bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR of α-Copper Phthalocyanine. II. Powder Line Shape and MO Calculations
Authors: Chen Inan , Abkowitz Martin , Sharp James H.
Published: February 2004

The ESR spectrum of polycrystalline α-Cu phthalocyanine, reported by us previously, has been analyzed in detail by powder line shape and MO calculations. The superhyperfine (shf) tensors are shown to be essentially isotropic and hence the system can be described by an axial spin Hamiltonian. The low-field spectrum consists of four well-defined peaks from which the spin-Hamiltonian parameters g‖ and A can be readily determined. The high-field spectrum is a superposition of four sets of nine-component lines over-lapping to result in 15 almost equally spaced peaks. This fact suggests that the hyperfine (hf) constant B is about twice the shf constant aN. This relation has been used to estimate the values of g⊥, B, and aN. Only a slight adjustment of parameters was needed to synthesize a derivative line shape which fitted well to the experimental spectra. For one of the hf components (M = 32), the resonance field is not a monotonic function of θ, the angle between molecular axis and the magnetic field. The effect of this anomaly on the spectrum, particularly the intensity ratio of the shf lines is discussed. The final set of parameters (g‖ = 2.158, g⊥ = 2.041, | A | = 0.0212 cm−1, | B | = 0.0029 cm−1, | aN | = 0.0017 cm−1) are in good agreement with those obtained by a semiempirical MO calculation which takes into account the out-of-plane π bonding with the 16-membered ring of the phthalocyanine molecule.
New Approximation Method for Lattice Statistics
Authors: Woodbury George W.
Published: February 2004

An approximation method for treating the statistical mechanics of lattice models is derived, and some of the lower-order approximations are applied to the hard-sphere lattice gas. The results are consistent with previous work on this model. The approximation is of interest because it uses information obtained from small systems—the kind of information obtainable from Monte Carlo calculations. Also, the approximation is of potential importance because it can be generalized to continuum models. The role of the boundary in establishing the long-range order in the hard-sphere lattice gas is investigated. From the approximation it appears evident that the boundary can cause preferential occupation of one sublattice over the other. Furthermore, it is shown to be rigorously true that this behavior must correspond to the largest and smallest eigenvalues (in the standard eigenvalue problem) being equal in magnitude but opposite in sign.
Heat Capacity of Silver Sulfide
Authors: Perrott C. M. , Fletcher N. H.
Published: February 2004

The heat capacity of silver sulfide has been measured over the range 50°–400°C using an adiabatic calorimeter. The heat capacity of the α form, stable between 177° and about 600°C, is anomalous and has a form typical of an order–disorder transition with critical temperature at 350°C. If the sample deviates from stoichiometry by as little as one mole percent in either direction, its heat capacity is near normal at about 20 cal/mole·°C throughout the range of measurement. An interpretation of these results in terms of lattice disorder is suggested.
Zero-Field EPR of Fe3+ in Quartz
Authors: Cook A. R. , Matarrese L. M.
Published: February 2004

The zero-field EPR transition frequencies of Fe3+ in synthetic brown quartz (SBQ) and natural amethyst (NA) have been measured directly. The values obtained, 7113.2 ± 0.2 and 8812.5 ± 0.2 MHz for SBQ and 24 157.5 ± 0.5 and 35 365 ± 2 MHz for NA, are in excellent agreement with those calculated from the spin Hamiltonians derived from ordinary high-field EPR spectroscopy.
Comparison of Continuum and Discrete Lattice Results for Gas–Surface Interactions
Authors: Karamcheti Krishnamurty , Scott Lawrence B.
Published: February 2004

Closed-form analytical results for trapping and gas–surface energy exchange have been derived for a simple model employing a one-dimensional elastic continuum representation of the solid with (1) a truncated harmonic potential and (2) a Morse potential for the interaction between the gas atom and the surface of the continuum. The results consist of formulas for the thermal accommodation coefficient (a.c.) and critical trapping energy, which are compared with corresponding results of McCarroll and Ehrlich and of Trilling for one-dimensional discrete lattices. With the truncated harmonic potential, the continuum gives practically the same values of a.c. and critical trapping energy as the discrete lattice, in accordance with Landau's 1935 prediction, for cases in which the collision frequency is considerably smaller than the cutoff frequency of the lattice. With a Morse potential, the variation of a.c. with temperature is qualitatively correct for the continuum solid model, but the a.c. values appear to be considerably larger than those predicted by Trilling for a discrete lattice. The analysis for the continuum brings out the fact that both the truncated harmonic and Morse potential formulas for a.c. can be expressed in the form of a similarity relation (Bμ)−1/2α = H(ρ), where α is the a.c., H is a function of ρ, B is the dimensionless potential-well depth, μ is the gas-atom–solid-atom mass ratio, ρ is the average energy per gas atom/potential-well depth. Experimental a.c. data for several gas–solid combinations appear to be correlated fairly well on a plot of α / (Bμ)1/2vsρ.
Optical Properties of Certain Cholesteric Liquid-Crystal Films
Authors: Adams J. E. , Haas W. , Wysocki J.
Published: February 2004

