bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculations of He(2 1,3S)+H ionization cross sections using a
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o potentials and widths derived from Siegert eigenvalues
Authors: Isaacson Alan D.
Published: February 2003

Associative and Penning ionization cross sections are calculated for collisions of H atoms with He(21S) and He(23S) in the energy range 0.01–1.0 eV, using the classical theory of Miller. Ab initio potential energy curves V* and widths Γ recently obtained by the author from the variational calculation of the Siegert eigenvalues for these systems are used. Generally good agreement with the previous theoretical work of Hickman and Morgner is obtained. In addition, somewhat better agreement of the present results with the available experimental data, especially for the singlet total ionization cross section, demonstrates that the Siegert potentials and widths are reasonably accurate.
Charge overlap effects in dispersion energies
Authors: Krauss M. , Neumann D. B.
Published: February 2003

Charge overlap effects in dispersion energies are calculated using frequency dependent atomic polarizabilities. The dispersion energy is expanded in the usual multipole interaction series but the dispersion coefficients are found to be given as a product, C (LA,LB) χ (LA,LB;R) where C (LA,LB) is the usual coefficient for nonoverlapping fragments and χ is called a damping function which equals one asymptotically. Damping functions have been calculated for He(11S)–He(11S), Be(11S)–Be(11S), and combination of He(23S), He(21S), He(11S), and H(12S). The results are used to analyze qualitatively the extent of the dispersion contribution to the energy of interactions at either the equilibrium separation or the critical distance for orbiting collisions.
The variational method and the stochastic-Liouville equation. II. ESR spectral simulation via finite elements
Authors: Stillman Arthur E. , Zientara Gary P. , Freed Jack H.
Published: February 2003

A Galerkin finite element (FE) method, closely related to the variational FE method of Zientara and Freed, is developed for the solution of the stochastic Liouville equation (SLE). The particular illustrative application considered is the ESR spectral simulation of the simple axially symmetric g tensor problem. Both linear and quadratic interpolating functions are considered. It is found for this simple case that the Galerkin FE is almost, but not quite, as efficient as eigenfunction expansions (EE). However, the potential advantages of the Galerkin FE in more complex problems are discussed.
Fluorescence decay of the O+u and 1u states of Xe2
Authors: Thornton G. , Poliakoff E. D. , Matthias E. , Southworth S. H. , Rosenberg R. A. , White M. G. , Shirley D. A.
Published: February 2003

Synchrotron radiation from the Stanford storage ring (SPEAR) was used to measure the radiative decay constants of the lowest-lying excited electronic states of Xe2. Both a monochromator and interference filters were used in the fluorescence channel. The results suggest that at low pressures (PXe<125 Torr) there is substantial deviation from the Stern–Volmer behavior predicted by the three-state models used previously to describe this lasing system. A new theoretical analysis was developed that includes participation in the kinetic scheme of intermediate vibrational levels of the O+u and 1u manifolds.
Calculation of scavenging yield from the initial distribution of electrons in radiolysis of hydrocarbon solutions
Authors: Friauf R. J. , Noolandi J. , Hong K. M.
Published: February 2003

Previous theoretical work on the analytical solution of the time-dependent Onsager problem is used to calculate the scavenging yield for arbitrary scavenger concentration. By comparing calculations for three types of initial distribution functions with experimental results for cyclohexane, we find that the exponential distribution gives best agreement, as found previously by Abell and Funabashi and by Mozumder. We have extended the earlier work by also calculating the scavenging yield in the presence of an applied electric field.
Crystalline vanadium (II) fluoride, VF2. Preparation, structure, heat capacity from 5 to 300 °K and magnetic ordering
Authors: Stout J. W. , Boo W. O. J.
Published: February 2003

Crystalline VF2 was prepared by the reduction of VF3 in an atmosphere of 3 H2:1 HF at 1100°C. The VF2 formed deep blue crystalline needles. The crystal structure is of the rutile type, space group P42/mnm. Parameters determined by x-ray diffraction are a=4.804±0.005 Å, c=3.237±0.005 Å, u=0.306±0.005. The low temperature heat capacity of VF2 is reported from 5 to 300 °K. A sharp peak in heat capacity associated with the development of long-range magnetic order is observed at 7 °K. Smoothed values of the total heat capacity, entropy, enthalpy, and Gibbs energy are tabulated between 5 and 300 °K. Values at 298.15 °K are: C °P=15.10 cal °K−1 mole−1, S °=18.217 cal °K−1 mole−1, H°−H°0=2661.0 cal mole−1. By a corresponding states approximation the magnetic contributions to the heat capacity and entropy are calculated. The magnetic heat capacity has a gradual maximum at 26.8±1 °K. The heat capacity curve agrees with that calculated for a one-dimensional chain with antiferromagnetic Heisenberg interactions. A value of the exchange constant, J/k=−9.4±0.4 °K is obtained.
Ferrimagnetism in FeCoF5⋅2H2O
Authors: Jones Edwin R. , Dawson Robert
Published: February 2003

The magnetic susceptibility of FeCoF5⋅2H2O was measured over the temperature range from 3 to 296 °K. A ferrimagnetic phase transition was observed at 27.0±0.25 °K. At temperatures between 80 and 296 °K, FeCoF5⋅2H2O was paramagnetic and could be described by the Curie–Weiss law χ=C/(T+ϑ) with ϑ=56 °K and an effective magnetic moment per formula unit of 6.8±0.1 μB. In the ordered region the magnetization did not saturate at fields up to 11 kOe. At applied fields above 500 Oe the magnetization departed from the usual Brillouin behavior suggesting the occurrence of a second ordered phase at temperatures below 10°K.
On the valence bond diatomics-in-molecules method. II. Application to the valence states of FH2
Authors: Faist Michael B. , Muckerman James T.
Published: February 2003

