bluuebunny/crossref_metadata_2025 huggingface dataset:
Mössbauer studies of trimethyl and triphenyl tin chloride adsorbed on grafoil
Authors: Bukshpan S. , Kemerink G. J.
Published: February 2003

Trimethyl tin chloride [(CH3)3SnCl] and triphenyl tin chloride [(C6H5)3SnCl] adsorbed on grafoil were studied by the Mössbauer resonance in 119Sn. The temperature dependence of the Mössbauer fraction and the anisotropy ratio of the quadrupole transitions in (CH3)3SnCl measured at two different angles supplied information on the structure of the substrate and on the anisotropy of the recoilless fraction. The relative orientation of (C6H5)3SnCl adsorbed on grafoil was found to be with the Sn–Cl axis perpendicular to the exposed basal planes of grafoil, contrary to (CH3)3SnCl, where the molecules have their symmetry axes parallel to the grafoil plane.
State-to-state differential cross sections for rotationally inelastic scattering of Na2 by He
Authors: Bergmann K. , Hefter U. , Witt J.
Published: February 2003

State-to-state differential cross sections for rotational transitions of Na2 in collisions with He are measured in the electronic and vibrational ground state at thermal collision energies using a new laser technique. Single rotational levels ji are labelled by modulation of their population via laser optical pumping using a dye laser. The modulation of the fluorescence induced by an Ar+ laser tuned to the level jf=28 is proportional to the cross section for collisional transfer ji→jf and is detected at the scattering angle ϑ. A single optical fiber and a fiber bundle provide a flexible connection between the detector and the laser and photomultiplier, respectively. Transitions as large as Δj=20 are observed. At small angles elastic scattering is dominant, but rotationally inelastic processes become increasingly important at larger scattering angles. Rotational rainbow structure causing a steep onset of the cross section with the scattering angle ϑ (at fixed Δj) or a sharp cutoff with Δj (at fixed ϑ) is found. Preliminary results on rotational energy transfer in v=1 indicates that vibrational motion of the molecule favors larger rotational quantum jumps. semiclassical picture for the scattering of a hard ellipsoid gives a
State-selected ion–molecule reactions by a threshold electron–secondary ion coincidence (TESICO) technique. I. Apparatus and the reaction H2++H2→H3++H
Authors: Koyano Inosuke , Tanaka Kenichiro
Published: February 2003

A technique which enables the direct observation of state-selected ion–molecule reactions through coincident measurements of secondary ions with threshold electrons has been developed. Using this technique, the reaction H2++H2→H3++H has been studied in detail at average collision energies between 0.11 and 0.93 eV. State-selected reaction cross sections for individual vibrational states v=0–3 of the H2+ ion have been determined. It has been found that while the cross section decreases with increasing vibrational energy at low collision energies, this decreasing tendency becomes less and less prominent as the collision energy increases and the cross section is almost independent of vibrational energy at the highest energy studied. This feature qualitatively agrees with the previous study by a different technique. A detailed description of the apparatus and its performance is also given.
Energetic electron degradation spectra and initial yields in argon
Authors: Parikh Mihir
Published: February 2003

The complete degradation of an energetic electron in argon has been calculated. The input to this calculation consists of a complete set of internally consistent inelastic scattering cross sections for five distinct excitations and two (M and L shell) ionizations as well as L shell Auger emission. A Monte–Carlo procedure has been developed that efficiently calculates the complete degradation of all electrons generated in the medium. Our results provide (1) initial yields (species per incident electron) and radio-chemical W values for all species and their dependencies on T0. (2) Distribution of electrons, delineated by kinetic energy and by generation (secondary, tertiary, etc.); such distributions are shown to be explicitly related to the Spencer–Fano track length. (3) The effectiveness of these electrons in the production of various excited and ionized species.
On the relationship between the Kirkwood correlation factor and the dielectric permittivity
Authors: Bordewijk P.
Published: February 2003

The calculation of Kirkwood correlation factors with the technique of molecular dynamics is discussed. It is argued that the relationship between Kirkwood correlation factors and dielectric permittivity, derived by Frölich, is preferable in relation to that of Refs. 5 and 7. (AIP)
Temperature dependence of thermal vibrations in cubic ZnS: A comparison of anharmonic models
Authors: Moss B. , McMullan R. K. , Koetzle T. F.
Published: February 2003

Accurate integrated intensities for the Bragg reflection of neutrons from a ZnS single crystal have been measured at temperatures between 285 and 1173 K. After correction for thermal diffuse scattering and extinction effects the data were interpreted with different models that allow anharmonic contributions to the temperature factor. Both the cumulant expansion and the one-particle potential (OPP) model with quasiharmonic temperature dependence describe the data satisfactorily, although the Grüneisen parameter obtained in the OPP analysis differs greatly from the value calculated from known thermodynamic quantities. Predictions based on Matsubara’s anharmonic formalism are not in accord with the behavior observed at the highest temperatures.
An excited state of acetylene: Photochemical and spectroscopic evidence
Authors: Laufer Allan H.
Published: February 2003

Absorption spectra of a long-lived transient in the 140 and 157 nm region have been observed as the result of direct excitation of C2H2. The strongest features also are seen as the result of CH2CO photolysis. The carrier is identified as C2H2. A possible alternate assignment of the transient carrier to a geometrical isomer, such as H2C=C (vinylidene) radical is discussed.
Accuracy of the iterative method for swarm transport coefficients
Authors: Kleban P. , Foreman L. , Davis H. Ted
Published: February 2003

