bluuebunny/crossref_metadata_2025 huggingface dataset:
Picosecond infrared double resonance studies on pentafluorobenzene
Authors: Sharp Richard C. , Yablonovitch Eli , Bloembergen N.
Published: February 2003

Utilizing synchronized 50 ps pulses from two independently tunable CO2 lasers, a pump–probe experiment is performed on pentafluorobenzene. The molecule, which has two infrared active modes accessible to the CO2 laser wavelengths, allows an extensive investigation into the statistical nature of the intramolecular vibrational energy relaxation process. We find discrete state effects, indicated by oscillatory behavior in the time-resolved absorption spectrum, disappear when the molecule is heated into the quasicontinuum. Using the anharmonic redshifting and broadening of the normal mode absorption features in the infrared spectrum as a measure of local temperature, our results indicate rapid equilibration (<50 ps) of absorbed energy among modes, with the final distribution of energy consistent with thermal heating.
Mean spherical approximation for charged hard spheres near a charged hard wall in a neutralizing background
Authors: Badiali J. -P. , Rosinberg M. -L.
Published: February 2003

The distribution of charged hard spheres near a charged surface in a nonuniform neutralizing background is calculated using the integral equation method based on the mean spherical approximation for both bulk and surface direct correlation functions. The contact value of the distribution and the total electric potential drop are given and compared to the exact result. Various possible extensions of the model are discussed.
Molecular dynamics simulation of a bilayer membrane
Authors: van der Ploeg P. , Berendsen H. J. C.
Published: February 2003

We have applied the computer simulation method of molecular dynamics (MD) to a realistic representation of a lipid bilayer, which serves as a model for a biological membrane. The bilayer consists of 2×16 decanoate molecules and is periodic in two dimensions. Interactions include Lennard-Jones, dihedral, and bond angle potentials while bond lengths are constrained. Head groups are confined near the bilayer surfaces by harmonic forces representing their interaction with the water layer. After equilibration, a simulation extending over 80 ps at 300 K was carried out for a head group surface area of 25 Å2. Experimental order parameters are perfectly reproduced. A highly interesting cooperative tilt of the molecules, persisting over several tens of picoseconds, is observed. The molecular plane is strongly correlated with the plane of tilt. The popular kink model for the hydrocarbon chain order and dynamics is not supported. In view of the observed extended spatial correlation, a simulation was also carried out for a bilayer consisting of 2×64 decanoate molecules.
Radiative decay lifetimes and optical excitation functions for the e 3Σ−(v = 2, 3, 4) states of CO
Authors: Paske W. C. , Garrett A. W. , Shadfar S. , Golden D. E. , Twist J. R.
Published: February 2003

The radiative lifetimes and optical excitation functions have been measured for the e 3Σ−(v = 2, 3, 4) levels of CO using pulsed low energy electron impact excitation and delayed coincidence detection. The v = 2, 3, and 4 lifetimes were found to be 4.12±0.14, 4.08±0.29, and 3.73±0.06 μs, respectively. Cascade components were observed to feed all three vibrational levels and these lifetimes were measured to be 13.8±6.5, 11.8±1.3, and 14.9±3.6 μs. The threshold energies of these states are discussed. The optical excitation functions indicated the presence of thresholds above those of the e states which appear to be due to nearby Asundi band vibrational levels ranging from v = 8 to v = 16.
Exact time-dependent wave packet propagation: Application to the photodissociation of methyl iodide
Authors: Lee Soo-Y. , Heller Eric J.
Published: February 2003

We propose a technique for exact wave packet propagation by a straightforward extension of the semiclassical wave packet propagation procedure. This is an efficient method to calculate photodissociation, Raman, and resonance Raman scattering cross sections. It is applied to the photodissociation of CH3I. The potential surfaces for CH3I are those suggested by Shapiro and Bersohn [J. Chem. Phys. 73, 3810 (1980)]. The results that we obtained by this time-dependent approach differs significantly from those of Shapiro and Bersohn, where a time-independent technique is used to calculate the cross sections.
Intermolecular forces via hybrid Hartree–Fock–SCF plus damped dispersion (HFD) energy calculations. An improved spherical model
Authors: Douketis C. , Scoles G. , Marchetti S. , Zen M. , Thakkar A. J.
Published: February 2003

Molecular interactions are partitioned in SCF and correlation energy parts. It is shown that for atomic systems, one can join high quality ’’a priori’’ SCF calculations with a semiempirical estimate of the correlation energy, made using the standard long range multipolar expansion and corrected assuming the 3Σ+u state of H2 as a model (scaling the ’’size’’ of the atomic charge distribution as the ionization potential to the negative 2/3 power) to obtain very good agreement with the available experimental information.
Energy differences using an accurate local density functional
Authors: Jones R. O.
Published: February 2003

The accurate local spin density (LSD) functional of Vosko, Wilk, and Nusair, based on electron gas correlation energies of Ceperley and Alder, has been used to calculate interconfigurational energies for atoms and binding energies for first row diatomic molecules. The description of ionization and sp-transfer energies in first row atoms and of low-lying states in B2 and C2 are better than those obtained with earlier parametrizations. Interconfigurational energies in iron series atoms are essentially unchanged from values obtained using previous electron gas parametrizations. Spin–flip energies using the Xα approximation are uniformly inferior to those given by LSD.
Errors in the Slater transition state method for spin-polarized calculations of localized core levels
Authors: Lamson S. H. , Messmer R. P.
Published: February 2003

