bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Susceptibility, Anisotropy, and ESR Studies on Some Copper Dialkyldithiocarbamates
Authors: Gregson A. K. , Mitra S.
Published: February 2004

The method of measuring the magnetic anisotropy of single crystals is briefly described, and a suitable calibrant for this type of work is suggested. The magnetic anisotropy, average susceptibility, and g values have been measured on several Cu(II) N, N dialkyldithiocarbamates where the Cu ion has been shown to be in a square pyramidal environment. The magnetic anisotropy is very low, while the principal molecular susceptibilities (K‖ and K⊥) obey a Curie–Weiss Law with θ ≃ 10°K between 80°–300°K. The single crystal g values and the average moments are very close to the spin-only values. The linewidth of the diethyl and di-n-butyl derivatives shows an unusual narrowing which is partly attributed to an exchange interaction through the bridging sulfur atoms within the Cu dimer unit. The expressions for K‖ and K⊥ have been deduced, and the experimental data has been fitted. The ligand-field parameters are greatly reduced from their free-ion values, the spin–orbit coupling constant, the orbital reduction parameter, and the exchange integral being slightly anisotropic. The spin–Hamiltonian parameters of the Cu diethyldithiocarbamate diluted in the analogous Ni and Zn derivatives have been obtained and the stereochemical implications discussed. They have also been used in the discussion of the σ and π bonding in these compounds.
Calculation of the Electric Field Gradient at the Nucleus in H2+
Authors: Bishop David M.
Published: February 2004

The electric field gradient at either nucleus in H2+ is calculated from electronic wavefunctions which use two kinds of basis sets. One basis set is composed entirely of Gaussian-type functions and the other, the so-called improved set, includes an additional function of the form, χ = (ρ − r)l for r ≤ ρ, χ = 0 for r > ρ, centered on each nucleus, where r is the distance from the nucleus and ρ and l are parameters chosen to minimize the electronic energy. The purpose of this χ function is to improve the quality of the wavefunction near the nuclei. The effect of such a function on the electric field gradient at a nucleus is determined in this paper.
Some of the Parameters Affecting Knudsen Effusion. IV. Monte Carlo Calculations of Effusion Probabilities and Flux Gradients for Knudsen Cells
Authors: Ward John W. , Fraser Malcolm V.
Published: February 2004

Data are presented for effusion probabilities and cell-wall flux gradients calculated dynamically by means of Monte Carlo computer studies. Typical effusion cell dimensions were programmed for both knife-edged and Clausing orifices; all calculations apply to a flat sample. The influence of the size and the length-to-radius ratio of the orifice and the effects of different condensation coefficients are described. An analytical expression relating the equilibrium sample flux to the flux at steady state has been derived. It is shown that for a given cell design, the ratio of these fluxes is constant and independent of the nature of the vaporizing species. Because the Monte Carlo method requires no mathematical approximations or simplifying assumptions, results analogous to real cell behavior are to be expected. Comparison of these results with the treatment derived by Motzfeldt shows that his formula is applicable and quite accurate over a wide range of experimentally encountered conditions.
Phosphorescence and Triplet←Singlet Absorption Spectra of Benzophenone Crystal at 4.2°K
Authors: Udagawa Yasuo , Azumi Tohru , Ito Mitsuo , Nagakura Saburo
Published: February 2004

The phosphorescence spectrum of benzophenone crystal at 4.2° has been measured to determine whether or not pure molecular crystals phosphoresce. The comparison of its vibrational structure with the infrared and Raman spectra leads to the conclusion that the phosphorescence really comes from benzophenone, not from some chemical impurities. Furthermore, the triplet←singlet absorption has been observed with the benzophenone crystal at 4.2°K for the purpose of comparison with the emission spectrum. The 0–0 band of the phosphorescence has been found to be lower in energy by 81 cm−1 than that of the triplet←singlet absorption. The origin of the gap between the absorption and the emission is discussed in an effort to understand the mechanism of the phosphorescence in the crystalline state. Finally, the oscillator strength of triplet←singlet absorption is theoretically evaluated to be 1.74 × 10−7, in agreement with the experimentally estimated value of 3.2 × 10−7.
Emission and Decay of Liquid-Benzene and Naphthalene Derivatives Excited by Electron Impact
Authors: Christophorou L. G. , Abu-Zeid M-E. M. , Carter J. G.
Published: February 2004

Our earlier work on the emission from organic liquids excited by electron impact has been extended to a large number of liquid-benzene and naphthalene derivatives. In all cases the emission under intense electron impact is characteristic of excimers. A detailed comparison of the spectral characteristics of the electron-impact- and ultraviolet-induced emissions suggests that the emitting species for the organic liquids studied under electron impact are singlet-state excimers, 1M2*. In six benzene derivatives, in addition to the dominant emission attributed to 1M2*, a weaker emission band appeared at ∼500 nm which may be due to emission from triplet-state excimers, 3M2*. Measurements have been made also of the lifetimes of the emitting species under electron impact. The lifetimes (in nanoseconds) are 12.25 ± 0.2, 15.65 ± 0.2, 8.56 ± 0.1, 12.56 ± 0.2, 8.73 ± 0.1, 11.71 ± 0.14, 11.13 ± 0.24, 11.9 ± 0.3, and 22.86 ± 0.3 for benzene, toluene, ethylbenzene, n-propylbenzene, iso-propylbenzene, o-xylene, m-xylene, p-xylene, and mesitylene, respectively, and 68.67 ± 0.2, 25.39 ± 0.1, 48.45 ± 0.36, and 35.4 ± 1 for 1-methylnaphthalene, 2-ethylnaphthalene, 1,2-dimethylnaphthalene, and 1,6-dimethylnaphthalene, respectively. Our values for the lifetimes of benzene, toluene, and p-xylene are almost identical with those of 1M2* deduced from ultraviolet studies on these systems. This supports the spectroscopic result on the origin of the emission under electron impact and indicates that 1M2* is immune to ionization quenching, in contrast to the strong quenching of excited monomers 1M1*.
Raman Spectrum of a Crystalline Polyethylene
Authors: Frenzel Charles A. , Bradley Eugene B. , Mathur Maya S.
Published: February 2004

