bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic wave attenuation in the critical temperature region of binary liquid mixtures
Authors: Bains Elizabeth M. , Breazeale M. A.
Published: February 2003

By assuming that there is a ’’viscosity−like’’ contribution to the attenuation of ultrasonic waves in binary liquid mixtures which has the frequency dependence of the viscosity contribution, one is able to fit the critical temperature values of both αλ and α/f2 to the frequency dependence predicted by the Fixman theory. Liquid mixtures tested are nitrobenzene−n−hexane, nitrobenzene−iso−octane, triethylamine−water, n−heptane−o−toluidine, aniline−cyclohexane, and hexane−β,β′−dichloroethyl ether.(AIP)
Magnetothermodynamics of Ce2Zn3(NO3)12⋅24H2O. II. Determination of absolute temperature and other thermodynamic properties of CZN to 0.80 m°K
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2003

An adiabatic demagnetization−sample isolation calorimeter, in which 3He gas provides equilibrium above 0.3°K, and isolation below 0.2°K as 3He condenses on the sample during demagnetization, has been used to investigate the properties of CZN to 0.8 m°K. The determination of entropy gain during magnetic field changes, for correcting ’’adiabaticas’’ to isentropes, has been discussed. The entropy gain was probably due essentially to heat leak (vibration) arriving at the lower temperatures. The effect of hysteresis at modest rates of field change appeared to be too small to contribute to entropy gain within the limit of error. Heat introduction at zero field has enabled the evaluation of the absolute temperature and heat capacity over the range 0.8−30 m°K. A heat capacity maximum occurred near 1.5 m°K. The heat capacity below 1.4 m°K is given by C = 3.6×1014 T5 gibbs/mole Ce3+. Below 1.7 m°K, the initial magnetic susceptibility is constant at 86.7 cm3/mole Ce3+, which extrapolates to a critical field of 58.5 G. Above 30 m°K the temperature is given by the equation T = [0.3098/(χ0 − 0.02632)] − (0.32±0.1)10−3 °K, where χ0 represents the initial susceptibility/mole Ce3+. In the region of constant susceptibility, the temperature is given in terms of entropy. The scale has been designated the Berkeley−CZN−T−Scale 1974. It has been compared with the Berkeley−CMN−T−Scale 1973. The entropy, enthalpy, heat capacity, and temperature of CZN below 0.5°K have been correlated at 0, 1000, 2500, and 5000 G by heat introduction, and at 1000, 2500, 5000, 10000, and 15000 G, by the measurement of work on isentropes. The fifth power dependence of entropy and heat capacity near and below a m°K are believed to be characteristic of relatively pure and weak dipole interactions, for which there appears to be no suggested model.
Fluorescence of mono-olefinic hydrocarbons
Authors: Hirayama Fumio , Lipsky Sanford
Published: February 2003

A weak fluorescence has been observed from propylene, 1−butene, cis−2−butene, trans−2−butene, 1−hexene, cis−2−hexene, trans−2−hexene, 2−methyl−2−pentene, and 2,3−dimethyl−2−butene excited at 184.9 nm in vapor and/or liquid phases. Emission spectra and emission quantum yields are reported. For 2,3−dimethyl−2−butene (tetramethylethylene) the emission intensity was sufficiently strong to permit more detailed study of its properties, and accordingly the effect of longer wavelength excitation, the effectiveness of CCl4 and O2 as quenchers, and the effect of solution in low−temperature hydrocarbon matrices are additionally reported. Possible assignments for the olefin emissions are discussed.
Theoretical studies of molecular ions: BeH−
Authors: Kenney John , Simons Jack
Published: February 2003

In this paper we present the results of our theoretical work on BeH− in which we have used the equations−of−motion method to obtain the 1Σ+ → 2Σ+ vertical ionization energies of BeH− at several internuclear distances. Calculated potential energy curves, equilibrium internuclear distances, and spectroscopic constants are presented for BeH− and BeH. From the ion and neutral potential energy curves we are able to calculate a thermodynamic ionization energy and a dissociation energy for BeH− as well. We also report an interesting correlation between our equations−of−motion results and the Koopmans’ theorem estimate of ionization energies. The effects of basis set optimization on our BeH− calculations are discussed.
Energy dependence of high resolution integral-collision-cross-section measurements for elastic scattering of H and D atoms by Hg at thermal energies
Authors: Schutte A. , Bassi D. , Tommasini F. , Scoles G.
Published: February 2003

High resolution measurements of the energy dependence of the integral collision cross section for the elastic scattering of H and D atoms by Hg at thermal energies are presented and the experimental setup described. Evidence for resonant scattering due to quasibound states is obtained. The results are compared with the predictions of a potential obtained from spectroscopic data, after averaging the calculated cross sections over experimental parameters. Modifying the potential in the transition region, between the wall and the long−range part, improves the agreement between the results and the predictions of the spectroscopic potential in the region of the resonance. The new potential also slightly improves the agreement between energy level predictions and spectroscopic data.
Rigid cage effect on ICl photodissociation and B O+ fluorescence in rare gas matrices
Authors: Bondybey V. E. , Brus L. E.
Published: February 2003