Explicit methods are given for setting up the matrices involved in the projector approach of the preceding paper to the diatomics-in-molecules (DIM) method for obtaining potential energy surfaces. Application is made to the 14 spin–orbit surfaces of the FH2 system produced from the consideration of only the valence electrons on the atoms and ’’ionic–covalent’’ coupling in the HF diatomic fragment. This FH2 example contains an illustration of each type of complication one could encounter in the use of the DIM method as a semiempirical technique. Plots of the ground state spin–orbit FH2 surface are given along C∞v ’’abstraction’’, C2v, Cs, and C∞v ’’exchange’’ cuts, as well as reactant to product correlation energy diagrams produced from vertical cuts along minimum energy pathways of these symmetries. Comparison is made to existing information whenever possible.
Density functionals in unresticted Hartree–Fock theory
Authors: Payne Philip W.
Published: February 2003

The Hohenberg–Kohn theorem is generalized to unrestricted Hartree–Fock (UHF) wave functions. It is postulated that each N-electron density can be expanded in many sets of orbitals, and these orbital sets are continuously deformable into one another. Subject to these postulates several conclusions follow: The UHF wave function functional ψ[ρ] exists for all such densities. It consists of those orbitals which minimize the sum of kinetic and exchange energies, and it can always be chosen to be a ground state wave function. The exact exchange energy, including self-repulsion, is also a functional of the electron density. It is implicitly defined as the expectation value of exchange energy for the wave function functional ψ[ρ]. This work also addresses some general properties of local exchange potentials. A local exchange potential is a multiplicative potential which replaces the exchange operator in the UHF equations. Every method which employs a local exchange potential is variationally equivalent to minimization of kinetic energy alone, subject to constant density constraint. Many ad hoc local exchange potentials are currently in use, but it is here shown that the functional derivative of exchange energy δK/δρ (r) is the optimal choice for a local exchange potential. This choice is best because the resultant orbitals reproduce the correct UHF ground state energy and electron density.
Forced rotational diffusion of linear molecules. Nonlinear aspects
Authors: Warchol Mark P. , Vaughan Worth E.
Published: February 2003

The decay of fluctuations in orientation of a system of linear molecules interacting via electrostatic forces is determined by solution of the forced diffusion equation in its nonlinear form. The results consist of series expansions of the time dependent coefficients of the expansion of the distribution function for orientation in spherical harmonics. Separate expansions in terms of the scale of fluctuations and in terms of the magnitude of the dipole–dipole forces are given. The nonlinearity causes the appearance of terms in the expression for the fluctuation decays which evolve on a time scale shorter than that of the free diffusion.
A study of the motions of NH3 in TaS2 by quasielastic neutron scattering
Authors: Riekel C. , Heidemann A. , Fender B. E. F. , Stirling G. C.
Published: February 2003

We have used quasielastic incoherent neutron scattering to study the molecular motions of NH3 in TaS2. We show that the diffusion mechanism involves instantaneous jumps between equivalent next nearest neighbor sites in the basal plane and measure an activation energy for translational diffusion of 9.6±0.3 kcal/mol. The motional jump frequencies measured by neutron scattering and NMR are compared.
Tempered orbital energies and the potential curve within a molecule
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2003

It is shown that the sum of the tempered orbital energies behaves much the same way as does the some of the Hartree–Fock orbital energies. The H2 moluecule in its minimum basis set description is chosen as an example and comparison of orbital energies is carried out. (AIP)
The selective decomposition of CF3 13COCF3 molecules at natural abundance: Multiphoton dissociation at threshold
Authors: Hackett P. A. , Gauthier M. , Willis C. , Pilon R.
Published: February 2003

The first example of a system is reported in which isotopic selectivity increases dramatically with increasing substrate pressure. Hexafluoroacetone is studied using infrared laser induced multiple photon decomposition. The parametric variations of pressure, laser frequency, and fluence to the reaction yield are reported. (AIP)
On the photochemical stability of H3O+(H2O)n
Authors: Thomas Timothy F. , Rose Timothy L. , Paulson John F.
Published: February 2003

Cross sections for the photodissociation of hydrated oxonium ions with visible and ultraviolet radiation. A chromatrix CMX-4 tunable dye laser was used to extend the range over which reactions have been studied down to 265 nm. (AIP)
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o calculations of the nuclear spin–spin-coupling constants. II. Comparison of the FP and SOS methods
Authors: Fukui H. , Miura K. , Ishigami N.
Published: February 2003

Calculated nuclear spin–spin coupling constants of HF and H2O are presented. The calculations were performed on a FACOM 230−75 at the Hokkaido University Computing Center. (AIP)
Reply to a Comment on ’’Mobility of localized and quasifree excess electrons in liquid hydrocarbons’’
Authors: Schiller Robert , Nyikos Lajos , Berlin Yu. A.
Published: February 2003

