible systematic errors are taken into account in the determination of the uncertainties. Artificial, computer generated, statistical noise is added to the data. The extent to which noise must be added is evaluated by the correlation coefficient function. Such a degree of noise allows the total standard deviation of the derived structure parameters to be treated as a Gaussian distribution. This method is illustrated by eight sets of data collected for SF6 at electron energies of 54 keV on a counting electron diffraction unit. It is shown that, by addition of a maximum of 0.3% noise to the data, correlation was reduced to insignificance.
Mean amplitudes of vibration of SF6 and intramolecular multiple scattering
Authors: Miller Bruce R. , Fink M.
Published: February 2003

Precise gas phase electron diffraction data for incident electron energies of 43 and 54 keV have been collected for SF6 by counting techniques with emphasis toward a determination of root-mean-squared amplitudes of vibration and as a case study for the necessity of correcting the scattering cross sections for intramolecular multiple scattering. At first, the amplitudes and shrinkage values were found to disagree with predicted values based on spectroscopic results. However, after corrections for the multiple scattering had been applied, the values changed significantly. The new structural parameters obtained are ra (S–F) = 1.5622(7) Å, l(S–F) = 0.0416(5) Å, ra(F–F) (cis) = 2.2094(8) Å, l(F–F) = 0.0604(4) Å, ra(F–F) (trans) = 3.1240(21) Å, and l(F–F) = 0.0551(17) Å. The shrinkage values for the F–F trans distance changed from −0.0003(2) to +0.0018(2) Å due to the corrections and are now in agreement with the spectroscopic values. The success of the modified Glauber approximation warrants an introduction of this formalism into routine structure determination in electron scattering.
Dimer depletion by solute species in free jet expansion
Authors: Yamashita Masamichi , Sano Taeko , Kotake Susumu , Fenn J. B.
Published: February 2003

Mass spectrometric measurements in free jets of argon and carbon dioxide showed that small amounts of various solute species caused large decreases in the terminal concentration of host gas dimers. This dimer depletion by solute species cannot be accounted for by thermodynamic changes in the state of the jet gas, e.g., temperature, pressure, and concentration. Nor can it be explained by conventional kinetic factors such as relative cross sections for collision frequency and energy exchange. The most likely explanation seems to lie in the unique density distribution in free jets which allows the destruction of dimers by two-body processes in the later stages of the expansion after their earlier formation by three-body encounters in the region of high density.
The optical–optical double resonance spectrum of 7Li2 excited by a single tunable cw laser
Authors: Balz J. G. , Bernheim R. A. , Gold L. P. , Kelly P. B. , Veirs D. K.
Published: February 2003

The two-photon excitation spectrum of 7Li2 produced by a single tunable cw dye laser operating between 570 and 650 nm has been observed using ultraviolet fluorescence detection. The spectrum arises from optical–optical double resonance transitions from the X 1Σg+ ground electronic state to the F 1Σg+ and G 1Πg excited states via the A 1Σu+ intermediate state, in which vibrational and rotational relaxation also take place. Using the known molecular constants for these states, a theoretically predicted spectrum was found from which the prominent lines in the experimental spectrum could be assigned. The multiphoton ionization spectrum of Li2, previously observed and interpreted in terms of bound–free–bound triplet absorption bands, can be explained as OODR transitions among the above states followed by photoionization.
Proton NMR study of a discotic columnar mesophase
Authors: Vilfan M. , Lahajnar G. , Rutar V. , Blinc R. , Topic̆ B. , Zann A. , Dubois J. C.
Published: February 2003

The molecular ordering and the dynamics of the isotropic and the discotic columnar liquid crystalline phase of hexapentoxy-triphenylene have been studied by high resolution proton NMR, self-diffusion measurements and spin–lattice relaxation in the laboratory (T1) and the rotating frame (T1ρ). The onset of the columnar ordering is accompanied by the gradual appearance of a short ’’liquid crystalline’’ component in the proton free induction decay (FID) in addition to the long component characteristic of the isotropic phase. The proton T1 is frequency dependent in the isotropic and in the columnar phase. It changes discontinuously at the clearing point at low frequencies where as it is continuous at 270 MHz. An analysis of the possible relaxation mechanisms is presented.
ESR and ENDOR studies of irradiated cysteine HCl: Decarboxylation
Authors: Matsuki Kiyoshi , Nelson William H. , Hadley Joseph H.
Published: February 2003