Optical scattering data have been used to investigate molecular order in certain cholesteric mixtures. When films of these materials are deposited on a reflecting substrate, their colors can be shifted by several thousand angstroms for any condition of illumination and observation by a mechanical disturbance. The dispersive color reflections in both the undisturbed and disturbed films can be attributed to Bragg-type crystallite sites embedded in a material with refractive index n. When the films are mounted on a reflective substrate, there are effectively two angles of incidence. One angle corresponds to the actual angle of incidence and the other angle corresponds to the reflected beam. Accordingly, for some fixed combination of incidence and observation angles, two wavelength peaks should be observed for an isotropic distribution of scattering sites. Scattering data in both reflection and transmission indicate that the distribution is far from isotropic and that the effect of disturbance is to reorient the sites such as to produce a large increase in the intensity of light scattered from the direct beam and a corresponding decrease in the intensity of visible light scattered from the reflected beam. There is evidence that the basic helical pitch parameter is not changed significantly by the mechanical disturbance.
Approximate Analytical Solutions of the Thomas–Fermi–Dirac and Thomas–Fermi–Dirac–Gombás Equations
Authors: Csavinszky P.
Published: February 2004

Approximate analytical solutions of the Thomas–Fermi–Dirac (TFD) and Thomas–Fermi–Dirac–Gombás (TFDG) differential equations are obtained for neutral and positively charged atoms. The approximate solutions are of the form ψ = φ0 + η and Ψ = φ0 + η̃, respectively, where φ0 is a universal approximate analytical solution of the Thomas–Fermi (TF) differential equation for neutral atoms and η and η̃ are correction functions. The function φ0 has been obtained previously, by making use of a variational principle (the equivalent of the TF equation), and the functions η and η̃ are determined by solving second-order inhomogeneous linear differential equations with the boundary and subsidiary (normalization) conditions that are required in the TFD and TFDG models, respectively. The correction functions η and η̃ depend on the atomic or ionic radius, which, in turn, depends on the atomic number Z and electron number N of the system considered. The approximate solutions ψ and Ψ are tested by calculating the first ionization energies of Ar, Kr, and Xe. The values obtained are about the same as those calculated from the exact numerical solution of the TFD and TFDG equations. In three Appendices approaches for improved approximate analytical solutions of the TFD and TFDG equations are outlined. Appendix A proposes an iterative procedure for obtaining the correction functions η and η̃ in successively more refined approximations, which is expected to be of importance for multiply charged ions or for neutral atoms of low atomic number. Appendix B establishes a variational principle (which to the author's knowledge has not been formulated before) for obtaining approximate analytical solutions of the TFD and TFDG equations, or for achieving further refinements in the approximate solutions ψ and Ψ that are derived in this paper. Appendix C describes Jensen's modification of the TFD and TFDG models, which, with the technique developed in this paper, enables one to obtain approximate analytical solutions for negative ions.
Dielectric Properties of Slightly Polar Organic Liquids as a Function of Pressure, Volume, and Temperature
Authors: Mopsik Frederick I.
Published: February 2004

The dielectric constant and density have been measured simultaneously for carbon tetrachloride, carbon disulfide, isopentane, and toluene. The Clausius–Mossotti polarization for all liquids at constant temperature shows a linear decrease with increasing density. Only isopentane and toluene show a temperature dependence of the Clausius–Mossotti polarization at constant density consistent with the presence of a permanent dipole moment. The dipole moments derived from the constant density data are 0.105 D for isopentane and 0.332 D for toluene. Also, the Böttcher–Onsager equation is shown to be incompatible with the measured data.
Structure of Nitric Oxide Adsorbed on 4A Molecular Sieve
Authors: Hoffman Brian M. , Nelson Norvell J.
Published: February 2004

We have studied the ESR of nitric oxide (NO) adsorbed onto Linde 4A molecular sieve, and have observed that at least two different surfaces sites can be produced, depending on the nature of the surface activation process. Upon quench cooling the sieve activated at high temperature to 77°K, we find trapping of NO at metastable sites and subsequent migration to equilibrium sites. We have obtained the hyperfine interaction constants for NO absorbed onto the equilibrium sites. Comparison of these values with those of a series of molecules which can be formally considered as substituted nitric oxide radicals apparently rules out a model in which NO is singly coordinated to the surface. The comparison also suggests as a possible model NO doubly coordinated at nitrogen, and bridging two surface atoms.
Y2+ as a Color Center in Irradiated CaF2
Authors: Theissing H. H. , Ewanizky T. F. , Caplan P. J. , Grosse D. W.
Published: February 2004

The absorption spectrum of blue, γ-irradiated CaF2: Y3+ crystals shows several bands in the visible region whose intensity is roughly proportional to the yttrium concentration. Bleaching into the individual bands indicates that more than one center is responsible for the whole spectrum. Inconsistent color response of various crystal samples to γ irradiation suggests that only the crystals with sufficient Y3+ in cubic sites, i.e., with the charge compensator some distance away, are colorable. In this case the Y2+ formed by γ irradiation, as well as the defects produced at the remote charge compensators, become color centers and share in the generation of the spectral bands. The question of which band(s) would be due to Y2+ is examined by fitting the band frequency to the energy difference “e”–“t” of the cubic field-split d1 level of Y2+ and the bandwidth to the spread of the “t” level into its components due to a dynamic Jahn–Teller effect. The best fit turns out to be the 17 500-cm−1 band which yields reasonable values for cubic field strength Dq, vibrational displacement of F− ions, and Jahn–Teller energy.
Transition Rates in Multilevel Systems
Authors: Williamson J. H.
Published: February 2004

