bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental and theoretical study of the dispersion of the site shift surface exciton on anthracene crystals
Authors: Sceats M. G. , Tomioka K. , Rice Stuart A.
Published: February 2003

The resonance in the normal incidence reflection spectrum of anthracene crystals at 25 298 cm−1 has been assigned to a site shift surface exciton. This paper reports studies of this resonance, by the method of attenuated total reflection, as a function of the magnitude of the component of photon momentum parallel to the surface of the anthracene crystal. It is found that the resonance can be observed in both the radiative and nonradiative regions of the energy-momentum plane. We also report theoretical calculations that show this behavior is consistent with the site shift surface exciton assignment.
Thermodynamic consistency of vapor pressure and calorimetric data for argon, krypton, and xenon
Authors: Schwalbe L. A. , Crawford R. K. , Chen H. H. , Aziz R. A.
Published: February 2003

A new two-parameter vapor pressure equation has been derived which, unlike the Salter equation, is shown to be equally applicable to quantum or classical solids and even liquids. The condensed phase enthalpies and entropies are given directly by the fitted parameters with accuracies comparable to those which have been claimed for existing independent calorimetric measurements. Recent vapor pressure data for the solid and liquid phases of argon, krypton, and xenon are analyzed in this manner, and the results are compared with the available calorimetric data. New values for the cohesive energy at T=0 are also derived for these substances.
Percus–Yevick equation of state for the two-dimensional Lennard-Jones fluid
Authors: Glandt Eduardo D. , Fitts Donald D.
Published: February 2003

Values of the radial distribution functions and thermodynamic properties for the two-dimensional Lennard-Jones fluid are obtained from the Percus–Yevick theory. Results are reported for a wide range of temperatures and densities and are compared with computer simulations. The energy equation of state is found to give the best agreement with the computer simulations. The reduced critical temperature as predicted by the Percus–Yevick theory from the compressibility equation is about 0.495.
Photodetachment and de-excitation of excited NO2−
Authors: Huber B. A. , Cosby P. C. , Peterson J. R. , Moseley J. T.
Published: February 2003

The photodetachment of excited NO2− formed by charge exchange of O− and O2− with NO2 has been studied at photon energies of 1.97 to 2.34 eV, below the electron affinity of NO2 (2.36±0.10 eV). These data indicate that the subthreshold photodetachment takes place from excited vibrational levels of the NO2− ground electronic state, which are populated by the ion–molecule reactions producing this species. De-excitation of the excited NO2− is observed in collisions with O2 and CO2 molecules with apparent rates in the range of 10−12 cm3/sec and with NO2 molecules at a rate of nearly 10−9 cm3/sec. The absolute photodetachment cross section of nascent NO2− is determined at three photon energies. No evidence is found for a structural (peroxy) isomer of this ion.
Studies of Ar and N2 using threshold photoelectron spectroscopy by electron attachment (TPSA)
Authors: Chutjian Ara , Ajello Joseph M.
Published: February 2003

Threshold photoelectron spectra of Ar and N2 are studied by the technique of attachment of the threshold electron to SF6 followed by detection of the SF6−. Studies on Ar provide a measure of the rejection ratio for nonthreshold electrons of this technique. This ratio is compared to that for two other types of electron detectors. Collisional ionization of high Rydberg-state electrons by SF6 is also observed and discussed. In N2 direct ionization to vibrational levels of the X 2Σg+, A 2Πu, and B 2Σu+ states of N2+ are clearly resolved. Moreover, resonant autoionizations are found to greatly enhance the population of the vibrational levels of the X state and the v′=2 level of the A state over that expected from direct photoionization alone. Extra peaks lying between the vibrational levels are detected which correspond to autoionization into high-J levels of the N2+ ion. From intensity considerations a rotational propensity rule is given which states that an autoionizing N2 state prefers to decay to N2+ states with a minimum change in rotational angular momentum. Normalization of the threshold spectra to the absolute cross section scale is also discussed.
Solvent perturbations of extravalence excitations of atomic Xe by rare gases at high pressures
Authors: Messing Itzhak , Raz Baruch , Jortner Joshua
Published: February 2003

In this paper we present the results of an experimental study of the lowest doublet excitations (1S0→3P1 and 1S0→1P1) of atomic xenon in dense supercritical fluid neon and helium and the 1S0→1P1 xenon excitation in dense supercritical and subcritical fluid argon. The spectral shift, the linewidth, the first moment, and the second moment of the absorption bands exhibit a strong density and a weak temperature dependence. The semiclassical statistical theory of line shapes was applied for the calculations of the first moment, the second moment, and the entire line shape. By fitting to the experimental moments over a broad density range, the excited state guest–host interaction potential parameters were derived. An analysis of the density dependence of the splitting and of the intensity ratio of the Xe doublet perturbed by high pressure rare gases was provided.
Studies of reactions of importance in the stratosphere. II. Reactions involving chlorine nitrate and chlorine dioxide
Authors: Birks John W. , Shoemaker Brian , Leck Thomas J. , Borders Richard A. , Hart Larry J.
Published: February 2003

