bluuebunny/crossref_metadata_2025 huggingface dataset:
Deuterium magnetic resonance in the discotic columnar mesophases of hexaalkyloxytriphenylenes: The conformation of the aliphatic side chains
Authors: Goldfarb D. , Luz Z. , Zimmermann H.
Published: February 2003

Deuterium NMR spectra of chain perdeuterated hexa-pentyloxy, -hexyloxy, -heptyloxy, and -octyloxy triphenylene (THE5, THE6, THE7, and THE8) were studied as functions of temperature in the mesophase region. The deuterium quadrupole splittings exhibited several characteristic features, in particular a steplike decrease in the splitting along the alkyl chain and an even–odd alteration in the methyl splittings within the homologous series. The results are interpreted in terms of possible conformational distributions of the alkyl chain. It is found that there is bending of the alkyl chains out of the aromatic plane, and a considerable degree of chain disorder.
Radiative lifetimes of trapped molecular ions: HCl+ and HBr+
Authors: Martner Cecilia C. , Pfaff Jürgen , Rosenbaum Neil H. , O’Keefe Anthony , Saykally Richard J.
Published: February 2003

Excitation spectra in the A 2Σ+−X 2Π system of HCl+(0,0) and HBr+(1,0) as well as radiative lifetimes of selectively excited rotational levels in the A 2Σ+ electronic states have been measured in a RF ion trap using laser induced fluorescence and time-resolved single-photon counting techniques. Coherent ultraviolet radiation was generated by frequency mixing of a Nd:YAG/dye laser system. For HBr+ the lifetimes of four rotational levels adjacent to the v′=1 predissociation limit at J′=25/2 were measured. No statistically significant variation with J was found. The average of these four values (3.89±0.15 μs) is therefore reported as the effective lifetime of the v′=1 level of A 2Σ+ HBr+. For HCl+ the lifetime measurements likewise indicate no strong variation with J. The average lifetime of the v′=0 level of the A 2Σ+ state of HCl+ is 3.4±0.4 μs. Measurements of radiative lifetimes of molecular ions by the RF ion trap technique eliminates the determinate error that results from drift of ions out of the detection volume in conventional experiments.
First quantum corrections to second virial coefficients for anisotropic interactions: Simple, corrected formulaa)
Authors: Pack Russell T
Published: February 2003

A simple formula for the first quantum correction to the second virial coefficient, valid for the interaction of any like or unlike combination of atoms, diatomics, spherical top, or symmetric top molecules is given. It is found that the commonly used formulas of Wang Chang contain an error that omits an anisotropic contribution. The sizes of the different contributions to the quantum correction are discussed. As examples, calculations for He–SF6 and He–CO2 are reported.
The periodically forced conversion of 2,3-epoxy-1-propanol to glycerine: A theoretical analysis
Authors: Rehmus Paul , Zimmermann E. C. , Ross John , Frisch H. L.
Published: February 2003

The kinetics of the hydration of 2,3-epoxy-1-propanol to glycerine in a continuous stirred tank reactor is studied both numerically and analytically. The agreement between our numerical and analytical results, and others' experimental measurements is extremely good for the autonomous system; we predict and then verify numerically the existence of normal and inverted Hopf bifurcations. We then periodically perturb the system to obtain details of entrainment: Entrainment bandwidths, phase locking, and resonance in the amplitudes of temperature and concentrations. We also numerically calculate the dissipation and find at fixed chemical flux, conversion rate, and average output temperature, that the total dissipation is unchanged under resonance conditions, but the dissipated energy can be varied among the different heat baths and free energy sinks by varying the perturbation frequency.
Scaling relations of two-dimensional athermal multichain systems by computer simulation
Authors: Okamoto Hiroshi , Itoh Kazuya , Araki Takabumi
Published: February 2003

The statistical mechanical properties of the systems of athermal multichain (n-mers) in two-dimensional lattices are investigated by the computer simulation. The mean dimensions of the chains follow a scaling relation with a scaling variable (n−1)2νn−1φ, where 2ν is the mean square end to end distance exponent and φ is the concentration. The logarithm of the state sum per chain and the osmotic pressure thereof can be described by the same variable in a way which is slightly lattice structure dependent. Because the application of the available theories to our short chain lattice systems may have some controversies, the current coarse graining procedure is appropriately reformulated. The simulation data including the mentioned ones and the chain element distributions around a mass center are well understood by the proposition.
Electronic structure of small copper clusters. II. Localized d hole in excited states and ionized states of Cu2 and Cu3
Authors: Miyoshi Eisaku , Tatewaki Hiroshi , Nakamura Takashi
Published: February 2003

The electronic structure of Cu2 and Cu3 clusters is investigated by ab initio SCF calculations. The geometry optimization is performed. Because of the Jahn–Teller effects the obtuse and acute isosceles triangle configurations of Cu3 are energetically lower than the regular triangle one. The ‘‘localized’’ orbital which is located at the top or center atom is commonly found through the obtuse, regular, acute, and linear triangle Cu3’s. The excited and ionized states where the localized d electron participates are energetically close to those of (s → s or s*) and (s → ∞) states, which suggests that the electronic structure of Cu3’s is similar to that of bulk. The calculated excitation energies and ionization potentials for these states agree with experiment within error of 1.0 eV. The localized d hole excited states and the ionized states are found in Cu2 as well. The effect of the basis set superposition on Cu2 and Cu3 and the band structure of larger Cu clusters are also discussed.
Theoretical study of the reaction C(3P)+N2O(X 1Σ+). I. Potential energy surfaces
Authors: Rayez J. C. , Rayez M. T. , Duguay B.
Published: February 2003