The relaxation dynamics of matrix isolated ICl have been studied via time and wavelength resolved emission. Vibrationally relaxed B O+ fluorescence occurs following irradiation both above and below the gas phase dissociation barrier. The fluorescence quantum yield is near unity independent of excitation wavelength, and I35Cl and I37Cl progressions clearly separate in the emission spectrum. The excitation spectrum shows discrete thresholds for v′ = 0−3 and only smooth structure above the dissociation barrier, indicating that constrictive cage forces cause no significant vibrational quantization in the B O+ repulsive region. Irradiation below the v′ = 0 threshold also yields B O+ fluorescence by a weak sequential two photon process. Vibrational line shapes show that excitation below the barrier produces relaxed phonon emission, while irradiation above the barrier produces unrelaxed phonon structure. It is proposed that unrelaxed emission occurs from metastable orientational (librational) local minima in the v′ = 0 B O+ state. The photodissociation−recombination sequence appears to be a general method for populating phonon states not Franck−Condon accessible in bound−bound absorption.
Simple pair distribution function theory for the calculation of Helmholtz free energy differences
Authors: Chaback Joseph J. , Smith Buford D.
Published: February 2003

A first order theory is developed for the calculation of Helmholtz energy differences. The theory is easy to use and requires only the well−known hard sphere pair distribution function and the pair intermolecular potential function for the species under considerationTriacC%%%%%ermolecular potential Lennard−Jones fluids and mixtures of Lennard−Jones fluids indicate that the theory has a domain of validity limited to molecules with nearly equal ε and σ values.
Quadrupole–quadrupole interactions in CO and N2: Effect on the thermodynamics of mixing
Authors: Chaback Joseph J. , Smith Buford D.
Published: February 2003

A first−order theory for the calculation of Helmholtz free energy differences is used to calculate the free energy (relative to an ideal gas at the same temperature and number density) of N2, CO, and their equimolar mixture. Results show that the superposition of the quadrupole−quadrupole interactions on the Lennard−Jones interactions does not provide an intermolecular potential model that quantitatively describes the mixing thermodynamics. However, such a model does appear to be an effective pair potential for CO. Additional calculations are presented that further establish the accuracy of the selected first−order theory.
Electron attachment and compound formation in flames. VI. Negative ion and compound formation in flames containing rhenium and potassium
Authors: Gould Robert K. , Miller William J.
Published: February 2003

The addition of rhenium−containing additives to H2/O2/N2 flames containing potassium is shown to result in reductions in the concentrations of free potassium and electrons and in the production of the negative ions ReO4− and ReO3−. The observations can be qunantitatively accounted for by the following reaction schemes and thermochemical data: K + HReO4 ? KReO4 + H, ΔH0° = −49±50 kJ mole−1; e− + HReO4 ? ReO4− + H, ΔH0° = 18±50 kJ mole−1; H + ReO4− ? ReO3− + OH, ΔH0° = 136±50 kJ mole−1. These enthalpy changes imply that the electron affinities of ReO3 and ReO4 are approximately 290 kJ mole−1 and 430 kJ mole−1, respectively.
Photoemission from doped solid rare gases
Authors: Ophir Zohar , Raz Baruch , Jortner Joshua , Saile Volker , Schwentner Nikolaus , Koch Ernst-Eckhard , Skibowski Michael , Steinmann Wulf
Published: February 2003

In this paper we report the results of an experimental study of the photoelectric yield of doped solid rare gases in the extreme ultraviolet (h/ω = 8−30 eV) spanning the range of impurity excitations, exciton states, and interband transitions. Results were obtained for Xe in Kr, Xe in Ar, Kr in Ar, and benzene in Ar, Kr, and Xe. For dilute atomic and molecular impurities in solid rare gases three intrinsic photoemission mechanisms are exhibited: (a) direct excitation from the impurity state above the impurity threshold, (b) electronic energy transfer from the host exciton states to the impurity states resulting in exciton induced impurity photoemission, and (c) direct photoemission from the host matrix at energies above the matrix threshold. The photoemission thresholds from impurity states via processes (a) or (b) result in detailed information regarding electron affinities of solid rare gases which are in good agreement with recent data for the pure solids. A detailed study of exciton induced photoemission was conducted on Xe/Ar mixtures. The energy dependent photoemission line shape at different film thicknesses and at different concentrations was analyzed in terms of a kinetic picture involving competition between energy transfer from ’’free’’ excitons and exciton trapping. A quantitative estimate of the diffusion length of Wannier excitons in solid Ar was extracted.
Proton spin–lattice relaxation in cerous magnesium nitrate hydrate
Authors: Utton D. B.
Published: February 2003

The proton spin−lattice relaxation in powdered Ce2Mg3(NO3)12⋅24H2O has been measured in the temperature range 65−335 K. In contrast to other paramagnetic salts it has been found that the nuclear relaxation due to nuclear dipole−dipole interactions is comparable in magnitude with the relaxation due to the electronic moments on the paramagnetic ions in this temperature range. Below 160 K the relaxation times are independent of the resonance frequency and have a temperature dependence given by τ1 = 0.375 exp(−182/T) sec. This is attributed to relaxation via the Ce3+ ions and hence makes it possible to calculate a value for their relaxation times. It is also concluded that the second excited doublet of the Ce3+ ions is at an energy of 200±18 K. At higher temperatures two relaxation time minima are observed. At 14 MHz the minimum values are 71 and 69 msec at 244 and 303 K, respectively. The weak temperature dependence of the NMR second moment indicates that 180° flips of the water molecules provide the relaxation mechanism in this temperature range. Calculated values of τ1, using the published crystallographic data, and assuming that there are two types of water molecule, are in reasonable agreement with experiment. The observed activation energies are approximately 6.8 and 9.5 kcal/mole.
Inelastic scattering in atom–diatomic molecule collisions. II. Effect of rotation on vibrational transition
Authors: Stallcop James R.
Published: February 2003