The rate of formation of chlorine nitrate, ClO+NO2+M→ClONO2+M, has been studied over the temperature range 250–356 °K and the pressure range 1–5 torr using the discharge flow technique with mass spectrometry for detection. The resulting low pressure third order reaction rate constant in N2 is given by the Arrhenius expression kN2=4.40±0.66 ×10−33 exp(1087±70/T)cm6 molecule−2 sec−1. Helium was found to be one-half as effective as N2 as a third body for this reaction. No reaction of ClONO2 with NO, NO2, O3, or HCl could be observed. Upper limits of 4.×10−17, 2.×10−17, 7.×10−17, and 1.2×10−15 cm3 molecule−1 sec−1 for the respective bimolecular reaction rate constants preclude the importance of these reactions as sinks for ClONO2 in the stratosphere. A heterogeneous reaction, ClONO2+HClsurface→HONO2+Cl2, was observed, and may be useful as a selective reaction for the measurement of chlorine nitrate in the stratosphere. An upper limit of 10−16 cm3 molecule−1 sec−1 was found for the reaction ClO+O3→OClO+O2 and an upper limit of 5.×10−14 cm3 molecule−1 sec−1 for the reaction ClO+O3→ClOO+O2 at 298 °K. The rate constant for the reaction OClO+O3→ClO3 +O2 was found to be 1.20±0.15×10−19 cm3 molecule−1 sec−1 at 298 °K by a static method, the concentrations of OClO and O3 being followed by optical absorption. These results, combined with the calculated photolysis constant for OClO of 7.6×10−2 sec−1, rule out of the successive oxidation of chlorine as a path to the photochemically stable species perchloric acid.
Absorption spectra of the Cs2 molecule
Authors: Benedict R. P. , Drummond D. L. , Schlie L. A.
Published: February 2003

The absorption spectra of the Cs2 molecule, over the wavelength range 0.8–1.3 μ, has been measured in pure Cs and a Cs–Ar mixture. The observed spectra, taken from 182 °C to 325 °C, were interpreted as both the allowed X1Σg+−A1Σu+ and the normally forbidden X1Σg+−a3πu transitions. Based on the classical Franck–Condon principle, the temperature dependence of the absorption of the X1Σg+–A1Σu+ transition for the wavelength range 0.9–1.21 μ was used to determine the potential energy curve for the A1Σu+ state. Also, the potential curve for the a3πu state was estimated. The bands of the X1Σg+–a3πu transition are blue-shaded, indicating that the equilibrium internuclear separation of the a3πu is less than that of the X1Σg+; whereas, in the X1Σg+–A1Σu+ transition the bands are shaded to the red, indicating a greater equilibrium radius for the A1Σu+ state. Because of the short equilibrium radius of the a3πu state, the possibility exists that the a3πu and the x3Σu+ cross and that predissociation occurs. The implications of this on the possibility of the Cs2 molecule lasing at 1.13 or 1.19 μ are mentioned.
Polarized Raman scattering studies of orientational order in uniaxial liquid crystalline phases
Authors: Jen Shen , Clark Noel A. , Pershan P. S. , Priestley E. B.
Published: February 2003

The measurement of vibrational Raman depolarization ratios has been used to study molecular orientational order in uniaxial single domain nematic and smectic liquid crystal samples. This technique is demonstrated to obtain the same microscopic order parameter 〈P2〉=1/2 〈3 cos2ϑ−1〉, where ϑ is the angle between a molecular long axis and the uniaxial direction, as other existing methods. In addition, the next higher moment of the orientational distribution function 〈P4〉=1/8 〈35 cos4 ϑ−30 cos2ϑ+3〉 has been measured for the first time. The physical basis, theoretical apparatus, and experimental methods necessary for the application of this technique are thoroughly detailed in this paper. Measurements are presented of the temperature dependence of 〈P2〉 and 〈P4〉 of N- (p′-butoxybenzylidene) -p-cyanoaniline (BBCA) dissolved in N- (p′-methoxybenzylidene) -p-cyanoaniline (MBBA) and of pure MBBA in the isotropic and nematic phases, and in the isotropic, nematic, smectic A, and smectic B phases of N- (p′-butoxybenzylidene) -p-n-octylaniline (40.8). In the nematic phases the new quantitative information marks significant discrepancies with existing theories of nematic ordering. In the smectic phases the results show unambiguously the anticipated high degree of molecular orientational order.
Infrared-microwave double resonance spectroscopy of GeH4
Authors: Kreiner W. A. , Andresen U. , Oka Takeshi
Published: February 2003

The highly sensitive method of infrared-microwave double resonance in a laser cavity has been used to observe the distortion-induced rotational spectrum for the ground vibrational state of GeH4. Coincidences between the (ν2, ν4) fundamental vibration–rotation bands and infrared laser lines (CO2, isotopic CO2, and N2O) were used for detection of the very weak rotational transitions. Four resonances with J=18 and one resonance with J=11 were assigned. The frequencies of these resonances give accurate information on the quartic, sextic, and octic tensor distortion coefficients of GeH4.
Matrix isolation spectroscopic study of the free radical HCCN
Authors: Dendramis A. , Leroi G. E.
Published: February 2003

The free radical HCCN was produced in an Ar matrix via photolysis of its precursor diazoacetonitrile, NNCHCN, with radiation of wavelengths longer than 350 nm. The ir spectra of HCCN and three isotopic modifications (DCCN, HC13CN, and HCC15N) were obtained, and normal coordinate analyses based on two different geometries, bent and linear, were carried out. The results provide a determination of the general valence force field, and favor the linear, allenic configuration H–Ċ=C=Ṅ. The electronic spectrum of HCCN in an argon matrix was also obtained. A tentative assignment of the band system observed in the uv part of the spectrum has been made.
A theoretical investigation of symmetry-forbidden transitions in magnetic circular dichroism and electronic spectra of benzene
Authors: Lee S. T. , Yoon Y. H. , Eyring H. , Lin S. H.
Published: February 2003

