bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of diffusion-controlled processes in dense polymer systems. II. Effects of entanglements
Authors: de Gennes P. G.
Published: February 2003

Using the general scheme of the preceding paper (part I), we analyze the rates for diffusion-controlled reaction between two partners A and B attached to two long, flexible chains in a homodisperse polymer melt. We assume a degree of polymerization N much larger than the entanglement threshold Ne. Our discussion of entanglements is based on the reptation model. We find three regimes, depending on the reaction time t. (a) When t is larger than the reptation time Trep, we expect a time-independent rate constant k=const Drep≃R0 (where Drep≃R02/Trep∼N−2 is the macroscopic self-diffusion coefficient, and R0∼N1/2 is the coil size). Thus, k is predicted to vary like N−3/2. (b) When TR<t<Trep (where TR∼N2 is the Rouse relaxation time), we find a regime of compact exploration with a time- dependent rate constant k(t)≃Drep R0(Trep/t)1/4. (c) When t<TR, we are led to another regime of compact exploration, with k(t)∼t−3/8 (independent of N). The difference between (c) and (b) reflects the fact that, for t<TR, it is only a portion of the chain which is dragged along with the reactant.
A kinematic, classical mechanical theory of reactive collisions
Authors: Elsum Ian R. , Gordon Roy G.
Published: February 2003

A classical mechanical theory has been formulated for reactions of the form A+BC → AB+C. The essential features of the model are a classical Franck–Condon transition from reactants to products, and the use of kinematics to describe relative motion of the reactants and the products. In the present work, the theory has been applied to reactant–product angular momentum coupling. The general limiting cases of light- and heavy-atom transfer reactions are discussed. Comparison with the quantum theory of Schulten and Gordon [J. Chem. Phys. 64, 2918 (1976)] shows excellent agreement between the classical and the quantum theories, particularly for the location and magnitude of the peak in the product angular momentum distributions. The classical theory has the advantage that the contributions of different reactant orientations can be obtained separately. Comparisons are made between product angular momentum distributions obtained from the present model and from quasiclassical trajectory calculations. The agreement between the two sets of results can be excellent, e.g., for F+D2 → DF+D, clearly showing that for some reactions kinematic coupling of the reactant and product states can dominate the coupling between states due to the interaction potential.
Excited states and photochemistry of saturated molecules. X. A
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o calculations on the vertical states of methylsilane
Authors: Gordon Mark S.
Published: February 2003

The vertical excitation energies are investigated for singlet and triplet states of methylsilane. To analyze the importance of Rydberg functions and of both valence and Rydberg d functions, a sequence of ten different basis sets are considered in conjuction with a single excitation configuration interaction. It is found that all of the singlet states below the first ionization potential may be characterized as Rydberg states, while there is considerable valence character in some of the low-lying triplets. If the valence s and p functions are represented reasonably well (e.g., with a split valence basis set), the role of valence d orbitals is found to be minor.
Semiclassical theory of radiation interacting with a molecule
Authors: Lee Soo-Y.
Published: February 2003

An approximate theory for the interaction of classical radiation with a quantum mechanical molecule is given. The theory is based on the idea that when the field frequency is of the order of the electronic frequency, a separation of the electronic and nuclear motions is possible in the presence, as in the absence, of the field. A weak field is assumed, and time-dependent perturbation theory is used to obtain the amplitudes and cross sections for photodissociation and Raman scattering. The semiclassical coordinate-space (sc) results are shown to correspond to accurate short-time dynamics on the excited Born–Oppenheimer surfaces for nuclear motion. Calculations are performed for ICN using a two-dimensional collinear model.
Molecular dynamics simulation of the frequency spectrum of amorphous silica
Authors: Garofalini Stephen H.
Published: February 2003

The dynamic behavior of atoms in bulk amorphous silica SiO2 has been investigated by using the molecular dynamics computer simulation technique to generate the frequency spectrum. A modified Born–Mayer–Huggins equation was used as the interatomic potential function. Due to the covalency of the Si–O bond, the ability of using a central-force model to reproduce the short time atomic motion in SiO2 was evaluated. The frequency spectrum was generated from the Fourier transform of the velocity autocorrelation function and was compared with the experimentally obtained spectrum presented in the literature. Results show that the frequency spectrum generated here has the three major peaks which are characteristic of silica— i.e., peaks at ∼400, ∼800, and ∼1100 cm−1. Changes in the Si–Si or O–O repulsive parameters in the potential function can be used to alter the frequency spectrum. The 800 cm−1 peak, due to oxygen bending and Si motion, and the 150 cm−1 correlated motion peak are the most affected by the alteration of the repulsive parameters. The results indicate the adequacy of using the model and potential function used here to simulate the short time motion of atoms in amorphous silica.
Infrared spectra of the CO2⋅⋅⋅HF and N2O⋅⋅⋅HF complexes in solid argon at 12 K
Authors: Andrews Lester , Johnson Gary L.
Published: February 2003