We report a theoretical study of the reaction C(3P)+N2O(X 1Σ+) which leads exclusively to the formation of CN(X 2Σ+) and CN(A 2π). The determination of the potential energy surfaces, after extended CI calculation, allows us to interpret these facts through differences of activation barriers, avoided crossing, and nonadiabatic transitions.
On the RML dependence of 10D
q
Authors: Bermejo M. , Pueyo L.
Published: February 2003

The RML dependence of 10Dq is analyzed in terms of the R−nML law and the harmonic representation of the electronic states associated with 10Dq. A simple formula relating the exponent n to the geometrical parameters of these states is presented. The RML dependence of 10Dq near the equilibrium nuclear configuration could be determined approximately by means of this expression and some data from the normal-pressure optical spectra. On the other hand, the formula suggests that the theoretical calculation of such dependence should be particularly accurate on (a) the vertical transition energy and (b) the theoretical displacement of the excited state. Other aspects of theoretical interest, concerning the use of frozen orbitals in computing 10Dq are discussed. The main conclusions of this analysis are compared with experiments and Hartree–Fock calculations on CrF3−6 and CrF4−6.
Generalized muffin-tin orbitals for electronic structure studies of surfaces, interfaces, and organic solids
Authors: Casula F. , Herman F.
Published: February 2003

We have developed an improvement formalism for carrying out electronic structure calculations for surfaces, interfaces, and organic solids using muffin-tin-orbital (MTO) basis sets. We will first show how the variational flexibility of MTO tail functions can be improved by introducing generalized MTO tail functions composed of modified spherical Bessel functions Kl(κ, r) and their derivatives with respect to κ. Next, we will show how energy dependent MTOs can be constructed by using double basis sets, the first partners being keyed to the radial solutions of the wave equation inside the MT spheres, and the second partners to the energy derivatives of these radial solutions. The energy dependence of these double MTO basis sets introduces additional variational flexibility. Since the first partners will normally be considerably larger than the second partners, the double-dimension secular equations can be solved economically by using the Löwdin partitioning scheme. Finally, we will indicate how the calculation of the interstitial matrix elements, which is usually the time-limiting step for open structures, can be approximated rather nicely by calculating these matrix elements inside a suitably chosen set of overlapping atomic spheres, and then extrapolating to a set of larger overlapping atomic spheres which enclose the most important portion of the interstitial region. With these improvements, it should be possible to carry out accurate calculations for open structures having large numbers of atoms per unit cell considerably more rapidly and economically than by existing MTO-type methods.
Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Rh–Cu clusters
Authors: Meitzner G. , Via G. H. , Lytle F. W. , Sinfelt J. H.
Published: February 2003

An investigation of the structure of the bimetallic clusters present in rhodium–copper catalysts was conducted with the use of extended x-ray absorption fine structure (EXAFS) measurements. Two catalysts were studied, both employing silica as a support for the clusters and both containing 1 wt. % rhodium. In one catalyst the Cu:Rh atomic ratio was 1:2 and in the other 1:1. Studies were made of the EXAFS associated with the K absorption edges of the rhodium and copper. The results of the EXAFS studies indicate that copper concentrates at the surface of the rhodium–copper clusters. In this regard the results are similar to our earlier reported results on ruthenium–copper clusters. However, the extent of surface segregation of the copper appears to be less pronounced for rhodium–copper clusters. This result is reasonable on the basis that rhodium and copper, unlike ruthenium and copper, exhibit at least some miscibility in the bulk.
The influence of instrumental resolution on high frequency incoherent neutron scattering
Authors: Dorner B. , Griffin A.
Published: February 2003

The instrumental energy resolution Δω limits the analysis and interpretation of experimental data to times t≲(Δω)−1. Investigating high frequency molecular modes with a resolution Δω much bigger than the characteristic frequency of the lattice phonon spectrum the observed intensity has a dependence on momentum transfer Q and temperature T which is described by a Debye–Waller factor which contains only the amplitudes of the high frequency molecular modes. With improved resolution details of the signal coming from the molecular mode itself and from the lattice phonon, sidebands can be studied. This paper generalizes the recent analysis of Griffin and Jobic, which ignored instrumental resolution.
Low temperature magnetization study on high spin iron (III) porphyrins
Authors: Marathe V. R. , Mitra S.
Published: February 2003

Accurate and detailed measurements of average magnetic susceptibility (4–100 K) and magnetization (2–20 K and 10–50 kOe) are reported on a number of high spin iron (III) prophyrins, namely protoporphyrin-, octaethylporphyrin-, and deuteroporphyrin iron (III) chlorides. Adequate precautions were taken to ensure that the crystallites did not orient during the magnetization measurements, in high magnetic fields at low temperatures. The experimental magnetization data show complete saturation below 4 K at magnetic fields above 40 kOe and the saturation moment 〈μ〉 lies between 3.0–3.4 in these compounds, indicating large deviation from the expected value of 5.0, due to sizeable zero-field splitting. The magnetization results at low temperatures show varying degrees of exchange interaction, which was considered within molecular field framework to quantitatively account for the data. A fit to the data gave reasonable values for the zero-field splitting and exchange-interaction parameters.
Computer simulation of liquid anisotropy. V. Nonlinear molecular dynamics at high field strengths
Authors: Evans M. W.
Published: February 2003