In this paper, the vibronic coupling calculation in the π-electron framework has been carried out for 〈B2u‖?′vc‖E1u〉, 〈A1g‖?′vc‖B2u〉, and 〈B1u‖?′vc‖E1u〉 of benzene by using the so-called linear displacement method. Our method differs from that of Liehr’s by the fact that in our calculation all multicenter integrals have been evaluated exactly. The vibronic coupling matrix elements obtained have then been applied to calculate the magnetic rotational strengths and dipole strengths of symmetry-forbidden transitions 1A1g→1B1u and 1A1g→1B2u and the electronic matrix elements involved in radiationless transitions. It is well known that the 1A1g→1B2u transition is symmetry-forbidden in MCD and uv spectra and becomes allowed through the mixing of both B1u and B2u states with the E1u state through the E2g modes of vibration. We have developed a method for determining the dipole strengths and magnetic rotational strengths associated with each individual E2g promoting mode from the experimental MCD and uv spectra. Theoretical and experimental results are compared.
Binding energies of Li2H and Li2H+ and the ionization potential of Li2H
Authors: Wu C. H. , Ihle H. R.
Published: February 2003

The existence of the stable molecule Li2H was proved experimentally for the first time by mass spectrometric measurements over dilute solutions of hydrogen in liquid lithium. From measurements of the gaseous equilibria Li2H(g)+Li(g) ?LiH(g)+Li2(g) and Li2H(g)+Li2(g) ?LiH(g) +Li3(g), a dissociation energy D00(Li2H) =89.7±5.0 kcal/mole was obtained. The ionization potential of Li2H was determined as I.P.(Li2H) =4.5±0.2 eV, from which the binding energy D00(Li2H+) =299.0±6.0 kcal/mole results.
Correlation functions of classical fluids. V. The perturbation theory for soft spheres
Authors: Lee Lloyd L.
Published: February 2003

From the inhomogeneous functional derivation formalism of Percus, we derive here a perturbation equation on correlation functions which represents a generalization of the hard sphere equation of Barker, Henderson, and Smith. It is particularly suited to the expansion from the hard spheres to the soft spheres due to fast numerical convergence. To render our development independent of machine simulation input, we use the Verlet–Weis hard sphere construction. Comparison of our calculations with the Monte Carlo (MC) results on two types of soft spheres, the inverse-12 model and the repulsive part of the Lennard-Jones (LJ) potential due to the Weeks–Chandler–Andersen (WCA) division, shows that this theory improves over the widely used WCA approximation and the Percus–Yevick (PY) theory for the radial distribution functions. For the shorter-ranged LJ repulsion, superior agreement with MC data on equilibrium properties and radial distribution functions is obtained for temperatures T<2.8 and all densities. A mixed theory combining the perturbation equation and the PY approximation is found to work well for the inverse-12 potential for x=ρT−1/4<0.63.
Frequency-dependent rate coefficient in diffusion-controlled reactions
Authors: Felderhof B. U.
Published: February 2003

Diffusion-controlled reactions between particles and a nondilute system of sinks are studied. It is shown that in time-dependent situations it is necessary to take account of retardation effects in the building-up of correlations between competing sinks. The retardation leads to a frequency dependence of the rate coefficient. We derive corrections to the dilute limit value of the rate coefficient in the low concentration, low frequency regime. As an application we consider the effect on the time dependence of a quenching process.
Light scattering studies of rotational and vibrational relaxations of acetonitrile in carbon tetrachloride
Authors: Whittenburg S. L. , Wang C. H.
Published: February 2003

The rotational and vibrational relaxation times of acetonitrile–carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering. Using a Fabry-Perot interferometer and single frequency laser source, we have shown that reliable results for the single particle orientational correlation times (τs) for CH3CN can be obtained by carrying out a concentration dependent depolarized Rayleigh scattering study. Raman scattering was shown to yield inconsistent results for τs in CH3CN. At constant viscosity, it was found that the Rayleigh scattering relaxation time (τRay) of CH3CN in CCl4 does not change with CH3CN concentration, indicating that the orientational pair correlation factor of liquid CH3CN is close to unity. This result suggests that the dynamic pair correlation in CH3CN is just as important as the static pair correlation. The experimental data were also compared with the predictions of the hydrodynamic stick and slip models for a rotational diffusion. The CH3CN data were found to be close to the prediction of the slip model. The isotropic relaxation time (τiso) of the C≡N stretching mode was also studied as a function of concentration and viscosity using Raman spectroscopy. This viscosity dependence of τiso also decreases with decreasing number density of CH3CN, suggesting that pair correlations are also important in the Raman scattering of CH3CN.
On the glass transition in mixtures between the normal alcohols and various Lewis bases
Authors: Lesikar Arnold V.
Published: February 2003

The glass transition temperatures (Tg) of binary mixtures of the lower normal alkanols with several aprotic Lewis bases have been measured as a function of composition. The initial molar slope (IMS) at the pure alcohol end of the curve of Tg against mole fraction of base was accurately determined for each base. A related quantity, the reduced IMS, is shown to be proportional to the excess configurational entropy per bead of base introduced into dilute solution with the base. The reduced IMS is found to be a linear function of the length of the alcohol backbone for the heavier alkanols and to be an increasing function of the base Tg. The results are interpreted in terms of alcohol and base self-association. Some form of network association is suggested for the lighter alkanols in the supercooled liquid, while the bases most likely associate under the action of dipole–dipole or other specific nonhydrogen bonding forces. The reduced IMS values suggest association between alcohol and base, but this association usually does not seem to be by means of hydrogen bonding in solutions dilute in the base. The Tg values of concentrated base solutions in the alcohols are discussed as well.
Electronic relaxation of acridine as studied by picosecond spectroscopy
Authors: Sundstrom V. , Rentzepis P. M. , Lim E. C.
Published: February 2003