We consider the iterative method of solving the Boltzmann equation for swarm experiments. The accuracy of this technique has been called into question by Lin, Robson, and Mason for parallel diffusion coefficient (D11) calculations in certain circumstances. We have performed several numerical tests of the iterative method and find no errors outside of the original estimates. Furthermore, independent work using a standard two-term expansion of the Boltzmann equation finds results for the two-term approximation to D11 in significant disagreement with those reported by Lin, Robson, and Mason.
Topological theory of entanglement (two body topological interaction approximation). I. Friction coefficients of the center of polymer chains
Authors: Iwata Kazuyoshi
Published: February 2003

The topological theory of entanglement presented in the previous papers [J. Phys. Soc. Jpn. 37, 1413, 1423, 1429 (1974)] is generalized to a system composed of N three dimensional (D3) linear polymer chains and a system composed of a two dimensional (D2) linear polymer chain and N fixed barriers. The fundamental assumption of the present theory is that entanglement states of the systems are described by a set of (slightly modified) Gauss linking coefficients, ea, each of which represents topological states of two D3 polymer chains or of a D2 polymer chain and a point. These ea’s are called ’’(two body) entanglement coordinates.’’ The Verdier–Stockmayer model is used for representing the Brownian motion of the polymer chains, and diffusion equations are derived for simultaneous distribution functions in regard to the entanglement coordinates {e} and the Rouse coordinates {q}. It is found that the previous theory leads two contradictions: (i) When it is applied to the so-called phantom chains, nonzero interactions, which must be essentially zero, appear among the D3 chains or between the D2 chain and the barriers. (ii) The friction coefficient of the center of the polymer chains derived before diverges in the present systems, when N is infinity. These contradictions are removed by considering the non-Fokker–Planck terms explicitly in the diffusion equations, and nondivergent expressions of the friction coefficient are derived.
Validity of the superposition approximation in an application of the modified Oseen tensor to rigid polymers
Authors: Yoshizaki Takenao , Yamakawa Hiromi
Published: February 2003

The validity of the superposition approximation in the Kirkwood–Riseman formulation of polymer transport problems with the modified Oseen tensor is examined. For rigid polymers composed of spherical beads, the frictional forces exerted by them are obtained as the iterative solutions of coupled integral equations equivalent to the Stokes equation under the nonslip boundary condition. From a comparison with these exact solutions, it is found that the Kirkwood–Riseman formulation with the modified Oseen tensor gives correct results to terms of order σ3 in the case of uniform translation in a fluid at rest, but not for these terms in the case of uniform rotation in linear or vanishing flow, where σ is the ratio of the radius of the bead to the separation between the two.
Electronegativity: The bond charge and the chemical potential approaches
Authors: Pasternak A.
Published: February 2003

The close relationship between the ’’bond-charge electronegativity’’ of Ref. 1 and the chemical potential approach to electronegativity is investigated. (AIP)
Discrete resonance CARS emission from NO2: Its temporal and spectral properties
Authors: McIlwain M. E. , Hindman J. C.
Published: February 2003

Coherent anti-Stokes emission has been observed for resonance excitation of NO2 within an optical pumping geometry similar to that employed for CARS spectroscopy. Spectra have been measured for excitation of NO2 in three wavelength regions of its absorption: 585, 564, and 542 nm. These spectra have been used to investigate the four wave process which produces this emission and to determine the ro–vibronic contributions to the absorption of NO2 at these wavelengths. Results from pressure quenching and time dependence studies indicate that a coherent level is produced which has a relatively long lifetime. The anti-Stokes emission has the same temporal properties as the Stokes pulse. This indicates that only the first pump photon is in resonance with an electronic transition. A comparison of these results with those expected for resonance Raman and discrete resonance Raman in particular indicates that the resonance CARS process can be interpreted by theoretical and phenomenological considerations developed to describe resonance Raman.
Laser pumping of SF6 in the collisional region of a nozzle beam: Bolometric detection of internal excitation
Authors: Coulter D. R. , Grabiner F. R. , Casson L. M. , Flynn G. W. , Bernstein R. B.
Published: February 2003

The influence of low-power CO2 laser radiation upon the internal and translational energy of a supersonic SF6 molecular beam has been investigated. A line-tunable cw (chopped) laser beam, approximately 7 W, is used to irradiate the gas in the expansion region at the exit of the nozzle. Time-of-flight analysis of the skimmed SF6 beam has been carried out using an electron bombardment ionizer–mass filter for monitoring number density. A pumped, liquid He-cooled (1.8 K) bolometer was used to measure laser-induced changes in total energy flux (power) of the incident beam. Vibration–translation/rotation relaxation converts some of the absorbed infrared (IR) energy into translational kinetic energy, as manifested by an increase in both transverse and axial velocity of the SF6 molecules. A significant loss of forward beam flux due to the enhanced radial velocity component is observed. From data on the number density of the SF6 beam, its velocity distribution and the power delivered to the bolometer, the laser-induced enhancement in internal energy per SF6 molecule can be determined. A significant fraction (90%) of the absorbed energy is found to be ’’frozen’’ in the internal degrees of freedom of SF6. Under typical conditions, there is a 15% laser-induced increase in total energy content of the transmitted beam molecules, corresponding to a net energy deposition of 0.22 IR photons per SF6 molecule in the beam.
Electron paramagnetic resonance of VO2+ in hydrated crystals
Authors: Jain Vimal Kumar , Venkateswarlu Putcha
Published: February 2003