K-band ESR and ENDOR spectra of irradiated single crystals of L-cysteine hydrochloride monohydrate at 65 K provide evidence for an unstable carbon-centered radical produced by decarboxylation. The unpaired electron is localized in a 2p orbital on the alpha carbon. An α-proton hyperfine coupling with principal values −104.8, −65.4, and −33.1 MHz has been measured. Five β-proton couplings have also been observed, of which three are exchangeable.
Chemical shift scaling in NMR of rotating solids
Authors: DiVerdi J. A. , Opella S. J.
Published: February 2003

An improved version of the chemical shift scaling multipulse cycle is demonstrated that eliminates the dependence of the direction of the axis of precession on the extent of scaling. This prevents the formation of a zero-frequency artifact in the final spectrum. Results from liquid, as well as stationary and spinning solid samples, are described.
Infrared diode laser spectrum of the ν1 band of CF2 (X̃ 1A1)
Authors: Davies P. B. , Lewis-Bevan W. , Russell D. K.
Published: February 2003

The ν1 fundamental band of difluorocarbene (CF2) in its ground electronic state has been investigated using diode laser absorption spectroscopy. Several RQ branches have been assigned and analyzed. The effects of asymmetry doubling become measurably large in Q branches with low K and in RQ3 provide a rigorous test of the assignment. Combined with microwave data for the ground state, the diode laser spectra yield v = 1 rotational constants and the first accurate measurement of the band center: ν1 = 1225.0793(40) cm−1.
Polarized two-photon fluorescence excitation studies of pyrimidine
Authors: Callis Patrik R. , Scott Thomas W. , Albrecht A. C.
Published: February 2003

Two-photon fluorescence excitation studies are reported for pyrimidine (1, 3-diazine) dissolved in a hexane solution at room temperature. Quantitative two-photon absorption strengths for the three lowest electronic absorption bands are measured relative to the benzene B2u ← A1g two-photon transition. The B1(nπ*) ← A1 excitation profile matches the one-photon absorption band closely, indicating an allowed two-photon transition. However, the B2(ππ*) two-photon intensity is vibronically induced by a 1600 cm−1 b2 vibration, even though transitions into this state are formally two-photon allowed. In addition, polarization analysis is used to uncover a new transition in pyrimidine in a region of overlapping absorptions. This new transition is assigned to the lowest A2(nπ*) state. If this assignment is correct, the A2(nπ*), B1(nπ*) splitting is 1.4 eV. Spectroscopic CNDO and INDO calculations of the two-photon absorption strengths are also reported.
Fluorescence spectroscopy of cold and warm naphthalene molecules: Some new vibrational assignments
Authors: Behlen Fred M. , McDonald Daniel B. , Sethuraman V. , Rice Stuart A.
Published: February 2003

The fluorescence excitation spectrum of naphthalene seeded in a supersonic free jet and the single vibronic level fluorescence spectrum of room temperature naphthalene vapor have been used to determine assignments for a number of combination and sequence transitions that were previously unassigned. Our data, when combined with data in the literature, require some changes in previous assignments. The spectroscopic literature on naphthalene and naphthalene-d8 is reviewed and up-to-date tables of vibrational frequencies are presented.
Direct energy minimization of excited singlet states
Authors: Bouscasse Luc , Bouin-Roubaud Danielle , Avignon Thierry , Jaffé H. H.
Published: February 2003