Internal conversion (IC) and intersystem crossing (ISC) rates of the lowest excited singlet state (S1) of acridine have been measured in n-hexane at room temperature by picosecond spectroscopy. The rates deduced from the buildup of triplet–triplet absorption and the quantum yield of intersystem crossing were found to be 3×1010 sec−1 for the internal conversion and 3×1010 sec−1 for the intersystem crossing. Corresponding rates for perdeuterated acridine are found to be similar. These rates, when combined with the upper limit of the unobserved fluorescence, lead to the nπ* assignment of the lowest excited singlet state. The kinetics of repopulation of the ground state following a pulsed excitation of the sample give strong indication of the occurrence of S1→S0 internal conversion.
Infrared laser-induced photochemistry of cyclopropane
Authors: Lesiecki Michael L. , Guillory William A.
Published: February 2003

The ir laser photolysis of cyclopropane (CP), with the focused gigawatt power of the 9.552 μm(P20) line of a CO2 laser, results in two chemical processes. One, a non-Boltzmann high energy decomposition, gives rise to the major products acetylene, propylene, methane, and ethylene and the minor product methylacetylene. The other is a typical flame reaction characterized by the luminescence of the C2+(d3Πg) Swan band. The latter process plays a minor role in terms of the precent consumption of CP. Both temporal and wavelength resolved spectroscopy were used in the identification of the emitting species as well as in the characterization of the elementary reactions producing them. In mixed CP–NO photolysis, CN+(B2Σ), C2+(d3Πg), CH+(A2Δ), and NH+(A3Π) were observed emitters, whereas only C2+(d3Πg) and CH(A 2Δ, B 2Σ−, and C 2Σ+) emissions were observed in the CP–O2 photolysis.
Negative ion properties of tetracyanoquinodimethan: Electron affinity and compound states
Authors: Compton R. N. , Cooper C. D.
Published: February 2003

Bound and excited negative ion states of gaseous 7,7,8,8-tetracyanoquinodimethan (TCNQ) are studied from experiments involving collisions of electrons and fast cesium beams with TCNQ. The electron affinity of TCNQ is measured to be 2.8+0.05−0.3 eV by the collisional ionization technique. TCNQ attaches electrons with energies of ∼0, 0.7, and 1.3 eV (values represent peaks in cross section) to form long-lived compound negative ions which are metastable with respect to autodetachment. The lifetime for the decay of TCNQ−* decreases from ∼2×10−3 sec at ∼0 eV to ∼10−4 sec at ∼4 eV. Evidence for a third compound negative ion state is seen as a peak in the TCNQ− signal at ∼3.2 eV. This state is metastable with respect to autodetachment and dissociation into the products C11N3H−3+HCN0.
An experimental determination of absolute half-cell emf’s and single ion free energies of solvation
Authors: Gomer R. , Tryson G.
Published: February 2003

The concept of absolute half-cell emf is discussed and defined as VMS-φM for the reaction M→M+(solution)+e−(M), where VMS is the electrostatic potential difference between metal electrode and solution and φM the work function of metal in contact with solution. It is shown that this quantity is equal to VRS-φR, where VRS is the electrostatic potential difference between a reference electrode in air above the solution and the solution, and φR the work function in air of this reference. The quantity VRS′, the potential difference between reference electrode and the solution surface, was found experimentally by the vibrating condenser method for a number of half-cells, and φR was determined photoelectrically. It is shown from the variation of VRS′ with electrolyte concentration that the potential difference betwen the bulk of pure H2O and its air interface is ∼0.05 V, the surface being negative relative to bulk, and that this potential is increasingly screened out as electrolyte concentration increases. From these results for several different half-cells the absolute value of the standard half-cell emf for H2→2H+ is found to be −4.73±0.05 V. This result permits the calculation of single ion free energies of solvation. It is shown that the simple Born model as used by Latimer, Pitzer, and Slansky works remarkably well for simple cations, including polyvalent ones, and for spherical anions, but breaks down for complex anions like OH−, NO−3, etc. Ions in which chemical bonding effects to the solvent play an important role show anomalously high solvation energies. The solvation energy of H+ is −10.98 eV in H2O and varies very little from this value in several different solvents, suggesting that free H+ may predominate in these solvents. This could result from the fact that the small effective radius of free H+ leads to a greater solvation energy than the combination of bond formation and solvation of the resultant much larger ion (H solvent)+. Similar arguments can be used to explain why for instance Fe3+ is not reduced by H2O despite the fact that the third ionization potential of Fe is 30 and that of water 12.6 eV. Other possible applications of the method used in these experiments are discussed.
The influence of molecular orientation on the vapor pressure isotope effect in liquid methanes
Authors: Pollin J. S. , Ishida Takanobu
Published: February 2003