The comments of Freeman [J.Chem.Phys. 71,564(1979] on a previous paper by the authors [(J.Chem.Phys. 69,2401(1978)] are considered in this reply. It is contended that the ’semihydrodynamic’ expression in Eq.(2) of the former reference gives the mobility of localized electrons within a factor of two. (AIP)
Unification of the methods of Onsager and Monchick for calculating the probabilities of various fates in diffusion-controlled reactions, with applications to diffusion in space and in a plane
Authors: Naqvi K. Razi , Waldenstro/m S. , Mork K. J.
Published: February 2003

We have unified the methods of Onsager and Monchick for calculating the probabilities for the various fates (reaction, escape, re-encounter, etc.) of a particle undergoing a diffusion-controlled reaction in three dimensions; the unified treatment applies also to diffusion in a plane and leads easily to some results which have either not been derived before or have required considerable labor. Finally, explicit solutions for a specific force field representing both attraction and repulsion are given.
An ESR study of chlorine containing radicals in x-irradiated N-chlorosuccinimide at 77 K
Authors: Pace D. , Ezell K. , Kispert L. D.
Published: February 2003

Three different radicals were identified by ESR studies in x-irradiated single crystals of N-chlorosuccinimide; radicals I and II, stable at 77 K and radical III, stable at 240 K. Radical I was identified as the previously reported sigma anion radical, ≳N-Cl−. Radical II was found difficult to saturate at 200 mW and was assigned to a chlorine atom interacting weakly with a nearby nitrogen with gz=2.008, gx=2.120, and gy=2.126. The chlorine and nitrogen hyperfine couplings were found to be Az=116.0, Ax=6.4, Ay=4.2 G, and Az=8.4, Ax=4.7 and Ay=4.4 G, respectively. At 240 K, radical III was formed by the abstraction of a ring proton from a neighboring N-chlorosuccinimide molecule when radical I decayed.
Polarized absorption spectra and energy levels for U3+(5f3) in LaCl3
Authors: Gruber John B. , Morrey John R. , Carter Daniel G.
Published: February 2003

Polarized absorption spectra covering the wavelength range 5600 to 25 000 Å are reported for U3+(5f 3) doped into single crystal LaCl3. Spectra were recorded at liquid helium, liquid nitrogen, and at room temperatures. Temperature-dependent polarized spectra help establish many crystalline electric-field (CEF) split J levels not directly excited from the ground state due to selection rules for C3h symmetry. Analysis of the data confirms the earlier (1959) assignments made by S. P. Cook at The Johns Hopkins University to the ground state manifold Stark levels. For 4I9/2, the ground state manifold, we find: μ (±5/2) =0, μ (±1/2) =210, μ (±3/2) =241, μ (±5/2) =440, and μ (±3/2) =458 all in energy units of cm−1. Uncertainty in establishing these levels is within several wave numbers and involves over 150 temperature-dependent transitions.
The structure of the (√3×√3) R30° sulfur overlayer on the iridium (111) surface
Authors: Chan C.-M. , Weinberg W. H.
Published: February 2003

At one-third of a monolayer coverage, sulfur forms an ordered (√3×√3) R30° superstructure on the Ir (111) surface. A comparison between dynamic calculations of the intensity–voltage profiles of diffracted beams for different assumed surface geometries and measured low-energy electron diffraction beam profiles demonstrates that the sulfur adatoms occupy one of the two inequivalent types of threefold hollow sites. In particular, the sulfur resides in the threefold sites directly above a vacancy in the second substrate layer with an interlayer spacing of 1.65 Å corresponding to an Ir–S bond length of 2.28 Å.
Continuous wave intracavity dye laser spectroscopy: Dependence of enhancement on pumping power
Authors: Harris Stephen J.
Published: February 2003

Enhancement of cw intracavity dye laser spectroscopy (IDLS) is measured as a function of pumping power for two different dye laser thresholds. Enhancement ranges from less than 500 at high powers to greater than 104 near threshold. The results are in good agreement with the predictions of Brunner and Paul, but do not support the theory of Hänsch, Schawlow, and Toschek.
Electron momentum distributions in the π orbitals of small hydrocarbons from the (e,2e) experiment
Authors: Coplan Michael A. , Moore John H. , Tossell John A. , Gupta Abha
Published: February 2003

Momentum distributions have been obtained by the (e,2e) technique for the π electrons of acetylene, ethylene, and butadiene, and for the pseudo-π electrons of cyclopropane. The first and second ionization potentials of butadiene are unambiguously assigned to π orbitals from the shape of the associated momentum distributions. Experimental momentum distributions are compared with those calculated from a number of approximate wave functions. Hückel, INDO approximate SCF, and minimum basis set ab initio SCF MO wave functions all predict maxima in momentum distributions at values about 0.2 a0−1 higher than observed experimentally for the compounds studied, although differences between compounds are described correctly. Double zeta basis ab initio SCF calculations give considerably more accurate momentum distributions, although some discrepancies between calculation and experiment remain for the more diffuse of the π orbitals. The expected linear relation between the positions of the momentum distribution maxima and orbital energies is observed.
Photon-enhanced dissociative electron attachment in SF6 and its isotopic selectivity
Authors: Chen C. L. , Chantry P. J.
Published: February 2003