Codeposition of argon diluted samples of CO2 and HF at 12 K produced new absorptions at 3871, 2354, 656, and 313 cm−1 which are assigned to the CO2⋅⋅⋅HF complex. The 3871 and 313 cm−1 absorptions are due to the H–F stretching and librational motions of the HF submolecule in the complex, as verified by DF substitution, and the 2354 and 656 cm−1 bands are due to CO2 submolecule modes. The N2O⋅⋅⋅HF complex spectrum contained bands at 3851, 2250, 1306, 583, 328, and 325 cm−1. The greater observed displacement in the HF submolecule modes suggests slightly stronger hydrogen bonding in the N2O complex. The lack of splitting in the degenerate librational mode for CO2⋅⋅⋅HF shows that this complex is linear, whereas the 3 cm−1 splitting in this mode for N2O⋅⋅⋅HF is consistent with a nonlinear complex, in agreement with microwave spectra.
Crystal-field splittings of gadolinium (4f7) levels in C-type rare earth oxides
Authors: Antic-Fidancev E. , Lemaitre-Blaise M. , Caro P.
Published: February 2003

The absorption spectrum of C-Gd2O3 was recorded at room temperature up to 40 600 cm−1. 47 Stark levels of the 4f7 configuration were obtained. The fluorescence spectra from the 6P7/2 level were recorded for Gd3+ in Y2O3 and Yb2O3. The crystal-field splittings are large. Because of the peculiarities of the half-filled shell, the experimental results (32 Stark levels) were fitted with a C2v-type crystal field Hamiltonian restricted to operators of rank 2 and 4, applied on six different basis sets for J = 3/2, 5/2, 7/2 (two matrices), and 9/2 (two matrices) limited by a truncation choice depending on free-ion wave vectors and ignoring J mixing. Real crystal field parameters of rank 2 and 4 were obtained for the C2 site of C-Gd2O3 and are in agreement with those previously determined for Eu3+. The fluorescence data yielded a large value (−1700 cm−1) for the B20 parameter of the S6 site in C-Y2O3.
Electron density measurements in a laser induced Na plasma
Authors: Krebs D. J. , Schearer L. D.
Published: February 2003

The optical emission spectrum of a recombining Na plasma is observed. The shift and broadening of the spectral line emission due to electron collisions is observed. Electron densities on the order of 5×1014 cm−3 are calculated from the shift measurements. The results agree well with electron densities obtained in the same system from Saha plots of excited state densities.
Dissociation of N2+2 ions into N+ fragments
Authors: Edwards A. K. , Wood R. M.
Published: February 2003

Pairs of N+ ions emitted in the dissociation of N2+2 ions were observed in coincidence. Three distinct dissociation channels are reported with total kinetic energy releases of 7.8, 10.2, and 14.8 eV. The dissociative states of N2+2 were formed by bombardment of N2 by 1 MeV He+ ions. The kinetic energy spectra of the N+ ions were measured using the time-energy spectroscopy technique, wherein the ions released in the dissociations can be separated according to their mass-to-charge ratios and their kinetic energy spectra can be recorded. Essentially all of the N+ ions observed resulted from the dissociation of N2+2. The results reported here are in generally good agreement with published reports of electron induced dissociation of N2+2.
Xe(3P2)+HCl(v = 1): Vibrational enhancement of XeCl* formation
Authors: Chang R. S. F.
Published: February 2003

Formation of XeCl* from the Xe+(3P2)+HCl is slightly endothermic. In this work laser excitation of HCl (v = 1) in the presence of Xe(3P2) produced in a flowing afterglow apparatus allows direct observation of XeCl* fluorescence from the Xe(3P2)+HCl(v = 1) reaction. The formation rate constant is determined to have a lower limit of 2×10−10 cm3 s−1.
Crystal field analysis of REOCl:Tb3+
Authors: Hölsä Jorma , Porcher Pierre
Published: February 2003

The fluorescence spectra of REOCl:Tb3+ powder samples were recorded at 300, 77, and 4 K. The assignment of the different 5D3,4 → 7F0–6 transitions between 400 and 730 nm allowed determination of the Stark level sequences of the 7F0–6 levels. The sets of five nonzero Bkq crystal field parameters for the C4v symmetry reproduce the experimental energy level schemes within a rms deviation of 7–8 cm−1. The high ‖B20‖ values indicate the presence of a strong crystal field in REOCl compounds, especially in LaOCl. The evolution of the Bkq parameters in the REOCl:RE3+ series as a function of both the host cation and the doping ion (Eu3+ and Tb3+) is discussed.
Lithium ion distribution and motion in β-alumina: An NMR and Raman investigation
Authors: Villa Marco , Bjorkstam John L. , Mariotto Gino , Fontana Aldo , Cazzanelli Enzo
Published: February 2003

NMR and Raman evidence is presented to show that, above room temperature, a change occurs in the distribution of lithium ions in Li+-containing β-aluminas. We interpret the results in terms of a model in which, below room temperature, lithium ions reside predominantly in positions off the center of the conduction plane (’’out-of-plane’’ positions). As the temperature increases, they spend an increasing fraction of their time in the middle of the conduction plane (’’in-plane’’ positions). It is then possible, from the experimental data, to follow temperature changes of the in-plane ion fraction and to estimate the average energy difference between in-plane and out-of-plane Li+ configurations. A discussion of the Li+ dynamics is then presented, which is based upon the 7Li NMR spin-lattice relaxation and spectral data, as well as upon Raman data.
Highly vibrationally excited benzene: Overtone spectroscopy and intramolecular dynamics of C6H6, C6D6, and partially deuterated or substituted benzenes
Authors: Reddy K. V. , Heller Donald F. , Berry Michael J.
Published: February 2003