New data have been obtained for the Raman spectrum of a crystalline polyethylene and a detailed examination of the Raman spectrum is presented from 40 to 3000 cm−1. Raman bands correlating with neutron-scattering data are observed. The region of rotary and translational crystalline bands has been searched for bands correlating with calculated infrared-active crystal lattice modes.
Electrical Conductivity of Molten Mercuric–Mercurous Halide Systems
Authors: Grantham L. F.
Published: February 2004

The electrical conductivities of the molten HgCl2–Hg2Cl2 system and the molten HgI2–Hg2I2 system were measured from the liquidus temperature to approximately 600°C. In both systems the electrical conductivity increased orders of magnitude as the composition of Hg2X2 was increased. The initial “activation energy” for conduction decreased in the chloride system and increased in the iodide system as the concentration of Hg2X2 was increased. In contrast to the BiX3–BiX systems where semiconduction was found above 400°C, the results of this study suggest that little or no semiconduction occurs in these systems and that the conductivity increase is due to the dissolution of a conducting salt (Hg2X2) in a nonconducting solvent (HgX2).
Deuterium Isotope Effects on the Lifetime of the Phosphorescent Triplet State of Naphthalene
Authors: Watts Richard J. , Strickler S. J.
Published: February 2004

The effect of the number and position of deuterium substituents on the phosphorescence lifetime has been studied for eight different isotopic naphthalenes at 76°K. These studies reveal a significant dependence of the rate of radiationless decay to the ground state on the positions of the protons in the molecule. This conclusion is contrary to the conclusion of Lin and Bersohn that the radiationless decay is independent of the positions of the protons. It is found that protons in the α positions are about 1.6 times as effective as protons in the β positions in promoting radiationless transitions. A simple empirical relation is found to give a reasonable fit to the data. A small intermolecular isotope effect on the triplet-state lifetime of naphthalene-d8 in ethanol is also found upon deuteration of the solvent. The experimental results are discussed in terms of existing theories of radiationless processes.
Phenomenological Analysis of Reactive Scattering
Authors: Bernstein R. B. , Levine R. D.
Published: February 2004

An analysis of the angular distribution of elastic scattering concomitant with chemical reaction by means of an “opacity function” (reaction probability) is discussed. Computational results (i.e., differential elastic scattering cross sections) based on a partial wave expansion are presented for a model problem with various reasonable assumed forms of the opacity function pl. The semiclassical “inversion” procedure of Ross and Greene is tested and found to be of quite usable accuracy, except when pl has an abrupt “cutoff.” Such a sharp-edged opacity function is in any case an oversimplification, whose use can, moreover, lead to erroneous conclusions regarding the range of impact parameters b contributing to reaction. Proper account should be taken of the “diffuse” shape of pl or P(b) in the region of its decline. In the absence of a detailed understanding of the microscopic dynamics of the reaction, when the optical model is most advantageously employed, the phenomenological analysis of experimental scattering data in terms of an energy-dependent opacity function appears to be the optimum means of characterization of the reacting system.
Shock-Tube Study of Ionization of Titanium in Ti–Ar Mixtures
Authors: Boni A. A.
Published: February 2004

Time-resolved emission measurements were performed behind the reflected-shock region, on mixtures of TiBr4 and Ar, with TiBr4 mole fractions of about 1 × 10−4, for wavelengths corresponding to three Ti(I) and to three Ti(II) transitions. The temperature ranged from about 6500°–8500°K. The ionization occurred at nearly constant temperature. The intensity–time profiles for both Ti(I) and Ti(II) exhibited intermediate maxima. The observed data are consistent with a two-stage ionization process in which the rate-controlling step is excitation to intermediate energy levels of Ti(I). Further excitation and subsequent ionization occur rapidly, presumably because of close spacing of the upper energy levels.
ESR Study of VOF53− Ion
Authors: Manoharan P. T. , Rogers M. T.
Published: February 2004

Spin-Hamiltonian parameters for the VOF53− ion were determined from solution, frozen glass, powder, and single-crystal ESR spectra. The most important finding is the presence of superhyperfine splittings due to the equatorial and axial fluorine ligands; the strongest interaction is found to result from the in-plane π bonding between the 3dxy orbital of vanadium and the 2py orbitals of fluorine. Bonding in the complex ion has been discussed in terms of LCAO MO theory.
Correlations between 35Cl Nuclear Quadrupole Resonance (NQR) Frequencies of Chlorobenzene Derivatives and Characteristic Reaction Parameters of the Substituents
Authors: Biedenkapp D. , Weiss Alarich
Published: February 2004

