bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam photoionization study of OCS, (OCS)2, (OCS)3, and OCS⋅CS2
Authors: Ono Y. , Osuch E. A. , Ng C. Y.
Published: February 2003

Photoionization efficiency (PIE) data for OCS+ near the threshold (1080–1111 Å) were obtained with a resolution of 0.14 Å (FWHM) using the molecular beam method. The ionization energies (IE) for the 2Π3/2 and 2Π1/2 states of OCS were determined to be 11.1736±0.0015 eV (1109.62±0.15 Å) and 11.2204±0.0015 eV (1104.95±0.15 Å), respectively. These values are found to be in agreement with those obtained in previous photoionization experiments. PIE data for (OCS)2, (OCS)3, and OCS⋅CS2 have also been obtained in the wavelength region 750–1270 Å. The observed IE’s for (OCS)2, (OCS)3, and OCS⋅CS2 are 10.456±0.026, 10.408±0.026, and 9.858±0.024 eV, respectively. From the measured IE’s and the estimated dissociation energies of (OCS)2 and OCS⋅CS2, the binding energies for OCS+⋅OCS and CS+2⋅OCS are deduced to be 17.2±1 and 5.8±1 kcal/mol, respectively. From the shifts in energy of the Rydberg series of CS2 and OCS in the OCS⋅CS2 and (OCS)2 dimers, and from the symmetry of the Rydberg orbitals, possible geometries for OCS⋅CS2 and (OCS)2 are discussed.
On the competitive roles of reagent vibration and translation in the exothermic proton transfer reaction H+2+Ar→HAr++H
Authors: Bilotta R. M. , Farrar J. M.
Published: February 2003

We present a crossed beam study of the title reaction at fixed collision energies of 1.2 and 2.3 eV with reagent H+2 average vibrational energies of 0.44 and 0.89 eV; we also present data at fixed total energies with variable proportions of reagent vibrational and translational energy. At fixed collision energy, reagent vibrational excitation is found to have negligible effect on the total cross section for proton transfer. At fixed total energy, a decrease in reagent vibrational excitation with a corresponding increase in reagent translation leads to partial disposal of the incremental translation in product translation: At a total energy of 3.5 eV, 50% of this incremental reagent translation appears as product translation. At a total energy of 4.6 eV, 78% of the incremental translation appears in product translation. The experimental data are discussed in terms of induced attractive and repulsive energy release on an attractive potential surface. The role of noncollinear geometries and compressed reactant configurations is judged to be of substantial importance in assessing product rotational excitation and dissociation.
On the argon–methane interaction from scattering data
Authors: Buck Udo , Schleusener Jens , Malik David J. , Secrest Don
Published: February 2003

Total differential cross sections have been measured for Ar–CH4 at E=90.1 meV in the center of mass angular range from 5° to 55°. The well resolved rainbow maximum and the superimposed rapid oscillations are used to establish a reliable isotropic interaction potential V0(R). With this V0(R), the torque and low temperature second virial coefficients are analyzed to establish constraints on the anisotropic potential V3(R) which obeys tetrahedral symmetry. In a final step a complete potential surface is determined based on all three data sets. The scattering calculations are performed in the coupled-states approximation for rotational state-to-state transitions which are summed for the total differential cross section. Small variations of anisotropic parameters lead to dramatic changes in the inelastic differential cross sections, while only small effects are observed in the total differential cross section.
Factorization of the direct correlation function. II. Relation to walls
Authors: Wertheim M. S.
Published: February 2003

We continue our analysis of the closed form factorization of the matrix of direct correlation functions cij(12) of a classical molecular fluid. The starting point is a constructive equation for the factorizing functions ξij. It resembles a transformed Ornstein–Zernike equation in expanded form, but contains limits of integration extraneous to the realm of intermolecular forces. It is shown that these limits arise from the molecular surface which describes the spatial exclusion due to the interaction of a molecular hard core with a plane, hard wall. An alternative expression is found for the ξij, as well as similar representations for the functions κij which factorize the pair correlation functions hij(12). The Percus–Yevick equation for hard particles of arbitrary shape is considered, and a general result for the range of the factorizing function ξij is derived. Similar results are obtained for the mean spherical approximation (MSA) for hard particles with added electrostatic interactions. Two types of factorization are discussed for the MSA. The problem of the inhomogeneities of the singlet densities near a plane, hard wall is treated by applying the factorization to the wall–particle Ornstein–Zernike equation. The MSA applied to the wall–particle interactions is considered. The approximation used in dealing with the wall is decoupled from the treatment of the bulk phase, which could be represented by exact correlation functions. Factorization of the bulk correlation functions relative to the hard cores of the wall–particle interactions is sufficient to obtain a complete solution. Explicit formulas are given in terms of the factorizing functions ξij and κij, and the soft parts of the wall–particle potentials.
Absorption and resonance Raman spectra of Pb2, Pb3, and Pb4 in xenon matrices
Authors: Stranz David D. , Khanna Raj K.
Published: February 2003

Lead metal was vaporized and trapped in solid xenon at 12 K. Electronic absorption and resonance Raman spectra were recorded of the resulting matrix, which was shown to contain Pb2, Pb3, and possibly Pb4 molecular species. The vibrational frequency for Pb2 is determined to be 108 cm−1 for the ground state, with a dissociation energy of ∼8200 cm−1. A D3h symmetry is suggested for the Pb3 species, with ν1=117 and ν2=96 cm−1. The existence of Pb4 is suggested by a fundamental and overtone of 111 cm−1 spacing.
Kinetic theory of the hydrodynamic interaction between two particles
Authors: Cukier Robert I. , Kapral Raymond , Mehaffey J. R.
Published: February 2003

