bluuebunny/crossref_metadata_2025 huggingface dataset:
Quadrupole interactions in chlorides of indium
Authors: Martin P. W. , Dong S. R. , Hooley J. G.
Published: February 2003

With 111In incorporated as a probe into anhydrous powders of InCl, InCl2, and InCl3, time-differential perturbed angular correlation measurements were performed on the 173–247 keV γ–γ cascade in 111Cd. From Fourier analysis of the data information on static electric quadrupole interactions was obtained comprising interaction frequencies, electric field gradient components, and asymmetry parameters. For the trichloride at room temperature the angular correlation is heavily damped and structureless; at T=203 °C InCl3 reveals two static interactions with frequencies ν(1)q =38.8±0.7 MHz and ν(2)q =95.7±2.0 MHz. For InCl2 a single interaction is detected at room temperature, with νq =135.0±1.1 MHz. The α and β phases of InCl are readily distinguished; for the former νq =284.1±2.6 MHz while for the latter at T=167 °C the angular correlation is unperturbed.
Diode laser probes of vibrational excitation in CO2 caused by hot atoms from excimer laser photolysis
Authors: Chu Jack O. , Wood Carol F. , Flynn George W. , Weston Ralph E.
Published: February 2003

Hot H atoms were produced by photolysis of H2S. The CO2 transition 0001→0002 caused by the hot atoms was studied with a very precise laser absorption probe. (AIP)
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3C NMR determination of the in-plane carbon–carbon bond length in graphite intercalation compounds
Authors: Miller Gerald Ray , Poranski Chester F. , Resing Henry A.
Published: February 2003

The 13C NMR spectrum of AsF5 intercalated graphite is shown to be particularly simple when the applied magnetic field is perpendicular to the graphite sheets. Doublets centered on the main resonance are observed. These result from the dipolar interaction with 13C atoms in nearest neighbor positions, next nearest neighbor positions, etc. In this special orientation, the splittings depend only on r−3ij, where rij is the carbon–carbon distance between two atoms in the same sheet. Accurately determined splittings in the 13C NMR spectra of carefully oriented samples of graphite intercalation compounds can, therefore, be utilized to measure in-plane carbon–carbon distances.
Structure and properties of the argon–cyanogen van der Waals complex
Authors: Ebenstein William L. , Muenter J. S.
Published: February 2003

The Ar–NCCN van der Waals complex has been studied by molecular beam radiofrequency and microwave spectroscopy. The complex is T shaped having C2v equilibrium geometry. The Ar to NCCN distance is 3.58(1) Å and the zero point bending amplitude is specified by γav=arc cos<cos2γ≳1/2=5.0(2)°. This is analyzed to give 30 cm−1 for the van der Waals bending frequency. Nitrogen quadrupole coupling for the isolated cyanogen molecule is −4.611(2) MHz. The dipole moment of the complex is 0.0979(1) D.
The structure of NH3–acetylene
Authors: Fraser G. T. , Leopold K. R. , Klemperer W.
Published: February 2003

The microwave spectrum of the weakly bound complex NH3–acetylene has been measured by molecular beam electric resonance spectroscopy. A spectrum characteristic of a symmetric top is observed and the following spectroscopic constants are determined:  The observed spectrum is consistent with an axially symmetric complex in which the acetylene hydrogen bonds to the ammonia with a hydrogen bond length of 2.33 Å.
Calculation of the magnetic hyperfine interaction in the E and X states of iodine with the separated-atom theory
Authors: Pique J. P. , Bacis R. , Broyer M. , Churassy S. , Koffend J. B.
Published: February 2003

Using the separated-atom representation of a molecular state, simple analytic calculations of the magnetic hyperfine interaction in the E and X states of I2 are given. The value of the magnetic hyperfine constant C in the ion-pair state E was found to be strongly dependent on the assumed dissociation asymptote for this state. Comparison with the experimental result clearly shows the correlation of the E state to the 3P2 state of I+. In the ground state X our predicted value for the C constant in the v″=83 level, C83=51 kHz is in good agreement with the measured value C83=59±5 kHz. Thus, the separated-atom theory provides a simple way of evaluating the hyperfine structure of molecular states with respect to their dissociation limits, giving an excellent test of their atomic origin.
Collisional effects on the internal and translational energy distributions of laser-excited and thermally heated SF6 supersonic beams
Authors: Lester M. I. , Casson L. M. , Spector G. B. , Flynn George W. , Bernstein R. B.
Published: February 2003

Collision induced multiple-photon absorption by SF6 of cw CO2 laser radition [P(16) 10.6 μm, 8.5 W] has been carried out inside a transparent, capillary, nozzle beam source. Resonant laser excitation of the gas just upstream of the nozzle exit enhances the internal energy by 0.38 eV molecule−1 over its value at Tnz=290 K. In comparison, simple thermal heating of the nozzle to 544 K, which provides a similar velocity distribution in the supersonic beam to that found with laser irradiation, produces a beam enhanced in internal energy by only 0.03 eV molecule−1. Energies were determined using bolometer, mass filter (or flux meter), and time-of-flight measurements. Laser excitation in the nozzle induces high vibrational temperatures in the beam which cannot be achieved by simple thermal heating of the nozzle. For an assumed Boltzmann distribution of vibrational energy, the ‘‘vibrational temperature’’ of laser excited SF6 increases (from Tnz=290 K) to Tvib=680 K. Tvib for the thermally heated SF6 is always less than the nozzle temperature. The internal energies measured are lower than those predicted using a free-jet isenthalpic expansion equation.
Forces in pseudopotential molecular calculations
Authors: Martins José Luís , Car Roberto
Published: February 2003