Production of SF−5 by dissociative attachment of very low energy electrons to SF6 is known from previously reported work to be strongly enhanced by increasing the gas temperature. Data on this effect is presented and analyzed to give an activation energy of εa=0.2 eV for the reaction. The expectation that this effect can be produced by direct optical excitation of the ν3 vibrational mode is confirmed by using a tunable cw CO2 laser focused collinearly with an electron beam inside a collision chamber. The product ions are monitored using a quadrupole mass filter. By chopping the laser beam and monitoring ion signals and electron current during the laser on, and laser off, periods it is possible to isolate the desired signals from the interfering effects of heating of the collision chamber and the electron gun filament, caused by the laser beam. The observed enhanced of the SF−5 signal by the radiation is strongly dependent on the laser wavelength, and is confined to the attachment peak at very low (<0.1 eV) electron energy. This is consistent with the thermal excitation data. The tuning curves for the production of 32SF−5 and 34SF−5 are well resolved and are separated by the known isotope shift of the ν3 SF6 absorption. Both peaks, however, are red shifted by 8 cm−1 from their respective room temperature small-signal absorption peaks. Possible reasons for this shift are discussed. They suggest that efficient promotion of the (SF−6) * dissociative decay channel requires a total of two or more vibrational quanta to be present in the SF6. The peak enhancement of 32SF−5 was found to occur at the P (28) CO2 laser line (936.85 cm−1). At this wavelength the enhancement effect was found to be linearly dependent on laser intensity. The interpretation that this implies single-photon absorption is rejected on the grounds that the laser fluence levels are too high for such conditions to prevail. The linearity remains unexplained, in common with similar observations by others on absorption effects in SF6 at similar fluence levels. Future measurements of the present type, in particular, of the dependence on laser fluence at other wavelengths should provide additional insight to this general problem of understanding the mechanisms contributing to the absorption of the first few photons in any multiple photon absorption process.
Infrared spectroscopic study of activated surface processes: CO chemisorption on supported Rh
Authors: Yates John T. , Duncan T. Michael , Vaughan Robert W.
Published: February 2003

The infrared spectrum of CO chemisorbed on alumina-supported Rh surfaces has been studied following chemisorption at cryogenic temperatures. Major differences are observed in the distribution and spectroscopic character of chemisorbed CO species produced at low temperatures (110–170 K) compared to chemisorbed CO species produced on Rh at 295 K. It has been found that the species Rh(CO)2, formed on isolated Rh sites, is produced rapidly via an activated chemisorption process above ∼200 K. On more ’’crystalline’’ Rhx sites, containing chemisorbed CO, an activated CO adsorbate-conversion process has been detected in which ?CO decreases by ∼50 cm−1 on warming the adsorbed layer above ∼265 K. Isotopic exchange between 13CO(g) and 12CO(ads) has been shown to occur rapidly at low temperature (∼200 K) for Rh(CO)2 species, whereas Rhx(CO) species exchange rapidly only at higher temperatures (≳250 K). These results, taken together, serve to confirm a model in which isolated Rh sites coexist on the alumina support with crystalline Rhx sites; the two kinds of sites are separable on the basis of the spectroscopic character of the chemisorbed CO species they adsorb as well as by means of their chemical properties.
Relation between the anharmonic properties of TTF–TCNQ and those of naphthalene and anthracene
Authors: Weger M. , Kaveh M. , Gutfreund H.
Published: February 2003

Data on the pressure and temperature dependence of the frequency of some translational and librational modes in naphthalene and anthracene are used to estimate the properties of analogous modes in TTF–TCNQ.
High temperature vaporization and Raoult’s-law studies with 243Am metal
Authors: Ward John W. , Kleinschmidt Phillip D. , Haire Richard G.
Published: February 2003

The vapor pressure of high purity 243Am metal has been measured over the temperature range 1200–1600 K, using combined target and mass spectrometric Knudsen effusion techniques. This work was performed to extend data into the liquid phase, and to compare results with earlier 241Am experiments. Second-law and third-law heats of vaporization are in close agreement with the earlier work, and no isotope effect was found. An additional study of the vaporization of 243Am from a liquid La host was made to explore solubility relationships and activities for systems with similar electronic properties. Lanthanum was found to be a nearly ideal solvent, giving the correct heat of vaporization for Am, and activity coefficients slowly changing with temperature, representative of the effects of a small heat of mixing.
UV laser photochemistry of CF2Br2
Authors: Wampler F. B. , Tiee J. J. , Rice W. W. , Oldenborg R. C.
Published: February 2003

CF2Br2 has been irradiated at room temperature with KrF (248.4 nm) and ArF (193.3 nm) lasers. The fluorescence produced by the KrF laser irradiation appears to consist of only two ν2 progressions, v′2=6 and 5 for the CF2 (1B1−X 1A1) transition. The collision-free lifetime of the CF2 emission was found to be 59 ns. The fluence dependence of the emission is quadratic. Upon irradiation of CF2Br2 with an ArF laser various emitting species were noted. Emission from CF(A 2Σ+–X 2Π), CF(B 2Δ–X 2Π), CF2(2B1–X 1A1), and Br2(3Πo+u–1Σ+ g) molecules was noted. Laser-induced fluorescence excitation spectra confirmed the presence of CF2. The ArF laser fluence dependence of CF2(X 1A1) formation was found to be 1.0.
One-electron model potential calculations of van der Waals forces. I. He* (2 1S, 2 3S) + Ne, Ar, Kr, Xe
Authors: Siska P. E.
Published: February 2003

