bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Spin Resonance Study of the Photolysis of Polystyrene and Poly(α-Methylstyrene)
Authors: Cozzens R. F. , Moniz W. B. , Fox R. B.
Published: February 2004

The photolysis of polystyrene and poly (α-methylstyrene) was studied by ESR techniques using highly concentrated glassy solutions of the polymers near liquid-nitrogen temperature. Every attempt was made to insure detection of the earliest free-radical species. The use of poly (1-vinylnaphthalene) and polystyrene-2,3,4,5,6-d5 verified that the primary radical species is located on the polymer chain and not the ring. The ESR spectra obtained for both polystyrene and poly (α-methylstyrene) are consistent with the structure HH–C–Ċ–C–HφH. Interpretation of the observed spectra is made on the basis of the stereochemistry of the polymer chain.
Electronic Spectra of Benzene in Cyclohexane at 77°K
Authors: Spangler John D. , Kilmer Nelson G.
Published: February 2004

Absorption, fluorescence, and phosphorescence of solid solutions of benzene in cyclohexane at 77°K have been investigated. The bands obtained for slowly cooled samples are attributed to benzene molecules occluded in the low-temperature monoclinic crystal form of cyclohexane. The additional bands obtained with fast cooling are attributed to benzene molecules occluded in the high-temperature cubic crystal form of cyclohexane. Detailed analyses of the fluorescence and phosphorescence of slowly frozen samples are given. The benzene molecules occupy sites that possess at least a center of symmetry. The phosphorescence lifetime for benzene in the monoclinic cyclohexane lattice is 4.6 sec for concentrations ≲0.01M and decreases slowly with increasing concentration. The phosphorescence lifetime for benzene in the cubic cyclohexane lattice at a 0.01M concentration is 1.1 sec. Relative intensities of spectra of benzene in the two cyclohexane lattices are reported for various concentrations. For concentrations ≲0.01M, the relative intensities for obsorption and fluorescence are the same, but the phosphorescence from the cubic lattice is less efficient than from the monoclinic lattice. The relative intensities of both fluorescence and phosphorescence from the cubic lattice decrease with increasing benzene concentration. This is attributed to long-range energy transfer with trapping in the monoclinic lattice.
NMR Studies of Iron (III) N-Methyl-N-Phenyldithiocarbamate and Its meta- and para-Fluorophenyl Derivatives
Authors: Golding R. M. , Tennant W. C. , Bailey J. P. M. , Hudson A.
Published: February 2004

The proton and fluorine magnetic resonance spectra of these compounds are interpreted using a model where the iron atom is in an intermediate crystal field of octahedral symmetry. The various proton and fluorine isotropic hyperfine-interaction constants in the A61 and the T22 states are calculated, and the approximations to determine these constants are examined. A method is outlined whereby an estimate of the ratio of the molecular vibrational partition functions in the T22 and A61 states can be ascertained from the NMR and the magnetic moment measurements. From the aromatic proton and fluorine hyperfine-interaction constants the electron spin densities in the A61 state are estimated and the results discussed. It is shown that fluorine substitution in the aromatic ring has little effect on the various hyperfine-interaction constants in both states.
Mayer's Theory of Condensation and Homogeneous Nucleation
Authors: Parlange Jean-Yves
Published: February 2004

Mayer's theory is re-examined and is shown to yield the proper onset of condensation. Evaluation of reducible integrals for large clusters leads to a formula analogous to Volmer's classical result in nucleation theory.
Electronic Structure and Spectra of Niobium Metal Atom Clusters
Authors: Schneider Robert F. , Mackay Raymond A.
Published: February 2004

Electronic absorption spectra have been obtained for a number of (Nb6Cl12n+ (n = 2,3,4) compounds in ethanol, or nitromethane solution and in some instances, over a limited frequency region in KBr pellets. A qualitative scheme for the bonding in the polynuclear transition metal complexes is proposed and compared with previous models. A new assignment of the electronic transitions in Nb6Cl12n+ species is made and criteria for the identification of metal–metal transitions in these systems are proposed. The effects of terminal ligands on the spectra are considered.
Viscosity of Some Quadrupolar Gases and Vapors
Authors: Pal A. K. , Barua A. K.
Published: February 2004

Viscosity of acetylene, carbon dioxide, carbon disulfide, and benzene has been measured in the gaseous state (at pressures below 10 cm Hg) by a precision all-metal oscillating-disk viscometer. All of these substances have comparatively large quadrupole moments. Attempts have been made to derive information on quadrupole-quadrupole interactions from these data.
Local Energies, the Integral Hellmann–Feynman Method, and Partitioning the Hamiltonian
Authors: Lowe John P. , Mazziotti Alexander
Published: February 2004

The connection between local-energy functions and the integral Hellmann–Feynman (IHF) method is discussed. Richardson and Pack's method of partitioning the Hamiltonian is related to local energies and their numerical results are rationalized. It is shown that local-energy concepts can be useful in choosing the best from among the many possible IHF calculations for a process. IHF calculations already in the literature are analyzed from this standpoint. Calculations on HeH+ are reported which indicate that the IHF method may be particularly useful for shorter one-center expansions.
Theory of Thermal Transpiration in a Knudsen Gas
Authors: Wu Yau
Published: February 2004

