bluuebunny/crossref_metadata_2025 huggingface dataset:
Time of flight measurements of the vibrational excitation of CO2 and N2O by collision with 3–8 eV Li+ ions
Authors: Eastes Walter , Ross Ulrich , Toennies J. Peter
Published: February 2003

The relative differential cross sections for the excitation of the first few vibrationally excited states of CO2 and N2O by collision with Li+ ions have been measured by the time of flight technique in a crossed beam scattering experiment. The individual vibrational transitions between the ground state and the first excited bending mode and stretching mode have been resolved for various center of mass energies between 3.0 and 6.9 eV and center of mass angles in the range of 9° to 35°. These angles are larger than the rainbow angle, indicating that the repulsive part of the intermolecular potential was sampled. Both CO2 and N2O exhibit little rotational excitation. At nearly all angles and energies, CO2 shows more vibrational excitation than the equally massive N2O. The bending mode excitation is particularly strong in CO2. Evidence is presented to show that these differences and the lack of rotational excitation cannot be explained purely by differences in the masses of the constituent atoms but must be due to significant differences in the intermolecular potentials. The CO2 observations can be qualitatively explained by a simple potential model involving coulomb forces between the Li+ ion and charges on the atoms of the molecule which are chosen to give the known quadrupole moment. From the rainbow structure of the measured total differential cross sections, the effective depth of the intermolecular potential well was estimated to be 0.52 eV for both systems.
Coulombic reactions of polyelectrolytes with counterions of different sizes
Authors: Gregor Harry P. , Gregor John M.
Published: February 2003

Implicit equations were derived for interactions between a charged rod polyelectrolyte model and counterions of different size. The selectivity of the polymer for the smaller of two counterions as a function of its charge density, distances of approach and annular volume was calculated. Ion binding (site binding) was calculated by assigning a finite thickness to the Stern layer so as to include a finite number of closely held counterions. Further refinements included the consideration of counterion polarizability as a function of the electric field.
The enthalpy of formation and the experimental crystal binding energy of tetrathiofulvalenium 7,7,8,8-tetracyanoquinodimethanide (TTF TCNQ)
Authors: Metzger Robert Melville
Published: February 2003

By rotating-bomb and static-bomb combustion calorimetry, the standard enthalpies of formation at 298.15 K were measured for TTF (290.83±1.73 kJ mol−1), TCNQ (644.94±0.74 kJ mol−1), TTF+0.59TCNQ−0.59(918.37±2.05 kJ mol−1), and TMPD+TCNQ−(662.47±1.85 kJ mol−1). The inferred experimental crystal binding energy for the organic metal TTF+0.59 TCNQ−0.59 is Uρexp=−471±16 kJ mol−1 (−4.88±0.17 eV molecule−1).
The irreversible thermodynamic approach to the fluctuations in chemical reactions
Authors: Chen Yi-der
Published: February 2003

Irreversible thermodynamics is used to obtain the variance matrix of a chemical kinetic system at equilibrium. In contrast to the stochastic master-equation approach, the variance matrix of the present approach does not depend on the rate constants of the reactions. It is thus possible to obtain a general formula for the variances σij=〈 (Ni−Nie) (Nj−Nje) 〉, where Nje is the equilibrium concentration of species i, which applies to linear systems as well as to some nonlinear systems.
Proton spin–lattice relaxation studies of molecular motion and phase transitions in solid choline chloride, bromide, iodide, and perchlorate
Authors: McDowell C. A. , Raghunathan P. , Williams D. S.
Published: February 2003

Proton spin–lattice relaxation time measurements in both the Zeeman and rotating frames (T1 and T1ρ) are reported for the choline ion, Me3+NCH2–CH2OH, in four of its polycrystalline salts, the chloride, bromide, iodide, and perchlorate. In each system, the following motional processes are identified as being responsible for spin–lattice relaxation: (i) rotation of the methyl groups at low temperatures, followed successively by (ii) the onset of motion of +NMe3 moiety about the long chain C–N (denoted as C′3) axis, (iii) general reorientation of the whole choline cation, and (iv) additional slow motion of the long chain CH2CH2OH in the case of the chloride and bromide, and (v) diffusion of the choline ion in the case of the iodide and perchlorate. From a quantitative analysis of the data, activation energies for the above types of motion are determined. A crystal–crystal phase transition which is known to occur at 353, 364, and 362  K in the chloride, bromide, and iodide, respectively, is found to occur at a much lower temperature (272  K) in the perchlorate lattice. Evidence is also presented for a new high temperature phase transition at 430  K in the iodide, at which point a ’’quenching’’ of the diffusional process is found in this structure.
Self-consistent molecular orbital methods. XVIII. Constraints and stability in Hartree–Fock theory
Authors: Seeger Rolf , Pople John A.
Published: February 2003

Constraints that may be applied to the spin orbitals used in Hartree–Fock theory are classified and discussed. Once a constrained stationary wavefunction has been obtained by a self-consistent procedure, it may be tested for stability both internally (with constraints remaining) and externally (with some constraints removed). Methods for carrying out these tests are presented. In addition, a general technique is described for further energy minimization following detection of an instability.
Collisional relaxation of electronically excited bismuth: 6p3(2D°3/2) and 6p3(2D°5/2)
Authors: Trainor Daniel W.
Published: February 2003

