bluuebunny/crossref_metadata_2025 huggingface dataset:
Vacuum-Ultraviolet Absorption Spectrum of Carbon Suboxide. II. The Effect of Low Temperature and the Effect of High Pressure of an Inert Gas on the 1780-Å Band
Authors: Roebber John L.
Published: February 2004

The gas-phase absorption spectrum of the 1780-Å band of carbon suboxide has been measured photo-electrically at both room and dry ice temperatures and in the presence of a high pressure of argon using a 1-m vacuum monochromator having a 1.0-Å bandwidth. The addition of 1500 psi of argon greatly broadens the vibrational structure and shifts the whole band to higher energies. On cooling from 298°K to 195°K, the size of the 14 vibrational bands on the 1780-Å transition remain unchanged relative to each other, but the intensity of the transition is decreased. The constancy in relative size of the vibrational bands at different temperatures rules out the possibility that they are a vibrational sequence in the 63-cm−1 ground-state πu bending mode and confirms their assignment as a progression in a 400-cm−1 excited-state bending vibration. The decrease in oscillator strength as the temperature is lowered and the regularity of the progression as it passes over the peak of the band imply that the linear–linear vertical transition is forbidden. The effect of the high pressure of argon on the 1780-Å band indicates that it is borrowing its intensity from a Rydberg band. The presence of a long progression in a bending mode is strong evidence that the equilibrium configuration in the excited state is nonlinear. The Herzberg–Teller theory of vibrationally induced electronic transitions and an INDO molecular orbital calculation have been used to assign the upper states of the 2650-, 1780-, and 1587-Å bands.
Studies of Chemical Shift Anisotropy in Liquid Crystal Solvents. IV. Results for Some Fluorine Compounds
Authors: Yannoni Costantino S. , Dailey Benjamin P. , Ceasar Gerald P.
Published: February 2004

Measurement and analysis of the nuclear magnetic resonance spectra of 19F nuclei in nematic liquid crystal solutions have been used to obtain the fluorine chemical shift anisotropy in sym-C6F3Br3, sym-C2F3Cl3, and for CF3I. Values of the chemical shift anisotropy relative to the molecular symmetry axis were 112 ppm, 76 ppm, and − 8 ppm, respectively. An attempt to account for these results and other similar ones for 19F using the Karplus–Das equation was unsuccessful. A probable source of difficulty was the necessity of assuming axial bond symmetry for the C–F bond in order to transform the chemical shift anisotropies from the molecular symmetry axis to the C–F bond axis.
Infrared Chemiluminescence from the Reaction of Hydrogen Atoms with Oxygen Difluoride
Authors: Perona M. J.
Published: February 2004

Infrared emission from the reaction H+OF2→HF*+OF was observed in a flow system under a variety of conditions. Possible mechanisms for the relaxation of HF* are discussed, and attempts are made to estimate the extent of relaxation. These estimates are used to calculate the vibrational energy distribution of the initially formed HF*. The fraction of the available energy partitioned to the HF product is ≥ 32%. Reaction (1) is compared with its chlorinated analogue on the basis of mechanism and energy partitioning.
Vibration→Vibration Energy Transfer in Hydrogen Chloride Mixtures
Authors: Chen Hao-Lin , Moore C. Bradley
Published: February 2004

Laser-excited vibrational fluorescence experiments on HCl mixtures have given cross sections for vibration→vibration energy transfer from HCl to other molecules: σHCl→HBr = (2.1 ± 0.2) × 10−17 cm2, σHCl→N2 = (4.2 ± 0.4) × 10−19cm2, σHCl→HI = (3.5 ± 0.5) × 10−18cm2, σHCl→CO = (1.3 ± 0.15) × 10−18cm2, σHCl→DCl = (1.66 ± 0.1) × 10−18cm2, σHCl→CH4 = (3.7 ± 0.3) × 10−17cm2, and σD2→HCl (transfer from D2to HCl) = (2.1 ± 0.2) × 10−17cm2. The cross sections are considerably larger than for other diatomic–diatomic systems and decrease comparatively slowly with increasing energy difference between the vibrational levels. This behavior may result from strong “chemical” intermolecular forces, from energy transfer to rotation, and from the large amplitude of hydrogen atom stretching vibrations. The lack of a smooth correlation between cross section and energy difference illustrates the importance of the nature of the collision partners.
Ultrasonic Investigation of Acetic Acid Hydrogen Bond Formation. I. Acetic Acid–Acetone Solutions
Authors: Corsaro Robert D. , Atkinson Gordon
Published: February 2004

Ultrasonic absorption has been measured in acetic acid–acetone mixtures in the concentration range 5.47M acetic acid to 17.38M (glacial). The frequency range covered was 0.5–30 MHz, and all the systems fit a single relaxation mechanism. It is demonstrated that the chemical process responsible for the relaxation is an equilibrium of the form D ⇄ lim krkf C, where D and C are believed to be the “closed” (two H bond) and “open” (one H bond) forms of the acetic acid dimers. This scheme gives a quantitative fit of the ultrasonic data and complete thermodynamic and kinetic parameters if the rate constants are assumed to be viscosity dependent.
On the OH Stretching and the Low-Frequency Vibrations of Carboxylic Acid Cyclic Dimers
Authors: Redington Richard L. , Lin Kenneth C.
Published: February 2004