A kinetic theory derivation of the hydrodynamic interaction between two massive, large spheres in a dilute gas is presented. The calculations start from microscopic expressions for the two particle diffusion and friction tensors obtained from a pair kinetic equation. The hydrodynamic expression for the friction tensor is obtained as an expansion in the ratio of particle diameter σ to particle separation r12 to order (σ/r12)3. This calculation displays the microscopic collision mechanisms which are responsible for the viscous drag and hydrodynamic interaction experienced by the particles.
Monte Carlo study of polyelectrolyte behavior. I. Technique
Authors: Brender Chava , Lax Melvin , Windwer Stanley
Published: February 2003

A dynamic Monte Carlo method for the relaxation of a polyion in the presence of its counter ions is reported. A lattice model incorporating long range interaction of a Coulombic and excluded volume nature is considered. Results are listed for the configurational energy 〈UNI/NIkT〉, as well as the mean square end-to-end distance 〈R2N〉, and the mean square radius of gyration 〈S2N〉, for short chains.
Spatial monomer distribution for a flexible polymer in a good solvent
Authors: Witten T. A. , Schäfer L.
Published: February 2003

We calculate the fourth moment 〈r4〉 of the average monomer–monomer separation in a flexible linear polymer in the excluded volume limit. The ratio 〈r4〉/〈r2〉2 is a universal number expressible in terms of the exponents γ and ν. The ratio is 8% smaller for the excluded volume chain than for the ideal chain. To account for the excluded volume interaction we use field theory methods to renormalize the Mayer–Fixman cluster expansion. Our approximation method of expanding in dimension of space minus four introduces an estimated uncertainty of 1%. The end point moment ratio 〈r4e〉/〈r2e〉2 behaves similarly.
On the validity of the Flory–Huggins approximation for semiflexible chains
Authors: Gujrati P. D. , Goldstein Martin
Published: February 2003

We have found exact limits on the validity of the Flory–Huggins approximate treatment of stiff chains on a lattice for small values of g, the fraction of gauche bonds, by obtaining lower bounds for the total number of Hamilton walks WH(g) as a limiting case of the lattice model. The Flory–Huggins approximation underestimates the true entropy for all g<0.325. Specifically, the entropy does not become zero for g?0.227: there is a nonnegligible entropy at all g other than g=0. From this we show (1) the Flory model cannot have a first order transition from a disordered phase to a completely ordered crystal, and (2) the Gibbs–DiMarzio conclusion, that there is a second order phase transition at T2 in the supercooled liquid phase when the state of zero entropy with g=g0≳0 is reached, can be at best only a conjecture. The present analysis implies that one must use caution in predicting phase transitions when using the Flory–Huggins approximation.
Monte Carlo lattice simulation of a simple electrolyte
Authors: Brender Chava , Lax Melvin
Published: February 2003

Monte Carlo simulations are reported for the primitive electrolyte model of Card and Valleau [Ref.4(a)]. (AIP)
Two-photon excitation of indium atoms by photodissociation of InCI and InBr
Authors: Cool Terrill A. , Koffend John B.
Published: February 2003

Measurements are presented of two-photon dissociative excitation cross sections for InCl and InBr for photolysis with a 248 nm KrF laser source. Values of the two-photon coupling parameter σ/I (cm4/W) of 4.9×10−27, 2.4×10−28, 7.9×10−28, and 7.8×10−28 are measured for the respective processes: 2hν+InCl→In(5s26s)+Cl, 2hν+InCl→In(5s25d)+C1, 2hν+InBr→In(5s26s)+Br, and 2hν+InBr→In(5s25d)+Br.
Quenching rate constants of metastable states of neon, argon, and krypton by mercury atoms
Authors: Wren D. J. , Setser D. W.
Published: February 2003

Room temperature rate constants (thermal average cross sections) for the quenching of electronically excited state rare gas metastable atoms by mercury atoms have been measured using the flowing afterglow technique. The thermal cross sections are σQ[Ne(3P2)]=70 Å2;σQ[Ar(3P2)]=194 Å; σQ[Ar(3P0)]=219 Å2; and σQ[Kr(3P2)] =124 Å2. The mechanism for quenching by mercury atoms is Penning ionization for Ne* and Ar*, and excitation transfer for Kr*. These results are discussed in terms of the cross section of similar reagents and the cross section predictions of the close collision criteria. The large experimental cross sections indicate that the total quenching cross section is dictated by interactions occuring at large internuclear distances associated with a long range attractive potential. However, the interactions at shorter range are responsible for the actual conversion from reactants to products. The Kr(3P2) +Hg excitation transfer reaction provides a way to generate Hg(3P2) metastable atoms in a flowing afterglow apparatus.
On the low-lying states of MgO. II
Authors: Bauschlicher Charles W. , Lengsfield III Byron H. , Silver David M. , Yarkony David R.
Published: February 2003