The 35Cl NQR frequencies (at 77°K) of a number of chlorobenzene derivatives have been measured. The frequencies (including additional data from the literature) have been correlated with characteristic parameters, such as Taft's σI and σR. It is found that the Bray–Barnes relation can be somewhat improved by introducing a parameter κ: ν = ν0 +  ∑ iκı. The following relations are found: (a) the effects of more than one substituent on the benzene are additive; (b) steric effects (o-substituents) are not important for the NQR frequencies; (c) a correlation between the NQR frequency ν and Taft's σI and σR (correlation coefficient r = 0.976) shows the importance of the inductive effect on NQR. The mesomeric effect plays only a minor role in 35Cl NQR in benzene derivatives. Unknown σI values may be gained from NQR measurements; for the evaluation of σR, the determination of the chemical shift of 19F NMR seems to be the better method.
Excitation of Molecular Vibration on Collision. I. Preferential Orientations for Vibrational Transitions
Authors: Shin Hyung Kyu
Published: February 2004

The problem of preferential orientations in vibrational transitions has been investigated for collision systems involving two diatomic molecules or a molecule and an atom. Orientation- and temperature-dependent transition probabilities were obtained for such systems. Applications of the final formulas to O2–Ar, O2–O2, HBr–Ar, and HBr–HBr show that the vibrational transition (0 → 1) is most effective for colinear configurations in the collisions involving homonuclear molecules, while such configuration is either most effective or least effective when the molecule is asymmetric. In HBr–HBr the colinear configuration in which two H atoms are in head-on interaction is most effective, while the Br···Br head-on colinear collision is least effective. In HBr–Ar the Br–H···Ar colinear configuration is most effective and the H–Br···Ar is least effective. In O2–O2 the parallel configuration is least effective, but in HBr–HBr the efficiency of such configuration is intermediate between the two extreme colinear configurations.
Inequalities for Critical Indices near Gas–Liquid Critical Point
Authors: Choy Teresa Ree , Ree Francis H.
Published: February 2004

By studying behavior of the cell-pair correlation function χ(R) near the critical point we deduce the following new inequality under a plasusible assumption on χ(R): [φ(n)]2[φ(1)]−n−1+(n−1)d/(2−η) < ∞, n = 1, 2, ···, where d is the dimensionality of the system under study, and φ(n) denotes ρn[∂n−1ρ−1(∂βP / ∂ρ)β / ∂ρn−1]β [ρ = number density, P = pressure, β = 1 / (kBT), T = temperature, kB = Boltzmann constant]. The quantity η is a correction factor from the Ornstein–Zernike behavior of the leading term of χ(R) at the critical point at large distance R[χ(R) ∼ R2−d−η]. The above inequality unifies further inequalities for the critical indices which can be generated from it by tracing different thermodynamic paths. Using Fisher's notations for the critical indices, we find the following relations from the above inequality: η ≥ 2 − d(δ − 1) / (δ + 1), 2Δn ≤ γ + dν, 2Δn′ ≤ γ′ + dν′, and 2β ≤ dν′ − γ′.
High-Resolution NMR Spectra of Polycyclic Hydrocarbons. III. Molecular-Orbital Calculations of Spin–Spin Coupling Constants
Authors: Mainster M. A. , Memory J. D.
Published: February 2004

The method of Fahey, Graham, and Piccioni for computing nuclear spin–spin coupling constants is modified by the explicit inclusion of the effects of the π-electron system and used to study the proton–proton coupling constants of polycyclic hydrocarbons. Values for adjacent protons are reasonable and the experimentally observed absence of significant inter-ring coupling is predicted, but neither the sign nor the magnitude of nonadjacent intraring couplings can be accurately determined by this technique.
Modulation of Spin Echoes in Multi-Half-Spin Systems. I. Closed Formulas of Carr–Purcell Spin Echoes in Several AaBXx Systems
Authors: Tokuhiro Tadashi , Fraenkel Gideon
Published: February 2004

A density-matrix approach to derive the effects of chemical shift and both homo- and heteronuclear spin coupling in a molecule on the Carr–Purcell spin-echo (CPSE) train is developed. Closed formulas are derived for several multi-half-spin systems of the “AaBXx” type where a and x are arbitrary numbers of spins, and X is either the same nuclear species as A and B or different. As a special case of this type, the formulas are also obtained for both homo- and heteronuclear AA′XX′ systems. In heteronuclear multi-half-spin systems, the general equation is derived as a function of all the coupling constants. Features of the modulation patterns in “AaBXx” systems are discussed and the following relation is obtained: By introducing “effective internal chemical shifts” the modulation pattern of AaB resonance in a heteronuclear AaBXx system can be related to that in the homonuclear AaB system. Modulation patterns in homonuclear “AaBXx” systems are not summations of those in simpler spin systems and these facts arise from the effect of the 180° pulse on homonuclear systems. In heteronuclear AXx systems, there are only unmodulated terms. When the coupling constants between two magnetically equivalent sets are equal in AaXx systems, the results show that the heteronuclear system has no modulation and only one modulation frequency exists in the homonuclear system.
Pre-exponential Factor in Semiconducting Organic Substances
Authors: Rosenberg Barnett , Bhowmik Benoy B. , Harder Harold C. , Postow Elliot
Published: February 2004

Experimental data on semiconducting organic substances are usually processed by use of the two-constant equation, σ(T) = σ0exp(−E / 2kT). Evidence from a number of cases now indicates that σ0 is dependent on E, when the equation is applied to certain single substances where E varies with preparation. A three-constant equation of the following form applies: σ(T) = σ0′ exp(E / 2kT0) exp(−E / 2kT) where T0 is a new constant, the “characteristic temperature” of the substance. A method of evaluating σ0′ and T0 is to vary the activation energy for semiconduction by any of at least three processes: (1) hydration of the crystals; (2) formation of weak donor–acceptor complexes; (3) using different cis–trans isomers of the substance when possible. One method of evaluating the constants is to plot logσ0vs E. The slope of this line yields (2kT0)−1, and the intercept yields σ0′. Other methods are possible and yield consistent results. These methods are demonstrated for the substances oxidized cholesterol, retinal, and nucleic acids. The implication of these results is that the Meyer–Neldel rule for compound inorganic semiconductors is valid for organic semiconductors as well. No reasonable theoretical explanation has yet been proposed to account for this rule.
Relationship for Condensed Materials among Heat of Sublimation, Shock-Wave Velocity, and Particle Velocity
Authors: Rodean Howard C.
Published: February 2004