Ultrasensitive dye laser photoacoustic spectra have been obtained for CH and CD stretch overtone excitations of gas phase benzene (C6H6, C6D6, C6HD5), toluene, and fluorobenzenes (C6H5F, C6HF5) in the visible and near infrared spectral regions. Interpretations of the spectral observables (band positions, intensities, and widths) clarify the nature and dynamics of highly vibrationally excited states in benzene and related polyatomic molecules: (1) the states we initially prepare by direct one-photon absorption involve highly localized and selective excitations of CH (CD) bond mode sites; (2) these localized excitations cause dynamical symmetry lowering of the molecular systems; and (3) ultrarapid (i.e., subpicosecond) temporal evolution occurs by highly nonstatistical intramolecular rate processes. Analyses of the energy and state dependence of overtone bandwidths support a mechanistic picture in which sequential state-to-state decays are the preferred dynamical pathways for intramolecular vibrational energy redistribution.
Laser-induced emission spectrum of CuO2 in argon matrices
Authors: Tevault D. E.
Published: February 2003

When argon matrices containing atomic Cu and O2 or O3 molecules at 10 K are excited with the blue laser lines of a krypton ion laser, several electronic emissions with extensive vibrational structure are observed. These were characterized as CuO2 emissions by the use of oxygen-18 isotopic enrichment experiments where each member is split into a triplet, thereby indicating a CuO2 molecule with equivalent oxygen atoms. A second progression observed only when Cu atoms were deposited with argon–ozone samples is tentatively attributed to a resonance Raman progression of the Cu2O molecule. No emissions from CuO have been observed in these experiments.
Generalization of the geometric optical series approach for nonadiabatic scattering problems
Authors: Herman Michael F.
Published: February 2003

The geometric optical series approach of Bremmer is generalized for multisurface nonadiabatic scattering problems. This method yields the formal solution of the Schrödinger equation as an infinite series of multiple integrals. The zeroth order term corresponds to WKB propagation on a single adiabatic surface, while the general Nth order term involves N reflections and/or transitions between surfaces accompanied by ’’free,’’ single surface semiclassical propagation between the points of reflection and transition. Each term is integrated over all possible transition and reflection points. The adiabatic and diabatic limits of this expression are discussed. Numerical results, in which all reflections are ignored, are presented for curve crossing and noncrossing problems. These results are compared to exact quantum results and are shown to be highly accurate.
A comparative study of the reaction dynamics of several potential energy surfaces for O(3P)+H2 → OH+H. II. Collinear exact quantum and quasiclassical reaction probabilities
Authors: Lee Ki Tung , Bowman Joel M. , Wagner Albert F. , Schatz George C.
Published: February 2003

Exact quantum and quasiclassical reaction probabilities for the collinear O(3P)+H2 reaction are presented for five potential energy surfaces. These surfaces include the diatomics-in-molecules surface of Whitlock, Muckerman, and Fisher, the LEPS surface of Johnson and Winter, the ab initio fitted surface of Schinke and Lester, the ab initio fitted surface of Schatz, Wagner, Walch, and Bowman, and a modification of this last surface newly reported here. On each surface, the quantum and quasiclassical probabilities are compared and interpreted. A vibrationally adiabatic analysis based on recent work by Pollak proves useful in interpreting the dynamic thresholds and quantum oscillations in the reaction probability and other features. A systematic variation in both the quantum and quasiclassical reaction probabilities with the saddle point location of the surface is observed.
A comparative study of the reaction dynamics of the O(3P)+H2 → OH+H reaction on several potential energy surfaces. III. Collinear exact quantum transmission coefficient correction to transition state theory
Authors: Lee Ki Tung , Bowman Joel M. , Wagner Albert F. , Schatz George C.
Published: February 2003

Collinear exact quantum and quasiclassical rate constants and transmission coefficients are presented for the O(3P)+H2 (ν), ν = 0,1 reaction, using the quantum and quasiclassical trajectory reaction probabilities calculated in the preceding paper and by Clary, et al. [D. C. Clary, J. N. L. Connor, and C. J. Edge, Chem. Phys. Lett. 68, 154 (1979)] on a total of five potential energy surfaces.
Methylene singlet–triplet energy splitting by molecular beam photodissociation of ketene
Authors: Hayden Carl C. , Neumark Daniel M. , Shobatake Kosuke , Sparks Randal K. , Lee Yuan T.
Published: February 2003

The singlet–triplet splitting in methylene has been determined from the measurements of fragment velocities from ketene photodissociation at 351 and 308 nm in a molecular beam. The splitting is found to be 8.5±0.8 kcal/mol. This agrees with many experimental results, but not with the value of 19.5 kcal/mol derived from recent photodetachment experiments on CH−2.
Rotationally inelastic collisions between a diatomic molecule in a 2Σ+ electronic state and a structureless target
Authors: Alexander Millard H.
Published: February 2003

We present the full close-coupling formulation of the collision between a diatomic molecule in a 2Σ+ state and a structureless target. Due to the possibility of transitions which are inelastic in the parity index of the doublet states, the scattering displays an additional degree of complexity not seen in rotationally inelastic collisions of 1Σ+ molecules. The well-known coupled states and infinite-order-sudden approximation techniques can be applied in a straightforward manner. The factorization and scaling relations between the various cross sections, which are valid in the energy sudden limit, are explored. These allow the entire matrix of cross sections, both parity conserving and parity violating, to be expressed in terms of the cross sections for parity conserving transitions out the lowest (J = 1/2) level. Within the sudden limit it is also possible to show that at large values of the total angular momentum, transitions which conserve the parity index of the molecular wave functions will be strongly favored, a propensity rule which has been seen in previous experimental studies of rotational relaxation in 2Σ+ molecules. If the doublet states are unresolved, the sudden scaling relations become identical to those derived previously for collisions of 1Σ+ molecules.
Measurement of absolute state-to-state rate constants for collision-induced transitions between spin-orbit and rotational states of NO(X 2Π, v = 2)
Authors: Sudbo/ Aa. S. , Loy M. M. T.
Published: February 2003