The theory of thermal transpiration has been revised in a rigorous treatment. This phenomenon, discovered by Newmann, Feddersen, and Reynolds, has been treated by Maxwell and Knudsen from kinetic theory considerations. In the present theory, it has been shown that the Maxwell and Knudsen theories do not give a detailed, microscopic description and are only valid for a near-Maxwellian distribution function. However, the revised and exact theory contains a set of new invariants which deviate from the classical theory by a geometrical factor I. This factor (isotropy) is a measure of the isotropy of the velocity distribution function in the thermal transpiration system. The new invariants in the Knudsen regime are pI / T1 / 2 and n(T)1 / 2I. In general, I is not always equal to unity or a constant value in a thermal transpiration system.
Experiments on N2(A3Σu+). II. Excitation of NO
Authors: Young Robert A. , John Gilbert A. St.
Published: February 2004

The rate coefficient for the process N2(A 3Σu+υ′ = 0, 1) + NO(X 2Π)→N2(X 1Σ) + NO(A 2Σ+υ′ = o) is measured to be 3 × 10−11 cm3/sec. Essentially half of all de-exciting collisions of N2(A 3Σu+) with NO result in excitation of NO. The rate coefficient of N2(A 3Σu+υ′ = 1) + NO(X 2Π)→N2(X 1Σ) + NO(A 2Σ+υ′ = 3) is measured as 1.3 × 10−12 cm3/sec.
Evolution of Reduced Distribution Functions. II. The Classical Two-Body Function
Authors: Mortimer Robert G.
Published: February 2004

A nonequilibrium BBGYK hierarchy is truncated at the two-body equation by a dynamical superposition approximation equivalent to neglecting three-body deviations from equilibrium in the triplet distribution function. This truncated hierarchy is solved by iteration in the case of a fluid system near equilibrium. The solutions are partially summed to series that are nearly series in the strength of the potential.
Fluctuation Theory of Light Scattering from Pure Water
Authors: Litan Adiel
Published: February 2004

In the preceding article it has been shown that the conventional fluctuation treatment of light scattering, which for a pure liquid yields the Einstein-Smoluchowski-Cabannes formula, will, in principle, usually underestimate, but never overestimate, the correct amount of scattering. In this study an expression for the excess scattering, over that calculated by the Einstein-Smoluchowski-Cabannes formula, is derived for a simple “iceberg” model of pure water. The excess scattering is estimated and found to be within the range of experimental error, which agrees with the fact that it has not been observed in previous experimental studies.
Spin-Other-Orbit Interaction in Many-Electron Atoms
Authors: Malli Gulzari
Published: February 2004

Spin-other-orbit interactions have been calculated for atoms with pn and dn configurations up to radon (Z = 86) using the radial integrals evaluated from numerical Hartree-Fock wavefunctions. It is found that the absolute value of the spin-other-orbit interaction increases for the atomic configuration (nl)N as the principal quantum number n increases; it also increases with N in a given shell.
Cation Distribution in the Garnet Eu3Fe1.94Ga3.06O12
Authors: Marezio M. , Remeika J. P. , Zocchi M.
Published: February 2004

A single crystal x-ray diffraction study of the cation distribution in the garnet Eu3Fe1.94Ga3.06 has been made. The greater preference of the Ga3+ ions for the tetrahedral sites with respect to the one of the Fe3+ ions, already postulated from magnetic measurements, has been confirmed. The fraction ft = 0.91 ± 0.03 of the total Ga3+ in the crystal is found in the tetrahedral sites, while only 0.103 of the total Fe3+ is found in these sites.
Spin-Resonance Properties of Scheelites. I. Vanadium in CaWO4
Authors: Mahootian N. , Kikuchi C. , Viehmann W.
Published: February 2004

This paper is intended as the first of a series of investigations directed at obtaining information about charge compensation in CaWO4. Vanadium, which lies immediately above niobium in the periodic table, is introduced as the microprobe. The EPR spectra produced by X irradiation and observed at 77° and 4.2°K indicate that vanadium can occupy a variety of sites. Arguments are given that two of these, referred to as Group A and Group C, are due to vanadiums in W and Ca site, respectively.
New Scaled Atoms-in-Molecules Theory for Predicting Diatomic Potential-Energy Curves. II. Studies of the Calibration Technique and Applications to HeH+, HeH, He2+, H2−, and He2
Authors: Wu Ay-ju A. , Ellison Frank O.
Published: February 2004

Applications of a recently developed scaled atoms-in-molecules theory are reported. In general, the basis used in this theory consists of linear combinations of antisymmetrized products of atomic substate eigenfunctions. Each such basis function Ψn is modified by introducing scaling parameters snA and snB into its component atomic eigenfunctions. Exact expressions have been derived for determining, by reference to experimental atomic energies, all intra-atomic contributions to the energy matrix elements. All remaining contributions, interatomic in nature, are computed using approximate atomic eigenfunctions. In the present study of HeH+, HeH, He2+, H2−, and He2, the Ψn have been constructed exclusively from ground-state eigenfunctions for H, He+, He− and He, as appropriate. For evaluating interatomic contributions, the optimum 1s2 orbital approximations for H− and He have been used. For the homopolar molecules, the theory is applied with exact evaluation of all integrals which occur in the interatomic parts; for all molecules considered, calculations also are done using the Mulliken integral approximation. Finally, results of a calibration technique in which the overlap integral S (1sA, 1sB), whether appearing directly or through the Mulliken approximation, is replaced by C1sAC1sB S(1sA, 1sB) are also given; here, C1sH = 0.88 and C1sHe = 0.8936 were previously determined by forcing the computed X 1Σg+ energies of H2 and He2+ + to be equal to the corresponding exact energies at their potential-energy minima (a relative minimum for Ee2++). With few exceptions, the calibration technique leads to energy predictions which are significantly better than those obtained at this level of approximation with or without the Mulliken integral approximation.
Photoionization of CH3; Heat of Formation of CH2
Authors: Chupka W. A. , Lifshitz Chava
Published: February 2004

