bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-consistent many-body theory of π-electron systems. II. Self-energy effects
Authors: Baldo Marcello , Pucci Renato , Tomasello Pasquale
Published: February 2003

In the framework of the theory presented in a preceding paper (I) we analyze the electron self-energy (SE) effects on the low energy spectrum and oscillator strength of ethylene molecule. The SE is expressed through the same degrees of freedom (the one-body and two-body Green’s functions) of the local field corrections (LFC) terms, which have been studied separately in I. The SE and LFC corrections are thus calculated by means of a self-consistent procedure. All the calculations are carried out in the Pariser–Parr–Pole (PPP) model. The results show that the SE terms play a decisive role in the self-consistent conditions, at least for the coupling constant g≳1.
A light scattering study of the molecular motion in hexanetriol 1,2,6
Authors: Dorfmüller Th. , Dux H. , Fytas G. , Mersch W.
Published: February 2003

The structural relaxation of hexanetriol 1,2,6 was studied between −80 and +150 °C by use of photon correlation spectroscopy, low frequency depolarized light scattering spectroscopy, Brillouin spectroscopy, dielectric relaxation, and shear viscosity measurements. The relaxation functions and the relaxation times obtained were compared in order to obtain a consistent picture of the molecular motion. The comparison has led to a distinction between the motions following a longitudinal stress and pure reorientation. The latter is describable in terms of a segmental reorientation following a breaking of hydrogen bonds, this mechanism being essentially the same at low viscosities as well as at very high viscosities approaching the glass point.
Correlation function of an anisotropic fluid of hard rods to first order in the density
Authors: Wulf A.
Published: February 2003

The pair correlation function of an anisotropic fluid of hard rods, allowed to point only in three perpendicular directions, is calculated to first order in the density. Using this correlation function, the average of a model isotropic intermolecular attraction is evaluated; the results support a previous suggestion that short range correlations in a liquid crystal affect very significantly the dependence of the internal energy on the liquid crystal orientational order parameter.
Electron impact study of the 50 000 cm−1 band of benzene
Authors: Doering J. P.
Published: February 2003

The 5.7–6.7 eV energy loss region of the electron scattering spectrum of benzene which contains the 50 000 cm−1 (2100 Å) optical absorption band has been studied with incident energies from 10 to 42 eV, scattering angles from 0° to 15°, and energy resolution from 25 to 35 meV. Three different inelastic processes have been detected including the S2 1B1u←So transition whose diffuse vibronic bands extend from 6.0 to 6.7 eV, a process at 6.31 eV which occurs strongly at incident energies above 20 eV and increases in intensity relative to the rest of the spectrum with increasing scattering angle and a weak, featureless process below the onset of the S2←So transition starting at 5.67 eV. Aside from the weak process below the onset of the S2 state and a singlet–triplet transition observed at very low impact energy, the electron impact spectrum at incident energies below 20 eV and scattering angles to 15° agrees completely with the optical absorption spectrum. The 6.31 eV process arises from a second electronic state at this energy which causes the apparent shift in vibronic band intensities with scattering angle of the S2←So transition first observed by Lassettre et al. The state responsible for this effect is shown to be the same state observed in two photon absorption by Johnson and assigned as 1E1g or 1E2g. Neither the 6.31 eV process nor any energy-shifted analog of it is observed in toluene—providing additional evidence that the 6.31 eV state is a Rydberg state.
Effect of ionic size on the Koopmans ionization potentials in positive ions
Authors: Sen K. D.
Published: February 2003

The effect of ionic size on Koopmans ionization potential is discussed for ions containing 10 electrons. A quantitative estimate is given for the decrease in Koopman’s ionization potential for 10-electron ions. (AIP)
Mobility of localized and quasifree excess electrons in liquid hydrocarbons
Authors: Freeman Gordon R.
Published: February 2003

A recent model of electron transport in liquid hydrocarbons is compared with results of others. The use of input parameter values beyond their limits of applicability may have given rise to inconsistencies within values of other parameters derived from the model.
Effective convergence to complete orbital bases and to the atomic Hartree–Fock limit through systematic sequences of Gaussian primitives
Authors: Schmidt M. W. , Ruedenberg K.
Published: February 2003

Optimal starting points for expanding molecular orbitals in terms of atomic orbitals are the self-consistent-field orbitals of the free atoms and accurate information about the latter is essential for the construction of effective AO bases for molecular calculations. For expansions of atomic SCF orbitals in terms of Gaussian primitives, which are of particular interest for applications in polyatomic quantum chemistry, previous information has been limited in accuracy. In the present investigation a simple procedure is given for finding expansions of atomic self-consistent-field orbitals in terms of Gaussian primitives to arbitrarily high accuracy. The method furthermore opens the first avenue so far for approaching complete basis sets through systematic sequences of atomic orbitals. It is shown that, for expansions of atomic SCF orbitals in terms of even-tempered Gaussian primitives, the energy- optimized exponents are simple analytic functions of the number of primitives used in the expansions.With the help of these formulas, accurate atomic SCF calculations in terms of very large sets of primitives can be carried out without exponent optimization and the energies from such calculations converge to the Hartree–Fock limit on smooth curves. It proves possible to extrapolate to the limit and to give estimates for the error bounds of the extrapolation. Quantitative data are given for all atoms in the first three periods of the periodic system. The Hartree–Fock limits obtained in this manner are equal or superior to previous calculations based on numerical methods or on expansions in terms of exponential type primitives. From the given atomic SCF orbitals, extended basis sets for molecular calculations are easily obtained by Raffenetti’s method.
Estimates of helium l-limit energies
Authors: Morell Glenn O. , Parr Robert G.
Published: February 2003

