bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar power generation with the pyroelectric effect
Authors: van der Ziel A.
Published: February 2004

It is shown with the help of a small-signal model that the pyroelectric effect cannot be used for efficient generation of electrical power from solar radiation.
Single-Crystal Studies of Electrical Conductivity, Seebeck Effect, and Hall Voltage in Sodium Vanadium Bronze and a Crystal-Field Model of Electron Transport
Authors: Perlstein Jerome H. , Sienko M. J.
Published: February 2004

New data are presented for single crystals of Na0.33V2O5. Conductivity along the b axis follows a dependence of the form σT = A exp( − E / kT) with E = 0.067 eV below 140°K and E = 0.057 eV above 140°K. The Seebeck coefficient changes from − 225 μV deg−1 at 70°K to − 135 μV deg −1 at 150°K; thereafter, it remains constant to 300°K. The Hall coefficient at 300°K is − 3 × 10−3cc C−1 which corresponds to n-type carriers at a density of 2.2 = 1021 cc−1 and a Hall mobility of 0.2 cm2V−·sec−1. At 189°K, the Hall data indicate identical carrier density but a mobility about half as large as at room temperature. All the above data together with reported magnetic susceptibility results can be fitted by a small-polaron (hopping) model. Donor states are believed to be Γ6 levels of V4+. These are 0.016 eV below Γ7 conduction states between which hopping occurs with an activation energy of 0.050 eV. Detailed calculation shows a good fit with a crystal-field model in which d1-ion levels are split under tetragonal distortion Δ = 0.10 eV with spin-orbit coupling constant λ = 0.02 eV, and delocalization parameter k = 1.0. Arguments are given for believing that the electrons responsible for the conduction and the observed paramagnetism hop from vanadium to vanadium and are not delocalized over the oxygen framework through V(3d) − O(pπ) overlap. There is, however, evidence for considerable covalent bonding of the σ type between the vanadium and oxygen atoms.
Comparison of the Purity and Perfection of Vapor- and Melt-Grown Anthracene Crystals
Authors: McGhie A. R. , Voshchenkov A. M. , Reucroft P. J. , Labes M. M.
Published: February 2004

The purity and perfection of anthracene crystals have been examined for melt-grown and thick ( > 1 mm) vapor-grown crystals. The physical properties studied were the charge carrier lifetime and mobility of holes, dislocation density, and the bulk self-diffusion coefficient. Chemical purity was assessed by gas chromatography. Melt-grown crystals had hole lifetimes > 1 msec compared with 220 μsec for the best vapor-grown crystal, although vapor-grown crystals had lower dislocation densities and fewersubboundaries. Vapor-grown crystals had lower measurable impurity concentrations, ∼2 ppm compared with ∼10 ppm for melt-grown crystals, but these impurities appear to have no effect on charge carrier trapping. Both types of crystals gave the same self-diffusion coefficient at 190°.
Investigations on Bi3+-Activated Phosphors
Authors: Blasse G. , Bril A.
Published: February 2004

The fluorescence of a number of Bi3+ -activated phosphors is reported. Only host lattices containing a sublattice of large, trivalent cations are used, so that charge compensation of the activator is superfluous. The position of the broad emission band of these phosphors depends strongly on the host lattice and is found in the spectral region between 35 000 and 15 000 cm−1. The position of the absorption and excitation bands of the Bi3+ ion depends also on the host lattice but in a different way. The absorption and emission of those Bi3+- activated host lattices that absorb considerably in the ultraviolet region even without the activator are discussed. These materials probably do not contain simple Bi3+ centers.
Chemistry of Detonations. I. A Simple Method for Calculating Detonation Properties of C–H–N–O Explosives
Authors: Kamlet Mortimer J. , Jacobs S. J.
Published: February 2004

Detonation pressures of C–H–N–O explosives at initial densities above 1.0 g/cc may be calculated by means of the simple empirical equation P = Kρ02φ, K = 15.58, φ = NM1 / 2Q1 / 2, detonation velocities by the equation D = Aφ1 / 2(1 + Bρ0), A = 1.01, B = 1.30. N is the number of moles of gaseous detonation products per gram of explosive, M is the average weight of these gases, Q is the chemical energy of the detonation reaction ( − ΔH0per gram), and ρ0 is the initial density. Values of N, M, and Q may be estimated from the H2O–CO2 arbitrary decomposition assumption, so that the calculations require no other imput information than the explosive's elemental composition, heat of formation, and loading density. Detonation pressures derived in this manner correspond quite closely to values predicted by a computer code known as RUBY, which employs the most recent parameters and covolume factors with the Kistiakowsky-Wilson equation of state.
He–He Interaction in the SCF–MO Approximation
Authors: Kestner Neil R.
Published: February 2004

The interaction of the two helium atoms between 1 and 6a0 has been calculated using the homonuclear diatomic SCF program of the Laboratory of Molecular Structure and Spectra at the University of Chicago. Adequate results are obtained when the basis set consists of three s-type and one p-type atomic functions on each center. The Hartree-Fock energy of the He2 system is always greater than that of two helium atoms.
Monte Carlo Calculations for Hard Disks in the Isothermal-Isobaric Ensemble
Authors: Wood W. W.
Published: February 2004