Rate constants for the collisional deactivation of Bi 6p3(2D°3/2) and 6p3(2D°5/2) are reported for these states by Ar, Xe, N2, H2, D2, CO, O2, CO2, and SF6 at room temperature. The excited atoms were produced by the flash photodecomposition of trimethyl bismuth and concentrations of these excited states were monitored by time resolved atomic resonance absorption techniques. Comparison of these results is made with the quenching rate constants for these states reported by M. J. Bevan and D. Husain, J. Phys. Chem. 80, 217 (1976).
Pressure-broadened infrared linewidths of HF:Ar and HCl:Ar at moderate densities
Authors: Wormhoudt J. , Steinfeld J. I. , Oppenheim I.
Published: February 2003

The widths of several HCl and HF absorption lines broadened by 10 to 140 atm of argon have been measured using a tunable optical parametric oscillator. The lower pressure data yield values for the linear pressure-broadening coefficients. The data taken at higher densities are used to obtain corrections to the linewidth which are second order in the density. These second density effects are compared with a formal theory for the absorption coefficient at moderate densities due to Albers and Oppenheim, as well as with measurements of the diffusion coefficient obtained in other experiments.
An approximate analytical solution to the three rotational isomeric state model
Authors: Baram Asher
Published: February 2003

An approximate analytical solution is presented for the rotational isomeric state model of flexible polymer configurations. λmax, the largest eigenvalue of the generating matrix, is obtained as a perturbation expansion in powers of σ/λ1, where λ1 is the largest eigenvalue of the statistical matrix and σ=exp(−Eg/kT), where Eg is the gauche energy relative to the trans. The method results in a characteristic polynomial for which λmax is the largest root. For the cubic polynomial the results differ from the exact results, obtained by diagonalizing the generating matrix, by 0.5–5% depending on σ/λ1. The method was applied to calculate 〈r2n〉 and 〈D200(Ωn) 〉.
Polymorphism of the crystalline methylchloromethane compounds. V. The mechanism of the solid–solid phase transition in methylchloroform and the nature of the relation between the ordered forms of carbon tetrachloride and methylchloroform
Authors: Rudman Reuben
Published: February 2003

An analysis is presented of the known lattice parameters of the ordered and orientationally disordered phases of carbon tetrachloride and methylchloroform. It is shown that the phase transition in methylchloroform can be understood in terms of a 0.5 Å shift of the molecular centers parallel to one of the cell edges of the face centered disordered cubic unit cell (which is the a+c direction in the ordered orthorhombic unit cell). A similar mechanism occurs in carbon tetrachloride, but is accompanied by the combination of eight pseudo-orthorhombic unit cells into one monoclinic unit cell containing 32 molecules. As these molecules lose their orientational disorder the volume per molecule decreases approximately 7%.
Ligand field theory for actinides
Authors: Judd B. R.
Published: February 2003

The tendency of a 5f electron to drift from an actinide ion to the neighboring ligands is taken into account by introducing different radial functions for each 5f orbital. The approximation that this amounts to no more than a scaling of the wavefunction in the region of the actinide ion itself leads to a mere doubling in the number of crystal-field parameters. The theory is developed with particular reference to ions at sites of octahedral symmetry. The effective operators that produce equivalent results when acting between unmodified 5f-electron states are two-electron operators. Their irreducible parts, which possess specified group-theoretical properties, are defined and thus made available for more general analyses.
The elastic and inelastic scattering of CsI by Ar and Xe
Authors: Greene E. F. , Hall R. B. , Sondergaard N. A.
Published: February 2003

Further measurements by velocity analysis of differential cross sections for the elastic and inelastic scattering of CsI by Ar and Xe are reported at relative translational energies E in the ranges 4–12 and 6–17 kJ mol−1, respectively. Measurements without velocity analysis for CsI+Ar extend the range to E=117 kJ mol−1. These results for in-plane scattering permit estimates for the total cross sections integrated over the scattering angles for energy exchange by specific amounts ΔE between the internal energy of CsI and the relative translational energy. Both excitation and deexcitation of CsI occur with differential cross sections comparable to or larger than those for elastic scattering except at scattering angles near zero. CsI colliding with Ar or Xe at small impact parameters appears to exchange energy statistically between all the degrees of freedom available.
The vibrational deactivation of HF(v=3) and HF(v=2) by H atoms
Authors: Bott J. F. , Heidner R. F.
Published: February 2003

The rate of HF(v=2 and 3) removal by H atoms was measured at T=295 K. The measurements were performed by laser-induced fluorescence in a discharge flow tube in which H atoms were produced by a microwave discharge. The absolute H-atom concentrations were measured by isothermal calorimetry with a Pt wire coil as a catalytic probe. A small fraction of the injected HF(v=0) was pumped first to HF(v=1) and subsequently to HF(v=2) and HF(v=3) by the multiline output from a pulsed HF transverse excitation atmospheric (TEA) laser. The exponential decay times of the HF 3–0 fluorescence with and without the microwave discharge and the measured H-atom concentrations were used to calculate a removal rate of 6.3×1013 cm3/mol-sec for HF(v=3). This rate is ∼400 times faster than the deactivation of HF(v=1) by H atoms and ∼100 times faster than the deactivation of HF(v=2) also reported in this study. Thus, it many account for the low laser output from the higher vibrational levels that has been observed in pulsed HF lasers. There are several vibrational deactivation processes and reactions that may contribute to the measured removal rate. The present results bear directly on the construction of potential energy surfaces used for theoretical predictions of upper level deactivation rates.
Dielectric studies in solid phase MBBA
Authors: Agarwal V. K. , Arora V. P. , Mansingh Abhai
Published: February 2003

