bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoionization and Delayed Fluorescence of Dyes in Rigid Organic Matrices. I. A Proposed Model
Authors: Lim E. C. , Lazzara C. P. , Yang M. Y. , Swenson G. W.
Published: January 2005

The decay modes of the delayed fluorescence from rigid-glass solutions of acridine dyes at 77°K have been studied and compared with those of the transient absorptions which have previously been assigned to the radical ions produced from photoionization. While the decay of the radical-ion absorption is nearly exponential from the beginning, the decay of the emission is highly nonexponential and becomes approximately exponential only in the later stage of decay. The lifetime of the ``exponentially'' decaying component of the emission is identical with that of the ``radical ion.'' Although flash and steady excitations produce considerably different initial decay for the emission, the decay rate of the absorption shows very little or no dependence on the excitation mode. Both the integrated intensity of the delayed fluorescence and the initial absorbance of the radical-ion absorption are directly proportional to the intensity of the monochromatic flash-excitation source. These, as well as other results, are interpreted in terms of a model requiring the formation of solute—solvent charge-transfer states from the excited singlet states of the solute molecules as the primary process in photoionization. It is assumed that charge-transfer states which are unstable with respect to a complete charge separation dissociate and produce radical ions (holes) and trapped electrons, while the more stable ones return slowly to the excited singlet state by thermal activation. The formation of the excited singlets from the charge-transfer states and the hole—electron recombination is proposed to be responsible for the occurrence of the delayed fluorescence.
Fluorescence Decay of Rare-Earth Ions in Crystals
Authors: Barasch G. E. , Dieke G. H.
Published: January 2005

The decay of individual fluorescent transitions excited by monochromatic radiation was measured for most rare earths in hexagonal LaCl3 and other lattices. At 4°K the decay was found to be invariably exponential within the experimental errors; at higher temperatures it could occasionally be represented by several exponentials with different lifetimes. The data show that the free interval below the excited level is important for determining the probability for radiationless transitions. For Pr3+ in LaCl3, there is evidence that imprisonment of radiation prolongs noticeably the fluorescence lifetimes.
Guillemin—Zener Energy of H2+
Authors: Kim Sungwoon , Chang Tai Yup , Hirschfelder J. O.
Published: January 2005

The energy of the H2+ ground state 1sσ calculated with the Guillemin—Zener approximate wavefunction, ψs=Nsexp(−Raλ/2) cosh(Rbμ/2) lies within 0.0005 e2/a0 of the exact for the full range of internuclear separations. In the limit of zero separation, ψs=Nsexp(−rA−rB) cosh[(rA−rB)/3]. The energy still lies within 0.0010 e2/a0 when the additional requirement is imposed that Hψs remains finite at the nuclei. The Guillemin—Zener energy is less accurate for the first excited 2pσ state.
On the Evaluation of the Thermal-Diffusion Coefficient of Heavy Particles Using a Theory of Brownian Motion in a Nonuniform Medium
Authors: Nicolis G.
Published: January 2005

An extension of the theory of Brownian motion of heavy particles in a condensed medium of light particles is presented, which accounts for deviations of the state of the medium from equilibrium. The case of media under a thermal gradient is especially considered and the coefficients of diffusion and thermal diffusion of the heavy component are identified by solving the generalized kinetic equation for the Brownian particle distribution. The first terms of a systematic expansion of the thermal-diffusion coefficient in powers of the mass ratio are explicitly given, and their sign is found by an approximate further evaluation. It is suggested that the thermal-diffusion coefficient follows an asymptotic saturation law as far as the isotopic effect is concerned.
Exact Solutions for Many-Level Multiple-Resonance Problems
Authors: Freed Karl
Published: January 2005

The matrix elements of the time-development operator are obtained exactly for the influence of many resonant or near-resonant fields on a system with a finite number of levels for arbitrary initial conditions in a wide class of problems. Perturbative techniques are presented which enable the exact treatment of all perturbations to a desired order. As examples, a three-level double-resonance and two eight-level triple-resonance systems are given. The applications of these exact solutions to the treatment of perturbations, including relaxation phenomena, are presented using both standard-perturbation-theory and density-matrix techniques.
Paramagnetic Resonance of Trivalent 57Fe in Double Nitrate Crystals
Authors: Culvahouse J. W. , Olsen L. C.
Published: January 2005

The paramagnetic resonance absorption spectra of trivalent iron in double nitrate crystals have been identified and fitted by two spin Hamiltonians which correspond to the two sites into which the iron enters these crystals. The two sites appear to be the same as those occupied by trivalent chromium ions. The spin-Hamiltonian constants are reported for lanthanum zinc and cerium zinc double nitrates at temperatures of 4.2°, 77°, and 193°K. The hyperfine interaction constant for 57Fe in either site is (10.9±0.3)×10−4 cm−1 which is very close to the value anticipated for a hydrated complex.
Normal Coordinate Analyses of Hydrogen-Bonded Compounds. IV. The Acid Carbonate Ion
Authors: Nakamoto Kazuo , Sarma Y. Anantarama , Ogoshi Hisanobu
Published: January 2005

The infrared spectra of potassium acid carbonate and its deutero analog have been obtained from 4000 to 160 cm−1. The Raman spectrum of the latter has also been obtained in the crystalline state. A normal coordinate analysis has been carried out to estimate the force constants as well as to make theoretical band assignments. The infrared bands of the nondeuterated compound at ∼2620, 1405, and 248 cm−1 have been assigned to the O–H stretching, O–H···O in-plane bending, and O···H stretching coupled with C=O bending modes, respectively. The corresponding force constants are: O–H stretching, 3.20, O–H···O bending, 0.22, and O···H stretching, 0.76 mdyn/Å. Plots of these force constants versus O–H···O distances for three compounds thus far investigated yield a linear relationship for each force constant.
Paramagnetic Resonance in L-Cysteine Hydrochloride Irradiated at 77°K
Authors: Akasaka Kazuyuki
Published: January 2005