The electron paramagnetic resonance of VO2+ ion impurities in single crystals of M″Rb2(SO4)2⋅6H20 where M″=Mg, Fe; MgSO4⋅7H2O; NaKC4H4O6⋅4H2O; and (NH4)2C2O4⋅H2O has been studied at room temperature and at X-band frequency region. Multiple trapping sites for vanadyl are observed in all the crystals. The vanadyl ions enter the lattices at substitutional sites and a correlation is found to exist between the directions of the metal–oxygen bonds and the V–O bonds. The spin-Hamiltonian parameters have been evaluated from single crystal as well as from powder spectra.
Pseudopotential SCF–MO studies of hypervalent compounds. I. XeF2 and XeF4
Authors: Bartell Lawrence S. , Rothman Michael J. , Ewig Carl S. , Van Wazer John R.
Published: February 2003

The (ab initio) effective potential theory developed by Ewig et al. has been applied to a series of hypervalent compounds with a view to elucidating the anomalous properties of several of the higher fluorides of xenon and iodine. In this initial paper the development of a minimal basis set substantially better than an STO-4G atom-optimized set is described. Calculations carried out on XeF2 and XeF4 give valence orbital energies in fair agreement with those obtained with the more flexible, all-electron SCF–MO calculations by Basch et al. Equilibrium structures of XeF2 and XeF4 provided by the effective potential calculations possess the correct symmetries. Bond lengths, although too long by 0.09 Å, correctly reproduce the contraction observed experimentally upon fluorination of XeF2. Calculated bending and stretch–stretch interaction force constants are in pleasing agreement with experiment, as is the stretching anharmonicity. Stretching frequencies evaluated at the experimental bond length, however, are 25% high. Overall, the ability of the present treatment to give a reasonable account of the structures and force fields of XeF2 and XeF4 justifies its application to the higher fluorides where interpretations of observations are more speculative.
Pseudopotential SCF–MO studies of hypervalent compounds. II. XeF+5 and XeF6
Authors: Rothman Michael J. , Bartell Lawrence S. , Ewig Carl S. , Van Wazer John R.
Published: February 2003

New evidence bearing upon the anomalous properties of xenon hexafluoride has been obtained via the ab initio molecular orbital approach applied successfully to the di- and tetrafluorides in paper I. Structures of both XeF+5 and XeF6 are governed by a stereochemically active lone pair. In the case of the square–pyramidal cation the Fax–Xe–Feq angle calculated for the bare ion is within 2° of the value observed in the crystalline complex. For the hexafluoride, however, the calculated deformation from Oh symmetry is appreciably greater than that deduced from electron diffraction intensities. Nevertheless, the results of calculations are in sufficient conformity with the Bartell–Gavin, Pitzer–Bernstein interpretation and at variance with the ’’electronic-isomers’’ interpretation to leave little doubt about the answer. With increasing fluorination in the XeFn series the HOMO–LUMO energy difference decreases and the second-order Jahn–Teller effect is enhanced. Increasing fluorination (and increased positive charge on Xe) also shortens bond lengths; calculated shortenings parallel observed shortenings. The deformation of XeF6 from Oh is along t1u bend and stretch coordinates to a C3v structure with long bonds adjacent to the lone pair, as expected according to the valence-shell–electron-pair-repulsion model. Pure t2g deformations are destabilizing but anharmonic t1u–t2g coupling significantly stabilizes the deformation. Steric aspects of the structure and force field are diagnosed and found to be minor. Values for the force constants f44, f55, f̄4444, f̄444′4′, and f̄445 are derived and found to be of the magnitude forecast in the Bartell–Gavin and Pitzer–Bernstein treatments except that the calculations do not reproduce the delicate balances believed to lead to almost free pseudorotation in XeF6.
The electronic structure of zirconium monosulfide
Authors: Nguyen Thuy-Hoa , Franzen Hugo , Harmon B. N.
Published: February 2003

The electronic structures of ZrS with the NaCl-type and the WC-type lattice structures were calculated by the LAPW method. The results are interpreted in terms of chemical bonding effects in the two forms of ZrS. The results of the calculations are compared with photoelectron spectroscopic and low-temperature heat capacity results. The agreement between the experimental and theoretical results is noted and the discrepancies are commented upon.
Far infrared spectra of van der Waals molecules in HCl–noble gas mixtures
Authors: Boom E. W. , van der Elsken J.
Published: February 2003

Results of far infrared measurements on HCl–noble gas mixtures in the region 14–240 cm−1 at low temperatures and densities between 0.4 and 4 amagat, are presented. Between the free HCl rotational lines distinct absorption features are observed that are assigned to X–HCl van der Waals molecules (X=HCl, Ar, Kr, Xe). Various internal motions of the complexes are considered and it is concluded that the spectra originate from internal rotatory motion of the HCl subunit. A model for an effective angular potential governing this motion is discussed. The trends in the experimental spectra suggest that the well depth increases in the series Ar–Kr–Xe, reflecting an increase in anisotropy in the above order.
The influence of the Li/Nb ratio on the luminescence properties of LiNbO3
Authors: Krol D. M. , Blasse G. , Powell R. C.
Published: February 2003