Rotational and vibrational transitions in a diatomic molecule caused by collisions with an atom are analyzed by a semiclassical method for conditions where the rotational transitions can be handled well by the sudden approximation and the vibrational transitions belong to the adiabatic regime. The contribution to the vibrational transition probability from the correction, which takes the finite value of the spacing between rotational energy levels into account, is examined.
Polarized Raman scattering from a helical biopolymer
Authors: Wilser W. T. , Fitchen D. B.
Published: February 2003

Polarized Raman spectra are reported for thin films of oriented α−helices of poly−γ−benzyl−l−glutamate. All four independent spectra were measured using 180° scattering at near−normal incidence and 90° scattering at grazing incidence. Polarization ratios are analyzed in terms of scattering from a helical array of units with a Raman tensor of axial symmetry and definite orientation depending on the mode involved. The method is applied to three stretching modes: the amide I, the ester carbonyl stretch, and the N−H stretch. Orientation angles of the principal axis relative to the helix axis are found to be 39°±2°, 55°±3°, and 28°±3°, respectively, in good agreement with the results of infrared dichroism.
Rate of the O + SO3 reaction
Authors: Westenberg A. A. , deHaas N.
Published: February 2003

The rate of the O + SO3 reaction has been measured under pseudo−first−order conditions in a discharge flow reactor with ESR detection. The reaction is shown to be a fast third−order process at pressures up to 7 torr, a fact not brought out in previous work. Third−order rate constants obtained for M = He at 298, 385, and 507°K are 7.3±0.2, 3.8±0.2, and 2.4±0.2×1017 cm6 mole−2⋅sec−1, respectively, the data obeying k = 5.0×1016 exp(785/T) in this range. At 298°K, the ratio k (M = N2)/k (M = He) is 1.4, and it is shown that the ratio k (M = SO3)/k (M = He) probably cannot be greater than about 10. The reaction products are written as SO2 + O2, no evidence being found for a stable SO4 in the gas phase. Analogous measurements on N + SO3 indicate it is too slow to measure by this technique (bimolecular rate constant <6×106 cm3 mole−1⋅sec−1), in disagreement with other reported results.
Use of double cosets in constructing integrals over symmetry orbitals
Authors: Davidson Ernest R.
Published: February 2003

Double cosets are used to reduce the formulas for integrals over symmetry orbitals to unique integrals over atomic orbitals.
Molecular beam kinetics: Angular distributions and chemiluminescence in reactions of alkali dimers with halogen atoms and molecules
Authors: Struve W. S. , Krenos J. R. , McFadden D. L. , Herschbach D. R.
Published: February 2003

Crossed−beam studies are presented for several reactions of diatomic alkali molecules with halogen atoms and molecules. The alkali dimers are generated by association of atoms in a supersonic nozzle expansion, the halogen atoms by thermal dissociation of molecules. For both the X + K2 and X2 + K2 reactions (X = Cl, Br), the angular distributions of reactively scattered KX peak forwards (in the center−of−mass system) with respect to the incoming alkali dimer, the final relative translational energy of products is fairly high, ∼10−20 kcal/mole, and the total reaction cross sections are large, ∼50−150 Å2. For the X + A2 reactions (X = Cl, Br, I; A2 = Na2, K2, Rb2), excited alkali atom emission is observed from nearly all energetically accessible transitions which fall within the spectral range of the experiments (2200−8000 Å). Some of these lines come from states located above the reaction exoergicity and thus indicate that the initial relative translation of the reactants is converted into electronic excitation of the product atom. The chemiluminescence spectra for X + K2 correspond to a statistical distribution of excited states, roughly characterized by a temperature of ∼5000°K. The cross sections for chemiluminescence from the lowest excited 2P alkali atom state are ∼10−100 Å2. The X + A2 results are interpreted in terms of electron jumps forming X− + A2+ at crossings of potential surfaces. Calculations using a semiempirical pseudopotential method show the orbital degeneracy of the halogen atom has an important role. This is indicated also by a study of the analogous H + A2 reaction, where orbital degeneracy is lacking and no chemiluminescence is observed. For the X2 + A2 reactions, the angular distributions indicate that the dominant reaction path forms A + AX + X. Chemiluminescence is also observed from the two paths which yield A* + AX + X and AX + AX* (for X2 = Cl2, Br2, I2, ICl, and IBr; A2 = K2, Rb2, and Cs2). For the K2 reactions, the cross sections are ∼0.3−3 Å2 for A* emission and smaller for the AX* emission; for Rb2 and Cs2 the AX* emission becomes stronger. No AX* emission is observed for the analogous X2 + Na2 reactions, although it is energetically allowed. The molecular emission in reactions of ICl and IBr with K2 comes from KI*. These observations are consistent with an electron−jump mechanism which allows facile four−center reaction via (A-) A+⋅⋅⋅X− (X-), a biradical ion−pair intermediate.
Statistical partitioning of electronic energy: Reactions of alkali dimers with halogen atoms
Authors: Krenos J. R. , Tully J. C.
Published: February 2003

The phase space theory of chemical kinetics is applied to reactions of alkali dimers with halogen atoms. Predicted populations of excited electronic states of the product alkali atoms are in good agreement with the results of recent chemiluminescence experiments. This agreement suggests that for this system, in contrast to most other thermal energy collision processes, there is relatively free transfer of energy between electronic and other internal degrees of freedom during reaction.
The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium
Authors: Etters Richard D. , Dugan John V. , Palmer Raymond W.
Published: February 2003