The forces derived from the Hellmann–Feynman theory, are calculated for a molecule, using the local density approximation and within the pseudopotential scheme. We show that, in contrast to the general result of all-electrons calculations, the pseudopotential scheme allows us to obtain accurate and reliable forces with a small number of basis functions. Fast convergence in the basis set is crucial for calculations of large molecules. We apply our method to the Na2 molecule and discuss the convergence rate in detail.
Studies of dispersion energy in hydrogen-bonded systems. H2O–HOH, H2O–HF, H3N–HF, HF–HF
Authors: Szczȩśniak M. M. , Scheiner Steve
Published: February 2003

Dispersion energy is calculated in the systems H2O–HOH, H2O–HF, H3N–HF, and HF–HF as a function of the intermolecular separation using a variety of methods. M≂ller–Plesset perturbation theory to second and third orders is applied in conjunction with polarized basis sets of 6-311G** type and with an extended basis set including a second set of polarization functions (DZ+2P). These results are compared to a multipole expansion of the dispersion energy, based on the Unsöld approximation, carried out to the inverse tenth power of the intermolecular distance. Pairwise evaluation is also carried out using both atom–atom and bond–bond formulations. The MP3/6-311G** results are in generally excellent accord with the leading R−6 term of the multipole expansion. This expansion, if carried out to the R−10 term, reproduces extremely well previously reported dispersion energies calculated via variation-perturbation theory. Little damping of the expansion is required for intermolecular distances equal to or greater than the equilibrium separation. Although the asymptotic behavior of the MP2 dispersion energy is somewhat different than that of the other methods, augmentation of the basis set by a second diffuse set of d functions leads to quite good agreement in the vicinity of the minima. Both the atom–atom and bond–bond parametrization schemes are in good qualitative agreement with the other methods tested. All approaches produce similar dependence of the dispersion energy upon the angular orientation between the two molecules involved in the H bond.
A finite-length-dipole model of the double layer in polar, polarizable materials
Authors: Macdonald J. Ross , Kenkel S. W.
Published: February 2003

Because no relatively simple theory exists for the electrical double layer in polar, polarizable material such as an aqueous electrolyte, we develop here and solve in closed form, a semidiscrete lattice gas double layer theory applicable over a range of applied potential difference up to that leading to full dielectric saturation. It considers for the first time in the present context solvent molecules with finite-length permanent dipoles and induced ideal dipoles. The latter dipoles are treated in two distinct ways: semidiscretely or as leading to a continuum background dielectric constant ε∞. We consider statistical averaging of the permanent dipoles in a given layer over all possible orientations and include competition for lattice-site occupancy between ions and solvent molecules self-consistently. Results for the diffuse region with multiple lattice layers and finite ionic concentration will be discussed in subsequent work. Here the full equations are first developed and then specialized for the case of a charge-free molecular monolayer at a metal electrode; they thus apply best to an adsorption situation or to the inner Helmholtz layer region of the full electrical double layer, but their predictions are compared with bulk dielectric constants as well. We present the dependences of various electrical quantities of interest on position across the monolayer and on applied field and permanent dipoles (p.d.), with the monolayer taken between two conducting plates. The semidiscrete treatment of the induced polarizability leads to a ferroelectric Mossotti catastrophe, but that for the finite-length permanent dipoles alone does not. The present work also demonstrates that the finite-length dipole model leads to negligible dielectric saturation, when applied to water molecules, e.g., up to fields larger than those expected to occur in the actual aqueous electrolyte double layer. This surprising result is a direct consequence of the behavior of the finite-length rather than the ideal permanent dipoles assumed in other treatments of the dielectric constant and dielectric saturation.
Electrical double layer forces. A Monte Carlo study
Authors: Guldbrand Lars , Jönsson Bo , Wennerström Håkan , Linse Per
Published: February 2003

Using a novel method the force between two charged surfaces with an intervening electrolyte solution has been determined from Monte Carlo simulations. We find large deviations from the standard Poisson–Boltzmann treatment of the so called double layer force for divalent counterions at high surface charge densities and at short separations. The deviations have two causes: (i) Due to the inclusion of the effect of ion–ion correlations the counterions concentrate more towards the charged wall reducing the overlap between the double layers; and (ii) correlated fluctuations in the ion clouds of the two surfaces lead to an attractive interaction of a van der Waals type. For some realistic values of the parameters the attraction overcomes the repulsive part and there is a net attractive force between similarly charged surfaces. This finding leads to a modification of our conceptual understanding of the interaction between charged particles and it shows that the DLVO theory is qualitatively deficient under some, realistic, conditions.
Coalescent resonances in atom–surface scattering
Authors: Bosanac S. , Micha D. A.
Published: February 2003

Conditions are given under which two resonance poles of the S matrix for atom–surface scattering coalesce into a single pole leading to increased structure in resonance cross sections. The conditions are applied to He–LiF (001) elastic scattering.
Excitation of localized oscillations: The high vibrational overtone spectrum of SF6
Authors: Levene Harold B. , Perry David S.
Published: February 2003