Recent calculations using a hyperspherical basis set have yielded the lowest energies yet found for the p, d, ...i limit energies for ground-state helium and showed that prior estimates of the angular energy increments were too small. Empirical fits of the new calculated angular energy increments are used to estimate the exact energy increments. An empirical formula, E=−2.87902859−Σk=1 l{0.078177278[k (k+1)]−2+0.015603056[k (k+1)]−3}, is obtained for accurate helium l-limit energies.
Piecewise polynomial configuration interaction natural orbital study of 1 s2 helium
Authors: Carroll Dennis P. , Silverstone Harris J. , Metzger Robert Melville
Published: February 2003

We report here an analysis of extensive configuration interaction (CI) wave functions for the 1s2 ground state of the helium atom using piecewise polynomial basis functions. Large numbers of natural radial orbitals (NROs) with l ranging from 0 to 11 have been treated accurately and analyzed systematically. The contribution of each NRO to the total energy is found to follow the formula ΔE∼−0.42(l+1/2) × (n−1/2)−6a.u., where n is the principal quantum number, and the expansion coefficient of the NRO configuration is found to follow the formula, c∼−0.35(l+1/2)2/3 (n−1/2)−4. (The constants for l=0 are a little different). From an examination of the tails of the NROs, we are able to suggest an l-dependent universal asymptotic formula, rβ−l−1+δe−ζr, where β is a constant, where δ=δl0, and where ζ2/2 is the ionization potential. The nodes of the NROs are also found to behave in a systematic way that yields valuable information on the choice of basis functions. So-called ’’L’’-limit energies EL, more accurate than any we could find in the literature, have been determined for L=0 through 11, with a final CI energy calculated here of −2.90370 a.u. from a wave function containing 118 NROs. The increments EL−EL−1 are found to follow the formula −0.0740(L+1/2)−4−0.031 (L+1/2)−5 a.u., which is useful for extrapolation and extension of the CI energy by two significant digits. The n- and l-dependent formulas for the energy contributions make it possible to estimate the size of a CI calculation required for a given accuracy. The high accuracy of these CI calculations is made possible by the flexibility and numerical stability of piecewise polynomial basis functions.
Crossed-beam study of the reaction H2+ (CO, H)HCO+ at 1.89 eV
Authors: Preuninger F. N. , Bilotta R. M. , Farrar J. M.
Published: February 2003

Employing a ’’seeded’’ supersonic nozzle source for the CO beam and a electrostatic energy analyzer-quadrupole mass spectrometer, the angular distribution and energy spectra of the reaction products were determined. (AIP)
Electron-impact excitation cross sections for N III
Authors: Ganas P. S.
Published: February 2003

Calculations of generalized oscillator strengths and integrated cross sections from threshold to 1 keV are reported for the electron-impact excitation of N III in the Born approximation. (AIP)
Stable gas phase hydrates of the CO−2 anion
Authors: Klots Cornelius E.
Published: February 2003

The observation of ions with the formula (H2O)x (CO2)y− where x,y⩾1 is reported. The ions show no sign of autodetachment even for x=y=1. (AIP)
Few-atom 3He–4He mixed molecules
Authors: Nakaichi S. , Lim T. K. , Akaishi Y. , Tanaka H.
Published: February 2003

The existence of seven helium molecules, consisting of admixtures of up to five atoms of the two isotopes, is found on the basis of variational calculations using realistic phenomenological helium–helium potentials. The smaller mass of 3He has a significant effect on the binding energies, sizes, and particle distributions of these molecules. Also, a generalization of Tjon’s line to other few-body systems is discovered.
Rotational compound state resonances for an argon and methane scattering system
Authors: Smith Leslie N. , Malik David J. , Secrest Don
Published: February 2003

A broad compound state (closed channel) resonance in the argon–methane system is investigated using a realistic model potential, and approximations are developed which allow one to search for such resonances easily. Methane is treated as a rigid rotor and the energy of the resonance is such that there are only three rotational states with open channels. The coupled states approximation proved invaluable in characterizing the resonances. A perturbation technique was developed which allows one to predict accurately the position of the peaks due to the resonance. Fully converged close coupled differential and integral cross sections are presented.
A new functional form for representing vibrational eigenenergies of diatomic molecules. II. Application to H2 ground state
Authors: Hashemi-Attar Ali-Reza , Beckel Charles L.
Published: February 2003