Infrared spectra for the hydroxyl stretching region of matrix-isolated CF3COOH, CF3COOD, and CH3COOH are reported, and the vapor-phase spectrum of CF3COOH in the region below 500 cm−1 is given. Characteristic line spacings that are found to reproduce the observed spectral features of the high-frequency region are also found to be associated with the low-frequency spectra. Fundamental frequencies for the cyclic dimer ring vibrations are suggested. It is concluded that the well-known band broadening in the hydroxyl stretching region is due to combination bands of the low-frequency modes with the OH fundamental vibration and with nearby binary excitations of the COH(D) bending and the C–O stretching vibrations. A model such as that proposed by Marechal and Witkowski, which considers interactions between the low-frequency and the high-frequency vibrations, seems appropriate in order to explain the intensities of the high combination bands that occur. Further emphasis for the unusual vibrational properties of the mixed COH bending and C–O stretching coordinates in these acids is provided by the spectrum of matrix-isolated monomeric CF3COOH(D). In this case the nominal COH bending vibration of monomeric CF3COOH is clearly doubled while the corresponding COD vibration appears as a single band shifted to lower frequency. The behavior is compared with that for matrix-isolated acetic acid monomers.
Low-Resolution Study of the Inelastic Continuum of N2
Authors: Tisone Gary C.
Published: February 2004

The energy-loss cross section for 500−eV electrons incident on N2 in the range 30–110−eV energy loss has been studied in the angular range 10°-30°. This region of the ionized continuum of N2 was studied with an energy resolution (Δε/ε) of 1.5% and an angular resolution of about 1.5°. The contribution of the differential cross section to the total energy-loss cross section was found to be significant.
Photosensitized Ionization of Molecules by Argon: Comparison with the Photoionization Mechanism
Authors: Klots Cornelius E.
Published: February 2004

Photoionization efficiencies of 16 molecules at the wavelengths of the argon resonance lines have been measured and compared with the analogous efficiencies obtained when these molecules quench photo-excited argon atoms. The characteristic equivalence between the two excitation modes and the kinetics of the quenching corroborate the long-range dipole—dipole energy-transfer model. Exceptions are noted. Monte Carlo simulations of radiation imprisonment are illustrated and used to interpret the experiments.
Determination of Interatomic Potentials by the Inversion of Elastic Differential Cross Section Data. I. An Inversion Procedure
Authors: Klingbeil R.
Published: February 2004

A computational procedure is developed for obtaining a numerical potential from a set of well-resolved differential cross sections. The inversion procedure is performed in two steps: (1) the phase shifts are extracted from the differential cross sections by a least-squares fitting procedure, and (2) the numerical potential is obtained from the phase shifts by a modified Firsov method. A numerical example is given and the method is shown to be very accurate.
Measured Radiative Lifetimes and Electronic Quenching Cross Sections of BaO(A 1Σ)
Authors: Johnson S. E.
Published: February 2004

Lifetimes of the A 1Σ state of BaO have been measured for the vibrational levels v′ = 0 to 11 from the fluorescence decay excited by a short-pulsed (10 nsec) tunable dye laser. Radiative lifetimes were found to vary with vibrational level from 0.275 ± 0.022 to 0.389 ± 0.016 μsec, with a value of 0.356 ± 0.007 μsec for v′ = 0. Electronic transition moments and absorption oscillator strengths have been calculated from the measured lifetimes. Measured quenching cross sections of BaO (A 1Σ) by helium vary with vibrational level by nearly an order of magnitude from 0.28 to 2.28 × 10−16cm2, suggesting that part of the electronic quenching is through collisional transfer into a perturbing state. Consistent with this model of quenching is the fact that a second fluorescence decay, with a lifetime of 10 ± 2 μsec, was observed at high helium pressures from vibrational levels exhibiting strong quenching.
Order-Disorder Phenomena. VII. Critical Variations in the Length of NH4Cl Single Crystals at High Pressures
Authors: Weiner Bruce B. , Garland Carl W.
Published: February 2004

A high-precision capacitance method has been used to investigate variations in the length L of an NH4Cl single crystal in the vicinity of its order—disorder transition line. At low pressures, there is a small first-order discontinuity ΔL superimposed on the lambdalike variation in L. At 255.95°K and 1491.8 bar, L varies continuously but κT and α appear to diverge. At higher pressures, the variation in L at the transition becomes progressively more gradual as the pressure increases. The linear isothermal compressibility in the immediate vicinity of the transition is well represented along an isotherm by κ L = (κ lim ∼L + B φ −y) / (1 + 2 pB φ −y), where φ ≡ |  p−p c  | /  p c and pc is the transition pressure for the given isotherm. The quantity κL has been assigned the constant value 1.57 × 10−6bar−1 for all isotherms; B and y (which are assumed to be independent of pressure) vary with the temperature. The linear isobaric coefficient of thermal expansion is fairly well represented along an isobar by α L = α lim ̃L + Aε−x, where ε ≡ |  T−T c  |/T c and Tc is the transition temperature for the given isobar. The quantity α lim ̃L has been assigned the constant value 5.0 × 10−5deg−1 for all isobars; A and x (which are assumed to be independent of temperature) vary with the pressure. The exponents x and y, which range from 0.4 to 0.9, are much larger than those associated with an ideal Ising lattice.
Measurement of the Triplet-Triplet Absorption Spectrum of Tetracene Using cw Argon Laser Excitation
Authors: Pavlopoulos T. G.
Published: February 2004