The computer simulation method has been used to investigate the molecular dynamics of C2v symmetry asymmetric tops at points along the Langevin function to saturation. The first order linear/angular velocity correlation function is visible in a moving frame of reference and becomes increasingly oscillatory at high field strengths. A single molecule rototranslational Langevin equation cannot explain these results without involving nonlinear interactions between the molecule and it surroundings. The computer simulation has been used to predict the results of experiments on laser-induced birefringence.
Critical and tricritical phenomena in ‘‘living’’ polymers
Authors: Kennedy Stephen J. , Wheeler John C.
Published: February 2003

The equilibrium polymerization of ‘‘living polymers’’ such as polytetrahydrofuran and poly-α-methylstyrene can be usefully described by the n=0 limit of the n vector model of magnetism. Nonclassical critical behavior is predicted near the ceiling temperature when the initiator concentration is sufficiently small. The small initiator concentration implies a small magnetic field in the n→0 vector model. The agreement of our theory with the limited experimental data available is good, and appears to confirm nonclassical critical behavior. Solutions of living polymers can be described by an annealed dilute n→0 vector model, and interesting new phase diagrams are predicted that include tricritical points analogous to those found in He3–He4 mixtures at very low temperature and in models of sulfur solutions and dilute ferromagnets. The relationship between the phase diagrams in these systems is elucidated.
Surface-enhanced Raman scattering from vapor-deposited copper, silver, and gold. Excitation profiles and temperature dependence
Authors: Ladouceur H. D. , Tevault D. E. , Smardzewski R. R.
Published: February 2003

Surface-enhanced Raman spectra (SERS) of pyridine adsorbed on copper, silver, and gold films vapor deposited on low temperature substrates are reported. Similar spectra were also obtained on a sputter-cleaned silver single crystal. Excitation spectra (450–750 nm) for all three metals revealed an overall increase in SERS activity at longer wavelengths, the relative increase being greater for copper and gold than silver. A broad excitation maximum near 2 eV was observed for the 1006 cm−1 pyridine SERS signal on silver. A lesser-defined maximum was revealed for copper in the same general vicinity (1.7–2.0 eV) while a broad onset extending below 1.7 eV was observed for gold. Temperature studies (15–300 K) indicate that the observed SERS originate from molecular pyridine chemisorbed to the metal surfaces. In the cases of copper and gold, SERS were also observed from samples maintained at room temperature in vacuum. The intensities of the SERS signals were proportional to incident (cw) laser power at low power densities (<1 MW/cm2).
Intermolecular Raman active vibrations of hydrogen bonded acetic acid dimers in the liquid state
Authors: Nielsen O. Faurskov , Lund P.-A.
Published: February 2003

Low frequency Raman spectra (20–250 cm−1) of liquid CH3COOH, CH3COOD, and CD3COOD at room temperature were studied. The experimental data were directly transformed to the R(ν̄) representation, previously described. The three Raman active intermolecular vibrations of the cyclic dimer (C2h symmetry) were assigned by use of depolarization ratios and a comparison of vibrational frequencies for the different isotopic molecules.
Fluorescence yield from photodissociation of CH4 at 1060–1420 Å
Authors: Lee L. C. , Chiang C. C.
Published: February 2003

The photoabsorption and fluorescence cross sections of CH4 were measured using synchrotron radiation at 1060–1420 Å. The fluorescence starts to appear at 1330 Å, and its cross section increases with decreasing photon wavelengths. The fluorescence cross section at 1060 Å is 0.38×10−18 cm2, which is much smaller than the theoretical expectation. It is unlikely that the CH2 production from CH4 photodissociation will have a population inversion in the singlet system. A vibrational structure observed at 1060–1120 Å is probably the 1t2→3p Rydberg transition of CH4.
The C–Cl bonds in trichloroethylidene trichlorolactic ester, Cl3CCHOCOCHOCCl3. A 35Cl–NQR single crystal study
Authors: Hashimoto M. , Nagarajan V. , Weiden Norbert , Weiss Alarich
Published: February 2003

By single crystal 35Cl–NQR with a 4π Zeeman spectrometer, the six independent 35Cl-nuclear quadrupole coupling tensors in trichloroethylidene trichlorolactic ester (chloralide) Cl3CCHOCOCHOCC13 have been studied at T=21 °C. The directions of the electric field gradient (EFG) tensor components have been determined. The main axes φzz are within ±0.5° parallel to the C–Cl bound directions. Very small asymmetry parameters in the range 0.005≤η≤0.053 are characteristic for the EFG tensors of Cl bond to carbon in aliphatic systems, and the six nuclear quadrupole coupling constants are found in the range 76.053≤e2qQh−1/MHz≤78.790. The orientations of the principal axes φxx and φyy is explained as due to intramolecular interactions likely of through space origin.
Polarized Raman spectra of a single crystal of bromine
Authors: Halac E. , Bonadeo H.
Published: February 2003

The polarized Raman spectra of a single crystal of bromine have been obtained and the results lead to an unambiguous assignment of the corresponding fundamental bands. The resulting vibrational pattern is similar to that reported for solid iodine from inelastic neutron scattering experiments.
Excitation energy dependence in the photoemission satellite structures in solid CO and N2
Authors: Eberhardt W. , Freund H.-J.
Published: February 2003