An expression previously proposed for representing vibrational eigenenergies Ev as a function of quantum number v is applied to the H2 ground electronic state. The expression is Ev=D−(vD−v)m[L/N], where D is the dissociation limit energy, vD and m are parameters, and [L/N] is a rational fraction in (vD−v). We integrate the vibrational Schrödinger equation to obtain 15 Born–Oppenheimer (BO) Ev with reduced mass μ0=918.048 electron masses, and 77 BO Ev with 25 μ0; error in Ev attributable to the potential is estimated to be 0.02 cm−1. The proposed functional form with a variety of [L/N] is fitted to the 14 BO μ0 first differences ΔE (v+1/2); with the exception of [4/0] all L+N=4 fits have an rms error in calculated ΔE of 0.02 cm−1. The proposed formula is then fitted to 15 BO differences including D−E14. The error in calculated D−E14 can be made negligible while the rms error in calculated energy differences remains 0.02 cm−1. Mass 25 μ0 is used to check applicability of the proposed functional form to a large number of levels; several fits yield all 76 ΔE with an rms error of only 0.04 cm−1. Finally, the proposed expression is applied to experimental vibrational energies. For these, better fits have an rms error of ∼0.07 cm−1, presumably due primarily to experimental errors.
A study of the vibrational level dependent quenching of CO(v =1–16) by CO2
Authors: Caledonia George E. , Green Byron David , Murphy Randall E.
Published: February 2003

The technique of time resolved Fourier spectroscopy has been used to determine rate constants for the processes CO(v)+CO2→CO(v−1)+CO2, where the vibrationally excited CO is created through electron irradiation of Ar/CO2 mixtures. The CO production mechanism, predominantly dissociative recombination of CO2+, is found to produce CO excited to as much as v=19. The CO(v) deactivation rate constants are deduced from examination of the time histories of the vibrational population distribution. From a Stern–Volmer analysis, the residual quenching not due to CO2 is attributed entirely to CO(v=0) relaxation of CO(v) and radiative decay. Experimentally determined upper bounds for the CO(Δv=1) transition probabilities for spontaneous emission have been obtained for levels 7–12.
On the concentration and time dependence of the energy transfer to randomly distributed acceptors
Authors: Blumen A. , Manz J.
Published: February 2003

In this paper we derive a general exact expression for the ensemble averaged time decay of the excitation of a donor due to the incoherent direct energy transfer to randomly distributed acceptors in a solid. Various acceptor species may be present simultaneously. The formula found is valid for all times and for arbitrary acceptor concentrations. It lends itself readily to numerical evaluation and can, for microscopic interactions of particular interest, be approximated analytically. As special cases we retrieve the Förster–type decay laws for isotropic multipolar interactions in spaces of arbitrary dimensions, and the Golubov–Konobeev exact expression for a single acceptor species. From the numerical results we establish the limits of validity of the Förster-type equations, and determine the influence of the lattice structure on the excitation decay. In some cases the lattice leads to an additional pattern superimposed on the smooth decay.
Electron energy-loss spectra in molecular fluorine
Authors: Nishimura Hiroyuki , Cartwright David C. , Trajmar Sandor
Published: February 2003

Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5° to 140°. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features for which there are no identification appear in the spectra.
Temperature dependence of the reaction of ClO and HO2 radicals
Authors: Stimpfle R. M. , Perry R. A. , Howard Carleton J.
Published: February 2003

The rate constant for the reaction of ClO with HO2, k1, was measured over the temperature range 235⩽T⩽393 K using laser magnetic resonance detection to monitor directly the concentrations of both reactants. Measurements were made at low pressures, 0.8⩽P⩽3.4 Torr, in three different discharge-flow tubes, 14.0, 25.4, and 36.7 mm i.d., and with two different sources for ClO radicals, Cl+O3 and Cl+Cl2O. The observed temperature dependence is fitted by the expression, k1=3.3×10−11 exp(−850/T)+4.5×10−12 (T/300)−3.7 cm3 molecule−1 s−1 The products of the reaction were not detected but the possible channels HOCl+O2 and HCl+O3 have important implications for stratospheric chemistry.
Direct determination of the intermolecular interaction contribution to the refractive index of carbon dioxide and sulfur hexafluoride
Authors: St-Arnaud J. M. , Bose T. K.
Published: February 2003

The experimental values of the first and the second refractivity virial coefficients have been determined for carbon dioxide and sulfur hexafluoride. In the case of carbon dioxide the experimental second refractivity virial coefficient is less than the classically calculated theoretical value and for sulfur hexafluoride the experimental value is larger than the theoretical value. Combined with the earlier values of the second dielectric virial coefficient, the present experimental results agree well with the integrated collision induced absorption in the infrared and the far infrared.
Model networks of end-linked polydimethylsiloxane chains. IV. Elastomeric properties of the tetrafunctional networks prepared at different degrees of dilution
Authors: Llorente M. A. , Mark J. E.
Published: February 2003

Highly elastomeric ’’model’’ networks were prepared by end-linking polydimethylsiloxane chains of known molecular weight, using a tetrafunctional orthosilicate. The reactions were carried out in both the undiluted state and in solution, with n-dodecane, cyclic dimethylsiloxane oligomer, and linear dimethylsiloxane oligomer as diluents. The networks thus prepared were studied with regard to their stress–strain isotherms in the unswollen state, in elongation at 25° C, and with regard to their equilibrium swelling in benzene at room temperature. The results obtained did not depend significantly on the amount of diluent present during the preparation of the networks, which indicates that the end-linking reaction employed must be very nearly complete even in the undiluted state. Values of the modulus in the reaction employed must be very nearly complete even in the undiluted state. Values of the modulus in the limits of large and small elongation were obtained from the stress–strain isotherms and were found to be in satisfactory agreement with theoretical predictions for nonaffine and affine deformations, respectively. The results from the swelling equilibrium measurements were found to fall between these two extremes. They are in excellent agreement, however, with the results of a very recent theory of network swelling in which the degree of nonaffiness depends on both the network structure and the equilibrium degree of swelling. The relatively good agreement between experiment and theory suggests that interchain entanglements do not make a large contribution to the equilibrium elastomeric properties of a polymer network.
Binding energies of LiH2 and LiH2+ and the ionization potential of LiH2
Authors: Wu C. H.
Published: February 2003