An optical parametric oscillator and photoacoustic detection are used to obtain the vibrational overtone spectrum of 193 K SF6 (g) in the range 2800–4200 cm−1. Ten quaternary combinations and one band of five vibrational quanta 2ν23ν3 are identified. Four bands ν12ν2ν3, ν23ν3, ν13ν3, and 2ν23ν3 exhibit similar absorption contours to 3ν3. Combination bands of the stretching modes (ν1,ν2,ν3) are the dominant features in the spectrum. For these bands, the absorption is attributable to the lowest energy member of the several allowed (F1u) components of each band. The vibrational motion is localized along a single Cartesian axis of the molecule, because of the strong kinetic coupling of vibrations of opposing S–F bonds. The global nature of the SF6 overtone spectrum is reproduced by a model that assumes radiation selectively excites levels according to their degree of local character.
KrF laser excitation of the D(1/2)←X(1/2) transition of XeF
Authors: Helm H. , Jusinski L. E. , Lorents D. C. , Huestis D. L.
Published: February 2003

XeF (Xv″) produced by KrF laser photodissociation of XeF2 is excited by photons of the same KrF laser pulse to XeF(D) and the fluorescence in the XeF (D–X) system is detected. The KrF laser excitation occurs primarily in the 7-1, 8-3, and 9-6 bands of the (D–X) system. The spectrally resolved fluorescence in the (D–X) system show the bound–bound band progressions originating in v′=7, 8, and 9 as well as Condon diffraction bands which result from transitions of XeF(D) into the dissociation continuum of ground state Xe+F. Model calculations for the bound-free transitions demonstrate that the observed diffraction bands are adequately described by transitions in the Dv′→Xfree system. For the vibrational levels v′=7, 8, and 9 they constitute about 70% of the total emission intensity. The quenching rate coefficient for XeF (Dv=9) in collisions with XeF2 is measured to be 5.7±0.8 10−10 cm3 s−1. The radiative lifetime of XeF (Dv=9) is found to be 19.1±0.5 ns.
Photochemistry and kinetics of the O*2–HI system
Authors: Koffend J. B. , Gardner C. E. , Heidner R. F.
Published: February 2003

Rate coefficients of <2×10−17 and (2.7±1.0)×10−14 cm3/molecule s have been measured by flow tube techniques for HI quenching of O2(1Δ) and O2(1Σ), respectively. In a separate experiment, the quantum yields of I(2P1/2) from HI and CF3I photolysis at 249 nm were determined to be (0.65±0.04) and (0.88±0.06), respectively, relative to a quantum yield of 1.0 from the photolysis of n-C3F7I. The quenching rate of I* by HI was determined to be (5.7±1.0)×10−14 cm3/molecule s. Experimental data and modeling results are presented for photolysis of a mixture of O*2 and HI. These data are relevant to consideration of a pulsed version of the chemical oxygen–iodine laser (COIL).
A theoretical study of the interaction of N2 with water molecules. (H2O)n:N2, n=1–8.
Authors: Curtiss L. A. , Eisgruber C. L.
Published: February 2003

A b initio molecular orbital calculations including correlation energy have been carried out on the interaction of a single H2O molecule with N2. The potential energy surface for H2O:N2 is found to have a minimum corresponding to a HOH ⋅⋅⋅ N2 structure with a weak (<2 kcal mol−1) hydrogen bond. A second, less stable, configuration corresponding to a H2O ⋅⋅⋅ N2 structure with N2 bonded side on to the oxygen of H2O was found to be either a minimum or a saddle point in the potential energy surface depending on the level of calculation. The minimal STO-3G basis set was used to investigate the interaction of up to eight H2O molecules with N2. Two types of clusters, one containing only HOH ⋅⋅⋅ N2 interactions and the other containing both HOH ⋅⋅⋅N2 and H2O ⋅⋅⋅ N2 interactions, were investigated for [N2:(H2O)n, n=2–8].
Irreversible thermodynamics of nonlinear transport processes and instability: Application to the current fluctuation phenomena in semiconductors
Authors: Ali Jaleel , Eu Byung Chan
Published: February 2003

The kinetic and irreversible thermodynamic theory for nonlinear transport processes reported previously is applied to study implication of a nonmonotonic entropy production with a specific example of the current fluctuations observed in the GaAs semiconductor. The study shows evidence that there is a connection between the nonmonotonicity in the entropy production and the instability phenomenon observed, which may be generic to nonlinear processes in macroscopic systems. It is proposed that the current fluctuations in GaAs is basically due to a bifurcation phenomenon in the current-field characteristic, as the field strength is increased past a critical value.
Properties of a liquid direct correlation function at melting temperature related to vacancy formation energy in condensed phases of rare gases
Authors: Bhatia A. B. , March N. H.
Published: February 2003

For condensed phases of rare gases, the approximate relation [EV+(1/2)BΩ] =−(kBT[c(r=0)+2]/2)Tm (I) is derived, EV being the vacancy formation energy, B−1 the isothermal compressibility, Ω the atomic volume, c(r) the liquid direct correlation function, and Tm the melting temperature.
Magnetic phase diagram and spin glass behavior of Fe1−xMnxCl2⋅2H2O
Authors: DeFotis Gary C. , Pohl Christoph , Pugh Spencer A. , Sinn Ekk
Published: February 2003