Dielectric measurements have been made in the metastable solid phase of MBBA in the frequency range 1–100 kHz and in the temperature range −196 to 0°C. The results indicate a Debye-type dispersion with symmetric distribution of relaxation times. The dielectric relaxation strength (Δε=ε0−ε∞) varies with temperature and shows a maxima at about −60°C. The results can be qualitatively explained by assuming the free rotation of the dipoles in the temperature range above −60°C and a restricted rotation of the dipoles (or restricted number of active dipoles) in the low temperature region.
Nonlinear optical susceptibilities of triphenylbenzene, resorcinol, and metanitroaniline
Authors: Bergman J. G. , Crane G. R.
Published: February 2003

The nonlinear optical susceptibilities of three π-bonded, molecular systems, (symmetrical triphenylbenzene, resorcinol, and metanitroaniline) possessing large variations in dipole moments (δμ≳50:1) are reported. The results show that the proportionality constant (k) which relates the vector portion of the nonlinear susceptibility (v) to the crystalline spontaneous polarization (Ps), viz., (v=kPs) is ∼30 times larger for these π-bonded systems than for σ-bonded systems and that the spontaneous polarization of triphenylbenzene is ∼0.1 μC/cm2.
Elastic scattering studies of the van der Waals potential for D–HCl and D–HBr
Authors: Bauer W. , Rusin L. Y. , Toennies J. P. , Walaschewski K.
Published: February 2003

The energy dependence of the total integral cross sections and the angular dependence of the nonreactive differential cross sections of D atoms from HBr and HCl has been measured and the Lennard-Jones (12,6) potential parameters are obtained.(AIP)
The intensity distribution in the Na2 and Li2 A–X bands
Authors: Lam L. K. , Gallagher A. , Hessel M. M.
Published: February 2003

The accuracy of the quasistatic or classical Franck–Condon approximation for unresolved bound–bound molecular bands is investigated by comparison with appropriately averaged quantum mechanical calculations. Wavelength-averaged absorption and stimulated emission cross sections are calculated for the A–X bands of Na2 and Li2, representing low resolution or collision broadened spectra, and comparisons are made with experimental spectra. These A–X bands exhibit a red edge, due to a head of heads or a classical satellite, and a comparison of quantum mechanical, classical, and semiclassical satellite shapes is made. The overall quantum mechanical band shapes agree with the classical calculation, except for approximately periodic band structures and nonclassical behavior at the satellites. The emission spectrum resulting from white light or electron excitation of Na2, is also calculated and compared to that observed in an electrical discharge. Finally, emission spectra of Na2 for thermal distributions at various temperatures are compared to the fluorescence spectrum observed from excited dimers formed by an atom–molecule excitation transfer process.
Dissociation of Br2 in shock waves
Authors: Macdonald R. G. , Burns George , Boyd R. K.
Published: February 2003

The rate of dissocation of Br2 in the presence of Ar and Br2 has been investigated using three independent experimental techniques in the same shock tube: molecular absorption spectroscopy (AS), two-body emission spectroscopy (ES), and laser schlieren technique (LS). Present results yield recombination rate constants in good agreement with each other and with earlier high temperature flash photolysis data. The temperature range over which dissociation was studied was extended from 1200 to 3000 °K. Recombination rate constants can be summarized in terms of the following equations: log10krAr(LS) =8.251(±0.002)−1.36(±0.29)log10(T/2300) or log10krAr(LS) =8.378(±0.001)−1.05(±0.30) log10(T/2300). The difference between these two equations arose because in the first equation RBr=RBr2 was assumed, while in the second RBr=RKr was used. Here Rx is the Gladstone–Dale constant of X. These equations are valid between 1600 and 3000°K. The analogous equations for krBr2 are: log10kBr2=8.718(±0.001)−2.35(±0.41)log10(T/1900) and log10krBr2=8.767(±0.001)−2.18(±0.42) log20(T/1900), valid between 1600 and 2000 °K. Furthermore, it is found that log10krAr(AS+ES) =8.182(±0.003)−1.42(±0.18)log10(T/1963), valid between 1180 and 2890 °K. The laser schlieren technique, as applied to chemical reactions in shock waves, was studied. In particular, the effect of finite width laser beam, optical absorption of reacting gas, temperature dependence of its refractive index, and composition dependence of its Gladstone–Dale constant, were investigated. It was found that calculated values of rate constants are sensitive functions of refraction, and hence polarizabilities, of reaction products. Although generally these properties are not known, they can be estimated empirically.
The high temperature vaporization and thermodynamics of the titanium oxides. XI. Stoichiometric titanium monoxide
Authors: Sheldon Robert I. , Gilles Paul W.
Published: February 2003

Vaporization measurements by the Knudsen technique and by mass spectrometry have been performed on the incongruently vaporizing titanium monoxide at the stoichiometric composition. Over this sample at 1806 K Ti(g) has a higher pressure than TiO(g) by a factor of about 3.5. The free energy difference between TiO(g) and TiO(s) is the first primary result, and its value at 1806 K of 63.3±2.0 kcal/mole is independent of auxiliary data. The second primary result is the activity of Ti, 0.13±0.04, in nearly stoichiometric TiO at the same temperature. Over the temperature range 1694–1919 K, the pressures of the various species are given by the equation lnP=−A/RT+B/R, and the values of the parameters A in kcal/mole and B in e.u. are for Ti 116.3±3.2 and 31.8±1.8; TiO, 130.2±3.0 and 37.0±2.0; O, 175.6±4.9 and 34.0±2.7; O2, 229.4±9.8 and 36.2±5.4, respectively. The second-law enthalpy and entropy of vaporization at 298 K of TiO to form TiO(g) are 138.2±3.0 kcal/mole and 45.0±2.0 e.u., respectively. The third-law value is 141.2±0.1 kcal/mole. The results corroborate the values given in the 1975 Supplement to the JANAF Tables, but show that previously reported values of the O2 potential are too high by a factor of about 43.
Modulated perturbation theory for molecular interactions. III. Variational calculations of the second-order energy for the ground state of H2+
Authors: Magnasco V. , Figari G. , Battezzati M.
Published: February 2003