The transition rates between levels in a multilevel system can be measured by perturbing the system and observing the response. Previous work has shown that, in general, many different sets of transition rates could account for the same response. In consequence, statistical errors in the computed rates are much larger (e.g., 10 000 times larger) than those in the original data. It is shown here that it is possible to design the experiment so as to avoid this instability. The ideal experiment uses fairly high-frequency sinusoidal perturbations in place of the impulsive or steady-state perturbations usually employed. The application to the measurement of atomic lifetimes and collisional transition rates among excited states is discussed. The method is tested with data obtained from two 6-level electronic circuits which simulate a hydroxyl molecule and a hydrogen plasma, respectively.
Diphenylamino Radical Dimer as a Color Center in a Molecular Crystal
Authors: Wiersma Douwe A. , Lichtenbelt Jan H. , Kommandeur Jan
Published: February 2004

Radical pairs of diphenylamino (DPA) can be formed in a single crystal of tetraphyenylhydrazine (TPH) by uv photolysis. The structure of these radical dimers can be elucidated by ESR measurements. These studies show that eight configurationally different dimers occur, which fall into two classes with 3- and 4-Å separation, respectively. Optical measurements reveal long-wavelength charge resonance absorptions arising from the dimers; this interpretation is supported by polarization measurements. Temperature-dependent ESR measurements were used to determine the singlet–triplet splittings of the two spin systems, yielding about 130 and 40 cm−1 for the 3- and 4-Å dimers, respectively. The radical dimer crystal defect can be regarded as a color center in a molecular crystal.
Kinetics of the Thermal and Nitric Oxide-Catalyzed Geometrical Isomerization of cis- and trans-Propylene-1-d1
Authors: Flowers M. C. , Jonathan Neville
Published: February 2004

The thermal cis–trans isomerization of propylene-1-d1 has been studied from 460°–541°C over a pressure range of 3–250 mm Hg in a Pyrex reaction vessel. The reaction below 20 mm Hg is homogeneous and unimolecular but just in the pressure-dependent region, k∞,cis–trans(sec−1) = 1013.16exp(− 61 300 / RT). Above 20 mm a second-order reaction begins to contribute to the isomerization rate. The nitric oxide-catalyzed isomerization of cis-propylene-1-d1 was studied between 398° and 452°C at propylene pressures of between 8 and 22 mm. Hg and NO pressures of 5–35 mm Hg. The reaction is first order in propylene and nitric oxide. The second-order rate constant is given by k(liters mole−1·second−1) = 108.27exp(− 27 900 / RT).
Raman Scattering and Band Assignments in Polytetrafluoroethylene
Authors: Koenig J. L. , Boerio F. J.
Published: February 2004

The laser-excited Raman spectrum of polytetrafluoroethylene (PTFE) is reported. A new band, an E1 mode at 198 cm−1, is observed. Additional bands, which are apparently E2 modes, are observed at 308 and 676 cm−1 at a sample temperature of − 50°C and at 389 and 741 cm−1 at a sample temperature of − 130°C that are not observed in samples at room temperature. Bands at 575 and 595 cm−1 are found to change in intensity as a function of temperature. Band assignments in PTFE are discussed utilizing the Raman spectra of n-C5F12, n-C6F14, C14F30, and C18F38, which are reported here for the first time.
Vibrational Spectra and Structure of Small-Ring Compounds. XII. Propylene Imine and Propylene Imine-d1
Authors: Durig J. R. , Bush S. F. , Harris W. C.
Published: February 2004

The infrared spectra of propylene imine and propylene imine-d1 have been recorded from 33 to 4000 cm−1 in the gas phase and from 250 to 4000 cm−1 in the liquid phase. The Raman spectrum of the liquid phase has also been recorded. The assignment of the 27 normal vibrations has been made based upon band position, intensity, and isotopic shift. The cis and trans isomers have been observed and the barrier to internal rotation of the methyl group in the cis and trans forms has been calculated to be 2.97 and 2.51 kcal/mole, respectively. The intensity of the 3220 cm− line of propylene imine has been studied as a function of temperature. The ΔH° for H–bond formation is found to be − 1262 cal/mole. Thermodynamic functions have been calculated for the temperature range 200°–1000°K on the basis of a rigid rotator, harmonic oscillator model for all vibrations except the internal rotation for which appropriate corrections have been made.
Theory of Dipolar Lineshifts in Free-Radical Crystals
Authors: Strebel Paul J. , Soos Zoltán G.
Published: February 2004

The spin absorption spectrum of a free-radical crystal containing several inequivalent radicals per unit cell is obtained in the high temperature and the large magnetic field limit. A direct, approximate solution of the total (Zeeman+dipolar) Hamiltonian is used rather than a moment calculation. The spectrum is found for arbitrary ωd / Δω where ωd is the dipolar coupling between radicals whose Larmor frequencies differ by Δω. For both small and large ωd / Δω, the dipolar lineshifts agree with results based on the moment method.
“Ab Initio” Calculation of the Quadrupole Coupling Constant of 14N in HCN, FCN, ClCN, HC2CN, CN−, OCN−, SCN− and the Examination of the Townes–Dailey Interpretation in Terms of Exclusive Orbitals
Authors: Bonaccorsi Rosanna , Scrocco Eolo , Tomasi Jacopo
Published: February 2004