The medium cluster model has been used to study the influence of mutual molecular orientation in the liquid state on the vapor pressure isotope effect (vpie) of 13C, 14C, D, and T-substituted methanes. Both the first quantum correction to the classical translational and rotational effect and the isotopic differences in zero-point energy shifts on condensation are cyclic functions of conformational angles. The cyclic behavior for a 3-cluster of spherical top methanes can be attributed, in light of the finite orthogonal polynomial approximation of the reduced partition function ratio, to the interaction of rotation with internal bending and stretching motions. The effects of changing molecular orientation on the predicted vpie decrease with increasing cluster size, until the variations become negligibly small compared to experimental uncertainties in isotopic vapor pressure ratio measurements.
The hyperfine spectrum of CsCl by molecular beam electric resonance
Authors: Cederberg James
Published: February 2003

The zero-field hyperfine spectrum of the v=0, 1, 2, 3, J=2 states of 133Cs 35Cl and the v=0, J=2 states of 133Cs 37Cl has been observed with a linewidth of 200 Hz. The values of the molecular constants obtained by fitting the spectrum are (in units of kilohertz; 90% confidence intervals in parentheses): Cs35Clv=0 Cs35Clv=1 Cs35Clv=2 Cs35Clv=3 Cs37Clv=0 (eqQ)Cl 1765.17(6) 1636.75(6) 1510.02(6) 1385.08(6) 1392.30(6) (eqQ)Cs 1030.90(20) 1022.88)20) 1015.21(20) 1007.68(20) 1031.15(20) CCl 0.5872(37) 0.5736(37) 0.5703(37) 0.5684(37) 0.4630(37) CCs 0.6790(15) 0.6735(15) 0.6690(15) 0.6621(15) 0.6505(15) C3 0.0280(15) 0.0273(15) 0.0286(15) 0.0286(15) 0.0286(15) 0.0318(15) C4 0.0605(16) 0.0621(16) 0.0640(16) 0.0597(16) 0.0554(16)
Pressure dependent Raman spectra of the fast ion conductors Ag2HgI4 and Cu2HgI4
Authors: Greig D. , Shriver D. F. , Ferraro J. R.
Published: February 2003

The pressure dependent Raman spectra of the simple ionic conductors Ag2HgI4 and Cu2HgI4 is reported.(AIP)
Correlation between the average energy of reaction and system composition in recoil hot reaction studies
Authors: Stevens Don J. , Spicer Leonard D.
Published: February 2003

An expression is derived for the average energy of reaction as a function of system composition in recoil hot atom reactions.(AIP)
Role of angular momentum in unimolecular kinetics: Kinetic energy release in fragmentation of C4H6+
Authors: Klots Cornelius E. , Mintz Donald , Baer Tomas
Published: February 2003

The kinetic energy release distributions in the fragmentation C4H6+→C3H3++CH3 at selected energies are reported and are compared with the analogous distributions from ’’metastable’’ C4H6+ and from C2H2++C2H4 collision complexes. The data seem to reflect the role of angular momentum in the collision experiments, as predicted by the Langevin model of the quasiequilibrium theory.
Determination of the vibration frequency of the high temperature species AuLi by means of matrix isolation spectroscopy
Authors: Ihle H.R. , Langenscheidt E. , Zmbova B.
Published: February 2003

The high temperature species AuLi has been studied by matrix isolation infrared spectroscopy, and its stretching force constant has been found to be (1.90±0.03) ×105 dyn/cm. Sufficiently high concentrations of this molecule were achieved by application of a double-Knudsen cell arrangement, from which metallic gold and lithium could be evaporated at different temperatures.
Theory of ultraviolet spectra for Ni2 and Ni3 and hypothesis for argon matrix frequency shifts for Ni atoms
Authors: Anderson Alfred B.
Published: February 2003

Atomic orbital 3d and 4s ionization energies and the 4p orbital exponent are assigned using gas phase uv Ni atom spectra. These parameters are used in a molecular orbital theory, producing an accurate description of the three observed electronic transitions in Ni2 and the two observed transitions in Ni3, and they show the latter has a linear geometry. It is found that HOMO–LUMO transitions are not necessarily the strongest in intensity. It is suggested that antibonding interactions with the Ar matrix are responsible for the Ni atom frequency shifts.
On the character of the melting transition in small atomic aggregates
Authors: Etters R. D. , Kaelberer Jaya
Published: February 2003

The melting transition in small clusters of N atoms is investigated, using a biased random walk, Monte Carlo procedure. A high density of data points, with small statistical uncertainities (about 0.3%) is generated near the melting transitions Tm(N). The results show an abrupt change in physical properties near melting, but there is no evidence that the transition is either first or second order in character. Rather, the transition is more gradual. The Tm(N) for N=13, 11, 8, and 6 are 28.75, 20.0, 10.2, and 9.6K, respectively. N=6 and 8 evaporate at TB?31 K. The low temperature structures are dynamically determined to be octahedron, pentagonal bipyramid plus one, pentagonal bipyramid plus four, and icosahedron, for N=6, 8, 11, and 13, respectively.
Model potential calculations for ground and excited states of LiNa
Authors: Habitz Peter , Schwarz Wilhelm Hans Eugen , Ahlrichs Reinhart
Published: February 2003

Potential curves of nine low lying electronic states of LiNa have been determined by full valence CI calculations within the pseudopotential approach. The estimated accuracy is a few 0.01 eV. Molecular constants are derived. The close agreement of the experimental and calculated dipole moment for the ground state indicates proper description of core–valence correlation effects by our model potential.
The Li+–He interaction potential
Authors: Gatland I. R. , Morrison W. F. , Ellis H. W. , Thackston M. G. , McDaniel E. W. , Alexander M. H. , Viehland L. A. , Mason E. A.
Published: February 2003