Hylleraas variational calculations of the second-order energy for the ground state of H2+ have been performed in the modified form of Murrell–Shaw–Musher–Amos (MS–MA) perturbation theory including exchange described in Paper I. Simple first-order trial functions consisting in a single optimized Slater function for each multipole are found to be effective in representing nonexpanded multipole components of the interaction energy. The modulated form of the theory includes a large part of the spherical component of the polarization function already in first order, leaving dipole polarization as the dominant second-order contribution.
On moment index displacement
Authors: Small Enoch W. , Isenberg Irvin
Published: February 2003

Moment index displacement can determine the amount of light scatter and zero point displacement in fluorescence time decay data. Two different types of light scatter are considered and shown to have significantly different effects on the analysis of the data. The amplitude correction factor determined by Eisenfeld and Mishelevich is experimentally verified.
Generalized oscillator strengths and total cross sections for H2, N2, and O2 with an independent particle model
Authors: Domenicucci Anthony G. , Miller Kenneth J.
Published: February 2003

Generalized oscillator strengths, oscillator strengths, and total cross sections are calculated within the first Born approximation for 1σg→nσu and nπu transitions in H2; for selected 2σu, 1πu, and 3σg to nπg, nπu, nσg, nσu, and nδg transitions in N2; and for the 1πg→nπu excitations in O2 in addition to transitions equivalent to those studied in N2. When compared with the corresponding experimental spin-allowed excitations good agreement is obtained in most cases. The spheroidal potential approximation within the independent particle model (IPM) is analyzed as the source of the problem for several of the transitions in N2 and O2 which yield properties smaller than the experimental results by 2 orders of magnitude. The theoretical result, previously unreported, for the 1πu→1δg transition in N2 suggests that its intensity should be compared to the 1πu→1πg(b′←X) and that it corresponds to the e←X transition. The theoretical result for the 1πu→1δg transition in O2 for which there is no experimental data is also reported.
A study of the chemisorption of phenol and its derivatives on plasma-grown aluminium oxide by inelastic electron tunneling spectroscopy
Authors: McMorris I. W. N. , Brown N. M. D. , Walmsley D. G.
Published: February 2003

Inelastic electron tunneling spectroscopy has been applied to study the adsorption of a series of phenols on plasma-grown aluminium oxide. Vapor phase doping was used and spectra recorded for o-, m-, p-chlorophenol, p-fluorophenol, p-bromophenol, o-, m-, p-cresol, and phenol. The high resolution spectra obtained at 2 K allow most of the possible modes to be identifield. The relative strengths of these modes are compared in terms of the proposed molecular orientation of the absorbates in an effort to observe the predicted directional sensitivity of the tunneling process. No systematic line intensity variation is evident, and it is postulated that for large molecules this may be because of the complexity of the motions involved in the vibrational modes. It is also suggested that the contouring of the lead electrode round the adsorbate has the important effect of obscuring the directional sensitivity of the tunneling process. An attempt has also been made further to characterize the chemical nature of the oxide and its surface.
Colloidal suspensions as soft core liquids
Authors: Schaefer Dale W.
Published: February 2003

The structure of a suspension of highly charged macromolecules indicates both solidlike and liquidlike phases separated by a distinct melting point. Here the structure factor of the liquidlike phase measured by optical techniques is analyzed using methods previously developed for simple fluids. The hypernetted-chain approximation is found to be superior to the Percus–Yevick and Kirkwood-superposition approximations.
Coherence-length anisotropy above the isotropic-to-nematic transition in a series of benzylidene anilines
Authors: Courtens Eric
Published: February 2003

The relative depolarized scattering strength and the coherence length anisotropy have been measured in a series of p-N-alkoxybenzylidene p-n-butylanilines with alkyl chain length n=1,2,4,7, and 8. All compounds appear to obey mean-field theory. The depolarized scattering strength at a given reduced temperature (T−T*)/T* decreases with increasing chain length, whereas the free-energy parameter L2 that characterizes the anisotropy is roughly constant. There is no apparent modification in the observed pretransitional effects when the transition changes from isotropic-to-nematic (n<8) to isotropic-to-smectic (n=8).
Determination of absolute rate constants for an excited triplet state
Authors: Leenstra Willem R. , Gouterman Martin , Kwiram Alvin L.
Published: February 2003

Absolute values for the rate constants for intersystem crossing to each of the triplet sublevels have been determined. This has been achieved by monitoring both the phosphorescence and the fluorescence in an optically detected magnetic resonance experiment. Using the above absolute values togethr with the measured value for the phosphorescence quantum yield allows us to determine the absolute values for the radiative and nonradiative rate constants for decay from the individual sublevels of the triplet state.(AIP)
Radical pairs in irradiated aromatic crystals
Authors: Matsuyama Tomochika , Yamaoka Hitoshi
Published: February 2003

Radical pair formation is observed in irradiated aromatic crystals by EPR technique. Single crystals of benzene anthracene and naphthalene were irradiated at 77°K by 60Co γ rays up to a dose of 109 rads. The EPR spectra of the resulting species is reported. (AIP)
Far-infrared and Raman spectra, powder x-ray diffraction, and symmetry of crystalline ethylene oxide
Authors: Bertie John E. , Jacobs Stephen M.
Published: February 2003