A general method is developed which permits the minimization of the energy of an excited singlet or triplet state. The conditions for energy minimization are obtained without introduction of Lagrange multipliers by a highly concise matrix formulation. The method is applicable to excited states expressed as linear combinations of an unlimited number of singly excited configurations. The method reduces to an iterative system of matrix diagonalizations and is thus equivalent to a pseudoeigenvalue problem. Calculations for the lowest n→π* and π→π* states of thiazole and 2-methylthioimidazole are reported.
A study of the arsenic, black phosphorus, and other structures derived from rock salt by bond-breaking processes. II. Band structure calculations and the importance of the g
a
u
c
h
e effect
Authors: Burdett Jeremy K. , Haaland Peter , McLarnan Timothy J.
Published: February 2003

Band structure calculations based on the extended Hückel method order energetically the 36 arsenic-like structures having the NaCl size unit cell in a way which is compatible with the observed crystal structures. Black phosphorus is the most stable of the 36, and the arsenic layer type is number seven. Energy differences among these structures can be explained by different energetic contributions from syn-, gauche, and anti-arrangements, of both bonded and nonbonded pairs of atoms, and by a destabilization accompanying small bond angles. The order of stability is gauche ≳ anti ≳syn. Lone pair repulsions are important in determining the total energy, but play only a minor role in the relative energies of these structures. The energies ascribed to all these local geometries are compatible with molecular orbital calculations on small molecules and with observed molecular conformations described by the ’’gauche effect.’’
Thermodynamic partial derivatives
Authors: Gilmore Robert
Published: February 2003

A systematic method for computing thermodynamic partial derivatives is described. (AIP)
Laser photodissociation of Na+2
Authors: Kushawaha V. S. , Leventhal J. J.
Published: February 2003

Photodissociation of Na2+ formed by sequential excitation and ionization of Na2 by an Ar+ laser has been studied. Experiments using a single frequency cw dye laser tuned to a D line are also described, and compared to previous multimode experiments. The results of both sets of experiments support our previous hypothesis that Na+ formed in sodium vapor irradiated with light from a cw multimode dye laser tuned to a D line result from photodissociation of incipient Na2+ formed in Na(3p)/Na(3p) associative ionization. (AIP)
Slater transition state calculations of valence electron spin–orbit splitting in atoms
Authors: Sen K. D.
Published: February 2003

The transition state calculations for the valence electron binding energy in Ar, Kr, Xe, Ba, and Hg and Pb are reported. (AIP)
Probabilities of vibration–vibration energy exchange in H 35Cl(2) +H 37Cl(0)→H 35Cl(0)+H 37Cl(2)
Authors: Shin H. K.
Published: February 2003

The vibration-vibration energy exchange in H35cl(2) + H35cl(O) → H35cl(O) + H37cl(2) is calculated by using a model from ref. 8. (AIP)
On the solid–solid phase diagrams of Ar–O2 and Ar–N2 mixtures
Authors: Ahmad S. F. , Kiefte H. , Clouter M. J.
Published: February 2003

The growth of large single crystals of Ar–O2 and Ar–N2 alloys is reported. The crystals were formed under near or quasiequilibrium conditions and it was found that minimum solute concentrations of about 4 1/2% (N2) and 5% (O2) were required in order to produce the hcp phase. Lower concentrations resulted in the fcc phase.
Light scattering studies on the deformation mechanism of liquid crystals under electric and magnetic fields
Authors: Matsuo Masaru , Kakei Kumiko , Nagaoka Yoshie
Published: February 2003

This paper provides theoretical treatments for the deformation mechanism of liquid crystals by the light scattering technique. Several calculations are carried out in two cases. One is the time dependence of the change in light scattering patterns when a rectangular phase of an electric field strength is applied to nematic liquid crystals. The calculated result indicates that the molecular aggregates having rodlike textures have large orientational disorder of optical axes with respect to the rod axis in the absence of an applied field, but, with time, the degree of the disorder tends to decrease and rods orient predominantly in the direction of an electric field. The other is the change in light scattering patterns when a magnetic field is applied to cholesteric liquid crystals. The calculation result is obtained by considering twist angle disorder, reflecting the uncertainty of cholesteric twisting along the screw axis. The calculated results in the two cases are in rather good agreement with the results observed already.
Theory of the effective Debye–Waller factor in neutron scattering from high frequency molecular modes
Authors: Griffin A. , Jobic H.
Published: February 2003