Using a double zeta plus polarization basis set of Slater orbitals, full valence MCSCF (FVMCSCF) calculations were performed for the low-lying states of MgO. For each state the FVMCSCF calculations were used to identify the important configurations which are then used in an MCSCF calculation and subsequently as references in a single and double excitation CI calculation. This approach is found to treat all states equivalently, with the maximum error in the computed Te’s and Re’s of 800 cm−1 and ∼0.03 ̊, respectively. The b 3Σ+ state which has yet to be characterized experimentally is predicted to have a Te of ∼8300 cm−1 and a bond length of 1.79 Å. A spectroscopic analysis of the potential curves indicates that their shapes are in quite reasonable agreement with the range of experimental results.
Coupled Hartree–Fock and finite perturbation–configuration interaction calculations of nuclear spin–spin coupling constants in the second-row hydrides
Authors: Kowalewski Jozef , Laaksonen Aatto , Saunders Victor R.
Published: February 2003

Nonempirical calculations are reported for the one-bond and geminal nuclear spin–spin coupling constants in the hydrides of the second-row elements, HCl, H2S, PH3, and SiH4. For the Fermi contact term, the calculations are performed using the finite perturbation method at the Hartree–Fock and configuration interaction levels of approximation. The correlation effects are found to be of importance. The noncontact terms are calculated using the infinitesimal coupled Hartree–Fock method. These terms are sizable for the one-bond couplings in HCl and H2S but small in other cases. In general, the trends in the calculated values are found to differ substantially from the situation in the first-row hydrides, in agreement with the experimental evidence. The calculated values agree quite well with the available experimental data.
Charge and spin distributions of copper and silver porphine
Authors: Ellis D. E. , Berkovitch-Yellin Ziva
Published: February 2003

Electronic energy levels and charge and spin distributions for copper and silver porphine (CuP, AgP) have been calculated, using the one-electron Hartree–Fock–Slater theory. Calculated spectroscopic properties are compared with the available optical, photoelectron, and hyperfine data and with previous theoretical efforts. Using density difference contour maps and a Mulliken population analysis based upon the LCAO variational expansion of the eigenfunctions, we verify and make quantitative traditional ideas about bonding and charge transfer in these systems. In contrast with a recent MS–Xα calculation on CuP, we find a ground state level structure essentially in agreement with semiempirical extended Hückel calculations of Zerner and Gouterman. Detailed x-ray and neutron scattering experiments are desirable to verify extended features of the charge and magnetization density.
Monte Carlo simulations of the rate of intramolecular end-to-end contact in alkane chains
Authors: Nairn J. A. , Braun C. L.
Published: February 2003

We report Monte Carlo simulations of the dynamics of intramolecular contact in alkane chains and in end-labeled alkane chains. The chain is confined to a diamond lattice except during conformational jumps. Rotational jumps around internal bonds provide the mechanism for change in the end-to-end separation but crankshaft-like motions of the chain are also permitted. No adjustable parameters are used. End-to-end contact is found to obey first-order kinetics, and the rate constants for contact decrease monotonically with chain lengths of from 10 to 20 atoms. Simulations for end-labeled chains are compared with experimental measurements of intramolecular electron transfer and intramolecular fluorescence quenching.
Matrix-isolated bismuth. I. The A→X band system of Bi2 in solid argon
Authors: Ahmed Fakhruddin , Nixon Eugene R.
Published: February 2003

The A→X fluorescence system of the Bi2 molecule in solid argon has been explored by means of tunable dye laser radiation. About 135 bands involving A state levels from v′=0 to v′=6 and X state levels up to v′′=26 are observed. Analysis yields ωe values of 133.4 and 174.3 cm−1 for the A and X states, respectively, and a band system origin at 17 719 cm−1. The Raman spectrum of the fundamental vibration and two overtones of Bi2 appear along with the fluorescence.
Absolute cross sections for beam-surface reactions: N2+ on Ti from 0.25 to 3.0 keV kinetic energy
Authors: Hu Hsin-Kuei , Murray P. Terrence , Fukuda Yasuo , Rabalais J. Wayne
Published: February 2003

Analytical expressions for the absolute cross sections of beam-surface reactions are derived and applied to the N2++Ti→TiN reaction over the kinetic energy range 0.25–3.0 keV. The model assumes that the amount of reaction product P formed near the surface is a function of the collisional dissociation probability of the primary molecules Pd, the reaction cross section σr, and the cross section for product sputtering by the impingent reactant beam σsp. For a dosage R0 of reactant molecules impingent on M0 target atoms, P/M0?rPd/A) R0 in the limit R0→0 (initial reaction), and P/M0=[α+(β/Pd)(σsp/σr)]−1 in the limit R0→∞ (saturation dose), where A is the surface area bombarded and α and β are stoichiometric factors for the product MαRβ. The techniques of x-ray and UV photoelectron spectroscopy (XPS and UPS), secondary ion mass spectrometry (SIMS), thermal desorption spectrometry (TDS), and depth-concentration profiling are used to characterize the reaction product and measure the product film thickness and composition for the reaction of N2+ with the (101̄1) face of a titanium single crystal. The measurements yield a film composition of Ti0.89N and show that the properties of the film, including its extremely high stability, are identical to those of commercial TiN. The reaction cross section is determined as σr,0.5=2.1×10−16 cm2 and σr,2.0=1.0×10−16 cm2 at primary N2+ kinetic energies of 0.5 and 2.0 keV, respectively. The formation and profile of the film near the surface, the interpretation of and uncertainties in the cross sections obtained, and comparison of this system to other N2+ metal systems are discussed.
Calculation of zero field splitting parameters for trimethylenemethane
Authors: Feller David , Borden Weston Thatcher , Davidson Ernest R.
Published: February 2003