A simple model which treats only the outer s electron on He* explicitly is shown to account for the main features and trends in the potential energy curves derived from scattering measurements on the title systems. The calculations demonstrate the importance of hybridization of the 2s orbital (2s–2pσ mixing) in determining the van der Waals forces, confirming earlier conclusions based on all-electron ab initio studies and experimental findings on He* (2 1S) systems.
The mechanism of vibrational relaxation in solids: Multiphonon relaxation of O2(c 1Σ−u) in Ar, Kr, and mixed Ar–Kr matrices
Authors: Rossetti R. , Brus L. E.
Published: February 2003

The vibrational relaxation of 16–18O2(c 1Σ−u) has been directly time resolved in Ar, Kr, and mixed Ar–Kr matrices. A vibrational cascade (v=2→1→0) is produced following near resonant intersystem crossing from v=0 C 3Δu. The vibrational relaxation rates slow in Kr host despite the fact that O2 (c 1Σ−u) is more strongly solvated in Kr. In solid Kr, relaxation is slower than host induced fluorescence. The C 3Δu→c 1Σ−u intersystem crossing rate, the spectral shift, and the vibrational relaxation rates are monitored in mixed matrices as the environment changes from pure Ar to pure Kr. The spectral shift shows partial saturation, or weak complex formation, behavior; the vibrational relaxation behavior is consistent with pairwise additive forces. The relaxation rates are strongly temperature dependent. It is suggested that O2(c 1Σ−u), as well as other first row diatomics such as NO(a 4Π) and C−2(a 4Σ), relax via a direct multiphonon mechanism. An analogy with vibrational predissociation in gas phase van der Waals clusters is considered. Symmetric and antisymmetric multiphonon processes are considered in terms of an earlier pseudotriatomic complex model. An isotopic test for symmetric vs antisymmetric multiphonon relaxation is proposed and applied to C−2.
The gas phase laser induced fluorescence spectroscopy of chlorofluoromethylene
Authors: Bialkowski S. E. , King D. S. , Stephenson J. C.
Published: February 2003

The CFCl radical has been produced in the gas phase by both IR multiphoton photolysis of C2F3Cl and He metastable reaction with C2F3Cl. Single vibronic level fluorescence and excitation spectra taken of this species have yielded sufficient information to determine certain vibronic constants. The excited state was found to have an origin of T0=25 283±5 cm−1 with vibrational frequencies: ω2′=394±3 cm−1 and ω3′=739±5 cm−1. In the ground state, the vibrational frequencies were found to be: ω3″=118±10 cm−1, ω2″=448±6 cm−1, and ω3″=750±6 cm−1. The rotational structure of the vibronic bands is similar to those of band transitions of a near prolate top, and the electronic transition has been tentatively identified as ? 1A″←? 1A′ by analogy to similar CF2 transitions. The radiative lifetime of the excited state, τr=700±10 nsec, was found to be independent of the rovibronic excitation frequency. The change in the major rotational constant was found to be A′−A″=1.8±0.2 cm−1.
Electron transfer and excitation in low energy N+2–alkali atom collisions
Authors: Barrett J. L. , Leventhal J. J.
Published: February 2003

Inelastic collisions between N+2 ions and alkali atoms Li, K) have been investigated in the kinetic energy range 50–1000 eV (lab) using a crossed beam apparatus and spectroscopic analysis of collision-produced radiation (180–850 nm). Collision-induced excitation to the lowest alkali atom excited state was observed to compete favorably with near resonant charge transfer to N2(C). The vibrational state distributions within N2(C) from N+2–K collisions are in accord with a vertical transition model, while the distributions resulting from N+2–Li and Na collisions are not. These results are discussed within the framework of a surface crossing model developed to describe such collisions. Absolute cross sections for the observed processes are also reported.
Verdet constant of liquids; measurements with a pulsed magnetic field
Authors: Villaverde A. Balbin , Donatti D. A.
Published: February 2003

The dispersion of the Verdet constant of several inorganic and organic liquids was measured at room temperature with a pulsed magnetic field in the spectral range from 0.3471 μm up to 0.6943 μm. We also measured the Verdet constant, at the wavelength of 0.4579 μm and at room temperature, of the three binary systems methanol–water, ethanol–water, and acetic acid–water. We found that the Verdet constant of mixtures is not additive. The deviation from additivity is positive for the three systems.
The factor group splittings in the molecular vibrations of crystalline phenol
Authors: Tripathi G. N. R.
Published: February 2003

Evidence for dynamic coupling in the molecular vibrations of crystalline phenol, a hydrogen bonded polymer, has been obtained for the first time. The factor group splittings in the vibrational spectra are resolved and interpreted on the basis of the orthorhombic symmetry approximation of the space group. The crystal frequencies are classified into symmetry species B1 and B2 of the D2 factor group, having dipole moment vectors along the crystal axes a and b, respectively. The relation between the polarization behavior of the multiplet components and the symmetry species of the internal modes has been established. Some of the vibrational assignments are discussed.
Photodissociation and photodetachment of molecular negative ions. VII. Ions formed in CO2/O2/H2O mixtures, 3500–5300 Å
Authors: Smith G. P. , Lee L. C. , Moseley J. T.
Published: February 2003