Polarization data for the triplet-triplet (T-T) absorption spectrum of tetracene over the region 310–490 nm were obtained. This spectral range includes the region where strong overlap with singlet-singlet (S-S) absorption occurs. An approximate method was developed to obtain the degree of polarization P of triplet levels in regions of strong S-S absorption. For excitation, the 476.5-nm line from a continuous wave (cw) argon laser was employed. The polarization curve indicates the presence of two different electronic transitions. The three strong absorption bands at 485, 468, and 440 nm are negatively polarized and could be assigned to the B3g-3←B2u+3 transition. The weaker bands at 412, 385, 360, and 320 nm are positively polarized and are thus assigned to the A1g-3←B2u+3 transition. These new data provide a better test of the validity of theoretical predictions on the triplet energy levels of tetracene by Pariser and Orloff than was previously possible without polarization measurements. A correlation diagram is given, which compares the observed and calculated triplet energy levels for naphthalene, anthracene, tetracene, and pentacene. While Orloff's predictions of the intensities of the T-T absorptions agree well with experiment, his energy values are not in good agreement for the high-energy triplet states. Pariser's energy predictions are in better agreement with experimental results than Orloff's, however, his intensity predictions are not in good agreement with experimental data.
Theory of Frequency-Dependent Dielectric Behavior of Mixtures of Polar Liquids near a Critical Point
Authors: Snider Neil S.
Published: February 2004

Two-component, partially miscible liquids of which at least one component is polar have been found to exhibit substantial increases in dielectric constant and dielectric loss near their critical solution points. A theory of this phenomenon is here proposed. The theory is closely analogous to the theory of sound absorption in the critical region which was originally proposed by Fixman. The theory is in partial agreement with experimental results. Possible sources of the observed discrepancies are suggested.
Paramagnetic Resonance of Tetravalent Neptunium-237 in Single Crystals of ThO2
Authors: Richardson Riley P. , Gruber John B.
Published: February 2004

The electron paramagnetic resonance spectrum of Np 4+−237 (nuclear spin, I = 5/2) in single crystals of ThO2 has been investigated at 1.7 and 4.2°K in the 24 and 34 GHz bands, respectively. Studies were carried out on both unstrained and strained crystals. For unstrained crystals, the ground electronic state of Np 4+−237 in cubic sites in ThO2 was found to be a Γ8 quartet in accordance with the predictions of Lea, Leask, and Wolf and could be explained in terms of Bleaney's Γ8 spin Hamiltonian for I = 5/2 and S=3/2. The Lea, Leask, and Wolf parameter χ, relating the crystal field splitting parameters of the cubic field, was found to be χ = −0.61 for the unstrained samples. The spectrum of the strained crystals clearly showed the degeneracy of the Γ8 state had been lifted. The zero-field splittings were estimated to be between 5 and 20 cm−1 in order to be consistent with both EPR and optical data, respectively. A partial analysis of the spectrum of Np 4+−237 in the strained crystals was carried out and could be explained using a simpler spin Hamiltonian with I =5/2 and S = 1/2. Considerable hyperfine splitting due to the nuclear spin of neptunium-237 (I=5/2) has been observed.
Nuclear Magnetic Resonance of 27Al in Topaz, Al2SiO4(F, OH)2
Authors: Tsang Tung , Ghose Subrata
Published: February 2004

The 27Al quadrupolar coupling constant, | e2qQ/h | and asymmetry parameter η in topaz have been determined to be 1.67 ± 0.03 MHz and 0.38 ± 0.05. These values and the orientations of the principal axes are consistent with the Fe3+ paramagnetic resonance data and with the symmetry of the AlO4F2 octahedron.
Theory of Semiclassical Transition Probabilities (S Matrix) for Inelastic and Reactive Collisions. III. Uniformization Using Exact Trajectories
Authors: Marcus R. A.
Published: February 2004

A canonical transformation of coordinates in Part I is made using exact trajectories. The transformation tends to uniformize all coordinates including that for the radial motion, thus removing the singularities in the simple semiclassical exponential wavefunction in typical cases. The new coordinates are ``time'' and certain constants of the motion. A symmetrical choice for the transformation then yields an integral expression for the S matrix satisfying the principle of microscopic reversibility. Topics discussed include semiclassical unitary transformations and time-reversal properties of action-angle variables and of semi-classical wavefunctions. Applications and numerical tests of the integral expression for Smn are in progress.
Photolysis of Carbon Dioxide at 1633 Å
Authors: Loucks L. F. , Cvetanović R. J.
Published: February 2004