The magnetic phase diagram of Fe1−xMnxCl2⋅2H2O has been determined. A tetracritical point appears to be present at x≂0.74 and T≂2.8 K. The upper paramagnetic–antiferromagnetic phase boundaries exhibit an unusually rapid descent, and the mixed ordered region below the tetracritical point is quite small. Moreover, regions exhibiting spin glass character also occur in the diagram. The unusually complex behavior is presumably due to the unique constitution of this system: A mixture of two antiferromagnets with different periodicities, competing orthogonal spin anisotropies, competing ferromagnetic and antiferromagnetic near neighbor intrachain exchange interactions, and substantial next nearest neighbor antiferromagnetic interchain exchange interactions.
Thermodynamically consistent truncations of distribution function hierarchies. I. General formulation
Authors: Jones Gerald L. , Kozak John J. , Lee Eok K.
Published: February 2003

In this paper we initiate a study of the closure problem in the statistical mechanical theory of fluids, with particular emphasis on the problem of identifying thermodynamically consistent truncations of distribution function hierarchies. Our approach is: (i) to choose an appropriately restricted set of variables for the reduced distribution functions  ρ(n) and to generate corresponding hierarchies; (ii) to retain, for a kth order truncation, all those equations involving only the  ρ(n) with n≤k; and (iii) to choose the truncation for which all these equations can be satisfied simultaneously. In this paper we focus on the problem of identifying self-consistent, third-order truncations for translationally invariant systems. We show that the analytical approach taken provides guidance in the construction of such closures and we comment on the factors involved in implementing numerically a specific choice of closure identified in our study.
Generalized hydrodynamic theory of viscoelasticity
Authors: MacPhail Richard A. , Kivelson Daniel
Published: February 2003

A generalized hydrodynamic treatment of the dynamic behavior of transverse phenomena in a fluid is presented. An attempt is made to describe such phenomena (VH depolarized light scattering, flow birefringence, transverse sound or shear waves and viscous flow) in a consistent manner over a range of temperatures for which the fluid ranges from a low viscosity liquid to an amorphous solid or glass.
Energy transfer from rare-gas Wannier impurity states in rare-gas matrices
Authors: Scott W. F. , Walker W. C.
Published: February 2003

Photoluminescent excitation spectra are reported for matrices of Ar doped with Xe and with N2,O2,NO, or N2O. The spectra give evidence for energy transfer from the Wannier impurity states of Xe to the guest molecules. A measurement of the effective range of energy transfer to NO is reported.
Core-level photoelectron and Auger shape-resonance phenomena in CO, CO2, CF4, and OCS
Authors: Truesdale C. M. , Lindle D. W. , Kobrin P. H. , Becker U. E. , Kerkhoff H. G. , Heimann P. A. , Ferrett T. A. , Shirley D. A.
Published: February 2003

Cross sections and angular-distribution asymmetry parameters were measured directly for C(KVV) Auger electrons and C 1s photoelectrons from CO, CO2, CF4, and OCS, O(KVV) Auger electrons and O 1s photoelectrons from CO and CO2, and S(LVV) Auger electrons and S 2p photoelectrons from OCS using synchrotron radiation. The measurements were made in the photon-energy ranges 270–350, 545–680, and 160–190 eV, respectively. Shape resonances were observed in all of these molecular systems. The cross-section results are compared with previous experimental data obtained by electron energy-loss measurements, electron–ion coincidence results, and photoabsorption studies. The asymmetry-parameter results are the first of their kind for these molecular core levels. The present results are compared with available theoretical predictions obtained from Stieltjes–Tchebycheff imaging techniques, Hartree-Fock static-exchange calculations, and the multiple-scattering method.
Ã 2Σ+ → X̃ 2Πi emission spectrum of the C-fluorophosphaethyne cation FCP+
Authors: King M. A. , Klapstein D. , Kroto H. W. , Kuhn R. , Maier J. P. , Nixon J. F.
Published: February 2003

The Ã 2Σ+ → X̃ 2Πi emission spectrum of FCP+ has been observed in the region 395–485 nm. The cations were produced by electron impact on an effusive beam of FCP molecules. Derived constants are (in cm−1): T0=24 077.7(0.6); A″0=−190.2(0.6) ν1″ =1729(2); ν3″=765(1); ν1′=1866(2); ν3′=817(2). The rotational structure indicates that B′≳B″.
Vibrational predissociation in van der Waals complexes of glyoxal with Ar and Kr
Authors: Halberstadt N. , Soep B.
Published: February 2003

Vibrational predissociation (VP) of glyoxal–Ar and glyoxal–Kr complexes formed in a supersonic expansion has been studied in several vibrational levels of the first excited singlet electronic state S1 (1Au) of glyoxal. Analysis of the fluorescence spectrum, together with lifetime measurements, has shown that VP is in competition with other intramolecular vibrational energy redistribution processes in these systems, as well as intersystem crossing (ISC). Glyoxal–Ar and glyoxal–Kr behave very similarly. In particular, two isomers exist with different dissociation schemes (but similar for the same isomer of Ar or Kr complexes), and Kr does not seem to enhance ISC. A comparison with collisional results is presented. Another interesting result of this work is that 710, a forbidden transition of free glyoxal, was found in the excitation spectrum of complexed glyoxal. The corresponding 7̄01 emission line of the complex was also observed, as well as combination bands. This suggests a strong interaction between mode 7 and one of the van der Waals modes. This interaction is the basis for a simple theoretical model which reproduces the experimental lifetime of the excited complex (7̄2).
Spectral analysis of light scattered by liquid films. I. General considerations
Authors: Joosten J. G. H.
Published: February 2003