An electron paramagnetic resonance study has been made on a single crystal of L-cysteine hydrochloride irradiated with a 1.5-MeV electron beam at 77°K. The hyperfine structure of the main resonance pattern was found to be an almost isotropic double doublet, whereas the g factor was found to be highly anisotropic but axially symmetrical, the principal values being 2.29, 1.99, and 1.99. The main resonance has been attributed to the free radical HOOC–CH–CH2–S.          –         NH3Clwith the unpaired electron occupying one of the two nearly degenerate orbitals of the sulfur atom. A remarkable broadening of the resonance spectrum was observed at elevated temperatures, and evidence is given that this broadening is due to a short spin—lattice relaxation time due to a large spin—orbit coupling in this free radical.
Physical-Adsorption Isotherm Based on a Triangular-Site Model
Authors: Taylor Lyle H. , Longley William W. , Bryant Paul J.
Published: January 2005

A multilayer physical-adsorption-isotherm theory is developed; it assumes that a gas atom cannot be physically adsorbed in an upper layer unless there is a triangular array of three adsorbed atoms in the layer below forming a site for adsorption. Neighbor interactions via Lennard-Jones intermolecular potentials are included in the calculation of the adsorption energy. The resultant isotherm is linear for low coverages, indicates a horizontal interaction correction to the Langmuir adsorption isotherm when there is only first-layer coverage, and may yield a series of steps for sufficiently low temperature. Numerical adsorption isotherms for He on glass at 4.28° and 77°K are presented. The former isotherm exhibits distinctive steps when each layer is condensed, whereas the latter isotherm is quite smooth.
Optical Transmission of Graphite Compounds
Authors: Hennig G. R.
Published: January 2005

Lamellar compounds of graphite are often, but not always, deeply colored. To study this color, a number of different compounds have been prepared from very thin flakes cleaved from annealed single crystals. The spectral transmission of these samples has been measured between 0.2 μ and either 2.2 μ or, in a few cases, 25 μ. All lamellar compounds exhibit a transmission ``window'' of half-width about 0.2 μ, in which the absorption coefficient is three to five times lower than that of graphite. The frequency of the transmission maximum is closely proportional to the square root of the density of holes or electrons in the graphite part of the compound, suggesting that it is the plasma oscillation of the excess electrons or holes which is responsible for the transmission. The effective mass of these carriers is close to unity. In addition to these transmission maxima, a related broad absorption is observed in the far infrared. These optical measurements permit rapid evaluation of ionization efficiencies in concentrated lamellar compounds, and facilitate kinetic studies of reaction rates and diffusion.
Oxidation of CO. II. Influence of H2 on the Induction Period Preceding Rapid CO2 Formation in Shock-Heated CO–O2–Ar Mixtures
Authors: Myers B. F. , Sulzmann K. G. P. , Bartle E. R.
Published: January 2005

The influence of small amounts of hydrogen on the induction period, τi, preceding rapid CO oxidation in argon-diluted CO–O2 mixtures, has been studied at temperatures between 1500° and 3300°K and at pressures between 0.4 and 1.6 atm behind incident shock waves. The initial reaction regime was investigated by using spectral portions of the CO2-ν3 fundamental and CO-fundamental infrared bands and spectral portions of the ``CO flame emission.'' Up to 0.13% hydrogen was used in dilute mixtures containing between 5% and 20% O2 and between 10% and 20% CO. For constant temperature and hydrogen concentration, τi is inversely proportional to the square root of the product of the mole concentrations of (CO)i and (O2)i of the unreacted gas behind the shock front. The induction period is generally decreased with increasing amounts of hydrogen present; however, above 2400°K for an initial hydrogen concentration of 0.011%, this effect becomes negligible. Under the latter conditions, the dependence on temperature of τi can be represented by τi=k̄−1([O2]i[CO]i)−12,with k̄−1=6.4×10−15(±25%)×exp[40 000(±15%)/RT]mole·sec cm−3.It is demonstrated that a modified Haber—Semenov mechanism can be used to account qualitatively for the observed dependence on hydrogen of the induction period.
Polarized Ultraviolet Spectrum of Crystalline 2,4-Di-Iododecaborane
Authors: Smallwood Evelyn , Eberhardt W. H.
Published: January 2005

The absorption spectrum of 2,4-di-iododecaborane-12 has been studied in solution at 25°C and as a single crystal at 77°K with polarized radiation. The lowest electronic transition is interpreted as an allowed transition in the free molecule to either a B1 or B2 excited state. The origin is probably at 21 800 cm−1; the band has an oscillator strength of 0.037 in cyclohexane. The parent compound decaborane has an origin at 31 050 cm−1 and an oscillator strength in cyclohexane of 0.10. Simple MO arguments suggest that the spectrum may be described as a transition from an essentially nonbonding orbital mostly on the iodines into a boron framework orbital similar to that responsible for the lowest excited state of decaborane itself.
Spectroscopic Investigation of the Helium—Neon Molecule
Authors: Henderson W. R. , Matsen F. A. , Robertson W. W.
Published: January 2005