The photolysis of CO2 at 1633 Å has been re-examined with particular emphasis on the material balance of the products over the range of reactant pressure from 10 to 760 torr. The products observed included CO, O2 and O3; the latter has been identified by infrared and ultraviolet absorption and by the iodometric technique. At high CO2 pressure a reasonable material balance is obtained from the observed yields of CO, O2, and O3, while at low pressures surface reactions appear to be important in an unconditioned vessel. The presence of water vapor has been shown to change the product distribution substantially, with O2 becoming more important and O3 less important. The observations made provide potential explanation for the discordant previous results in the literature. The over-all reaction mechanism is discussed in terms of an initial photolytic formation of O(1D2) atoms and their rapid deactivation to O(3P) in collisions with CO2. The reactions, H + O 3 → OH + O 2 and OH + O → H + O 2, are tentatively suggested to account for the catalyzed chain decomposition of ozone in the presence of water vapor.
Lifetime and Quenching of CO(a 3Π) Produced by Recombination of CO2 Ions in a Helium Afterglow
Authors: Wauchop T. S. , Broida H. P.
Published: February 2004

Rapid dissociative recombination of CO2+ in a flowing, helium afterglow has been shown to be an efficient source of CO in the a 3Π metastable state. Ions produced by mixing CO2 with He(23S) recombine to produce a CO metastable afterglow with a number density as great as 109 cm−3. Monitoring of the (a 3Π—X 1Σ) Cameron transition in CO was used to study the lifetime and quenching of CO(a 3Π) by CO2, N2, NO, and He. Recombination of CO 2 + also produces CO in the d 3Δ and a′ 3Σ states.
Equilibrium Structure of Polarized Ice
Authors: Babcock R. V. , Longini R. L.
Published: February 2004

The equilibrium state is described for pure ice containing parallel electric and polarization fields by giving the concentration profiles of the four principal classes of defect in hydrogen bonding. The velocities of the bonding defects are found from random-walk computations, using the concept of a trace to keep strict track of interaction between the defect motions and the lattice polarizations. The resulting kinetic equations, and a free energy argument, each lead to the same differential equations. The solutions have the following properties: A skin region less than 2 μm thick exists, in which positive ionic defects and positive Bjerrum defects are drawn toward the cathode surface. In the skin, the lattice is polarized in opposition to the field. In the rest of the sample, positive Bjerrum defects and negative ionic defects (or vice versa) mix to give approximate charge neutrality, and lattice polarizability and dielectric constant exhibit their experimental values. The complete solutions are determined by the potential existing at each surface.
Light Scattering of Transition-Metal Ions. I. Phonons of Three Normal Spinels and Electronic Raman Scattering of Co2+ in Co2GeO4
Authors: Koningstein J. A. , Grunberg P. A. , Hoff J. T. , Preudhomme J. M.
Published: February 2004

Polarized Raman studies of the three normal spinels Ag2MoO4, Co2GeO4, and ZnAl2O4 are reported. Electronic Raman scattering to levels of Co2+ in a surrounding of D3d symmetry is discussed and wave-functions of ground and excited states are given.
External Optic Phonons in Tetrazole
Authors: Baglin F. G.
Published: February 2004

The laser Raman spectrum of polycrystalline tetrazole has been recorded at 300°K and at 95°K. The external optic phonon spectrum of tetrazole is shown to be consistent only with the P1 space group. High frequency shoulders have been observed on the three librational 0→1 transitions and have been assigned as quasi LO phonons. Relative infrared band intensity ratios have been calculated from these shoulders and are in agreement with experimental results. The N··· N distance has been calculated as 2.85 ± 0.02 Å. The mean librational (torsional) displacements, harmonic force constants, and dipole derivatives have also been calculated. The three 0→1 phonons have been assigned by means of a linear lattice model.
Energy Decay Characteristics of Benzophenone
Authors: Busch G. E. , Rentzepis P. M. , Jortner J.
Published: February 2004

We have studied the energy-resolved decay of benzophenone in the gas phase at various pressures. In the ``isolated-molecule'' case benzophenone is shown to exhibit the characteristics of strong coupling between the S1 and T1 vibronic levels. A small contribution from weakly coupled vibrational levels may also be present and is discussed in the context of a weak coupling model.
Excimer Formation in Vinyl Polymers. I. Temperature Dependence in Fluid Solution
Authors: Harrah L. A.
Published: February 2004

The fluorescence spectra of solutions of poly (2-vinyl naphthalene) in both fluid and glassy solvents have been studied at room temperature and at liquid-nitrogen temperature. Excimer emission was observed at all temperatures in glassy solution, but this emission is quenched at lower temperature in fluid solution. This behavior is interpreted in terms of excimer-forming main chain conformations which are of higher energy than the most favored conformation and maintain thermal equilibrium in fluid solution only. The temperature dependence of monomer chromophore emission in fluid solution is accurately fit with a kinetic model of intrachain excimer formation in which the chain conformer lifetime is limited by collision with solvent molecules. In n-propyl benzene solution, the energy barrier to excimer formation above the lowest-energy chain conformation was found to be 3608 cal/mole.
Raman Scattering: Orientational Motions in Liquids
Authors: Bartoli F. J. , Litovitz T. A.
Published: February 2004

A systematic study of reorientational motions by Raman scattering is undertaken for 10 liquids. The theory of orientational broadening of Raman lines is presented with emphasis on the use of symmetry of molecular vibrations to obtain information of reorientational motions about different axes. The rotational diffusion tensor of benzene was obtained and found to be approximately isotropic. The time for reorientation of the major molecular axis was measured for nine liquids and the mechanism for reorientation for these liquids discussed. Liquids are classified according to whether reorientation is determined by structural dynamics or collisional motions. Finally it was possible to obtain the time between collisions for liquids in which reorientation is collision limited and occurs in small angular steps.
EPR Study of Irradiation Products of NO2− and NO3− in KN3
Authors: Fuller A. M. , Tarr C. E.
Published: February 2004