The existence of the stable molecule LiH2 was proved experimentally for the first time by mass spectrometric measurements over dilute solutions of hydrogen in liquid lithium. From the measurements of the gaseous equilibria Li(g)+LiH2(g) =2 LiH(g), and LiH2(g)+Li2(g) =LiH(g)+Li2H(g), an atomization energy D°0(LiH2) =127.0±7 kcal/mole was obtained. The ionization potential of LiH2(g) was determined as I.P. (LiH2) =6.14±0.2 eV, from which the binding energy of the ion LiH+2, D°0 (LiH+2) =109.0±8 kcal/mole was deduced. The heat of formation was determined as ΔH°0 (LiH2) =14.75±7.0 kcal/mole. The results from this study were compared with those predicted using diatomic-in-molecules and valence only electronic structure theories.
Short range caging effects for reactions in solution. I. Reaction rate constants and short range caging picture
Authors: Northrup Scott H. , Hynes James T.
Published: February 2003

The effects of short range solvent structure and short range dynamical correlations are investigated for the steady state rate constant k for solution reactions influenced by diffusion. The description is in terms of a Smoluchowski equation describing relative motion of two molecules in an outer spatial translational region, supplemented by a sink term that accounts for dynamics in an inner reaction zone. In the outer region, solvent structural effects are included by a potential of mean force, which exhibits a short range well and barrier combination leading to ’’potential caging.’’ Outer region short range dynamical correlations are included via a separation-dependent diffusion coefficient, leading to ’’dynamical caging’’ as relative motion is showed at small separations. These two short range effects are neglected in standard diffusion treatments. We find that k is only modestly influenced by the above short range effects. In order to expose short range structure and correlation influence in a more sensitive way, we formulate the short range caging picture. This information focuses on events occuring at the small separations usually implied by the term ’’solvent cage.’’ At this level of description, short range effects are clearly revealed. We compare our formulation with the encounter formulation of Noyes.
Chemiluminescent ion–molecule reactions of O+ ions with CH4, C2H4, C2H6, C3H8
Authors: Kusunoki I. , Ottinger Ch. , Zimmermann S.
Published: February 2003

UV emission in the wavelength range 3060–3300 Å was observed from OH(A 2Σ+), produced in a beam experiment by reactive collisions of O+ ions with hydrocarbon molecules at energies from 1 to about 150 eVCM. The rotational population distribution in the v′=0 and 1 levels of OH(A) was determined from computer simulations of the observed spectra. At low energies (?10 eVCM) the v′=0 distributions peak at rotational quantum numbers of N′=2–6 with CH4, but at about N′=20 with C2H4, C2H6, C3H8. The luminescent reaction is first order in the target gas pressure with C2H4, C2H6, C3H8, but second order with CH4. These results are rationalized in terms of a direct H− transfer reaction in the former case. With CH4, OH+ is formed in the primary reaction step, which is followed by a luminescent charge transfer reaction to give OH(A). Cross sections were measured for OH(A), CH(A), CH(B), Hβ and C(1P0) production as a function of collision energy. The OH(A) cross section suggests a transition from stripping to a sequential quasihard-sphere collision mechanism. The energy dependence of the cross section for luminescence from O++H2, D2 collisions was also measured.
Computation of crystal field parameters using lattice sums as evaluated by the Ewald method
Authors: Misra Sushil K. , Lewis Norman R.
Published: February 2003

Spend order crystal field parameters are computed for Gdcl3.6H2O, using lattice sums as evaluated by Ewald. A ’’correction’’ term in the reciprocal space, obtained for the limit ?→0 is calculated and used to evaluate 2nd order crystal field parameters.(AIP)
Higher-lying singlet states of poly-n-vinylcarbazole: A CNDO/S study
Authors: Bigelow Richard W.
Published: February 2003

The CNDO/S technique has been used to study the higher-lying singlet states in poly-N-vinylcarbazole PVK. This study finds correlations with features observed in optical absorption and electron energy loss measurements.(AIP)
The adiabatic semiclassical perturbation theory for vibrationally inelastic scattering. I. Collinear calculations
Authors: Cross R. J.
Published: February 2003

A semiclassical approximation is developed to treat vibrationally inelastic scattering. The vibrational basis set used is adiabatic with respect to a reference potential which is chosen to be as close as possible to the true potential and yet give easily obtainable solutions to the vibrational wave equation. The radial wave functions are obtained using the WKB approximation, and the coupled Schrödinger equations are solved by a first-order perturbation method (similar to the distorted-wave approximation) to yield a phase shift matrix which is then exponentiated to give the full scattering matrix. Results, including high-order transitions, were obtained for all the cases computed by Secrest and Johnson and by Clark and Dickinson. The agreement is excellent, being better than 10% for half of the cross sections and, except for one system, rarely off by more than a factor of 2.
Picosecond relaxation processes in excited state quinoxaline
Authors: Anderson Robert W. , Damschen Donald E. , Scott Gary W. , Talley Larry D.
Published: February 2003