The electric field gradient at 14N nucleus in some RCN molecules or RCN− ions has been calculated using the accurate SCF wavefunctions obtained by McLean and Yoshimine. From these computed values and the experimentally known 14N quadrupole coupling constant of four molecules of this series, a value of 1.66e × 10−26cm2 for the quadrupole moment of 14N nucleus has been estimated. A check for the semi-empirical interpretative theory of Townes and Dailey is made in terms of localized orbitals (Boys exclusive orbitals). Some other characteristics of these exclusive orbitals are also displayed.
Quantum Corrections to the Momentum Relaxation Time of a Brownian Particle
Authors: Hynes James T. , Deutch J. M.
Published: February 2004

The long-time, heavy-mass limit of the quantum-mechanical momentum autocorrelation function of a massive particle immersed in a bath of light particles is considered. An expression for the momentum relaxation time is obtained. It is found that the symmetrized and canonical correlation functions yield identical results in this limit. The momentum relaxation time, which is the inverse of the friction constant of the quantum Fokker–Planck equation, is expanded in powers of Planck's constant to obtain the first quantum correction to the classical result. Quantum corrections for canonical correlation functions are discussed.
Far-Infrared Spectra of Crystalline Ethylene C2H4 and C2D4
Authors: Brith Malka , Ron Arza
Published: February 2004

The far-infrared spectra of polycrystalline ethylene were recorded at various temperatures between 65° and 20°K and at 8°K. Two bands were observed both for ethylene and ethylene-d4. The frequency ratio of corresponding bands in ethylene and deuteroethylene prove that these absorption bands are due to translational lattice modes. Absolute intensities of the observed bands in ethylene were measured. The frequencies of the translational lattice modes were calculated for two different models of intermolecular forces, i.e., center-to-center Lennard-Jones potential and atom–atom repulsion potential.
Anisotropic Chemical Shifts in Cobalt (III) Complexes
Authors: Spiess H. W. , Haas H. , Hartmann H.
Published: February 2004

The 59Co NMR was studied in single crystals of a number of cobalt (III) complexes at room temperature. A procedure was developed for the numerical analysis of the spectra, and the chemical shift and quadrupole coupling tensors were determined. In cobaltocenium nitrate (e2qQ / h = 165.6 Mc/sec) one shift tensor component was used to obtain an improved gyromagnetic ratio for 59Co: γ = 1.0035 kc/sec·G. For the substituted octahedral complexes trans-[Co en2Cl2]Cl·HCl·2H2O (e2qQ / h = 71.7 Mc/sec); [Co(NH3)5CN]Cl2 (e2qQ / h = 26.6 Mc/sec); [Co(NH3)4CO3]Br (e2qQ / h = 18.8 Mc/sec; and trans-[Co en2(NO2)2]NO3 (e2qQ / h = 13.2 Mc/sec), a linear dependence of the shift anisotropy (σzz−σyy = + 4.6‰, − 2.2‰, + 1.5‰, and + 0.4‰) on the quadrupole coupling constant was found. The molecular orbital theory was used to interpret the results.
Laser Light Scattering by Poly-α-amino Acid Solutions
Authors: Ford N. C. , Lee W. , Karasz F. E.
Published: February 2004

An improved self-beat spectrometer has been used to study the spectrum of light, from a He–Ne laser, scattered by solutions of poly-γ-benzyl-l-glutamate (PBG). From the observed spectral broadening, the translation diffusion constants of the solvated polymer were calculated. Diffusion constants were measured also as a function of solvent composition. A change in the diffusion constant at about 76% dichloroacetic acid (at 25°C) reflected the well-known helix–coil transition of PBG.
Characterization of Ground-State Wavefunctions by Measured Electronic Properties. II. Dipole Moment and Field Gradient of Nitrogen Trifluoride
Authors: Unland Mark L. , Dunning Thomas H. , Van Wazer John R.
Published: February 2004

A particular localized-orbital type of LCAO MO wavefunction is used to calculate the dipole moment and field gradient at the nitrogen atom in NF3. Because the wavefunction is not obtained by the usual self-consistent-field procedure, the results for the various observables depend on the choice of calculation parameters such as the polarity of the σ bonds, the amount of π bonding, and the hybridization of the lone-pair orbitals on the fluorine atoms. This dependence is studied in detail and it is concluded that with reasonable choices of input parameters, good agreement with experiment can be obtained. Thus, the localized orbitals specified by setting the σ-bond coefficient equal to 0.875, the π-bond coefficient equal to 0.0, and the fluorine lone-pair orbital angle equal to 112.7°, yield a dipole moment of 0.236 D and a total field gradient at the N atom of − 2.007 a.u. The experimental dipole moment is 0.234 ± 0.004 D and the experimental field gradient is − 1.505 to − 3.010 a.u. depending on the exact value of the nuclear quadrupole moment of nitrogen.
Structure and Free Energy of the Interface between Fluid Phases in Equilibrium near the Critical Point
Authors: Fisk S. , Widom B.
Published: February 2004

The theory of van der Waals and of Cahn and Hilliard, which yields the density or concentration profile through an interface and the associated interfacial tension, is generalized by replacing the equation of state assumed originally by one that reproduces more accurately the known thermodynamic singularities at the critical point. Though the correct equation of state is not known, its presumed homogeneity of form is alone sufficient to allow most features of the interface to be determined explicitly. In particular, the maximum density gradient in the interface, the asymptotic behavior of the interface profile at large distances from the position of its maximum gradient, and the surface tension, are each obtained up to a dimensionless, and presumably universal, proportionality constant that reflects only the functional form of the equation of state. Numerical evaluation of the surface tension requires a knowledge of the limits approached by the correlation length and compressibility in the homogeneous fluid as the phase transition point is approached. These are only imperfectly known, so the surface tension calculated from the theory is subject to some uncertainty, but within its limits of uncertainty it is in agreement with experiment.
Spectroscopic Study of Anthracene Cation Trapped in Boric-Acid Glass
Authors: Zaidi Z. H. , Khanna B. N.
Published: February 2004