The N p T ensemble for hard disks is formulated as an equivalent N V T ensemble for a pseudopotential interaction in a reduced configuration space, with exact relations for small periodic systems emphasized. The Monte Carlo method originally devised by Metropolis et al. is then adapted to the calculation of the equation of state and radial distribution function. The present paper then describes some results obtained for a small system (12 hard disks), as an example of the method, and with emphasis upon the statistical reliability of the results and on the effect of different pseudorandom-number-generating procedures. At least for such small systems it is possible to obtain, as a byproduct, the N V T -ensemble equation of state over a range of densities from an N p T -ensemble calculation at a single pressure. Subsequent papers will describe results already in hand for larger systems, including reasonably reliable extrapolations to the “thermodynamic” limit.
Chemistry of Detonations. III. Evaluation of the Simplified Calculational Method for Chapman-Jouguet Detonation Pressures on the Basis of Available Experimental Information
Authors: Kamlet Mortimer J. , Dickinson Charles
Published: February 2004

It is shown that the simplified calculational scheme discussed in Parts I and II of this series accomodates the total body of inexact and often self-contradictory experimental information almost as well as might reasonably be expected of any computational method. Some possibly systematic discrepancies in the reported experimental C-J pressures are discussed on the basis of methods used to carry out and interpret the measurements in the various laboratories.
Uniform Semiclassical Approximations for Elastic Scattering and Eigenvalue Problems
Authors: Miller William H.
Published: February 2004

The uniform semiclassical wavefunction of Langer is used to obtain a modified quantum condition. The result [contained in Eqs. (1) and (2)] has the integral quantum numbers replaced by known, nonintegral constants and gives considerably better results for the example of the quartic oscillator. An approximation for the Franck-Condon factor is obtained which is qualitatively correct for all values of the parameters involved. The result, contained in Eqs. (4) and (5), reduces to the known semiclassical results in the appropriate regions and is uniformly valid in the transition regions. The method used by Carrier for evaluating integrals by the method of stationary phase in the case of more than one point of stationary phase is used to extend the semiclassical scattering amplitude of Ford and Wheeler to include the glory and rainbow regions uniformly. The result is contained in Eq. (6) of the text.
Magnetic and Crystallographic Characteristics of Praseodymium Hydrides
Authors: Wallace W. E. , Mader K. H.
Published: February 2004

The susceptibilities (χ) and lattice parameters are reported for a series of praseodymium hydrides represented by the formula PrHx in which x varies from 0.99 to 2.57. χ was measured from 4° to 300° and at field strengths up to 21 kOe. The samples are two-phase for x ≤ 1.85. Curie–Weiss behavior is observed for all samples above 100°K with slopes in fairly good agreement with that expected for an assemblage of free tripositive ions. Deviations occur below 100°K. These are two kinds—negative for x < 2.1, and positive for x > 2.1. The deviations in the first case are small and appear to result from the crystal-field interaction. The positive deviations are ascribed to a change of valence for Pr from 3 + to 4 +. Magnetic, electrical, and crystallographic evidence is in accord with this postulate. There is no indication of magnetic ordering in the hydrides at 4.2°K.
Yield of Solvated Electrons in the γ Radiolysis of Water + 10% Ethanol: Nonhomogeneous Kinetics of Electron Scavenging in Water
Authors: Russell J. C. , Freeman G. R.
Published: February 2004

The effect of nitrous oxide concentration over a very wide range, and at low dose, on the radiolysis of the system water + 10% ethanol has been investigated. At very high concentrations G(N2) = 4.0 compared to approximately 2.7 between 10−4 and 10−2M nitrous oxide. The results are discussed in terms of a nonhomogeneous kinetics model for the scavenging of solvated electrons, with G (total ionization) = 4.0. The free ion yield is G(esolv−)fi = 2.7. These values apply to both the present system and to pure water. The wide variation in previously reported values of G(eaq−) is understandable in terms of the present model. The previously published model for charge scavenging in liquids [J. Chem. Phys. 46, 2822 (1967) ] has been moderately successful in describing charge scavenging in the γ radiolysis of hydrocarbons, alcohols, and water. This emphasizes the earlier suggestion that the behavior of extra electrons in nonpolar and polar liquids differs in degree but not in kind.
Visible Afterglow Emission of Krypton
Authors: Turner R. , Riccius H. D.
Published: February 2004

The early afterglow from a pulsed discharge in krypton has been investigated in the visible region of the spectrum. Measurements on the decay of atomic and molecular emission have been made in both diffuse and constricted discharges. The pressure dependence of the observed exponential decays indicates that a two-body collision process controls the early afterglow lifetime. A collision-induced vibrational relaxation of the krypton molecular ion is proposed as the dominant two-body process. The coefficient for this process is 9.0(±0.5) × 102p, leading to a cross section for vibrational relaxation of 1.4(±0.07) × 10− 18 cm2.
Interstitial Conduction in BaF2 Crystals
Authors: Barsis E. , Taylor A.
Published: February 2004

The behavior of the F− interstitial in BaF2 crystals has been examined using ionic-conductivity measurements on BaF2 crystals doped with various amounts of GdF3. The interstitial mobility was found to be μ = (4 × 103 / T) exp(−0.79 ± 0.03 / kT), and the association energy between the Gd3+ ion and the interstitial was 0.44 ± 0.04 eV. Very similar results were obtained for BaF2 doped with monovalents halides. A detailed comparison between the present work, dielectric and anelastic loss measurements, and NMR studies has been made.
Generalized Theory of Nucleation Kinetics. I. General Formulations
Authors: Ziabicki Andrzej
Published: February 2004