When a discharge is excited in a helium—neon mixture a band spectrum appears that is absent in the spectra of the separate gases. This spectrum has been attributed to the HeNe molecule. Although investigated here under fairly high resolution, the spectrum was not completely analyzed. However, substitution of 3He for 4He resulted in isotopic shifts in agreement with those calculated for the rotational structure of a diatomic HeNe molecule. Investigation of the spatial distribution of intensity of the atomic and molecular radiation in the cathode region of a dc discharge in a helium—neon mixture and of its behavior under a superimposed microwave field yielded an indication of the origin of the molecular spectrum. The molecular ion HeNe+ is evidently formed by the reaction He++Ne+X→HeNe++X and then recombines partially into bound states. The molecular radiation observed is thus attributed to transitions between weakly bound states of the neutral molecule HeNe populated from above by electron—ion recombination.
Infrared Absorption Spectra of Isotopic Dimeric Hydrogen Chloride Molecules
Authors: Rank D. H. , Glickman W. A. , Wiggins T. A.
Published: January 2005

The spectra of HCl and of HCl mixed with DCl at 195°K have been observed in the region of the HCl fundamental band. In the case of HCl three prominent lines occur in the null gap. Smaller complex features were observed in the region extending from R(0) to P(3). The intense lines at 2891.2, 2889.8, and 2889.0 cm−1 had relative intensities of 1:0.6:0.1. These lines have been shown to be due to the HCl dimer with a heat of formation of 2.1 kcal/mole. Treating the HCl–HCl molecule as a coupled nearly resonant system only two lines of relative intensity of 1:0.3 would be expected corresponding to the dimers (H35Cl–H35Cl, H35Cl–H37Cl) and (H37Cl–H35Cl, H37Cl–H37Cl) for the resolution possible with these broad features. If these are Q branches corresponding to a slightly bent dimer, the wide spread features would correspond to the other branches of the band. With the HCl—DCl mixture two additional lines were observed of separation 2.1 cm−1 and relative intensity 1:0.34. These are attributed to the dimers (H35Cl—D35Cl, H35Cl—D37Cl) and (H37Cl—D35Cl, H37Cl—D37Cl). Assuming nonresonant coupled oscillators, the measured frequencies can be computed within experimental error using a reduced mass for the molecule calculated by adding to the 35Cl or 37Cl the ΔH/D0 fraction of the mass of DCl, where ΔH is the heat of formation and D0 the dissociation energy of HCl.
Molecular Motion in Infrared and Raman Spectra
Authors: Gordon R. G.
Published: January 2005

It is suggested that Fourier transformation of infrared and Raman band shapes reveals the meaning of the spectrum in terms of molecular rotation much more clearly than does the usual frequency shape. By looking at the time dependence directly, one may separately examine the molecular motion at short and long times The motion at short times may be analyzed directly in terms of the molecular dynamics, by the use of a power series in the time, whereas the behavior at long times is best examined by statistical arguments. This kind of analysis is illustrated by several examples, including the spectra of liquid CO and CH4.
Bis(1-Phenyl-1,3-Butanedionato) Vanadyl. I. Molecular and Crystal Structure of the cis Form
Authors: Hon Ping-Kay , Belford R. Linn , Pfluger C. E.
Published: January 2005

The crystal structure of vanadyl bis(1-phenyl-1,3-butanedione) has been determined by two- and three-dimensional Fourier methods, and accurate atomic coordinates were obtained by three-dimensional least-squares refinements. The crystals are monoclinic with four molecules per unit cell. The space group is P21/c. The unit cell dimensions are a0=8.103,  b0=22.599,  c0=10.505 Å;  β=106∘47′.Both Cu Kα and Co Kα radiations were used for collecting the intensities. The over-all reliability factor (R) for 1894 independent reflections is 0.088.

The ligands are arranged in a cis configuration, and each phenyl ring is nearly coplanar with the chelate ring to which it is attached. The resulting balance of resonant and inductive effects appear in the bond distances and angles about the vanadium atom.
Ring Currents and Proton Shielding in Polycyclic Hydrocarbons
Authors: Parker G. W. , Memory J. D.
Published: January 2005

The ring-current contribution to the shielding constant, σring, is shown to depend on (A·p)Av. In an LCAO perturbation approach σring is then determined as a sum of two terms, each term depending on the same three-center integral. The derivation further indicates that an appropriate partition of the shielding constant in an arbitrary molecule would be σ=σring+σlocal+σ′, corresponding to a current density j=jring+jlocal. The term σ′ arises from (A2)Av. Numerical calculation of the ratio σring/σring (benzene) for the two naphthalene protons gives values 1.39 and 1.21. Estimates of these ratios experimentally are 1.28 and 1.0.
ESR and Optical Absorption Studies in Copper Diethyldithiocarbamate
Authors: Reddy T. Ramasubba , Srinivasan R.
Published: January 2005

ESR investigations at X band and optical-absorption measurements have been reported in single crystals of copper (II) diethyldithiocarbamate Cu[S2CN(C2H5)2]2 diluted to 0.2% with the corresponding zinc complex. The measurements have been made both at room and liquid-oxygen temperatures. ESR measurements gave the following values for the parameters in spin Hamiltonian g‖ = 2.1085, g⊥ = 2.023(6), A63 = 142.4×10−4 cm−1, A65 = 152.0×10−4 cm−1, B = 22.4×10−4 cm−1, Q′∼3×10−4 cm−1. Polarized optical absorption study has made possible a proper assignment of the absorption bands to their corresponding transitions. This has led to information regarding the ordering of the MO levels of the complex. The coefficients used in the MO description of the complex have been calculated from the observed parameters. The results show that the metal ligand B1g σ bond is purely covalent and that the out-of-plane π bonding is appreciably covalent whereas the in-plane π bonding is ionic. Further, it is noted that the metal ligand binding is more covalent with sulfur as ligand than with oxygen or nitrogen.
Influence of Intramolecular Hydrogen Bonding on Electronic De-excitation in Amidophenylbenzotriazoles
Authors: Merrill John R. , Bennett R. G.
Published: January 2005