Methyl radicals produced by pyrolysis at various temperatures have been photoionized by photons in a 1.6-Å bandwidth over the energy range 9.5-16.5 eV with mass-spectrometric detection. The curve of photoionization cross section for the parent ion shows that direct ionization predominates in the threshold region, and that the geometrical form of the positive ion in its ground state is very similar to that of the neutral radical. Hot bands and other vibrational features observed near threshold are only partly explained. The data are compared with absorption spectra and electron-impact curves. The ionization efficiency curve for production of CH2+ from CH3 is measured at several pyrolysis temperatures and the threshold for 0°K is determined to be 15.09±0.03 eV. This yields the value 91.9±1.0 kcal/mole for the heat of formation of the CH2 free radical.
Shape Fluctuations of Free Liquid Films with Diffuse Electric Double Layers
Authors: Felderhof B. U.
Published: February 2004

The fluctuations in shape of free liquid films which may be observed by light scattering yield information about the forces determining film stability. The main forces are the van der Waals force and the electric force caused by the overlap of diffuse electric double layers formed by the ions in solution. A detailed analysis employing the thermodynamic theory of fluctuations is made of the electric contribution to the fluctuations in shape. The thermodynamics of the double-layer system is kept as simple as possible but account is taken of the nature of ion adsorption at the film surface.
Microwave Spectrum, Vibration–Rotation Interaction, Molecular Structure, and Dipole Moment of 1-Methylpentaborane (9)
Authors: Cohen Edward A. , Beaudet Robert A.
Published: February 2004

The microwave spectra of a number of isotopic species of 1-methylpentaborane (9) have been analyzed. All spectra are consistent with a model having free internal rotation and vibration–internal-rotation interactions. Lack of barrier perturbations leads to an upper limit of 1 cm−1 for the 12-fold barrier. The theory for the vibration–internal-rotation interaction is extended to low-barrier molecules having an N-fold barrier. The boron framework was determined to be identical with that in pentaborane (9). The dipole moment is 1.93 ± 0.05 D.
Elementary Description of the Equation of State of a Simple Fluid
Authors: Kozak John J. , Rice Stuart A.
Published: February 2004

In this paper we describe an improved equation of state for classical fluids. We consider a system of molecules interacting with a Lennard-Jones potential with a rigid-sphere cutoff. An algorithm for the equation of state is based on the idea that the major contributions to the pressure arise from the statistical geometry imposed by the rigid-core repulsion, the mean field acting on a molecule, and a limited number of fluctuations about the mean field. The rigid-core contribution is calculated from the solution to the Percus-Yevick equation, and the mean field directly from the corresponding theoretical radical distribution function. The first five fluctuation terms are computed. The equation of state of argon is calculated at a temperature slightly above its critical point, and at a high temperature (T* = 2.74). The results are found to be in good agreement with experiment.
Application of a Shell Model to the Calculation of the Surface Distortion in Alkali Halide Crystals
Authors: Benson G. C. , Claxton T. A.
Published: February 2004

Previous calculations of the distortion in the five outermost layers of a {100} face of an alkali halide hemicrystal with NaCl-type structure are extended to incorporate the shell model of Dick and Overhauser. Previous difficulties with the sodium halide crystals are removed and results for the lithium halides are presented for the first time. The qualitative configuration of the surface layers seems to be insensitive to the model used. Some difficulties remain with the lithium halide results.
Direct Observation of the Infrared Torsional Spectrum of C2H6, CH3CD3, and C2D6
Authors: Weiss Shmuel , Leroi George E.
Published: February 2004

The torsional spectra of gaseous C2H6, CH3CD3CD3, and C2D6 have been observed directly in the infrared under high-pressure-path-length conditions (30-70 atm·m). The fundamental was observed for all three species, at 289, 253, and 208 cm−1, respectively. Hot bands were observed for C2H6 (255 cm−1 [A], 258 cm−1[E]) and CH3CD3 (228 cm−1) as was the first overtone for CH3CD3 (482 cm−1). All the experimental frequencies can be very well accounted for by use of a single internal rotation potential function with a barrier height V3 = 2928 cal / mole. This implies that V6 (and higher terms) are negligibly small. Two alternative explanations for the occurrence of these spectra in the infrared, one in terms of Coriolis interaction with an infrared-active vibration and one in terms of a ν4 + νx − νx vibration, are discussed. A more reliable determination of ν12, the “uncertain frequency” of C2H6, has been obtained from the ν12 − ν9 difference band, giving ν12 = 1206 cm−1.
Absorption and Emission Spectra of OH and OD in Solid Ne. Evidence for Rotation
Authors: Tinti D. S.
Published: February 2004

The A 3 ∑  + −X 2 ∏ i system of OH and OD has been studied in solid Ne at 4.2°K. Both absorption and emission spectra have been recorded, the latter for the first time for OH or OD in a solid matrix. Emission is seen from υ′ > 0, establishing a relatively slow vibrational relaxation rate in the A 3 ∑ + state for OH and OD in solid Ne. Considerable fine structure is seen, which differs for the two isotopes and is not a mirror image in absorption and emission. This structure bears no resemblance to the structure previously observed for OH and OD in the other rare gases. The observed structure in solid Ne can be partly interpreted in terms of slightly perturbed rotational motion in the solid. The larger perturbation for OH compared with OD suggests that translation-rotation coupling may be important. Rotational relaxation times shorter than 10−6 sec have been established from the lack of rotational “hot-band” structure in the emission spectrum.
Numerical Investigation of the Variational Principle Treatment of the Excluded Volume Problem
Authors: Torrens Ian McC.
Published: February 2004