The classical nucleation theory by Frenkel–Turnbull-Fisher is extended to describe, in a unique formal treatment, formation of anisodiametric and anisotropic nuclei in isothermal and nonisothermal conditions. Based on the theory of absolute reaction rates the differential equation for the distribution of clusters dimensions is derived. The expressions for concentration of nuclei, thermal, and athermal, nucleation rates are formulated in general terms.
Absorption Spectrum of Manganese Acetate Tetrahydrate
Authors: Mehra Anjani , Venkateswarlu Putcha
Published: February 2004

The absorption spectrum of Mn(CH3COO)2·4H2O has been studied at 300° and 77°K. The band positions have been fitted in terms of the parameters B, C, Dq, and α, and the values of the parameters obtained for the 300°K spectrum are 820, 3000, 760, and 76 cm−1, respectively. There are two types of Mn2+ sites in the crystal and the expected features of the fine-structure lines arising from the two types of ions in the 77°K spectrum are discussed.
Electronic Quenching and the Rotational Relaxation Rate of OH*(2Σ+) Produced by the Vacuum-Ultraviolet Photodecomposition of Water
Authors: Kaneko Motohisa , Mori Yuji , Tanaka Ikuzo
Published: February 2004

The quenching of fluorescence and the rotational relaxation of OH radicals in the electronically excited state (2Σ+) have been measured in the presence of foreign gases such as H2, D2, N2, CO, and He. The electronically excited state (2Σ+) of OH radicals has been produced by the photodecomposition of water vapor with a 1236-Å Kr resonance line. The intensity of the fluorescence of OH*(2Σ+) has been measured in the (0, 0) band. With the collision partner H2O or CO, a single collision is enough for the electronic quenching, and for other molecules, only a few collisions are sufficient. These phenomena have been explained by the long-range chemical force between OH*(2Σ+) and foreign gases. The rotational relaxation of OH*(2Σ+) has been measured from the intensity change of K = 20 of (0, 0) band. In OH–diatomic-molecule systems, the cross section is the largest for the collisions with H2 and about the same order of magnitude for those with D2, N2, and CO. This can be explained by the simple classical model.
Electric Dipole Moment of Carbonyl Sulfide
Authors: Muenter John S.
Published: February 2004

The electric dipole moment of OCS has been determined by measuring pure Stark transitions with molecular-beam electric resonance methods. The value obtained is 0.71521 ± 0.00020 D, which is in disagreement with a previous measurement of 0.7124 ± 0.0002 D.
Electron Spin Resonance of the Organic Semiconductor, α-Copper Phthalocyanine
Authors: Abkowitz Martin , Chen Inan , Sharp James H.
Published: February 2004

Various concentrations of polycrystalline powders of α-copper phthalocyanine diluted in nonparamagnetic α-metal-free phthalocyanine matrices have been studied by 8-mm ESR at room temperature. The superhyperfine (SHF) spin Hamiltonian used in analyzing earlier results of ESR investigations on square-bonded copper complexes has been reconsidered and a new SHF term is derived. The concentration-dependent study has revealed enough separate features to enable observations to be interpreted by essentially considering the contributions of only two molecular orientations to the over-all derivative line shape. Although single crystals of many organo-metallic complexes, including α-copper phthalocyanine, are not available, this study indicates that the relevant parameters of the spin Hamiltonian can in some cases be readily deduced from polycrystalline spectra.
Study of “Non-Fickian” Diffusion Anomalies through Time Lags. III. Simple Distance-Dependent Anomalies in Microporous Media
Authors: Petropoulos J. H. , Roussis P. P.
Published: February 2004

The time-lag treatment developed in Paper II is here applied to a microporous medium with porosity varying with position in the direction of flow. It is assumed that diffusion in such a medium can occur in both pore and adsorbed phases without sensible disturbance of the adsorption equilibrium and that the relevant diffusion and distribution coefficients are constant. The case of gaseous Knudsen diffusion through microporous powder compacts formed by uniaxial compression is then considered in some detail. It is found that the time-lag anomalies, which characterize many experimental systems of this kind, can plausibly be ascribed in large part to distance-dependent “non-Fickian” diffusion behavior and interpreted qualitatively or semiquantitatively in terms of the present treatment.
Quantum-Mechanical Calculations of the Inelastic Cross Sections for Rotational Excitation of Para and Ortho H2 upon Collision with He
Authors: Johnson B. Robert , Secrest Don
Published: February 2004

Using the method of amplitude densities, we derive the equations for computing the scattering T matrix in the total-angular-momentum representation. We also show that in the appropriate limit this method reduces to a first-order differential equation for the T matrix. In an Appendix a similar discussion is presented for the reaction matrix. Using the T-matrix approach, we have obtained numerical solutions to the helium-atom–hydrogen-molecule scattering problem in both the close-coupling and distorted-wave approximations. Cross sections were computed for the J = 0 to J = 2 transitions in parahydrogen and the J = 1 to J = 3 transition in orthohydrogen. These results were calculated using both an interaction potential computed by Roberts and a potential computed by Krauss and Mies. The close-coupling and distorted-wave results are compared, and it is found that, in general, the distorted-wave cross sections are about 20% too high when Roberts potential is used and are about 10% too high when the less anisotropic Krauss and Mies potential is used.
Electron Spin Resonance Study of the Pairing Theorem for Alternant Hydrocarbons. II. 13C Hyperfine Splittings in the Positive and Negative Ions of Biphenylene
Authors: Hindle Peter R. , Veiga Jorge dos Santos , Bolton James R.
Published: February 2004