Infrared absorption spectra show that the ortho isomer of a 2-(amidophenyl)-2,1,3-benzotriazole is intramolecularly hydrogen bonded. The quantum yields for fluorescence and chemical reaction of the ortho isomer are much lower than those of the non-hydrogen-bonded meta and para isomers. To establish how the hydrogen bond affects the response of these molecules to electronic excitation, measurements were made from which the rate constants of all deactivation processes have been calculated. Internal conversion from excited singlet to ground state is a hundredfold more rapid in the hydrogen-bonded species. Most of the photoexcitation energy is dissipated thermally within its singlet system. Hydrogen bonding does not affect the triplet levels nor change the chemical reaction rate constant of the excited singlet state. The rate of intersystem crossing in the compounds examined is unchanged in the temperature interval 77° to 300°K, while the rate of internal conversion within the singlet system is significantly reduced at the lower temperature.
Charge-Transfer-Controlled Vaporization of Cadmium Sulfide Single Crystals. II. Effect of Copper Doping on the Evaporation Rate of the (0001) Face
Authors: Somorjai G. A. , Lyon H. B.
Published: January 2005

The evaporation rate of copper-doped CdS single-crystal c face was measured in the temperature range 680°—740°C. The evaporation rate was decreased markedly with respect to that of the undoped crystals. The copper surface concentration dependence of the vaporization rate was studied by simultaneous diffusion of copper into, and vaporization of the crystal at the (0001̄) and (0001) crystal faces, respectively. The presence of copper impurity in the bulk of the crystal was found to also have an effect on the evaporation rate of CdS. The results were interpreted in terms of self-compensation in CdS via sulfur-vacancy formation, and copper- and sulfur-vacancy diffusion toward the vaporizing surface. Copper doping rendered the crystal vaporization insensitive to light.
Corrections to the Incoherent Scattering Factors for Electrons and X Rays
Authors: Bonham R. A.
Published: January 2005

The usual use of the closure relation in the derivation of the incoherent scattering factor for electrons and x rays involves approximations and introduces errors in the final result. In this paper corrections through third order for these errors are given. The correction terms are found to be of a simple form and can be quite important not only in the limit of low energy for the incident electron or x-ray beam but also for atoms of large atomic number. The magnitudes of the corrections for Ne and Ge are given for 40-kV electrons. In the x-ray case corrections are given for Ge for Cu Kα x radiation.
Reaction of Atomic Oxygen with Acetylene. II. Chemi-Ionization and Chemiluminescence
Authors: Arrington C. A. , Brennen W. , Glass G. P. , Michael J. V. , Niki H.
Published: January 2005

The chemiluminescence and chemi-ionization resulting from the room-temperature reaction of atomic oxygen with acetylene have been investigated. The absolute intensity of chemiluminescent radiation and the over-all rate of chemi-ion formation have been measured and the relative concentrations of various individual chemi-ions have been observed with a T.O.F. mass spectrometer.

It has been shown conclusively from these measurements that chemi-ionization does not arise primarily from the reactions: CH (A 2Δ)+O=CHO++e−,CH (A 2Δ)+C2H2=C3H3++e−.It has been shown also that if ionization arises from the reactionCH (X 2π)+O=CHO++e−,a mechanism that has also received wide support, then the ground state CH (X 2π) molecule must be produced by some mechanism other than that producing CH (A 2Δ).

The CH (A 2Δ—X 2π) system was found to be the most intense feature of the chemiluminescent spectrum. Weak emission from the C2 Swan bands and from the CN violet system was also observed. The intensity of the weak OH emission was found to be consistent with it being produced by reactions with molecular oxygen. The CH emission was shown to arise from a complex series of reactions involving the participation of three molecules of acetylene and two atoms of oxygen. Two possible mechanisms for its production are discussed.
Experimental Verification of the ``Dusty-Gas'' Theory for Thermal Transpiration
Authors: Hanley H. J. M.
Published: January 2005

A theory for thermal transpiration based on the dusty-gas model has been proposed by Mason, Evans, and Watson. For verification the theory ideally requires both nonisothermal and isothermal measurements on a sample of porous material. Such measurements are reported and it is found that the dusty-gas theory satisfactorily reproduces the experimental results except when the gas adsorbed appreciably on the sample.
Line Shapes of Triplet ESR Spectra: The Effects of Intermolecular Exciton Transfer
Authors: Hudson A. , McLachlan A. D.
Published: January 2005

The system considered is a molecule like triptycene where triplet excitation can jump between several equivalent sites whose Hamiltonians do not commute. The line shapes are calculated from the Bloch equations for the density matrix, and the result involves inverting a certain matrix with complex elements which depend on the jumping rate. The method is similar to Sack's method for sites whose Hamiltonians do commute. The complete line-shape function is found in zero magnetic field and when the field is along the triad axis. General perturbation formulas are derived for finding the broadenings and frequency shifts which occur in the limits of very fast and very slow jumping. The direct calculation of the line shapes for tribenzotriptycene in a glassy matrix has not been attempted, but the results obtained for the oriented triplet agree quite well with the observed ESR spectra of the glass. The method is also applied to the problem of a spin ½ which jumps between two sites with different g tensors.
Energy Transfer from Solvent to Solute in Organic Solutions under Excitation in the Vacuum Ultraviolet
Authors: Laor U. , Weinreb A.
Published: January 2005