This paper deals with dynamic light scattering from liquid films. We have obtained the thermal fluctuation power spectrum of surface waves on films by solving the electrohydrodynamic equations of motion where the interaction forces (electrical double layers repulsion and London–van der Waals attraction) are included in the momentum equation. The resulting power spectrum for the mixed transversal-longitudinal surface waves can be split up into two contributions: a squeezing mode part and a bending mode part. In this paper the general expressions for both modes are discussed for arbitrary film thicknesses and arbitary frequencies in the hydrodynamic regime. When the film is thick the spectrum exhibits the well known two peak structure of a single fluid interface. When the film becomes thin the spectrum consists of three peaks for each mode, i.e., the time evolution of both modes comprises a purely diffusive and a propagating component. It is found that the squeezing mode shows an intense diffusive peak, whereas for the bending mode the propagating peak is strong compared with the diffusive peak.
The scaling principle in classical inelastic collisions
Authors: Ramaswamy Ramakrishna
Published: February 2003

The scaling principle in classical molecular collisions given earlier by DePristo [J. Chem. Phys. 75, 3384 (1981)] is rederived. Using the method of variation of constants in classical mechanics, it is possible to obtain explicit expressions for the collision-mapping function. A variety of related scaling forms are shown to result from this map.
A multichannel quantum defect analysis of diatomic predissociation and inelastic atomic scattering
Authors: Mies Frederick H.
Published: February 2003

Given an NT×NT interaction matrix W∞(R) which describes the dissociation of a diatomic molecule into NT asymptotic atomic channel states, we can generate exact numerical solutions to the close-coupled scattering equations. At total energies E above the highest dissociation threshold we obtain an NT×NT scattering matrix S(E) which defines the asymptotic structure of the NT- fold degenerate multichannel scattering or continuum wave functions. This matrix varies rapidly with energy and is nonanalytic at thresholds. However, based on a multichannel quantum defect analysis (MCQDA) of the coupled equations we find that the numerical S(E) matrix can be made to yield a real, symmetric matrix Y(E) which is analytic in E. This matrix can then be analytically continued across threshold to provide rigorous analytic descriptions of the multichannel diatomic wave functions in the predissociating and bound-state regions of the energy spectrum. Since the extraction of Y(E) is predicated on assigning a reference potential 𝒱γ(R) to each channel, the detailed energy variation of Y(E) is dependent on the choice of potentials. Fortunately, the physics contained in W∞(R) generally dictates an obvious set of reference potentials which usually make Y(E) slowly varying. As E is reduced below threshold we can use Y(E), often well represented as a constant over a wide range of energies, to provide a description of the predissociating molecule, including such observable properties as linewidths, level shifts, and branching ratios. At still lower energies, when all channels are closed, Y(E) offers a complete, nonperturbative description of the configuration interaction between bound electronic-rotational states of the molecule. Although many insights in this paper are provided by a WKB analysis of the reference solutions associated with each reference potential, the MCQDA yields a complete quantum mechanical description of the exact close-coupled wave functions. The quality of these wave functions is limited only by the accuracy of the molecular potentials and interaction matrix elements that are used to construct W∞(R), and by the number NT and specific set of channels we choose to include in the close-coupled theory. The analysis is equally valid when applied to either adiabatic avoided crossings or diabatic curve crossings. More importantly, the formal structure of the close-coupled wave functions dictated by MCQDA yields a rigorous framework for the analysis of strongly interacting continuum, predissociating, and bound state channels without recourse to perturbation theory.
Electric-dipole moment of CaF (X 2Σ+) by molecular beam, laser-rf, double-resonance study of Stark splittings
Authors: Childs W. J. , Goodman L. S. , Nielsen U. , Pfeufer V.
Published: February 2003

The molecular beam, laser-rf, double-resonance technique has been used to measure the electric-dipole moment of the X 2Σ+ (v=0) electronic ground state of CaF. The moment was determined to be 3.07(7) D by measuring the Stark shifts of rf transitions within specified rovibrational states of X 2Σ+.
Velocity modulation infrared laser spectroscopy of molecular ions: The ν1 and ν3 bands of fluoronium (H2F+)
Authors: Schäfer Eckhard , Saykally Richard J.
Published: February 2003

The infrared absorption spectrum of the fluoronium ion (H2F+) has been observed in the gas phase using velocity modulation laser absorption spectroscopy of a H2/HF plasma. Over 300 transitions were measured in the frequency range 3080–3500 cm−1 and assigned to the ν3 and ν1 bands of H2F+. The band centers are 3348.710(20) cm−1 for ν1 and 3334.679(5) cm−1 for ν3. 150 transitions in ν3 have been fit with a least squares procedure yielding rotational constants and centrifugal distortion constants for the ground and first excited ν3 states. The r0 structure of fluoronium has been determined: rH–F=0.968(9) Å; αHFH=113.9(1.0)°.
An all-inclusive solution for the theory of inhomogeneous polymers
Authors: Tagami Yukiko
Published: February 2003

Presented is a new solution for the one-dimensional case of a system of nonlinear equations, derived by Helfand and Tagami, for the analysis of the interface between immiscible polymers. The solution will be useful for the reason that it represents in one form a nonperiodic solution relevant to the description of a mixture of homopolymers and at the same time a new periodic solution pertinent to the problem involving block copolymers.
Quantification of orientational ordering of SF6 in solid xenon matrices
Authors: Jones Llewellyn H. , Swanson Basil I.
Published: February 2003