The approximations involved in a recent analytical investigation of the excluded volume problem are examined and the zeroth-order self-consistent field of the polymer segments is used to obtain numerical solution of the integrodifferential equations involved. It is concluded that the final result of the zeroth-order approximation is unrealistic, and further cycling of the results to produce higher-order approximations is necessary to achieve self-consistency and hence solve the problem.
Ion-Molecule and Chemi-ionization Reactions in H2 by Photoionization
Authors: Chupka W. A. , Russell M. E. , Refaey K.
Published: February 2004

The production of H3+ by ion-molecule and chemi-ionization processes initiated by photon impact in H2 has been studied as a function of photon energy with resolution widths varying from 0.05 to 0.002 eV. The purpose was to determine how the vibrational energy of the reactant ion affects the reaction cross section. The data indicate that the reaction H2+ + H2→H3+ + H proceeds by at least two different mechanisms. At very low kinetic energies, the dominant mechanism has a reaction cross section which decreases slowly as the vibrational energy of the ion increases. At higher kinetic energy, a mechanism for which the cross section increases with increasing vibrational energy of the ion becomes more prominent. The characteristics of the first mechanism suggest the formation of a collision complex while those of the latter suggest a mechanism such as stripping. At low kinetic energies, the rotational energy of the ion has only a small effect on the reaction cross section. Some of the production of H3+ by chemi-ionization below the ionization threshold of H2 is shown to involve excited H atoms, probably in the 22 S metastable state, as well as excited H2 molecules. The cross section for chemi-ionization by excited H atoms was found to decrease with kinetic energy; this behavior is discussed. The proton affinity of H2 was found to be ≥ 3.936 eV.
Infrared Spectrum of the Matrix-Isolated OH Radical
Authors: Acquista Nicolo , Schoen Louis J. , Lide David R.
Published: February 2004

Infrared absorption in the region of 3450 cm−1 has been observed in water–rare-gas matrices subjected to vacuum-ultraviolet photolysis at 20.4° and 4.2°K. The splittings and isotope frequency ratios obtained from H216O–D216O, H216O–H218O, and D216O–D218O mixtures lead to the assignment of these spectra to trapped OH radicals. No evidence for rotational motion of OH is found in these experiments.
Fluorescence Quenching Via Charge Transfer: The Perylene-N,N-Dimethylaniline System
Authors: Ware William R. , Richter Herbert P.
Published: February 2004

The mechanism of fluorescence quenching in a system where there was evidence that quenching proceeds via a charge-transfer complex has been investigated using the direct observation of fluorescence decay as a tool to explore the kinetics of the quenching process. The system studied was perylene in its fluorescent state quenched by amines in a variety of solvents with dielectric constants ranging from 2.3 to 37. In solvents with dielectric constant greater than 12, the fluorescence decay is exponential and no CT emission is seen. In low-dielectric media (ε = 2.3 to 4) the decay of the perylene emission consisted of a two-component exponential decay and CT emission was observed as well. The results obtained can be explained on the basis of the mechanism of Leonhardt and Weller, in which the excited-state charge-transfer complex, once formed from the excited molecule and quencher, can decompose into its components in a feedback step, emit CT fluorescence, or undergo one or more nonradiative processes. In media of high dielectric constant, the importance of the nonradiative decay increases compared to the other two paths. From an analysis of the decay curves the rate constant for the formation of the charge-transfer complex from excited perylene and N , N-dimethylaniline was evaluated over the full dielectric constant range. Its magnitude suggests a diffusion-controlled reaction. The rate constant and activation energy for the feedback step were also obtained.
Nanosecond Pulse Radiolysis Studies of the Reaction of Ions in Cyclohexane Solutions
Authors: Thomas J. K. , Johnson K. , Klippert T. , Lowers R.
Published: February 2004

The positive and negative ions of biphenyl and anthracene are observed in the pulse radiolysis of solutions of these molecules in deaerated cyclohexane. Most of the ions (G∼0.9) decay rapidly over 50 nsec, while a small yield (G∼0.2) decays over many microseconds. The rapid decay is indicative of a heterogeneous kinetic condition, namely the formation of ion pairs. The product of the neutralization of these ions is the triplet state of the molecule (Gtriplet∼1 at high concentrations), and a small yield of luminescence. This luminescence may indicate that a small yield ( < 0.25) of singlet excited states is formed. A large yield (Gtriplet > 2) of triplet excited states, is formed in less than 1 nsec. It is suggested that these excited states are formed directly from subexcitation electrons.
Attempt to Determine Bond Magnetic Anisotropies from Principal Diamagnetic Susceptibilities of Crystalline γ- and δ-1,2,3,4,5,6-Hexachlorocyclohexane
Authors: Allen Harold A. , Muller Norbert
Published: February 2004