Photodestruction cross sections have been measured for CO3−, CO3−⋅H2O, CO4−, CO4−⋅H2O, HCO3−, and HCO3−⋅H2O at various ion laser and dye laser wavelengths between 5300 and 3500 Å using a drift tube mass spectrometer as the source of the ions. CO3− shows a structureless peak centered about 4500 Å, which is attributed to photodissociation. The possible excitation of CO3− in these studies was investigated in detail and no evidence was found for any excitation. Additional evidence is presented which indicates that the bond energy D (CO2–O−) is less than or equal to 1.9 eV. The CO3−⋅H2O cross section decreases smoothly with decreasing wavelength over this wavelength range. CO4− photodestruction was observed at 3500 Å, but the other ions listed above have cross sections below 10−19 cm2, and possibly zero, throughout this spectral region.
Infrared emission bands from transitions between excited states of cesium–noble gas molecules
Authors: Novak R. , Bhaskar N. D. , Happer W.
Published: February 2003

New emission bands have been observed from cesium–noble gas molecules in the infrared spectral region beyond 1.0 μ. These bands are associated with the allowed transitions 7S→6P in the free cesium atom. They provide a stringent consistency check on earlier work on cesium–noble gas excimer emission and absorption bands in the visible and near infrared regions of the spectrum.
Critical dynamics of the order parameter fluctuations and the anomalous sound propagation of nematics just above the clearing point
Authors: Matsushita Mitsugu
Published: February 2003

Kinetic equations are derived for two kinds of gross variables of nematics in the isotropic phase, i.e., the independent components of orientational tensor order parameter and the transverse local momentum density, using Kawasaki’s mode-coupling theory. Based on them, the time correlation function and the relaxation rate for the critical fluctuations of the order parameter is obtained. The latter result explains why the conventional Landau–de Gennes theory is valid for the usual experiments like flow birefringence and light scattering. The sound attenuation coefficient due to the critical fluctuations of the order parameter is formulated by taking account of the mode-coupling effects between the two kinds of gross variables. The result is compared with the available experimental data with good improvement upon previous conventional theory.
Analytic theory of extrema. I. Asymptotic theory for Fokker–Planck processes
Authors: Lindenberg Katja , Seshadri V.
Published: February 2003

We develop a simple method that yields analytic results for the mean first passage time and mean extreme value of Fokker–Planck processes in the asymptotic regime. The results are very sensitive to the detailed structure of the drift and diffusion terms in the Fokker–Planck equation. We apply our method to a variety of systems with additive fluctuations such as a Brownian particle. We also analyze processes with multiplicative fluctuations and obtain explicit results for the extreme value statistics of the energy envelope of a lightly damped harmonic oscillator and of the Verhulst and Gompertz population models.
The Lennard-Jones 9:3 adsorptive system I: The Percus–Yevick and hypernetted chain theories and their modifications
Authors: Smith Linda S. , Lee Lloyd L.
Published: February 2003

The growing adsorbent molecule model is solved for the Lennard-Jones 9:3 wall/Lennard-Jones 12:6 fluid system using the Percus–Yevick and hypernetted chain closures. Both low density (ρ*=0.06707) and high density (ρ*=0.65) cases are examined. Comparison with Monte Carlo simulations of Rowley et al. and Abraham et al. is made. Due to the Henderson–Abraham–Baker formulation, it is possible to obtain the direct correlation function, C′12  (z), inside the wall. Its behavior is exhibited. At low densities, HNC and PY results are close to each other at high temperatures, but differences appear at low temperatures where HNC density profile exhibits more pronounced structure. Surface properties for the argon–graphite adsorptive system, such as the surface energy, excess number, and surface pressure, are calculated. The PY results seem to be more accurate in comparison with the Monte Carlo values. At higher densities, two modified PY and HNC theories are presented, called the ’’enhanced’’ PY theory (EPY) and the enhanced HNC theory (EHNC). The EHNC theory gives better description of the wall density profile than the EPY theory. They are recognized as the lowest (zeroth) order terms in an inhomogeneous system perturbation theory.
A calorimetric study of liquid cesium–cesium chloride mixtures at 925 K
Authors: Yokokawa H. , Kleppa O. J. , Nachtrieb N. H.
Published: February 2003

The enthalpies relative to 298 K of cesium, of cesium chloride, and of liquid cesium–cesium chloride mixtures have been measured at 925 K by a Calvet-type twin calorimeter using a high-precision digital integrator. From the results we have calculated the enthalpies of mixing for the cesium–cesium chloride mixtures at 925 K. The following empirical relation has been derived from a least squares treatment of the data: ΔHmix/x1x2= (36.42−16.04x2) ± 0.74 kJ mol−1. In this expression x1 and x2 represent the mole fractions of cesium chloride and of cesium, respectively. From the relative enthalpies of cesium chloride at 925 and at 910 K we determined the enthalpy of fusion to be 19.52±0.45 kJ mol−1. The excess Gibbs energies of mixing at 918 K have been derived from the recent cryoscopic data of Hsu and Nachtrieb, taking into account the partial enthalpies and the enthalpy of fusion of cesium chloride. The excess entropies were derived from the enthalpies and the excess Gibbs energies and show large positive values and strong asymmetry.
Surface-induced ordering of a liquid crystal in the isotropic phase
Authors: Miyano K.
Published: February 2003

A detailed account of a measurement of order parameter of a liquid crystal at the boundary by means of the wall-induced pretransitional birefringence is given. Several surface treatments were studied including surfactants and evaporated films. Although all treatments produced good alignment in the nematic phase, the boundary order parameter (hence the strength of the aligning force) in the isotropic phase differed very much depending on the treatment, indicating the diverse nature of the alignment process.
Superposition model analysis of the cubic spin-Hamiltonian parameters for Mn2+ and Fe3+ in the alkaline earth oxides, fluoroperovskite, and II–VI compounds
Authors: Rubio O. J. , Murrieta S. H. , Aguilar S. G.
Published: February 2003