The shock-wave velocity U and the particle velocity u in many condensed materials are linearly related (in the absence of phase changes) according to the equation U = a + bu, where a and b are empirical constants. If the shock compression does not produce phase changes, a is approximately equal to a0, the “adiabatic,” “bulk,” or “hydrodynamic” sound speed at the initial condition. On the basis of a theoretical analysis in which it is assumed that a = a0, it is proposed that a0 and b are related to the initial cohesive energy Eχ0 by the equation Eχ0 = − a02 / 2b2, and that this relation is exact (neglecting the residual zero-point energy) at zero pressure and temperature. This equation is consistent with experimental data for 32 metals and 11 alkali-metal halides if Eχ0 is identified as a heat of sublimation Hs. The definition of Hs is a function of the material and is the energy required to transform the material from the solid state to an un-ionized gas (diatomic in the case of the alkali-metal halides, perhaps a diatomic–monatomic mixture for the alkali metals, and monatomic in the case of the other metals). This suggests that the molecular bonds of gases may be preserved in the condensed state, or perhaps they become effective in the shock-compression process.
Dielectric Constant of Simple Gases
Authors: Levine Howard B. , McQuarrie Donald A.
Published: February 2004

A general expression for the second dielectric virial coefficient for a rare gas is derived by a simple cluster method. The resulting formula requires for its evaluation a knowledge of the exact form of the polarizability of a pair of interacting atoms as a function of their separation. Previous analyses have replaced this exact form by its asymptotic long-range limit. To explore the validity of this approximation, we use metallic spheres as a model of atoms. For this model, it is possible to determine the polarizability exactly by solving Laplace's equation in bispherical coordinates. It is found that the exact expression is sharply peaked at contact, which suggests that for real atoms overlap effects are of paramount importance. Comparison of the exact and asymptotic forms shows the latter to lead to a second dielectric virial coefficient which is too small by a factor of about 2.
Ion–Molecule Reactions of C+ with N2 and O2
Authors: Lao R. C. C. , Rozett R. W. , Koski W. S.
Published: February 2004

Using a tandem mass spectrometer, the reactions C++X2→X2++C →X+X++C →CX++C, where X is either nitrogen or oxygen, were studied in the ion energy range 5–200 eV. By studying the attenuation of the C+ ion beam as a function of N2 pressure at various electron energies, and by measuring the ion–molecule reaction cross sections at different electron energies, it was possible to estimate the contribution of the 2P and 4P states of C+ to the reactions.
Stark-Broadened Hydrogen Lines as Temperature Probes in Nitrogen Plasmas
Authors: Buttrey D. E.
Published: February 2004

Trace quantities of hydrogen have been introduced into shock waves in nitrogen to determine the ion density behind the reflected shock by measuring the widths of time-resolved, Stark-broadened, Balmer lines. A 3-in.-diam, stainless-steel, shock tube with a combustion driver was employed for starting down-stream pressures in N2 of 5.0, 1.0, and 0.5 mm Hg. The temperatures inferred from the measured ion densities are compared with those obtained from the measured starting pressures and incident shock velocities. Agreement to 10% of the ion-density inferred temperatures with the calculated reflected-shock temperatures was found throughout the 50, 25 and 15 μsec of testing time, respectively, for the calculated conditions of 8800°K and 0.58ρ0 (p1 = 5 mm N2), 10 000°K and 0.168ρ0 (p1 = 1 mm N2), and 13 000°K and 0.09ρ0 (p1 = 0.5 mm N2). Initial overshoots of as much as a factor of 2 were found in the spectral radiation signals for both the p1 = 1 mm N2 and the p1 = 0.5 mm N2 data. Representative photomultiplier-scope traces of radiation signals from the 3914-Å (0, 0) N2+ first negative system, the 5666-Å multiplet of N ii, and the nitrogen continua processes are discussed in conjunction with the ion-density histories.
Infrared Spectroscopic Study of Polycrystalline NH4CN
Authors: Clutter Dale R. , Thompson Warren E.
Published: February 2004

The infrared absorption spectrum of polycrystalline NH4CN is reported at temperatures between 125° and 4°K. At 77°K the main features occur near 3165, 3030, 2854, 2094, 1850, 1438, and 215 cm−1. A few of these features show two or more components at lower temperatures. The NH4+ torsional fundamental does not appear in the spectrum, but a value of ∼ 410 cm−1 is inferred for it from other observed frequencies. The spectrum does not show the complexity allowed by factor-group analyses based on the x-ray symmetry of the crystal. The results at 77°K are understandable on the basis of an effective NH4+ site symmetry of Td, and the plausibility of this is discussed. A comparison of the frequencies with those of other ammonium salts indicates moderate hydrogen bonding in NH4CN, comparable to that in NH4Cl and NH4N3. The possibility of hydrogen bonding of NH4+ to either the four nearest C or N atoms of adjacent CN− ions or to CN− π orbitals is considered; evidence favoring the former is presented, but the data do not permit a decision.
Distorted-Wave Approximation in Faddeev's Theory of Reactive Scattering
Authors: Eu B. C. , Ross John
Published: February 2004