The pairing theorem predicts that for alternant hydrocarbon radical ions, the spin densities at corresponding positions should be the same. Although proton hyperfine splittings do show significant differences, the 13C splittings appear to be more analogous, at least for the anthracene ions. The biphenylene ions are unusual in that one of the proton hyperfine splittings shows an anomalous variation. It is thus of interest to see whether this variation is due to a breakdown of the pairing theorem or to an anomalous variation in the sigma–pi parameter QCHH. Two of the three 13C splittings were obtained in both the negative and positive ions of biphenylene. Signs and assignments were obtained on the basis of linewidth variations. The 13C splittings at corresponding positions were found to be almost identical. This result seems to imply that the anomalous variation in the proton hyperfine splittings is due to a change in QCHH and not to a redistribution of the spin densities.
Variational Upper and Lower Bounds on the Dynamic Polarizability at Imaginary Frequencies
Authors: Epstein Saul T.
Published: February 2004

Variational upper and lower bounds are derived for the dynamic polarizability at imaginary frequencies, and some theoretical applications are given.
Matrix-Isolation Study of the Reaction of F2 and of F Atoms with NCN. The Infrared Spectra of the Species NF2CN and FNCN
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

NCN, produced by the photolysis of cyanogen azide isolated in an Ar matrix at 14°K, has been found to react readily with F2 also present in the system, leading to the stabilization of NF2CN. The absorption patterns observed for the most prominent infrared absorptions of NF213CN and of the two singly 15N-substituted difluorocyanamides are consistent with the previous vibrational assignment. When both NCN and F atoms are present in appreciable concentration, absorptions appear at 873 and at 2068 cm−1 which may be tentatively assigned to the FNCN free radical. Upon prolonged photolysis, incompletely characterized products of more extensive fluorination reactions are observed.
Study of Some Electronic Transition Probabilities in CO and CN
Authors: Moore John H. , Robinson Dean W.
Published: February 2004

The transition probabilities of the CO third positive (b 3Σ→a 3II), the CO Ångstrom (B 1Σ+→A 1II), and the CN violet (B 2Σ+→X 2Σ+) systems have been obtained from measurements of radiative lifetimes by the phase-shift method. In the CO Ångstrom system the probability of B 1Σ+→A 1II was distinguished from the (greater) probability for B 1Σ+→X 1Σ+ by taking advantage of reabsorption (or resonance trapping) of the shorter wavelength radiation. In the CN (B 2Σ+→X 2Σ+) transition there is found to be no measurable dependence of the electronic transition moment on internuclear distance.
NMR Studies of Aqueous Electrolyte Solutions. II. Hydration of Al(NO3)3 Determined from Temperature Effects on Proton Shift
Authors: Malinowski Edmund R. , Knapp Paul S.
Published: February 2004

Proton shifts of aqueous Al(NO3)3 solutions are measured as a function of temperature and concentration. Using a two-state model which is applicable to dilute solutions, the total hydration of Al(NO3)3 is found to be 13.4. Two explanations of this value are postulated: (1) Each of the six water molecules in the primary layer of the aluminum ion are bound to two molecules of the secondary layer, with nitrate ions replacing some secondary water molecules; (2) The aluminum ion is hydrated to six water molecules whereas each nitrate ion is hydrated to two or three water molecules.
NMR Subspectral Analysis Applied to Polyfluorobenzenes C6HnF6–n. II. 1,2,3,4-Tetrafluorobenzene
Authors: Lustig Ernest , Duy Nicholas , Diehl Peter , Kellerhals Hanspeter
Published: February 2004

The nuclear magnetic resonance spectrum (1H and 19F) of 1,2,3,4-tetrafluorobenzene is described. Subspectral analysis is applied to this AA′MM′XX′ system, and the direct method of analysis is used for the part of the spectrum that cannot easily be expressed in closed form because of the two 4 × 4 Hamiltonian matrices. The magnitudes of the coupling constants fall within ranges of these known for similar molecules. The simultaneous appearance of JFF's ortho and a JHH ortho makes it possible to establish firmly that these two types of J's have opposite sign.
Localized Saturation Effects in Nuclear Magnetic Double Resonance
Authors: Freeman R. , Gestblom B.
Published: February 2004

In a high-resolution nuclear magnetic resonance spectrum where the dominant line-broadening influence is the spatial inhomogeneity of the magnetic field, it is possible to impose a sufficiently weak rf field (H2) on a given line ωpq such that saturation is localized in a restricted region of the sample volume. This has been called “burning a hole” in the line. When a second line ωqr that is regressively connected to ωpq is examined in a double resonance experiment, a similar hole appears in an exactly corresponding region of the line profile, due to the disturbance of the spin population on the common level q. This correlation, which arises from the intramolecular nature of the coupling, forms the basis of a technique for measuring frequency separations with a precision that is not primarily limited by the inhomogeneous linewidth. Experimental evidence suggests a reliability of ±1 mHz. The persistence of this effect down to rf levels as low as γH2 / 2π = 0.005 Hz distinguishes it from the well-known coherence effect of the irradiation field (“spin tickling”). The technique has been employed to detect the small displacements of the lines of a complex spectrum attributable to the presence of the two radiofrequency fields H1 and H2—the indirect Bloch–Siegert shifts. The transition frequencies of a complex three-spin system (2-chlorothiophene) have been measured by an extension of this double resonance method in order to provide a test case for the iterative analysis programs marip and laocoon. Experimental and calculated transition frequencies agree within a mean deviation of 0.0008 Hz.
Formation of Excited States in the Nanosecond-Pulse Radiolysis of Solutions of Benzene and Toluene
Authors: Cooper R. , Thomas J. K.
Published: February 2004