The x-ray diffraction pattern of powdered oxirane at 90°K, the far-infrared spectrum of polycrystalline oxirane at 4.3°K, and polarized Raman spectra of oriented crystals of oxirane between 125 and 22°K, are reported. The spectra of the solid are reassigned and crystalline oxirane is found to belong to the monoclinic system, crystal class C2h, with four molecules on general positions in the primitive unit cell.
Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. IV. Determination of absolute temperature scales and other properties below 0.5°K with constant magnetic fields along the a crystal axis
Authors: Fisher R. A. , Brodale G. E. , Hornung E. W. , Giauque W. F.
Published: February 2003

The magnetic moment of a 3.930 cm diam spherical single crystal of Nd(C2H5SO4)3⋅9H2O (NES) has been measured below 0.5 °K after cooling by demagnetization from fields of 25, 15, 10, and 5 kG along the a crystal axis. Small amounts of irreversibility, believed to be due to the different rates of cooling of the 79.5% spin-free Nd3+ isotopes and the 20.5% Nd3+ isotopes with nuclear spin, was measured by ’’entropy gain,’’ enabling correction to true magnetic moments on isentropes. Equilibrium between the lattice and electron system was lost at fields of about 40 kG and temperatures below 0.5 °K. Entropy gain values were recorded for 0, 1000, 2500, and 5000 G on isoerstedics. An ’’Adiabatic Demagnetization-Sample Isolation-Calorimeter’’ was used to measure enthalpy as a function of entropy by means of electrical heating after demagnetization, thus enabling the derivation of thermodynamic temperature scales at zero and constant fields of 1, 2.5, and 5 kG as a function of entropy. The temperature-dependent component of the initial susceptibility, (χa,0−χa,T-ind), obtained from the magnetic moment data leads to the expression (χa,0−0.00576) = (0.3899/T)[1−0.0028/T −2.56×10−4/T2+5.06×10−6/T3−3.15×10−8/T 4] cm3/mole NES, which is valid down to 0.014 °K. The ’’high temperature’’ limiting magnetic component of the heat capacity was found to be CH=0(mag) =2.29×10−3/T2 −9.0×10−3/T3 gibbs/mole Nd3+. After correcting for the nuclear hyperfine structure term, 1.87×10−3 gibbs °K2/mole Nd3+, the dipole–dipole interaction term ADD=0.42×10−3 gibbs °K2/mole Nd3+. This, and the similar ADD=0.40×10−3 gibbs °K2/mole Nd3+ found from c-axis data, may be compared to the theoretical value, 0.396×10−3 gibbs °K2/mole Nd3+. The agreement shows that, aside from the hyperfine nuclear effect, the magnetic interactions are essentially ideal dipole–dipole. A heat capacity maximum occurred at 0.014 °K and zero field. The thermodynamic temperature, relative enthalpy, relative internal energy, heat capacity, and magnetic moment were tabulated as a function of entropy over the range 0.01–0.5 °K for zero field. Tabulations are also included for 1000, 2500, and 5000 G. Comments on the magnetic ground state of NES are given. Evidence for ’’frozen-in’’ magnetic structure at zero field and low temperature is presented.
Neutron molecular spectroscopy using a white beam time-of-flight spectrometer
Authors: Chen S.-H. , Jorgensen J. D. , Berney C. V.
Published: February 2003

An inverted-geometry white beam TOF neutron spectrometer using an extended graphite crystal analyzer was constructed at the CP-5 reactor at Argonne. A performance test of the spectrometer for incoherent inelastic scattering studies was made with five selected molecular solids. The results demonstrate the utility of such a spectrometer for investigation of lattice vibrational spectra of hydrogenous compounds in the energy range 0–400 cm−1. We describe design considerations and energy resolution of the spectrometer, and discuss observed low-frequency spectra of acetic acid (CH3COOH, CD3COOH, and CH3COOD), cyclohexane, and cyclopentane.
Spin–orbit coupling in exciton bands of molecular crystals
Authors: Cooper D. E. , Fayer M. D.
Published: February 2003

The problem of spin–orbit coupling (SOC) of exciton bands in molecular crystals is considered. In addition to the usual intramolecular SOC terms, intermolecular SOC terms are obtained if the exciton Bloch functions are properly antisymmetrized and if finite overlap of nearest neighbor molecular functions is accounted for. The magnitude of the intermolecular terms depends on the exciton wave vector k. Numerical calculations on the first triplet exciton bands of 1,2,4,5-tetrachlorobenzene crystals indicate that intermolecular SOC terms are approximately 2×10−3 as large as allowed one-center intramolecular terms. This is comparable in magnitude to vibronically induced SOC which is important in many isolated molecules. The effects of triplet exciton intermolecular SOC on intersystem crossing, radiative relaxation, and nonradiative relaxation are discussed for ππ* triplet exciton bands.
Methyl isocyanide photodissociation: Chemical laser determination of energy partitioning into the cyanide radical photochemical product
Authors: Knudtson J. Thomas , Berry Michael J.
Published: February 2003

Chemical laser techniques have been used to study the photodissociative excitation of cyanide radical by photolysis of methyl isocyanide: CH3NC→h/ωλ≳1550ÅCH3+CN* (A 2Πi) and to identify efficient spin-orbit relaxation of cyanide radical between its A 2Π1/2 and A 2Π3/2 manifolds. Many new chemical laser transitions have been obtained within the cyanide radical 0,0 red band [CN* (A 2Πi, v′=0) →CN(X 2Σ+, v″=0)] by selective cavity Q spoiling with a diffraction grating. In addition, measurements of the relative gain coefficients of grating-tuned laser transitions establish that photochemical reaction branching strongly favors CN* (A 2Πi, v=0) production; other possible product states [e.g., CN* (A 2Πi, v?1) and CN(X2Σ+, v=0)] are minor components (<10%) of the nascent cyanide radical concentration. The observed cyanide radical product state distribution is highly surprising (i.e., highly nonstatistical), signifying that strong dynamical effects govern the process of photodissociative excitation. All available spectroscopic, photochemical, and product energy partitioning data are used to formulate a state-to-state photochemical reaction mechanism for CN* (A 2Πi, v′) production by CH3NC photodissociation.
Magnetic interactions between nitroxide free radicals and lanthanides or Cu2+ in liquids
Authors: Hyde James S. , Sarna T.
Published: February 2003