New measurements of the mobility of Li+ ions in He gas at 300°K are reported for a wide range of E/N, the ratio of the electric field strength to the gas number density. These data are used in conjunction with kinetic theory to test various Li+–He interaction potentials over a wide range of separation distance. It is shown that the ab initio potential of Hariharan and Staemmler gives mobility values in excellent agreement with experiment at low and moderate E/N, but that significant discrepancies exist at high E/N. The mobility data are also directly inverted to give the Li+–He interaction potential. This directly determined potential is in excellent agreement with the ab initio at intermediate and long range, but differs significantly in the short-range region. In the latter region, however, it is in agreement with the potential obtained by analysis of beam-scattering experiments.
On the optimal photon energy for photon-assisted nonresonant charge exchange
Authors: Copeland Drew A. , Tang C. L.
Published: February 2003

In the weak field limit the dependence of the photon-assisted charge exchange reaction A++B+h/ω→A*+B+ on the applied photon energy is discussed. It is shown that the optimal photon energy for enhancement of the reaction depends on the relative collision energy and is not when the total energy defect of the reaction partners, at infinite internuclear separation, is zero.
A new, simple a
b i
n
i
t
i
o pseudopotential for use in FSGO calculations: Application to some lithium compounds
Authors: Topiol Sid , Frost A. A. , Moskowitz J. W. , Ratner M. A.
Published: February 2003

A new model potential designed for use within an FSGO framework is proposed. Results of calculation using this new model for Li compounds are in good agreement with all-electron FSGO results.
Utility of multiple-pulse NMR to determine the amorphous fraction of polyethylene
Authors: Pembleton R. G. , Wilson R. C. , Gerstein B. C.
Published: February 2003

Multiple pulse NMR techniques are utilized to determine the amorphous fraction of polyethylene. The averaging condition of the multiple pulse experiment, tc∥?int∥≪1, where tc is the cycle time and ∥?int∥ the magnitude of the internal interaction averaged by the multiple pulse sequence in question, allows for unique separation of the response of the protons in the amorphous phase from the response of the total system by means of appropriate adjustment of tc.
Dense gas transport calculations
Authors: Cafky James W. , Babb Stanley E.
Published: February 2003

The Rice–Allnatt theory of dense gas transport coefficients is examined numerically for several sources of radial distribution functions. The viscosity predictions become physically unacceptable at sufficiently high densities, and all predictions generally show poor agreement with experiment.
Neutron diffraction study of the structure and phase transitions of alkali cyanide crystals
Authors: Rowe J. M. , Rush J. J. , Prince E.
Published: February 2003

The structures of sodium and potassium cyanide have been studied by neutron powder diffraction as a function of temperature between 6 and 300 K. The orientation of the CN ions in the lowest temperature phase has been established, and the mechanism of the order–disorder phase transitions has been elucidated by a careful study of a superlattice line intensity in KCN.
Compressional moduli for liquid diphenyl hexachloride
Authors: Miles D. O.
Published: February 2003

Due to unavoidable sensitivity problems, direct measurement of the imaginary compressional modulus, or compressional viscosity, has proven extremely difficult. This attempt, with a special liquid (Diphenyl Hexachloride) whose high shear viscosity facilitates delicate preparation of a suitable spherical sample, is but partially successful. A possibility exists that at least a portion of the effect measured arises from apparatus imperfection wherein the intended applied sinusoidal radial compressive strain is contaminated by an unintentional shear component. Nevertheless, much is learned from the effort, and analysis of data not only indicates compressional viscosity exists and is contributing to the effects observed, but also that it might be isolated from inherent shear mechanisms at high static pressures (upon which the applied sinusoidal pressure is superposed) so as to allow for a completely definitive experiment.
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o configuration interaction studies of the electronic states of S2N2
Authors: Jafri Jawed A. , Newton M. D. , Pakkanen Tapani A. , Whitten J. L.
Published: February 2003

A b initio SCF and CI calculations are reported for the sulfur nitride, SN, and disulfur dinitride, S2N2, molecules. Calculations on SN, varying the internuclear distance, are performed using a variety of basis sets to determine a suitable basis for S2N2. The total energy, internuclear distance, and force constant of SN are reported for several choices of basis. Extended basis computations on S2N2 are performed, and midbond polarization functions are found to contribute significantly to a description of the ground state, affecting the higher MO’s and the charge density. A prominent feature of the virtual spectrum is the existence of a low energy π* orbital which could play a role in low lying excited states, the polymerization process, and polymer conductivity. CI studies of the ground and excited states of S2N2 show several low lying singlet and triplet states of the type π→σ*, π→π*, and σ→π*, and possible identifications with experiment are discussed. A possibility of relating the observed paramagnetism on polymerization to (SN)x to properties of the monomer S2N2 was considered, but the calculations do not support this hypothesis for the monomer in its square equilibrium geometry since no excited states were found to be accessible by thermal excitation.
Normal coordinate analysis for CaNb2O6 of columbite structure
Authors: Husson E. , Repelin Y. , Dao N. Q. , Brusset H.
Published: February 2003

The Raman and infrared spectra of CaNb2O6 are assigned by normal coordinate analysis according to Shimanouchi’s method. The Raman spectroscopy results enabled us to refine the force field, which was then checked by the infrared spectroscopy results. The obtained force constants show that there are three different types of Nb–O bonds in the columbite structure and that the Ca–O bonds are of electrostatic nature. The potential energy distribution calculation gives us a precise assignment for all the observed frequencies.
Transferability of electron pair wavefunctions. III. A minimal basis strongly orthogonal geminal calculation of the hydrogen peroxide hindered rotation potential
Authors: Howard Robert E. , Levy Mel , Shull Harrison , Hagstrom Stanley
Published: February 2003