Relations are derived from which one can estimate the degree of orientational ordering of molecules trapped in low temperature matrices from polarized infrared absorption spectra. Application of these relations to SF6 in xenon matrices is presented.
On the dynamics of polyelectrolyte solutions
Authors: Akcasu A. Z. , Benmouna M. , Hammouda B.
Published: February 2003

A general formalism to study the dynamics of polyelectrolyte solutions is presented. We show in particular that the Berne–Pecora equations for charged pointlike particles are obtained by neglecting the memory function and using the Debye–Huckel potential with the linear approximation exp(−U/kBT)≂1−U/kBT. We generalize Berne–Pecora results by introducing the effect of hydrodynamic interaction. Our calculations show a plasmon mode which corresponds to a nonzero frequency at zero scattering angle.
Equation of state and optical luminosity of benzene, polybutene, and polyethylene shocked to 210 GPa (2.1 Mbar)
Authors: Nellis W. J. , Ree F. H. , Trainor R. J. , Mitchell A. C. , Boslough M. B.
Published: February 2003

Dynamic equation-of-state data for benzene, polybutene, and polyethylene were measured in the shock pressure range 19–210 GPa using a two-stage light-gas gun. Shock-front spectral luminosities were measured for benzene and polybutene using a fast five-channel optical pyrometer. The pressure–volume Hugoniot data above 20 GPa for benzene and polybutene are in agreement with both a statistical mechanics model and a Grüneisen model for shocked hydrocarbons decomposed into a two-phase mixture of carbon in a dense diamond-like phase and hydrogen in the condensed molecular phase. Published Hugoniot data of benzene up to 13 GPa are in good agreement with a model in which benzene retains its C6H6 molecular structure. The measured, effective, radiating temperatures of shock fronts in benzene are substantially lower than the temperatures calculated theoretically assuming thermal equilibrium. This substantial difference suggests that the measured, effective, radiating temperatures are not the chemical equilibrium temperatures behind the shock front for benzene and possibly for polybutene. Chemical equilibrium calculations which include up to 12 species suggest the presence of small concentrations of a few high-molecular-weight species in strongly shocked benzene and polybutene.
Velocity field and self-diffusion in liquid binary mixtures. A generalized Stokes–Einstein relation
Authors: Munakata T. , Kawakatsu T.
Published: February 2003

With the use of a microscopic velocity field and some hydrodynamic approximations a generalized Stokes–Einstein (GSE) relation among the self-diffusion constant Ds, the viscosity η, and the electric conductivity σe is derived for ionic binary mixtures. Our approach, when applied to nonionic binary mixtures of arbitrary molar fraction, gives a GSE relation among Ds, η, and the interdiffusion constant DAB. The self-diffusion constant is calculated from the GSE relation for molten salts and some organic binary mixtures and the results are compared with the experimental ones.
Thermal conductivity at high pressure of solid odd-numbered n-alkanes ranging from C9H2 to C19H4
Authors: Forsman Hans , Andersson Per
Published: February 2003

The thermal conductivity λ has been measured in the temperature range 190–330 K and at pressures up to 1.0 GPa for the various phases of odd-numbered n-alkanes ranging from C9H20 to C19H40. We used the transient hot-wire technique. At 0.03 GPa, the thermal conductivity for the plastic crystal phase was about 0.2 W m−1 K−1 and showed no clear variation with chain length. For all n-alkanes the increase in λ at the liquid→plastic crystal phase transition was about 35%. At low pressures λ increased monotonically with increasing chain length for the low temperature phase. At pressures above 0.5 GPa and at 273 K the λ results of C9H20 and C11H24 indicate that these two substances transform into another, more close-packed, structure than that of the longer odd-numbered n-alkanes.
Length distribution of polyelectrolyte chains in reversible thermodynamic equilibrium
Authors: Dinter Manfred
Published: February 2003

Concentration and temperature dependent equilibrium distribution functions of chain molecules with varying lengths are derived for the special example of dyes by applying the law of mass action corrected by activity coefficients. The polymers, formed by cations, shown strong Coulomb charge influence when short, but approach neutral conditions with increasing lengths due to counterion condensation. Results are compared to data from light absorption experiments on pseudoisocyanine chloride in solution.
Kinetic isotope effects for hydrogen abstractions from n-alkanes by hydrogen atoms in the gas phase
Authors: Fujisaki Noboru , Ruf Amanz , Gäumann Tino
Published: February 2003

Kinetic isotope effects kH/kDfor the reactions H•+n-Cn H2n+2(n-Cn D2n+2) →kH(kD)H2(HD)+Cn H2n+1•(Cn D2n+1•) have been measured using hydrogen atoms produced in the radiolysis of water vapor. The normal alkanes investigated were n-hexane, n-heptane, n-octane, n-nonane, and n-decane. Regardless of the chain lengths of the n-alkanes studied, the results can be expressed within the experimental error with an Arrhenius type equation kH/kD =(0.47±0.03) exp [(9.41±0.21) kJ mol−1/RT] over the temperature range of 363–463 K. The experimental results were compared with theoretical calculations using transition-state theory and the London–Eyring–Polanyi–Sato (LEPS) potential-energy surface. Good agreement between experimental and calculated values was obtained when allowance was made for tunneling effects.
Wave packet dynamics and chaos in the Hénon–Heiles system
Authors: Feit M. D. , Fleck J. A.
Published: February 2003