The spin dipole–dipole contribution to the zero field splitting of the 3A′2 ground state of trimethylenemethane has been computed with ab initio CI wave functions which included selected single and double excitations from the Hartree–Fock configuration. The resulting value of D is 0.020 cm−1. Isotropic and anisotropic proton hyperfine coupling constants were also computed. The difficulty of quantitatively reproducing experimental values for these properties is discussed.
Electron paramagnetic resonance of Li–CO2 complexes in a CO2 matrix at 77 K
Authors: Borel J. -P. , Faes F. , Pittet A.
Published: February 2003

Li–CO2 complexes have been obtained by the condensation of a Li atomic beam in a CO2 matrix at 77 K. Electron paramagnetic resonance measurements show that the Li 2s electron is strongly localized on a CO2 molecule and consequently CO−2 molecular ions are nearly formed. The g tensor and the C13 and O17 hyperfine tensors are characterized by two principal values. This axial symetry can be explained by a rotation of the CO−2 ions around the molecular axis O–O.
Comment on the paper ‘‘The role of shallow traps on the mobility of electrons in liquid Ar, Kr, and Xe,’’ by G. Ascarelli, J. Chem. Phys. 71, 5030 (1979)
Authors: Schmidt W. F. , Sowada U. , Yoshino K.
Published: February 2003

The electron drift velocity in liquid Ar, Kr and Xe is furthe discussed. It is proposed that the electron transport occurs via shallow traps. Some experimental evidence is cited for the presence of hot electrons in liquefied rare gases. (AIP)
Temperature dependence of the vibrational relaxation rate coefficient of N2(1)+N2(0)
Authors: Shin H. K.
Published: February 2003

The vibrational relaxation process N2(1)+N2(0)→N2(0)+N2(0) has been investigated over a wide temperature range including the liquid nitrogen phase by use of the WKB formulation of energy transfer probabilities. When the collision frequency correction is introduced, the model gives rate coefficients which are consistent with observed data in the liquid phase.
Long-lived high-Rydberg molecules formed by electron impact: H2, D2, N2, and CO
Authors: Tarr Susan M. , Schiavone James A. , Freund Robert S.
Published: February 2003

High-Rydberg (HR) molecules of H2, D2, N2, and CO have been observed with lifetimes of the order of 100 μsec. They are stable with respect to predissociation and autoionization and have sufficiently long radiative lifetimes to be detected because they are formed in states of high orbital angular momentum (ℓ). These high-Rydberg molecules are produced by electron impact and are detected by electric field ionization. The measurements used to characterize them are time of flight (TOF) distributions, principal quantum number (n) distributions, excitation functions, and absolute cross sections.
Influence of flow on chemical reaction rates
Authors: Samson René , Deutch J. M.
Published: February 2003

The influence of convective flow on diffusion-controlled steady-state reaction rates in chemically reactive mixtures is studied for a number of different model systems. Two different flow types are considered: flow in a frictional medium and constant flow in a medium containing many reactive centers. The significance of the results for the combustion of fuel sprays is discussed.
Theory of vibronic coupling in linear molecules
Authors: Köppel H. , Domcke W. , Cederbaum L. S.
Published: February 2003

Vibronic coupling between different electronic states of linear molecules is investigated by an expansion of the molecular Hamiltonian in powers of the bending amplitude ρ. A matrix Hamiltonian is derived which describes the simultaneous interaction between Σ+, Σ−, Π, and Δ electronic states and represents a generalization of the well-known Hamiltonian of the Renner–Teller effect in an isolated Π electronic state. We discuss the influence of the vibronic coupling on the adiabatic potential energy surfaces as well as on the spectral intensity distribution for the transition from a well separated initial (linear) state into the manifold of interacting states. In contrast to the Renner–Teller effect even the linear (in ρ) vibronic coupling between Σ and Π or Π and Δ electronic states can lead to nonlinearity of the lower electronic state if the coupling is sufficiently strong. To facilitate the interpretation of the spectrum it is also calculated in the adiabatic and Franck–Condon approximations and compared to the exact result. Model spectra are presented for a wide range of parameters where perturbation theory breaks down and numerical methods have to be applied. Two main regimes can be distinguished. When the energy difference between the interacting states is much larger than the bending frequency (’’off-resonant case’’) the bands of the different electronic states do not overlap and can be considered separately. In this case Σ electronic states are well understood adiabatically and Π electronic states as exhibiting an induced Renner–Teller effect. When the above energy difference is smaller than or equal to the bending frequency (’’resonant case’’) additional interstate nonadiabatic interactions occur and the separation of the different electronic states is no longer possible. The nature of the nonadiabatic interactions is discussed in detail.
On the accuracy of the iterative method for swarm transport coefficients
Authors: Braglia G. L.
Published: February 2003

The moment theory of electron transport in an electric field in a gas, by Lin, Robson, and Mason, has been seriously called into question (in CH4) by Kleban and co-workers. This paper is a contribution to resolve the discrepancy. Results of Monte Carlo calculations in the above gas are presented which show that the moment theory is, on the contrary, correct.
Transverse relaxation of dipolar coupled spin systems under rf irradiation: Detecting motions in solids
Authors: Rothwell W. P. , Waugh J. S.
Published: February 2003