Using a pulsed, time resolved IR–UV double resonance technique, we have measured initial and final state specific rates for collision-induced rotational and spin-orbit transitions in NO in its (X 2Π, v = 2) vibronic state. A systematic study of the rates was done for initial and final rotational states with J between 1/2 and 35/2, for both Ω = 1/2 and the Ω = 3/2 spin-orbit components of the X 2Π state. Collision partners were room temperature NO, He, Ar, N2, CO, and SF6. No propensity rules favoring ΔΩ = 0 or ΔJ = 0,±1 were observed, except in NO–He collisions, where ΔΩ = 0 was favored. The state-to-state rates do not vary much with initial state and fall off slowly with increasing ΔJ. Total cross sections for collision-induced rotational transitions were found to be tens of Å2, insensitive to initial state, and correlated with the size of the collision partner.
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o effective Hamiltonian study of the electronic properties of conjugated polymers
Authors: Brédas J. L. , Chance R. R. , Baughman R. H. , Silbey R.
Published: February 2003

The valence effective Hamiltonian technique is applied to a series of polymers to compute ionization potentials, bandwidths, and band gaps. The polymers considered represent systems of interest to the conducting polymers area and include various derivatives of polyacetylene and polyphenylene, polydiacetylene, polyacene, polybenzyl, and polyyne. The theoretical results for relative ionization potentials are in excellent agreement with available experimental estimates, as well as with the observed behavior of the electrical conductivity of these systems on exposure to weak (I2) versus strong (AsF5) electron acceptors. The bandwidths of the highest occupied band show a qualitative correlation to the conductivities achieved with acceptor doping. Band gaps for the planar systems considered are also in good agreement with experiment.
Spin splitting in the X 2Σ+ state of MgH
Authors: Cooper David L.
Published: February 2003

The spin splitting constant for the X 2Σ+ state of MgH is calculated to be γ0 = 0.019 cm−1, using second-order perturbation theory with ab initio wave functions. The nature of the spin splitting constant is considered and comparison is made with the Λ-doubling parameter p0.
Vapor pressure isotope effects in liquid fluoroform
Authors: Popowicz Anthony , Oi Takao , Shulman Jan , Ishida Takanobu
Published: February 2003

The vapor pressures of isotopic fluoroforms 12CHF3, 13CHF3, and 12CDF3 have been measured at temperatures between 125 and 212 K in a modified Bigeleisen–Brooks–Ishida–Ribnikar cryostat. At all temperatures of measurement P(12CHF3)≳(12CDF3) and P(12CHF3)<P(13CHF3). The results support the blue-shift of the C–H stretching frequency on condensation of fluoroform molecules due to a kinetic energy coupling between the stretching motion and the molecular translation in the direction of the molecular figure axis, caused in large part by a weak but directional coulombic interaction between hydrogen and fluorine atoms of neighbor molecules.
Analysis of sound velocity in supercoled H2O, D2O, and water–ethanol mixtures
Authors: Conde O. , Teixeira J. , Papon P.
Published: February 2003

Measurements of the sound velocity c in water, heavy water, and water–ethanol mixtures have been carried out in a temperature range extending from room temperature to the supercooled region above -20 °C, by Brillouin light scattering technique. Pure H2O and D2O show a strong anomalous behavior which can be described by critical laws. The addition of ethanol to water decreases the importance of the anomalies, and the sound velocity c(T) is no longer described by critical laws. For some concentrations, a minimum in the curve c(T) is observed at low temperatures. The adiabatic compressibility is evaluated for all the samples and discussed for different theoretical models. Arguments are given in favor of a percolation model of supercooled water.
Energy and tangential momentum accommodation coefficients of Ne and He on different vacuum flashed tungsten surfaces
Authors: Shields F. Douglas
Published: February 2003

The acoustical method has been used to determine energy and tangential momentum accomodation coefficients on three different polycrystalline tungsten surfaces. To obtain the second surface, the first was highly oxidized and then cleaned by vacuum flashing at 2150 K. The third surface, manufactured by the same chemical deposition process as the first, was specified as having half the microscopic roughness of the first. Photographs made with the scanning electron microscope indicate that though the oxidation dramatically increased the roughness of the surface, this roughness was removed in the flashing process. The electron micrographs also showed that flashing dramatically increased the grain size in the third surface. This third surface, though supposedly smoother, was found to have larger AC values than the first. This has been attributed to a shorter accumulated flashing time at the time the measurements were made and, therefore, smaller grain size. The microscopic roughness does not appear to be an important factor in determining AC values after the surface is flashed. The problem of simultaneously determining energy and tangential momentum accomodation coefficients is discussed.
Long transients in surface reactions at high pressures
Authors: Klein R. L. , Schmidt L. D.
Published: February 2003

