bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquids: Surface tension, compressibility, and invariants
Authors: Sanchez Isaac C.
Published: February 2003

A new equation has been dervied which relates the surface tension (σ) to a liquid’s isothermal compressibility (κ) and mass density (ρ). The derivation is based on a generalized square-gradient approximation for the free energy density of a nonuniform fluid. The equation is   σ(κ/ρ)1/2=A1/20=constant   in the normal liquid range. Except for water, A0 is temperature independent for a variety of inorganic, organic, and polymer liquids. Among 50 nonpolar and polar organic liquids, including hydrogen bonding liquids, A1/20 appears to be an invariant with a value of 2.78±0.13×10−4 (erg cm2/g)1/2. Among the diatomic elements (except hydrogen), A1/20 is an invariant with a value of 1.8×10−4. Among the heavy noble elements, A1/20 is an invariant with a value of 1.36×10−4. For the quantum noble elements helium and neon, A1/20=1.0×10−4. The constant A0 is shown to be proportional to a second moment of a direct correlation function. A semiempirical formula has been derived for A0 relating it to the parameters ε0 and σ0 that characterize the pair interaction potential. For a Lennard-Jones 6-12 potential, it is shown that   A1/20=0.26(ε0σ20/M)1/2,   where M is molecular weight. This result combined with the experimental evaluations of A0 implies that the parameter combination (ε0σ20/M) is an invariant for certain classes of molecules. It appears that this surprising observation has never been made before; its physical implications remain unclear.
Phase transition at 538 K in strontium nitrite
Authors: Liminga R. , Abrahams S. C. , Gallagher P. K.
Published: February 2003

A new phase transition at 538 K has been found in Sr(NO2)2 with an entropy gain, on passing from phase II to phase I, of 18.9(9) J mol−1 K−1. On quenching, phase I is metastable to 296 K but reverts on heating to phase II at about 467 K. Phase II is orthorhombic, with lattice constants at 296 K of a=7.5320(8), b=8.1496(9), c=6.4820(8) Å, and four Sr(NO2)2 per unit cell. Thermal expansion coefficients, as given by aT=a296[1+αΔT+β(ΔT)2], are: α(a)=33(4), α(b)=39(3), and α(c)=62(1)×10−6 K−1, β(a)=−119(17), and β(b)=61(13)×10−9 K−2, i.e., the thermal expansion of the a and b axes is nonlinear, that of the c axis is linear. The volume expansion, as given by VT=V296[1+βΔT], is linear with β(V)=123(2)×10−6 K−1. Phase I is cubic with a=7.5752(8) Å at 538 K, α(a)=29(2)×10−6 K−1; crystals of phase I melt at 637 K. The increase in volume at the phase transition is 6.0%. The postulate of threefold positional disorder by the nitrite ions about the cubic body diagonals results in an expected entropy increase of R ln 9=18.27 J mol−1 K−1.
Sphericalization of nonspherical interactions
Authors: Lebowitz Joel L. , Percus Jerome K.
Published: February 2003

A density and temperature-independent spherically symmetric reference potential is constructed for an interacting classical fluid of nonspherical molecules. It annuls the first order correction to the free energy and, in special cases, the second as well. The potential is a limiting form of that used successfully for N2 by Shaw et al., and reproduces numerically the Y4 approximation of Barboy and Gelbart for homonuclear dumbbell molecules.
Raman spectroscopic study of molecular orientation in AgTCNQ thin films
Authors: Kamitsos Efstratios I. , Risen William M.
Published: February 2003

Preferential orientation of TCNQ− units in thin AgTCNQ films, which were prepared by thermal treatment of vapor-deposited materials on various substrates, is demonstrated by laser Raman spectroscopy. The polarization dependence of Raman intensities in four scattering arrangements have been obtained by varying the polarization direction of the incident light. The experimental results for Raman intensities as a function of substrate orientation are compared with those predicted for films with TCNQ− units with various postulated types of orientation relative to the substrate and to each other, and also compared with those obtained from AgTCNQ solution. The data show that AgTCNQ thin films are characterized by preferred orientation of the TCNQ− units relative to the substrate at an angle θ≂45°. The lack of other orientation in the sampled region is taken to indicate that there are many relatively small domains, within each of which θ≂45°, which are not oriented with respect to each other.
Energy transfer in surface enhanced luminescence
Authors: Wokaun A. , Lutz H.-P. , King A. P. , Wild U. P. , Ernst R. R.
Published: February 2003

Radiationless energy transfer from excited dye molecules to silver islands has been studied. The dye is separated from the metal surface by a thin layer of SiOx. When the spacer layer thickness is increased from d=0, an increase in the luminescence intensity is observed. For the low quantum yield dye Basic Fuchsin, a maximum luminescence enhancement of 200 is observed at dSiO≂25 Å, relative to dye on an inert substrate. With further increase in spacer thickness, the luminescence intensity drops rapidly toward the unenhanced value. The results are interpreted in terms of competition between local field enhancement and loss of excitation by energy transfer to the metal.
Ab initio Hartree–Fock calculation of the elastic electron scattering cross section of sulphur hexafluoride
Authors: Pulay Péter , Mawhorter R. J. , Kohl D. A. , Fink M.
Published: February 2003