Krishnan's method was used to measure the principal diamagnetic susceptibilities of single crystals of γ- and δ-1,2,3,4,5,6-hexachlorocyclohexane. The results were used in conjunction with available values of the atomic coordinates to compute “bond” anisotropies for the C–C, C–H, and C–Cl groups. The analysis required that one assume that each bond is axially symmetric and that all bonds of a given type (e.g., C–Cl) have the same anisotropy. Essentially the same assumptions have been used in attempts to rationalize chemical-shift data from proton magnetic resonance spectra on the basis of bond anisotropy effects. The self-consistency of the bond-anisotropy values obtained in this work is poor, probably because these assumptions are unsatisfactory. No evidence was found for the presence of an appreciable induced ring current in the saturated six-membered ring.
Semiclassical Treatment of Multiple Turning-Point Problems—Phase Shifts and Eigenvalues
Authors: Miller William H.
Published: February 2004

A simple, physically intuitive, expression has been obtained for the scattering phase shift δ (l, E) in the case that the effective radial potential possesses a maximum. The result [Eq. (3)] is seen to modify the usual WKB phase shift [Eq. (5)] by replacing a step function by a particular “smooth step function.” On the basis of this result, resonances in the energy dependence of the total elastic cross section are discussed. From qualitative arguments it is seen that metastable states more than ∼0.6 ℏωB energy units above the top of the barrier are too short lived to have physical significance (ωB is the harmonic frequency related to the inverted barrier). Application is also made to the eigenvalues of a hindered rotor.
Molecular Fragments of Heterocyclic Aromatic Compounds. II
Authors: Sharp-Ritter Janet D. , Lykos Peter G.
Published: February 2004

Pi-electron approximations, and semiempirical theories based on them, have come to be widely used, not only for pi-electron (planar-conjugated) systems alone but for other molecules as well. Inherent in all of these methods is the LCAO-MO approach. Thus, when one gets down to the “nitty gritty,” integrals over AO's become the basic units which need somehow to be estimated. Even in those cases of gross empiricism, overlap integrals appear and cannot be estimated empirically. Thus the AO's used need to be specified. In this work an attempt has been made to determine AO's to be used in defining MO's, which are conditioned to a molecular environment designed to simulate fragments of heterocyclic aromatic compounds and thus to go beyond the use of AO's determined for free atoms. In this spirit, numerous planar hydrides of B, C, N, and O have been handled within a one-center representation of an open- and closed-shell Hartree-Fock approach and the results presented.
Paramagnetic Study of Ionized Thiourea Derivatives
Authors: Box Harold C. , Budzinski Edwin E. , Gorman Thomas
Published: February 2004

The positive and negative ions of thiourea, allylthiourea, and dimethylthiourea produced by x irradiation at 4.2°K were studied by electron spin resonance (ESR) spectroscopy. The g tensors for the positive ion absorptions were measured in single crystals and correlated with the molecular structure of thiourea and allylthiourea. Some predictions concerning the crystal structure of dimethylthiourea are made from ESR data. The g shift associated with the negative ion is small compared with that of the positive ion. The spectra of the aforementioned planar molecules contrast sharply with the spectra obtained from irradiated tetramethylthiourea and dibenzylthiourea, which are nonplanar molecules.
Magnetic Susceptibility of Thorium Carbides, Nitrides, and Carbonitrides
Authors: Aronson S. , Auskern A. B.
Published: February 2004

The magnetic susceptibility of thorium carbides, nitrides, and carbonitrides has been measured at temperatures of − 190°, − 76°, and 22°C. All the compositions exhibited a small, temperature-independent paramagnetism. The data are compared with the results of electrical property measurements on these compounds. It is concluded that whereas the electrical properties are primarily determined by the conduction electrons, the magnetic susceptibility is primarily a property of the holes in the band structure.
Excimer Formation with Polar Molecules: Oxazole and Oxadiazole Derivatives
Authors: Lami H. , Laustriat G.
Published: February 2004

Experimental results, concerning excimer formation with oxazole and oxadiazole derivatives, are used to test the theory of intermolecular interaction in excimers based on configuration interaction between molecular exciton and charge resonance states. SCF molecular orbitals are computed and used to obtain the approximate energies of the molecular exciton and charge resonance states. The polar nature of the considered molecules is taken into account. A clear correlation between the relative location of the interacting states and the ability to form an excimer is found, which strongly supports the above-mentioned theory.
B
2
Σ→A
2
Π
i
Bands of CN
Authors: LeBlanc F. J.
Published: February 2004

The B 2Σ→A 2Πi bands of CN have been observed in a mixture of active nitrogen and a trace of organic substance. There have been no previous reports of observations of this system. Here, nine bands were observed in the wavelength range 4000-5000 Å. Each band has two sharp heads about 60 cm−1 apart.
Metastable Phases in the Pb–Sb and Pb–Bi Systems
Authors: Borromee-Gautier Claude , Giessen Bill C. , Grant Nicholas J.
Published: February 2004

Utilizing the splat cooling technique of rapid quenching from the melt, the Pb–Sb and Pb–Bi alloy systems were investigated at –190°C. In large parts of both systems, metastable single-phase alloys were obtained instead of equilibrium two-phase alloys. New phases found include a bcc (W-A2-type) Pb–Sb phase, a primitive cubic coordinated Pb–Sb phase (possibly of the NaCl–B1 type), and a complex Pb–Bi phase. The terminal solubilities, especially those of Pb in Sb and Bi, were strongly enhanced with an appreciable decrease of the rhombohedral angle α; atomic volumes are given.
Dielectric Study of Intermolecular Association in Isomeric Octyl Alcohols
Authors: Dannhauser Walter
Published: February 2004