Heisenberg exchange has been found in all previous work to be the dominant intermolecular magnetic interaction between paramagnetic species in solutions of low viscosity, and this conclusion is confirmed here in analysis of interactions between Cu2+ and a nitroxide free radical. Exchange between a fast relaxing metal ion and a slow relaxing radical contributes equally to the transverse and longitudinal relaxation probabilities, T−12 and T−11, of the radical. A new result that could be of significance in investigations of molecular dynamics in liquids is that dipole–dipole interactions between ions of the lanthanide series and free radicals are dominant in all conditions over Heisenberg exchange. In the liquid phase, Gd3+ is particularly effective in inducing free radical longitudinal relaxation.
Theory of melting in simple polymers. II. Contribution from phonon anharmonicity
Authors: Boyle F. P. , Taylor P. L. , Hopfinger A. J.
Published: February 2003

The effect of phonons is introduced in a previously described formalism for calculating the Helmholtz energy of a polymer crystal and its melt. The phonon frequencies are functionals of the distribution of torsional angles in the system, but this distribution must in turn be self-consistently determined by minimization of the total free energy, including phonon contributions. The theory was applied with the use of intrachain potentials calculated by molecular orbital techniques and interchain potentials found by molecular mechanics. Inclusion of phonons leads to improved agreement with the experimentally observed melting temperature in polymethylene, but aggravates a discrepancy in the case of polytetrafluoroethylene.
Coupled molecular reorientational relaxation kinetics in mixed binary liquids directly measured by picosecond laser techniques
Authors: Ho P. P. , Alfano R. R.
Published: February 2003

The reorientational kinetics of binary liquid mixtures of Kerr active solute and Kerr nonactive solvent molecules have been measured directly using the picosecond optical Kerr effect. The relaxation times are attributed to the reorientation of the system of solute and solvent molecules.
Low-temperature magnetic properties of [(C2H5)2NH2]CuCl4, a two-dimensional magnetic system
Authors: Landee C. P. , Roberts S. A. , Willett R. D.
Published: February 2003

The static magnetic susceptibility and EPR spectra of the low temperature phase of [(C2H5)2NH2]2CuCl4 have been measured. The susceptibility is indicative of a low-dimensional antiferromagnet, and on the basis of structural characteristics, has been interpreted as a two-dimensional system. Analysis of the susceptibility in terms of the high temperature series expansion for the two-dimensional Heisenberg system gave an excellent fit to the data with ‖J‖/k =1.87 K. The EPR data confirmed the presence of exchange coupling. The narrow EPR linewidths (3–6 Oe) are explained on this basis. The angular variation is shown to arise from g tensor anisotropy as well as anisotropic and antisymmetric exchange terms.
Surface tension, compressibility, and surface segregation in liquid binary alloys
Authors: Bhatia A. B. , March N. H.
Published: February 2003

The phenomenological treatment of Cahn and Hilliard, which relates the product κTσ of the isothermal compressibility κT and the surface tension σ to the thickness l of the liquid surface is generalized to liquid alloys. The result obtained is σ∼ (l/κT)[1+δ2SCC(0)/nkBTκT] −1, where δ (1/V)(∂V/∂c) is the size difference factor, SCC(0) represents the concentration fluctuations nV< (Δc)2≳, while n is the number density in the alloy. This formula affords a ready explanation of the remarkable variation of surface tension in the amalgams of the alkali metals. Surface segregation occurs in a dilute alloy c→0 when dσ/dc is negative, from the Gibbs formula. The above result for σ yields, with ϑ=nkBTκT, (1/σ)(dσ/dc) ‖c=0∼ (1/l)(dl/dc)− (1/κT)(dκT/dc)−(δ2/ϑ) ‖c=0. Screening arguments due to Friedel suggest, at least for simple metals with a valence difference between components, that dl/dc‖c=0 will be zero. Then the above formula for dσ/dc‖c=0 shows that favorable circumstances for segregation are: (a) positive dκT/dc; (b) large size difference δ and small ϑ. Finally the relation of our work to that of Burton and Machlin, who correlate bulk phase diagrams and surface segregation, is briefly considered.
A determination of adatom–adatom interaction energies: Application to oxygen chemisorbed on the tungsten (110) surface
Authors: Williams Ellen D. , Cunningham S. L. , Weinberg W. H.
Published: February 2003

A Monte Carlo simulation has been carried out to describe two-dimensional order–disorder phenomena. The model contains (attractive) first, (repulsive) second, and (attractive) third neighbor pairwise interactions. The special case of oxygen chemisorption on a tungsten (110) surface, on which an ordered p (2×1) overlayer is formed at low surface temperatures, is considered explicitly. From the measured order–disorder transition temperatures at both quarter- and half-monolayer surface coverages, (nonunique) values of the three pairwise interaction energies have been determined. These pairwise interaction energies have been used to determine the variation in the total interaction energy, the heat capacity and the entropy with surface temperature.
Existence of the dielectric constant in fluids of nonlinear rigid polar molecules
Authors: Ramshaw John D.
Published: February 2003