It is shown that competitive adsorption should in general increase the time required to approach steady state in coadsorption and bimolecular reactions. For a single species or an unimolecular reaction the time constant is less than the reciprocal of the rate of adsorption and this predicts rapid approach to steady state except at low pressures. However, competitive adsorption yields a time constant which does not contain the adsorption rate except as a ratio of adsorption rates, and this can yield a much slower approach to steady state than for a single species. For N competitively adsorbed species, linearization yields N time constants of which one contains gas pressures and the others represent replacement. Numerical examples show that a succession of replacement processes can occur as more strongly bound species at lower pressures replace more weakly bound ones. These ideas are illustrated by the kinetics of the reaction between NO and CO on clean polycrystalline Pt at a total pressure of ∼0.1 Torr. This reaction initially exhibits a rate which is several orders of magnitude slower than the steady state value because CO blocks the adsorption of NO which is necessary for reaction.
Cell cluster calculations of the surface entropy of harmonic fcc crystals
Authors: Kincaid Robert H. , Huckaby Dale A.
Published: February 2003

The cell cluster approximates to Sz/k for the (111) and (100) faces of harmonic fcc crystals are calculated to fifth order. (Ss being the surface entropy per particle.) (AIP)
The stability of the phase III structure in solid CH4–CD4 mixtures
Authors: Lushington K. J.
Published: February 2003

These phase diagrams of solid CH4–CD4 mixtures has been explored at low CD4 concentrations (below 30% CD4). The phase III structrue of solid methane is found to be metastable below a CD4 concentration of about 15 mol %.
A remark on the constant relating total molecular energy to the sum of valence eigenvalues
Authors: Villar H. , Castro E. A. , Fernández F. M.
Published: February 2003

A numerical test is performed on the constant relating total molecular energy to the sum of valence eigenvalues. It is shown that such a constant is not related to the stability of a given conformer, as previously stated. (AIP)
Solution of the spin Hamiltonian with orthorhombic hf and g tensors (I = S = 1/2). I. Theory
Authors: Kawazoe H. , Hosono H. , Nishii J.
Published: February 2003

A theory was developed appropriate for analyzing ESR spectra characterized by ℋ = βH ⋅ g ⋅ S+S ⋅ A ⋅ I, where S = I = 1/2 and g and A tensors are of orthorhombic symmetry using the perturbational method. The theory reproduced the reported solutions of special cases; the Breit–Rabi solution, when g and A are isotropic, the zero field solution, when H = 0, and the solution for axial symmetry solved under the limited conditions of H along or perpendicular to z (the principal coordinate of g and A). The perturbation was found to become zero when H is along one of x, y, and z. Therefore, the theory gives the exact solution for the orientations, from which resonance field ESR parameters can be derived.
Rare gas diatom polarizabilities
Authors: Dacre Peter D. , Frommhold Lothar
Published: February 2003

Large scale self-consistent field (SCF) computations of the polarizabilities of the rare gas symmetric diatoms were recently reported, the effect of electron correlation was evaluated for the He2 and Ne2 systems, and a new procedure proposed of scaling SCF results to approximate diatom polarizabilities. In this work, these new results are used to compute from an exact wave mechanical theory binary collision-induced Raman spectra of the rare gases for comparison with recent measurements. Depolarized spectra show agreement typically within the small experimental uncertainties and over a range of intensities that may exceed 100 000:1. Computed and measured polarized spectra similarly agree, but with lesser precision. The scaling of SCF polarizabilities appears to be remarkably successful. Uncertainties arising from the use of semiempirical potentials are not always negligible.
Brillouin scattering study of hypersonic relaxation in a Ca(NO3)2 –KNO3 mixture
Authors: Torell Lena M.
Published: February 2003

Brillouin spectroscopy has been used to provide information about the hypersonic velocity and absorption of thermal waves in a glass-forming 60% KNO3–40% Ca(NO3)2 mixture (mol %) in a temperature range of 90–380°C for gigahertzian frequencies. A relaxation process was revealed in both the longitudinal velocity and attenuation. The data are consistent with ultrasonic results for the limiting low-frequency velocity. The limiting high-frequency velocity is considerably larger than that reported from ultrasonic studies and the position of the maximum of the amplitude absorption coefficient is shifted to higher temperatures. The variation of the relaxation time with temperature was found to be Arrhenius with a temperature-independent activation energy in excellent accordance with the model proposed by Weiler, Bose, and Macedo. At low temperatures, a transverse mode due to shear waves was observed close to the Rayleigh line.
Carbon skeletal rearrangement of the propane ion
Authors: Gilman J. P. , Hsieh T. , Meisels G. G.
Published: February 2003

The elimination of methane from the propane molecular ion has been investigated using propane-2-13C. Breakdown graphs obtained by threshold photoelectron-coincident photoion mass spectrometry indicate that approximately 11% of all methane loss includes the central carbon and that this amount is independent of internal energy over nearly 1.2 eV. These results are interpreted in terms of a potential energy surface and rate constant curves. We conclude that isomerization of the propane molecular ion does not precede fragmentation to ethylene ion and methane, but that fragmentation occurs by a concerted stepwise cleavage involving a tight transition state.
Mode-to-mode energy transfer in 1B2 aniline induced by very low energy collisions with He
Authors: Tusa James , Sulkes Mark , Rice Stuart A. , Jouvet Christophe
Published: February 2003