The bulk, ground state properties of atomic hydrogen, deuterium, and tritium systems are calculated assuming that all pair interactions occur via the 3Σ+u atomic triplet potential. The conditions required to obtain this system, including inhibition of recombination through the energetically favorable singlet interaction, are discussed. The internal energy, pressure, and compressibility are calculated over the volume range 40 cm3/mole ? V ⩽200 cm3/mole applying the Monte Carlo technique with a quantum mechanical variational wavefunction. The system studied consisted of 32 atoms in a box with periodic boundary conditions. Results show that atomic triplet hydrogen and deuterium remain gasous at 0 K; i.e., the internal energy is positive at all molar volumes considered. Under the same conditions, tritium forms a liquid with a binding energy of E0 ? −0.75 K per atom, at a volume of V ? 130 cm3/mole. The pair distribution function for these systems is also calculated. A brief discussion of the predicted superfluid behavior of 3Σ+u hydrogen and tritium is presented.
Potential energy surface for the model unimolecular reaction HNC → HCN
Authors: Pearson Peter K. , Schaefer Henry F. , Wahlgren Ulf
Published: February 2003

A b initio electronic structure theory has been used to determine the more important features of the potential energy surface for the simple isomerization reaction HNC → HCN. Extended basis sets were used in conjunction with both self−consistent−field (SCF) and configuration interaction (CI) wavefunctions. For nonlinear or Cs geometrical arrangements of the three atoms, the CI included 11735 configurations, i.e., all single and double excitations. This large scale CI reproduces the HCN ground state geometry quite accurately and has been used to tentatively identify HNC in the interstellar medium. The SCF calculations predict HNC to lie 9.5 kcal/mole above HCN, while CI yields 14.6 kcal/mole. Similarly, barrier heights of 40.2 and 34.9 kcal/mole are predicted by SCF and CI. Thus, the SCF approximation is qualitatively reasonable for HNC → HCN. If HNC is designated by a reaction angle of 180° and HCN by 0°, then the saddle point or transition state is predicted to lie at 73.7°, significantly closer to HCN. A reaction path is determined from the SCF potential surface. The surface will be used in RRKM and classical trajectory studies of the dynamics of this reaction.
Photoelectron and far-ultraviolet absorption spectra of chlorofluoro derivatives of ethane
Authors: Doucet J. , Sauvageau P. , Sandorfy C.
Published: February 2003

The Hei photoelectron and vacuum ultraviolet absorption spectra of the following chlorofluoro derivatives of ethane have been measured: C2F5Cl, CH3CF2Cl, CF2Cl−Cf2Cl, CF2Cl−CFHCL, and CF2CL−CFCl2. The lowest ionization potentials (12−13 eV) and all absorption bands from 50 000−84 000 cm−1 are due to transitions from the chlorine lone pair orbitals (Cl). The I.P.’s between 14 and 16 eV are due to ionization from orbitals mainly populated in the C−Cl, C−C, and C−H bonds, while at higher energies, ionization from orbitals of F lone pair (F) and C−F bonding character takes place. The lowest electronic transition is of the valence−shell type; at higher frequencies, Rydberg bands are found due to 4s→Cl and 4p→Cl type transitions.
Photoelectron and far-ultraviolet spectra of CF3Br, CF2BrCl, and CF2Br2
Authors: Doucet J. , Gilbert R. , Sauvageau P. , Sandorfy C.
Published: February 2003

The Hei photoelectron and vacuum ultraviolet spectra up to about 20 eV of CF3Be, CF2Br2, and CF2BrCl have been measured. In both spectra, we find bands at energies lower than in the corresponding chlorine derivatives. Otherwise, the spectra can be interpreted along similar lines. The lowest ionization potentials and the lowest frequency bands in the ultraviolet spectra are due to transitions from the bromine lone pair orbitals.
Vibrational deactivation of O3 molecules in gas mixtures. II.
Authors: Rosen David I. , Cool Terrill A.
Published: February 2003

Experimental measurements of the rate constants for vibrational deactivation of O3 by O3, O2, CO2, H2, D2, CH4, N2, He, Ar, SF6, CH3Cl, CH2Cl2, CCl4, and C2H2 are presented. Vibrational relaxation of O3 is shown to follow the sequence (1) rapid V → V intermode coupling between the ν1 and ν3 modes, (2) a slower coupling of the ν1, ν3 modes to the ν2 mode, and (3) V → T relaxation through the O3(010) level. The results are described in terms of a simple analytic model for vibrational relaxation of O3.
Kinetics of diffusion-controlled reactions: Transient effects in fluorescence quenching
Authors: Nemzek Thomas L. , Ware William R.
Published: February 2003

A test of the continuum model for diffusion controlled reactions as applied to fluorescence quenching is presented and discussed. By proper selection of systems, it was possible to observe nonexponential decay which followed the decay law exp(−at − 2b√t) as predicted by the continuum model. Analysis of these decay curves gave the encounter radius and pair diffusion coefficient. Reasonable values were obtained for both. Steady−state fluorescence quenching measurements were also made and compared with fluorescence decay studies. Evidence was found for ground−state complex formation. When this was taken into account, good agreement between the continuum model and the experimental results was obtained.
Thermal diffusion in isotopic mixtures of polyatomic gases. I. The thermal diffusion coefficient
Authors: Matzen M. Keith , Hoffman D. K.
Published: February 2003