In analogy to the Slater transition state method for calculating ionization energies, which takes account of electronic relaxation effects, one may construct an unrelaxed transition state method, which gives Xα ionization energies which are the analog of Koopmans’ theorem ionization potentials of Hartree–Fock theory. As the unrelaxed method is more algebraically tractable, it can be analyzed in detail. Comparisons of unrelaxed transition state energies and unrelaxed Xα total energy differences for LCAO calculations reveal an anomalous error for spin-polarized localized core orbitals. This discrepancy is shown to arise from poor convergence of the series used to derive the transition state energy. Similar discrepancies are shown to exist in relaxed transition state calculations.
An alternative semicontinuum model for the F center in alkali halides
Authors: Marín J. L. , Clark A. , Rodríguez R. , Aceves R. , Cruz S. A.
Published: February 2003

In this paper, we propose a semicontinuum model for the F center ’’alternative’’ to the Simpson semicontinuum and point-ion models, which at present are used to perform calculations concerning various properties of this center. The model mainly assumes the F center to be an electron within a spherical box with penetrable walls. The Schrödinger equation is solved assuming the potential inside the box to be the same as that used by Simpson (corrected by Krumhansl and Schwartz); the Coulombian tail outside the box is not taken into account. The radius of the box is varied in order to fit the 1s–2p transition energy. We have determined for this system the eigenfunctions and energy eigenvalues for the lowest states, as well as the oscillator strength for the F band. The results are in good agreement with those reported in the literature.
Near Hartree–Fock calculation of the H+H2 potential energy surface
Authors: Lewchenko Victor , Hancock Gene C. , Certain Phillip R.
Published: February 2003

The SCF potential energy surface for H+H2 is reported for atom–molecule distances R in the range 2.5–6.0a0 and diatomic bond lengths r between 1.2a0 and 1.6a0. The leading harmonic components V0(R, r) and V2(R, r) are obtained. The SCF energies are estimated to be within 2 meV of the Hartree–Fock limit, while the error in V0 is estimated to range from 0 to 7 meV, due mainly to the neglect of higher harmonic components.
Application of the polarization model to the study of phosphoric acid media
Authors: Stillinger Frank H. , Weber Thomas A. , David Carl W.
Published: February 2003

The polarization model, previously introduced to approximate both intramolecular and intermolecular interactions in water, has been extended to include pentavalent phosphorus. The extension appears to be successful in representing structures of simple compounds of P5+ with O2− and H+. The model has been applied to statistical mechanical study of liquid phospheric acid at 200 C, using the Monte Carlo method of computer simulation for 216-atom systems. Two versions of the simulation have been implemented corresponding to stoichiometrically equivalent but experimentally distinguishable materials: (a) 27 orthophosphoric acid molecules, and (b) a mixture of water and polyphosphoric acid. Pair correlation functions for all types of atom pairs, as well as details of acid dissociation statistics, have been computed for both materials.
Spontaneous electric dipole moments for small particles
Authors: Das Purna C. , Gersten Joel I.
Published: February 2003

The spontaneous electric dipole moments for systems consisting of small particles with or without nearby molecules are obtained theoretically. The study is divided into two parts—homogeneous systems and inhomogeneous systems. Under homogeneous systems we evaluate the dipole moment of a hemispherical jellium shape. Under inhomogeneous systems we evaluate the dipole moment of an atom near a spheriod and the dipole moment of a bimetallic spheriod.
Study of sulfur-containing molecules in the EUV region. II. Photoabsorption cross section of COS
Authors: Wu C. Y. Robert , Judge D. L.
Published: February 2003

Using synchrotron radiation as a continuum background, the absorption cross sections of COS have been measured using a double ion chamber. The cross sections range from 7 to 50 Mb in the 175–760 Å region. The window resonance series VII (and VII′) and IX (and IX′) are tentatively assigned as nsσ and npπ converging to the C̃ 2Σ+ ion state of COS+. A dip at about 846 Å, which possibly corresponds to the n = 3 member of the VII series, is found in the high resolution photoionization curves previously published [Eland and Berkowitz, J. Chem. Phys. 70, 5155 (1979); Ono et al., J. Chem. Phys. 74, 1645 (1981), and Delwiche et al., J. Chem. Phys. 74, 4219 (1981)]. Broad structures observed in the 580–650 Å region may be Rydberg series converging to the highly excited ion states which are yet to be resolved and analyzed.
The effect of randomly distributed surface bumps on local field enhancements in surface enhanced Raman spectroscopy
Authors: Laor Uri , Schatz George C.
Published: February 2003