The luminescence properties of several different undoped and Eu3+-doped LiNbO3 crystals and powders have been investigated. Emission and excitation spectra and fluorescence lifetimes were measured at low temperatures and the diffuse reflectance spectra were measured at room temperature. The results show that the luminescence behavior of LiNbO3 is very sensitive to the Li/Nb ratio. In stoichiometric samples the emission originates from the intrinsic niobate groups, whereas in samples with a Li/Nb ratio of 48.6/50.0 only emission from niobate groups in or near defect sites is observed.
Nuclear spin–lattice relaxation and site symmetry in phase II of solid CH4
Authors: Calvani P. , De Luca F.
Published: February 2003

On the basis of Nijman’s theory of relaxation in solid CH4, T1 measurements at low T are here recognized to be important for determining the exact symmetry of the orienting field in phase II. An experiment in the range 60–100 MHz would check unambiguously the EJK model prediction of a D2d site symmetry. The existing T1 data are shown to agree with this latter as far as the dependence on the Larmor frequency, the dependence on temperature and the T1 behavior during the fast conversion of free-rotating molecules are concerned. The twofold reorientations are probably responsible for the spin–lattice relaxation at low T.
Optical absorption spectra and kinetic behavior of helium excited diatomic molecule (a 3Σu+)
Authors: Takao Satoshi , Kogoma Masuhiro , Oka Takefumi , Imamura Masashi , Arai Shigeyoshi
Published: February 2003

The transient absorption spectra of electron-irradiated 12-atm helium have been measured in the wavelength region 3000–11 000 Å. The observed molecular absorptions correspond to the c 3Σg+←a 3Σu+, e 3Πg←a 3Σu+, and i 3Πg←a 3Σu+ transitions, short-lived atomic absorptions arising from He*(23S) being observed at several wavelengths. The rotational temperature of He*2(a 3Σ+u, v″=0) produced initially is estimated to be room temperature from the intensity distribution of the P branch. The vibrational deactivation rate of He*2(a 3Σu+, v″=1) depends linearly on helium pressure, the rate constant being 1.0×10−14 cm3 sec−1. The rate constants of the quenching reactions of He*2(a 3Σu+, v″=0) by Ne, Ar, Kr, Xe, H2, N2, O2, CO, NO, N2O, and CO2 have been determined from time-dependent measurements of the absorption decay. The rate constants range from 0.4×10−10 cm3 sec−1 for Ne to 1.0×10−9 cm3 sec−1 for CO2. An intense emission and absorption were observed at 7772 Å in the quenching processes of He*2(a 3Σu+, v″=0) by oxygen-containing compounds.
Dynamic effects of pair correlation functions and hydrodynamic interactions on reaction kinetics in liquids
Authors: Hwang Lian-Pin
Published: February 2003

The time-dependent reaction rate and cumulative reaction probability are solved numerically with the incorporation of an effective force and hydrodynamic interaction in the relative diffusion expression. The use of finite difference methods permits the solution no matter how complex the form of the pair correlation function (pcf) and the hydrodynamic interaction utilized. In particular, a Percus–Yevick pcf as well as pcf’s derived from Debye–Hückel theory are utilized to account for the initial distribution and interacting forces for the reactant (pair) molecules. Two measures of time-dependent reactivity, namely the cumulative reaction probability and the observed reaction rate, are found to exhibit significant effects of molecular interaction.
The determination of deuterium atom coordinates and nuclear quadrupole interactions in lanthanum nicotinate dihydrate crystals by Nd3+–deuterium double resonance
Authors: Hutchison Clyde A. , Orlowski Thomas E.
Published: February 2003

We have obtained the ENDOR (electron nuclear double resonance) spectra of the four deuterons of the two D2O molecules coordinated to Nd3+ dilutely substituted for La3+ in La2(C5H4NCO2)6 (D2O4)4 (dimeric lanthanum nicotinate dihydrate) molecules in single crystals. From the measurements of the values of the anisotropic magnetic hyperfine interactions between Nd3+ and the deuterons we have determined the coordinates of the deuterons in the principal axis system of the Nd3+ Zeeman interaction with average standard deviation, 0.011 Å. We have made detailed comparisons of the ENDOR values of the coordinates with values determined by x-ray diffraction. We have also obtained the values of the quadrupole coupling constants, asymmetry parameters, and directions of the principal axes of the electric field gradient tensors at each deuteron site. The analysis of the magnetic hyperfine and electric quadrupole interactions in relation to water molecule geometry, orientations of water molecules, hydrogen bond lengths, and isotope effects in hydrogen bonding, is discussed. Comparisons are made with earlier ENDOR results for the same molecule with H2O coordinated to the metal ion.
Dynamics of electron–hole recombination in anthracene
Authors: Altwegg L. , Zschokke-Gränacher I.
Published: February 2003

A model for the dynamics of electron–hole recombination and the prompt and delayed components of the electroluminescence of anthracene is presented. Mixing of triplet and singlet charge pair states due to a Δg interaction is considered. The theory is compared with a measurement of the magnetic-field dependence of the electroluminescence.
Vibrational relaxation of D2O (ν2)
Authors: Miljanic Šćepan S. , Moore C. Bradley
Published: February 2003