Perturbation techniques are used to derive an analytical expression for the thermal diffusion coefficient for isotopic, polyatomic gas mixtures. The expansions isolate the contributions to the thermal diffusion coefficient which are subject to isotopic variation and elucidate the effect of external fields on the phenomena.
Dynamics of the reaction of N+ with H2. II. Reactive scattering at relative energies below 3 eV
Authors: Fair James A. , Mahan Bruce H.
Published: February 2003

The reaction N+ (H2,H) NH+ has been investigated in the range of initial relative energies from 0.79 to 2.8 eV. Despite the deep potential energy well (6 eV) associated with the symmetric NH2+ molecule ion, the reaction proceeds predominately by a direct interaction mechanism at relative energies as low as 2 eV. Only when the initial relative energy is near or below 1 eV does a long−lived complex mechanism appear to predominate. This behavior can be rationalized in terms of the qualitative features of potential energy surfaces deduced for the system from an electronic state correlation diagram.
Theoretical studies of molecular ions. The ionization potential and electron affinity of BH
Authors: Griffing Karen M. , Simons Jack
Published: February 2003

We have carried out a thorough study of the lowest energy 1Σ+ → 2Σ+ ionization potential and the 1Σ+ → 2Π electron affinity of BH at several internuclear distances within 0.5 a.u. of the equilibrium bond length. Potential energy curves and spectroscopic constants (Re, ωe) are computed for the ground state (2Σ+) of BH+ as well as for the 2Π diabatic state of BH−. Comparisons with experimental results on the 2Σ+ state of BH+ are reasonably encouraging. The electron density in BH (1Σ+) is compared to that in the isoelectronic negative ion BeH− (1Σ+) in an attempt to better understand the roles of electron repulsion and electron−nuclear attractions in the bonding in these two interesting species.
Raman spectra of aluminum fluoride containing melts and the ionic equilibrium in molten cryolite type mixtures
Authors: Gilbert B. , Mamantov G. , Begun G. M.
Published: February 2003

The structure of molten aluminum fluoride−alkali fluoride mixtures has been investigated by Raman spectroscopy at 700−900°C using a captive liquid windowless cell. Changes in spectra with temperature and melt composition reflect an equilibrium between the species AlF4− and AlF63−. Complete spectrum of the AlF63− was obtained confirming an octahedral coordination; the frequencies of the ν1, ν2, and ν5 vibrations were found to be 555, 390, and 345 cm−1, respectively. A strong cation effect on the bandwidth of the AlF63− ν1 band was observed when the cation is changed from Li+ to Cs+. This effect is believed to be due to a restriction of the rotational mobility of the anion in the presence of a smaller cation. Quantitative analysis of the intensity ratios of the AlF4− and AlF63− ν1 bands as a function of the composition of the melt permits the calculation of the stoichiometric dissociation constant K = XAlF4−XF−2/XAlF63−. An average value of 3±1×10−2 (concentration scale in mole fractions) was found at 780°C. The spectrum of molten cryolite was reinvestigated and found to be different from the previously published spectrum. By extrapolation of the results obtained at lower temperatures and other compositions, the AlF62− ion in molten cryolite dissociates into AlF4− to the extent of ∼25% at 1015°C. This degree of dissociation and the calculated ΔH of the equilibrium are in good agreement with thermodynamic and other methods of investigation.
Properties of HxTaS2: Correlation between the superconducting T
c and an electronic instability in layer compounds
Authors: Murphy D. W. , Di Salvo F. J. , Hull G. W. , Waszczak J. V. , Meyer S. F. , Stewart G. R. , Early S. , Acrivos J. V. , Geballe T. H.
Published: February 2003

The preparation of HxTaS2 (0 < x < 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly H2O in air). Magnetic susceptibility data show that a low temperature transformation in 2H⋅⋅⋅TaS2 (at 80°K) is suppressed with the addition of hydrogen, and at the same time the superconducting transition temperature Tc rises from 0.8 to ∼4.2°K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and Tc measurements in other intercalation compounds, we suggest that the rise of Tc (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity.
Monodispersed tantalum disulfide and adsorption complexes with cations
Authors: Murphy D. W. , Hull G. W.
Published: February 2003

Cathodic electrolysis of 2H⋅⋅⋅TaS2 in a dilute sulfuric acid electrolyte results in intercalation of hydrogen and water. The water content increases as the ionic strength of the electrolyte is decreased. Addition of neutral surfactants (1%−10% Triton X−705 or glycerol) followed by high−speed stirring gave TaS2 layers monodispersed in the aqueous surfactant. Electronic absorption spectra of the dispersions agree well with spectra of cleaved solids. Dyes were used to study adsorption on the layers. Only cationic dyes were adsorbed and the adsorption was determined to be due to an ion exchange reaction with protons. Solid adsorption complexes were prepared by ultracentrifugation of the dispersion or by adding dyes to undispersed, water swollen TaS2. The solid adsorption complexes gave no x−ray powder patterns, and were deficient in sulfur. Ac susceptibility measurements did not indicate bulk superconductivity in any of the complexes. Electron transfer from the TaS2 layers to reducible dyes was observed, the apparent reduction potential being 0.25 V vs NHE.
Study of solvation of excess electrons in ethylene glycol/water and methyltetrahydrofuran matrices by matrix ENDOR
Authors: Hase Hirotomo , Ngo Frank Q. H. , Kevan Larry
Published: February 2003