A model is presented for determining the enhancement of local electromagnetic fields which occurs close to rough metal surfaces through surface plasmon excitation. The model considers a random distribution of metal hemispheroids on a perfectly conducting flat plane. The electrodynamics of this system is described using the long wavelength approximation and with only the dipole coupling between different hemispheroids included. The square of the local field is averaged over all locations on the surface to provide an estimate of the enhancement in Raman intensity pertinent to surface enhanced Raman spectroscopy (SERS). Application is made to rough Ag, Cu, Au, Hg, and Pt surfaces, simulating the roughness produced by electrochemical anodization. For Ag, the roughness induced SERS enhancement is found to be about 102, with a weak dependence on wavelength down to 350 nm, where a sharp drop is observed. The variation of this result on the parameters which characterize the hemispheroid distributions is studied, including the variation with the distribution of hemispheroid heights and widths, with the number and arrangements of hemispheroids on the surface, with hemispheroid dielectric constant, and with hemispheroid coverage. Most of these parameters do not change the overall enhancement factors significantly, although the wavlength dependence of the enhancement does change significantly with hemispheroid coverage. The polarization of the local electric field close to the surface is studied, and found to be primarily perpendicular to the local surface for globally perpendicular applied fields. The SERS enhancement on Cu is found to be comparable to Ag for λ≳600 nm, with a drop in intensity by a factor of 5 at 600 nm. Au is similar to Cu, except that the drop occurs at 500 nm. Hg is similar to Ag in both the magnitude and frequency dependence of the enhancement, while Pt is uniformly smaller throughout the visible. All of these enhancements are ∼103 smaller than is seen experimentally using SERS, although the observed change in SERS intensity due to anodization does closely match the predictions of our model. Overall, we conclude that surface roughness probably contributes 102 to 103 to the overall enhancement with a frequency dependence which is close to that seen experimentally. This conclusion indicates that some other enhancement mechanism must be responsible for the remaining factor of 103 needed to explain the observed overall enhancement of 106.
Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Pt–Ir clusters
Authors: Sinfelt J. H. , Via G. H. , Lytle F. W.
Published: February 2003

The extended x-ray absorption fine structures (EXAFS) associated with the LIII absorption edges of platinum and iridium were investigated for several catalysts consisting of metal clusters of these elements dispersed on silica or alumina. Previous x-ray diffraction studies on silica supported platinum–iridium catalysts containing 5%–20% by weight of platinum plus iridium indicated that these elements were present in the form of bimetallic clusters with sizes in the approximate range of 25–50 Å. The present EXAFS investigation has provided more detailed structural information on such clusters and has extended the scope of the research to include more highly dispersed platinum–iridium catalysts which cannot be investigated satisfactorily by x-ray diffraction. In this way, it has been possible to extend the structural evidence for platinum–iridium bimetallic clusters to the case in which the ratio of surface atoms to total atoms approaches unity.
Crystal field effects in REOBr:Eu3+
Authors: Hölsä Jorma , Porcher Pierre
Published: February 2003

Crystal field parameters (Bkq) were obtained for the REOBr:Eu3+ series (RE = Y, La, Gd) and LaOI:Eu3+ from the analysis of fluorescence spectra. The sets of five nonzero Bkq parameters for the C4v symmetry reproduce the experimental 7FJ Stark level schemes within a few cm−1. The Racah (E0–3) and spin–orbit (ζ) parameters were determined for the REOBr:Eu3+ series with the aid of excitation spectra. Only insignificant shifts were observed in the parameter values along the series. A simulation of the Stark level sequences of excited levels was carried out on a strongly reduced basis set of 2S+LLJM levels. A poor simulation was obtained unless the free-ion wave functions were well defined. A comparison of the crystal field parameters for the whole REOX:Eu3+ series (RE = Y,La,Gd; X = Cl, Br,I) shows an increase in the strength of the crystal field with increasing ionic radius of the RE3+ host cation. A similar pattern prevails in the oxyhalide series from the oxychloride to the oxybromide host. The crystal field effect in LaOI:Eu3+ is practically equal to that in LaOBr:Eu3+.
Chemi-ionization reactions of electronically excited lithium
Authors: Mariella R. P.
Published: February 2003

Chemi-ionization reactions of atomic lithium in the 4 2S1/2 state have been observed with NO2, Cl2, and F2 collision partners in a crossed-beam system. The reaction products have been analyzed with a mass filter to be Li++NO2−, LiCl++Cl−, and Li++F+F−, with reaction cross sections of 0.02, 0.2, and 2×10−16 cm2, respectively.
Nonadiabatic treatment of the intensity distribution in the V–N bands of ethylene
Authors: Petrongolo Carlo , Buenker Robert J. , Peyerimhoff Sigrid D.
Published: February 2003