The evolution of wave packets under the influence of a Hénon–Heiles potential has been investigated by direct numerical solution of the time-dependent Schrödinger equation. Coherent state Gaussians with a variety of mean positions and momenta were selected as initial wave functions. Three types of diagnostics were used to identify chaotic behavior, namely, phase space trajectories computed from the expected values of coordinates and momenta, the correlation function P(t)=‖〈ψ(0)‖ψ(t)〉‖2, and the uncertainty product or phase space volume V(t)=ΔxΔyΔpxΔpy. The three approaches lead to a consistent interpretation of the system’s behavior, which tends to become more chaotic as the energy expectation value of the wave packet increases. The behavior of the corresponding classical system, however, is not a reliable guide to regular or chaotic behavior in the quantum mechanical system.
The chemical kinetics and thermodynamics of sodium species in oxygen-rich hydrogen flames
Authors: Hynes A. J. , Steinberg M. , Schofield K.
Published: February 2003

Measurements of sodium and OH concentrations in ten oxygen-rich H2/O2/N2 flames by respective saturated and low-power laser-induced fluorescence techniques have led to a much improved understanding of the complex flame chemistry of sodium in such oxygen-rich media. Previous interpretations have been shown to be largely incomplete or in error. The one-dimensional flame downstream profiles indicate that the amount of free sodium approximately tracks the decay of H atom and as the flame radicals decay sodium becomes increasingly bound in a molecular form. A detailed kinetic model indicates that the sodium is distributed between NaOH, which is dominant, and NaO2. Concentrations of NaO are very small and NaH negligible. The actual distribution is controlled by the temperature, the oxygen concentration, and the degree of nonequilibration of the flames’ basic free radicals. Na, NaO, NaO2, and NaOH are all coupled to one another by fast reactions which can rapidly interconvert one to another as flame conditions vary. NaO2 plays an indispensable role in providing alternate efficient channels by which NaOH can be produced. Its contribution becomes increasingly important at lower temperatures where the flux through the NaO2 intermediate becomes dominant over that for the direct reaction between Na and H2O. As a consequence, the ratio of NaOH to Na can become enhanced by up to two orders of magnitude at lower temperatures over what might have been expected from the Na+H2O direct reaction alone. The dissociation energy D°0(Na–O2) is established to be 39±5 kcal mol−1 and the value of the rate constant for the Na+O2+M reaction of 2×10−28 T−1 cm6 molecule−2 s−1 for the flame gases. The sodium distribution within the highest temperature, low-O2 flame, in which NaOH is dominant and equilibrated, supports a value of D°0(Na–OH) of 78.9±2 kcal mol−1. The rate constants for several reactions of Na, NaOH, NaO2, and NaO with flame species have been established approximately. An analysis of the total kinetic scheme shows that the chemical fluxes are carried predominantly by four reactions only. These considered alone, reproduce the data surprisingly well. An analysis of the implications of the corresponding large rate constants for the termolecular reaction of the other alkali metals with oxygen suggests that these will undoubtedly show to varying degrees similar behavior to sodium. Values for the bond dissociation energies of the other alkali dioxides are discussed. It appears that in practical combustion systems, even at low temperatures, the conversion of alkali metals to the corresponding hydroxide will not be kinetically constrained and its concentration will be at or in excess of the expected equilibrium value.
T-matrix scaling relations: Necessary and sufficient conditions for the existence of dynamically invariant scaling coefficients
Authors: Eno Larry , Chang Britton , Rabitz Herschel
Published: February 2003

It is well established that a multiplicative in internal coordinates transition operator is a sufficient condition for the existence of dynamically invariant scaling coefficients. Here we show that by defining the dynamical invariance of the scaling coefficients with respect to a Lippman–Schwinger equation of motion, the same multiplicative in internal coordinates transition operator arises as a necessary condition.
A self-consistent eikonal treatment of diabatic rearrangement: Model H++H2 calculationsa)
Authors: Olson John A. , Micha D. A.
Published: February 2003

An eikonal treatment of nonadiabatic reactions, in which nuclear positions and momenta are self-consistently coupled to electronic transition amplitudes in a Hamiltonian formalism, is applied to H++H2 collisions where both electron transfer and nuclear rearrangement may occur. The approach is based on the diabatic electronic representation and uses potential energy surfaces and momentum couplings obtained within the method of diatomics-in-molecules. Equations of motion are obtained for hyperspherical coordinates in a model collinear treatment. Calculations carried out at collision energies 1 eV above the n=4 threshold of H2 illustrate reactive and nonreactive processes, electron transfer, and translational-vibrational energy transfer. Results for total electron transfer probabilities are compared with other calculations within the same model.
Quantum chemistry by random walk: Linear H3
Authors: Mentch Frank , Anderson James B.
Published: February 2003

The random walk method for calculating wave functions and energies of molecular systems is investigated in its application to the H3 system in a symmetric linear configuration (R=1.757 a.u.) matching the expected saddle point for the reaction H+H2→H2+H. Four different types of trial wave functions were examined for the importance sampling method used. A product type of wave function explicitly incorporating interelectron distances and having a simple node structure was found optimum. The calculated total energy is −1.6582±0.0003 a.u. which corresponds to a reaction barrier height of 10.2±0.2 kcal/mol. This energy is slightly lower than the upper bound of 10.28 kcal/mol previously established in variational calculations by Liu and 0.5 kcal/mol above Liu’s estimate of 9.68 kcal/mol as the exact value. The value 10.2 kcal/mol lies at the upper extreme of the range of barrier heights compatible with reaction rates measured experimentally. For the linear asymmetric configuration with R=1.41, 4.33 a.u. the calculated energy is 0.6±0.4 kcal/mol below Liu’s value. Further optimization of node structure for the random walk calculations may (or may not) result in lower values.
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o dipole surfaces, vibrationally averaged dipole moments, and infrared transition intensities for KCN and LiCN
Authors: Brocks Geert , Tennyson J. , van der Avoird A.
Published: February 2003