Matrix proton ENDOR signals have been measured for stabilized excess electrons produced by x irradiation at 4 K in ethylene glycol/water and in 2−methyltetrahydrofuran glasses. The matrix proton ENDOR linewidths are smaller when irradiation is carried out at 77 K. The contribution to the matrix ENDOR linewidth comes principally from predominantly dipolar interactions between the unpaired electron and the surrounding matrix protons. The change in ENDOR linewidth can be interpreted as due to a slight increase in the average distance from the trapped electron to the matrix protons contributing to the matrix ENDOR line as the temperature is raised to 77 K. This is a reflection of the solvation process for the excess electron in these organic glasses. Based on a simple model, the CH bond and molecular dipoles reorient such that the negative H end of the average CH dipole moves 0.2−0.4 Å further away from the unpaired electron as solvation becomes more complete at higher temperature. These results are consistent with the change in electron solvation implied by irreversible changes upon warming of the optical absorption spectra and the EPR linewidths of excess electrons generated at 4 K in these matrices.
Ionic intermediates produced by gamma irradiation at 4 K: Halogenated naphthalene and benzene derivatives in ethanol
Authors: Namiki Akira
Published: February 2003

Optical absorption and ESR measurements have been performed for the irradiated halogenated benzene and naphthalene derivatives in ethanol at 4 K. The anions of both bromo− and chloronaphthalene derivatives were observed under steady state at 4 K, while the former anion at 77 K results in dissociation and the latter anion results in protonation. Both anions of benzene and fluorobenzene were stable at 4 K, whereas not at 77 K, indicating that protonation is inhibited at 4 K. Irradiated iodobenzene and bromobenzene solutions at 4 K showed a doublet band whose energy separation was 0.8−0.9 and 0.41−0.48 eV, which are close to the energy separation between 2P3/2 and 2P1/2 of I and Br, respectively. The transition energies of the long wavelength bands of these compounds and of chlorobenzene is linear with the ionization potentials of respective halide ions with a slope of close to unity. Therefore these bands may be assigned to an electron transfer band from halide ion to its counterpart benzene ring. As the electron acceptor, two models were discussed, one of which is the orbital of neutral benzene, and the other is the orbital of the phenyl radical. In solid phase, dissociative electron attachment to halogenated benzene goes through a state of metastable CT complex of a halide ion and its counterpart molecule. The irradiated p−C6H4BrI showed also a well resolved doublet band, suggesting that C−I bond rupture is more dominant that C−Br bond rupture. The absorption spectrum of irradiated p−C6H4BrCl in ethanol did not resemble either the irradiated chlorobenzene or bromobenzene derivatives, suggesting that both C−Br and C−Cl are ruptured at the same time.
Evidence for a molecular J–J coupling scheme for KI neutral potentials
Authors: Carter Gary M. , Pritchard David
Published: February 2003

We have measured the differential probability of electron spin depolarization for scattering polarized potassium from atomic iodine with several different orientations of the axis of quantization relative to the collision axes. No dependence on this orientation was found, contrary to the predictions of our model for spin depolarization when a strong coupling of the electron spin to the internuclear axis is present during the collision. Consequently, we conclude that the coupling scheme for the lowest neutral states of the KI molecule involved predominantly a coupling of the total electronic spin of the potassium and the total electronic spin of the iodine.
Calculation of radial couplings in collision of slow atoms
Authors: Riera A. , Salin A.
Published: February 2003

A method, similar to the Born−Oppenheimer approximation for bound molecular states, is developed for the calculation of radial coupling matrix elements. (AIP)
Pyroelectric Nd(IO3)3⋅H2O. Crystal structure of the transition-metal iodates. II
Authors: Liminga R. , Abrahams S. C. , Bernstein J. L.
Published: February 2003

Neodymium iodate monohydrate, Nd(IO3)3⋅H2O, crystallizes in the monoclinic system with space group P21 and two formulas in the unit cell. The pyroelectric coefficient at room temperature is about 2.2×10−5 cm−2/°K. The lattice constants at 298°K are a = 10.2012±0.0013, b = 6.70530±0.00004, c = 7.3538±0.0009 Å, and β = 113.11±0.02° (λ CuKα1 = 1.540562 Å). A total of 8060 reflections were measured within a reciprocal hemisphere having (sin ϑ)/λ ? 1.02 Å−1, using PEXRAD. The crystal structure was solved by the interpretation of Patterson and Fourier series and refined by the method of least squares using 2603 independent Fmeas, with final agreement factor R = 0.058. The three independent IO3− ions share oxygen atoms to form a three−dimensional framework of corner−sharing polyhedra. Two iodine atoms are coordinated by seven and the third by six oxygen atoms. All iodine polyhedra have three short I−O distances averaging about 1.81 Å, and longer I−O distances ranging to 3.3 Å. The water molecule links all three independent iodate groups together. Nd3+ occupies a distorted bicapped trigonal prism with average Nd−O distance of 2.45 Å . The piezoelectric coefficient d22 is strong and readily detected.
Dielectric constant of compressed solid methane at low temperature
Authors: Costantino M. S. , Daniels W. B.
Published: February 2003

Measurements of the static dielectric constant and the derived Clausius−Mossotti (CM) values for the solid phases of methane at densities ranging to 20% above the triple point density are reported. The dielectric constant data for 60<T<260 K and 0.52<ρ0.60 g/cm3 may be fitted within experimental error to εs(ρ,T) = 0.7293±0.0006 − (3.2±0.3) × (10−5) T + (2.066±0.008) ρ and the CM data to CM (ρ,T) = 6.497±0.022 − (1.76±0.16) × (10−4) T + (0.061±0.04) ρ. Within experimental error, the CM function is constant across the fluid−solid transition at T = 157.2 K and is independent of density in the solid phase. These data are discussed in terms of a model based on the dielectric behavior of octupole−induced dipoles. The low temperature solid−solid P−T phase diagram is mapped using dielectric anomalies at the transitions and calculated pressures. The existence of a fourth, or δ, phase is demonstrated by a dielectric anomaly that is suggestive of ferro− or antiferroelectric behavior.
Theorems on chemical network stability
Authors: Clarke Bruce L.
Published: February 2003