Excited state absorption spectra of quinoxaline in benzene, isooctane, and cis-1,3-pentadiene at 7 and 130 ps after excitation are reported. Picosecond absorption kinetics at 422 and 533 nm are also reported. In the nonaromatic solvents, bands at ∼425 nm (Sn←S1 and Tn←T1) and ∼ 530 nm (mostly Sn←S1) are observed in the transient spectra. Decay of the ∼530-nm band gives k−1isc?23 ps in the nonaromatic solvents. In benzene solvent, the excited state spectra are more complex, the decay kinetics are longer, and quinoxaline–benzene exciplex formation is suggested.
Bounded error analysis of experimental distributions of relaxation times
Authors: Colonomos Peter , Gordon Roy G.
Published: February 2003

A method is presented for analyzing experimental data from dielectric relaxation, acoustic relaxation, or other measurements related to a distribution of relaxation times. A consistency test is derived showing whether or not there is any distribution of relaxation times consistent with the data. For consistent data, the analysis then provides bounds on possible interpolations at frequencies between the measured points. Bounds are placed on the cumulative distribution of relaxation times and these bounds are shown to be the most precise attainable on the basis of any given set of experimental data. The analysis is illustrated by application to ’’data’’ generated theoretically from some simple distributions of relaxation times and to some experimental data on dielectric relaxation.
Laser induced fluorescence spectra of symmetrically substituted trihalobenzene radical cations
Authors: Bondybey V. E. , Miller Terry A. , English J. H.
Published: February 2003

Laser induced fluorescence excitation and resolved emission spectra are obtained in a Ne matrix for the radicals cations of C6H3F3, C6H3Cl3 and all their deuterated analogs. The excitation spectra show that the excited state in each of the ions is characterized by extremely sharp, extremely regular vibrational structure. The majority of the a′1 and e′ species vibrational modes are assigned. The resolved emission spectra of the ions, however, show irregular structure for the e′ modes, which is entirely consistent with a Jahn–Teller distortion of the ground state. Gas phase hot band spectra confirm that the Ne matrix does not perturb the vibrational structure. Although spectral assignments are more difficult in the ground state, it is shown that ν″13, the C–C–C bond angle deformation mode, is principally affected by this distortion. Jahn–Teller distortion parameters are derived for the four species: C6H3F3+, C6D3F3+, C6H3Cl3+ and C6D3Cl3+.
High temperature thermodynamics of dilute solutions of hydrogen in palladium–copper alloys
Authors: Kleppa O. J. , Shamsuddin  , Picard C.
Published: February 2003

The thermodynamic properties of dilute solutions of hydrogen and deuterium in palladium-copper alloys with copper contents of 10, 25, and 40 at.% have been determined by a calorimetric-equilibrium method at 555 K. The results are compared (a) with corresponding data for hydrogen in palladium–silver at the same temperature and (b) with equilibrium data for palladium–copper measured near room temperature. (1) The partial excess entropies of hydrogen in dilute solutions in palladium–copper alloys are reduced significantly compared to pure palladium. In palladium–copper this effect is only about one-half that in palladium-silver. Even so, it is believed to reflect in both systems a nonrandom distribution of the hydrogen atoms among the available interstitial sites. (2) It is shown that to a first approximation the dissolved hydrogen atoms may be considered to be isotropic, three-dimensional Einstein oscillators. In this approximation the observed differences between hydrogen and deuterium may be used to calculate the vibrational frequency of hydrogen. For palladium–copper these differences do not vary with copper content within experimental error. This points towards ?H being essentially independent of alloy composition. This behavior contrasts with that of hydrogen in palladium–silver, for which Picard et al. [J. Chem. Phys. 70, 2710 (1979)] recently found increasing values of ?H with increasing silver content. It is suggested that the different behavior of ?H in large measure may account for the observed difference between the concentration dependence of the excess entropy of hydrogen in palladium–copper and in palladium–silver.
ESR studies of irradiated methane and ethane at 4.2 K and mechanism of pairwise trapping of radicals in irradiated alkanes
Authors: Toriyama Kazumi , Iwasaki Machio , Nunome Keichi
Published: February 2003

The spatial distributions of trapped hydrogen atoms and methyl radicals in CH4 and CD4 irradiated at 4.2 K have been studied by ESR. Most of the hydrogen atoms are trapped within ∼16 Å from each parent methyl radical forming distributed radical pairs. This indicates that the thermalization distance of hydrogen atoms produced by 4.2 K radiolysis is ≲16 Å in methane. Evidence has been obtained for the formation of a small amount of ĊH3...ĊH3 pairs, which are supposedly formed from hot hydrogen atom reactions. No evidence has been obtained for the formation of a pair of hydrogen atoms. There has been also obtained the experimental evidence that thermal hydrogen atoms unreactive with methane can abstract a hydrogen atom from ethane at 10–20 K. In the light of these results, the following conclusions are deduced: A part of hydrogen atoms produced in radiolysis of alkanes undergo hot abstraction to form very close alkyl radical pairs whereas the rest is thermalized and immobilized at the place close to each parent alkyl radical. The thermalized hydrogen atoms also abstract a hydrogen atom from the surrounding molecules to form distributed alkyl radical pairs, when the matrix molecule is reactive with thermal hydrogen atoms. On the other hand, the hydrogen atoms are mobile at elevated temperatures and the isolated alkyl radicals are mainly formed.
Correlation functions for an ionic solution in a polar solvent
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