Short-lived species have been observed via absorption in the 5000-Å region and fluorescence below 4000 Å in the nanosecond-pulse radiolysis of benzene and toluene. The decay of the absorption and fluorescence is first order with t1/2 = 18.2 ± 1.5 nsec in benzene and t1/2 = 21.6 ± 1.5 nsec in toluene. In benzene we assign the fluorescence and absorption at 5150 Å to the B2u1> state. Solutions of biphenyl in benzene and toluene show only a low yield of negative and positive ions (∼0.1), while solutions of naphthalene, anthracene, and biacetyl show large yields (G = 3–4) of triplet states. Naphthalene and anthracene quench the B2u1 of benzene, while at the same time, the characteristic fluorescence of naphthalene and anthracene are observed. The triplet states of these molecules are derived from the B2u1 and triplet 3B state of benzene, the latter state having a t1/2 ∼ 20 nsec. By using piperylene to preferentially scavenge triplet states in naphthalene–benzene solutions, the following G values are measured: G(1B2u) = 1.62 ± 0.28 and G(3B) = 1.85 ± 0.3. Ionic scavengers such as methanol, nitrous oxide, and cyclohexene reduce the yield of the B2u1 state, while the t1/2 remains unaffected. It is concluded that this state is derived from ion recombination, along with the triplet state. The yield of anthracene triplet is larger than naphthalene triplet, and from the effect of ionic scavengers and xenon on these solutions, it is concluded that the difference is due to a higher singlet state of benzene. This higher singlet, which may be the E1u1 state formed directly by the secondary electrons, is scavenged by anthracene but not by naphthalene.
Diffusion and Heterogeneous Reaction. X. Diffusion Coefficient Measurements of Atomic Oxygen through Various Gases
Authors: Yolles Robert S. , Wise Henry
Published: February 2004

Steady-state and time-transient measurements of the decay of oxygen atoms in a cylinder with catalytic walls have been used to determine the diffusion coefficient of atomic oxygen in O2, He, Ar, and Kr. The relative change in atom density as a function of distance (under steady-state conditions) and time (after the atom source is shut off) was followed by observing the luminescence associated with the reaction of oxygen atoms with nitric oxide. The diffusion coefficients at 298°K and 1 atm were found to be: Do−o2 = 0.27; Do−He = 0.73; Do−Ar = 0.39; Do−Kr = 0.16 cm2sec−1.
ESR Studies of Lithium Borate Glasses and Compounds γ Irradiated at 77°K: Evidence for a New Interpretation of the Trapped-Hole Centers Associated with Boron
Authors: Griscom D. L. , Taylor P. C. , Ware D. A. , Bray P. J.
Published: February 2004

Five glasses and four polycrystalline compounds of the lithium borate system have been subjected to γ irradiation at 77°K and subsequently examined by ESR techniques at 9.1 and 35 GHz while maintaining this low temperature. The familiar “five-line-plus-a-shoulder” spectrum is observed at X band for both the Li2O·4B2O3 compound and the glasses containing ≲25 mole % Li2O. However, previously unreported structure is noted on the low-field shoulder of the spectrum for the compound. This new structure, like the “five-line” part, is due to a hyperfine interaction with boron. An entirely new spin Hamiltonian having orthorhombic symmetry is proposed to account for the over-all spectrum and is substantiated by successful computer simulations of the experimental line shapes. The spectra observed in the glasses of both low and high lithium oxide contents are also simulated by computer, under the assumption that the ensembles of centers induced in the glasses are characterized by substantial spreads or distributions in certain spin-Hamiltonian parameters. Aside from these distributions, the centers in the low-alkali-oxide glasses are qualitatively the same as those encountered in crystalline Li2O·4B2O3. There are at least two inequivalent paramagnetic sites in the latter material: for site I the parameters are found to be A1 = 12.2 G, A2 = 14.4 G, A3 ≈ 7 G, g1 = 2.002, g2 = 2.010, and g3 ≈ 2.035, with the other site(s) differing principally in the values of g3 and A3. Analyses of the g and hyperfine tensors for site I show the unpaired spin to be located in a boron–oxygen π system; the hyperfine interaction is with a three-coordinated boron and the oxygen is one that is shared between the latter boron and a boron in four coordination. Most of the centers exhibiting boron hyperfine structure which are observed in alkali borate materials are probably of this same fundamental nature.
Electron Paramagnetic Resonance Studies of Transient Free Radicals Produced by Pulse Radiolysis
Authors: Smaller B. , Remko J. R. , Avery E. C.
Published: February 2004

Electron paramagnetic studies have been conducted on the transient free radicals produced by pulse radiolysis in liquids. The instrument design permitted observation of radical lifetimes ≥2 − 3 μsec and corresponding rate constants ≤1010M − 1·sec − 1. The effect of radical scavengers such as sulfur-containing compounds or oxygen on the transient behavior of the cyclopentyl and cyclohexyl radical were studied and the pertinent rate constants determined for the reaction. Recombination rate constants for cycloalkyl as well as alkyl- and cycloalkyl-peroxy radicals were compared along with the activation energy for representative species.
Studies on the Paramagnetism of Sulfur-Coordinated Copper Diethyldithiocarbamate
Authors: Pal A. K. , Mitra S. N. , Sengupta P.
Published: February 2004