We use the relative intensity of photoemission satellites in the outer core, inner valence region measured as a function of photon energy in order to identify the spectroscopic assignment for each individual satellite. The outer valence satellites show a decrease in intensity relative to the outer valence single particle emission over the excitation energy range from 40 to 140 eV. The 3σ(2σg) derived structures, on the other hand, increase in intensity, measured relative to the outer valence emission as expected from the general behavior of the 3σ(2σg) single particle cross section.
Voronoi polyhedra for studying solvation structure (IV)
Authors: David Elaine Eisler , David Carl W.
Published: February 2003

Voronoi polyhedra are employed to generate a coherent description of the immediate solvent sheath of glycine and glycyl zwitterion in water solution.
X-ray study of the rotator phase of paraffins (III): Even-numbered paraffins C18H38, C2H42, C22H46, C24H5, and C26H54
Authors: Denicolò I. , Doucet J. , Craievich A. F.
Published: February 2003

We present here a study of the ‘‘rotator’’ phase displayed by the even-numbered paraffins CnH2n+2 with n ranging from 22 to 26. We also include a few data and discussions about the crystalline phases of the even-numbered compounds with n ranging from 18 to 26. The rotator phase of these compounds is characterized by a bilayer packing with the molecular axes perpendicular to the layer planes and within each layer the packing is hexagonal. The three-dimensional space group seems to be P (63/m) mc. Finally we propose an explanation accounting for the differences between the structures of the rotator phases exhibited by the even-numbered compounds and the odd-numbered compounds.
The determination of the elastic constants of a series of n-alkylcyanobiphenyls by anisotropy of turbidity
Authors: Hakemi H. , Jagodzinski E. F. , DuPré D. B.
Published: February 2003

Measurement of the anisotropy of turbidity of aligned nematic liquid crystals in three selected geometries can yield the splay, twist, and bend elastic constants (K11, K22, and K33, respectively) which, along with the viscosity coefficients of the medium, govern director fluctuations that lead to a strong light scattering. We have utilized this procedure to determine the temperature dependence of the elastic constants of a homologous series of n-alkycyanobiphenyls (n-CB, where n=5, 6, 7, 8) in the nematic range. K33≳K11≳K22 at all temperatures for each member of the series. The absolute values of the moduli are consistently higher than those obtained by magneto- and electro-optic distortion methods (Frederik’s transitions). Odd–even effects are displayed as the number of methylene carbons in the alkyl chain increases. Distinctly larger K33 values for 8CB may be attributed to the short range smectic ordering in this liquid crystal, which has a lower temperature smectic-A phase.
Effects of fluctuating hydrodynamic interaction
Authors: Fixman Marshall
Published: February 2003

Dynamical simulations of Gaussian chains with fluctuating hydrodynamic interaction (HI) have been performed for the purpose of evaluating the diffusion constant and intrinsic viscosity from time correlation functions. Equilibrium simulations have also been performed to provide upper and lower bounds for the same quantities. The largest chain used for dynamical work had 56 beads. The effect of fluctuating HI on the diffusion constant is estimated to amount to a 5% decrease in the long chain limit. This decrease seems to be independent of the friction constant assigned to the beads, within statistical and extrapolation errors. However, most of the decrease seems to arise, unexpectedly, in modification of the short time correlation function. Our results for the intrinsic viscosity do not allow extrapolation to a long chain limit that is independent of assigned friction constant. For the smallest friction constant used, corresponding to a Stokes diameter of 0.1 in units of the root-mean-square bond length, the extrapolated decrease in intrinsic viscosity due to fluctuating HI amounts to about 10%. For our largest Stokes diameter of unity, the extrapolated decrease is about 30%. It seems possible that the transport coefficients of long chains are determined by gross configurational properties only if the friction constant is small.
An adiabatic study of the X 1Σ+ state of LiH
Authors: Bishop David M. , Cheung Lap M.
Published: February 2003

Using a 411-term configurational-interaction wave function with an elliptical orbital basis, the potential curve for the ground state (X 1Σ+) of lithium hydride has been calculated. The curve is of superior quality to those previously published. With the corresponding wave functions, the adiabatic corrections to this curve have been found and are compared with recent values derived from an analysis of the available spectroscopic data for the four LiH isotopes.
Magnetic properties and electronic structure of high spin iron(III) porphyrins
Authors: Birdy Roshun , Behere D. V. , Mitra S.
Published: February 2003

Magnetization and magnetic anisotropy data for the high-spin complexes Fe(TPP)X (X=NCS, Cl, Br, and I) are analyzed on the basis of a strong crystal field model assuming tetragonal symmetry about the ferric ion. The values of the crystal field parameter ΔOh lie in the range 28 900–31 551 cm−1, close to the upper limit (∼32 000 cm−1) for ‘‘pure’’ high-spin Fe3+; ΔOh increases from the NCS to I complexes. Eigenvalues and eigenfunctions are calculated for the lowest-lying states. The 6A1 ground state in Fe(TPP)I has ∼6% 4A2 character, the 4A2 level lying ∼2000 cm−1 above it.
Raman intensity calculations of formamide with the CNDO method
Authors: Schmid E. D. , Brodbek E.
Published: February 2003

Within the polarizability theory, absolute and relative Raman scattering cross sections are calculated using a variational method and the finite field perturbation theory. The calculations are performed within the CNDO approximation and the basis set in the variational scheme is extended to include polarization functions. Satisfactory numerical results are obtained for the formamide molecule with the variational procedure. The FFP theory which was used up to now only for calculating relative Raman scattering cross sections is adequate in reproducing the relative values for formamide. The absolute scattering cross sections are too small. Because we are interested in calculations of biological relevant molecules, it is necessary to consider also the FFP method in the standard CNDO version, which is much more economical with respect to computer time and capacity than the variational method.
Brillouin scattering study of elastic properties in a glass forming KNO3–Ca(NO3)2 mixture
Authors: Torell L. M. , Aronsson R.
Published: February 2003