The existence of the dielectric constant ε is investigated for fluids composed of nonlinear rigid polar molecules. The investigation is performed using the functional-derivative approach previously employed to establish sufficient conditions for the existence of ε in fluids of linear (axially symmetric) molecules. It is shown that these same conditions are sufficient for nonlinear molecules of arbitrary symmetry. An expression for ε in terms of the direct correlation function emerges automatically from the development. This expression, which involves the inversion of a 3×3 matrix, is a slight generalization of one obtained earlier by Ho/ye and Stell using an entirely different approach.
Transfer of vibrational energy to oscillatory, restricted rotational, and translational motion in HCl+Cl
Authors: Shin H. K.
Published: February 2003

A collision model is developed for the de-excitation of HX(v) by X based on the mechanism that the vibrational energy of HX is transferred to the oscillatory and restricted rotational motion of HX in the X–H⋅⋅⋅X intermediate and the translational motion of the collision system. For HCl+Cl, calculated values of the rate constant are in fair agreement with experiment, but their temperature dependence is found to significantly different.
Calculation of the photoionization cross section of the 1Σu+ excimer state of Ar2
Authors: Rescigno T. N. , Hazi A. U. , Orel A. E.
Published: February 2003

The vertical photoionization profiels of the bound 1Σu+ excimer state of Ar2 are reported.(AIP)
Deuteration effects in irradiated inositol
Authors: Budzinski Edwin E. , Box Harold C.
Published: February 2003

A primary reduction product in partially deuterated and x-irradiated inositol has been detected. The conformations of the alkoxy radicals produced are discussed.
Note on Miller’s method to compute partition functions for the case of hard spheres
Authors: Berrondo M. , Larsen S. Y.
Published: February 2003

A classical path approximation devised by Miller is applied to the 2nd virial coefficient of hard spheres, used as a test case. The result is compared to the known high temperature asymptotic expansion. A note of caution is sounded.
Cubic force constants and equilibrium geometry of methane from Hartree–Fock and correlated wavefunctions
Authors: Pulay Péter , Meyer Wilfried , Boggs James E.
Published: February 2003

The ab initio harmonic and cubic force field of methane has been determined, both from Hartree–Fock and from highly correlated CEPA wavefunctions. The effect of correlation is small on the force field, particularly on the cubic constants. The ab initio cubic force constants were used to calculate the equilibrium CH bond length from the electron diffraction rg and from the spectroscopic r0 values. The weighted mean of the results is re=1.0862 ±0.0005 Å. There remains a small but disturbing discrepancy between the best ab initio and the present corrected experimental results, both for the bond length and for the CH stretching force constants.
Solution of the Smoluchowski equation with a Coulomb potential. I. General results
Authors: Hong K. M. , Noolandi J.
Published: February 2003

The time-dependent Smoluchowski equation with a Coulomb potential is solved analytically for a general boundary condition, and expressions for the distribution function, reaction rate, and survival probability are given. The expressions are evaluated numerically and the long-time behavior is derived. The theoretical results apply to experiments involving ion recombination without an electric field (or where there is a time delay in the application of the field), to scavenging experiments, and to fluorescence quenching.
Intermolecular potentials and the simulation of liquid water
Authors: McDonald I. R. , Klein M. L.
Published: February 2003

A recently proposed intermolecular potential for the (H2O)2 dimer, obtained in part by fitting to the second virial coefficient of steam, is used in a molecular dynamics simulation of liquid water. The calculated distribution of oxygen atoms is compared with the distribution of molecular centers derived from x-ray data. Agreement with experiment is somewhat worse than for the CI model of Clementi and his co-workers.
Theoretical studies of MHD plasma molecules. I. Potential energy curves and dipole moments of linear KOH
Authors: England Walter B.
Published: February 2003

Uncorrelated and correlated potential energy curves and dipole moments are reported for linear KOH. The compound is found to be ionic, K+OH−. Minimum energy bond lengths are RKO=4.2913 au and ROH=1.7688 au, with an estimated accuracy of 2%. The corresponding dipole moment is 3.3 au (8.46 D) with a similar accuracy estimate. This is to our knowledge the first value ever reported for the KOH dipole moment, and the large value suggests that KOH will be an effective electron scatterer in MHD plasmas.
Vibronic coupling in deoxyhemoglobin and deoxymyoglobin
Authors: Bacci M.
Published: February 2003

The importance of the vibronic coupling for the interpretation of magnetic susceptibility and Mössbauer data of deoxygenated hemoglobin and myoglobin is stressed. Calculations are performed on a simplified model consisting in a square pyramidal iron (II) complex coupled with a β1 vibrational mode and the results obtained are discussed in relation to available structural data. From our analysis it turns out that the large rhombic components, introduced in previous works, are unnecessary and can be safely reduced.
Absorption bands and lines in the KrF laser spectrum
Authors: Shimauchi Midori , Karasawa Shiro , Miura Tokiwa
Published: February 2003

Many absorption lines observed in the discharge-pumped KrF laser emission spectrum are reported at high resolution. (AIP)
Counterintuitive orbital mixing
Authors: Whangbo Myung-Hwan , Hoffmann Roald
Published: February 2003

In both extended Hückel and ab initio SCF molecular orbital calculations instances of anomalous orbital interaction are occasionally observed. The lower energy combination of two interacting orbitals is found to be the out-of-phase, antibonding one. Such cases have been called counterintuitive orbital mixing. We present an argument based on SCF perturbation methodology demonstrating that the counterintuitive orbital mixing effect is not an artifact but a natural consequence of orbital interaction between two orbitals that differ greatly in energy but overlap significantly.
Diffraction oscillations in rotationally inelastic differential cross sections: HD+D2
Authors: Buck U. , Huisken F. , Schleusener J.
Published: February 2003