The spin–spin relaxation time T2 for an S spin dipolar coupled to an unlike I spin under conditions of random isotropic rotational motion and I spin rf decoupling is calculated. The results of the analysis form the basis for a method to detect and analyze rotational motions in solids. The technique is sensitive to motions which occur on the time scale of the rotating-frame Larmor frequency of the applied rf field and is presented in the context of a variable temperature magic-angle sample-spinning experiment where the S spins are observed and the I spins are decoupled. The previously well characterized molecules hexamethylbenzene, hexamethylethane, and adamantane are studied (S=13C and I=1H), and the resulting motional parameters are found to be in good agreement with previous results. As well, the theoretically predicted dependence of T2 on the strength of the decoupling field is experimentally borne out. Finally, the question of resolution of heteronuclear coupled spin systems and the role of decoupling is addressed.
Laser magnetic resonance spectroscopy of the ν1 and ν3 fundamental bands of DCO
Authors: Lowe R. S. , McKellar A. R. W.
Published: February 2003

The ν1 (C–D stretch, ν0=1909.774 cm−1) and ν3 (C–O stretch, ν0=1794.587 cm−1) fundamental bands of the deuterated formyl radical DCO have been studied by the technique of CO laser magnetic resonance spectroscopy in the 5.2 to 5.6 μm region. DCO was produced in a flow system by reacting F atoms from a microwave discharge in CF4+He with D2CO molecules. Numerous relatively strong a-type (ΔKa=0) resonances and a few weaker b-type (ΔKa=±1) resonances were recorded for ν1, whereas for ν3 the resonances were weak and entirely b type. The data were assigned to transitions involving 1⩽N⩽9 and 0⩽Ka⩽7, and the two bands were analyzed in a simultaneous fit which included the effects of Coriolis and higher order interactions which couple the two vibrations. The results of the analysis were the band origins and the rotational, centrifugal distortion, spin–rotation, and Coriolis coupling constants for the v1=1 and v3=1 states, as well as some improved constants for the ground vibtational state. The ν1 and ν3 band origins show quite large shifts from their previously determined values in solid matrices at low temperatures.
Interpretation of the optical absorption spectrum and of the paramagnetic susceptibility of neodymium trifluoride
Authors: Caro P. , Derouet J. , Beaury L. , Teste de Sagey G. , Chaminade J. P. , Aride J. , Pouchard M.
Published: February 2003

The absorption spectrum of single crystal NdF3 of tysonite structure was recorded at liquid helium temperature up to 33 800 cm−1. 127 Stark levels were obtained and fitted to a mean square deviation of 24 cm−1 with a Hamiltonian involving 12 free atom parameters and four D3h crystal field parameters. The fit was improved to a mean square deviation of 14 cm−1 by adding five supplementary crystal field parameters to approach the real C2 symmetry of the site. The paramagnetic susceptibilities parallel and perpendicular to the trigonal axis in the structure were measured from 4.2 to 1100 K and compared with the values derived from the wave vectors of the 18 lowest Kramers doublets through the application of the Van Vleck formula. An overall good agreement was found. The material is anisotropic, χ∥ being larger than χ⊥.
Absorption spectrum, energy levels, and crystal-field parameters of Tm3+:LaCl3
Authors: Gruber John B. , Leavitt Richard P. , Morrison Clyde A.
Published: February 2003

Optical absorption spectra and energy levels of Tm3+ in LaCl3 are reported. A crystal-field Hamiltonian of C3h symmetry is used to fit the data; a best fit rms deviation of 3.0 cm−1 is obtained between 27 experimental and theoretical energy levels with the following crystal field parameters: B20=226.9, B40=−241.0, B60=−423.6, and B66=256.3 (all in cm−1). Results obtained here for Tm3+ are compared with results on other lanthanides in LaCl3. Point–charge and dipole lattice sums are performed and compared with phenomenological crystal-field components obtained from Bnm of various lanthanides in LaCl3.
Raman light scattering studies of the depolarized low frequency region of water and aqueous solutions
Authors: Brooker Murray H. , Perrot Michel
Published: February 2003

Raman spectra of the depolarized Rayleigh wing (20–350 cm−1) for water and aqueous solutions have been recorded in digital form and recast in the R2(?) format as described previously. Studies of water, aqueous fluoride, and perchlorate suggest that the weak peak at 191 cm−1 has its origin in the hydrogen bonded water structure. Temperature and isotopic substitution (D2O, H2 18O) measurements support this conclusion. Anisotropic ions and molecules such as NO3−, CN−, and acetone superimpose an intense librational peak on the water spectrum.
Collisional decomposition of UF−6
Authors: Haywood S. E. , Doverspike L. D. , Champion R. L. , Herbst E. , Annis B. K. , Datz S.
Published: February 2003

Absolute cross sections for the collisional decomposition of UF−6 into its three lowest asymptotic channels in collisions with the rare gases have been measured for collision energies ranging from below the threshold for decomposition up to a laboratory collision energy of 500 eV. The product velocity spectra have also been measured for one of the decomposition channels at the highest collision energy. The experimental results are found to be consistent with the predictions of a two-step collision model where the unimolecular decomposition of excited UF−6 ions is described in a statistical framework.
On the critical behavior of the optical activity of a fluid
Authors: Kim Shoon K. , Lee Dong J.
Published: February 2003