The electronic absorption spectrum of anthracene in the boric-acid glass, irradiated with uv light and x rays at room temperature, has been obtained in the region 2200–7000 Å. The spectrum of the irradiated film of anthracene has been attributed to the molecular monopositive ion of anthracene. The electronic energy levels of the ion of anthracene have been calculated by FE–MO method and compared with the LCAO–MO calculations of earlier workers. FE–MO calculations have been found to give satisfactory agreement with the experimentally observed energy levels. On the basis of these calculations, assignment of the observed bands is discussed and an attempt is made to remove the discrepancies in the assignment by earlier workers. The state of aggregation of anthracene in the boric acid along with the effect of temperature on the trapped ionic species is discussed.
Raman Spectrum and Intermolecular Forces of the Chlorine Crystal
Authors: Suzuki Masako , Yokoyama Tohru , Ito Mitsuo
Published: February 2004

The Raman spectrum of the chlorine crystal has been observed at low temperatures for lattice and intramolecular vibrational regions. The observed spectrum supports the x-ray determined crystal structure Cmca with two molecules in a unit cell, with which the lattice vibrational Raman lines have been assigned. Normal-coordinate calculations showed that the central force field is inadequate for the chlorine crystal and noncentral forces must be taken into account to reproduce the observed frequencies. The force constants obtained based on a central and noncentral force field indicated the importance of charge-transfer interaction in the crystal.
Kinetic Analysis of the Reaction of Hot Chlorine Atoms with Alkanes; Collisional Dissociation of Translationally Excited Products
Authors: Spicer Leonard , Wolfgang Richard
Published: February 2004

The reactions with methane and ethane of hot chlorine atoms recoiling from the 40Ar (γ, p)39Cl nuclear reaction have been studied. Displacement reactions, analogous to those of hot hydrogen with alkanes, were found. In the case of methane, these gave CH339Cl and CH239Cl. Yields of these molecules show little pressure dependence, providing negative evidence for unimolecular decomposition due to internal excitation of primary products. A kinetic theory analysis of moderator data indicates that fast chlorine atoms are relatively less reactive than is hydrogen. Furthermore, energy transfer in inelastic collisions with methane appears to be relatively ineffective. The indicated weak coupling between translational and vibrational modes appears due to poor matching between the mean time of collision and the C–H bond vibration period. This study appears to provide the first definite evidence for collisional decomposition of hot molecules. CH339Cl as formed by reaction of 39Cl with CH4 must be translationally excited. A kinetic theory analysis shows that this hot molecule has a considerable probability of breaking up on striking argon atoms. The likelihood of decomposition on collision with methane is, as expected, much less.
Theoretical Study on Isotropic Hyperfine Coupling Constants of Second-Row Elements in π-Electron Radicals
Authors: Yonezawa Teijiro , Kawamura Takashi , Kato Hiroshi
Published: February 2004

The isotropic electron–nuclear spin interactions of the second-row elements in the Periodic Table are interpreted semiquantitatively on the basis of the molecular orbital theory. For an atom Y that is bonded to m atoms, Xi(i = 1, 2, ···, m), the hyperfine constant, aY, has the form aY = QYYpYY0 +  ∑ i = 1m QXiYpii0 +  ∑ i = 1m RYXiYpYi0, where pYY0, pii0, and pYi0 are elements of the π-electron spin density matrix, and QBA and RABA are the σ–π parameters for the nucleus A and resulting from the π AO spin density matrix elements, pBB0 and pAB0. The spin polarization through the σ–π interaction is shown to be divided into three terms according to their mechanisms; (i) the spin polarization in the AB σ bond, which induces opposite spin densities on atomic orbitals of atoms A and B, (ii) the spin polarization which appears as the difference in the hybrid ratios of the hybrid σ-atomic orbitals for different spins, and (iii) the spin polarization of the inner-shell electrons. An empirical analysis correlating the observed hyperfine coupling constants with the calculated π-atomic-orbital spin density matrix elements by the above equation gives the following results: for a coplanar CHC2 fragment QCC, QC′C, and RCC″C are found to be 46.0 ± 0.1, − 17.3 ± 0.1, and − 1.95 ± 0.25 G, respectively; for a NC2 fragment QNN = 29.0 ± 1.6, QCN = − 4.3 ± 0.8, and RNCN = 0.9 ± 1.5 G and for 17O in a carbonyl fragment QOO = − 22.0 ± 3.0, QCO = 75.4 ± 7.6, and ROCO = 71.8 ± 9.6 G.
Electron Spin Resonance Studies on Gamma-Irradiated Ferrocene
Authors: Saito Eiichi
Published: February 2004