The ab initio Hartree–Fock calculation of the elastic electron scattering cross section of sulphur hexafluoride is reported. The integrals for the Born scattering amplitudes have been evaluated by a new simple technique, based on Gaussian quadrature. Spherical averaging was performed numerically; different techniques for spherical averaging are discussed. An estimated re structure was used and vibrational effects have been neglected. In order to assess the effect of the basis set on the intensities, calculations have been performed for the nitrogen molecule with six different basis sets. Using these results as a guide, a triple-zeta basis set, augmented with polarization functions and diffuse functions, was selected for SF6. The results confirm Bartell’s hypothesis that the observed residuals from the independent atom model intensities are due to electronic bonding effects. It is suggested that, for very accurate electron diffraction work, the effect of electron redistribution has to be taken into account by ab initio calculations.
Infrared gas phase intensity measurements. Polar tensors and effective charges of cis-dichloroethylene-d and d2
Authors: Hopper M. J. , Overend J. , Ramos Mozart N. , Bassi A. B. M. S. , Bruns Roy E.
Published: February 2003

The gas phase fundamental intensities of cis-dichloroethylene and its dideuterated modification have been measured. Isotopic invariance, the G sum rule and the results of molecular orbital calculations have been used to select preferred experimental values for the dipole moment derivatives and polar tensor elements of these molecules. The F sum rule has been used to determine individual intensity values of the ν4, ν12 overlapped band system of the dihydrogen molecule. Values of the polar tensor elements for cis dichloroethylene are compared with those previously determined for cis-difluoroethylene. The hydrogen effective charge values in these molecules are essentially identical (0.17 and 0.18e). The polar tensor of cis-dichloroethylene is used to predict the vibrational intensities of trans-dichloroethylene.
Polarized infrared spectra of oriented polycrystalline films. Intermolecular vibrational coupling in crystalline 2,4,6-tribromoaniline
Authors: Jaiswal R. M. P. , Katon J. E. , Tripathi G. N. R.
Published: February 2003

Highly oriented crystal films of 2, 4, 6-tribromoaniline have been grown on cesium iodide substrates and their polarized infrared spectra recorded. In addition, the infrared and Raman spectra of this compound have been measured on bulk solid and solution samples. The factor group splittings arising from the intermolecular vibrational couplings in the crystal have been resolved and assigned and the crystal spectra correlated with the ‘‘isolated molecule’’ spectra according to their various symmetries. The interplane angle of the NH2 and phenyl groups is estimated as about 46° in the crystal. An earlier vibrational assignment has been modified to be consistent with the new experimental data obtained.
Photodissociation of bromine azide
Authors: Coombe R. D.
Published: February 2003

Bromine azide was photodissociated by using excimer laser sources at 222 and 308 nm. The primary fragments produced are N2(A 3Σu+) and NBr(X 3Σ−), with some N2(B 3Πg) produced at 222 nm. In contrast to analogous experiments with ClN3, NBr(b 1Σ+) was not observed. From the formation of these products, it is concluded that the heat of formation of BrN3 is greater than 122 kcal/mol. The N2(A 3Σu+) produced by photodissociation decays by a combination of pseudo-first order and second order processes. The first order process is reaction with the parent BrN3, generating N2(B 3Πg) as a product. The rate constant for N2(A 3Σu+) quenching by BrN3 is 1.2±0.2×10−12 cm3 molecule−1 s−1. This first order process dominates for photolysis at 222 nm. The second order process involves reaction of N2(A 3Σu+) with another photodissociation fragment, and produces intense emission in the vicinity of 292 nm. This emission has been tentatively identified as the D′(3 Π2g) → A′(3 Π2u) transition in Br2. The second order process is much more important in the decay of N2(A 3Σu+) produced by photolysis at 308 nm.
Solid state effects in the electronic structure of TiCl4 studied by XPS
Authors: Mousty-Desbuquoit Christine , Riga Joseph , Verbist Jacques J.
Published: February 2003

High resolution x-ray photoelectron spectra of TiCl4 have been obtained in the solid state. Core levels, their shape-up satellites and valence levels are described and discussed in detail. From comparison with gas phase XPS data, UPS spectra, and theoretical models from the literature, emerge specific characteristics of this molecular solid. Special attention is paid to peculiarities of chlorine orbitals, which are discussed in the light of similar data for organic and inorganic chlorides.
Discrete variable theory of triatomic photodissociation
Authors: Heather R. W. , Light J. C.
Published: February 2003

The coupled equations describing the photodissociation process are expressed in the discrete variable representation (DVR) in which the coupled equations are labeled by quadrature points rather than by internal basis functions. A large reduction in the dimensionality of the coupled equations can be realized since the spatially localized bound state nuclear wave function vanishes at most of the quadrature points, making only certain orientations of the fragments important in the region of strong interaction (small separation). The discrete variable theory of photodissociation is applied to the model dissociation of bent HCN in which the CN fragment is treated as a rigid rotor. The truncated DVR rotational distributions are compared with the exact close coupled rotational distributions, and excellent agreement with greatly reduced dimensionality of the equations is found.
Propensity rules in rotationally inelastic collisions of diatomic molecules in 3Σ electronic states
Authors: Alexander Millard H. , Dagdigian Paul J.
Published: February 2003