Collision induced vibrational relaxation of selected single vibronic levels of 1B2 aniline has been studied for the collision energy range ∼1–∼100 cm−1. We find that very low energy collisions with He lead to efficient and selective mode-to-mode energy transfer, with the collision energy required for efficient relaxation varying with the nature of the initial vibrational excitation. This dependence on initial vibrational state is consistent with the orbiting resonance model of the collision previously proposed.
The proton transfer from ArH+ to various neutrals
Authors: Villinger H. , Futrell J. H. , Howorka F. , Duric N. , Lindinger W.
Published: February 2003

The proton transfer reactions from ArH+ to H2, D2, CH4, N2, O2, CO, CO2, and the corresponding deuteron transfer reaction of ArD+ with H2 and D2 have been investigated in a drift tube with mass selected ion injection. The use of helium and argon buffer gases permits a qualitative assessment of vibrational energy effects along with a quantitative assessment of the influence of translational energy on reaction rates. These exothermic reactions all proceed with large rate coefficients which approach the collision rates for the respective reactants. All except the reaction of ArH+ with H2 (D2) were independent of translational energy over the range investigated. In an argon buffer equilibrium is readily established for the reaction ArH++H2⇄H3++Ar. A treatment of the center-of-mass kinetic energy as a ’’translational temperature’’ permits the construction of a van’t Hoff plot for this reaction from which a value of Δ(PA)=0.55 eV is obtained, which is consistent with the accepted proton affinities of H2 and Ar.
Raman spectroscopy at high pressures applied to the fundamental vibration of N2 in solid argon and nitrogen
Authors: Jodl H. J. , Bolduan F.
Published: February 2003

The matrix isolation technique, Raman scattering, and high-pressure technology have been combined and applied to the study of nitrogen molecules in Ar and in N2 crystals. The aim of the study is to gain a deeper insight into the following physical questions: (1) Are the assumptions used in models for matrix energy shift calculations valid? (2) How strong is the coupling between the defect vibration and the lattice modes? (3) Which anharmonic contributions are responsible for observed temperature and pressure shifts?
Multiphoton ionization photoelectron spectroscopy of CCl2F2 and CCl3F
Authors: Hepburn J. W. , Trevor D. J. , Pollard J. E. , Shirley D. A. , Lee Y. T.
Published: February 2003

Multiphoton ionization of CCl3F by an ArF laser is studied for processes in which extensive & sequential fragmentation taken place. (AIP)
Autoionizing Rydberg states in Na2
Authors: Leutwyler S. , Heinis T. , Jungen M. , Härri H.-P. , Schumacher E.
Published: February 2003

Extended autoionization structure has been observed in sequential two-photon ionization of Na2 via different vibronic levels of the intermediate B 1Σu state. Partial snalysis of this structure has now been achieved. A dominant Rydberg series (quantum defect δ = 0.4) and a second, weaker series (δ = 0.57) are assigned. Convergence to many different vibronic levels of the ion core is observed, allowing a preliminary determination of ω e and ωexPde for the Na2+ 2Σ+g ground state. A difference of +49 cm−1 between the spectroscopically extrapolated ionization potential and the previously observered ionization threshold is noted and discussed.
Statistics of self-avoiding ring polymers
Authors: Baumgärtner A.
Published: February 2003

Some important statistical properties of the self-avoiding freely jointed ring-polymer model are studied. Using dynamic Monte Carlo techniques, which yield proper ring configurations, the probability distribution function Pn(r) of intrachain distances, the bond correlation function 〈u0u0+n〉 and related quantities as mean-square intrachain distances 〈R2n〉, mean-square radius of gyration 〈S2N〉, and structure function SN(q) are calculated. These quantities are analyzed using scaling assumptions and are compared to the same quantities of the corresponding linear polymer model. Closed analytical expressions for Pn(r) and 〈u0u0+n〉 are proposed. From the latter quantity, 〈R2n〉 and 〈S2N〉 are calculated and compared with Monte Carlo estimates. We show that all these quantities are governed asymptotically by exponents which have been found for linear polymers; but in contrast, the analytical expressions are rather different. The experimental relevance of these results is briefly discussed.
Self-induced multipole contribution to the single-electron crystal field
Authors: Morrison Clyde A. , de Sá Gilberto F. , Leavitt Richard P.
Published: February 2003

We consider the interaction of electrons in unfilled shells of an ion substituted as an impurity in an insulating host crystal with their self-fields induced through polarizable ligands. All orders of the interaction (dipole, quadrupole, etc.) are considered, thereby extending previous treatments that included induced dipole interactions only. By means of a correct inclusion of all the electrons and the nucleus of the impurity ion and by a proper consideration of the lattice-induced multipole problem (also described here), we show that previous treatments of the self-induced dipole problem are incorrect. Our result, up to the quadrupole term, is applied to the classic example of rare earths in LaCl3 and is shown to give a significant contribution to the one-electron crystal field.
Some moments of radial electron density in closed-shell atoms and their atomic scattering factors
Authors: Pucci R. , March N. H.
Published: February 2003