The method of laser-excited vibrational fluorescence has been used to measure vibrational relaxation rates for the bending mode of D2O in collisions with D2O, D2, HD, H2, He, and Ar. The rate constants at 295 K are found to be (3.2±0.2)×10−11, (3.6±0.2)×10−13, (1.2±0.1)×10−12, (3.3±0.2)×10−12, (7.1±0.9)×10−14, and (3.0±1.2)×10−14 cm3 molecule−1 sec−1, respectively. Relaxation times have been measured for two D2O–HDO–H2O mixtures and relaxation probabilities, PD2O–HDO and PD2O–H2O were estimated to be not very different from PD2O–D2O. The temperature dependence of the relaxation was measured for pure D2O. The rates are (1.80±0.08)×10−11 at 400, (2.1±0.1)×10−11 at 350 and (4.0±0.3)×10−11 cm3 molecule−1 sec−1 at 260 K. The corresponding probabilities are fit by P(T)=C exp(ε/kT) with ε = (778±34) K and C=1.1×10−2.
Exact mathematical expressions for the time-dependent behavior of successive first-order reversible reactions
Authors: Morita Akio
Published: February 2003

The Laplace transform of ai(t) with respect to the time t where ai(t) represents the concentration of Ai in the following first-order chemical reaction: has been expressed exactly in terms of continued fractions. In the particular case of k=ki and k′=k′i, we have obtained the exact analytical result for ai(t) expressed explicitly as a function of t.
Comparison of variational transition state theory and the unified statistical model with vibrationally adiabatic transmission coefficients to accurate collinear rate constants for T+HD→TH+D
Authors: Garrett Bruce C. , Truhlar Donald G. , Grev Roger S. , Walker Robert B.
Published: February 2003

We report accurate quantum mechanical reaction probabilities, rate constants, and activation energies for collinear T+HD→TH+D on an accurate potential energy surface. We also report approximate calculations by conventional transition state theory, the unified statistical model, and three versions of variational transition state theory. We include tunneling contributions by two quantum mechanical and three semiclassical methods based on a vibrationally adiabatic treatment of reaction in the ground state. The most accurate approximate calculations for temperatures up to 1500 K are the improved canonical variational theory with Marcus–Coltrin path vibrationally adiabatic ground state (MCPVAG) transmission coefficient and the microcanonical variational theory with MCPVAG transmission coefficient. These two theories and the unified statistical theory with MCPVAG transmission coefficient are accurate within 41% for 400–2400 K but underestimate the rate constant by factors of 2.0 and 2.6 at 300 and 200 K, respectively. The two most accurate approximate theories overestimate the energy of activation for 300–1000 K by 0.46 kcal/mole. The unified statistical model with MCPVAG transmission coefficient produces slightly less accurate rate constants for 600–1500 K and more accurate ones at 2400 K. It overestimates the activation energy for 300–1000 K by only 0.40 kcal/mole.
Product branching ratios in the reaction of O(1D2) with NH3
Authors: Sanders N. D. , Butler J. E. , McDonald J. R.
Published: February 2003

We report the branching ratios amongst various product channels of the O(1D2)+NH3 reaction in addition to the partial internal energy distributions determined for the OH(X 2Πi) and NH(a 1Δ) product molecules.
Indirect determination of concentrations in coexisting phases
Authors: Knobler Charles M. , Scott Robert L.
Published: February 2003

A general method is reported for the determination of the compositions of existing phases in multicomponent mixtures. A previous study of tricritical phenoena in ternary mixtures of hydrocarbons is used to demonstrate the method of analysis.
Product state distribution in the reaction O(1D2)+HCl→OH+Cl
Authors: Luntz A. C.
Published: February 2003

Laser flash photolysis combined with laser induced fluorescence detection has probed the nascent OH internal state distribution produced in the reaction O(1D2) + HCL → OH + CL. This distribution is compared to the predictions of stastical models, and the dynamics is discussed.
Concentration dependence of the self-diffusion coefficient
Authors: Marqusee J. A. , Deutch J. M.
Published: February 2003

The first order concentration dependence of the self-diffusion coefficient for macro-particles in solution is calculated. The role of direct interactions in determining the concentration dependence is considered. (AIP)
On the use of minimal valence basis sets with the coreless Hartree–Fock effective potential
Authors: Topiol Sid , Osman Roman
Published: February 2003

We investigate the reliability of calculated properties obtained by the coreless Hartree–Fock effective potential method with minimal valence basis sets. Three different types of minimal valence basis sets are constructed and tested. Optimized bond lengths are typically too long, while bond angles are similar to those obtained from all electron calculations. Properties closely related to the electronic charge distribution, such as dipole moments and orbital energies, are quite satisfactory when calculated at fixed geometries.
Semiempirical effective Hamiltonians from a first principles’ viewpoint
Authors: Westhaus Paul A.
Published: February 2003

We extend the formal apparatus for generating effective electronic Hamiltonians by a unitary (canonical) transformation on the Coulomb Hamiltonian to model spaces having various numbers of valence electrons. This formal structure is then used to analyze the problem of deducing effective Hamiltonians from empirical data. It is found that certain ambiguities generally arise since there is no way of empirically establishing the unitary transformation within the model space. At best, one can find a family of unitarily equivalent effective Hamiltonians. Examples are given for the π-electron system of ethylene, and the implications of this point of view are discussed for understanding semiempirical theories of electronic molecular structure.
Self-consistent field with pseudopotentials. II. Average energy of configuration calculations for atoms between lithium and krypton
Authors: Szasz Levente
Published: February 2003