Brillouin scattering (GHz) experiments were performed on a glass-forming 60% KNO3–40% Ca(NO3)2 mixture (mol %) through the glass transition in a temperature range of 295–398 K. Sound velocities for the transverse and longitudinal waves were determined both in the glass and in the melt. The elastic constants and the modulii in the glass and the shear modulus of the melt were evaluated as a function of temperature. The hypersonic results of the glass agree, within the experimental error, with ultrasonic results obtained at room temperature. Present hypersonic values for the shear modulus of the melt, calculated from the transverse velocity at infinite frequencies, are considerably larger than those reported from ultrasonic studies.
Emission spectra of CF3 radicals. II. Analysis of the UV emission spectrum of CF3 radicals
Authors: Suto Masako , Washida Nobuaki
Published: February 2003

The spectra of the UV emission bands of the CF3 radicals produced by the photolysis of CF3H by the argon resonance lines and by the reaction of CF3H with metastable Ar atoms were analyzed. Most of the bands were identified to be the combination of the ν″1 and ν″2 vibrational modes. The energies of the v″1 and v″2 vibrational levels of the ground state CF3 are A progression having about 804 cm−1 separation was observed and assigned to the ν′1 mode in the upper excited state. The system origin of the UV emission bands was calculated to be 6.41 eV. Since the 0–12 transition was strongest in the (0–v″) progression of the ν″1 mode, the geometry of the electronically excited state should differ from that of the ground state. Further, since only the total symmetric modes (ν1 and ν2 modes) were observed, the geometry of the upper emitting state may be D3h or C3v structure. High vibrational excitation up to v′1=7 was observed in the photolysis of CF3H by the Ar lamp. The energy of the excitation agrees well with the available excess energy in the photodecomposition process.
The kinetics of the reaction of OH with ClO
Authors: Ravishankara A. R. , Eisele F. L. , Wine P. H.
Published: February 2003

The rate constant for the reaction OH+ClO→ Products (1) was measured in a discharge flow tube under pseudo-first order conditions in OH. OH was monitored via the resonance fluorescence detection scheme. The measurements were made at low pressures (∼1 Torr) and at temperatures between 248 and 335 K. The measured rate coefficients, corrected for the interference due to OH regeneration via the reaction Cl+HO2→OH+ClO, were found to be nearly temperature independent with a mean value of (1.17±0.33)×10−11 cm3 molecule−1 s−1.
Vibration–vibration energy exchange in iodine molecules
Authors: Ree J. B. , Ree Taikyue , Shin H. K.
Published: February 2003

Vibration–vibration energy exchange probabilities between iodine molecules (X 1Σ+g) have been calculated by use of the solution of the time-dependent Schrödinger equation. The interaction potential is constructed by summing four orientation averaged atom–atom interactions. One-quantum probabilities Pv,0v−1,1(T) for v−1,1→v,0 are found to be very large in a temperature range of 100–3000 K. At lower temperatures, the approximate linear relation pv,0v−1,1(T)≂vP1,00,1(T) holds. When v is small, the probability increases linearly with temperature. Multiquantum transitions v,0→v−n,n with n≳1 are found to be negligible near room temperature, but they become quite efficient at higher temperatures. Energy exchange probabilities are formulated in infinite order and their reduction to first-order expressions are discussed in detail. The effects of molecular attraction are also discussed.
Study of CS2 in the 3–10 eV energy range by electron energy loss spectroscopy
Authors: Hubin-Franskin M.-J. , Delwiche J. , Poulin A. , Leclerc B. , Roy P. , Roy D.
Published: February 2003

Electron impact energy loss spectra are obtained in CS2 in the energy loss range of 3–10 eV with high and medium energy resolution. Measurements have been performed at various incident electron energies (∼10–100eV) and scattering angles (4°–90°). The high energy resolution (∼25 meV) has made possible the detailed analysis of the vibrational progressions and Rydberg series, and some identifications are supported by the plots of the differential cross sections of the studied transitions. New bands are evidenced in the region of the low-lying states 3–5 eV and classifications are proposed. The features appearing between 6.5 and 10 eV are classified into ten Rydberg series converging to the X̃ 2Πg ground state of CS+2, and assignments are proposed for most of them. New triplet features are also evidenced around 6.6 eV, while the triplet character proposed by Greening and King for some transitions is not confirmed.
Copper atom as a one-electron system: Theoretical study of Cu2 and CuH
Authors: Jeung G. H. , Barthelat J. C.
Published: February 2003

The ground state characteristics of Cu2 and CuH have been calculated by using explicitly only one electron for each copper atom. The remaining 28 electrons are kept as a frozen core, employing a nonempirical pseudopotential. A recently proposed perturbation method for core-valence polarization and correlation effects has been used to study, these molecules. The results are in fairly good agreement with the experimental values. Study of copper clusters with this method is suggested.
Divalent rhodium hexacyanide in KCl host lattice: An ESR study
Authors: Vugman N. V. , Franco W. O.
Published: February 2003