The formalism for the treatment of rotationally inelastic collisions of molecules in 3Σ electronic states is exposed, for the general case of intermediate coupling. The reduced matrix elements of the T operator are expressed in a Hund’s case (a) basis. Within the infinite-order-sudden (IOS) limit, the symmetry of the reduced T-matrix elements and the large-J limit of certain vector coupling coefficients can be used to derive several propensity rules bearing on changes in the Fi(i=1–3) label. In particular, for large J only the Fi conserving transitions will have large cross sections. From a physical viewpoint this propensity rule implies that the scattering, at least in the IOS limit at large J, is independent of Σ, the spin projection quantum number. The experimental study by Caughey and Crosley [J. Chem. Phys. 71, 736 (1979)] of rotational relaxation in the B 3Σu− state of S2 confirms our theoretical propensity rules, although the experimental rate constants for the F1 → F2, F3 transitions are considerably larger than would be predicted theoretically.
Quantum mechanical rate constants for bimolecular reactions
Authors: Miller William H. , Schwartz Steven D. , Tromp John W.
Published: February 2003

Several formally exact expressions for quantum mechanical rate constants (i.e., bimolecular reactive cross sections suitably averaged and summed over initial and final states) are derived and their relation to one another analyzed. It is suggested that they may provide a useful means for calculating quantum mechanical rate constants accurately without having to solve the complete state-to-state quantum mechanical reactive scattering problem. Several ways are discussed for evaluating the quantum mechanical traces involved in these expressions, including a path integral evaluation of the Boltzmann operator/time propagator and a discrete basis set approximation. Both these methods are applied to a one-dimensional test problem (the Eckart barrier).
On nonadiabatic transitions and the Wigner path integral
Authors: McLafferty Frank
Published: February 2003

We continue our study of dynamics in terms of the Wigner path integral. We investigate how nonadiabatic electronic transitions are described in the formalism. We find, using the approximation of Miller and George for the reduced propagator, and the classical path approximation for the nuclear degrees of freedom (i.e., assuming nuclear localization), that the Wigner path integral leads to a Tully–Preston surface hopping model. We discuss the relation of this result to general classically forbidden processes and to the dynamics of molecular systems in intense laser fields.
Electric and magnetic field effects in the infrared multiphoton dissociation of CF3D
Authors: Gozel P. , Braichotte D. , van den Bergh H.
Published: February 2003

The effect of static electric and magnetic fields on the infrared multiphoton dissociation (IRMPD) yield of CF3D is investigated in the range 0–4.3 kV cm−1 and 0–17.3 kG. The applied static fields can induce increases in the reaction yield of up to a factor of 5 at moderate energy fluences in the essentially collision free dissociation. These enhancements in the yield are ascribed to the breakdown in the angular momentum selection rules in the electric and magnetic fields. For all cases considered, the field effects are independent of the orientation of the laser beam polarization relative to the direction of the applied electric and magnetic fields. At somewhat higher pressures, where collisions enhance the reaction yield, lower yields are observed in the 17.3 kG magnetic field than in the magnet’s residual field of about 100 G. This effect is tentatively attributed to a decrease in collisional energy transfer rates in the applied magnetic field. The measurements on the magnetic field effect are completed with some new results on the IRMPD of CF2HCl. Possible IR spectral changes induced by a 5 kV cm−1 field in CF3D, CF3H, and CF2HCl are investigated at a resolution of 0.06 cm−1.
Adiabatic molecular properties beyond the Born–Oppenheimer approximation. Complete adiabatic wave functions and vibrationally induced electronic current density
Authors: Nafie Laurence A.
Published: February 2003

The conceptual and mathematical basis for describing adiabatic molecular behavior beyond the Born–Oppenheimer (BO) approximation is presented. The traditional nonadiabatic corrections to the BO approximation are shown to contain a kinetic energy induced adiabatic part and a complete nonadiabatic, or diabatic, part. The lowest order contributions to the new adiabatic terms can be described as momentum adiabatic and are complementary to the traditional BO position adiabatic terms. A complete adiabatic wave function comprised of contributions involving position and momentum is obtained that provides a complete description of the response of the electron probability density to the dynamics of the nuclear motion. This response is comprised of nuclear momentum induced electronic current density and nuclear displacement induced electronic charge flux density for all points in the Cartesian coordinate space of the molecule. These nuclear induced charge fluxes and currents are shown to obey an equation of continuity for the conservation of electronic charge. Relations between the position and velocity formulations of infrared absorption intensity and the charge fluxes and currents are provided.
Bistability and hysteresis in laser-driven polyatomic molecules
Authors: Yuan Jian-Min , Liu Erning , Tung Mingwhei
Published: February 2003

A model for multiphoton excitation of a polyatomic molecule by an IR laser derived by Narducci, et al. has been analyzed by using bifurcation theory. The steady state surface formed by plotting average vibrational excitation vs laser frequency and field amplitude takes the shape of a cusp catastrophe. Linear stability analysis for a wide region in the parameter space shows that the upper branch is always stable and the middle branch unstable. The lower branch is stable for small λ (the ratio of the longitudinal relaxation time to the transverse one). But for large λ the lower branch loses stability as laser intensity increases. Analysis according to Hopf’s theorem shows that the bifurcation point is subcritical. Unstable limit cycles around the birfurcation point are found by both perturbation analysis and numerical calculations. Isotope selectivity, red-shiftedness of the optimal frequency and threshold phenomenon observed in IR multiphoton excitation of molecules can be explained in terms of this model. Practical importance of molecular bistable and hysteretic properties concerning memory devices and vibrational relaxation studies are discussed.
Static and dynamic behavior of the vortex–electrohydrodynamic instability in freely suspended layers of nematic liquid crystals
Authors: Faetti S. , Fronzoni L. , Rolla P. A.
Published: February 2003