The Hartree–Fock equations for all electrons of an arbitrary configuration of an atom or molecule are exactly transformed into pseudopotential equations and the exact pseudopotential operator is approximated by a density-dependent local pseudopotential which is derived using the Thomas–Fermi model. Calculations are presented for the weighted average energies of the ground-state configurations of neutral atoms. Representing each pseudo-wave-function by a single Slater orbital (’’single zeta’’) the energies of the atoms from Li to Ar and of every second atom from Ar to Kr were computed. The results for the total energies and total radial densities agree well with the Hartree–Fock data.
High temperature thermodynamics of the yttrium–hydrogen systems
Authors: Dantzer P. G. , Kleppa O. J.
Published: February 2003

The binary system, yttrium–hydrogen, has been studied at 919 K at pressures up to 1 atm by a calorimetric–equilibrium method. From the calorimetric measurements we found the enthalpy of formation of YH2 at 919 K to be −52.8±0.4 kcal mole−1. The calorimetric results are in very good agreement with some of the enthalpies reported in a recent equilibrium investigation. Comparisons between the calorimetric measurements and the available equilibrium data provide new information on the partial entropy of hydrogen both in close packed hexagonal yttrium, and in the nonstoichiometric dihydride YH2−δ. For both phases we find the partial excess entropy of hydrogen near 1000 K to be about +5 cal mole−1 K−1; this value is essentially fully accounted for by the vibrational entropy contributions of hydrogen.
Shock compression data for liquids. II. Condensed hydrogen and deuterium
Authors: Dick R. D. , Kerley G. I.
Published: February 2003

Dynamic high pressure equation-of-state data are reported for liquid hydrogen and deuterium. Standard high explosive techniques were used to obtain the data from single and double shock compression. The shock velocity–particle velocity data on the principal Hugoniot curves are best fit by a quadratic expression in particle velocity. Intercepts of these expressions with the shock velocity axes agree very well with the measured sound speed. Over the pressure range studied, neither liquid exhibited a transition for the principal Hugoniot curves and no abnormal behavior was observed from the double-shock data. Theoretical Hugoniot curves for these liquids were computed using an equation of state from the Sesame library. The calculations agree with the measurements to within experimental error.
Line broadening in a strong radiation field: Application to electron–phonon systems
Authors: Mukamel Shaul
Published: February 2003

A theory is developed for the treatment of dephasing (line broadening) phenomena in strong radiation fields. The theory is valid for an arbitrary correlation time of the perturbing bath (relative to the broadening) and thus allows for non-Markovian effects (i.e. non-Lorentzian line shapes). Using this theory we are able to describe the behavior of a general line shape in strong radiation fields. In the Markovian limit of fast correlation time we recover the well known results of the Bloch equations. A specific application is made to electron–phonon systems where the necessary correlation functions may be explicitly calculated.
Effect of compressibility upon polymer interface properties
Authors: Tagami Yukiko
Published: February 2003

The theory developed by Helfand and Tagami, and by Helfand and Sapse, to predict the interfacial properties between two immiscible polymers is extended to the case of compressible, nonsymmetric mixtures of polymers. Use is made of the previously discussed analogy between the modified diffusion equations describing the statistics of the two polymeric constituents and the equations of motion of a single particle in a plane. Introduction of a new trajectory for the particle helped to circumvent the complexity previously encountered in the direct perturbational calculation. It is pointed out that the presence of finite compressibility of the polymers tends to diminish slightly the interfacial tension, and that this tendency appears more prominent according as the two polymers become physically indistinguishable, when the intersegment interaction is of nonlocal nature. This is approximately the case with the polyethylene/polyvinylacetate or the polydimethylsiloxane/polyvinylacetate pair. Extensive calculations of the thickness of the interface, the interfacial tension, and the behaviors of the density profiles of the polymer segments are performed for fourteen pairs of polymers.
Orientational and electronic contributions to the third-order susceptibilities of cryogenic liquids
Authors: Kildal Helge , Brueck S. R. J.
Published: February 2003

Alternating current Kerr effect and third-harmonic generation (THG) are reported for the cryogenic liquids CO, O2, N2, and Ar pumped by CO2 TEA laser radiation. The THG experiments measure the hyperpolarizability, while the Kerr effect measurements probe the total nonresonant third-order susceptibility χ(3), arising from both molecular orientation and electronic hyperpolarizability. The THG process in liquid CO is dominated by a vibrational two-photon resonant contribution for the CO2 R(6) pump line at 9.35 μm. By studying the interference between the resonant and nonresonant contributions in liquid CO–O2 mixtures the hyperpolarizability of liquid O2 has been determined relative to the two-photon resonant χ(3) of liquid CO. These measurements give the first experimental confirmation for liquid media that the two-photon resonance contribution to polarized scattering consists of both narrow and broad linewidth components associated with, respectively, the isotropic and anisotropic Raman polarizabilities.
Orientation of tensorial interactions determined from two-dimensional NMR powder spectra
Authors: Linder M. , Höhener A. , Ernst R. R.
Published: February 2003

Methods are described for determining the mutual orientation of molecular interaction tensors based on two-dimensional NMR powder spectra. Necessary conditions are derived under which this determination can be made, procedures for the computation and analysis of 2D powder spectra are indicated and a technique for the construction of ridge plots is worked out. Chemical shift resolved dipolar powder spectra provide an easily interpreted representation of the mutual orientation of chemical shielding and dipolar coupling tensors. The various features and practical applications of such spectra are demonstrated with 2D powder spectra of benzene, lead formate, and methyl formate.
Multiphoton induced isomerization: Dynamics and thermodynamics
Authors: Ben-Shaul A. , Haas Y.
Published: February 2003