The [Rg(CN)6]4− paramagnetic species is unambiguously identified by electron spin resonance spectroscopy. This species is produced when KCl single crystals doped with small amounts of K3Rh(CN)6 are submitted to 2 MeV electron irradiation at 77 K. The existence of an asymmetrical localized phonon mode is postulated in order to explain the temperature dependence of the measured spin Hamiltonian parameters.
A comment on the derivation of the atomic kinetic energy functionals with full Weizsäcker correction
Authors: Acharya Prabhat K.
Published: February 2003

In a recent paper [J. Chem. Phys. 76, 1467 (1982)], Gázquez and Robles derive a kinetic energy functional of the type T[ρ]=TW[ρ]+[1−(2/N)][1−(C0/N1/3) +(C1/N2/3)−⋅⋅⋅]TTF[ρ] (TW and TTF are the Weizsäcker and the Thomas–Fermi functionals) by considering the sine waves of free particles in a cube. We get different C0 and C1 values from those of Gázquez and Robles by considering periodic complex exponential waves instead of the sine waves.
Short time dynamics of harmonic oscillator coherent states in anharmonic systems. I. One-dimensional motion
Authors: Brickmann Jürgen
Published: February 2003

The dynamics of an initially excital Gaussian wave packet (harmonic oscillator coherent state, HOCS) in a general one-dimensional anharmonic system is studied analytically with the aid of a second quantization formalism for times shorter than a classical oscillation period. The initial state population probability PQ(t), its classical counterpart PC(t), and the overlap probability PQC(t) between a time evolved wave packet and a classically moving Gaussian with stationary shape are calculated in order to analyze the spreading of the wave packet. It was found that, in general, PQ(t) and PC(t) agree very well if the potential energy function has no strongly changing low order derivatives. This agreement is held even if the wave packet spreads drastically within the time scale considered as can be demonstrated by analyzing PQC(t). The analytical expressions for PQ(t), PC(t), and PQC(t) are applied to a dissociative third-order oscillator and a strongly anharmonic fourth-order oscillator. While for a harmonic system, the initial decay time of PQ(t) and PC(t) (which are identical in this case) are only dependent on the energy expectation value 〈H〉 with respect to the initial HOCS, differences up to an order of magnitude occur for HOCS with the same energy in the model systems.
Ohmic friction on an ion in a conducting pore
Authors: Kayser R. F. , Hubbard J. B.
Published: February 2003

We compute the energy dissipation associated with an ion moving along the axis of a cylindrical pore, the exterior of which is a conductor.
Effects of molecular properties on electron transport in hydrocarbon fluids
Authors: Gee Norman , Freeman Gordon R.
Published: February 2003

The electron momentum transfer cross sections σm of each of the hydrocarbon gases possess a minimum at the energy ε(eV) noted: propene (0.16), cyclopropane (0.10), propane (0.13), n-butane (0.14), and i-butane (0.19). The minimum is much shallower for cyclopropane than for the other molecules. When σm∝ε−p with p≳0.5 over the energy distribution of the electrons in the sample, the electron mobility μ increases with increasing gas temperature T, and with increasing applied electric field strength above the threshold (E/n)th. However, upon increasing the gas density n to where an electron can interact with more than one molecule at a time, and at temperatures near the coexistence curve, the temperature dependence of μ increases and the field dependence decreases; these are symptoms of quasilocalization of electrons by density fluctuations in the fluid. The Arrhenius temperature coefficient of mobility Eμ in the constant density vapors, over the range 0.1<n/nc<1.0 at temperatures a few degrees above the vapor–liquid coexistence curve, increases superlinearly with density. The subscript c refers to the critical point. Near the critical region Eμ≊1×102 kJ/mol. The extent of quasilocalization is similar at the same n/nc and T/Tc in vapors as diverse as xenon, ethane, the pentane isomers, and dimethyl ether. Molecular orientational disorder makes a much smaller contribution to the (shallow) traps in the dense vapor than to the (deeper) traps in the normal liquids. At n≳nc the value of Eμ decreases and reaches values <20 kJ/mol in the normal liquids at n/nc≳2.6; electron traps in the dense liquids are less sensitive to temperature than are those in the dense vapors near the coexistence curve. Electron behavior in liquid hydrocarbons is dominated by the degree of molecular sphericity. A higher degree of sphericity is related to an enhanced mobility in the liquid. This is opposite to the effect in the low density gas where a higher degree of sphericity is related to a lower mobility. The density induced transition between these two effects of sphericity is examined.
Cluster expansions for hydrogen-bonded fluids. III. Water
Authors: Dahl Larry W. , Andersen Hans C.
Published: February 2003

The cluster theory of hydrogen-bonded fluids, described previously [H. C. Andersen, J. Chem. Phys. 59, 4714 (1973); 61, 4985 (1974)], is extended to describe fluid water. For classical nonvibrating models of the water molecule, we show that the intermolecular potential can be separated into a reference potential and a hydrogen-bonding potential and that the hydrogen-bonding potential can be separated into parts corresponding to the four hydrogen-bonding functional groups on a molecule. These separations of the potential are accomplished by defining a set of characteristic functions, one for each of the eight types of hydrogen bonds that can form between a pair of molecules. The characteristic functions also allow us to define precisely the average number of hydrogen bonds that are made by each functional group in fluid water in terms of the pair correlation function. The cluster expansion method for classical fluids is used to develop approximation methods for calculating this average number of hydrogen bonds as a function of temperature and density. These approximations will be used in the following paper to calculate the thermodynamic properties of a simple model for water.
The dynamical behavior of a small probe molecule dissolved in a nematic liquid crystal studied by NMR
Authors: Luyten P. R. , Bulthuis J. , Bovée W. M. M. J. , Plomp L.
Published: February 2003