Preliminary to wavefunction transfer studies, we present an ab initio strongly orthogonal geminal (SOG) calculation of the H2O2 hindered rotation potential. With geometry optimized, a cis barrier of 8.6 kcal/mole and a zero trans barrier are computed. The optimum OO bond length (2.811 bohr) and OOH angle (97.0°) agree well with experiment, but the OH bond length (1.950 bohr) is longer than experimental. The trans barrier is discussed and attributed to an eclipsed OH bond–lone pair interaction which stabilizes the experimental equilibrium conformation. It is argued on the basis of (a) electron distribution differences, (b) correlation effects in the OO bond, (c) differences between SCF calculations and experiment, and (d) SOG improvement of SCF minimal basis results that correlation cannot be ruled out as a factor in the cis barrier.
Energy and angular distributions of electrons ejected from water vapor by 0.3–1.5 MeV protons
Authors: Toburen L. H. , Wilson W. E.
Published: February 2003

Absolute cross sections, differential in electron energy and ejection angle, have been measured for ejection of electrons from water vapor by protons with energies from 0.3 to 1.5 MeV. These cross sections are compared with similar measurements for ionization of molecular hydrogen and oxygen and previously published results for hydrocarbon. The criteria for additivity and scalability of electron ejection cross sections are discussed.
Electronic to vibrational energy transfer from I*2P1/2 to HF
Authors: Coombe Robert D. , Pritt A. T.
Published: February 2003

The fraction of the total quenching of I*52P1/2 by HF that occurs by electronic to vibrational (E–V) energy transfer has been determined. Measurements were made by analysis of the HF vibrational fluorescence following photolytic creation of I*. The near-resonant process populating HF (v=2) was found to account for 35±4% of the quenching. The fraction of the quenching proceeding by the nonresonant E–V process populating HF (v=1) was found to be 5±4%. The results demonstrate the influence of resonance in the E–V mechanism and suggest that the most significant relaxation route for this system is electronic to rotational and translational (E–R,T) energy transfer.
Effect of interactions with nonspherical molecules on 129Xe magnetic shielding
Authors: Jameson Cynthia J. , Jameson A. Keith , Cohen Sheila M.
Published: February 2003

Second virial coefficients of chemical shielding are reported for Xe interacting with HBr, HCl, CO2, N2O, C2H2, C2H4, C2H6, and BF3 from 230 to 440 K. Values range from 0.15 to 0.52 ppm amagat−1. There is some evidence for the anisotropy of the potential function for Xe and these molecules.
Kinetics of the reaction of bromine atoms with molecular fluorine
Authors: Strattan Laurence W. , Kaufman Myron
Published: February 2003

The rate constant of the reaction of bromine atoms with molecular fluorine is determined by mass spectrometrically monitoring BrF produced at fixed reaction time as a function of the concentration of F2 added to a flowing mixture of Br and Br2 in He diluent. The rate constant is 1.31×10−13 exp(−17.9 kJ mole−1/RT) cm3 molecule−1 sec−1 over the temperature range 296–418° K. Br+F2 is thus another example of the anomalously slow rate which is characteristic of the reactions of F2 with many atoms.
The composition dependence of glass transition properties
Authors: Gordon J. M. , Rouse G. B. , Gibbs J. H. , Risen W. M.
Published: February 2003

The configurational entropy theory of glass formation is used to derive the composition dependence of the glass transition temperature (Tg) and of supercooled liquid transport properties for binary mixtures which obey the laws of regular solutions. The relations between expressions derived subject to specified approximations and known empirical equations are shown, and the parameters of the latter are thereby identified with defined measurable quantities. The predicted compostion dependence of Tg is compared with experimental data from binary mixtures with satisfactory agreement.
The isotope shift in NMR
Authors: Jameson Cynthia J.
Published: February 2003

The isotope shift observed in NMR is formulated in general for the diatomic molecule. The results are extended to polyatomic molecules and to a linear triatomic molecule in particular. General empirical observations which have been made on isotope shifts are explained in terms of the theoretical formulation given here.
Kinetics of the reactions of hydroxyl radicals with some halocarbons: CHFCl2, CHF2Cl, CH3CCl3, C2HCl3, and C2Cl4
Authors: Chang J. S. , Kaufman F.
Published: February 2003

Rate constants for the reactions of hydroxyl radicals with five halocarbons were measured in a discharge-flow apparatus using resonance fluorescence detection for OH in the 109 – 1011 cm−3 concentration range and with large excess of halocarbon. Over the approximate temperature range of 250 – 400°K the three saturated halocarbons CHFCl2, CHF2Cl, and CH3CCl3 had Arrhenius rate constant expressions of 1.16×10−12 exp(−1073/T), 1.20×10−12 exp(−1657/T), and 1.95×10−12 exp(−1331/T) cm3 sec−1, respectively. For the C2HCl3 and C2Cl4+OH reactions, Arrhenius expressions of 5.3×10−13 exp(445/T) and 9.4×10−12 exp(−1199/T) cm3 sec−1 are reported. These findings are compared with results by other investigators and their kinetic significance as well as their implications for stratospheric pollution problems are discussed.
Light scattering studies of transverse sound wave and molecular motion in benzonitrile
Authors: Whittenburg S. L. , Wang C. H.
Published: February 2003