Irradiation of an equilibrium mixture of two or more isomers by a high power infrared laser can lead to quantitative formation of a single component that is not necessarily the thermodynamically preferred one. The case of a binary mixture in which only one isomer absorbs the laser light is quantitatively discussed. Light absorption populates levels above the isomerization energy threshold followed by collisional cooling to either reform the reactant or prepare the product. In the limit of weak collisions the branching ratio depends essentially on the phase space available to each isomer at the reaction threshold energy. It is shown that the entropic factor can be dominant under certain conditions and that excess foreign gas is essential for a quantitative transformation.
A new approach to the two-particle Schrödinger bound state problem
Authors: Gazeau J. P. , Maquet A.
Published: February 2003

The Sturmian method, which has been successfully used in various one-particle problems, is extended here to the two-particle Schrödinger equation. The bound state energies are obtained as solutions of algebraic equations. After a pedagogical exposition of the method, results are given for the low-lying states of helium
Improved model calculations for the alkali–rare gas interaction
Authors: Düren R. , Moritz G.
Published: February 2003

The alkali–rare gas potentials are recalculated using the Baylis model for the electronic interaction. Discrepancies with experimental results found in earlier applications of this model are due mainly to numerical approximations. A more realistic cutoff function for the polarization term is introduced and its influence is investigated. For Na–Ne the model fails to reproduce the experimental results. For the A 2Π potential of Na–Ar, Kr, and Xe the remaining discrepancies, which are now entirely due to the model, are 10%–30% for the well depth and 10% for the equilibrium distance.
Molecular spectra, Fermi resonances, and classical motion
Authors: Heller Eric J. , Stechel Ellen B. , Davis Michael J.
Published: February 2003

Classically periodic molecular vibration (such as a totally symmetric stretch) can be unstable against the addition of small components of other modes, depending on anharmonic coupling strengths, near resonance of fundamental frequencies, and the total energy. We report here on some very strong correspondances between classical stability of the motion and quantum spectral features, wave functions, and energy transfer. The usual concept of a vibrational Fermi resonance turns out to apply best to the case where the transition to classical instability occurs at an energy below the first resonant quantum levels (this is the case for the famous Fermi resonance in CO2). In the (probably more common) event that resonant classical instability should set in above several quanta of energy in the mode of interest, the quantum spectrum shows tell-tale pre- and post-resonant signatures which include attraction of quantum levels (rather than the usual Fermi repulsion) and other features not normally associated with Fermi resonances. Evidence is presented which suggests that certain types of periodic motion in anharmonic molecules act as ’’traps’’, and are resistant to energy exchange with other types of motion. Numerical evidence linking the classical and quantum behavior, together with a new semiclassical theory presented here provides a very explicit connection between quantum and classical anharmonic motion.
Spectroscopic studies on doped polyacetylene and β-carotene
Authors: Harada Issei , Furukawa Yukio , Tasumi Mitsuo , Shirakawa Hideki , Ikeda Sakuji
Published: February 2003

In order to elucidate the structural details of doped polyacetylene (a highly conducting organic polymer), the optical absorption, Raman, and infrared spectra of not only trans-(CH)x doped with iodine, AsF5, and SO3 but also β-carotene doped with iodine and SO3 were studied. The infrared spectra of two kinds of isotopically substituted polyacetylenes (CD)x and (13CH)x doped with iodine were also observed. Analysis of the experimental results shows that upon doping each of the four vibrational branches (ν1–ν4) in the 1600–900 cm−1 region of a polyene chain splits into two groups, namely, the higher frequency group and the lower frequency one. The former group consists of the ’’gerade’’ vibrations of polyene parts which are not directly attacked by dopants but are perturbed along the chain, whereas the latter is made up of the ’’ungerade’’ vibrations of the positively charged polyene part with the doped site at its center. The Raman bands in the higher-frequency group of ν1 (mainly the C=C stretching mode) observed with various laser lines give definite information on the segments of conjugated trans double bonds existing in doped polyacetylene. The Raman spectra are also useful for clarifying the structures of dopants. In the infrared spectra of doped trans-(CD)x and (13CH)x the bands appearing on doping all showed respective isotope shifts which confirmed the view that these bands are of vibrational origin. In many respects doped β-carotene proved to be a useful model of doped trans-polyacetylene.
The Raman spectrum of solid carbon dioxide at high pressure
Authors: Schmidt James W. , Daniels William B.
Published: February 2003

Raman spectra of carbon dioxide were measured as functions of molar volume and temperature in the region 0 to 200 cm−1. In crystals constrained to remain at constant volume, the frequencies of the Raman active libron modes were found to shift much less with temperature than expected by comparison with solid nitrogen. In fact, when the slight expansion of the alloy steel cell is taken into account the frequency vs temperature plots show a slight positive temperature dependence as opposed to the fairly large negative shift observed in the nitrogen case. From these measurements, the value of the mode Gruneisen parameters (defined by γj=−d lnωj/d lnV) were determined to be 2.3±0.2, almost 3 times that predicted by the quadrupole–quadrupole model but in fairly good agreement with recent calculations by Gibbons and Klein, and Kobashi and Kihara. These are based on models which include short ranged intermolecular repulsive forces. Linewidths were measured and indicate that in carbon dioxide four phonon processes dominate the decay of the Eg mode, in contrast with nitrogen in which three phonon processes dominate.
Vibronic assignments and vibronic coupling in the 1E′′ state of s
y
m-triazine by two photon spectroscopy
Authors: Webb J. D. , Swift K. M. , Bernstein E. R.
Published: February 2003