The dynamical behavior of a small probe molecule CH3CN dissolved in a nematic liquid crystal is studied by NMR relaxation measurements on 1H, 13C, and 14N nuclei measured at six different field strengths. The results show a strong frequency dependent relaxation behavior that can be described by order director fluctuations in the nematic solvent. A major contribution from slowly relaxing local structures, as introduced by Polnaszek and Freed, is unlikely. Values for the rotational anisotropy, random local field contributions to the relaxation of the 13C and 1H nuclei, and order director fluctuation parameters are given. A comparison has been made with other studies of analogous systems and the necessity is demonstrated of extended frequency dependent measurements for a complete description of the dynamical processes involved.
Supersonic metal cluster beams of refractory metals: Spectral investigations of ultracold Mo2
Authors: Hopkins J. B. , Langridge-Smith P. R. R. , Morse M. D. , Smalley R. E.
Published: February 2003

A novel technique involving pulsed laser vaporization of the bulk metal within a pulsed supersonic nozzle has been shown to successfully produce ultracold bare metal clusters of even the most refractory of metals, tungsten and molybdenum. Clusters of up to 25 atoms may be readily prepared using this technique. Mass-selective resonant two-photon ionization spectra of Mo2 produced in this fashion show that the dimer is efficiently cooled in the expansion Ttrans<6 K, Trot∼5 K, and Tvib∼325 K. We have rotationally resolved the A 1Σ+u←X 1Σ+g (0–0) band for 92Mo2 and determined the bond length in the ground and excited states to be 1.940±0.009 and 1.937±0.008 Å, respectively. This confirms and extends the analysis of Efremov et al. [J. Mol. Spectrosc. 73, 40 (1970)] who prepared 98Mo2 by flash photolysis of isotopically pure Mo(CO)6. We have also observed the (1–1), (2–2), and (3–3) sequence bands which together with the ground state data of Efremov et al. determine vibrational constants ω′e=449.0±0.2 cm−1 and ωex′e=2.3±0.2 cm−1 for the A 1Σ+u state. The lifetime of the A 1Σ+u v=0 state of Mo2 has been measured to be 18±3 ns by time-delayed two-photon ionization. The ionization potential of Mo2 is found to be less than 6.42 eV (compared to 7.10 eV for atomic Mo) indicating a substantially stronger chemical bond in Mo+2 than in Mo2. A discussion of the electronic structure of Mo2 and the implications of these findings for bonding in other transition metal dimers is also presented.
K=3 doubling in the v2=1 state of PH3 studied by laser-Stark spectroscopy
Authors: Carlotti M. , Di Lonardo G. , Trombetti A.
Published: February 2003

Electric field induced transitions A1← A1 and A2←A2 have been observed in the laser-Stark saturation spectrum of qP(5,3), qP(7,3), and qR(8,3) ν2 transitions of PH3. In addition to the zero-field frequency differences Δν=νPH3−νlaser, we obtained the K=3 splittings for J=5 and 7 in the ground state, and for J=4 and 9 in the v2=1 state.
Vibrational-rotational energy transfer in collisions of HF (v=4, J=20) with rare gases
Authors: Thompson Donald L.
Published: February 2003

State-to-state energy transfer cross sections for He and Ne+HF(v=4, J=20) at 0.2 eV initial relative translational energy were computed using quasiclassical trajectories. These results are compared with previously published results for Ar+HF at the same initial conditions. The results show that the number of final J states populated in a given final v state increases and that the magnitudes of the state-to-state cross sections decreases as the size of the rare gas atom decreases. The cross sections for vibrational transitions are not sensitive to the size of the rare gas atom.
The dynamics of the reaction D+2+F(2P)→FD++D at kinetic energies between 0.002 and 30 eV
Authors: Schuette George F. , Gentry W. Ronald
Published: February 2003

The merged molecular beam technique has been used to study the reaction D+2+F(2P)→FD++D over the kinetic energy range from 0.002 to 30 eV. The energy dependence of the absolute total reaction cross section at low kinetic energies indicates that reaction occurs with unit probability for capture collisions on potential energy surfaces which correlate with Π intermediates. This result is consistent with the adiabatic state correlations, which connect the reactants to the ground state products FD+(2Π)+D(2S) via both the 1Π and 3Π surfaces in collinear approches. At higher energies, an inflection in the reaction cross section is thought to be caused by onset of the endoergic reaction to give excited state products FD+(2Σ)+D(2S). The reaction mechanism is direct over the entire range of collision energies, with the FD+ product scattered preferentially in the direction of the incident F-atom reactant in the center-of-mass system, except for extremely high collision energies (Ei=25 eV), where a roughly symmetric distribution is seen. Very little theoretical work has been carried out on the dynamics of reactions between two open-shell species. The relative simplicity of the D+2+F(2P) system makes it an attractive candidate for such studies.
An experimental study of the bridged and classical structures of the ethyl radical and cation by neutralized ion-beam spectroscopy
Authors: Gellene Gregory I. , Kleinrock Nancy S. , Porter Richard F.
Published: February 2003