The aim of this study was to determine the nature of the free radicals induced in ferrocene by 60Co gamma rays. The irradiations were carried out on the powder at 77°K, the temperature at which crystals have burst into powder form, and on the single crystals at 193°K. At 77°K two radicals are formed, I and II; I transforms itself into a third radical, III, on annealing at temperatures above 145°K. In the single crystals irradiated at 193°K, only radicals II and III are formed. When the single crystals were not too damaged, the disappearance of the radical III with concommitant appearance of a fourth radical, IV, which presents a hyperfine structure of five lines was observed. Taking into account the anisotropies of the g tensors, change in spectra upon deuterium substitution of the cyclopentadienyl protons, and behavior on annealing, the spectra of radicals I–IV were attributed tentatively as follows: I to a straight molecule-ferricinium ion, II to a protonated ferrocene radical, III to a bent molecule-ferricinium ion, IV to a C5H5–Fe–C5H4·radical. Mechanisms are given for the formation of these radicals as well as for their disappearance on annealing.
Radial Distribution Function of Fluids with the Square-Well Potential
Authors: Katsura Shigetoshi , Nishihara Katsuhiro
Published: February 2004

The term χ(r), the bridge diagram in g2(r) which is proportional to the square of the density in the expansion of the radial distribution function in powers of the density, is evaluated for fluids with square-well potential. The contribution of χ(r) to g2(r) is discussed.
Electron Spin-Echo Studies of Relaxation Processes in High-Spin Ferrimyoglobin
Authors: Bozanic D. A. , Krikorian K. C. , Mergerian D. , Minarik R. W.
Published: February 2004

The spin-echo technique is used to study the relaxation processes associated with the trivalent iron ion in horse heart myoglobin at 1.2°K. The destruction of transverse and longitudinal phase memory, as, respectively, measured by the two-pulse (T2p) and three-pulse (T3p) echo sequences, is attributed to a spectral diffusion process. Saturation-recovery data help to affirm this belief. The diffusion process is not dependent upon the concentration of myoglobin in a water solution, which means that it is not dependent upon the Fe3+ concentration (over the range 1017–1019 Fe3+ ions/cc). Moreover, values of T2p and T3p are the same for myoglobin powder as they are for hemoglobin powder. Both of these observations support the conclusion that interactions between the iron spins do not play a major role in the destruction of phase memory; but, rather, that the interaction between the iron magnetic dipoles with the surrounding nuclear moments (particularly the hydrogen nuclei of the water molecule at the sixth ligand and the water molecules of the solvent) is the dominant mechanism. Included in the experimental results are saturation-recovery spin–lattice relaxation measurements at 1.2°K as well as 4.2°K. The short spin–lattice time at 4.2°K (≦ 2μsec) makes it conceivable that the linewidth of paramagnetic centers in this and in similar biological specimens at temperatures of 77°K and above is largely determined by spin-lattice effects.
Hyperfine Structure of Sodium Iodide
Authors: Miller Carl E. , Zorn Jens C.
Published: February 2004

A molecular-beam electric resonance spectrometer has been used to study radio-frequency transitions between the hyperfine-structure sublevels of the J = 1 state of 23Na127I. Transitions for the first four vibrational states have been observed in very weak electric field and near zero magnetic field. The intramolecular interaction constants obtained for the ground vibrational state are: (eqQ)sodium = − 4073.0(10) kHz; (eqQ)iodine = − 262 140.7(10) kHz; csodium = 0.74(8) kHz; ciodine = 0.28(4) kHz; c3 = 0.17(8) kHz, c4 = − 0 27(8) kHz. The numbers in parentheses are the uncertainties in units of the last quoted digit. Constants for the excited vibrational states have been determined with less precision because fewer transitions were observed.
Quantum-Mechanical Study of the F 1Πu and f 3Πu States of He2
Authors: Gupta B. K. , Matsen F. A.
Published: February 2004

A quantum-mechanical study of the two states, F 1Πu and f 3Πu of the helium molecule is made using the valence-bond method with configuration interaction. A procedure for constructing valence-bond functions which give good energy values in the entire range of internuclear distances is described. The wave-function used for each calculation is a 49-term function of the generalized valence-bond type. The basis for the Πu1 state is a set of Slater-type orbitals, while the one for the Πu3 state contains both Slater and elliptic-type orbitals. Vibrational levels and spectropscopic constants are calculated and the results suggest the existence of more vibrational levels than have hitherto been observed for both states, the spectroscopic constants being in excellent agreement with experiment. The existence of maxima in the potential curves of both states is confirmed to be due to the avoidance of crossings of curves of the same group theoretical species.
Studies of the Nitrogen Yellow Afterglow at Low Pressures
Authors: Jonathan Neville , Petty Robin
Published: February 2004

The visible emission from the B 3Πg state of molecular nitrogen caused by the recombination of atoms has been studied in a fast flow system over the pressure range 35–1000 mtorr. Both N2 and argon have been used as major third bodies, and investigations have been made at a number of different wavelengths. In the case of the pure nitrogen system, the results clearly show the change from second-order to third-order kinetics as the total pressure is decreased. Half-quenching pressures are calculated and are in accord with the idea that electronic quenching is the main means of deactivation of the B3 state. When argon is the major third body, the light emission is still pressure dependent at 1 torr, and considerably higher half-quenching pressures are calculated. Several reaction mechanisms which might account for the observations are discussed.
Totally Symmetric Vibronic Perturbations and the Phenanthrene 3400-Å Spectrum
Authors: Craig D. P. , Small G. J.
Published: February 2004