EPR studies in the K band and measurements of magnetic anisotropy and susceptibility in the temperature range 90°–300°K on single crystals of sulfur-coordinated copper diethyldithiocarbamate are reported. The results have been correlated with x-ray, optical-absorption, and EPR (in the X band) studies of previous workers on the basis of molecular-orbital theory with the ligand-field approximation. The appreciable departure of the orbital reduction factors from unity indicates strong covalent binding of the sulfur ligands with the central Cu(II) ion. Further, it is suggested that a superexchange type of interaction might be responsible for the considerable reduction in anisotropy of the Cu(II) complex and the nearly isotropic reduction of orbital moment.
Absorption and Phosphorescence Spectrum of Matrix-Isolated Ferrocene
Authors: Smith J. J. , Meyer Beat
Published: February 2004

The absorption and fluorescence spectrum of ferrocene was studied in argon, krypton, xenon, nitrogen, and methane matrices at 20°K. Five electronic transitions were found in the region from 50 000–16 000 cm−1. The absorption bands appear sharper and the band structure simpler than in the vapor phase or solution. A weak but distinct phosphorescence spectrum was recorded, the lifetime of which varied between 1 and 4 sec in different matrices.
Translation–Rotation Paradox in the Theory of Nucleation
Authors: Reiss H. , Katz J. L. , Cohen E. R.
Published: February 2004

A detailed examination of the translation–rotation paradox in the theory of nucleation is presented. An earlier conclusion, due to Reiss and Katz, that the paradox is associated with the neglect of the fluctuation of the center of mass of a liquid-drop nucleus is reaffirmed. Transformations of coordinates are performed quantitatively in order to demonstrate this fact. Furthermore, the fluctuation of the center of mass is computed for a lattice model. A new factor not appearing in the classical theory of nucleation appears, but it is much smaller than the factor introduced by Lothe and Pound and only becomes important for large nuclei.
Electron Spin Resonance of the Monodeuterotropenyl Radical. Effect of the Deuterium Substituent
Authors: Volland Walter V. , Vincow Gershon
Published: February 2004

Monodeuterotropenyl radical, C7H6D·, is generated by thermal cleavage of liquid x,x′-dideuterobitropenyl (x,x′-dideutero-bi-2,4,6-cycloheptatrien-1-yl) and is investigated by means of electron spin resonance (ESR) spectroscopy. The major goal of this work is an assessment of the effect of the deuterium substituent on the vibronic near degeneracy of this radical. The ESR spectrum of C7H6D· appears to correspond to hyperfine interaction with six equivalent protons and one deuteron. The expected inequivalence of the proton splittings is less than the linewidth. From a detailed analysis of the magnitude of the linewidth, an upper limit of 25 cal/mole is estimated for the energy separation between the nearly degenerate vibronic levels of C7H6D·. This estimate is compared with the energy splitting of C6H5D− and is correlated with the prediction of the resonance integral perturbation model for the effect of a deuterium substituent [J. Am. Chem. Soc. 87 5260 (1965)]. The proton and deuteron hyperfine splittings are measured as a function of temperature (130 ≤ t ≤ 186°C). The temperature dependence of the proton splitting agrees closely with that of C7H7·. The ratio aH / aD decreases with increasing temperature and is most likely greater than 6.514. The g value, 2.00266, is in agreement with that of C7H7·. A small positive temperature coefficient is indicated by the g-value data.
Raman Intensity Study of Charge-Transfer Complexes of ICN
Authors: Bahnick Donald A. , Person Willis B.
Published: February 2004

Solution measurements have been made of the Raman intensity changes occurring in the fundamental stretching vibrations of the pseudohalogen ICN upon forming charge-transfer complexes with tetrahydrofuran (THF) and with benzene. For both complexes the Raman intensity of the C–I stretching mode of ICN increases by approximately 60%, and that of the C–N stretching mode decreases by approximately 20% to 30% from the free ICN species in methylene chloride. In the case of the THF–ICN complex the formation constant for the one-to-one complex was computed from the change in the Raman spectrum with concentration. A supplementary ultraviolet absorption study of the same system verifies the magnitude of the constant calculated from the Raman spectrum. The observed intensity changes of ICN are interpreted in terms of changes in the bond polarizability derivatives of the C–I and C–N bonds from the free to the complexed ICN species. These calculations are carried out using the computed normal coordinates, the measured Raman intensities and measured depolarization ratios for ν1 and ν3 of free and complexed ICN, and zero-order bond-polarizability theory.
Magnetic Circular Dichroism of Charge-Transfer Transitions: Low-Spin d5 Hexahalide Complexes
Authors: Henning G. N. , McCaffery A. J. , Schatz P. N. , Stephens P. J.
Published: February 2004

The magnetic circular dichroism (MCD) of IrCl62−, IrBr62−, and RuBr63− have been measured through the visible and near ultraviolet. Analysis leads to new assignments of the ligand-to-metal (t2g) charge-transfer bands. In particular, the conventional order of the first two allowed charge-transfer states is reversed so that the 2T1u state lies at lower energy than 2T2u.
Shock-Tube Study of OH Chemiluminescence in the Hydrogen–Oxygen Reaction
Authors: Gutman David , Lutz Robert W. , Jacobs Norman F. , Hardwidge Edward A. , Schott Garry L.
Published: February 2004

The exponential growth of OH*(2Σ+→2π) chemiluminescence was monitored during the induction period of the H2–O2 reaction in mixtures with [H2] / [O2] = 0.33 between 950° and 1150°K and at total gas densities between 0.50 and 1.1 × 10−2 moles/liter. An end-on technique with reflected shock waves provided the required sensitivity. The exponential growth constant for OH* emission was found to be a factor of 2 (2.07 ± 0.17) greater than that found for O–CO emission over the same range of conditions. This result shows that OH* is formed in a reaction between two products of the chain reaction and, together with other recent evidence, indicates that the reaction is H + O + (M)→OH* + (M). The use of OH* emission to study other combustion reactions is discussed.
Low-Energy Electron Diffraction Studies of Uranium Dioxide
Authors: Ellis W. P.
Published: February 2004