The V–N band system of ethylene between 6.0 and 8.5 eV has been investigated through ab initio nonadiabatic vibronic calculations. The N1(π2), V1(π,π*), and Ry1(π,3py) electronic states and energies involved in this transition have been calculated as functions of the torsional angle around the CC bond, at an extended CI level and the adiabatic torsional states have been expanded in a free-rotor basis. The nonadiabatic states corresponding to the V and Ry species have then been expanded in the adiabatic electronic–torsional basis with the help of explicit calculations of the vibronic coupling functions. The V and Ry electronic states undergo a sharply avoided crossing and configurational mixing during the torsion and have a significant contribution from (π,ndπ) species, the lower state changing from Ry at D2h to V at the D2d conformation and the upper showing the opposite variation. The V–Ry vibronic couplings are thus quite large in the region of the avoided crossing and the nonadiabatic states above 7.5 eV are strongly mixed; by contrast the lowest-lying species derive mainly from the π→π*V excitation. The computed 0–0 torsional origin at 6.00 eV and the following two levels are in very good agreement with the locations of the first three observed bands, whereas the deviations increase for higher levels in a regular way owing to a small overestimation of the computed ω4′ value; the discrete portion of the V–N system is well reproduced by the present calculations provided a renumbering of the observed bands is undertaken. The nonadiabatic coupling of the V and Ry states is very important near the intensity maximum of the V–N system, yielding a very diffuse intensity distribution in good agreement with the observed broad continuum. A theoretical progression shows two intensity maxima at 7.78 and 8.06 eV, somewhat above that deduced experimentally at 7.66 eV, which has been estimated by subtracting off the intensity of the sharp R 1(π, 3s)–N bands superimposed on the apparent continuum. Numerical tests show that the maximum at 8.06 eV is shifted to about 7.9 eV by taking into account some limitations of the present investigation. Finally, calculated vertical transition energies to various excited states of ethylene, obtained with a large AO basis set indicate that other Rydberg states should have nonadiabatic couplings in the 7.0–8.5 eV region with the electronic species here considered when antisymmetric vibrations are excited, thus leading to a further broadening of the V–N band system; accordingly a vibronically mixed Rx1(π,3px)–V1(π,π*) species is indicated as being the upper state in Wilkinson’s R′–N transition of T0 = 8.26 eV, as has earlier been suggested by various authors.
Energy transfer as a random walk. II. Two-dimensional regular lattices
Authors: Zumofen Gert , Blumen Alexander
Published: February 2003

In this paper, we study the incoherent energy transfer in two-dimensional regular systems where the intermolecular interactions are due to Coulombic and exchange forces. This work follows our treatment for three-dimensional lattices [Blumen and Zumofen, J. Chem. Phys. 75, 892 (1981)], where long-range transfer steps were also taken into account. We analyze the random walk of the excitation for the triangular, square, and hexagonal lattices both analytically and numerically, using series and matrix inversions as well as simulation techniques. We show that in a first passage model the survival probability of a random walker on a lattice with randomly distributed traps is known if the distribution of the number Rn of distinct visited sites is given. The decay law is expressed as a cumulant expansion which involves moments of Rn. The first few moments of Rn are obtained from the numerical procedures; here the simulation is particularly helpful. The determined mean Sn and variance σn2 agree well with analytical asymptotic expressions; we tabulate the results for all lattices and interaction types using convenient analytical forms. Also, the mean number Mn of visits to the origin is given. All results behave smoothly with respect to changes in the interaction range and in coordination number, a fact apparent from a diffusion model which we analyze. From the distribution of Rn, we calculate the survival probability and compare it to approximate forms of current use, thus checking their regions of validity.
Elastic properties of colloidal crystals and glasses
Authors: Lindsay H. M. , Chaikin P. M.
Published: February 2003

We have measured the shear modulus of lattices of charged polystyrene spheres. We describe a simple apparatus used in this study for determining the frequency of standing shear modes. For the monodisperse lattices, crystals form, stabilized by the repulsive Coulomb interaction, producing a classical ’’Wigner crystal’’ characterized by Bragg scattering and finite rigidity. We studied the rigidity as a function of volume fraction and electrolyte concentration for several particle diameters. Mixtures of colloids with different particle diameters form classical ’’Wigner glasses’’ characterized by the absence of long range order and Bragg scattering but the presence of a finite shear rigidity. We have studied the shear properties of these solids as a function of composition and electrolyte concentration.
Conformational changes in supercoiled DNA: 111In-histone as a label for perturbed γ–γ angular correlation studies
Authors: Martin P. W. , El-Kateb S. , Kuhnlein U.
Published: February 2003

Conformational changes induced in superhelical PM2 DNA by addition of the intercalating dye ethidium bromide have been observed by the technique of perturbed γ–γ angular correlations. Using 111In-histone as a probe, rotational correlation times were determined for dye to DNA nucleotide ratios of zero (τc = 8.2±0.6 ns), 5:1 (τc = 2.2±0.2 ns), and 25:1 (τc = 4.9±0.4 ns). These features are related to the superhelical turn density of the molecule. The theoretical fits also indicate the presence of components with shorter time fluctuations (≲1 ns).
The microwave spectrum of isotopically substituted CO+ ion
Authors: Piltch Nancy D. , Szanto Peter G. , Anderson Thomas G. , Gudeman Christopher S. , Dixon Thomas A. , Woods R. Claude
Published: February 2003

The frequencies of the N = 0–1 transitions of C18O+ and 13CO+ have been measured, and those of the main isotopic form have been remeasured. The hyperfine parameters of 13CO+ have been obtained and compared to those previously determined in the laser-ion beam experiments of Carrington et al. The isotopic variations of the spin-rotation parameter γ have been studied, and evidence for breakdown of the Born–Oppenheimer approximation has been observed in the isotopic dependence of the rotational constant B0.
Circular intensity differential scattering of light. IV. Randomly oriented species
Authors: Bustamante Carlos , Tinoco Ignacio , Maestre Marcos F.
Published: February 2003

The theory of circular intensity differential scattering (CIDS) of light by a solution of randomly oriented molecules of arbitrary geometry has been derived. The molecules are treated as a set of polarizability tensors. The CIDS as a function of scattering angle is obtained in closed form. The CIDS depends on the distances and angle between all the polarizabilities in the molecule. Numerical calculations of helices made up of uniaxial polarizabilities, directed along the tangent to the helix, are shown as a function of helix geometry. The calculated values of the CIDS indicate that they should provide a useful, new experimental technique to determine the structures of biomolecular aggregates.
1H and 2H NMR of methanes partially oriented in liquid–crystal phases: Separation of rigid and nonrigid molecule effects
Authors: Burnell E. E. , de Lange C. A.
Published: February 2003