Vibronic perturbations by totally symmetric vibrations are discussed with the help of the linear term in the dependence of transition moment on normal coordinate. Where the dependence is significant, mirror symmetry between fluorescence and absorption spectra is lost, and the fluorescence lifetime differs from the value calculated from the integrated absorption curve. The phenanthrene 3400-Å spectrum, in which totally symmetric vibrational perturbations have previously been identified, can be interpreted in some detail on this basis.
Possibility of Extracting Anisotropy Parameters from Total Cross-Section Measurements. II
Authors: Miller William H.
Published: February 2004

The total (integrated) cross section for the collision of an atom and a diatomic molecule (rigid rotor) is computed in the distorted-wave Born approximation (DWBA) in order to see how information concerning the anisotropic potential can be obtained from such measurements. It is seen that the anisotropy parameters can be obtained most directly from the amplitude of the oscillatory contribution to the cross section. The frequency of the oscillations is determined by the velocity dependence of the rainbow angle of the spherically symmetric distorting potential and (to lowest order) contains no dependence on the anisotropy. Elastic and inelastic transitions are treated.
Singlet–Triplet Transition Probabilities in Aromatic Hydrocarbons. I. A→31La Transitions in Linear Polyacenes
Authors: Krishna V. G. , Salzman W. R.
Published: February 2004

A general expression for the transition moment of A → 31La in linear polyacenes is derived from the matrix elements of spin–orbit interaction between (π, π) and (π, σ) states. Only one-center one-electron integrals are evaluated. The results indicate that the oscillator strength of this transition should decrease as the size of the linear polyacene increases. It is shown that this conclusion is most likely independent of the approximations employed. Interaction of (π, σ) and (π, π) states quantitatively accounts for the main part of the oscillator strength of A → 31La in naphthalene.
Uniform Bounding Functions for a Certain One-Dimensional Form of Poisson's Equation
Authors: Bownds John M.
Published: February 2004

A classical one-dimensional specialization of the more general Poisson–Boltzman equation for potential space distributions associated with the existence of a double layer at an electrode surface leads to a certain nonlinear two-point boundary value problem. The classical approach to solving this problem involves a formal procedure which assumes a certain preknowledge of the actual unknown solution, and it involves finding an approximate solution which is obtained by deleting “higher-order” terms in a certain expansion. This paper presents a different approach in that it makes use of a known existence and uniqueness theorem to establish bounds on the actual solution to the problem. In certain examples, as shown in the paper, the actual effect of ignoring the so called higher-order terms in the classical approach can be clearly established.
Study of “Non-Fickian” Diffusion Anomalies through Time Lags. IV. More Complex Cases of Axial Distance-Dependent Anomalies
Authors: Petropoulos J. H. , Roussis P. P.
Published: February 2004

The time-lag treatment of Paper II of this series is here extended by considering systems in which the thermodynamic diffusion (DT) and solubility (S) coefficients depend both on activity (a) and distance in the direction of flow (X) in such a way that the variables a, X are not separable. The properties of the steady-state permeation flux and of the time-lag quantities defined in Papers I and II of this series are examined by numerical solution of the diffusion equation in a few carefully selected cases and compared with the results obtained in Paper II. It is shown that considerable information can be obtained from such permeation measurements about the nature of the diffusion system, including the question of separability of a, X in S(a, X), DT(a, X).
Resonance Radiation from Interacting Atoms
Authors: Czarnik John W. , Fontana Peter R.
Published: February 2004

The frequency distribution of resonant radiation emitted by a system of two identical interacting atoms is calculated. The separation between the atoms is assumed to be much larger than the size of their charge distributions. Initially one atom is excited while the second one is in the ground state. The two atoms are coupled through the radiation field and the electrostatic interaction. For not too large internuclear separations the line shape of the emitted radiation exhibits two distinct peaks, and the general features are identical with the result obtained from resonance fluorescence scattering. In the decay process, however, there is equal probability of scattering through the symmetric and antisymmetric states, and thus the peak heights of the emitted radiation are different from the ones in the resonance fluorescent case. For large internuclear separations the two peaks merge into the one characteristic of the line shape of a single isolated atom.
Nanosecond Pulse Radiolysis and Nonhomogeneous Kinetics Involving Hydrated Electrons
Authors: Kenney Geraldine A. , Walker David C.
Published: February 2004

Nanosecond pulse-radiolysis studies on the behavior of hydrated electrons at concentrations of about 10−4M showed that the decay during approximately the first half-life (∼110 nsec) was characterized by a rate constant significantly different from that during the second half-life. The latter rate appeared to follow second-order kinetics. The initial decay is attributed to nonuniform distributions of species and to intratrack reactions involving eaq− before the system became truly homogeneous. Qualitative calculations on the period of nonhomogeneity were in agreement with the experimental transition time. It is apparent that in some pulse-radiolysis studies one cannot justifiably calculate second-order rate constants from concentrations evaluated from optical-density measurements. The experiments were performed on pure deaerated water subjected to an intense 3-nsec pulse of 0.5-MeV electrons from a Febetron accelerator. Spectrophotometric analyses were conducted over very small reaction volumes by using the 632.8-nm light from a He/Ne laser collimated to 0.07-mm2 cross-sectional area. One possible implication of the fast initial decay is that G(eaq− is much larger than 2.5.
Determination of Thermal Transport Properties from Thermal Transpiration Measurements
Authors: Ganzi Gary , Sandler Stanley I.
Published: February 2004