A theory is given of the incoherent scattering cross section from high frequency intramolecular vibrational modes (ωλ) in a molecular crystal. It is assumed that ωλ≫ωD, where ωD is the maxium frequency of the low frequency lattice phonon continuum. It is shown that the scattering from a ωλ mode is proportional to a Debye–Waller factor arising only only from the internal molecular modes, multiplied by Ss(K,ω−ωλ), where Ss(K, ω) is the self-correlation function of the molecular lattice. In the case when the Debye–Waller factor due to the lattice phonons is negligibly small, we show that Ss(K, ω−ωλ) is a Gaussian in ω−ωλ with Doppler broadening due to translational and rotational motion. Our theory is a development of the short-time approximation and explains the unexpectedly strong intensity of the C–H stretching and bending modes recently observed by Jobic, Ghosh, and Renouprez in hexamethylenetetramine (HMT). The present paper gives the theoretical basis for the quantitative interpretation of the high energy intramolecular vibrational spectrum measured by inelastic neutron scattering.
Spectroscopy of the transition state (theory). Emission from ABC‡* in A+BC → ABC‡* → AB+C*
Authors: Polanyi J. C. , Wolf R. J.
Published: February 2003

In this work we present results for a model calculation of emission occurring from the transition state of a reactive collision process. Structure in the computed spectra is related to the dynamics of the collision events and the potential energy surfaces employed in the calculation. (AIP)
Surface enhanced Raman scattering from pyridine adsorbed on cadmium
Authors: Loo B. H.
Published: February 2003

The SER spectrum of pyridine adsorbed on a Cd electrode is compared to that obtained for pyridine on Ag and Hg.(AIP)
Luminescence and energy transfer in EuAl3B4O12
Authors: Kellendonk F. , Blasse G.
Published: February 2003

The emission and excitation spectra of the Eu3+ luminescence and the energy transfer phenomena in single crystals of Gd1−xEuxAl3B4O12 (0<x?1) have been investigated using time-resolved site-selection techniques. In addition, the luminescence properties of single crystals and powders have been compared. The results show that in these compounds there are three major types of Eu3+ sites. Most Eu3+ ions are on the regular crystallographic sites, but a relatively high percentage of these ions are at nonregular (Al3+ and interstitial) sites. The crystals of EuAl3B4O12 show quenching at lower temperatures than do the powder samples. This behavior can be explained with the help of a model which takes into account diffusion-limited migration within the regular Eu3+ system and quenching by transfer to Mo3+ impurities. These impurities are incorporated into the crystals unintentionally during their growth. The concentration quenching in the single crystals is quite strong and can be explained by means of the percolation concept. In the powder samples, however, the concentration and temperature quenching had less influence due to the relatively low concentration of the quenching centers in these samples. In all samples there was evidence of direct transfer from ’’nonregular’’ Eu3+ ions to ’’regular’’ ions. The critical transfer distance was derived.
The luminescence characteristics of 3-hydroxyflavone as a function of pressure and viscosity
Authors: Salman O. A. , Drickamer H. G.
Published: February 2003

The effect of pressure on the emission of 3-hydroxyflavone has been studied in isobutanol, glycerol, and two mixtures of these solvents. Below a viscosity of ∼50 P there is an increase in the fraction of emission from the tautomeric state with pressure. At higher viscosities the fraction of tautomeric emission decreased. At viscosities less than ∼50 P the lifetimes obtained from the two emission peaks were the same, indicating that the two excited states were in equilibrium. At higher viscosities, the lifetimes differed, indicating that the distribution was kinetically controlled. In hexamethylnonane (HMN) only tautomer emission was observed even at very high viscosities; also, only tautomer emission occurs in a rigid polyisobutylene film. A few measurements on 7-hydroxyflavone are briefly discussed.
Conformation space renormalization of polymers. II. Single chain dynamics based on chain diffusion equation model
Authors: Oono Y. , Freed Karl F.
Published: February 2003