Expressions are derived for the ions-ion inn-solvent, and solvent-solvent correlation functions of a system of symmetrically charged hard-sphere ions in a dipolar hard-sphere solvent, with the particles of the same diameter R.(AIP
Absorption and laser excited fluorescence of hexavalent uranium in LiF
Authors: Runciman W. A. , Wong Eugene Y.
Published: February 2003

The absorption spectra of hexavalent uranium in LiF have been measured at 4.2 and 77 K. The fluorescence spectra have been obtained with excitation by an argon ion laser operating at eight wavelengths. Selective excitation of different uranium–oxygen complexes is observed, as well as polarized fluorescence following excitation with the polarized laser radiation. A distinctive feature of the fluorescence spectrum is the occurrence of pairs of associated lines. The short wavelength line in each pair is an electric dipole line which vanishes in fluorescence at 4.2 K. The long wavelength line in each pair is a magnetic dipole line which is enhanced in intensity at 4.2 K. The fluorescent half-lives have been measured at 4.2 and 77 K and interpreted in terms of a pair of excited levels for each type of complex.
Cubic and quartic anharmonic potential energy functions for octahedral XY6 molecules
Authors: Fox Kenneth , Krohn Burton J. , Shaffer Wave H.
Published: February 2003

We give the cubic and quartic anharmonic potential energy functions for XY6 molecules of Oh symmetry in terms of normal coordinates. The numbers of independent cubic and quartic potential constants are 22 and 92, respectively. A standard form, introduced here, is related to the tensor formalism developed for the potential energy of tetrahedral XY4 molecules by Hecht.
Radiative lifetime of the A 2Σ+ state of SnF
Authors: Bradburn G. R. , Armstrong R. A. , Davis S. J.
Published: February 2003

A pulsed dye laser has been used to measure the radiative lifetime and some quenching rates for the A 2Σ+ state of SnF. Ground state SnF was produced by reacting tin vapor with molecular fluorine. The average radiative lifetime of the v′=0,1,2, and 3 levels of the A 2Σ+ state is 3.2±0.3 μsec. The quenching of the A 2Σ+ state by species in the reaction: He, Sn, F2, and SnF is very inefficient.
Effect of solvent on ultrasonic relaxation due to rotational isomerism. I. Polar solvent
Authors: Okuwa Tsunemichi , Nishimura Michiko , Miyazaki Hiroyuki
Published: February 2003

In order to elucidate the effect of a solvent on ultrasonic relaxation, ultrasonic absorption and dispersion were measured in solutions of 1,1,2-trichlorethane and acetone. 1,1,2-trichlorethane shows ultrasonic relaxation due to rotational isomerism, and acetone is a polar solvent. The ultrasonic pulse method was applied to measure ultrasonic absorption and velocity. The concentration of solutions was changed from 0 to 100 mole% at 20°C. The measurements were performed at 20, 30, and 40°C for 90, 50, and 10 mole% solutions. In all cases, the characteristic values of the ultrasonic absorption and dispersion were calculated assuming a single relaxation time, and the effects of concentration and temperature were discussed. The experimental results were compared with the theoretical equations of ultrasonic absorption and dispersion in rotational isomerism, and the energy difference between the rotational isomers, the height of potential barrier of internal rotation and the velocity of isomerization reaction were derived.
Kinetic mechanisms in a 16 μm CO2 laser
Authors: Kerber R. L. , Jaul W. K.
Published: February 2003

A rate equation model is used to examine the time evolution of vibrational excitation and subsequent lasing of an optically pumped DF/CO2 or HBr/CO2 laser. With this model, one may simulate optical pumping of DF/CO2/He/N2 mixtures with a pulsed DF laser, or direct pumping of CO2 or HBr/CO2 mixtures with an HBr laser. This model includes the simulation of optical saturation at 9.4 μm. Rotational nonequilibrium phenomena are also included in the models. Model calculations reveal the relative importance of various kinetic relaxation mechanisms. Rotational hole burning effects are observed for all calculations simulating line selected operation. The effect of the strength and duration of the pump laser and the 9.4 μm saturation pulse are examined. Finally, the model is found to compare well with laboratory observations of pulsed HBr/CO2 laser performance.
Approximate and exact virial coefficients for hard rectangular parallelepipeds and cubes on a simple cubic lattice
Authors: Mitra S. K. , Allnatt A. R.
Published: February 2003

The first five virial coefficients for lattice gases of hard rectangular parallelepipeds of ld2 sites (l=2–6, d=2) and of hard cubes of l3 sites (l=2–6) were calculated exactly and in the Percus–Yevick, hypernetted chain, and complete star approximations. The corresponding terms in the direct correlation function for hard cubes were calculated in the Percus–Yevick approximation and it was concluded that simple analytical solutions are improbable for this class of model. The relevance of these results to recent model making for defect complexes in UO2+x was indicated.
Computational experiments on the lowest two electronic states of the N2H3 radical
Authors: Chandler G. S. , McLean A. D.
Published: February 2003