Differential cross sections are measured for rotational transitions j=0 to j′=0, 1 of HD+D2. Diffraction oscillations are resolved in the inelastic channel. (AIP)
Theory for BCl3+H2 laser induced chemistry
Authors: Kivel B.
Published: February 2003

The experimental data of Rockwood and Hudson are analyzed in terms of a binary collision mechanism for H2+BCl3→BHCl2 +HCl. The model assumes the atom interchange occurs during the collision and uses the known rate for H2+Cl→HCl+H to explain the experimental results. A qualitative account is given for the dependence of yield of BHCl2 on flux and gas pressure.
Spectroscopic characterization of ytterbium monohalide emission in a high pressure electrodeless microwave arc discharge
Authors: Kramer Jerry
Published: February 2003

Molecular emission has been observed in high-pressure electrodeless microwave arc discharges from the monochloride, monobromide, and monoiodide of ytterbium. The vibrational analyses of the electronic transitions in YbBr and YbI represent the first spectroscopic data for these molecules. Emission from the A (2Σ1/2) →X (2Π+) and A (2Π+) and R (2Π3/2) →X (2Σ+) transitions in YbCl have been observed. By analogy with YbF and YbCl, the blue degraded emission in YbBr and YbI has been assigned to the A (2Π1/2) →X (2Σ+) and A (2Π3/2) →X (2Σ+) transitions. The term values for YbBr and YbI are shifted to the red with respect to YbCl by <100 cm−1 and <300 cm−1, respectively, for both transitions. The spin–orbit coupling constants of the A (2Π) state in YbBr and TbI have been determined from the difference in the band origins of the two A→X transitions. The effect of the lanthanide contraction in the ytterbium monohalides has been examined by comparing the ground state vibrational frequencies of the ytterbium monohalides and the Group IIa monohalides. Finally, the spectra of YbCl observed under high-pressure arc conditions have been compared to the YbCl emission previously observed in a low-pressure chemiluminescent beam experiment.
The polar tensors, atomic effective charges, and infrared vibrational intensities of C6H6, C6D6, and C6F6
Authors: de Barros Neto Benício , Bruns Roy E.
Published: February 2003

The preferred experimental set of signs for the ∂p/∂Qi’s of C6H6 and C6D6 have been determined from the gas phase infrared intensities of these molecules. This set for C6H6 is in agreement with the one found previously for this molecule based on data for C6H6, C6H5D, and p-C6H4D2. Polar tensors, atomic mean dipole moment derivatives, anisotropies, and effective charges for C6H6, C6D6, and C6F6 are reported. The isotopic invariance of these quantities as indicators of the correct sign choice for the ∂p/∂Qi’s is investigated for C6H6 and C6D6. Several applications of the G-sum rule are made: (a) its usefulness in pointing out the correct signs of the ∂p/∂Qi is investigated, (b) corrected values for the intensity sums of C6H5D and p-C6H4D2 are calculated, and (c) intensity sums for C6H4F2 and C6H2F4 are predicted.
EPR spectroscopic determination and interpretation of g∥ of Gd3+ in single crystals of the lanthanide ethyl sulfate nonahydrates
Authors: Gerkin Roger E. , Rogers William J.
Published: February 2003

High-precision measured values of g∥ for Gd3+ dilutely substituted in single crystals of 13 lanthanide ethyl sulfate nonahydrates at room temperature (297.3 K) are presented. It is shown that, within the experimental uncertainties, the present observations are entirely accounted for in terms of a model invoking purely magnetic dipolar interactions between the Gd3+ guests and the host structures. On this model, the shift of g∥ depends upon the identity of the lanthanide host, the sample shape, the temperature, and the Gd3+ composition. Moreover, values of the shifts of g∥ at 77.2 K predicted by this model are in agreement, within the experimental uncertainties, with the 77.2 K data of Gerkin and Thorsell [J. Chem. Phys. 57, 2665 (1972)]. Consistent with this model, values of g∥ for spherical samples of 2.0×10−3 mole fraction Gd3+ in 14 of the lanthanide ethyl sulfate nonahydrates at 297.3 K and at 77.2 K are presented.
Reaction and deactivation of HCl (v=1, 2) by O atoms
Authors: Macdonald R. Glen , Moore C. Bradley
Published: February 2003

Laser-induced fluorescence, following direct excitation of HCl (v=2), was used to measure the total deactivation rate constant for HCl (v=2) by O(3Pg) atoms as (5.2±0.4) ×10−12 cm3 molecule−1 sec−1. This is partitioned into a reaction rate constant of (1.5±1.2) ×10−12 cm3 molecule−1 sec−1 for HCl (v=2)+O(3Pg) →OH (v=1, 0)+Cl and a relaxation rate constant for HCl (v=2)+O(3Pg) →HCl (v=1)+O(3Pg) of (3.7±1.2) ×10−12 cm3 molecule−1 sec−1. The total deactivation rate constant for HCl (v=1)+O(3Pg) atoms, including reaction and relaxation, was measured to be (8.9±1.3) ×10−13 cm3 molecule−1 sec−1. All measurements were carried out at 296±2 °K. The vibrationally enhanced chemical reaction rate constant for HCl (v=2) is roughly a factor of 104 greater than the reaction rate constant for HCl (v=0) with O atoms. The reaction appears to occur adiabatically on the lowest triplet potential hypersurface. For HCl (v=2, 1)+O vibrational relaxation is faster than chemical reaction even though the total energy is well above the barrier to reaction.