The vortex–electrohydrodynamic instability occurring in thin freely suspended layers of some nematic liquid crystals is investigated. The vortex pattern is observed both in the anisotropic and in the isotropic phase of the nematic liquid crystal. In this paper, we study the behavior of the vortex pattern when dc and ac electric fields are applied parallel to the free surfaces. The threshold electric field of the instability is measured as a function of the temperature, the thickness and the electric conductivity of the sample. In order to explain the main features of the vortex regime, we develop a new isotropic electrohydrodynamic model based on surface electric forces, which shows a satisfactory agreement with the experimental results.
An iterative scheme for the evaluation of discretized path integrals
Authors: Thirumalai Devarajan , Bruskin Eric J. , Berne Bruce J.
Published: February 2003

A simple iterative scheme which greatly facilitates the evaluation of discretized path integrals is presented. The method is applied to study the motion of a proton in a bistable potential and the resulting configurational distribution function is compared to both the path integral Monte Carlo calculation and to the ‘‘exact’’ result. As a second illustration we present calculations of the radial distribution function for an Ar2 van der Waals dimer at two temperatures.
The steady-state shear viscosities of some chloropentanes
Authors: Berberian John G.
Published: February 2003

The steady-state shear viscosities of 3-chloromethylpentane, 3-chloropentane, and 3-chloro-3-methylpentane are presented as a function of temperature. The temperature range of the measurements is from 128 to 99 K; the range of viscosities measured is from 2.98×103 up to 2.16×1011 Pa s.
Equilibrium properties of a hard-disk fluid via the hypernetted chain integral equation theory
Authors: Sainger Y. S. , Sinha S. K. , Singh Y.
Published: February 2003

Quantum corrections to the radial distribution function (RDF) and thermodynamic properties for a hard-disk fluid in the semiclassical limit are calculated by means of perturbation method using the extended hypernetted-chain integral equation theory. Numerical results are given for the first order correction to the RDF and for the first and second order corrections to the free energy and equation of state. It is found that quantum effect increases with density and makes the qualitative difference to the RDF near the hard core.
The microwave spectrum of an unstable molecule: Chloroketene ClHCCO
Authors: Gerry M. C. L. , Lewis-Bevan W. , Westwood N. P. C.
Published: February 2003

The microwave spectra of four isotopic species of the unstable molecule chloroketene ClHCCO have been observed from the flow pyrolysis of monochloroacetyl chloride and from the pyrolytic reaction of dichloroacetyl chloride with zinc metal. The spectra, which consist only of b-type transitions, were observed in the frequency range 26.5–80 GHz. Accurate rotational constants and quartic and sextic centrifugal distortion constants have been obtained for all isotopes. Large numbers of perturbations have been observed in the chlorine quadrupole hyperfine structure; consequently, the complete quadrupole coupling tensor has been evaluated. The dipole moment has been measured. The molecule has been shown to be planar, and a partial r0 structure has been determined.
Kinematic effects as revealed by two-photon spectra of isotopic benzenes in a supersonic beam
Authors: Rava Richard P. , Philis John G. , Krogh-Jespersen Karsten , Goodman Lionel
Published: February 2003

Two-photon spectra of the 1B2u ← 1A1g transitions of s-C6H3D3, p-C6H4D2, p-C6H2D4, m-C6H4D2, o-C6H4D2, and C6H5D have been recorded in supersonic beam–multiphoton ionization experiments. Harmonic mode scrambling principles using Robey and Schlag’s force field for the 1B2u state allow a nearly complete interpretation of the frequently complex spectra, including assignment of a number of new bands not reported in previous jet studies, and some reassignment of others. The Sur, Knee, and Johnson reassignment of the ν′12 vibrational frequency from the 990–1000 to the 910–915 cm−1 region is confirmed and refined observation of single quanta of ν12 validates the idea that identity forbiddenness may be broken by deuterium substitution. The activity of this mode is postulated to require stealing of activity from ν18 through a kinematic mechanism primarily involving perturbation of the ground state by E1u states of benzene parentage.
Simulation of quadrupole disturbed NMR field spectra by using perturbation theory and the triangle integration method
Authors: Ebert H. , Abart J. , Voitländer J.
Published: February 2003

It is shown that perturbation theory can be used to calculate the transition fields and transition probabilities of quadrupole disturbed NMR spectra. By this way, it is possible to calculate NMR field spectra without the conversion from frequency to field domain. To avoid the disadvantages of the conventional histogram method for the construction of powder patterns, we have developed a new integration method which will be called triangle integration method. By linearly interpolating the angular dependence of the resonance field (or frequency, respectively), our method permits a rapid and analytical calculation of field and frequency spectra, even for anaxial symmetry.
The rotational spectrum and molecular structure of the argon–carbonyl fluoride complex
Authors: Shea J. A. , Campbell E. J.
Published: February 2003