The (110), (111), and (100) surfaces of uranium dioxide have been studied by low-energy electron diffraction. Below 600°C the (110) face displays persistent fractional-order beams characteristic of contamination, and at higher temperatures in vacuum thermal faceting occurs. The (111) surface interacts with O2 at room temperature to produce rings around the integral-order beams, and if this surface is mechanically disrupted, fractional-order arrays are formed in the interval 200°–390°C. For UO2 + x (111) at all temperatures the most characteristic diffraction features are also rings around the integral-order reflections; fractional-order beams are observed from UO2 + x (111) only if the surface is disrupted. It is postulated that rings display a disordered U4O9 substructure which consists of clusters of two or three adjacent atoms occupying regular lattice sites, but separated from neighboring clusters by approximately three lattice spacings; it is further postulated that surface discontinuities act as sources of mobile species which migrate across the surface and in the presence of oxygen condense out as higher oxides in fractional arrays. The (100) surface is stable with respect to faceting up to at least 1600°C SBT, and apparently does not react with O2 to produce rings or fractional-order beams in the diffraction pattern.
Theory of Angular and Polarization Correlation in Tandem Two-Photon Processes: Application to Photoselection
Authors: Chiu Ying-Nan
Published: February 2004

To facilitate the interpretation of photoselection and photochemical experiments that depend on light intensity, generalized intensity distribution and polarization correlation formulas are derived. These are expressed in terms of Euler angles and multipole transition moments taking into account (1) molecular multipole radiation up to any order, inclusive of their coherent interference, (2) angular distribution of radiation for a given polarization, (3) application to molecules of arbitrary point-group symmetry, (4) arbitrary orientation of the second photon (pertaining to the daughter molecule) with respect to the first photon (pertaining to the parent molecule). For application to oriented molecular systems, examples of the angular characteristics of multipole moments responsible for a fixed polarization, are given up to quadrupole, inclusive of interference effects. It is emphasized that, in contrast to electric dipole radiation where the polarization is unique, for multipole radiation, both polarization and propagation directions must be specified, and that the commonly known dipole or quadrupole intensity which come from space average must be used with caution. For random molecular systems, the space average of the product of intensities for the two tandem and physically distinct one-photon processes are shown to contain “cross” terms, which otherwise vanish, if the space average of intensity were taken independently for the first (parent) and the second photon (daughter molecule). The cross terms are shown to be the consequence of the definition of light intensity for an arbitrary choice of the molecular coordinate system (vs the choice of the principal coordinate system) and of using the same coordinate system for the parent and the daughter molecule. In the space average over the product of four rotation matrices (vs four direction cosines for dipole radiation), use was made of the Clebsch–Gordan series for the coupling among these rotational transformation matrices. The intensity (or probability) products of the two tandem and distinct one-photon processes were then obtained as functions of bipolar harmonics of the transition moments. The coupling of these bipolar harmonics, in turn, gives rise to the polarization correlation between the parent and the daughter molecule. Specific examples, up to electric and magnetic quadrupole, are given for viewing the daughter molecule in directions parallel as well as perpendicular to the incident (first) photon. Also given are the cases of the two photons being in different radiation modes and of different wavelengths.
Optical Properties of Polystyrene Films in the Far Ultraviolet
Authors: Buck Warren L. , Thomas Bruce R. , Weinreb Arye
Published: February 2004

Measurements of the optical properties of solid polystyrene in the wavelength range 1100-2300 Å are reported. The real and imaginary parts of the complex index of refraction were determined from transmission measurements on a series of thin films. The absorption spectrum shows a strong peak at 1925 Å plus minor features around 1350 and 2170 Å as well as evidence for a second major peak below 1100 Å. The measured values of the optical constants were used to calculate the complex dielectric constant and the characteristic electron energy-loss function. The latter exhibits a maximum at 6.92 eV which appears to arise primarily from collective excitation effects.
Vapor Species of the Barium-Oxygen System
Authors: Newbury Ray S. , Barton George W. , Searcy Alan W.
Published: February 2004

Mass-spectrometric and vacuum-thermobalance studies of barium oxide between 1365° and 1917°K yield for the equilibrium pressure of BaO gas, logPatm = − 22610 / T + 7.90.

The enthalpy for the reaction BaO(a) = BaO(g) was calculated to be ΔH°298 = 110.9 ± 2.8 kcal / mole by the second-law method. The third-law date are consistent with this value if a 3Π state is assumed to be at or near (within a few hundred cm−1) the ground state of BaO(g).