The equilibrium dielectric constants of eight liquid isomeric octanols have been measured over a wide range of temperature, and the data are analyzed in terms of the Kirkwood correlation factor. A simple molecular model based on hydrogen-bond associative equilibria involving both ring dimers and linear chain n-mers is developed. Equilibrium constants for ring and chain formation are deduced, and it is concluded that entropic factors, which can be correlated with the geometry of the molecules, are the principal basis for differences between isomers. At relatively high temperatures those species whose − OH group is most sterically blocked prefer to form rings, while those whose − OH group is relatively accessible tend to form open chains. In all cases, chains become the preferred species at low temperatures. ΔH° for hydrogen-bond formation in chains is estimated as about − 6.7 kcal/mole; for rings, about − 4.5 kcal/mole. ΔS° varies from − 16 to − 30 eu/mole for chains and from − 13 to − 20 eu/mole for rings.
Growth and Decay of Delayed Luminescence
Authors: Srinivasan B. N. , Kinoshita M. , Rabalais J. W. , McGlynn S. P.
Published: February 2004

We have investigated the rise lifetimes and decay lifetimes of the long-lived luminescences of the following systems: a naphthalene-ds, a phenanthrene, and a triphenylene solution in a rigid-glass matrix; a phenanthrene-d10, a phenanthrene, a naphthalene-ds, and a chrysene solution in a biphenyl crystal; and chrysene in solution in a phenanthrene crystal. It has been found that the luminescence rise time is invariably shorter than the luminescence decay time. This phenomenon is satisfactorily explicable on the basis of the following attitudes: In rigid glasses, triplet-triplet absorption events contribute to depopulation of the triplet state and decrease the rise time; in mixed crystals, on the other hand, triplet-triplet annihilation events are dominantly responsible for abbreviating the rise time. The effects of excitation intensity and excitation wavelength on the delayed luminescence rise times of rigid-glass solutions, and the effects of excitation intensity, concentration of guest species, and temperature on the delayed luminescence rise times of mixed-crystal systems are discussed. The activation energies for the annihilation process were obtained from a first-order analysis of the luminescence decay and rise times. The agreement between calculated activation energies and T1H − T1G spectroscopic energy gaps is satisfactory and validates the postulated kinetic processes.
High-Temperature Vaporization and Thermodynamics of the Titanium Oxides. III. Vaporization Characteristics of the Liquid Phase
Authors: Gilles Paul W. , Franzen Hugo F. , Stone G. Duane , Wahlbeck Phillip G.
Published: February 2004

Vaporization experiments with liquid samples of TiO, Ti3O5, Ti4O7, Ti5O9, and TiO2 were performed, and the residues were analyzed by x-ray diffraction procedures. The results show that the congruently vaporizing composition lies between the composition Ti3O5 and the composition Ti4O7 instead of at the composition Ti3O5 as is the case for crystalline samples. The importance of this conclusion in vapor-pressure studies leading to thermodynamic values and for stuctural relationships between solid and liquid Ti3O5 is discussed.
Dissociative Electron Attachment to Hydrogen Halides and their Deuterated Analogs
Authors: Christophorou L. G. , Compton R. N. , Dickson H. W.
Published: February 2004

The swarm-beam technique has been employed to study the electron-attachment processes in HX and DX (X = halogen) molecules. Attachment cross sections as a function of electron energy σc(ε), corrected for the finite width of the electron beam, are reported for the direct dissociative attachment, i.e., HX(or DX) + e→H (or D) + X−. There is a strong increase in σc(ε) in going from HCl to HBr to HI, i.e., with decreasing energy of the dissociative-attachment peak. The ratio of σc(ε) for isotopic species is found to be very nearly equal to the square root of the inverse ratio of the reduced masses of the products. In addition to the direct dissociative electron attachment to HX and DX molecules, a separate attachment process occurs at thermal electron energies.
Absolute Oscillator Strengths of the Strongest Bands within the Dipole-Allowed Absorption Spectrum of Nitrogen
Authors: Lawrence G. M. , Mickey D. L. , Dressler K.
Published: February 2004

The absolute absorption f values of four bands of N2 in the 958-972-Å region, b 1Πu–X (3–0, 4–0), l 1Πu–X, and p′ 1Σu+–X (0–0), have been determined using a 3-m spectrometer as absorption cell with N2 gas pressures in the 10−6−10−4-torr range, using the helium continuum with differential pumping, and double-beam, windowless photoelectric recording with pulse-counting electronics. More than 10 times narrower spectral bandwidth (0.04 Å) was realized than previously reported in photoelectric absorption work at these wave-lengths, thus enabling work down to more than 100 times smaller numbers of absorbing molecules. The consequent reduction of the effects of line saturation made possible the evaluation of absolute f values which are compared with other absolute and relative determinations from lifetime and electron impact measurements.
Studies of IBr, ICl, and I2Cl6 Crystal Properties by Means of the Mössbauer Effect in 129I. II. Lattice Dynamics
Authors: Pasternak M. , Sonnino T.
Published: February 2004