A statistical theory is given for the dielectric tensor of a fluid composed of chiral molecules. Explicit expressions for circular dichroism and the optical rotations as functions of the optical frequencies in the critical region are obtained.
Phase transition studies in polar and nonpolar liquids at microwave frequencies
Authors: Dahiya J. N. , Jani S. K. , Roberts J. A.
Published: February 2003

A resonant microwave cavity technique was employed to study the dielectric behavior of polar and nonpolar liquids near the phase transition temperatures at microwave frequencies of 7.2, 9.2, and 10.8 GHz. The Slater perturbation equations for a resonant microwave cavity are briefly discussed to show that the above technique can be used to determine both the real and imaginary parts of the dielectric response, which in turn depends on the orientational polarizability of the medium perturbing the cavity. The dielectric relaxation phenomenon in liquids has been treated as a chemical rate process and the abrupt change in the dielectric response of the liquids near phase transition temperatures is shown to be related to the dramatic changes in the free energy of activation of the molecules. Some values for the free energy of activation of water were deduced from data obtained in this investigation.
Electronic relaxation of 1B3u(nπ*) pyrazine in a supersonic jet: Rotational state dependence of the nonradiative rate leading to biexponential decay
Authors: ter Horst Gerard , Pratt David W. , Kommandeur Jan
Published: February 2003

The decay of single rotational levels of the vibrationless first excited singlet state of pyrazine (1,4-diazabenzene) following expansion in a helium supersonic jet and excitation with a pulse dye laser is biexponential, as it is for single vibronic level excitation in the bulk gas phase. However, both the relative contribution and the lifetime of the fast, ’’nonradiative’’, component are strongly dependent on the initial rotational state. A fit to the data shows that the rate of nonradiative decay is proportional to K2, where K is the projection of the rotational angular momentum vector on the (near-symmetric) top axis. Both the interpretation of these results and their implications with respect to the theory of radiationless transitions are discussed briefly.(AIP)
On the evaluation of higher-order JWKB integrals
Authors: Chan C. K. , Lu P.
Published: February 2003

A more efficient algorithm is developed for evaluating higher-order JWKB phase integrals. As a result, the computing time used in generating the weights {Wmk} is reduced. (AIP)
Dielectric dispersion of glycerol from 2.0 to 4.0 GHz
Authors: Brady M. M. , Stuchly S. S.
Published: February 2003

Measurements are reported of the permittivity of glycerol at 2.00,3.00, and 4.00 GHz and 23±0.2 °C. (AIP)
Electronic energy levels of intermediates in the nickel carbonylation reaction
Authors: Howard I. A. , Pratt G. W. , Johnson K. H. , Dresselhaus G.
Published: February 2003

Using the multiple scattering Xa method, electronic energy levels have been found self-consistently for the intermediates Ni(CO)n, n = 1,2,3 in the formation of nickel tetracarbonyl via the Ni–CO surface reaction. Linear geometries have been assumed for NiCO and Ni(CO)2, and a trigonal planar conformation for Ni(CO)3, in accordance with previously published IR spectra. The intermediates were assumed to be in the gas phase, free of surface interaction. From the energy level structure found, all three of the intermediates were determined to be diamagnetic, as Ni(CO)4 is known to be.
Tricritical phenomena in ‘‘quasibinary’’ mixtures of hydrocarbons. I. Methane systems
Authors: Creek Jefferson L. , Knobler Charles M. , Scott Robert L.
Published: February 2003

Temperature, pressure, and composition measurements are reported for the three coexisting phases in the region of the tricritical points of two ternary mixtures of hydrocarbons: methane+n-pentane+2,3-dimethylbutane (I) and methane+2,2-dimethylbutane+2,3-dimethylbutane (II). These systems satisfy a ’’quasibinary’’ approximation in which the proportions of the two higher hydrocarbons [expressed as Z = xC/(xB+xC)] are the same in each of the three phases, so that the phase equilibrium is equivalent to that in a binary system with a solute of average properties. Least-squares analysis does not locate the tricritical point with high precision, but all the measurements are consistent with the predictions of the phenomenological theory that the exponents governing the approach to the tricritical point are the ’’classical’’ mean-field values. If, in accord with this view, we write the difference between the upper and lower critical-end-point temperatures (i.e., extent of the three-phase region) as Tu−Tl = B(Z−Zt)3/2, then the coordinates of the two tricritical points are (I) Zt = 0.28, Tt = 202.82 K, pt = 6.058 MPa and (II) Zt = 0.09, Tt = 201.60 K, pt = 5.938 MPa, xA = 0.965.
The structure of an aqueous ammonium chloride solution
Authors: Pálinkás G. , Radnai T. , Szász Gy. I. , Heinzinger K.
Published: February 2003

X-ray measurements have been performed on a 2 molal NH4 Cl solution at 25 °C. The scattering data have been evaluated with the first neighbor model (FNM). These results are compared with molecular dynamics (MD) simulations where the ST2 model for water is employed. The NH4+ is described by a rigid tetrahedron with point charges at the positions of the hydrogen atoms and the Cl− by a Lennard-Jones sphere with an elementary charge at the center. Good agrement has been found between the measurements and the simulation. Contrary to previous results the nearest neighbor distance for NH4+–water is found to be significantly different from the one for water–water. The structure of the solvent described by the nearest neighbor distance and its root mean square deviation is in the limits of error the same as in pure water and significantly different from the solvent structure in alkali halide solutions.
Time lag in nucleation: A variational treatment of relaxation times in the binary sulfuric acid–water system
Authors: Schelling F. Joseph , Reiss Howard
Published: February 2003