1H and 2H NMR results are presented for methane and its deuterated analogs dissolved in various nematic liquid crystals. Anisotropic couplings observed in CHD3, CH2D2, and CH3D arise partly from the small deviation from tetrahedral symmetry due to the deuterium substitution, and partly from nonrigid molecule effects which give rise to anisotropic couplings in CH4 and CD4. Excellent agreement is obtained with a simple model based on separability and additivity of these rigid and nonrigid molecule contributions. Order parameters for the rigid molecule contribution are positive along the longest and negative along the shortest molecular directions.
Laser-induced fluorescence of CsH (A 1Σ+→X 1Σ+) to levels near the dissociation limit of X 1Σ+
Authors: Ligare M. , Wu Zhen , Bhaskar N. D. , Happer W.
Published: February 2003

A new laser-induced fluorescent doublet of CsH [A 1Σ+(v′ = 19)→X 1Σ+(v\ = vm)] is reported. The final vibrational-rotational levels (v\ = vm, J\ = 9 or 11) are near the dissociation limit of the ground X 1Σ+ state. A comparison of the experimentally observed location and separation of the doublet with recent theoretical predictions is also presented.
Resonantly enhanced two-photon photoionization of NO in an atmospheric flame
Authors: Mallard W. Gary , Miller J. Houston , Smyth Kermit C.
Published: February 2003

Molecular multiphoton ionization experiments are reported for the first time in a flame environment. The resonantly enhanced two-photon photoionization spectrum of NO from 270 to 317 nm in an atmospheric pressure H2/air/N2O flame is essentially identical with respect to both line position and intensity to that which is predicted for the one-photon absorption to the intermediate A state. A model is developed here which accounts for this result by including rates for collisional repopulation of the laser depleted state. Based on this model, the rotational transfer rate constant for NO is estimated to be ⩾4×109 s−1 in the flame, corresponding to a cross section of ∼70 Å2. It is found that the photoionization spectra obtained in this work have far better signal-to-noise and resolution than those reported for NO in flames using laser-induced fluorescence methods and that the estimated detection limit for NO is 1 ppm.
Raman study of pressure effects on frequencies and isotropic line shapes in liquid acetone
Authors: Schindler W. , Sharko P. T. , Jonas J.
Published: February 2003

The Raman line shape of the symmetric C = O stretching band at 1710 cm−1 has been measured in liquid acetone as a function of pressure from 1 bar to 4 kbar over the temperature range from −25 to 50 °C. The experimental data obtained show several unusual features. First, there is a frequency difference 〈δν〉 of about 7 cm−1 between the polarized and depolarized components. Sceond, the isotropic linewidth Γiso decreases with increasing density, in contrast to the opposite trend usually found in other liquids. Third, the second moment M2(V) of the isotropic band appears to decrease with increasing density. The consideration of the experimental linewidth and frequency data leads to a conclusion that intermolecular dipole–dipole coupling between polar acetone molecules are responsible for the observed unusual behavior of 〈δν〉, Γiso, and M2(V).
Chemi-ionization reactions of metastable Ar(3P0,2) atoms
Authors: Golde Michael F. , Ho Yueh-Se , Ogura Hiroo
Published: February 2003

Using a discharge-flow system and the saturation ion-current technique, branching fractions for chemi-ionization of a wide range of reagents by electronically-excited Ar(3P0,2) atoms have been measured. In contrast to excited He and Ne atoms, ionization by excited Ar atoms is in no case the dominant channel, most branching fractions lying in the range 0.1 to 0.4. Significantly lower branching fractions are shown by the three reagents Cl2, Br2, and NO2 with the largest electron affinities. The results are discussed in terms of the charge transfer model for electronic quenching.
Semiclassical approach to spontaneous emission of molecular collision systems: A dynamical theory of fluorescence line shapes
Authors: Lam Kai-Shue , George Thomas F.
Published: February 2003

A dynamical theory of spontaneous emission of molecular collision systems is presented. The theory makes use of specific nuclear trajectories in the time-dependent Schrödinger equation, and hence can be described as semiclassical. Transitions between electronic states are considered. The description of the radiative interaction is effected by photon-dressed electronic states (electronic-field representation) in both the diabatic and adiabatic representations with respect to the field interaction Hamiltonian. In the diabatic representation, one has to deal with two coupled differential–integral equations [Eqs.(21)], whereas in the adiabatic representation, only one [Eq.(75)] is required. The solutions to these equations are sought for using perturbative–interative procedures. It is then found that the diabatic representation, coupled with the stationary-phase approximation, allows an intuitive and pictorial interpretation of the nuclear dynamics involved, but is incapable of providing a tractable computational scheme valid for all frequency regimes. Indeed the stationary-phase approximation is in general only suitable for line-wing regions. The adiabatic representation, on the other hand, yields a unified line-shape expression. The nuclear dynamics in this representation, however, involves motion on complex and nonlocal potentials. An attempt has been made to reconcile this complicated dynamics with the more intuitive approach of a product of Landau–Zener transition probabilities, and also the generalization (to the case involving a quasicontinuum of avoided crossings) of the Miller–George technique of the analytic continuation of classical mechanics.
High resolution absorption and emission spectroscopy of a silane plasma in the 1800–2300 cm−1 range
Authors: Knights J. C. , Schmitt J. P. M. , Perrin J. , Guelachvili G.
Published: February 2003