The heat of sublimation of the dimer Ba2O2(g) was found from the mass-spectrometer study to be about 142 kcal/mole and the heat of the reaction BaO(g) + Ba(g) = Ba2O(g) was found to be − 73 ± 15 kcal/mole at 1800°K. No reaction of barium oxide at 1800°K with O2(g) at pressures up to 10−3 atm was detected.
Uniform Localization of Atomic and Molecular Orbitals. II
Authors: Magnasco V. , Perico A.
Published: February 2004

Uniformly localized molecular orbitals (LMO's) have been obtained from one-determinant wavefunctions of minimal-basis-set LCAO-SCF-MO's for CH4, NH3, H2O, H2CO, HCN, C2H6, C2H4, C2H2, and B2H6. The localization criterion is based on the simultaneous maximization in all the available (doubly filled) orbitals of local electron populations which are required be to localized around atoms or between pairs (sometimes triplets) of atoms in the molecule. The well-defined inner shell, lone pair, and localized bond orbitals resulting for polyatomic molecules appear to fit well into the usual concepts of conventional chemistry. As in the case of diatomics discussed in a previous publication, the uniformly localized orbitals obtained in the present paper prove to be very close to the corresponding LMO's resulting from the rather cumbersome method of maximizing the sum of the orbital self-repulsion energies.
Microwave Spectrum, Barrier to Internal Rotation, Dipole Moment, and Structure of Trifluoromethylphosphine
Authors: Wang Irene Y. M. , Britt Chester O. , Cowley Alan H. , Boggs James E.
Published: February 2004

The microwave spectra of CF3PH2, CF3PHD, and CF3PD2 have been observed and analyzed. The barrier to internal rotation is 2360 ± 80 cal/mole, approximately 400 cal/mole higher than the barrier in CH3PH2. The dipole-moment components are μa = 1.77 ± 0.01 D, μc = 0.74 ± 0.03 D, and μtotal = 1.92 ± 0.02 D. The structural parameters are rC−P = 1.900 ± 0.006 Å, rP−H = 1.43 ± 0.08 Å, ∠FCF = 108.0 ± 0.4°, ∠CPH 91.9 ± 1.9°, and ∠HPH = 96.7 ± 1.8°. Compared with CH3PH2, the C-P bond is significantly longer, ∠CPH is smaller, and ∠HPH is larger.
Electron Correlation Models for Optical Activity
Authors: Höhn E. G. , Weigang O. E.
Published: February 2004

A two-system no-overlap model for rotatory strength is developed for electric-dipole forbidden as well as allowed transitions. General equations which allow for full utilization of symmetry in the chromophore and in the environment are obtained. The electron correlation terms are developed in full detail for an (1A2←1A1(C2υ) transition of a chromophore interacting with a nonpolar anisotropic perturber. It ensues that perturber anisotropy of polarizability makes substantial contributions even in such zero-order forbidden transitions. The correlation terms for a strong electric-dipole allowed transition (1A1←1A1) of the same chromophore gives sector rules that are decidedly different. An additive calculational scheme for the n − π* transition rotatory strengths of ketones shows the anisotropy effect to substantially modify, indeed sometimes become larger than, the simple octant rule behavior which occurs for isotropic perturbers. Since agreement with experimental rotatory strengths is correct in magnitude and sign and follows closely the observed variations, it appears that electron correlation is an important if not dominant perturbation mechanism for nonpolar substituents. An experimental prototype of the incomplete-screening-of-nuclei perturbation is considered which suggests that such a one-electron mechanism gives an incorrect sign of rotatory strength for the ketone back octants. The significance of the absolute signs associated with the octant rules of other chromophores are discussed.
Vibrational Spectra of Cyanuric Triazide
Authors: Shearer S. J. , Turrell G. C. , Bryant J. I. , Brooks R. L.
Published: February 2004

The infrared and Raman spectra of cyanuric triazide, C2N12, have been obtained using pure crystalline samples and CCl2 solutions. Twenty-three of the 26 vibrational fundamentals and a number of combination bands have been assigned. Some effects of the crystal symmetry have been considered in the factor-group approximation.
Molecular g-Value Tensor, the Molecular Susceptibility Tensor, and the Sign of the Electric Dipole Moment in Formaldehyde
Authors: Hüttner W. , Lo Mei-Kuo , Flygare W. H.
Published: February 2004

The diagonal elements in the molecular g-value and magnetic-susceptibility tensors in the principal inertial axis in formaldehyde have been determined by observing the molecular rotational Zeeman effect. A small J dependence was observed in the molecular g values where the absolute values increased with rotational excitation. The g values averaged over the three rotational states studied for each isotopic species are gaa = − 2.899 ± 0.002, gbb = − 0.2256 ± 0.0008, and gcc = − 0.1004 ± 0.0007 for H2CO, and gaa = − 1.445 ± 0.002, gbb = − 0.1917 ± 0.0005, and gcc = − 0.0788 ± 0.0004 for D2CO. The diagonal elements in the molecular magnetic-susceptibility tensor are χaa = − 6.2 ± 0.5, χbb = − 15.8 ± 0.4, and χcc = − 23.0 ± 0.4, all in units of 10−6erg/G2·mole. The sign of the electric dipole moment along the C-O bond in formaldehyde was determined to have +C-O− polarity from the isotope dependence in the above molecular g values. From the g values and the known structure of formaldehyde, the paramagnetic-susceptibility tensor elements can be calculated to be χaap = 29.5 ± 0.1, χbbp = 46.1 ± 0.5, and χccp = 47.7 ± 0.5, all in units of 10−6erg/G2·mole. These data, combined with our above experimental magnetic-susceptibility diagonal tensor elements give the experimental ground-state average values of the sums of squared Cartesian center-of-mass electronic coordinates. The results are 〈0 | Σixi2 | 0〉 = (3.2 ± 0.3) Å2, 〈0 | Σiyi2 | 0 = (5.2 ± 0.3) Å2, and 〈0 | Σizi2 | 0〉 = (11.4 ± 0.3) Å2. The z axis is along the O-C bond and the y axis is in the molecular plane. These new data are used to interpret the ground- and excited-state electronic structure of the formaldehyde molecule. The experimental information is also sufficient to determine the diagonal elements in the molecular quadrupole moment tensor.