Solutions of 2,5-diphenyloxazole (PPO) in benzene, toluene, cyclohexane, and hexane are selectively excited by radiation in the wavelength region 3000–1100 Å, and the resulting fluorescence is recorded. It is found that all four solvents transfer excitation energy to the solute in the region in which they strongly absorb. Possible implications of these results for γ and β excitation are considered.
Dipole Matrix Elements for Helium in the First-Order Shielding Approximation
Authors: Sando Kenneth M. , Epstein Saul T.
Published: January 2005

The first-order shielding approximation is used to calculate dipole matrix elements for the 21S–21P and 11S–21P transitions in two-electron atoms.
Numerical Spectroscopy
Authors: Rotenberg Manuel
Published: January 2005

A numerical procedure for solving the time-dependent Schrödinger equation is given. It is found that by observing the power spectrum generated by the time-dependent solution, the set of eigenvalues of the corresponding stationary problem can be determined directly. The procedure involves solving the time-dependent Schrödinger equation, Fourier analyzing the solution, and finally averaging the squared modules of the solution over space. Formulas to accomplish these tasks efficiently are given.
Theory of Radiation from a Wave Packet
Authors: Bierman Arthur
Published: January 2005

The theory of radiation from a time-dependent state (wave packet) is developed, using Heitler's method. It is first applied to a two-component wave packet, and general expressions for the radiation rate and the spectral distribution are derived. They are evaluated to lowest order in the perturbing Hamiltonian, and a number of special cases are considered. The theory is then generalized to an N-component wave packet, and formulas for the radiation rate and spectral distribution are derived. The latter is briefly discussed within the context of an approximation method. The general conclusions are: the radiation rate from a wave packet has a periodic component; energy nonconserving transitions appear; interference terms tend to distort the Breit—Wigner shape of the spectral distribution.
Radiation from an Exciton Wave Packet
Authors: Bierman Arthur
Published: January 2005

Properties of radiative transitions from exciton states in a linear chain and in a ring (periodic boundary conditions) are examined. The two models exhibit a persistent difference in the radiation rate even for stationary-state transitions. Exciton wave packets are shown to radiate weakly if they originate at the end of the linear chain, strongly if they originate near the middle of the chain. The latter radiation shows also a strong periodic component. The radiation rate of a wave packet from a ring turns out to be the same as the rate from an isolated monomer and has no periodic components. For both the ring and the chain the wave packet is much more stable against decay than a stationary state. Radiation from a wave packet shows little deviation from the Breit—Wigner shape.
Thermal Expansion of a Uranium Monocarbide—Zirconium Monocarbide Solid Solution
Authors: Kempter Charles P. , Merryman Roy G.
Published: January 2005

The thermal expansion of a polycrystalline (U0.30, Zr0.70)C0.97 solid solution was determined between 25° and 982°C by means of a high-temperature x-ray diffraction technique. For the range 25° to 1000°C the average linear thermal-expansion coefficient is 7.78×10−6/°C. The 25°C lattice parameter is 4.7822 Å, the calculated density 8.94 g/cm3, and the diamond pyramid hardness 1800 kg/mm2.
Thermal Expansion of Tantalum Monocarbide to 3020°C
Authors: Kempter C. P. , Nadler M. R.
Published: January 2005

The dilatometric thermal expansion of a tantalum monocarbide rod was measured from 21° to 3020°C in a 20 psig argon atmosphere using a split-beam optical comparator. The linear thermal expansion from 20° to 3000°C was found to be 2.5%, which corresponds to an average coefficient of linear thermal expansion of 8.4×10−6 per C°. No evidence of a high-temperature phase change was found.
Fluorescence of Trivalent Europium in D2O–H2O Mixtures
Authors: Gallagher P. K.
Published: January 2005

The absorption and emission spectra and fluorescent lifetimes of solutions of europium (III) chloride in D2O–H2O mixtures were measured. The lifetime of the most deuterated solution, 99.6%, was found to be 3.9 msec while that of the undeuterated solution was 0.12 msec. The decay curves of intermediate solutions exhibited two portions having lifetimes essentially equal to the end members. These results are discussed and compared with those of previous investigators.
Ion—Molecule Interaction in the Cathode Region of a Glow Discharge
Authors: Shahin M. M.
Published: January 2005

Studies of the ions arriving at the cathode of a glow discharge in nitrogen have been made by the use of a quadrupole mass spectrometer. Detailed investigation of the dependence of the relative intensities of the two major ions N2+ and N+ on the discharge conditions indicates that the latter species mostly originate within the cathode dark space, probably through the reaction N2++N2→N++N+N2. Calculation of the reaction time, with due allowance for the resonance charge exchange of N2+ ions, permits the treatment of the data to yield a value of 7.4×10−11 cc/sec for the rate constant of this reaction, at ion energies above the minimum of 17.4 eV required for this process.
Electric and Magnetic Properties of the Strontium Ferrates
Authors: MacChesney J. B. , Sherwood R. C. , Potter J. F.
Published: January 2005