The distorted-wave Born approximation is shown to hold to second order in the transition matrix elements of Faddeev's theory of three-particle scattering, with the choice of optical potential for the distortion potential.
Dipole Shielding Tensor
Authors: Epstein Saul T. , Johnson Robert E.
Published: February 2004

An exact formula is derived for the dipole shielding tensor of an atom in an arbitrary time dependent field. Conditions are given under which a variational calculation will yield similar results.
Electron Photoemission from Anthracene Crystals
Authors: Pott Gerald T. , Williams Digby F.
Published: February 2004

The electron photoemission (intensity dependence and the electron photoemission spectrum from 2600 to 4600 Å) has been measured for anthracene crystals provided either with a gold paste or with an electron injecting contact. No major differences have been found between the positions of the spectra maxima observed from crystals void of trapped electrons or containing a considerable space charge. Photoemission maxima are observed at wavelengths corresponding to maxima in the absorption coefficient, though in addition a maximum in electron photoemission at ∼3050 Å is observed. A kinetic analysis of the experimental results indicates different rate-determining processes are involved for electron photoemission in the region 2600–3300 Å compared to 3300–4100 Å. In the region 2600–3300 Å two competing processes determine the electron emission characteristics; a charge-transfer exciton–charge-transfer exciton annihilation together with charge-transfer exciton–trapped carrier interactions. The relative importance of each of these two mechanisms depends upon the density of space charge present in the crystal. The lifetime of this charge-transfer state involved is found to be ∼10−9 sec and its energy at least 4.1 eV above the anthracene crystal ground state. Singlet exciton–singlet exciton annihilation is found to be the rate determining process for photoemission between 3300–4100 Å. No evidence for a direct trapped carrier–photon interaction has been observed.
Proof of a Theorem on the Determinancy of Phenomenological Coefficients for Dependent Fluxes
Authors: Bartelt John L. , Horne Frederick H.
Published: February 2004

Although it is often convenient in both microscopic and macroscopic transport theories to use dependent fluxes, the extra phenomenological coefficients introduced thereby are apparently indeterminate unless mechanical equilibrium or the Onsager reciprocal relations are invoked. A simple proof based on entropy production verifies that the extra coefficients are generally determinate.
Electronic Absorption Spectra of Matrix-Isolated Uranium Tetrachloride and Uranium Tetrabromide Molecules
Authors: Clifton J. R. , Gruen D. M. , Ron A.
Published: February 2004

The electronic absorption spectra of UCl4 and UBr4 molecules isolated in nitrogen matrices cooled to liquid-helium temperatures have been observed and measured in the range 400–50 000 cm−1. The more than 30 narrow absorption bands, found in the 4000–24 000-cm−1 region for each of the two molecules, have been assigned to pure electronic transitions from the H43(Γ5) ground state to excited states of the f2 configuration. Energy-level calculations have been performed by simultaneously diagonalizing the electrostatic, the spin–orbit coupling, and the (tetrahedral) crystal-field interactions. The crystal-field parameters of fourth and sixth degree, designated as A 〈r4〉 and B 〈r6〉, were found to be − 593 and − 22 cm−1 for UCl4 and − 490 and − 15 cm−1 for UBr4. These values of the parameters were obtained by a least-squares fit of observed-to-calculated energy levels allowing A 〈r4〉 and B 〈r6〉 to vary while maintaining the values of F2, F4, F6, and ζ5f at 191, 34, 4, and 1796 cm−1, respectively. The magnitudes of A 〈r4〉 and B 〈r6〉 calculated on the basis of a point-charge model including induced dipole contributions were found to be − 345 and 26 cm−1 for UCl4 and − 309 and 22 cm−1 for UBr4.
Optical Measurements of Liquid Water in the Vacuum Ultraviolet
Authors: Painter L. Robinson , Birkhoff R. D. , Arakawa E. T.
Published: February 2004

Two methods have been used to determine the optical and dielectric properties of liquid water in the vacuum ultraviolet. In the first, the reflectance of water in equilibrium with its vapor at 1°C was measured in the spectral region from 3000 to 1050 Å for three angles of incidence. In the second, water was placed against the plane surface of a transparent semicylinder, which formed one side of a sealed cell, and the reflectance was measured at the water–semicylinder interface. Real and imaginary parts of the complex index of refraction and dielectric constant were deduced from the data and Fresnel's equations. Peaks in the complex dielectric constant occur at 8.3 and 9.6 eV. Though the absorption bands cannot at present be unambiguously assigned, possible mechanisms to explain the ultraviolet structure are presented.
Photoelectron Spectra of Molecules. II. The Ionization Potentials of Azabenzenes and Azanaphthalenes
Authors: Dewar Michael J. S. , Worley S. D.
Published: February 2004

The ionization potentials of pyridine, pyrazine, pyrimidine, pyridazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, and phthalazine have been derived from molecular photoelectron spectra. Simple first-order perturbation theory and the MINDO SCF MO method have been employed in assigning the experimental first ionization potentials to ionization from a π or nonbonding energy level.
Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of the Free Radical HCO. The Hydrocarbon Flame Bands
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