The microwave spectrum of the argon–carbonyl fluoride complex in the ground vibrational state has been assigned using a Fourier-transform microwave spectrometer, employing a pulsed supersonic nozzle as a molecular source. Argon–carbonyl fluoride is a nonplanar near-symmetric prolate top, with the argon atom situated above the plane of the F2CO molecule, nearly over the fluorine atoms. The spectroscopic constants are                     Information from centrifugal distortion is used to obtain the harmonic force constants, normal frequencies, and mean-square amplitudes of vibration for the van der Waals modes of Ar–F2CO.
Electronic structure and spectra of SnBi
Authors: Bondybey V. E. , English J. H.
Published: February 2003

An electronic transition with origin near 16 445 cm−1 is observed in vapor produced by YAG laser vaporization of an alloy of tin and bismuth and assigned to SnBi diatomic. Vibrational analysis yields vibrational frequencies ω″e=183.06 and ω′e=127.6 cm−1. A preliminary rotational analysis gives r″e∼2.612 Å and r′e∼2.814 Å. The observed transition is interpreted in terms of SnBi electronic structure, and bonding in heavy metal diatomics is discussed.
Optical study of polypyrrole perchlorate
Authors: Yakushi K. , Lauchlan L. J. , Clarke T. C. , Street G. B.
Published: February 2003

The optical transmittance spectra of polypyrrole perchlorate have been measured at various stages in the reduction to neutral polypyrrole at 300 and 120 K and at high pressure. Analysis of the results suggests that the polypyrrole chain is composed of conjugated segments of various lengths. The optical conductivity spectrum of polypyrrole perchlorate was obtained by the Kramers–Kronig transformation of the transmittance data from 0.025 to 6.25 eV. The spectrum is not consistent with Drude-like free carriers. The conduction mechanism probably involves hopping between the conjugated segments.
Identification of new ion-pair states of molecular chlorine
Authors: Ishiwata Takashi , Fujiwara Ichiro , Shinzawa Tsutomu , Tanaka Ikuzo
Published: February 2003

Three new ion-pair states of molecular chlorine have been identified by the double resonance method utilizing a sequential three-photon absorption. Two independently tunable dye lasers were used to excite the chlorine molecules into a specific rovibronic level of the B 3Π0+u state, and subsequently into levels of ungerade excited states by a simultaneous two-photon transition. The method enabled us to observe transitions to the low vibrational levels of ion-pair states in the energy range of 7.3–7.7 eV, which were directly inaccessible from the ground state due to the small Franck–Condon factors. Their spectroscopic parameters were derived from the vibrational and rotational analyses of two separate isotope species, 35Cl–35Cl and 35Cl–37Cl. The two-photon transitions from the B3Π0+u state to ion-pair ones consisted of simple O, Q, and S branches. The polarization effect on their transition probability established that the symmetry of three ion-pair states was 0+u in the Hund’s case c notation. The properties of these ion-pair states are discussed in terms of the electron configuration.
Dipole correlation functions and Kirkwood g(1) factor in liquid chlorobenzene
Authors: Rosenthal Lois C.
Published: February 2003

The Kirkwood g(1) factor for room temperature liquid chlorobenzene has been measured from (a) the integrated intensity of the far IR rotation-translation band, and (b) the long time slopes of the single-particle and total-particle dipole correlation functions, using the Keyes–Kivelson rotational diffusion model. The values are 1.13±0.11 and 1.18±0.10, respectively, and do not agree with the Kirkwood–Frohlich theory, which predicts 0.83. The vibrational and far IR band shapes are presented, along with their second moments and the dipole correlation functions. The vibrational band second moment is within experimental error of the theoretical value; the far IR band second moment is in excess by 153%.
Pulsed visible laser photolyis of B(C2H5)3, Al2(CH3)6, Ga(CH3)3, and In(CH3)3: Multiphoton ionization spectra of Al, Ga, and In atoms
Authors: Mitchell S. A. , Hackett P. A.
Published: February 2003

Multiphoton dissociation/ionization of the title compounds by focused visible laser pulses (390<λ<650 nm, 107–1010 W/cm2) has been investigated by use of a low-pressure (≂1 Torr) ionization cell. Al2(CH3)6, Ga(CH3)3, and In(CH3)3 fragment in the laser pulse to produce ground state and excited neutral metal atoms, which were detected by resonance-enhanced two- or three-photon ionization within the photolysis laser pulse. The observed MPI spectra are thus characteristic of the metal atoms, and carry information on the relative abundances of ground and excited state metal atoms produced in the fragmentation process. Analysis of these spectra provided new information on the np1 2PJ and nf1 2FJ Rydberg series of Al(I), Ga(I), and In(I). Evidence is presented to indicate that under relatively high visible laser flux conditions B(C2H5)3 undergoes a direct multiphoton ionization process to form the molecular ion.
Numerical analysis of the ionization of gaseous methane induced by pulsed electron beams
Authors: Arai Hidehiko , Hatada Motoyoshi , Hotta Hiroshi
Published: February 2003