The most accurate computational study to date of the hydrazyl radical N2H3 has resolved previous ambiguities in the lowest energy ground state conformation, showing it to have a nonplanar arrangement of the nuclei, derivable from a planar structure by depressing the NH2 group by approximately 28°. This structure is derived after complete geometry optimization using a ’’double zeta plus polarization’’ first-order configuration interaction wave function with 1771 configuration state functions. Other structures studied with this same wave function give the following information about the lowest two potential energy surfaces for this radical. The ground state inversion barrier about nitrogen is small, with a computed value of 0.5 kcal/mole. Rotation is shown to be the lowest energy path for interconversion between equivalent ground state structures; a rotational barrier of 24.9 kcal/mole being computed. An optimized structure for the alternative transition state, with a linear N–N–H arrangement, lies 51 kcal/mole above the lowest energy ground state structure. Vertical excitation requires 4.32 eV, to a point lying 2.95 eV above the minimum on the excited state surface. The f number for the transition is 0.0066. Nuclear relaxation following excitation changes the geometry to a symmetric perpendicular structure in which the NNH plane of symmetry bisects the NH2 group. The minimum on the second potential energy surface is shown to be a point of intersection for symmetric perpendicular 2A″ and 2A′ states.
Coexistence curve of the binary mixture nitroethane–isooctane
Authors: Beysens D.
Published: February 2003

The coexistence curve of the nitroethane–isooctane mixture is reported. Since the mixture is composed of liquids of nearly perfectly matched refractive indices, special care had to be taken. Two experimental techniques were used: (i) A visual method with 32 samples of different mass function c allowing the exponent β (0.318±0.006) the amplitude B (1.83±0.016 in Δc=Bεβ) and the critical composition (isooctane mass fraction 0.5350±6×10−4) to be obtained. (ii) An interferometer method on a single critical sample, giving β=0.31±0.02, the refractive index derivatives (∂n/∂T)p,φ=−(4.99±0.02) ×10−4 and (∂n/∂φ)p,T= (1.38±0.05) ×10−3 and the refractive index difference n1−n2= (0.95±0.04) ×10−3. The interferometer method is influenced by long time-scale relaxation effects. The value of the exponent β is found to be close to the three-dimensional Ising value and is nearly insensitive, as is also the quality of the fit, to the choice of the order parameter (volume, mass, or mole fraction). The coexistence curve was found to be entirely symmetrical when the mass fraction was used, and we did not find evidence of deviations from the rectilinear diameter. Nonanalytical corrections were necessary only with the mole fraction parameter when the value β=0.325 was imposed.
Translational friction coefficients of rigid, symmetric top macromolecules. Application to circular cylinders
Authors: Tirado Maria M. , de la Torre José García
Published: February 2003

The hydrodynamic interaction equations and the interaction tensor that appear in the theoretical formalism for calculating translational friction coefficients of rigid particles modeled as assemblies of beads, are formulated in cylindrical coordinates. For symmetric top particles, the cylindrical shielding tensors of symmetry-equivalent beads are the same, and have only five nonzero components. This effects a great simplification with respect to the Cartesian formalism. Application is made to the end-effect correction, for translational motion of right circular cylinders modeled as stacks of rings, extrapolated to zero bead size. No appreciable changes in the translational friction coefficients are found when the hollow cylindrical models are capped at the ends with disc-shaped plates. For finite cylinders with axial ratio p≳2, our results, as well as those from other theoretical and experimental studies, are in remarkable disagreement with the previous calculations by Broersma.
The thermal polymerization of styrene: A proton NMR study
Authors: Jeffrey Kenneth R. , Stevens James R.
Published: February 2003

The proton nuclear spin–lattice relaxation has been measured as a function of reaction time during the thermal polymerization of styrene. Initially the proton relaxation in the monomer is exponential and the measured T1 is 21 s, a value typical of oxygen free organic liquids. Within a few hours of the start of the experiment, the relaxation is observed to be the sum of two exponential components. The component with the longer relaxation time is due to the monomer. The second component which has a much shorter relaxation time is assigned to the polymer formed during the reaction. For a polymerization carried out at 86°C the proportion of monomer is observed to decrease initially at rate of 0.93%/h. T1 for the monomer decreases linearly until about 35% of the monomer remains when the polymerization rate becomes less. The results are independent of the NMR frequency and an analysis of the results indicates that the translational diffusion of the monomer decreases substantially during the reaction. T1 for the polymer depends on the NMR frequency. Initially it decreases with reaction time, goes through a minimum, then increases. The value of the T1 at the minimum suggests that the molecular motions involving the hindered rotation about the carbon backbone of the long polymer chain are being observed.
Order phenomena in aqueous AlCl3 solutions
Authors: Caminiti R. , Licheri G. , Piccaluga G. , Pinna G. , Radnai T.
Published: February 2003

X-ray diffraction data of two aqueous solutions of AlCl3 are interpreted using a model in which the Cl− ions have a coordination number of six and the Al(H2O)3+6 ions interact with twelve water molecules through short and linear H bonds, the water molecules nearest neighbor to the Al3+ ions having a trigonal orientation. Moreover, evidence is given that such a hydration structure tends to persist even when the total amount of water present in the system is rather small.
Note on the T1−1 and T2−1 relaxation rates for the NH3 microwave spectrum
Authors: McMahon D. R. A.
Published: February 2003