The magnitude of the thermomolecular pressure difference across capillary tubes has been measured for the gases argon, nitrogen, oxygen, carbon monoxide, and methane at mean temperatures of 162.3, 233.5, 292.0, and 340.5°K. From these data, the translational part of the thermal conductivity (Eucken factor) has been determined for each of the polyatomic gases. Estimates have been made for the rotational relaxation number and the total thermal conductivity (Eucken factor) for these gases using the thermal conductivity formulas of Mason and Monchick (in the full and linearized forms) and of Saxena and co-workers. It is observed that: (a) These three sets of formulas are equivalent, except for a scaling of the rotational relaxation number; (b) the rotational relaxation number for these gases is an increasing function of temperature; and (c) the values of the Eucken factor and rotational relaxation number obtained here are in very good agreement with the data for these parameters gotten by other methods.
Reactions of Na+, K+, and Ba+ Ions with O2, NO, and H2O Molecules
Authors: Johnsen R. , Brown H. L. , Biondi Manfred A.
Published: February 2004

Ion–molecule reactions of sodium, potassium, and barium ions with O2, NO, and H2O have been studied in a drift tube–mass spectrometer apparatus. The following rate constants or upper limits were obtained: Na+,K, +, Ba++O2(NO)→products, k < 10−13cm3/sec (0.04 − ∼ 5 eV), Na++H2O+M→Na+·H2O+M, k(3) = 1.0(+ 0.5, − 0.3) × 10−28cm6/secfor M = H2O, k(3) = 4.7(+ 1.2, − 1.0) × 10−30cm6/secfor M = He, K++H2O+M→K+·H2O+M, k(3) = 4.5(+ 2.3, − 1.5) × 10−29cm6/secfor M = H2O, k(3) = 2.6(+ 0.7, − 0.5) × 10−30cm6/secfor M = He. The consequences of these results for the D and E region of the upper atmosphere are briefly described.
Comprehensive Theory for Ion Cyclotron Resonance Power Absorption: Application to Line Shapes for Reactive and Nonreactive Ions
Authors: Comisarow Melvin B.
Published: February 2004

The equation of motion of an ion in an ion cyclotron resonance experiment has previously been shown to be dv / dt = (Eq / m) + [(qv × B) / m] − cv, where c is the reduced collision frequency. A power absorption expression has been obtained from the complete solution of the above equation which is valid at all pressures. This expression reduces in the appropriate limits to previously derived ICR power absorption expressions which are valid at either high or low pressure. The complete power absorption expression is used to derive ICR line shape expressions for an experimental ensemble of nonreactive ions and for an experimental ensemble of reactive primary, reactive secondary, and nonreactive tertiary ions. The power absorption expressions for the chemically reactive ions are dependent upon the assumed nature of the reactive ion–neutral collisions.
Soft-Mode Study of the Stress-Induced Phase Transitions near T in SrTiO3
Authors: Rokni M. , Wall L. S.
Published: February 2004

We have studied the stress-induced phase transitions of SrTiO3 in the vicinity of T0, by means of soft-mode Raman scattering. Theoretical expressions for the soft-mode frequencies, critical stresses, and linear displacements of the vibrating atoms are described in terms of the phenomenological theory. Experimental results of soft-mode frequencies versus stress in the [111] direction, for temperatures both below and above T0 are given. The temperature dependence of the coefficient of the harmonic force, in the vicinity of T0 is shown and discussed. Critical stresses for temperatures T > T0 are measured, and the equilibrium values of the linear displacements of the vibrating atoms are derived from the experimental results.
Reaction Kinetics in Stochastic Models
Authors: Widom B.
Published: February 2004

Two soluble models of chemical reaction kinetics are treated. It is found that the equilibrium approximation overestimates the true rate constants by a factor that is typically about 2 and may often be much larger. The mathematical mechanism by which a high activation energy is reflected in a long chemical relaxation time is studied and is found to be the same as the mechanism by which, in quantum mechanics, tunneling through a high potential barrier between two wells in resonance leads to a slight separation between the two lowest energy levels.
Resonance Offset Effects in Multiple-Pulse NMR Experiments
Authors: Haeberlen U. , Ellett J. D. , Waugh J. S.
Published: February 2004

The behavior of multiple-pulse NMR line narrowing experiments in solids as a function of the frequency offset from resonance is examined experimentally and theoretically. Resolution in the four-pulse, six-pulse, and phase-alternated tetrahedral angle experiments was found to increase on going off resonance. These results are explained using coherent averaging theory. The effective Hamiltonian which determines the width of the spectral line off resonance must be averaged over the motion caused by both the rf pulse Hamiltonian and the resonance offset Hamiltonian. It is assumed that the period of the motion caused by one of these two cyclic Hamiltonians is much shorter than the other so that the averages can be carried out sequentially rather than simultaneously. Two relaxation rates are evident in the four-pulse experiment on solids, corresponding to relaxation parallel and perpendicular to one of the body diagonals, e.g., the (111) direction, in the coordinate frame appropriate to that experiment. For solids containing a single magnetic nuclear species the two rates appear to be equal on resonance, but off resonance relaxation along the (111) direction is slower than relaxation perpendicular to it. This behavior is explained qualitatively by the fact that average Hamiltonians which do not in general commute with (Ix + Iy + Iz) do commute with this operator when they are further averaged over the motion caused by an offset from resonance. The effective heteronuclear dipole–dipole interaction Hamiltonian commutes with (Ix + Iy + Iz) both on and off resonance, which accounts for the difference in the two relaxation rates independent of resonance offset observed in solids containing more than one magnetic nuclear species.