Lattice-dynamics information on polycrystalline I2, IBr, ICl, and I2Cl6 molecular crystals was obtained by means of the Mössbauer effect in the 27.8-keV line of 129I. In the case of I2 and IBr, which are isomorphous, evidence was found that the mean-square displacement is larger in the direction of the molecular axis, and from considerations regarding the molecular arrangements, it is concluded that the larger 〈x2〉 is in the ac plane. Similar evidence was found also for ICl. No anisotropy in 〈x2〉 was detected in the case of I2Cl6. From the temperature dependence of the recoilless fraction and from its absolute value, the Debye temperature was calculated and found to be 58° ± 2°K for both I2 and IBr, suggesting a similar density of phonon states, in accordance with far-infrared results obtained with the halogens at 77°K. The 〈x2〉 found for I2Cl6 is compared with that calculated from Raman data for ICl4−, and it is concluded that the I-Cl intramolecular vibrations are not excited by the recoilless mechanism, which explains the relatively large effect observed.
Electronic Structure of Lithiumacetylene
Authors: Veillard Alain
Published: February 2004

A self-consistent field wavefunction has been calculated for the lithiumacetylene molecule LiCCH, using the Linear Molecule Program of McLean and Yoshimine. Expectation values of a number of one-electron operators are presented. Electronic structures of lithiumacetylene together with acetylene and fluoroacetylene are discussed through the results of population analysis. It is found that lithiumacetylene is a highly ionic compound and that long-range inductive effects play a major role in electronic transfers.
Phase Diagram of Ammonium Fluoride to 20 kbar
Authors: Kuriakose A. K. , Whalley E.
Published: February 2004

The phase boundaries and the transition volumes of ammonium fluoride in the range 1 to 20 kbar and 20° to 340°C have been measured, and the transition entropies calculated. A new phase is reported, designated IV, that has an entropy about Rln6 greater than that of its neighbors I and II. This entropy difference suggests that the ammonium ions in phase IV are orientationally disordered among six equivalent positions. The liquid-I boundary shows that the liquid is mainly ionic.
Mössbauer and Magnetic Susceptibility Investigation of the 5T2−1A1 Crossover in Some Octahedral Ferrous Complexes in the Solid State
Authors: Jesson J. P. , Weiher J. F. , Trofimenko S.
Published: February 2004

Octahedral ferrous chelates based on the hydrotris (1-pyrazolyl) borate ligand can be prepared which are fully high spin, or are fully low spin, or have an intermediate magnetic moment which is strongly temperature dependent. Mössbauer and magnetic susceptibility data characterizing this behavior in the solid state are presented and analyzed. The orbital splitting of the high spin ground state due to a trigonal component in the octahedral crystal field is ∼1000 cm−1 leaving an orbital singlet lowest. The thermal relaxation time between the singlet and quintet manifolds is anomalously long, leading to the observation of separate Mössbauer transitions for the two electronic states.
Effect of Adsorption of Gases on the Semiconductive Properties of All-trans β-Carotene
Authors: Misra T. N. , Rosenberg B. , Switzer R.
Published: February 2004

The presence of various adsrobed gases increases the semiconduction currents in crystalline powder of β-carotene by several orders of magnitude and decreases the activation energy for semiconduction. The current increase depends on the amount and nature of the adsorbed gas. The process is reversible simply by desorbing the gases. The kinetics of the conductivity rise follow the Roginsky-Zeldovich equation for the adsorption-time correlation. It has been noted that the adsorbed gases have no effect on the σ0 term, i.e., the mobilities of the charge carriers and the number of conducting states do not change. A value of σ0 ≈ 1.0 × 10−3(Ω·cm)−1 has been measured. Assuming a value for the radius of polarization field, R = 5.3 Å and using the measured values of the dielectric constant, values for the activation energies of β-carotene with adsorbed O2 and methanol, and also the increment in current expected, have been predicted. The measured values are in good agreement with these. We conclude that the changes in the effective dielectric constant (possibly due to formation of donor-acceptor complexes) and the consequent changes in the activation energy can satisfactorily account for the electrical behavior of all-trans β-carotene crystals when various gases are adsorbed on it.
Correlations between the Excluded Volumes and the Second Virial Coefficients of Linear Polymer Chains
Authors: Yamakawa Hiromi
Published: February 2004

By a hierarchy approach, it is shown that the Kurata theory of the second virial coefficient A2 for linear polymer chains is the one to be combined with the theory of the expansion factor αS developed in the previous paper. However, the equation for the expansion factor ᾱ of a chain in contact with another is assumed to be of the same type as the equation for αS. A comparison of theory and experiment is made using the following two properties as criteria of validity for the theory: (1) the consistency in the values of the excluded-volume parameter z determined from the theory of αS and from the theory of A2 with observed values for them; (2) the proportionality of z so determined to the square root of the molecular weight. For this purpose, light-scattering data obtained by Berry for polystyrene in decalin and toluene are used. It is shown that the present theories of αS and A2 do not violate the two criteria. Evidently his estimates of z are too large, and the binary-cluster integral is not proportional to 1 – Θ / T, except near the Θ temperature.
Microwave Spectrum of HPF4
Authors: Pierce Stephen B. , Cornwell C. D.
Published: February 2004

The microwave spectra of hydrido- and deuteridotetrafluorophosphorane (HPF4 and DPF4) are reported. The molecule is an asymmetric rotor, with the c axis being an axis of twofold symmetry. The spectra, therefore, support the C2υ trigonal bipyramid model, and rule out C3υ and C4υ models. Rotational constants A, B, C (Mc/sec) are, respectively, for HPF4, 6011.29, 4317.42, 3156.22 and for DPF4, 5822.24, 4222.98, 3154.51, with an uncertainty of ± 0.05 Mc/sec. The dipole moment, measured from Stark splittings, is 1.32 ± 0.02 D along the c axis. If the PH bond length for the C2υ trigonal bipyramid model is assumed to be 1.36 ± 0.05 Å, the other parameters are: PF (axial) = 1.594 ± 0.005 Å, PF (equatorial) = 1.55 ± 0.03 Å, ≮ HPFax = 90° ± 4°, ≮ HPFeq = 124° ± 2°. The c axis is along the PH bond, and the axial PF bonds lie in the a, c plane.
Zero-Field Splitting, Magnetic-Field Energies, Effective Magnetic Moments, and Electric-Field Gradients in High-Spin Ferric Porphyrin Compounds
Authors: Harris Gilda
Published: February 2004