Single crystals of KN3 doped with KNO2 and KNO3 were irradiated with ultraviolet light and x rays. EPR investigations of the paramagnetic centers stable at room temperature indicate that NO2− is the precursor for the NO2 and NO2−− centers observed, and that NO3− is the precursor for the NO2−− center only.
CNDO Study of the Properties of Ionic Defect Structure in a Model One-Dimensional Hydrogen-Bonded Chain
Authors: Sabin John R.
Published: February 2004

A CNDO/2 calculation is carried out on (HF)6, a model one-dimensional hydrogen-bonded system. An ionic defect is then introduced into the chain, and the energies of defect formation and propagation are determined. The effects of lattice relaxation and interaction of the defect with the lattice are considered. Some properties of the defect structure are considered.
Kinetic Study by EPR of the Production and Decay of SO(1Δ) in the Reaction of O2(1Δg) with SO(3Σ−)
Authors: Breckenridge W. H. , Miller Terry A.
Published: February 2004

The existence of the reaction of O2(1Δg) with ground-state SO(3Σ−) to produce SO(1Δ) and ground-state O2(3Σg−) has been confirmed using a fast-flow system and electron paramagnetic resonance detection of all four species. A kinetic study of this reaction has resulted in the determination of the absolute value of the rate constant: (2.12 ± 0.22 × 108) liter mole−1·sec.−1 The reaction is therefore faster, by an order of magnitude, than any quenching process by a neutral species yet reported for O2(1Δg) in the gas phase, reaction or deactivation. The rapid rate is in rough accord with predictions derived from observations of similar atomic processes by other workers, indicating that the reactive process probably involves simple spin-allowed transfer of electronic energy in which a resonance situation is approximated. The mechanism for the decay of the SO(1Δ) produced in the reaction has also been determined. It is shown that SO(1Δ) is heterogeneously deactivated to SO(3Σ−) at the reaction vessel walls with an efficiency about four orders of magnitude greater than that observed for deactivation of O2(1Δg) to O2(3Σg−). Such a high wall deactivation efficiency may explain the spectroscopic observations by other workers of SO(3Σ−) but not the expected SO(1Δ) in the pyrolysis products of ethylene episulfoxide.
Velocity Dependence of the Ionization of Ar, Kr, and Xe on Impact of Metastable Neon Atoms
Authors: Tang S. Y. , Marcus A. B. , Muschlitz E. E.
Published: February 2004

Measurements of the velocity dependence of the total ionization cross section of argon, krypton, and xenon on impact of thermal-energy metastable neon (Ne*) atoms have been made using a velocity-selected beam of the metastable atoms. The composition (3P2/3P0 ratio) of the Ne* atomic beam has been measured using an inhomogeneous-field deflecting magnet and found to be about 5/1, assuming equal detection efficiency for the two metastable species. The ionization measurements were of sufficient precision to allow simultaneous determination of both the secondary-electron-ejection efficiency and the cross section. The secondary-electron-ejection efficiency from an argon-covered gold surface on impact of metastable neon atoms was found to be 0.27± 0.14. In the relative velocity range investigated (g=320–1700 m/sec) the cross section Q was found to vary as g−m below g=650 m/sec and to rise at higher relative velocities. The value of m obtained is 0.622 for Ne*–Ar, 0.728 for Ne*–Kr, and 0.874 for Ne*–Xe. A simple semiempirical model based on a two-state impact parameter treatment is used to fit the experimental results at low velocities. The model indicates that the interaction leading to ionization is short ranged.
Vapor Pressure, Critical Isochore, and Some Metastable States of CO2
Authors: Sengers J. M. H. Levelt , Chen W. T.
Published: February 2004

An experimental method for obtaining precise PVT properties for gases in the critical region is described. Main features are absence of noxious volumes, small height of sample volumes, precise temperature control, and high pressure sensitivity. Some results are presented for CO2. The 0°C fixed point and the vapor-pressure curve have been measured and compared with literature values. Three liquid isochores including their metastable extensions into the two-phase region are also presented. The vapor-pressure data and pressures on the critical isochore above Tc are compared with the predictions of the thermodynamic scaling law and with those of a recently proposed extension of scaling. The equation of extended scaling fits the data between −2 and 46°C with a standard deviation of 1.5× 10−3 bar, for a ``best'' critical exponent α=0.09.
ESR Spectrum of O3− Trapped in a Single Crystal of Potassium Chlorate
Authors: Schlick S.
Published: February 2004