An analysis, in terms of Newman’s superposition model, of the cubic spin–Hamiltonian parameters for divalent manganese and trivalent iron in fluoroperovskite and II–VI compounds is presented. Values for the intrinsic parameter ?4 and for the power-law exponent t4 of Mn2+ with F−, S2−, Se2−, and Te2− ligands are reported for the first time. In addition, values are obtained for ?4 of Fe3+ surrounded by sulfur, selenium, and tellurium as ligands. Also, a re-evaluation of the previously reported power-law exponent t4 is made for Mn2+ with oxygen ligands, taking into account the local distortion around the impurity ion. Using the superposition model, the interaction distances between the Mn2+–F− and the Fe3+–F− pairs in the fluoroperovskite compounds KMgF3, KZnF3, KCaF3, RbCdF3, RbCaF3, and TlCdF3 are determined. This allowed us to make theoretical calculations of the value for the transferred hyperfine parameters As and Ap for both Mn2+ and Fe3+ in these compounds. A close relationship between the value of the intrinsic parameter ?4 with the ligand polarizability and the covalency of the bond as well, is proposed for Mn2+ and Fe3+ with F−, O2−, Cl−, S2−, Se2−, and Te2− as ligands.
Perturbation theory with a hard dumbbell reference system. I. Application to liquid nitrogen
Authors: Kohler Friedrich , Quirke N. , Perram J. W.
Published: February 2003

We present a perturbation theory of molecular fluids which uses an anisotropic reference assembly. At each orientation, the potential is divided according to the Weeks–Chandler–Andersen (WCA) prescription into a reference potential ε0 which contains the repulsive forces and a perturbation ε1 containing the attractive forces. To compute the properties of the reference system, a second perturbation is made about a reference system consisting of equivalent hard dumbells using the analogue of the WCA-blip function theory. The thermodynamic properties of the hard dumbell system are computed from an analytic equation of state due to Boublik and Nezbeda, and the correlation functions using a method developed by the authors. The theory is applied to a two-center Lennard–Jones model of nitrogen at high densities and shown to predict pressures in good agreement with computer simulations.
F+H2 collisions on two electronic potential energy surfaces: Quantum-mechanical study of the collinear reaction
Authors: Zimmerman I. Harold , Baer Michael , George Thomas F.
Published: February 2003

Collinear quantum calculations are carried out for reactive F+H2 collisions on two electronic potential energy surfaces. The resulting transmission and reflection probabilities exhibit much greater variation with energy than single-surface studies would lead us to anticipate. Transmission to low-lying product channels is increased by orders of magnitude by the presence of the second surface; however, branching ratios among product states are found to be independent of the initial electronic state of the reactants. These apparently contradictory aspects of the calculation are discussed and a tentative explanation put forward to resolve them.
A note on relation between Mayer cluster function and quantum two-body t matrix
Authors: Jafarpour Mojtaba
Published: February 2003

A relation is established between the classical mayer cluster function the quantum two body Lippmann-Schwinger t-matrix.
Rotational relaxation time of tRNA
Authors: Kochi M. , Gulari Erdogan , Chu B.
Published: February 2003

The rotational diffusion coefficient of tRNA is measured using two different techniques. Fabry-Perot interferometry and photoelectron pulse time of arrival technique are ccompared on fast decay rates in the nanoseconds range. (AIP)
Relaxation and spectral line shape in Fourier transform ion resonance spectroscopy
Authors: Marshall Alan G. , Comisarow Melvin B. , Parisod Gérald
Published: February 2003

Analytical expressions for Fourier transform ion cyclotron resonance (FT-ICR) line shape [absorption mode, dispersion mode, and magnitude (absolute value) mode] are derived for coherently excited ions that undergo both reactive and nonreactive ion–molecule collisions. The expressions are valid at arbitrary sample pressure, and reduce to particularly simple form in the ’’zero-pressure’’ limit (essentially no ion–molecule collisions during the data acquisition period) or ’’high-pressure’’ limit (many ion–molecule collisions during the data acquisition period). The zero-pressure line shape has been analyzed in earlier papers; in this paper, various useful properties of the high-pressure line shape (e.g., linewidth, mass resolution, and upper mass limit) are tabulated for various choices of the fraction of maximal absorption (or magnitude) peak height at which linewidth is to be measured. Absorption, dispersion, and magnitude spectra are plotted for zero-pressure and high-pressure limits, and also for an intermediate pressure. Convenient reference graphs of high-pressure FT-ICR linewidth, mass resolution, and upper mass limit as functions of ionic mass and time-domain ICR half-life for singly charged ions at magnetic field strength of 2 T are included. Finally, the intermediate-pressure resolution is calculated as a function of acquisition period at fixed pressure, to shown that near-optimal mass resolution (to within 90% of maximal absorption-mode resolution, or 95% of maximal magnitude-mode resolution) is achieved by truncating the FT-ICR time-domain signal after just three relaxation times. The particularly simple trade-off between signal-to-noise ratio and mass resolution in FT-ICR spectroscopy is noted and explained. Good agreement between experimental and theoretical line shape (and thus mass resolution) is demonstrated.
Field induced ion evaporation from liquid surfaces at atmospheric pressure
Authors: Thomson B. A. , Iribarne J. V.
Published: February 2003