A method for evaluating a lower bound to the time required for the establishment of steady state nucleation in binary mixtures of water and sulfuric acid vapors is described. The method is an extension of an earlier approach devised by Reiss and Katz for unary systems, and involves matrix algebra and the Rayleigh–Ritz variation principle. The mathematical development is described at some length. Application to laboratory-type mixtures of H2O and H2 SO4 indicate that times to the steady state may be very long and should seriously impede the measurements of critical supersaturations in both expansion cloud chamber and nozzle experiments.
Matrix–molecule interactions, dynamics, and exchange phenomena in low temperature matrices: SF6 in argon and krypton
Authors: Swanson Basil I. , Jones Llewellyn H.
Published: February 2003

High resolution infrared studies of argon/SF6 and krypton/SF6 matrices at 10 000/1 show an unexpected amount of structure; 10–12 peaks are observed in argon and six or more peaks in krypton matrices for the n3 mode. Studies in which the deposition temperatures are varied, in conjunction with the structure observed for combination modes and temperature reversible spectral changes, allowed differentiation between multiple trapping sites and site symmetry splittings. We conclude that there are at least six different sites for monomeric SF6 in argon and at least three sites in krypton. Two sites in argon and two in krypton exhibit site symmetry splittings. Temperature dependence studies have shown striking spectral changes wherin for three of these sites (one in argon and two in krypton) the peaks, due to site symmetry splitting, coalesce as the temperature is raised. The temperature dependence can be explained in terms of exchange dephasing involving two high energy fundamentals and a local phonon mode. The dynamics associated with motional collapse of the high enery fundamentals corresponds to rapid site-to-site exchange on a less than nanosecond time scale resulting in higher effective site symmetry as observed by infrared. Unusual 32S–34S isotope effects have also been observed for the spectra of these low temperature matrices.
The terbium chloride–aluminum chloride vapor system. III. Spectral intensity analysis
Authors: Caird J. A. , Carnall W. T. , Hessler Jan P.
Published: February 2003

The intensities of Tb3+ ground state absorption and 5D4 fluorescence transitions in the TbCl3(AlCl3)x(g) complex system have been analyzed according to the Judd–Ofelt theory of forced electric dipole transitions. This represents the first successful attempt to utilize observations of both absorption and fluorescence spectra in establishing the parameters of the theory. The positions of 19 Tb3+ energy levels were determined from the spectra and used to perform a parametric analysis of the Hamiltonian matrix for the ion’s 4f8 configuration. The wave functions obtained in diagonalization of the Hamiltonian were used to calculate unit tensor operator matrix elements required in the intensity analysis. A good fit to the measurements was obtained with intensity parameters W2 = 20.5, W4 = 2.3, and W6 = 3.0 pm2. These results were then used to compute intensities of fluorescence transitions from the higher lying 5D3, 5G6, and 5L10 levels, yielding additional qualitative agreement between theory and experiment. Some of the major discrepancies between theory and experiment may be due to the need for inclusion of odd-order intensity parameters or J mixing in the Judd–Ofelt theory.
Rayleigh–Brillouin spectra of polymer fluids: Polyphenylmethyl siloxane and polydimethylphenylmethyl siloxane
Authors: Fytas G. , Lin Y. -H. , Chu B.
Published: February 2003

Measurements of Rayleigh–Brillouin spectra of polyphenylmethyl siloxane (A) and of polydimethylphenylmethyl siloxane (B) over a wide range of temperatures (270 to 520 K for A; 280 to 390 K for B) are reported. By using the generalized hydrodynamic theory for Rayleigh–Brillouin spectra as developed by Lin and Wang, we have determined the relaxation strength R, the relaxation rate t, the activation energy Ea, and the adiabatic sound frequency ws (T), which are the characteristic physical quantities describing the dynamics of a viscoelastic polymer fluid in the GHz region. Based on those parameters, we were able to obtain excellent agreement between the theoretical and the measured spectra.
The Scheraga–Mandelkern parameters for slightly permeable spheroids
Authors: Kojima M. , Acrivos A.
Published: February 2003

Protein molecules in dilute solutions are modeled as porous spheroids within which Brinkman’s equation is assumed to apply. The stresslet, the force, and the torque exerted on the spheroid are calculated in the asymptotic limit of small permeability, and the results are used to compute values of the Scheraga–Mandelkern parameters b and d for varying axis ratios. It is found that, to first order, a small but nonzero permeability enhances the values of b for all axis ratios other than unity, thereby eliminating permeability as an explanation for why some experimentally determined values of b are lower than the theoretical minimum for rigid spheres.
Temperley’s model of gas condensation
Authors: Keller Joseph B.
Published: February 2003

Temperley’s imperfect gas model is discussed. The stability of the pressure-volume isotherm is considered in the light of Van Hove’s theorem.
Sulfur Kβ emission and K absorption spectra and electronic structure of copper sulfide: Cu1.8S
Authors: Sugiura Chikara , Gohshi Yohichi
Published: February 2003