The scattering factor f(K) for x rays from atomic ions with closed shells can be written in terms of the radial electron density D(r) = 4πr2ρ(r), with ρ(r) the electron density. The small K expansion of f(K) focuses on the moments 〈r2n〉 = ℱ∞0r2n D(r)dr. From Hartree–Fock calculations on Ar, Kr, Xe, and Rn it is found that 〈r2〉 proportional to the diamagnetic susceptibility, varies with atomic number Z approximately as Z0.75. For 〈r4〉, the Hartree–Fock results for closed-shell atoms give a dependence of Z0.95, while 〈r6〉∝Z1.25. These are interpreted in terms of an exact result for the asymptotic decay of D(r) at large r, which shows that 〈r2n〉/ 〈r2n−2〉∝ 1/I at sufficiently large n, I being the ionization potential. This is found to vary approximately as Z−1/3 for the closed-shell atoms. Some contact is then made with the predictions of the Thomas–Fermi theory. For the neutral atom, 〈r4〉TF diverges. But by plotting 〈r4〉 for radon against the degree of ionization, a strong dependence of the small angle scattering term ∝K4 is demonstrated from Hartree–Fock calculations, in qualitative accord with the Thomas–Fermi predictions. Finally, it is demonstrated that f(K) can be characterized solely by 〈r2〉, 〈r4〉, Z, and I over a wide range of K.
Convergence tests of coupling operators
Authors: Ishikawa Y. , Binning R. C. , Adams William H.
Published: February 2003

In the coupling operator formalism developed by Huzinaga, Hirao, and Nakatsuji the conditions for optimum orbitals are coupled via arbitrary constants {λij}. We show that these constants can be optimized to improve SCF convergence. An improved coupling operator scheme is proposed and tested on several open-shell states of selected atomic and molecular systems.
Evaluation of higher-order semiclassical phase integrals close to potential extrema
Authors: Pajunen Petri , Luppi Jussi
Published: February 2003

Recently developed techniques for evaluating higher-order semiclassical phase integrals are extended to allow the computation of phase integrals close to potential extrema, where the earlier procedure is numerically unstable. The new methods are required in the calculation of certain integrals encountered in double minimum and resonance scattering problems. Various distributions and ranges of the integration mesh points are studied and global recommendations for use of various versions of the general integration procedure and the choice of mesh points are given.
Higher-order semiclassical quantization of an asymmetric double minimum potential
Authors: Luppi Jussi , Pajunen Petri
Published: February 2003

Although the semiclassical quantization condition of a general (asymmetric) double minimum potential has been known for some time it has only been applied to the simpler symmetric case. In this work, new versions of a method for evaluating higher-order semiclassical phase integrals are applied to semiclassical quantization of an asymmetric double minimum potential. The quantization condition is discussed and energy eigenvalues for a model potential are determined in the first- , third- , and fifth-order phase integral approximations. Agreement of three, five, and seven significant digits, respectively, where the exact quantum mechanical eigenenergies are obtained.
Multiphase layered oxide growth on pure metals. I. General formulation
Authors: Fromhold A. T.
Published: February 2003

A general formulation for the simultaneous growth of any number of layered planar oxide phases on a pure metal under diffusion-controlled conditions has been developed. Four individual situations have been developed in detail, namely, situations in which the predominant mode of ion transport is by cation interstitials, cation vacancies, anion interstitials, or anion vacancies. The generalized formulation enables the determination of quasi-steady-state growth kinetics following step function changes in the experimental conditions such as ambient oxygen pressure or temperature. Numerical evaluation of the coupled growth equations for the individual phases is required to deduce the general predictions of the theory. In the limit of two-layer growth by cation interstitial diffusion, the present formulation reproduces the earlier results of Fromhold and Sato.
Spectral analysis and kinetics of uranyl glasses
Authors: Leung A. F. , Lai T. W.
Published: February 2003

The absorption spectra of uranyl doped soda–lime and lithium phosphate glasses at 77 K consisted of broad bands. The fluorescence due to various continuous monochromatic excitations showed fine structure and revealed two electronic levels within the full fluorescence band. The energy levels in the visible region were located by spectroscopic measurements and were used to calculate the intramolecular decay rates. There was agreement between the theory and experiment. Besides intramolecular relaxations, intermolecular relaxations were observed and they involved uranyl–acceptor interactions via dipole–quadrupole coupling. Analysis on the spectral kinetics yielded the acceptor concentration, which enhanced with increasing uranyl concentration in soda–lime glass. Such a relationship between the acceptor and uranyl concentrations implied that some acceptors were the by-products of thermal decomposition of uranyl ions during sample preparation. Fluorescence decay of uranyl doped lithium phosphate glass consisted of multiple fluorescence decay rates. The thermal dependence of polyphosphate metamorphosis was studied qualitatively by fluorescence decays of uranyl doped samples.
Depolarized Raman scattering in normal and supercooled antimony trichloride
Authors: Aliotta F. , Maisano G. , Micali N. , Migliardo P. , Vasi C. , Wanderlingh F. , Triolo R. , Smith G. P.
Published: February 2003

Depolarized low frequency Raman spectra obtained for molten antimony trichloride are discussed. Measurement has also been performed on the supercooled liquid down to 53.2° below the melting point (tm = 73.4 °C. The experimental results indicate that the spectral contributions, in the range 2–100 cm−1 of Stokes shift from the exciting line are due to: (1) a central Lorentzian line, whose width and intensity are connected to the dynamics of the break-up of intermolecular chlorine bridges; and (2) a solidlike contribution that furnishes an effective density of states, which corresponds to a convolution of ’’acoustical’’ and ’’optical’’ modes in a coupled linear chain structure with middle range order.
Hyperfine structure of the X 2Σ+ ground state of Ca 35Cl and Ca 37Cl by molecular-beam, laser-rf double resonance
Authors: Childs W. J. , Cok David R. , Goodman L. S.
Published: February 2003