The zero-frequency shear wave dip appearing in the depolarized Rayleigh spectrum in benzonitrile has been studied as a function of concentration and temperature. The solution study was carried out at constant viscosity equal to the viscosity of liquid benzonitrile at each temperature. The result indicates that the presence of shear wave fine structure does not depend on the collective orientational fluctuations. The orientational and vibrational relaxation times of benzonitrile were measured at various concentrations and temperatures. The orientational relaxation times show no concentration dependence at any temperature, suggesting that the pair correlation is negligible at all concentrations. The orientational relaxation times obtained from the Raman measurements are in good agreement with the depolarized Rayleigh values at the same temperature and concentration, again indicating pair correlation is negligible in benzonitrile. Thus, both the Raman and depolarized Rayleigh scattering techniques measure the single particle relaxation time of benzonitrile. The single particle times were compared with the predictions of the hydrodynamic slip and stick models for rotational diffusion. In contrast to the results obtained for most small molecules, the stick model better approximated the experimental results.
Quantitative intracavity laser detection of NO2 by optical multichannel analysis
Authors: Atkinson G. H. , Heimlich T. N. , Schuyler M. W.
Published: February 2003

The spectroscopic fidelity and quantitative characteristics of intracavity laser detection (ILD) are examined using low pressure NO2 samples and optical multichannel (vidicon) analysis. The ILD spectra obtained are shown to accurately replicate the discrete absorption features of NO2 and to exhibit a linear dependence on the concentration of the intracavity species over more than an order of magnitude. The use of the technique for monitoring reaction intermediates is discussed.
Equilibrium properties of dense simple fluids in the presence of three-body forces
Authors: Sinha S. K. , Ram J. , Singh Y.
Published: February 2003

Computationally convenient theoretical methods for calculating the structural and thermodynamic properties of a classical fluid in the presence of three-body forces are presented. The concept of the effective pair potential has been used to develop two approximations, one known as the Exp approximation for the pair correlation function and the other known as ORPA+B2 for the Helmholtz free energy. The theory has been applied to calculate the effect of the triplet potential on the radial distribution function for the hard-sphere and the Lennard-Jones fluids. At densities and temperatures away from the triple point the effect of the dipole–dipole–dipole and dipole–dipole–quadrupole interactions on the structure of fluids have been found to be small. It is shown that the direct correlation function outside the hard core is significantly affected by the presence of the three-body forces.
High frequency sound velocity and sound absorption in supercooled water and the thermodynamic singularity at 228°K
Authors: Rouch Jacques , Lai C. C. , Chen Sow-Hsin
Published: February 2003

The interpretation of our experimental results on the high frequency sound velocity and sound absorption in liquid and supercooled liquid water lends support to the existence of a thermodynamic singularity at about 228°K. We determine the respective critical exponents and find them in good agreement with those, whenever available, deduced from other techniques.
Vibrational excitons, resonant energy transfer, and local structure in liquid benzene
Authors: LeSar R. , Kopelman R.
Published: February 2003

The presence of vibrational excitons in liquid benzene has been tested by the method of isotopic dilution. A C6H6/C6D6 concentration study on the infrared and Raman fundamental modes reveals that the umbrella (A2u) vibrational exciton in solid benzene retains its characteristics upon melting and at room temperature. The total liquid exciton bandwidth is about 40 cm−1, practically the same as in the solid. This indicates an instantaneous local liquid structure similar to that of the solid (the Ci crystal site symmetry is also nearly preserved), in general agreement with indications from other methods. The fastest nearest neighbor vibrational resonant transfer takes about 1 psec. The residual linewidth at isotopic dilution is 3–4 cm−1, which is due to inhomogeneous and/or homogeneous broadening. The respective overall reorientational and/or translational relaxation takes about 2 psec or longer. The exciton linewidth is proportional to the square root of the isotopic concentration except for a sudden break at some critical concentration.
Nd3+ multiplet splittings in YAG using an effective ligand point-charge model
Authors: Mroczkowski J. A. , Randic M.
Published: February 2003

An investigation of the 4f3 4I9/2, 4I15/2, 4F3/2, and 4F9/2 multiplet splittings of Nd3+ in YAG was undertaken on the basis of an explicit point-charge model. A fit between optical data and the 20 calculated energy levels was made within a 22.7 cm−1 standard deviation using only three adjustable parameters. A physical representation of the crystal field at Nd3+ sites could not be achieved solely on the basis of a model of surrounding ion point charges located at the ion sites. However, when the effects of a strong covalency contribution to the crystal field were simulated by a model of effective ligand point charges, a satisfactory representation of the YAG crystal field was obtained.
Laser photoelectron spectrometry of FeO−: Electron affinity, electronic state separations, and ground state vibrations of iron oxide, and a new ground state assignment
Authors: Engelking P. C. , Lineberger W. C.
Published: February 2003

The photoelectron spectrum of FeO− ions, obtained with 2.54 eV Arii irradiation, consists of a well resolved series of vibrational transitions from the ground electronic state of the negative ion to two low-lying electronic states of FeO. Analysis of this spectrum gives the electron affinity of FeO (1.492±0.020 eV) and the vibrational frequency of the negative ion (740±60 cm−1). The vibrational frequency of the ground state of FeO is 970±60 cm−1; the term energy T0 of the first excited state of FeO is 3990±100 cm−1. The FeO vibrational frequency shows definitively that the accepted ordering of FeO states is incorrect, and that the previously assumed ground state must in fact be an excited state. Earlier spectroscopic studies of FeO are re-examined, and a new state ordering, consistent with all experimental data, is proposed.