High resolution infrared absorption and emission spectra have been obtained from an electrical discharge in silane. In addition to extracting vibrational and rotational temperatures for silane itself, emission from the ground electronic state of the free radical SiH is observed and vibrational and rotational temperatures of 2000 and 485 K determined.
Electric properties of negative ions. Dipole hyperpolarizability of the fluoride ion
Authors: Diercksen Geerd H. F. , Sadlej Andrzej J.
Published: February 2003

Hyperpolarizability γ of the fluoride ion is calculated. The calculations were performed using GTO/CGTO basis sets3. (AIP)
Laplace transforms of correlation functions for CARS
Authors: Desiderio Russell A. , Hudson Bruce S.
Published: February 2003

Analytic forms and series representations are presented for Laplace transforms of correlation functions derived from Kubo’s stochastic line shape theory. The absolute squares of these expressions describe CARS line shapes; theory real parts describe Raman line shapes.
Doubly charged cation representation by pseudopotentials and its performance in predicting water–cation interactions
Authors: Ortega Blake I. , Barthelat J. C. , Costes-Puech E. , Oliveros E. , Daudey J. P.
Published: February 2003

SCF calculations for Mg++–H2O and Ca++–H2O systems are carried out within the pseudopotential approach and compared with extended all-electron calculations. Various pseudopotentials are derived from the neutral atom and the monovalent and divalent cations; they are tested in molecular interaction calculations. Their transferability is illustrated by the fact that good agreement with all-electron calculations is obtained in all cases. As an example of the usefulness of the pseudopotential method, we study the intramolecular relaxation of water as it interacts with Mg++ or Ca++.
Pseudopotential SCF–MO studies of hypervalent compounds. IV. Structure, vibrational assignments, and intramolecular forces in IF7
Authors: Bartell Lawrence S. , Rothman Michael J. , Gavezzotti Angelo
Published: February 2003

Ewig’s pseudopotential procedure, applied with a small basis set, yielded a minimum energy structure with D5h symmetry instead of the deformed pseudorotating structure proposed to account for electron diffraction and electric beam deflection experiments. Nevertheless, calculated restoring forces for e\2 displacements were so feeble that a higher quality calculation making the postulated e\2 deformation spontaneous is not at all precluded. Otherwise, calculated molecular characteristics of IF7 closely resembled those deduced from the diffraction and beam experiments, from extended Hückel calculations, and from the simple valence shell electron pair repulsion theory in a repelling points-on-a-sphere (POS) variant. Axial bonds were shorter by 0.05 Å than equatorial bonds, and calculated mean bond lengths exceeded observed ones by only 0.03 Å. Furthermore, the calculated anharmonic coupling of e′1 polar displacements with large-amplitude e\2 puckering vibrations closely reproduced the coupling inferred from experiment. This favorable correspondance between theory and interpretation of experiment was found not to extend to vibrational assignments, however. Instead, the pseudopotential calculations were in suprisingly close agreement with the simple POS and EHT models predicting that equatorial in-plane bends are far stiffer, due to the close lateral contacts, than the other bending modes. None of the six published vibrational assignments had been interpreted on this basis. An alternative assignment was found which is reasonably consistent with both the calculated force field and the observed infrared and Raman spectra. A similar assignment seems appropriate for ReF7. Calculations with and without d orbitals on iodine furnished evidence that the role of d orbitals in hypervalent compounds is less important than it is often considered to be. Neither the second-order Jahn–Teller softening of the e\2 force constants nor the covalent binding of seven fluorines to iodine was found to depend crucially upon valence d orbitals.
Many-body perturbation theory electronic structure calculations for the methoxy radical. I. Determination of Jahn–Teller energy surfaces, spin–orbit splitting, and Zeeman effect
Authors: Bent Gary D. , Adams George F. , Bartram Ralph H. , Purvis George D. , Bartlett Rodney J.
Published: February 2003

Many-body perturbation theory calculations of the electronic structure are reported for C3v and Jahn–Teller distorted conformations of the methoxy radical CH3O. The Jahn–Teller distortion reduces the energy relative to the minimum energy for the C3v structure by −0.64 kcal/mol. Furthermore, the dynamic Jahn–Teller effect reduces the calculated spin–orbit splitting from 78 to 37 cm−1. An analysis of the Jahn–Teller energy surface yields the e mode vibrational frequencies (ν4 = 2314, ν5 = 1066, ν6 = 792 cm−1) and Coriolis coupling coefficients (ζ4 = 0.065, ζ5 = −0.152, and ζ6 = 0.186) for the ground state. The orbital g factor g0 = 0.647 was calculated and used to determine the components of the g tensor for free methoxy and matrix-trapped methoxy. For free methoxy, g∥ = 2.645 and g⊥ = 0; for the matrix-trapped radical, experimental data was used to calculate the splitting 1.7 kcal/mol of the methoxy energy level caused by its site environment. This splitting quenches g∥ to a value of 2.096.
Models for energy transfer in solids. II
Authors: Lawson Christopher M. , Freed Edwin E. , Powell Richard C.
Published: February 2003