A series of strontium ferrate compositions ranging from SrFeO2.7 to SrFeO3.0 have been produced by equilibration at oxygen pressures ranging from 0.2 to 855 atm. The stoichiometric composition SrFeO3.0 exhibits a simple cubic perovskite structure (a=3.850 Å). Ceramic disks of this material are conductive (ρ≈10−3 Ω·cm) and their temperature dependence is characteristic of metallic conduction. Magnetic measurements indicate that SrFeO3.0 is antiferromagnetic below 130°K. With increasing oxygen deficiency, specimens show increased cell constants and eventually tetragonal distortion. Decrease in the Néel temperature and increased resistivity accompany these changes.
Mobility of Negative Ions in O2 at Low E/N
Authors: Voshall R. E. , Pack J. L. , Phelps A. V.
Published: January 2005

Measurements of negative-ion mobilities in pure O2 were made as a function of gas pressure (2–700 Torr), gas temperature (77.4° to 373°K), and electric field. Values of E/N, electric field over gas density, ranged from 6×10−19 to 6×10−17 V·cm2 so that the ions were in thermal equilibrium with the gas. The ion mobility times gas density μN is independent of density for 195°K and above. Values of μN for this ion, O2−, are 5.7×1019, 6.5×1019, 6.8×1019 V−1·sec−1·cm−1 for temperatures of 195°, 300°, and 373°K, respectively. The density dependence of the measured mobilities at 77.4° and 87.6°K is consistent with an equilibrium between the concentrations of O2− and O4− ions. The low-density data yield values of μN for the O2− ion of 4.7×1019 and 4.9×1019 V−1·sec−1·cm−1 at 77.4° and 87.6°K. The μN value of O4− ions is 2.6±0.5×1019 V−1·sec−1·cm−1 at both temperatures. Correlation with models for the internal motion of O4− leads to an estimated dissociation energy of 0.06±0.02 eV.
Electron Spin Resonance of γ-Irradiated Sodium Citrate Pentahydrate and Pentadeuterate
Authors: Russell David B.
Published: January 2005

An analysis of the electron spin resonance spectra of γ-irradiated single crystals of sodium citrate pentahydrate and sodium citrate pentadeuterate, deuterated by exchange with deuterium oxide, indicates that two long-lived radicals are present in both the protonated and deuterated citrates. One radical is of the form {      ĊH–COONa       –HO–C–COONa       –      CH2–COONa}·5H2O,with principal values of the proton hyperfine tensor of −91.1, −54.2, and −36.7 Mc/sec. The second radical gives a triplet with relative intensities 1:2:1 and splittings of 16 and 15 Mc/sec along the [100] and [001] axes of the crystal, respectively, and a quartet of lines of equal intensity with splitting of 21.5 and 28.0 Mc/sec along the [010] axis of the crystal, due to the interaction of two protons with the unpaired electron. The radical is possibly of the form {      CH2–COONa       –·O–C–COONa       –      CH2–COONa}·5H2O,with the unpaired electron coupling with one proton of each methylene group.
Infrared and Raman Spectra and Valence Force Constants of Iodine Oxide Pentafluoride (IOF5)
Authors: Smith D. F. , Begun G. M.
Published: January 2005

The infrared and Raman spectra of IOF5 have been recorded. The data have been tabulated, and assignments made on the basis of an octahedral structure with a fourfold symmetry axis. Valence force constants have been calculated. The bond angles are close to 90°, and there is an indication that the equatorial I–F bond lengths are about the same as the axial I–F bond length.
Polarization of Aromatic Carbonyl Spectra
Authors: Shimada Ryoichi , Goodman Lionel
Published: January 2005

The polarization of the phosphorescence and the polarized excitation spectra (using the 0–0 band of the polarized T→S emission) covering the region 4000–2500 Å have been examined for nine aromatic carbonyl compounds in EPA rigid media at 77°K. The principal conclusions are: (1) The S—T3U(n, π*)→1A transition is predominantly z or z′ polarized (coordinate orientation is given in Fig. 2) in accord with spin—orbit coupling predictions. (2) The principal source of intensity in the 1U(n, π*)←1A bands is vibronic. The most important vibronic path involves a2 vibrations in C2v with analogs a in C2 and a″ in Cs. These vibronic sources of intensification are more significant than the intrinsic allowedness engendered by formal destruction of C2v symmetry in aromatic aldehydes and ketones. This conclusion requires the apparently allowed totally symmetric bands (possibly including the 0–0 band) in benzophenone to be predominantly vibronically induced. (3) The interaction of the rings in the double-ring compounds, anthrone and benzophenone splits the localized 1Lb(π, π*) states, giving rise to the A state at a lower energy than the B state. The observed sequence and large energy separation (3000–4000 cm−1) is not in accord with dipole—dipole interaction as the major source of splitting. (4) The 0–0 region of the 1Lb(π,π*)←1A transition in the single-ring carbonyl compounds is polarized predominantly perpendicular to the carbonyl-ring axis in accord with previous measurements on other substituted benzenes, and with the carbonyl group acting approximately as a C2v π-electron perturbation on the ring. Weaker bands are predominantly z′ polarized requiring vibronic coupling with long-axis states through b1 analog vibrations. (5) The observed z (or z′) polarization of the 2500-Å band in all the aromatic carbonyl compounds studied confirms Tanaka and Nagakura's hypothesis that this band is due to an intramolecular ring—carbonyl charge-transfer transition.
Thermochemistry of the Bromination of Chloroform and the Heat of Formation of the CCl3 Radical
Authors: Benson Sidney W.
Published: January 2005

From Sullivan and Davidson's measurement of the equilibrium constant for Br2+CHCl3⇌ lim AHBr+CCl3Brat 442°K, and accurate CP° and entropies for the species involved, we find ΔSA°(298°K) = 2.2±0.2 gibbs/mole and ΔHA°(298°K) = −0.80±0.13 kcal/mole. Using known ΔHf° we calculate the unknown ΔH°f,298(CCl3Br) = −8.7±1 kcal/mole.