The O3− radical obtained by x irradiation of oxygen-17 enriched KClO3 was studied by ESR. The molecule is trapped at three distinct sites in the potassium chlorate single crystal, one of which gives rise to a more intense ESR spectrum. For O3− at the dominant trapping site, the principal values of the g tensor are 2.0035, 2.0187, and 2.0123. Two distinct oxygen-17 hyperfine splittings were observed and their variation as a function of orientation studied. The principal values of the corresponding hyperfine tensors are 82.6, −8, −8 and 43.6, −5, −5 G. The direction of the maximum principal value for both oxygen-17 hyperfine tensors coincides with the direction of the minimum principal value of the g tensor, as expected for a bent 19-electron molecule. The higher splitting is assigned to the central atom and the lower splitting to the magnetically equivalent outer atoms. The spin density distribution in O3− deduced from experimental data is compared with theoretical results obtained from a CNDO/II calculation. The g values for O3− at the less populated sites are practically identical to the g values given above. Oxygen-17 hyperfine splittings observed from O3− at these sites seem to indicate a slight distortion of the molecule, possibly from C2v to Cs symmetrv. All magnetic parameters were measured at 77°K.
Localized Orbitals for Polyatomic Systems. IV. Case of Several Partially Filled Bands
Authors: Schlosser H. , Gilbert T. L.
Published: February 2004

We examine in detail the basic assumptions and philosophy of the Anderson pseudopotential approach to the construction of localized orbitals in polyatomic systems, and compare it with the Adams—Gilbert approach. We first of all investigate the differing philosophies of these approaches to the problem of the construction of the potential; second, we make some general comments on Anderson's method. In the final section we derive the Anderson pseudopotential equations for the general multiband, multiorbital case, discuss the general form of the localization potential, and derive the secular equation for the band energies for the optimal Anderson orbitals and for Adams' polarized atomic orbitals.
Quenching of the B 2Σ+ State of the CN Radical
Authors: Jackson W. M. , Faris J. L.
Published: February 2004

The quenching of the B 2Σ+ fluorescence from the CN radical has been studied as a function of the relative velocity of the quenching collision, vR, and the total gas pressure in the fluorescence cell. The rate constant for the quenching of the CN fragment by ICN vapor was found to be directly proportional to vR. Electronic quenching was also observed for CH4, H2, Kr, and Ar. Quenching cross sections of 1 and 46 Å2 were obtained for CH4 and ICN, respectively.
Phase Transitions of the Classical Hard-Ellipse System
Authors: Vieillard-Baron Jacques
Published: February 2004

By Monte Carlo calculations in the canonical ensemble, we have studied some properties of a two-dimensional system of 170 long hard ellipses (whose axis ratio equals 6). This system can be considered as a two-dimensional model for a nematic liquid crystal. We have shown that this system exhibits two first-order phase transitions: a solid-nematic type phase transition at high density and a disorientation phase transition at a density 1.5 times smaller. This result suggests that excluded volume effects might play an essential role in the disorientation phase transition of nematic liquid crystals.
Matrix Isolation Laser Raman Spectroscopy. I. Vibrational Raman Spectra and Depolarization Measurements for Matrix Isolated Group IVa Dihalides, MX2 and MXY (where M = Ge, Sn, Pb and X, Y = Cl, Br), in Solid Argon and Nitrogen
Authors: Ozin G. A. , Voet A. Vander
Published: February 2004

The vibrational Raman spectra together with polarization data are reported for most of the monomeric dihalides MX2 and mixed dihalides MXY of Group IVa (where M = Ge, Sn, or Pb and X, Y = Cl or Br) isolated in both argon and nitrogen matrices at 4.2°K. Laser induced resonance fluorescence effects which interfere with gas phase Raman studies are eliminated in Raman studies of matrix isolated dihalides. The isotope components of ν1 and ν3 are clearly resolved in the case of PbCl2 in argon and assigned to Pb35Cl2, Pb35Cl37Cl, and Pb37Cl2. Diffusion controlled warmup data are recorded for all species in the temperature range 4.2–40°K. All isolated monomers were found to diffuse rapidly at 30–35°K and only in the case of GeCl2 was a definite, stepwise polymerization process observed. The final spectrum obtained by warming GeCl2 showed the presence of a polymeric structure containing both terminal and bridging chlorine atoms. The matrix Raman results demonstrate that spectral sensitivities and resolution can be achieved which are comparable with the complimentary matrix infrared data and that matrix Raman polarization measurements add a valuable new tool for matrix isolation studies.
Proton Spin Echo NMR Spectra of 1,1-Difluoro-2,2-dichloroethane: Subspectral Analysis
Authors: Vold Robert L. , Shoup Regitze R.
Published: February 2004

Fourier transform spin echo NMR spectra have been obtained for the protons in 1,1-difluoro-2,2-dichloroethane as a function of rf pulse spacing. It is shown theoretically and experimentally that spin echo spectra for this ABX2 spin system can be analyzed in terms of three distinct subspectra of the AB variety. Effects of transverse relaxation are considered. In principle cross relaxation invalidates subspectral analysis, but for the case of 1,1-difluoro-2,2-dichloroethane such effects are shown to be small. The spin echo spectra yielded a precise value for the proton proton coupling constant, JAB=3.471± 0.011 Hz, and somewhat less precise values for the other spectral parameters. A few partially relaxed spectra were obtained by Fourier transformation of the free precession following individual spin echoes. The results of these experiments are in accord with previously developed theory, and show that derivation of selective relaxation rates from such spectra of coupled spin systems may be difficult in practice.
Velocity of Ultrasound in Cesium-Ammonia Solutions
Authors: Bailey K. E. , Bowen D. E.
Published: February 2004