The hyperfine structure of the X 2Σ+ state of Ca 35Cl and Ca 37Cl, unresolved in previous studies, has been investigated in detail by the molecular-beam, laser-rf, double-resonance technique. Results for the spin-rotation interaction and the dipole and quadrupole hfs constants are given in the form of Dunham coefficients so that the N\ and v\ dependence of each constant can be explicitly exhibited. The results, after dividing out the purely nuclear effects, fall between the corresponding values for CaF and CaBr, as expected.
Characterization of silver species: Locations and environments in A, X, and Y zeolites by electron spin echo spectroscopy
Authors: Narayana N. , Kevan Larry
Published: February 2003

Electron spin resonance and electron spin echo techniques are used to identify and characterize different types of isolated silver atoms observed on γ-irradiation of A, X, and Y zeolites. On the basis of 2D and 133Cs modulation analysis, the dominant species in A zeolites is located inside the β cage at a S2′ site and is coordinated to two waters. In X and Y zeolites, the Ag0 is found to be fully solvated by four waters and is located at the center of the β cage at site SU. Room temperature dehydration destroys the dominant species in A zeolites.
Light scattering and dynamics of interacting Brownian particles
Authors: Tsang Tung , Tang H. T.
Published: February 2003

The relative motions of interacting Brownian particles in liquids may be described as radial diffusion in an effective potential of the mean force. By using a harmonic approximation for the effective potential, the intermediate scattering function may also be evaluated. For polystyrene spheres of 250 Å mean radius in aqueous enviroment at 1.25×10−3 g cm−3 concentration, the results for the calculated mean square displacement are in qualitative agreement with experimental data from photon correlation spectroscopy. Because of the interactions, the functions deviate considerably from the exponential forms for the free particles.
The effect of Li+Li− ion-pair interaction on the vibrational energy spectrum of the second excited state of Li2 of 1Σ
g+ symmetry
Authors: Konowalow Daniel D. , Fish J. L.
Published: February 2003

The outer limb of the potential energy curve for the second excited 1Σg+ state of Li2 is dominated by the Li+–Li− ion–pair interaction. Consequently, the curve has a double minimum and has an unusual pattern of vibrational energy levels. We obtain excellent agreement with the vibrational levels 0⩽v⩽12 deduced from optical double resonance spectra.
The in-equivalence of the HCl molecules in (HCl)2: An SCF a
b i
n
i
t
i
o calculation
Authors: Allavena M. , Silvi Bernard , Cipriani Joseph
Published: February 2003

The geometry and the spectroscopic properties of (HCl)2 have been calculated at the SCF level. A nearly orthogonal dimer with an almost linear H bridge has been found. The optimized Cl–Cl distance is Re = 7.48 a.u., while Cl–H bond lengths are found to be r1 = 2.4133 and r2 = 2.4075 a.u. for the proton donor and acceptor monomeric units, respectively. The binding energy corrected for basis set superposition error is computed to be B = 3.61 kcal/mol. The spectroscopic properties (force constants, dipole and quadrupole moment derivatives) of monomeric units as a part of (HCl)2 are discussed.
Electrical double layers. II. Monte Carlo and HNC studies of image effects
Authors: Torrie G. M. , Valleau J. P. , Patey G. N.
Published: February 2003

The effect of surface polarization (i.e., image forces) on the properties of electrical double layers is studied by means of Monte Carlo calculations on a primitive model electrolyte next to a planar charged surface bounding a semi-infinite dielectric. Two cases are considered, that of a conducting material for which an ion is attracted by its own image and that of an insulator for which the self-image force is repulsive. At low surface charge densities the image forces cause quite dramatic changes in the ionic densities near the wall; the effect on the electrostatic potential is small but increases with surface charge density. The modified Poisson–Boltzmann theory of Outhwaite is quite successful in describing the Monte Carlo results for the range of parameters studied. A screened self-image model of image effects is also considered for which both Monte Carlo calculations and numerical solution of the HNC equation have been obtained.
Exciton transport in the band limit
Authors: Čápek V. , Munn R. W.
Published: February 2003

The approximate diffusion coefficient expression quoted by Yarkony and Silbey [J. Chem. Phys. 67, 5818 (1977)] is revised so that in the band limit it contains the transport relaxation time, where appropriate, rather than the exciton lifetime.(AIP)
ESR and proton ENDOR studies in urea oxalic acid (2:1) single crystal: Radical transformation
Authors: Reddy M. V. V. S. , Lingam K. V. , Gundu Rao T. K.
Published: February 2003

A radical transformation has been investigated in a single crystal of urea oxalic acid (2:1) irradiated at room temperature. ENDOR studies (∼−160 °C) have been performed on both the initial and final radicals. The initial species has been assigned to a protonated anion radical. The results indicated that a common proton was involved in the protonation of the anion and in the subsequent transformation to R–ĊHOH. Two important differences in relation to the earlier studies on the protonated anions were noted. The maximum dipolar coupling values (Bmax) for the O–Hβ protons are smaller than normal and the proton transfer is not across the hydrogen bridge. A qualitative estimation of the spin densities indicated delocalization and the possible causes for small values of Bmax are discussed. A mechanism proposed earlier is invoked to understand the radical transformation.