A polymer chain configuration space renormalization group method is developed for application to the polymer diffusion equation for a single continuous polymer chain with excluded volume and unaveraged hydrodynamic interactions. The method builds upon our chain configuration space equilibrium formulation which is based on a coarse graining procedure which utilized small chain contour length loop excluded volume interactions to define the renormalization procedure. This approach is generalized to include small loop hydrodynamic interactions within the renormalization scheme. Our coarse graining treatment is combined with the methods of Kawasaki and Gunton, designed to consider dynamical critical phenomena, to provide the chain configuration space renormalization group theory. Calculations are explicitly presented to order ε = 4−d, where d is the dimensionality of space. However, we show that the dynamical exponent can be obtained exactly from a consideration of the general renormalization scheme without the use of any ε expansion. Thus, it is demonstrated within the diffusion equation model that z = d with hydrodynamic interactions present. In the free draining limit z = 2+1/ν where ν is the exponent for the molecular weight dependence of the chain radius. In the non-free draining limit, this value of z justifies the equality of the so-called static and hydrodynamic radii exponents within the diffusion equation model.
Dynamics of helical wormlike chains. I. Dynamic model and diffusion equation
Authors: Yamakawa Hiromi , Yoshizaki Takenao
Published: February 2003

A model, called the discrete helical wormlike chain, is constructed to be suitable for the study of the dynamics of polymer chains, both flexible and stiff. It is a chain of N rigid sub-bodies such that, apart from its location, its configuration may be specified by N sets of Euler angles, each associated with one sub-body, and its equilibrium conformational behavior is almost identical with that of the continuous helical wormlike chain. It is shown that the model can simulate rather well several types of elementary motion of real chains, by evaluating the change in the potential energy caused by each motion. The configurational diffusion equation is then formulated. Following the procedure of Fixman, rigid constraints are imposed on the lengths of sub-bodies (and hence on the total chain length) by setting the components of the flux associated with the constrained coordinates equal to zero through constraining forces, so that the diffusion equation and all configuration-dependent properties may be written in terms of only the unconstrained coordinates, i.e., Euler angles. For the present model, all dynamic properties in the regime of linear response may be expressed in terms of time-correlation functions of the Wigner 𝒟 functions of Euler angles. Thus, formal expressions for them are given along with the formal solution for the Green’s function of the linearized diffusion equation. The eigenvalue problem which arises is also discussed.
Enhanced sensitivity of transient spontaneous Raman scattering in micellar solutions
Authors: Beck S. M. , Brus L. E.
Published: February 2003

A substantial increase in the sensitivity of transient Raman studies of chemical processes in hydrocarbon (hydrophobic) environments can be obtained through the use of aqueous micellar solutions. This increase is demonstrated in detection of the excited triplets of chrysens and anthracene on the nanosecond time scale. In micelles with negative surface groups, excited state ionization is favored and the cation spectra of both aromatics are also observed.(AIP)
Effect of rotational temperature on the glory undulations in the atom–diatom total collision cross section
Authors: Pirani F. , Vecchiocattivi F. , van den Biesen J. J. H. , van den Meijdenberg C. J. N.
Published: February 2003

The effect of the rotational temperature of the O2 molecules on the glory structure in the total collision cross section has been observed for O2–Ar and O2–Kr systems. For O2–Kr the effect has been well characterized by the comparison of the cross sections with those for Ar–Kr system. The cross sections with O2 molecules at a rotational temperture of ∼900 K are close to the atom–atom results, while the cross sections with O2 at low rotational temperature of 10–150 K show a modification of the glory structure due to the anisotropy of the interaction.(AIP)
On the geometry of NaPO3
Authors: Sen K. D.
Published: February 2003

A complete geometry optimization calculations using one ab inito Hartree-Fock method is carried out for one molecular sodium metaphosphate (NaPO3).(AIP)