Analyses of the kinetic data together with reasonable estimates of S°(ĊCl3) and CP°(ĊCl3) permit assignments to be made of the Arrhenius parameters of the rate constants in the detailed mechanism. Analysis of the initiation and termination steps permit fixing limits on the activation energies for these steps as follows: Br+CHCl3⇌ lim 21HBr+ĊCl3ĊCl3+Br2⇌ lim 43CCl3Br+Br.E2=E3+0.22 kcal/mole≤2.0 kcal≈1.0±0.5 kcal/mole. These then lead to ΔH°f,298(ĊCl3) = 19.7 kcal/mole and DH°(CCl3–H) = 95.7±1.5 kcal/mole. Some other DH°(CCl3—X) bond strengths are listed.
Effect of Chemical Combination on the Soft X-Ray K Emission Bands of Nitrogen and Carbon
Authors: Fischer David W. , Baun William L.
Published: January 2005

Chemical combination has a marked effect on the shape of the x-ray K emission bands of nitrogen and carbon. Nitrogen bands from a few nitrides and carbon bands from graphite, diamond, lampblack, and some metallic carbides are shown. The wavelengths of the most prominent parts of the bands are listed as are the half-bandwidths and full bandwidths. Results were obtained using electron excitation, a lead stearate crystal, and flow proportional counter.
Microwave Spectrum of Bromobenzene, Its Structure, Quadrupole Coupling Constants, and Carbon—Bromine Bond
Authors: Rosenthal Eli , Dailey B. P.
Published: January 2005

As part of a study of the effects of substitution in the benzene ring, an experimental investigation of the microwave spectrum of bromobenzene has been carried out. The spectrum of four isotopically substituted molecular species of bromobenzene have been obtained: C6H579Br, C6H581Br, C6D579Br, and C6D581Br. Rotational and quadrupole coupling constants were obtained in each case.

The number of experimental rotational constants obtained was insufficient to permit a determination of the structure of the molecule without additional assumptions. The following structure is obtained for bromobenzene if hexagonal symmetry of the ring is arbitrarily assumed: rC–C1.4020 Å;rC–H1.0698 Å;rC–Br1.8674 Å.

The quadrupole coupling data for these molecules are consistent with a value of 1%—2% double-bond character for the C–Br bond.
Vibronic Interaction of Nearly Degenerate States in Substituted Benzene Anions
Authors: Hobey William D.
Published: January 2005

The pseudo-Jahn—Teller effect, the vibronic interaction of nearly degenerate electronic states, arises in the same manner as the Jahn—Teller effect itself. An iteration method, suitable for desk calculation, has been developed to allow computation of the vibronic wavefunctions and energies of a system with two closely spaced electronic states. A calculation on benzene anion compares favorably with previously published results. The method, in combination with semiempirical evaluation of the necessary parameters, has been applied to various substituted benzene anions and the ESR spectra of these anions predicted. The results compare satisfactorily with experiment and indicate that the spectra are the net result of three principal factors, configuration interaction among the simple molecular orbital electronic states, vibronic coupling, and thermal equilibrium between at least two vibronic states.
Diffusion Along Dislocations
Authors: Luther Lars C.
Published: January 2005

The Smoluchowski pipe model for diffusion along dislocations is modified so as to allow an exact solution of the two-dimensional diffusion equation. Using the continuously variable diffusion coefficient: D=D0/r2, where r is the radial coordinate perpendicular to the dislocation, rather than a step function, yields a diffusion profile proportional to: (D0t)−¼ exp[−2z/a(D0t)¼], a=Γ(¼)(2π)−½≃1.45 for large z, where z is the coordinate perpendicular to the surface from which diffusion occurs. Near the surface, where the Smoluchowski theory fails, the penetration is predicted to be anomalously high.

A characteristic diffusion coefficient for a grain boundary composed of parallel dislocations was calculated on the present model and found to be inversely proportional to the spacing of the dislocations.
Spin—Orbit Interaction Terms for the p4—nd Configuration
Authors: Koozekanani S. H. , Ciftan M.
Published: January 2005

Spin—orbit interaction matrices for the configuration (p4LS)—nd are given in the LS coupling scheme.
X-Ray Determination of the Structure of Liquid Methane
Authors: Petz John I.
Published: January 2005

X-ray diffraction measurements from liquid methane at four conditions of temperature and pressure ranging from near the triple point to the critical point indicate a structure of molecules in the liquid resembling close packing of spheres. The first peaks in the density functions are asymmetric and have areas and positions which range from 11.4 nearest neighbors at 4.24 Å and 96°K to 7.2 nearest neighbors at 4.35 Å and 186°K. The methane x-ray form factor is derived from gaseous scattering experiments.
Electron Spin Resonance Studies of the Onset of Metallic Character in Metal—Ammonia Solutions
Authors: Catterall R.
Published: January 2005

Asymmetric electron spin resonance spectra are described for moderately concentrated solutions of the alkali metals in liquid ammonia as functions of temperature, metal concentration, and concentration of added electrolytes. Both the asymmetry and the linewidth increase markedly above a critical temperature, corresponding to a thermal promotion of electrons from trapping sites to a conduction band. The g factor of the asymmetric resonance is strongly dependent on the concentration of added iodides.
Irreducible Cartesian Tensors
Authors: Coope J. A. R. , Snider R. F. , McCourt F. R.
Published: January 2005