Two photon photoacoustically detected spectra are reported for the first excited singlet state 1E″ of sym-triazine in the gas phase. The origin has been positively identified as of E″ symmetry through contour calculations and hot band observations. The excited state absorption is dominated by a highly irregular ν6′ progression. These observations include: 610(A″1) ∼0 cm−1, 610 (E″) ∼227 cm−1, 620 (E″) ∼556 cm−1, 630 (E″) ∼693 cm−1, and possibly 640 (E″) [81o (E″) or 1910 (E″)] ∼836 cm−1 above the 1E″, origin. The one photon observed 610 (A2″) and 620 (A2″) bands at 677 and 1176 cm−1 respectively, fit in well with these assignments. These observations are strongly supported by a Jahn–Teller calculation which predicts: little coupling betwwen the A2″ and E″ electronic manifolds; a large quadratic coupling and a small linear coupling in the E″ manifold; and a quenched angular momentum in this state. Good agreement is shown to exist between one photon and two photon spectroscopic observations and the calculations.
Molecular Rydberg transitions. XVIII. Vibronic doubling in methyl iodide
Authors: McGlynn S. P. , Felps W. S. , Scott J. D. , Findley G.L.
Published: February 2003

A massive vibronic coupling (dynamic Jahn–Teller) effect has been observed in the first s-Rydberg transition of CD3I. The effect is conditioned more by energy-denominator (i.e., near degeneracy) sizes than by matrix element (i.e., 〈H′〉?15 cm−1) sizes. The effect is observed in four different transitions of CH3I and CD3I where, by virtue of energy-denominator variations, alterations of the effect by 2–3 orders of magnitude are observed and interpreted. A very simple model of the coupling is developed and is shown to be numerically powerful. Since the vibronic coupling takes place in an (Ωc,ω)-spin–orbit coupling regime, the smallness of 〈H′〉 is surprising. It is shown that this small magnitude of 〈H′〉 is attributable to spin-selection breakdown which the vibronic coupling in question must accomplish even in the (Ωc,ω) regime.
Specific heat anomalies and phase transitions in the solid electrolyte Ag26I18W4O16
Authors: Greer A. L. , Habbal F. , Scott J. F. , Takahashi T.
Published: February 2003

Changes in the heat capacity of the solid electrolyte Ag26I18W4O16 are measured in the temperature range 150–330 K by differential scanning calorimetry. Our measurements, done on a powder sample, showed that Ag26I18W4O16 has three phase transitions. At T1?199 and T2?248 K, this material exhibits a first order phase transition with heat of transformation H1=53±2 mcal/g and H2=56±4 mcal/g. The phase transition at T3?277 K is second order with characteristic lambda shape. The transition at T1 shows a broad onset and hysteresis (ΔT?4 K). Similarly, the transition at T2 is hysteratic but with ΔT?1 K. No hysteresis is associated with the continuous order–disorder transition at T3. It is concluded that Ag26I18W4O16 becomes a superionic conductor at 277 K, in agreement with F. Habbal, J.A. Zvirgzds, and J.F. Scott [J. Chem. Phys. 69, 4984 (1978)] and not at 247 K, as erroneously concluded by S. Geller, S. A. Wilber, G. F. Ruse, J. R. Akridge, and A. Turkovic, Phys. Rev. B 21, 2506 (1980).
Model for the surface of molten salt. III. Density profile
Authors: Goodisman Jerry
Published: February 2003

The Fowler model gives very poor results for surface properties of molten salts. A previously presented correction for electroneutrality led to qualitatively correct surface tension and surface energy and used only properties of the bulk phase. The integral equation for the electroneutrality function is solved here by a new direct method which works well for Fredholm equations of the first kind. Calculations are performed for different widths for the surface region for NaCl and LiF. The predicted width is less than the Debye length in each case. With the correction, reasonable surface properties are obtained.
Chemiluminescence during the course of a reactive encounter; F+Na2→FNaNa‡*→NaF+Na*
Authors: Arrowsmith P. , Bartoszek F. E. , Bly S. H. P. , Carrington T. , Charters P. E. , Polanyi J. C.
Published: February 2003

The intensity of the emitted visible radiation is studied for the temperature range 830–890 °K. (AIP)
Many-body perturbation theoretical studies of the dipole moments, polarizabilities, and electron affinities of LiF and BeO
Authors: Yoshioka Y. , Jordan K. D.
Published: February 2003

Second-order many-body perturbation theory is employed to obtain correlated values of the dipole moments, polarizabilities, and electron affinities of the isoelectronic LiF and BeO molecules. At their equilibrium bond lengths, correlation is found to decrease the dipole moments of LiF and BeO by 0.17 and 0.16 D, respectively, and to increase the mean polarizabilities by 2.35 and 8.81a30, respectively. The net effect of the inclusion of electron correlation is to increase the electron affinity of LiF by 0.02 eV and to decrease that of BeO by 0.13 eV. The redaction of the BeO electron affinity by electron correlation is attributed to the large decrease of the dipole moment from its Hartree–Fock value.