An accurate assessment of line widths is given for inversion lines of NH3 using the data from ref (l). (AIP)
On the chemisorption of molecular hydrogen on Be clusters
Authors: García-Prieto J. , Novaro O.
Published: February 2003

Ab-initio self-consistent field calculations are reported for the interaction of H2 with a few small Be clusters. A symmetrical linear Be3 is also considered. (AIP).
Multiphoton dissociation of ethyl acetate by a CO2 laser
Authors: Knott R. B. , Pryor A. W.
Published: February 2003

The dissociation of ethyl acetate to ethylene and acetic acid has been chosen as a suitable reaction to study, in a moderately large molecule, the dissociation per flash induced by CO2 laser pulses. Studies have been done of low pressures of ethyl acetate (∼1 Pa) entrained in nitrogen buffer gas (20–200 Pa). The dissociation per flash ranges up to 0.5 at a laser fluence of 3.8 J cm−2 in the pulse. Computer calculations can match the results assuming unimolecular dissociation of molecules in internal thermal equilibrium.
Fluorescence of acetylenic hydrocarbons
Authors: Hamai Sanyo , Hirayama Fumio
Published: February 2003

A structureless fluorescence with a half-width of ∼6.5 kK has been observed from optically excited alkylated acetylenes (from propyne to 1-, 2-, 3-, and 4-octynes) in cyclohexane solution. The emission maxima of the 1-alkyne series (propyne, 1-butyne, 1-pentyne, etc.) are all at 370 nm, and those of the 2-, 3-, and 4-alkyne series (2-butyne, 3-hexyne, 4-octyne, etc.) are all at 388 nm, regardless of the number of carbon atoms, NC, in the molecule. The fluorescence is subject to concentration quenching the efficiency of which is much higher for 1-alkynes than for 2-, 3-, and 4-alkynes. The fluoresence quantum yields, extrapolated to zero concentration, of 1-, 2-, 3-, and 4-alkynes are found to be independent of NC, and are 0.013, 0.014, 0.009, and 0.009, respectively. The fluorescence spectra in the vapor phase are very similar to those in solution except for a slight blue shift (by ∼5 nm). The observed emissions are interpreted as originating from the lowest singlet excited states (?) of the alkynes, the abnormally large Stokes shift (≳20 kK) being a consequence of the large disparity in equilibrium nuclear configurations of ground and excited states.
Singularity-free static lattice energy minimization
Authors: Griewank A. O. , Markey B. R. , Evans D. J.
Published: February 2003

Comparative analyses are made of static lattice energy minimization procedures based on Newton or quasi-Newton algorithms with rigid body orientations being parametrized in terms of Euler angles or quaternion parameters. It is shown that potential functions in terms of Euler angles can have artificial saddle points and artificial minima in the plane where the azimuthal angle ϑ (the angle between the body and laboratory z axes) is zero. Quaternions are found to form the only numerically acceptable parametrization of orientations in less than five variables and lead to a singularity-free energy function which can be minimized efficiently by any routine for unconstrained optimization.
Carbon interaction with nickel surfaces: Monolayer formation and structural stability
Authors: Eizenberg M. , Blakely J. M.
Published: February 2003

A first order phase transition occurs at Ni (111) surfaces under conditions of controlled chemical potential. For a dilute Ni–C alloy of fixed bulk composition an abrupt change occurs (as temperature is lowered) in the surface carbon coverage from a very low coverage state to a two dimensional crystalline C overlayer. In the present work the possible effects of substrate orientation on the occurrence and characteristics of the transition have been investigated. On surfaces vicinal to (111) and on the (311) and (110) planes abrupt segregation of a graphitic monolayer was observed. The observed coverage–temperature relationship was similar to that for (111) with the monolayer formation occurring at a temperature between 10% and 12% higher than the equilibrium precipitation temperature. Surface reconstruction accompanies the monolayer condensation and precipitation processes. At dilute carbon coverages and high temperatures the vicinal planes have arrays of monoatomic height steps; upon monolayer formation rearrangement of the surface steps occurs to produce facets of (111) and (110) for surfaces along the [11̄0] zone and of (111) and (311) for surfaces along the [011̄] zone. Qualitatively different behavior was observed with (100) and (210). Monolayer graphite condensation was also observed with both of the surfaces but the high temperature region was characterized by a gradually decreasing carbon coverage for which the Auger line shape was that of nickel carbide. Upon graphite precipitation at the solubility limit all surfaces become unstable with respect to formation of {111} facets.
Cross sections for excitation of Cd(5 3P1) and Cd(5 1P1) and of their magnetic sublevels in Na+–Cd collisions
Authors: Aquilanti V. , Casavecchia P. , Grossi G.
Published: February 2003

The cross sections for the excitation of 53P1 and 5 1P1 states of Cd in Na+ + Cd collisions are reported. (AIP)
Vibrational correlation splitting and chain packing for the crystalline n-alkanes
Authors: Snyder Robert G.
Published: February 2003

Vibrational correlation-splitting patterns for the infrared active methylene rocking–twisting fundamentals of the orthorhombic and monoclinic n-alkanes have been determined and analyzed. Polarization measurements show that the splitting patterns are different for the two structures. A simple two parameter coupled oscillator model accounts for the observed shapes of the c axis dispersion curves. It is suggested that the results of this analysis may be useful in establishing the type of packing involved in crystals containing long-chain hydrocarbon molecules.