A mass spectrometer system which is capable of sampling ions directly from an atmospheric pressure source has been constructed and used to investigate ions which are evaporated from the surface of highly charged water droplets. Solutions of electrolytes are sprayed into the air, and a large charge imparted to the droplets by induction; an electric field applied across the plume of evaporating spray extracts small ions, probably already clustered with solvent molecules, which are drawn through a 25 μm orifice into the vacuum chamber. Differential pumping is applied and the ions are focused into a quadrupole mass filter. Approximately 30 univalent anions and cations of various sizes and structures have been tested, and almost all have been observed to evaporate; significant exceptions are Ag+, Tl+, and Cu+. Furthermore, certain molecules such as urea and acetanilide, when present as neutrals in the sprayed water, are observed to remain attached to the ions when these evaporate. The experimental results are discussed: ion mass spectra are interpreted in terms of ion evaporation (or field emission) and ion–molecule reactions in gas phase, and the potential value of the process for ion research and analytical applications is considered. The main features of the experimental results are consistent with the predictions of the theory developed in a previous paper by the authors.
Photodissociation and photodetachment of molecular negative ions. VIII. Nitrogen oxides and hydrates, 3500–8250 Å
Authors: Smith G. P. , Lee L. C. , Cosby P. C.
Published: February 2003

Total photodestruction cross sections for the ions, NO2−, NO2−⋅H2O, NO3−, NO3−⋅H2O, and the peroxy isomers, O2−⋅NO and O2−⋅NO⋅H2O have been measured at wavelengths between 3500 and 8250 Å, using Ar+, Kr, and dye lasers and a drift tube mass spectrometer. A threshold of ∼2.5 eV was observed for the photodetachment of thermalized NO2−. Upper limits were set for the photodestruction cross sections of NO2−⋅H2O, NO3−, and NO3−⋅H2O over this wavelength range. The NO3− isomer O2−⋅NO and its hydrate, formed in N2O, have large photodissociation cross sections at wavelengths shorter than 5500 Å. Observations of collisional dissociation of cluster ions such as NO2−⋅H2O by laser-excited NO2 in the drift tube are also discussed.
Generalized Langevin theory for many-body problems in chemical dynamics: General formulation and the equivalent harmonic chain representation
Authors: Adelman S. A.
Published: February 2003

A comprehensive theoretical framework for classical trajectory simulations of many-body chemical processes is presented. This framework generalizes previous theoretical methods designed to treat the many-body problems arising in gas molecule collisions off perfect harmonic solids [S. A. Adelman and J. D. Doll, J. Chem. Phys. 64, 2374 (1976); S. A. Adelman and B. J. Garrison, J. Chem. Phys. 65, 3571 (1976)]. The present version of the theory is not restricted to the harmonic systems and thus provides a formal framework for treating liquid state as well as solid state chemical phenomena. Basic to the theory is the molecular time scale generalized Langevin equation (MTGLE), a formally exact representation of the dynamics of a chemical system coupled to an arbitrary heat bath in an arbitrary manner. The MTGLE is equivalent to but distinct from the conventional [Mori–Kubo] generalized Langevin representation. It, however, is more natural for chemical dynamics simulation work because in the MTGLE the apparent vibrational frequencies of the chemical system are those which govern the molecular time scale response of the system. In the conventional Langevin representation, the apparent vibrational frequencies are those which govern the static reponse of the chemical system. The MTGLE is next rigorously transformed into an effective equation of motion for a fictitious nearest neighbor collinear harmonic chain. The parameters characterizing the chain are calculable from the velocity autocorrelation function of the chemical system. The rigorous chain representation of many-body dynamics: (i) provides a simple quasiphysical picture of energy transfer between the heat bath and chemical system during a chemical process; (ii) provides an equivalent Hamiltonian for the chemical system; (iii) permits one to construct a sequence of heat bath models whose response converges to that of the true heat bath in a rapid and systematic manner. The heat bath models are sets of collinear nearest neighbor harmonic chains composed of N=1,2,3,... fictitious atoms. Atom N in the chain is subject to time-local functional damping and is driven by a white noise stochastic force. The remaining atoms 1,2,...N-1 are undamped. The heat bath models (i) produce effective equations of motion for the chemical process which do not involve time nonlocal kernels and which may, hence, be readily solved by standard classical trajectory methods; (ii) allow one to rigorously generalize the Fokker–Planck theory of stochastic dynamics to non-Markovian systems. Finally, the treatment of selected chemical processes via the theory is briefly outlined.
Kinetic energy relaxation of a test particle in a dense fluid
Authors: Pagitsas Michael , Hynes James T. , Kapral Raymond
Published: February 2003

The rate constant kε for the relaxation of the kinetic energy of a solute test hard sphere in a dense hard sphere solvent is studied. Microscopic boundary layer and ring kinetic theory methods are used to construct a simple expression for kε. It is found that kε−1 has three additive contributions arising from (a) uncorrelated binary collisions, (b) coupling to the solvent energy density, and (c) coupling to the solvent shear modes. Thus kε−1 is determined by the Enskog collisional relaxation rate and the rates of the hydrodynamic flows in the solvent of heat and momentum. The competition between these effects is studied as a function of particle size and mass ratios and solvent density. The regimes examined at higher density vary from the identical solute–solvent case, where kε is mainly collisional with a small hydrodynamic heat flow correction, to the large, massive solute case, where kε is governed by solvent momentum flow according to a Stokes law type relation.