The velocity of 10 MHz waves in solutions of cesium in liquid ammonia as a function of both temperature and metal concentration are presented. Comparison of these data with those previously reported for lithium-, sodium-, potassium-, calcium-, and barium-ammonia solutions is made. An analysis of the concentration dependence of the sound velocity reveals a structural change in the solutions as the metal concentration is increased. No evidence for compound formation was detected.
Vibrational Relaxation Times of Oxygen and Oxygen Mixed with Several Light Gases
Authors: Parker J. G. , Ritke D. N.
Published: February 2004

Vibrational relaxation times of τ of oxygen have been determined from sound absorption measurements in the pressure range from 14 to 35 atm. Values of τ−1 were found to increase more rapidly with increasing pressure than the linear dependence expected if binary collisions alone were important. The effect of adding trace amounts of H2, He3, and He4 at a total pressure of 35 atm was also studied. Resulting relaxation times for O2–H2 and O2–He4 collisions were found to be in good agreement with earlier data at lower pressures. He3 was found to be 3.5 times more efficient than He4 in exciting vibration in O2.
93Nb NMR Linewidths in Nonstoichiometric Lithium Niobate
Authors: Peterson G. E. , Carnevale A.
Published: February 2004

The angle variation of the 93Nb NMR linewidths is obtained for an off-stoichiometry lithium niobate crystal. It is shown that the widths can be calculated on the basis of a model in which both the magnitude and direction of the electric field gradient are treated as random quantities. A second type of niobium, with a near zero quadrupole coupling constant, is shown to exist in off-stoichiometric crystals. This amounts to roughly 6% of the total niobiums. This new resonance is undoubtedly associated with the mechanism of charge compensation and suggests that the excess niobium substitutes for lithium.
Ionic Soft Sphere Parameters from Hartree-Fock-Slater Calculations
Authors: Butterfield Charles , Carlson Edward H.
Published: February 2004

The soft sphere parameters for many closed shell ions from He through U6+, as well as many ions of the 3d, 4d, 5d, and 4f transition series were computed from charge densities obtained from Hartree-Fock-Slater calculations. For each ion, a radius R0 at which the charge density ρc is exp (−4.3) a.u., and a softness ρ which appears in ln(ρc)=−4.3+(R0−r)/ρ were obtained. These characterize the charge density in the outer region of the ion, that is, on the order of 0.5 electrons lie outside a sphere of radius R0. In addition, an electron affinity A was computed for each ion, being taken as the ionization potential for the ion with one added electron. Use of these parameters in semiempirical theories of ionic crystals, such as the Born-Mayer theory of hard core repulsive forces, and the soft sphere model of electric field gradients at nuclei, is briefly discussed.
Theoretical Studies of H + H2 Rotationally Inelastic Scattering
Authors: Wolken George , Miller William H. , Karplus Martin
Published: February 2004

Rotationally inelastic H,H2 scattering, without rearrangement, was studied quantum mechanically in three dimensions. A close-coupling technique was employed with a basis set consisting of unperturbed molecular functions. The resulting coupled differential equations were solved numerically by a technique recently developed by Gordon. The Porter-Karplus semi-empirical potential surface was used to represent the H3 system. Cross sections were calculated for relative kinetic energies of 0.05 to 0.50 eV. Various approximations were investigated and their effect on the inelastic cross sections were computed; they include variation of the number of terms in the expansion of the exact wavefunction, exclusion of high-order asymmetry contributions to the potential surface, treating the H2 target as a rigid rotor fixed at some specified internuclear distance, and modifying the long-range behavior of the Porter-Karplus surface. Differential cross sections in the helicity representation were also computed for various energies.
Neutron Structure Determination of Monosodium Acetylide, NaC2H, at 293 and 5°K
Authors: Atoji Masao
Published: February 2004

A neutron powder-diffraction study of monosodium acetylide has been carried out. The intensity data were deduced from a number of repeated measurements in order to attain a high statistical accuracy. The resultant structure confirms the previously reported unit cell and space group determined by the x-ray powder method. Regarding the atomic parameters, the neutron values obtained using the least squares method are of considerably higher accuracy than x ray's and hence enable us to interpret the structure features to a much greater extent. The structure is tegragonal (D4h7-P4/nmm) and exhibits a large anisotropic thermal expansion as indicated by a = 3.813 (2) and c = 8.104 (3) Å at 293°K and a = 3.764 (2) and c = 8.062 (2) Å at 5°K. The unit cell contains two NaC2H units. The interatomic configuration and the thermal libration modes support the conception that the negative formal charge is virtually localized on one carbon as represented by Na+C−≡ CH. The C−≡ C distance corrected for a large precessionlike libration is 1.27 (2) Å which is considerably longer than 1.204 Å in acetylene. The equilibrium bond angle, ∠ C−≡ CH, is likely 180° and the C–H distance is 1.07 (3) Å.
Uranium-Oxygen Lattice Vibrations of α-Sodium and Magnesium Monouranates
Authors: Ohwada Ken
Published: February 2004

Infrared spectra of α-sodium and magnesium monouranates have been measured in the frequency region from 4000 to 90 cm−1. A normal coordinate analysis of the optically active uranium-oxygen lattice vibrations of such compounds has been carried out on the assumption of a simple chain model of infinite [(UO2)O2]∞2− neglecting sodium and magnesium atoms. On the basis of the results of these calculations, some of the observed bands have been assigned reasonably to the uranium-oxygen lattice vibrations. The stretching and bending force constants for both the compounds have been obtained and discussed in relation to the uranium-oxygen bond distances.
Raman Spectra of Gases. I. Cyclopentene and 2,5-Dihydrofuran
Authors: Durig J. R. , Carriera L. A.
Published: February 2004