The Kb emission and K absorption spectra of sulfur in Cu1.8S are measured with a two-crystal spectrometer and a bent-crystal spectrograph, respectively. The Kb emission spectrum consists of two well-separated peaks and the K absorption spectrum has a shoulder at the threshold. These spectra are interpreted on the basis of Terakura’s theory. The two emission peaks are attributed to the transitions from the bonding and antibonding states formed by the redistribution of the sulfur 3p states as a result of hybridization with the copper 3d bands. The spectra of Cu1.8S are compared with those of FeS, CoS, NiS, and CuS reported previously. From the similarity of the overall aspect of the Cu1.8S spectra and those of the transition-metal sulfides, it is indicated that the local p-like density of states of sulfur in the copper and transition-metal sulfides are similar to each other.
Theoretical investigation of rotational rainbow structures in X–Na2 collisions using CI potential surfaces. I. Rigid-rotor X = He scattering and comparison with state-to-state experiments
Authors: Schinke Reinhard , Müller Wolfgang , Meyer Wilfried , McGuire Paul
Published: February 2003

An accurate CI potential energy surface for He–Na2 is determined, which is suitable for rigid-rotor scattering calculations for collision energies below 1 eV. In the calculation of the interaction potential electron correlation effects have been considered for the bond orbital of Na2 and the 1s orbital of He together with the dispersion attraction between these orbitals using the method of self-consistent electron pairs (SCEP). A very shallow van der Waals minimum of about 0.1 meV is obtained at large internuclear distances. Rigid-rotor infinite-order-sudden (IOS) calculations have been performed for collision energies of 0.05⩽E⩽0.15 eV using an analytical representation for the potential surface constructed with the 52 original ab initio points. The differential cross sections for rotationally elastic and inelastic transitions exhibit the recently predicted rotational rainbow structures. The comparison with the state-to-state experimental data of Bergmann et al. [J. Chem. Phys. 72, 4777 (1980)] is performed for DE/E distributions at fixed laboratory scattering angles and for angular distributions of single Dj cross sections. The qualitative and quantitative agreements are satisfactory. Small deviations occur only in the classically forbidden Dj or angular region.
Trajectory study of dissociation reactions. The single-ensemble method. II
Authors: Kutz H. Douglas , Burns George
Published: February 2003

The single uniform ensemble method was previously employed in 3D classical trajectory calculations [H. D. Kutz and G. Burns, J. Chem. Phys. 72, 3652 (1980)]. Presently it is applied to the Br2+Ar system to study nonequilbrium effects in diatom dissociation over a wide temperature range. It was found that, for a given large set of trajectories, observables, such as reaction cross sections or rate constants, are indepedent within four significant figures of the initial distribution function. This indicates a high degree of reliability of the single uniform ensemble method, once the choice of a set of trajectories is made. In order to study dissociation from the low lying energy states, the uniform velocity selection method in trajectory calculations was used. It was found that dissociation from these states contributes but little to the overall dissociation reaction. The latter finding is consistent with the attractive nature of the potential energy surface used, and constitutes an argument against those current theories of diatom dissociation reaction which explains experimental data by postulating a high probability of dissociation from low lying energy states of diatoms. It was found that the contribution from the low lying states to dissociation can be estimated with good accuracy using information theory expressions. Temperature dependence of nonequilibrium effects was investigated between 1 500 and 6 000 °K. In this range the nonequilibrium correction factor varies between 0.2 and 0.5. Angular momentum dependence of such observables as reaction rate constant and reaction cross section was investigated.
A hybrid method for improving MCSCF convergence
Authors: Bauschlicher Charles W. , Bagus Paul S. , Yarkony David R. , Lengsfield Byron H.
Published: February 2003

It has been found that the convergence problems for many ill conditioned single-configuration SCF calculations arise from mixing among only a small number of orbitals. This orbital set includes the highest closed, the partially filled, and (possibly) a few of the lowest virtual orbitals. The fact that convergence problems can be, in very large measure, linked to a small orbital set is used to design a hybird MCSCF procedure in which these orbitals are treated using a second-order MCSCF method, while other mixings are treated with a lower-order method which avoids the time consuming integral transformation. Tests on BeO show that the hybrid method yields convergence even when the simple lower-order treatment diverges. The method is expected to facilitate determination of MCSCF wave functions for large basis problems and for the construction of potential energy surfaces.
Gaussian core model in two dimensions. I. Melting transition
Authors: Stillinger Frank H. , Weber Thomas A.
Published: February 2003

The method of molecular dynamics computer simulation has been used to examine the solid–fluid transition for the Gaussian core model in two dimensions. The system contained 780 particles subject to periodic boundary conditions, and confined to a single reduced density p = 3−1/2. The virial pressure, mean potential energy, and pair correlation functions all indicate that the melting process is first order. However, the system is anomalous in that thermal expansivities of the solid and (low temperature) fluid phases are negative, and the density change on melting at constant pressure is positive.
Gaussian core model in two dimensions. II. Solid and fluid phase topological distribution functions
Authors: Weber Thomas A. , Stillinger Frank H.
Published: February 2003

Local structure in the two-dimensional Gaussian core model at p = 3−1/2 has been anayzed through the topology of nearest- neighbor polygons. Disorder is revealed by the presence of nonhexagonal polygons (disclinations). Near the melting point most disclination polygons have either five or seven sides and these are present in nearly equal concentrations. The concentrations increase by an order of magnitude upon melting the solid. Within the melting range phase coexistence is revealed by inhomogeneous distribution of disclinations. Pair correlation functions have been calculated for particles classified by polygon character; they show asymmetry with respect to disclination type. The first-order melting process can be described as condensation of a dilute gas of small disclination aggregates (solid phase) into a dense medium of disclinations (fluid phase).