The limiting assumptions underlying several of the basic theoretical models of energy transfer between ions and molecules in solids are elucidated and it is shown that in some cases experimental data has been analyzed using a model which is outside its range of applicability. Three examples are given of data that have been interpreted using the model of Yokota and Tanimoto which lie outside the range of validity of this model. In each case, one of three other models is shown to be a valid way to fit the data. In addition, a detailed comparison is made of fitting two sets of data involving energy migration on a random lattice with a Monte Carlo simulation and with Burshtein’s model which involves an average hopping time. It is shown that the assumption of an average hopping time for an exciton migration on a random lattice leads to an error of about a factor of 2 in estimates of the critical interaction distance.
Diffusion and absorption in a medium with spherical sinks
Authors: Felderhof B. U. , Deutch J. M. , Titulaer U. M.
Published: February 2003

We consider particles diffusing in a uniform medium and being absorbed by statistically distributed spherical sinks. We study the average diffusion–absorption equation, as derived to first order in the sink density by multiple-scattering theory. We show that for perfect sinks this equation must be modified to take proper account of instantaneous absorption of particles created inside the sinks.
Molecular motions in lipid bilayers. I. Statistical mechanical model of acyl chain motion
Authors: Pace R. J. , Chan Sunney I.
Published: February 2003

A statistical mechanical model of bilayer membranes is developed, based on the two-dimensional Ising ferromagnet formalism. Definite average geometries are proposed for the acyl chains in the gel and liquid crystalline states, allowing separation of the chain order parameter contributions arising from intramolecular and bulk motions. The model contains no freely disposable parameters, but the thermodynamic predictions are sensitive to the assumed energy difference (Eg) between gauche and trans states in the acyl chain. Best overall agreement (±∼10%) with experimental transition data for C12–C22 lipids requires Eg = 2.57 kJ/mol. Semiquantitative prediction of the effects of cis or trans chain unsaturation on the transition thermodynamics is obtained. Bulk motional order parameters inferred from the model geometry are consistent with reported data for rigid spin probes, and also with the results of a simple liquid crystal treatment of the bilayer. The model provides a rationalization for the apparent failure of lecithins with chains lengths less than 12 carbons to form stable bilayers.
A light scattering study of orientation of liquid–crystalline rodlike textures of poly(γ-benzyl-L-glutamate) in an electric field perpendicular to the direction of sample cell surface by means of saturation electric birefringence method. III
Authors: Matsuo Masaru , Kakei Kumiko , Ozaki Fumihiko , Ogita Tetsuya
Published: February 2003

The orientation behavior of liquid crystalline solutions of poly(γ-benzyl-L-glutamate) (PBLG) in chloroform was investigated with respect to characteristic electro-optical properties of macromolecules using polarizing microscope and small angle light scattering techniques, when an electric field was applied parallel to an incident beam. The birefringence phase exhibited an irregular patchwork of predominantly blue, yellow, and pink regions under cross polars without applying the electric field and the corresponding Hv light scattering was circular. When the field was applied, the brightness of the phase decreased with increasing voltage and the corresponding Hv patterns became a typical X-type characterizing the scattering from rodlike textures. The analysis was made for a model system. In this model system, rods orient randomly in the three-dimensional space in the absence of the electric field, whereas when the electric field is applied, the rods orient predominantly parallel to the electric field. The orientation distribution function of the rods was assumed to be the steady-state orientation distribution function of macromolecules under an electric field which was proposed to investigate electric properties of a dilute solution of rigid macromolecules by O’Konski et al. Thus, the light scattering patterns were calculated as a function of an electric field strength. The calculated results were found to be rather close to the observed ones with a proper choice of parameter associated with the magnitude of the disorder of the optical axes.
Transmission of 0–15 eV monoenergetic electrons through aliphatic and alicyclic hydrocarbon films
Authors: Sanche L. , Bader G. , Caron L.
Published: February 2003

High-resolution electron transmission spectra and their second energy derivatives were measured in thin (∼100 Å) organic films deposited on polycrystalline and single crystal metal substrates. For all compounds investigated (i.e., benzene, pentene, hexane, 1-hexane, trans-2, trans-4-hexadiene, 1,3,5-hexatriene, norbornene, norbornadiene, 1,3-cycloheptadiene, and 1,3,5-cycloheptatriene), these spectra contained broad maxima observable in dc curves and much sharper and less intense features, that were usually only visible in the doubly differentiated spectra (DDTS). The broad maxima were interpreted to result from a convolution of inelastically scattered electron currents that increased the total transmitted current, mainly due to a change in their reflection coefficient at the film-vacuum interface. The sharper features were more difficult to interpret. In hexatriene, norbormadiene, and heptatriene, they could be correlated with gas phase electronic transitions. As previously observed in C6-alicyclic hydrocarbons, this correlation could be achieved by shifting the energy scale of the DDTS relative to the gas phase electronic energy levels. This phenomenon is expected to result from either pronounced structure in the ’’conduction band’’ density of states or the production of electron–exciton complexes. Using a modified Wigner–Seitz model and variational electron wave functions we have shown that electron–exciton complex formation can explain the 2.2 and 0.8 eV shift in energy scale in solid benzene and cycloheptatriene, respectively. In other films of the present series, sharp features could not be correlated to gas phase energy levels and we suggest that they may result from interference effects.
Vibronic absorption spectra of the biphenyl and biphenyl-d10 cations in solid argon
Authors: Puiu A. C. , Andrews Lester , Chupka W. A. , Colson Steven D.
Published: February 2003