Using the rovibrational wave functions which have been obtained from ab initio potentials and making analytic fits to the ab initio calculated dipole surfaces, we have evaluated the dipole (transition) moments of KCN and LiCN for several vibrational states (for J=0 and 1). The ‘‘exact’’ rotational transition intensities of the a-type transitions in (triangular) KCN and those of (linear) LiNC and LiCN can be rather accurately reproduced by a rigid rotor model with the vibrationally averaged dipole moments; for the (weak) b-type transitions in KCN this model breaks down, however. Although the bending motions in these cyanides have large amplitudes, the vibrational transition intensities in LiNC and LiCN conform to the harmonic oscillator model. In KCN, where the large amplitudes of the bending modes and their coupling with the K–CN stretch leads to significant anharmonic shifts in the transition frequencies, the harmonic intensity pattern is perturbed by Fermi resonances, for instance, between the stretch fundamental and the second bending overtone. We have also calculated the lifetime for radiative decay of (metastable) LiCN into LiNC: 24 s for the ground state, much less for vibrationally excited states.
Multibody energy components for clusters of water molecules and ice Ih
Authors: Belford David , Campbell Edwin S.
Published: February 2003

Multibody and total nonadditive energy components have been calculated for (H2O)4 to (H2O)48 clusters chosen to determine the effects of different factors upon the interaction, using the water–water potential of Campbell and Mezei. For the first time, the total nonadditive energy of ice Ih has been calculated within the context of this model and cluster results have been used to obtain estimates for the three- and four-body components. The magnitudes of the four-body components for many clusters and for ice Ih have been shown to be in the energy range required for possible effects upon preferred orientations. Comparisons with the triple-dipole dispersion energy have confirmed the greater importance of the induction contribution. When the cooperative reinforcement of the induced dipole fields, hyperpolarizabilities, and field gradients are neglected, the induced dipole energy has been shown to be strictly two and three body. The relative efficiencies of three-body and self-consistent calculations of the induction energy have been determined.
Ground-state properties of alkali dimers and their cations (including the elements Li, Na, and K) from a
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o calculations with effective core polarization potentials
Authors: Müller Wolfgang , Meyer Wilfried
Published: February 2003

Extensive all-electron SCF and valence CI calculations are presented for alkali dimer systems with consideration of intershell correlation effects by use of an effective core polarization potential (CPP), which contains only a single adjustable atomic parameter. High accuracy is obtained for the ground-state spectroscopic constants of the studied molecules. The maximum deviations from accurate experimental data are as follows: 1% or 0.03 Å for Re, 2% or 100 cm−1 for De, 0.5% or 1 cm−1 for ωe, and 0.2% or 100 cm−1 for ionization energies. For experimentally uncertain or unknown values reliable predictions can thus be made. The calculated dipole moments for LiK and NaK agree with experiment to within 0.1%, but for LiNa we obtain a deviation of 8% or 0.036 D. An analysis of molecular core polarization contributions reveals the reasons for some systematic defects in previous pseudopotential calculations.
Theory of transport in dilute solutions, suspensions, and pure fluids. I. Translational diffusion
Authors: Sung Wokyung , Stell G.
Published: February 2003

We develop a microscopic theory of transport for dilute suspensions and solutions in which the dynamics of the solute–solvent (i.e., tagged particle–fluid particle) collision is treated on a level of the Enskog approximation, appropriately modified by the presence of the solvent sea, which is described hydrodynamically. The treatment of the solvent as a continuum using appropriate generalized boundary conditions gives rise to an effective solute–solvent core radius as well as an effective solute–solvent reduced mass. In this paper, we consider translational diffusion of the solute particle of arbitrary size and mass. We derive an analytically simple expression for the coefficient of diffusion, which yields the correct hydrodynamic limit (Stokes–Einstein law). Our expression for self-diffusion DS (diffusion of a tagged particle in a fluid of identical particles) is in excellent agreement with molecular-dynamical results, showing both an increase over the Enskog value DSE at low fluid density as well as a quite precipitous drop at liquid densities (the enhanced caging effect). Our result turns out to be in close agreement with the Stokes–Einstein law for a wide range of solute particle sizes provided the solvent is at liquid density.
Theory of transport in dilute solutions, suspensions, and pure fluids. II. Intrinsic shear and bulk viscosities
Authors: Sung Wokyung , Stell G.
Published: February 2003

We evaluate the intrinsic shear and bulk viscosities of a solution or suspension of hard-sphere solute in a hard-sphere solvent. We use the ideas, developed in the preceding paper, of the generalized boundary condition descriptive of the solute–solvent binary collision in the presence of the solvent treated as a continuum. Via an appropriate choice of the effective core radius and effective mass of the binary collision, we obtain analytically simple expressions that yield the correct hydrodynamic results in the limit K=l/σ11→0 as well as a reasonable approach to the Enskog result when K is large. Here l and σ11 are the mean free path in solvent and size of the solute particle, respectively. Our results also show for the case of a high-density solvent remarkable agreement with hydrodynamic results over a wide range of solute particle size.