The photoproduction of H or D atoms from a variety of sources in a carbon monoxide matrix or in an argon matrix to which a small concentration of carbon monoxide has been added leads to the appearance of prominent ultraviolet absorptions between 2100 and 2600 Å, all of which may be assigned to HCO or DCO. Both the CO-stretching and the bending vibrational modes are appreciably excited in the transition. Evidence is presented indicating that the transition observed in the matrix experiments is the same one responsible for the hydrocarbon flame bands. Using the frequencies observed in the matrix experiments, a tentative assignment for the hydrocarbon flame bands has been proposed which is in reasonable agreement with the observed band structure of the emission system. In the upper state, the carbon and oxygen atoms of HCO are approximately singly bonded. Observation of the infrared absorption frequencies of isotopically substituted HCO in an argon matrix has prompted reconsideration of the valence force field appropriate to ground-state HCO. Interaction between the CH-stretching and the CO-stretching modes has been found to play an important role. Factors leading to the stabilization of HCO in an argon matrix in the present experiments, in contrast to the results of previous studies, are discussed.
Spectroscopic Observation of Surface Distortion in Ionic Crystals. I. Lithium and Sodium Nitrate
Authors: Cooney R. P. J. , Thayer Chester , Li P. C. , Devlin J. Paul
Published: February 2004

Attenuated-total-reflection (atr) infrared data for the out-of-plane nitrate ion mode in crystalline LiNO3. NaNO3, and KNO3 are interpreted in terms of a distorted lattice surface structure. The surface distortion, which is manifested by atr curves which shift toward the higher-frequency bulk-transmission band position as one increases the penetration depth of the electric field of the totally reflected wave, apparently decays exponentially into the crystal. The atr data are fitted to a ν2-vs-Z (depth) function such that the calculated surface frequency shift reduces to e−1 of its surface value at a depth of 1.0 μ. This surface “depth” is orders of magnitude greater than that predicted theoretically for the alkali halides, but can be rationalized in terms of a cooperative phenomenon.
Pair Potential for Argon
Authors: Dymond J. H. , Alder B. J.
Published: February 2004

A study of the effect of variations in the interatomic potential of argon on the calculated properties of the dilute gas has led to a numerically tabulated potential which satisfactorily agrees with all available equilibrium and transport data. This potential differs significantly from previously used pair potentials.
Heat Capacity of RuO2 and IrO2 between 0.54° and 10°K
Authors: Passenheim B. C. , McCollum D. C.
Published: February 2004

The heat capacities of the metallic transition-metal oxides IrO2 and RuO2 have been measured between 0.54° and 10°K. Both compounds exhibited heat capacities characteristic of metals, with contributions due to nuclear quadrupole interactions apparent in the 3He region. The heat capacity of IrO2 was found to be C = 0.308T−2 + 0.0565T3 + 5.51T (mJ/mole·°K). The heat capacity of RuO2 was found to be C = 0.059T−2 + 0.0225T3 + 5.77T (mJ/mole·°K). The results are discussed in relation to electrical resistivity, paramagnetic susceptibility, and Mössbauer effect studies on these materials.
Optical Spectra of Small Rings. I. The n → π Transition of Difluorodiazirine
Authors: Lombardi John R. , Klemperer W. , Robin M. B. , Basch Harold , Kuebler N. A.
Published: February 2004

A rotational analysis of the (0,0) component of the n → π*(1A1 → 1B2) excitation of difluorodiazirine has been performed and demonstrates that in the upper state, the N=N distance increases by 0.060 ± 0.005 Å, whereas the F–F distance decreases by 0.034 Å. Comparison of the (0,0) Stark spectrum with the computer simulation of that part of the spectrum which behaves like a symmetric rotor yields an upperstate dipole moment of 1.5 ± 0.2 D, presuming the ground-state dipole moment of difluorodiazirine is zero. The vibrational structure of the n → π* band is assigned as consisting of a long progression in ν1′, the N=N stretch, together with only a few quanta of ν4′, the F–C–F angle bend, and hot bands assignable as either ν3′ − ν3″ or ν5′ − ν5″. An excellent fit to the relative intensities of the eight members of the ν1′ progression is obtained using Smith's one-parameter theory of the vibronic band shape. An apparent second origin is also observed, and is tentatively assigned as absorption to the π → π* triplet state B13. Using Gaussian-type orbitals, the ground- and n → π* excited-state dipole moments of difluorodiazirine were computed to be 0.082 and 1.964 D, respectively. While the predicted n → π* excitation energy is in excellent agreement with that observed, the predicted dipole velocity oscillator strength is too large by a factor of 10. Analysis of the MO's involved in the transition shows that n is nearly equally distributed among the C–N–N atoms of the ring, but that π* is completely localized on the N atoms. Consequently, the n → π* excitation involves the transfer of about 13 electron from the CF2 group to the N=N group of difluorodiazirine. The spin–orbit coupling between the n → π* singlet and π → π* triplet states is computed to result in a π → π* (1A1 → 3B1) oscillator strength of the order of magnitude observed for the second origin.
Chemisorption on Rhenium: N2 and CO
Authors: Yates John T. , Madey Theodore E.
Published: February 2004

The chemisorption of N2 and CO on polycrystalline Re has been studied using flash desorption. A number of binding states have been identified and their binding energies have been estimated kinetically. Isotopic mixing between chemisorbed species has been observed for the β-N2 and β-CO states on Re; there appears to be no evidence for dissociation of β-CO. The γ-N2 and two α-CO states on Re desorb without isotopic mixing. In general, the distribution and properties of binding states for N2 and CO on Re are remarkably similar to those found for these adsorbates on W. An enhancement in nitrogen adsorption on Re occurs upon electron impact (150 eV) on N2(g). A new set of strongly bound states are produced which are distinct from the β-N2 states populated by adsorption of ground-state N2(g). A comparison of the sticking coefficients for N2 and CO on Re is made, using two independent methods (uptake and isotopic mixing) over a wide temperature range. The sticking coefficient for N2 on Re decreases markedly with increasing temperature; for CO on Re, there is little effect of temperature on the sticking coefficient. A discussion is presented of migration-limited bimolecular kinetics at elevated temperatures in the chemisorbed layer.
Complex Radical–Ion Salts of TCNQ (Tetracyanoquinodimethan) with Cyanine Dye and Related Cations
Authors: Klanderman B. H. , Hoesterey D. C.
Published: February 2004