The stability of steady states of a chemical reaction system is considered within a diagrammatic formulation of the problem. The system’s stability depends upon the kinds of cycles that can be constructed from a set of arrows. The following theorems are proven. (1) A chemical network has no unstable steady states if the set of cycles which can be constructed contains only certain 2−cycles or is empty; (2) an m−cycle, which passes through a reactant whole self−vertex is exactly cancelled by autocatalysis destabilizes the network in certain restrictive circumstances; and (3) a 3−cycle as in (2) destabilizes the network under broader circumstances. The restrictive circumstances of the second theorem do not appear to be capable of being broadened in general because of complexities that can be understood within the full diagrammatic formulation of the problem.
Elastic continuum theory cutoffs and order in nematics and solids
Authors: Berreman Dwight W.
Published: February 2003

Thermal disorder in liquid crystal molecular orientation and thermal displacement of atoms in monatomic crystals can be described with analogous elastic continuum theories having short wavelength cutoffs. Half the short wavelength cutoff that gives the observed displacement is remarkably close to 1.8 times the cube root of the atomic volume in monatomic crystals. Half the short wavelength cutoff that gives the observed order parameter in PAA is also about 1.8 times the cube root of the molecular volume. Some data give a number about twice as large for MBBA. This large cutoff may be due to a large error in measured order parameter, or it may suggest that MBBA molecules tend to form groups in the nematic phase.
Comprehensive optical and collision data for radiation action. I. H2
Authors: Gerhart Donald E.
Published: February 2003

We apply a multistep program of Platzman to construct a complete set of inelastic cross sections for electron scattering at all incident energies. The initial step constructs a complete spectrum of optical oscillator strengths from photoabsorption and other optical data subjected to the constraint of sum rules. Measured cross sections for nonionizing collisions are then adjusted to fit Bethe’s formula. Experimental differential ionization cross sections are analyzed by a new method of Kim’s. The resulting set of all inelastic cross sections is subjected to the Inokuti−Kim−Platzman sum rule. The value of W, the mean energy per ion pair, is calculated from the adopted cross sections and compared with experiment, taking into account dissociation and recombination processes.
Comprehensive optical and collision data for radiation action. II. Ar
Authors: Eggarter E.
Published: February 2003

We present a complete set of optical oscillator strengths and electron impact cross sections for argon gas. The cross sections were obtained utilizing a semiempirical method of Platzman which stresses the close relationship between photoabsorption and fast electron−atom collisions. The data evaluation was done by analyzing a great variety of experimental measurements of various nature and piecing them together on the basis of theory, with the constraints of sum rules. The mean energy per ion pair, W, calculated from adopted cross sections allowing for inner shell contributions is 26.9 eV. This value is expected to exceed the measured value of 26.4 eV, which is reduced by the contribution of collateral ionization.
Vacuum ultraviolet absorption spectra of the bromomethanes
Authors: Causley G. C. , Russell B. R.
Published: February 2003

The vapor phase vacuum ultraviolet absorption spectra of methyl bromide, methylene bromide, bromoform, and carbon tetrabromide are reported for the region 40 000−90 000 cm−1 (250−110 nm). Many of the Rydberg and intravalent absorptions of the bromine electrons in the nonbonding p orbitals, which are perpendicular to the C−Br bonding axes, and the σ*←σ (C−Br) absorptions of the compounds have been assigned. A correlation of the molecular Rydberg series of methyl bromide to series in krypton, which has made possible the assignment of the 4d and 4f Rydberg absorptions, is presented. Expanded vibrational progressions of the first ns and np Rydberg transitions of methylbromide are presented. The analysis of these progressions indicates that transitions to the 5s and 5p Rydberg orbitals bring about a Jahn−Teller distortion of the molecule. Three ns Rydberg series of methylene bromide were assigned which converge on the ionization potentials of 10.629±0.010, 10.839±0.010, and 11.261±0.010 eV. The states formed upon ionization are assigned as the b2, b1, and a1, respectively, as the ns transitions of the a2 combination of bromine p orbitals are forbidden in C2v symmetry. Other absorptions of methylene bromide, as well as the majority of the first ns, np, and nd molecular Rydberg assignments of bromoform and carbon tetrabromide were made using the term values of the bands with respect to the ionization potentials of the molecules. It was found that the averaged ns term values of the bromomethanes vary slightly through the series, while the np term values were increased in methylene bromide and bromoform. In each spectrum the assignment of the σ*←σ (C−Br) bands was made based on an empirically derived relation.
Multiconfiguration self-consistent-field calculation of the dipole moment function and potential curve of NO(X2Π)
Authors: Billingsley Frank P.
Published: February 2003