The contributions of beam electrons (the first term) and secondary electrons (the second term) accelerated by the electric field induced by two pulsed electron beams (Febetrons 705 and 706) to the total ionization of methane in the pressure range of 10 to 760 Torr were calculated by a numerical analysis. The fraction of the secondary electrons neutralized during the pulse duration was also evaluated. The computation result showed that, for a Febetron 705, the ionization is mainly due to the first term and that most of the secondary electrons produced are neutralized during the pulse duration. For a Febetron 706, the contribution of the second term is large even at 300 Torr and the secondary electrons recombine only by 20%–30% with ions during the pulse duration. For this beam, the effect of the induced electric field remains after the pulse. The mean secondary electron energy during the pulse also was estimated.
Molecular dynamics investigation of the crystal–fluid interface. III. Dynamical properties of fcc crystal–vapor systems
Authors: Broughton Jeremy Q. , Gilmer George H.
Published: February 2003

Dynamical properties of the (111), (100), and (110) faces of a face centered cubic crystal–vapor system have been obtained at a series of temperatures along the crystal–vapor coexistence line by molecular dynamics techniques. The particles interact by means of a Lennard-Jones potential. We find that all three faces exhibit a signficant degree of surface disorder and atomic mobility near the bulk melting point. Although the diffusion coefficients in the surface layers vary markedly, the total surface mass transport is approximately equal for the three faces.
Long-time behavior in diffusion and trapping
Authors: Zumofen G. , Klafter J. , Blumen A.
Published: February 2003

In the framework of the continuous time random walk (CTRW), we center our attention on the role of the distribution of stepping times. As an application, we analyze both the mean-squared distance traveled and the probability for a walker to be trapped by randomly distributed traps. As a function of the stepping time distribution, we find that trapping shows a rich time dependence and that the onset of the asymptotic behavior for diffusion and for trapping may occur on widely different time scales.
Electron spin resonance and electron spin echo modulation studies of the location and water coordination of radiation produced Cd+ in Cd2+ exchanged A and Y zeolites
Authors: Narayana M. , Kevan Larry
Published: February 2003

Cd+ species have been generated by radiolysis of Cd2+ exchanged A and Y zeolites at 77 K. At least three different Cd+ species are detected by electron spin resonance in A zeolite. The dominant Cd+ species is studied by electron spin echo modulation spectrometry and shown to interact with four deuterons at 0.32 nm. The most probable assignment for this Cd+ species is an S2 site with trigonal bipyramidal coordination to two waters and three zeolite lattice oxygens. In Cd–Y zeolite only one Cd+ species is seen with a hyperfine structure tentatively assigned to an aluminum interaction. The most probable assignment for the Cd+ site is at SI′ or SII′ inside the sodalite cage.
Continuous one-dimensional average unsaturated coverage as the limit of a lattice model
Authors: Maltz A. , Mola E. E.
Published: February 2003

When particles occupying more than one compartment (β) are randomly placed on a one-dimensional array of N compartments we are simultaneously creating sequences of vacant compartments. Clearly, after a long period of time, a saturation situation arises in which the probability of placing an additional particle on such an array becomes zero even though the coverage has not attained the value of one. In the continuous version, particles of unit length are placed in a random manner on an interval of total length x. It is shown that with the interval length x appropriately defined (x=N/β), the average unsaturated coverage of the lattice model tends to that of the continuous one when the mesh of the lattice becomes infinitely fine (N → ∞), keeping the ratio N/β constant.
Thermalization-reaction-capture model for low dose active ion bombardment. I. Diffusionless case
Authors: Mintz Moshe H. , Jo Yangsun , Rabalais J. Wayne
Published: February 2003

A diffusionless thermalization-reaction-capture model has been developed and applied to active ion bombardment experiments. The model describes the product concentration distributions in the target as a function of active ion dose and energy specifically for low ion dose or initial bombardment conditions. Analytical expressions are derived for the reduced slopes of the AES or XPS intensities vs ion dose curves. Comparison of these theoretical reduced slopes with experimental plots yields a reaction probability for the specific ion/target combination. Plots are presented in the form of reduced parameters so that they can be used to predict the experimental slopes for various reactant ion/target combinations. Qualifications of the model as well as experimental examples are discussed.
Alkyl chain flexibility in discotic columnar mesophases
Authors: Samulski Edward T. , Toriumi Hirokazu
Published: February 2003

A steric model with a single adjustable parameter is employed to compute configurationally averaged quadrupolar splittings of deuterium labeled alkyloxy chains in a homologous series of hexaalkyloxytriphenylenes (THEn). A comparison with new experimental data [Goldfarb et al., J. Chem. Phys. (in press)] permits inferences about the alkyl chain flexibility in discotic mesogens. The parameter, a control of the constraints on the chain mobility, is first optimized by fitting deuterium NMR data in a homolgous series of nematogens with labeled alkyloxy chains. The same optimum value of the parameter is subsequently used to model the quadrupolar splittings in the columnar phase of THEn discotigens and succeeds in qualitatively accounting for the experimental observations. This result indicates that alkyl chain mobility is quite comparable in these two classes of liquid crystals. The distinctly different features of the quadrupolar splitting patterns observed for nematogens and columnar discotigens are shown to originate from the different orientation of the molecular order tensor relative to the mean direction of chain propagation in the two types of mesogens.
A quasiclassical trajectory study of the F+D2→FD+D reaction
Authors: Ron Shlomo , Pollak Eli , Baer Michael
Published: February 2003