The electrical conductivities of the complex radical–ion salts of TCNQ (tetracyanoquinodimethan) with cyanine dye and related cations generally increase with an increase in the polarizability of the cation. With large cations, however, the increase expected from the high polarizability is offset by the size of the cation. From the change in conductivity of the complex TCNQ salts accompanying the variation in structure of the corresponding cations, a plausible structure for the complex salts can be postulated.
Rodlike and Random-Coil Behavior of Poly(n-butyl Isocyanate) in Dilute Solution
Authors: Bur Anthony J. , Roberts Donald E.
Published: February 2004

The polymer chain configuration, molecular relaxation, and the dipole moment of poly(n-butyl isocyanate), (–CO–NR–)n, where R = C4H9, have been studied by dielectric measurements of the polymer in dilute solution. The complex dielectric constant, ε* = ε′ − jε″, was measured at room temperature over a frequency range 10−1–1 × 106 Hz for fractionated samples whose molecular weights cover a very broad range, 20 × 103–10 × 106. From observation of the dielectric relaxation time as a function of molecular weight we deduce that the low-molecular-weight molecule, Mw < 80 × 103, is rodlike and helical. Upon increasing the molecular weight, this rodlike conformation can not be sustained and chain flexibility accumulates with the addition of each monomer unit to the chain. Finally at high molecular weight, Mw > 106, the polymer chain configuration can be described as random coil. The relaxation time and dipole-moment measurements indicate that there is a one-to-one correspondence between the end-to-end distance and the dipole moment of the poly(n-butyl isocyanate) (PBIC) molecule. Using the dipole-moment data alone, we are able to show that the PBIC chain configuration as a function of molecular weight can be described by the Kratky–Porod wormlike model. The relationship between PBIC and biological molecules, especially the polypeptides, is discussed.
Linear Collision of a Classical Harmonic Oscillator with a Particle at High Energies
Authors: Secrest Don
Published: February 2004

The collision of a harmonic oscillator with a particle is studied classically. All three particles are constrained to lie in a line. A soft exponential interaction and a rigid sphere interaction are considered and the connection between these two interactions is investigated. A relation is given between the hardness of the interaction potential, the oscillator force constant, and the collision energy. Nonmonotonicity of the energy transfer at high energies is shown to be related to multiple collisions.
Thermal Expansion of the Polyethylene Unit Cell
Authors: Shen Mitchel , Hansen Wilford N. , Romo Paul C.
Published: February 2004

The 719–730-cm−1 doublet in the infrared spectrum of polyethylene (PE) is known to shift to higher frequencies with decreasing temperature. In this work we have measured these peak positions as a function of temperature down to 10°K for three bulk polyethylene samples of three different degrees of crystallinity, as well as solution-grown single polyethylene crystals both treated and untreated by fuming nitric acid. All these samples were found to behave similarly. X-ray diffraction measurements were performed for PE single crystals at four temperatures: 10°, 80°, 20°, and 300°K. The unit cell dimensions of polyethylene at these temperatures were found to correlate linearly with the infrared peak positions. On the basis of this correlation, a specific volume–temperature plot was made for the PE unit cell, from which thermal expansion coefficients were obtained as a function of temperature. The latter data can be fitted by the Debye–Grüneisen equation. Values of Grüneisen parameters were estimated and were found to increase monotonically with decreasing temperature.
Tn
Frequency Functions as Energy Contours for Photon Absorbance in Condensed Systems
Authors: Morrey John R. , Morgan Larry G.
Published: February 2004

Spectroscopic absorption contours of condensed systems appear to be described by one of several frequency functions, i.e., Gaussian, Lorentzian (T1), or Tn, where 1 < n ≤ 3. A phenomenological explanation is given in terms of a statistical model involving random perturbations on energy levels (〈ψm | H | ψn〉, 〈ψn | H | ψn〉) and orthogonal coupling matrix elements (〈ψm | Mq | ψn〉), where Mq is the light-coupling operator and n and m are the two states between which transitions occur. If the matrix elements are well shielded from perturbation or strong complexes exist such that only a few relaxations of the same order of duration can occur, Gaussian functions result. If, along with the energy levels, one of the orthogonal components is strongly perturbed by a statistically orientated environment, a Lorentzian function (T1) results. If two such components are perturbed, the predicted function is T2, and if all three components are significantly perturbed, then T3 results.
Theoretical Study of the Barriers to Internal Rotation in Hydrogen Persulfide, HSSH
Authors: Schwartz Maurice E.
Published: February 2004

Hydrogen persulfide, HSSH, has been studied by the ab initio self-consistent-field molecular-orbital method for the four dihedral angles of 0°, 90°, 135°, and 180°. The basis set consisted of Gaussian orbital expansions of best-atom Slater-type orbitals through 3p, tested in other calculations on H2S. The molecule has a calculated energy minimum for a dihedral angle in the range 90°–100°, in fair agreement with experiment (about 90.5°). The cis barrier is high (7.4 kcal), but the smaller trans barrier (1.9 kcal) seems low for consistency with experimental studies of the torsional vibrational levels. The S–S overlap population shows a pronounced maximum near a dihedral angle of 90°, just where the total energy shows a minimum. This reflects larger S–S bonding character near equilibrium and furnishes semiquantitative support for the discussion based on hyperconjugation used by the experimentalists to explain the structure. A partitioning of the total energy into attractive and repulsive components shows that both cis and trans barriers are dominated by the repulsive component (this is also true if the wavefunctions are scaled to satisfy the virial theorem).
Magneto-Optical Investigation of Trivalent Dysprosium in Gadolinium Trichloride
Authors: Leask M. J. M. , Smith D.
Published: February 2004