The states of ethyl radicals formed in electron capture reactions of a fast beam of C2H5+ with a series of metal target atoms (K, Na, Ca, Mg, and Zn) have been investigated by neutral beam scattering techniques. Reactions of C2H5+ with Mg or Zn atoms lead to formation of ground state radicals and an excited state about 0.5 eV above the dissociation limit of C2H4+H. Analysis of branching ratios for these processes over a range of Mg atom densities shows that the ion beam is a mixture of two isomers in the ratio of about 7.3/1.0 for beams generated either by electron impact or chemical ionization methods. From neutral-precursor ion relationships we propose that the major and minor components of the ion beam are the bridged and classical C2H5+ structures, respectively. Analysis of neutral beam profiles in experiments with Na or K targets indicate the formation of a dissociative state of the classical radical lying about 4.2 eV above the ground state. An upper limit of 2.2 eV to the barrier to 1, 2 hydrogen migration in the classical radical is provided by the energy of the lowest state of the bridged radical observed.
The photolytic cage effect of iodine in gases and liquids
Authors: Dutoit J.-C. , Zellweger J.-M. , van den Bergh H.
Published: February 2003

The photolytic cage effect is studied over a wide density range of several bath gases in the laser flash photolysis of iodine at 694.3 nm. Particular attention is paid to measurements in the ‘‘simple’’ solvents Xe and Kr, which are compared with molecular dynamics calculations. Measurements in polyatomic gases and liquids are also reported, as well as the variation of the cage effect with temperature and applied magnetic field. While measuring the cage effect under such a wide variety of conditions, we simultaneously obtain the second order rate constants for iodine atom combination, which help to establish the detailed mechanism of this elementary chemical reaction.
Dissociative recombination in electron-beam excited argon at high pressures
Authors: Kuo Chien-Yu , Keto J. W.
Published: February 2003

We report studies of dissociative recombination in electron-beam excited argon at pressures from 200 to 12 000 Torr. In these experiments, we measure the decay in absolute intensity of the fluorescence from Ar (3p5 4p) dissociative products. By summing over all significant product fluorescence, we determine the total effective recombination rate for electrons, the electron density, and the branching fraction for production of several individual states by recombination. For pressures above three atmospheres, similar quantities are observed by monitoring the Ar*2 excimer emission. At low pressures, we find that the rates are in good agreement with previous workers. At high pressures, we observe a factor of 6 increase in the recombination coefficient over that measured at 200 Torr. At a constant electron beam current, the electron density rises as the argon density increases, reaches a maximum at ∼5000 Torr, and decreases after 7000 Torr. A discussion of possible models to explain the pressure dependence of the recombination rate is presented.
Mobilities of Tl+ ions in Kr and Xe, Li+ in Kr and Xe, and Cl− in N2
Authors: Byers M. S. , Thackston M. G. , Chelf R. D. , Holleman F. B. , Twist J. R. , Neeley G. W. , McDaniel E. W.
Published: February 2003

The mobilities of Tl+ ions in Kr and Xe Li+ in Kr and Xe and Cl2u− in N2 are measured. The mobilities were measured at gas temperatures 300°K and gas pressures ranging from 0.025 to 0.44 Torr. (AIP)
Comment on: On the Chapman–Enskog solution method for mixtures [B. C. Eu, J. Chem. Phys. 74, 6373 (1981)]
Authors: Karkheck John , Kincaid J. M. , Stell G.
Published: February 2003

A recent criticism by Eu of the Chapman–Enskog method of solution for the mixture set of Boltzmann equations is reexamined. His proposed alternative is shown to be based upon a set of linear equations that in general has no solution. The new approach proposed by Eu is appropriately corrected and shown to be less general than the Chapman–Enskog method and contained within the latter as a special case.
Extended Brownian dynamics. II. Reactive, nonlinear diffusion
Authors: Lamm Gene , Schulten Klaus
Published: February 2003

An improved version of the ‘‘extended Brownian dynamics’’ algorithm recently proposed by the authors [J. Chem. Phys. 75, 365 (1981)] is given. This Monte Carlo procedure for solving the one-dimensional Smoluchowski diffusion equation is statistically exact near a boundary for a constant force and approximately correct for a linear force. The improved algorithm is both more accurate and simpler than the earlier version. In addition, the algorithm is extended to include diffusion near a reactive boundary or in a reactive optical potential. The treatment of diffusion for nonlinear forces is conveniently handled by choosing the time for a single diffusive jump locally. The algorithm converges as this jump time approaches zero. The appropriate modifications necessary to treat diffusion between two (possibly reactive) boundaries or diffusion with a spatially varying diffusion coefficient are also given. Finally, it is shown how multidimensional diffusion in a spherically symmetric force field may be treated by the one-dimensional algorithm described here. As in the earlier paper, numerical results are presented and compared with analytical and numerical descriptions of the diffusion process to demonstrate the validity of the algorithm.
Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Ir–Rh clusters
Authors: Meitzner G. , Via G. H. , Lytle F. W. , Sinfelt J. H.
Published: February 2003

The extended x-ray absorption fine structures (EXAFS) associated with the LIII absorption edge of iridium and the K absorption edge of rhodium were investigated for catalysts containing bimetallic clusters of these elements dispersed on silica or alumina. The catalysts contained 1 wt.% iridium and 0.5 wt.% rhodium, which corresponds to an Ir/Rh atomic ratio close to 1. From the EXAFS data, it is concluded that the rhodium concentration in the surface region of the iridium–rhodium clusters is greater than it is in the interior. The EXAFS data also indicate that the iridium–rhodium clusters are more highly dispersed on alumina than on silica.