This paper considers certain simple and practically useful properties of Cartesian tensors in three-dimensional space which are irreducible under the three-dimensional rotation group. Ordinary tensor algebra is emphasized throughout and particular use is made of natural tensors having the least rank consistent with belonging to a particular irreducible representation of the rotation group. An arbitrary tensor of rank n may be reduced by first deriving from the tensor all its linearly independent tensors in natural form, and then by embedding these lower-rank tensors in the tensor space of rank n. An explicit reduction of third-rank tensors is given as well as a convenient specification of fourth- and fifth-rank isotropic tensors. A particular classification of the natural tensors is through a Cartesian parentage scheme, which is developed. Some applications of isotropic tensors are given.
Flame-Photometric Determination of the Dissociation Energies of the Alkaline-Earth Oxides
Authors: Kalff P. J. , Hollander Tj. , Alkemade C. Th. J.
Published: January 2005

Two independent methods for determining dissociation energies of CaO, SrO, and BaO from optical measurements of band and line intensities in CO—air flames are described. The emitter of the measured bands has been shown not to be hydroxide molecules or molecules containing more than one metal atom. From a comparison of the results for both methods it can be concluded that the value of the electronic partition function of the alkaline-earth oxide molecule is around 6. Recommended values for the dissociation energies are (in electron volts): 3.96±0.06, 4.11±0.06, and 5.00±0.10 for CaO, SrO, and BaO, respectively. A comparison with the literature data is given.
Proton Dynamics in Hydrogen-Bonded Ferroelectrics
Authors: Imry Y. , Pelah I. , Wiener E.
Published: January 2005

A comparison between infrared absorption and neutron inelastic-scattering measurements indicates the existence of a broad low-energy (around 400 cm−1) protonic level in KH2PO4 above the Curie point. This level is only weakly discerned in the ir but is seen quite clearly in neutron scattering. The mode is explained as resulting from splitting of the ground level of the proton in a slightly asymmetric double minimum potential well where tunneling of the proton takes place. The asymmetry is caused by the interaction between the different protons, and it changes slowly with time as the result of the collective motions of the protons. Prominent changes in ir spectra in the 400-cm−1 range were found on cooling through the Curie point, indicating the disappearance of the tunneling mode.

This picture allows a simplified treatment of the system, leading to the existence of two correlated phase transition points, and a negative thermal expansion coefficient of the H bond at temperatures between these points. The two transition points are identified as the Curie point and the melting or dissociation point of the crystal. The theory also suggests an increase in the dielectric constant as the melting point is approached, corresponding to the Curie—Weiss behavior as the Curie point is approached.
Potential-Energy Curves for the X 1Σg+, b3Σu+, and C 1Πu States of the Hydrogen Molecule
Authors: Kol/os W. , Wolniewicz L.
Published: January 2005

Previous calculation of the ground-state energy of H2 has been extended to include large internuclear distances and accurate potential-energy curve for 0.4≤R≤10.0 a.u. is presented. For 0.4≤R≤4.0 a.u. expectation values of several operators have also been calculated. The calculation was made using a wavefunction in the form of an expansion in elliptic coordinates. The wavefunction depends on the interelectronic distance but, in contrast to the James—Coolidge expansion, is flexible enough to describe properly the dissociation of the molecule. Extensive calculations have also been made for the repulsive 3Σu+ state (1.0≤R≤10.0) and for the 1Πu state (1.0≤R≤10.0). In the former case a van der Waals minimum has been found at R=7.85 a.u. and 4.3 cm−1 below the dissociation limit. For the 1Πu state the computed binding energy De=20 490.0 cm−1 and the equilibrium internuclear distance Re=1.0330 Å are in a satisfactory agreement with the experimental values De=20 488.5 cm−1 and Re=1.0327 Å. In this case a van der Waals potential maximum has been found to occur at R=9.0 a.u. and 105.5 cm−1 above the dissociation limit. Preliminary results for the 1Σu+ state at R≈Re are also given.
Color-Center Kinetics in Cerium-Containing Glass
Authors: Stroud Jackson S.
Published: January 2005

The formation and thermal bleaching of radiation-produced color centers in cerium-containing soda—silica glass are studied to determine the effect of cerium on color-center kinetics. The optical absorption changes occurring during and after irradiation with gamma and x rays are measured. The data are fit by equations obtained by integrating a set of reaction-rate equations. These equations are an approximate description of the following three processes that account qualitatively for the effects of cerium concentration and oxidation state: Ce3+ ions, by capturing radiation-produced holes to form Ce3+ + centers, inhibit formation of all other kinds of centers due to trapped holes; Ce4+ ions, by capturing electrons to form (Ce4+ + electron) centers, inhibit formation of all other kinds of centers due to trapped electrons and inhibit recombination of electrons with trapped holes; after cessation of irradiation, holes are transferred from their traps to Ce3+ ions.
Method of Determining the Existence of Quasicontinuous Trap Distributions from Luminescence
Authors: McCubbin W. L.
Published: January 2005

It is shown that the usual analysis of luminescence decay is incapable of distinguishing between the very different physical situations of electron liberation from a single trap level, followed by recombination with kinetic order >1, and liberation from a quasicontinuous distribution, followed by recombination involving first-order kinetics. However, an exact solution for the case of a uniform distribution indicates departures from the hyperbolic decay curve which suggest a method of establishing the existence of a trap distribution, even when this is not uniform.