Quasiclassical trajectory calculations are reported for the F+D2 reaction. Using Muckerman11 V potential. Experiments were performed to determine the product angular distributions for DF molecules. The vibrational state-to-state integral and differential cross sections were calculated. (AIP)
Infrared spectra of LiNaSO4
Authors: Secco Etalo A.
Published: February 2003

The infrared transmittance spectra of LiNaSO4 are reported. Vibrational band assignments are made for the internal optic modes and for external optic modes were possible. These data complement and are compared with the literature data.
A statistical treatment of nucleation rates in boron thin films
Authors: DiMartini Raymond , Lacey Roy
Published: February 2003

A nucleation rate theory for boron films was developed using a statistical approach based on a critical nucleus model. Due to the unique bonding in boron, and its charge to size ratio, two center and three center bonding plays a dominant role in the formation of condensed nuclei. By proper choice of the ratio between two and three center bonding a critical nucleus consisting of 12 boron atoms linked together in an icosahedral structure appears to be a reasonable structure. Reduced nucleation parameters are then calculated to indicate stable growth regions. The statistical methods employed yield nucleation rates which are consistent with independently determined experimental parameters.
Physical properties of nematic mixtures. II. Polar–nonpolar systems
Authors: Schad Hp. , Osman Maged A.
Published: February 2003

The dielectric, diamagnetic, and elastic properties as well as the nematic–isotropic phase transition temperatures of terminal polar–nonpolar nematic mixtures have been studied. The properties of the mixtures are compared to those of their components. Deviations from the ideal behavior or the additivity rule have been observed and are partially attributed to the reduced degree of association of the polar compounds in these mixtures and to additional interactions between the polar and nonpolar molecules. Packing effects can also influence the physical properties of the mixtures. The bend elastic constant is more sensitive to these effects than the twist and splay elastic constants. Clearing points obtained by extrapolation are shown to strongly deviate (up to 40 °C) from the experimental values.
Light scattering from macromolecular solutions in oscillatory flows
Authors: Stasiak Wojciech , Cohen Claude
Published: February 2003

We obtain the dynamic light scattering time correlation for a dilute solution of macromolecules subjected to an oscillating shear flow. We consider the cases of Rouse coils and rigid rods. In the latter case, a perturbation method assuming small amplitudes of the flow oscillations (small shear rates compared to the rotational diffusion coefficient) is used. The general results are complex but are shown to simplify in the limiting cases of very low and very high frequencies of flow oscillations compared to the frequencies of macromolecular dynamics. The total intensity is shown to oscillate in phase with the applied flow at low frequencies but out of phase at high frequencies. For a solution of rigid rods, the influence of the particle anisotropy on the translational mode of the spectrum is considered.
Macromolecular extension in flow fields
Authors: Bird R. Byron , Saab H. H. , Dotson Paul J. , Fan X. J.
Published: February 2003

An expression is derived for the mean square end-to-end distance of Rouse chains in an arbitrary time-dependent flow field. For steady shear flow the resulting simplified expression is compared with incorrect formulas published earlier.

An expression is derived for the mean square end-to-end distance of Rouse chains in an arbitrary time-dependent flow field. For steady shear flow the resulting simplified expression is compared with incorrect formulas published earlier.
Anharmonic molecular spectra-self-consistent mode coupling, nonlinear maps, and quantum chaos
Authors: Abe Shuji , Mukamel Shaul
Published: February 2003

An exact reduced equation of motion which allows the calculation of zero temperature correlation functions in nonlinear (anharmonic) quantum systems is derived. A self-consistent procedure is subsequently developed which enables us to solve for the correlation functions by mapping the anharmonic problem into a harmonic problem with higher dimensionality. Our nonlinear map is of the type commonly used in classical nonlinear dynamics and may exhibit critical dependence on the anharmonic potential. Our procedure is particularly adequate for comparing quantum and classical spectra and may lead to a new definition of ‘‘quantum chaos’’ and its relevance to molecular vibrational spectroscopy.
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o studies of excited states of polyatomic molecules including spin-orbit and multiplet effects: The electronic states of UF6
Authors: Hay P. Jeffrey
Published: February 2003

The excited electronic states of UF6 between 3–10 eV are investigated by ab initio configuration interaction (CI) calculations using a relativistic effective core potential (RECP) on the uranium and nonrelativistic ECP’s on the fluorines. Spin-orbit coupling effects are incorporated by diagonalizing an effective one-electron operator over the CI wave functions. This represents one of the first studies of polyatomic molecules to treat both spin-orbit effects and multiplet effects arising from electron–electron interactions. A detailed analysis of the electronic states of UF6 is given both with and without spin-orbit coupling effects. Assignments for the major peaks in the 3–10 eV energy range are given, as aided by recent electron impact studies. Comparisons are made between the present many-electron states and previous one-electron theoretical treatments.
The relation between the hydrogen motion and the phase transition in the β phase of the Mg2NiHx system
Authors: Hayashi Shigenobu , Hayamizu Kikuko , Yamamoto Osamu
Published: February 2003