Recently, the lowest electronic energy intervals in a series of 10 related high-spin ferric porphyrin compounds have been measured directly by far-infrared spectroscopy. The zero-field splitting obtained ranged from 9.3 to 33−1. In the calculations described here, we have successfully explained all 10 of these observed values, using a strong crystal-field model with tetragonal symmetry and spin-orbit coupling of the sextet ground state to excited quartet and doublet states to all orders. To do this, we have used what we considered to be a physically reasonable and internally consistent variation of three crystal-field parameters. The corresponding eigenfunctions of the three A16 doublets were also calculated for all 10 compounds and very little spin mixing obtained. We have used these eigenfunctions for each compound to calculate the effective magnetic moments of the ferric ion as a function of temperature, the magnetic-field energies of the three doublets both to first order and also allowing magnetic-field mixing of all six A6 states, and finally the electric-field gradient at the ferric ion nucleus including both a lattice and valence electron contribution. All of these properties are discussed and the calculated results compared with experiments whenever possible. In most cases, the agreement with existing experimental data is quite good.
Transport Coefficients for a Diatomic Gas
Authors: Garbin Ronald A.
Published: February 2004

The transport coefficients in the Wang Chang and Uhlenbeck theory are calculated for a gas of rigid rotators in which the coupling between rotational and translational modes is very weak (hydrogen). Each molecule has a scattering center at both extremities, and from this, and the Born approximation a differential scattering cross section is derived for arbitrary encounters. When a delta potential is introduced between each “nuclear” pair, the result is a stronger temperature dependence of viscosity than that shown by a classical gas of hard spheres.
Quasielastic Scattering by Semidilute Polymer Solutions
Authors: Jannink G. , Gennes P.-G. de
Published: February 2004

We compute the coherent dynamic form factor for the scattering of neutrons by a “semidilute” solution of polymers, in which the radius of gyration RG of each coil is assumed much larger than the average distance between neighboring coils. In this case, in the presence of a strong excluded volume, the coils are nearly ideal, and correlations between monomers can be obtained accurately by a random phase approximation. Backflow effects (which complicated seriously the one-coil problem) are not important here for the longitudinal motion of interest, and a simple Rouse equation can be applied to describe the motion. The most interesting region corresponds to spatial wavelengths q−1 which are large compared to the screening length K−1 (although smaller than RG). In this domain, the frequency halfwidth Δωq at a fixed wave vector q becomes roughly proportional to q2. The effects of entanglement between chains are taken into account only in terms of a phenomenological effective viscosity of the solution.
Fluorescence and Bleaching of Organic Dyes for a Passive Q-Switch Laser
Authors: Spaeth M. L. , Sooy W. R.
Published: February 2004

An experimental study has been conducted of the bleaching of several families of saturable dyes by ruby-laser radiation. Measurements have been made of the time-resolved fluorescent spectra and the time-resolved transmission spectra of various dye–solvent combinations. These measurements have been used to determine the decay channels, the lifetimes, and the temperature dependence of the lifetimes involved in the desaturation of the dyes. The results show that the phthalocyanine dyes bleach over the whole red absorption band, while polymethine-type dyes bleach only over a narrow band around the exciting wavelength. The importance of absorption from the triplet state as a limiting mechanism in the saturation of a dye is also demonstrated by these experiments.
Optical Absorption and Fluorescence Spectra of Dy3+ in LaF3
Authors: Fry J. L. , Caspers H. H. , Rast H. E. , Miller S. A.
Published: February 2004

The absorption spectrum of Dy3+ (4f9) in LaF3 has been observed at 77° and 4.2°K in the 3000 − 30 000-Å wavelength region. The fluorescence spectrum was observed in the range from 4500 to 11 000 Å. From an analysis of the observed transitions, it was possible to assign J + 12 Stark components for most of the states below 24 000 cm−1. The intermediate coupling free-ion energy levels for Dy3+ have been calculated including the interactions of all the multiplets of the 4f9 configuration. The final least-squares fit, with the inclusion of configuration interaction, gave a mean error of 25 cm−1 with the following values for the parameters: F2 = 436.5, F4 = 64.12, F6 = 6.566, ζ = 1930, α = 28.85 cm−1. The calculated energy levels and wave-functions below 40 000 cm−1 are presented and discussed.
Reactions of Negative Ions in the Gas Phase. II. NH2−
Authors: Dillard John G. , Franklin J. L.
Published: February 2004

In mixtures of ammonia with carbon disulfide and carbonyl sulfide the NH2− ion is formed with considerable abundance and reacts to form several other negative ions. The principal products of reaction with CS2 were HS−, CS2−, and SCN. The principal products of reaction with COS were HS−, NH2S−, and OCN−. The rates of the various reactions are similar to those of many positive-ion-molecule reactions. The heats of formation of SCN− and OCN− ions were determined from appearance potentials of these ions from CH3NCS and CH3NCO to be − 4 and − 19 kcal/mole, respectively.