The optical absorption spectrum of 2% Dy3+ in the ferromagnet GdCl3 has been investigated and found to exhibit line shifts and splittings below the Curie temperature (2.2°K), which are attributable to magnetic dipole and exchange interaction between the various states of Dy3+ and the ordered Gd3+ system. These effects have enabled the exchange field to be measured for a number of different J multiplets, at the lowest temperature obtainable (1.35°K). The exchange field is found to be reasonably constant within a particular multiplet, but the variation between multiplets is more complex than the simple model would indicate. The temperature dependence of the shifts and splittings suggests that the optical effects are a measure of the long-range, rather than the short-range order, although the latter cannot be entirely ruled out.
Structure Studies of Solutions of Large Organic Molecules. II. End-to-End Distances of Alkanes from C8− to C22−
Authors: Brady G. W. , Cohen-Addad C. , Lyden E. F. X.
Published: February 2004

End-to-end distances for a series of alkanes in the range C8− to C22− have been measured by the technique described in the preceding article. There appears to be good agreement with the theoretical values of the characteristic ratio 〈r2〉 / nl2 cited by Flory. However, there is evidence that solvent effects are present. These are discussed.
Microwave Spectrum of Germacyclopentane
Authors: Thomas E. C. , Laurie Victor W.
Published: February 2004

The microwave spectrum of four Ge isotopic species of the five-membered heterocycle germacyclopentane (C4H10Ge) has been investigated in the region 8–22 GHz. Rotational constants for the ground state of the 74Ge species are: A = 5323.7, B = 2842.20, C = 2041.52 MHz. From excited states assigned to the lowest ring-deformation mode, a lower limit of about 500 cm−1 has been estimated for the barrier to pseudorotation. The molecule is found to be permanently twisted into a C2 conformation with a twist angle of 18°, and ∠CGeC = 98°, ∠GeCC = 106°, and ∠CCC = 115°. Stark-effect measurements give a dipole moment of 0.665 ± 0.007 D. For the 73Ge species, the nuclear quadrupole coupling constants are found to be χaa = 15.89 MHz, χbb = −10.29 MHz, χcc = −5.60 MHz.
ESR Studies of Trapped CO2− Radicals in X-Irradiated Succinic Acid
Authors: Schwartz Robert N. , Hanna Melvin W. , Bales Barney L.
Published: February 2004

Studies of the g tensor of the singlet in x-irradiated succinic acid suggest that this line is due to the CO2− radical ion. Temperature-variation studies indicate that this CO2− fragment arises from the decomposition of the anionic species [HOOCCH2CH2COOH]− which appears to be formed in the initial radiation-damage process. A mechanism rationalizing the ESR data on all irradiated carboxylic acids is proposed.
Vaporization of Uranium Mononitride and Heat of Sublimation of Uranium
Authors: Gingerich Karl A.
Published: February 2004

The vaporization of uranium mononitride UN has been investigated by the Knudsen effusion technique in combination with a mass spectrometer. The vaporization occurs incongruently by preferential loss of nitrogen forming the two-phase system nitrogen-saturated liquid uranium–uranium-saturated nonstoichiometric uranium mononitride. The vapor pressures of U and N2 have been obtained by silver calibration over the two-phase system UN0.4–UN0.9 in the temperature range 1910–2230°K. The enthalpies ΔH°298 for the simplified reaction (1) UN(s)=U(g)+0.5 N2 (g) and its partial reactions (2) UN(s)=U(l)+0.5 N2(g) and (3) U(l)=U(g) have been obtained from second- and third-law treatments. The experimental third-law value of Partial Reaction (3) of 130.7 ± 2.2 kcal mole−1 may be considered an upper value for the heat of vaporization of uranium metal. The third-law enthalpy of Partial Reaction (2) of 68.9 ± 0.4 kcal mole−1 is in general agreement with literature data for this reaction. The selected value for the enthalpy of Reaction (1) of ΔH°298 = 200.3 ± 4.0 kcal mole−1 yields with appropriate literature data a heat of atomization ΔH°298 = 313.3 ± 4.5 kcal mole−1 for solid UN, and a heat of vaporization ΔH°298 = 127.9 ± 4.9 kcal mole−1 for uranium. The difference of 2.8 kcal mole−1 between this value and the directly measured value for Partial Reaction (3) is attributed to an activity decrease of uranium in nitrogen-saturated liquid uranium that is in equilibrium with the UN phase.
Crystallographic Symmetry of the Internal Magnetic Field in the Magnetically Ordered State
Authors: Yallabandi Krishna K. , Parker Paul M.
Published: February 2004

The symmetry of the time-averaged internal magnetic field for all points of the magnetic unit cell and the symmetry of the Fourier components of the magnetic field in the reciprocal lattice are implicitly determined when the magnetic space group (Shubnikov group) of the crystal is specified. For the internal field, such symmetry determinations have been described in the literature. In this paper, general procedures for the symmetry determination of the Fourier components are developed and discussed, and these procedures are illustrated through application to seven particular magnetic space groups belonging to the tetragonal system. The relation between the internal magnetic field and the internal magnetization is discussed.