A phase transition between a monoclinic and a cubic structure takes place in the β phase of Mg2NiH4. The relation between the hydrogen motion and the phase transition in β-Mg2NiH4 was studied by 1H NMR. FT spectra and spin-lattice relaxation times were measured in the temperature range across the phase transition. The hydrogen motion is mainly an in-plane rotation of the NiH4 planar unit in the low temperature form, while it is a hybrid motion of an isotropic rotation of the NiH4 unit and a translational diffusion of the hydrogen atoms beyond the Mg cube in the high temperature form. A good correlation was obtained between the hydrogen motion and the crystal structure, and the origin of the phase transition was discussed.
Phase separation dynamics: Comparison of experimental results
Authors: Snyder H. L. , Meakin Paul
Published: February 2003

Experimental evidence suggests that phase separation dynamics are insensitive to the molecular details of the system. If time and length are properly scaled, using only experimental data, superposition of phase separation data from metallic alloys, inorganic glasses, small molecule systems, and polymer blends is obtained. An empirical equation, gm=τ−[ln(1+aτ)]/ln(τ), where a=0.05, fits the observed data. It is also shown that power law relations which have been widely applied to describe the time behavior of the structure factor are experimentally valid over only narrow time windows are not applicable throughout the entire phase separation process.
Contribution to the theory of freezing
Authors: Bagchi Biman , Cerjan Charles , Rice Stuart A.
Published: February 2003

We report a theory of freezing based on analysis of the solutions of the equation describing the inhomogeneous density distribution at phase equilibrium. This analysis takes the form of a search for a bifurcation point, where the uniform density characteristic of the fluid phase becomes thermodynamically unstable relative to the periodic density distribution of the crystalline phase. The theory described is an extension of the work of Ryzhov and Tareeva, and it properly accounts for the jump discontinuity in the density at the liquid–solid transition. If carried through exactly, the bifurcation analysis will locate the true equilibrium transition and not display metastability in either the fluid or solid phases. However, as in other many body theories, the approximations needed to reduce the general equations to a tractable form lead to errors. Our approximations are: (a) truncation of the exact expansion for the density in an inhomogeneous system at the level of the direct correlation function for pairs of molecules; (b) the use of a convenient but inexact direct correlation function for the liquid in three dimension; (c) the use of an order parameter expansion which neglects vibrational motion in the solid; and (d) the truncation of the order parameter expansion for the density difference between phases after a few terms. We successfully predict the existence of both the liquid–solid transition and a limiting density for the system without the use of auxiliary thermodynamic criteria. For the hard sphere fluid–solid transition the predicted transition parameters are in satisfactory agreement with (computer) experimental data. A universal bifurcation point is found which gives densities for the liquid and the solid phases which are very close to the dense random close packed and the crystal close packed values, respectively. We interpret this bifurcation point as signaling the end of possible compression in the system. A physical interpretation of all the bifurcation results is given.
Thermochemical properties of the gaseous molecules VO, VO2, and V2O4
Authors: Balducci G. , Gigli G. , Guido M.
Published: February 2003

The gaseous molecules VO, VO2, and V2O4 were characterized thermochemically from the study of various all-gas equilibria carried out by means of the high temperature-mass spectrometry. The bond dissociation energies here determined for VO and VO2 are compared and discussed with previous results, while the molecule V2O4 was clearly identified for the first time. The thermochemical results obtained are: D°0(VO)=625.5±8.5 kJ mol−1, ΔH°f,298(VO,g)= 133.2±8.5 kJ mol−1; D°0(VO2)=1 177±18 kJ mol−1, ΔH°f,298(VO2,g)=−174±14 kJ mol−1; D°0,at(V2O4)=2880±23 kJ mol−1, ΔH°f,298(V2O4,g)=−878±23 kJ mol−1.
Microscopic theory of membrane transport. I. Correlation function expressions for the permeability
Authors: Rumschitzki David , Ronis David
Published: February 2003

A correlation function expression for the diffusion permeabilities for membranes and other thin porous structures is derived for multicomponent isothermal systems. To leading order, only velocity-like time correlation functions are needed and, as such, should be readily amenable to short time numerical simulation. By examining corrections to the diffusion boundary conditions and thereby to the permeabilities, the surface of permeation (i.e., the analog of the transition state) can be specified. The required time correlation functions are modeled by a single exponential or by solving a Fokker–Planck equation in the high friction limit. For these cases the permeability exhibits Arrhenius behavior and in addition is proportional to τ/L, where τ is the velocity relaxation time and L is the thickness of the membrane.
Total spin coherence transfer echo spectroscopy
Authors: Garbow J. R. , Weitekamp D. P. , Pines A.
Published: February 2003

The sensitivity of multiple quantum NMR transitions to magnetic field inhomogeneity and the relative phases and amplitudes of multiple quantum lines are discussed. The technique of total spin coherence transfer echo spectroscopy (TSCTES) is described and experimentally demonstrated. The TSCTES method allows multiple quantum spectra to be obtained which are free of inhomogeneous magnet broadening, yet remain sensitive to spin–spin couplings and chemical shift differences. The method takes advantage of the properties of the total spin coherence, the unique transition between the extreme eigenstates of a coupled spin system. Experimental results are reported for partially oriented acetaldehyde and are analyzed in terms of irreducible tensor operators. Limitations on the method and extensions to heteronuclear spin systems are also discussed.