The electronic dipole moment function, potential energy curve, and other one−electron properties of the 2Π ground state of NO have been calculated from R = 1.6 to R = 3.4 bohr by the optimized valence configurations (OVC) multiconfiguration self−consistent−field method. At internuclear separations only 0.6−0.7 bohr larger than Re, the ground state wavefunction is found to exhibit a nearly equal mixing of electronic configurations corresponding to the X2Π and B2Π states of NO. This behavior and its manifestations in the OVC framework are discussed in detail. The theoretical OVC−MCSCF dipole curve is shown to be consistent with available experimental data in that (1) its first derivative near Re of 1.10 D/bohr is in excellent agreement with that deduced from observed infrared intensities, and (2) the v = 0 dipole expectation value obtained from the computed moment function and accurate vibrational wavefunctions is −0.139 D (N−O+), which is within 0.02 D of the Stark effect microwave result of ±0.158 D. A comparison of the calculated potential curve with an accurate RKR potential for NO (X2Π) indicates relative congruency to within 0.06 eV over the full range of inernuclear separations spanning the turning points of the v = 25 vibrational level. Comparisons with previous theoretical treatments of this molecule are also presented.
Molecular reorientation of carbon monoxide dissolved in dense simple fluids
Authors: Marsault J. P. , Marsault-Herail F. , Lévi G.
Published: February 2003

Extensive infrared measurements of the carbon monoxide fundamental vibration band for CO−Ne, CO−Ar, CO−Kr, CO−Xe, CO−N2, and CO−O2 systems have been carried out in the dense fluid region. We have investigated both the whole liquid range from the triple to the critical point along the saturation line and the continuous change from gas to liquid along an isobar well above the critical pressure. In the case of O2 and N2, we have also studied the liquid−solid transition. The rotational correlation functions Φu(t) and the orientational correlation time τu have been determined from band profile. An order of magnitude of the intermolecular mean square torques has been obtained from band moments analysis. We discuss the ability of ’’m’’ and ’’j’’ diffusion models to describe experimental dipolar momentum correlation functions when the solvent density increases continuously from gas to liquid. These models appear to be unsatisfactory in the liquid phase except for N2 solutions where the ’’j’’ diffusion model gives a rough description of the reorientational process. This has led us to use another description based on the memory function formalism [B. J. Berne and G. D. Harp, Adv. Chem. Phys. 17, 63 (1970); P. Desplanques, E. Constant, and R. Fauquembergue, Molecular Motions in Liquids (Reidel, Dordrecht, Holland, 1974), p. 133; C. R. Acad. Sci. B. 272, 1354 (1971); 274, 611 (1972)]. We discuss the temperature and density dependence of the two involved parameters: the mean square torque 〈 (OV)2〉 and its mean square temporal derivative 〈 (?V)2〉. These parameters have been obtained by fitting the approximate angular momentum memory function: KJ(t) = [〈 (OV)2〉/〈J2〉] exp{−[〈 (?V)2〉/〈 (OV)2〉 − 〈 (OV)2〉/〈J2〉]t2/2}. We show the important role on rotational motion of the local force field anisotropy (which decreases when the solidlike order is appearing in liquid).
Semiclassical collision theory. Application of multidimensional uniform approximations to the atom–rigid-rotor system
Authors: Kreek H. , Ellis R. L. , Marcus R. A.
Published: February 2003

The multidimensional Bessel and Airy uniform approximations developed earlier in this series for the semiclassical S matrix are applied to the atom rigid−rotor system. The need is shown for (a) using a geoemetrical criterion for determining whether a stationary phase point (s.p.pt) is a maximum, minimum, or saddle point; (b) choosing a proper quadrilateral configuration of the s.p. pts. with the phases as nearly equal as possible; and (c) choosing a unit cell to favor near−separation of variables. (a) and (b) apply both to the Airy and to the Bessel uniform approximations, and (c) to the Bessel. The use of a contour plot both to understand and to facilitate the search in new cases is noted. The case of real and complex−valued stationary phase points is also considered, and the Bessel uniform−in−pairs approximation is applied. Comparison is made with exact quantum results. As in the one−dimensional case, the Bessel is an improvment over the Airy for ’’k = 0’’ transitions, while for other transitions they give similar results. Comparison in accuracy with the results of the integral method is also given. As a whole, the agreement can be considered to be reasonable. The improvement of the present over various more approximate results is shown.
The EPR of Cf3+ in octahedral symmetry and the nuclear dipole moment of 249Cf
Authors: Edelstein N. , Karraker D. G.
Published: February 2003

The EPR spectrum of the ground Γ6 state of 249Cf has been measured. The derived spin Hamiltonian parameters are g = 6.273±0.010 and A = (7.52±0.20) ×10−3 cm−1. The nuclear spin I = 9/2 has been confirmed and a value ‖μ‖ = 0.28±0.06μN for the nuclear dipole moment has been calculated from the hyperfine coupling constant.
The interaction of rare gas atoms with graphite surfaces. I. Single adatom energies
Authors: Freeman David L.
Published: February 2003

The Gordon−Kim local density method is applied to the calculation of the interaction energy of helium, neon, argon, and krypton with the basal plane of graphite. In all cases, the binding site is found to be above the center of a hexagon, but the barrier to migration to other sites is less than 50 cal/mole. Comparisons are made with other studies on these systems, and the role of non−two−body additive effects is discussed.
On the use of Raman scattering to probe exciton–phonon coupling in molecular crystals
Authors: Sceats M. G. , Rice Stuart A.
Published: February 2003

An approach to the study of exciton−phonon coupling in molecular crystals using preresonance Raman scattering is developed and the method is illustrated by numerical calculations relevant to crystalline anthracene. Also reported are experimental results in the region preceding preresonance in anthracene; these indicate large contributions of exciton−phonon scattering from high lying electronic states.