Matrix photoionization of biphenyl vapor during condensation at 20±2 K with excess argon produced band systems at 382.8 and 669.4 nm which are assigned to biphenyl cation owing to agreement with earlier radiolysis studies. The bands are blue shifted from photoelectron band differences which indicate structural changes between the molecule and the ionic states in the gas phase or between the gas and condensed phase ionic states. Vibrational fine structure in both absorption systems exhibits appropriate deuterium shifts and correlates with symmetric modes in the Raman spectra of C12H10 and C12D10. The sharper 382.8 nm band system reveals a 1771 cm−1 splitting of this ionic state, presumably a result of inter-ring resonance interactions.
The three-dimensional potential energy surface for the ring-puckering, ring-deformation, and SiH2 rocking vibrations of 1,3-disilacyclobutane
Authors: Killough P. M. , Irwin R. M. , Laane J.
Published: February 2003

The mid-infrared and Raman combination and hot band spectra involving the ring-puckering (ν22), ring-deformation (ν6), and SiH2 in-phase rocking (ν21) vibrations have been analyzed for 1,3-disilacyclobutane in order to determine the ring-puckering energy levels for the ground and excited state of the other two vibrations. The puckering levels are only slightly perturbed in the rocking excited state but substantially altered in the ring-deformation excited state. The parameters of the three-dimensional potential energy function V = a1x41+b1x21+b2x22+ b3x23+c12x21x22+c13x21x2 3, where the subscripts 1, 2, and 3 refer to ν22, ν6, and ν21, respectively, were adjusted in order to obtain the best fit between the observed and calculated frequencies. For the energy level calculations, the Hamiltonian was symmetry factored into eight separate symmetry blocks. The basis functions for the three-dimensional calculation were determined by first solving the one-dimensional problem in x1 and multiplying the resulting eigenfunctions by harmonic oscillator functions in x2 and x3. An excellent correspondence between the calculated and observed frequencies was obtained. The potential surface, which has a barrier to ring inversion of 81 cm−1 and a minimum corresponding to a dihedral angle of puckering of 24.2° provides an accurate representation of the coupling between the puckering and the other two modes. The c12 constant is negative, indicating that ν22 and ν6 are cooperative modes; c13 is positive, showing that the simultaneous vibration of ν22 and ν21 results in a higher potential energy.
On the d bond in ScH
Authors: Bauschlicher Charles W. , Walch Stephen P.
Published: February 2003

Full valence MCSCF/CI calculations are reported for the lowest six states of ScH. All six states arise from the 2D (4s23d1) atomic configuration. The ground state is found to be 1Σ+ and to involve significant d-bond character, while the other low-lying states arise from sp hybrid bonds.
Mechanism of the sound absorption in H2O and D2O liquid water
Authors: Endo Harumi
Published: February 2003

By assuming the dynamical change in water structure as a double relaxation mechanism, we obtained the values of the relaxational and instantaneous thermodynamic parameters. The isobar expansibility (Λ0) as derived by thermodynamic means reduces to an approximate form Λ0 = A+C/VT2 +D/VT3, where V is the molar volume and T the absolute temperature. The quantities A and C/VT2+D/VT3 give the instantaneous part (Λ∞) and the relaxational part (Λr) of the isobar expansibility. The other thermodynamic relaxational and instantaneous parameters can be expressed in terms of Λ∞ and Λr. Assuming two independent relaxtion times, in which the longer one is the time for a framework molecule to reorient and the shorter is the time in transit during the jumping process of a molecule, the related relaxational compressibilities are subdivided into two parts according to the mechanisms. The longer relaxation time has a spread where the ratio of the times for the lower and upper limit is a constant (2) indepedent of temperatures. The spread of relaxation times can be explained by our model based on the dielectric relaxation times.
The cell model for polyelectrolyte systems. Exact statistical mechanical relations, Monte Carlo simulations, and the Poisson–Boltzmann approximation
Authors: Wennerström Håkan , Jönsson Bo , Linse Per
Published: February 2003

Some exact statistical mechanical relations have been derived for polyelectrolyte systems within the primitive model. Using the cell model, the osmotic pressure is determined through an explicit evaluation of the derivative of the partition function. Planar, cylindrical, and spherical systems are considered and for a planar charged wall the contact value theorem [Henderson and Blum, J. Chem. Phys. 69, 5441 (1978)] is obtained as a special case. Analogous relations are derived for the cylindrical and spherical geometries. It is argued that the exact relations can be used as consistency tests for analytical approximations. It is pointed out that one merit of the Poisson–Boltzmann approximation is that the validity of the exact equations is retained. Finally, a simple method is devised for determining the osmotic pressure from Monte Carlo simulations. Results from such simulations are used to assess the accuracy of the osmotic pressure calculated using the Poisson–Boltzmann equation. For monovalent ions, the pressure is overestimated by 10%–50% in the cases studied, while with divalent counterions the error is substantially larger and a discrepancy of one order of magnitude is found.