The Raman spectra of cyclopentene and 2,5-dihydrofuran, both in the gaseous state, were recorded from 70 to 3500 cm−1. Even the very weak ring puckering vibrations were observable. The selection rule for this normal mode is Δv=2 for the molecules studied even though the 2,5-dihydrofuran molecule is a planar molecule. The observation of these double quantum jumps can be a powerful check on the sometimes ambiguous assignment of the far-infrared transitions. It is also shown that the Raman combination and difference bands in the C–H stretching region may be useful for obtaining the ring puckering transitions.
Semiclassical Theory of Weak Vibrational Excitation
Authors: Pechukas Philip , Davis Jon P.
Published: February 2004

We discuss a semiclassical theory of vibrational excitation in low-energy collisions for the case that the interaction depends only weakly on vibrational coordinate and the process is strongly forbidden, classically, in the sense of Miller and Marcus. We argue that this may be the interesting case for purposes of extracting information, from differential cross sections, on the vibrational coordinate dependence of intermolecular potentials.
Studies of Light Emission in the Pulse Radiolysis of Gases: Electron-Ion Recombination in Nitrogen
Authors: Sauer Myran C. , Mulac William A.
Published: February 2004

An experimental method for studying ion recombination processes using pulse radiolysis is described. The electron-ion recombination coefficient in N2 (280–980 torr) has been determined to be 3± 0.6× 10−6cm3ion−1·sec−1 at 25°C by analysis of the light emitted by N2(C 3πu), which is produced in the neutralization reaction. This recombination coefficient obeys a T−1/2 dependence. The formation of O3 from an O2–SF6 system was used as a radiation dosimeter to obtain the concentration of ions produced by a pulse of 13 MeV electrons.
Influence of Molecular Shape on Dielectric Relaxation
Authors: Klug D. D. , Vaughan W. E.
Published: February 2004

Existing theories of dielectric relaxation, which employ the Onsager model of the liquid state, are extended to nonspherical molecules.
Magnetothermodynamics of Antiferromagnetic, Ferroelectric β-Gd2(MoO4)3. II. Heat Capacity, Entropy, Magnetic Moment of the Electrically Polarized Form from 0.4 to 4.2°K with Fields to 90 kG along the a Crystal Axis
Authors: Hornung E. W. , Brodale G. E. , Fisher R. A. , Giauque W. F.
Published: February 2004

The magnetic moment of a 2.49-cm-diam spherical single crystal of electrically polarized β-Gd2(MoO4)3 has been measured with stabilized fields of 500, 1000, 1500, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G, along the a crystal axis, and over the range 0.3–4.2°K. The approach to saturation was measured at about 0.43°K over the range 30–90 kG. The temperature independent susceptibility along the a axis (diamagnetic) was determined as −3.1×10−4 cm3/mole Gd3+ and the limiting saturation value was found to be 38 796 G·cm3/mole Gd3+, corresponding to a ga=1.985. The heat capacity has been measured in fields of 0, 1000, 2500, 5000, 10 000, 15 000, 25 000, 40 000, 65 000, and 90 000 G over a range 0.4–4.2°K. The heat of vaporization of momentum, h/2π, from the essentially saturated state was found to be 23.15 and 16.50 cal/mole at 90 and 65 kG, respectively. This may be compared with the work of this process, gaβH, which was 23.85 and 17.22 cal/mole at these two respective fields. Temperature-field observations on 38 isentropes were used to correlate the entropies along 10 isoerstedic heat capacity series. The entropy zero of the electronic and lattice systems was located at magnetic saturation by means of the heat capacity series at 90 and 65 kG. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, the differential isothermal magnetic susceptibility, and the isothermal work of magnetization have been tabulated over the range 0–90 kG and 0.4–4.2°K. Comments on the use of carbon thermometers at liquid helium temperatures are included.
Electronic States and Molecular Geometry of Xenon Hexafluoride: A Case of Electronic Isomerism
Authors: Goodman Gordon L.
Published: February 2004

It is proposed that XeF6 vapor is a mixture of three molecular isomers differing primarily in electronic state and nuclear geometry. The lowest energy form is octahedrally symmetric and has two anti-bonding electrons in an a1g orbital, yielding a 1A1g electronic state. The first excited states arise from promoting one of the anti-bonding electrons to a f1u orbital. For an octahedral nuclear geometry this produces a 3F1u electronic state, which however is subject to Jahn-Teller distortion forces. These forces lead to a D3d molecular symmetry and two separate electronic states 3A2u and 3Eu. The 3A2u state is about 450 cm−1, and the 3Eu state about 1200 cm−1 above the ground state. Because of high statistical weights, these excited states are well populated at the temperatures usually used for physical measurements, and any detailed interpretations of data must take this into account.
Bending Frequency of the C3 Molecule
Authors: Liskow Dean H. , Bender Charles F. , Schaefer Henry F.
Published: February 2004

Ab initio calculations have been carried out to determine a potential curve for the bending motion of C3. The work was in part motivated by the disagreement between theoretical and experimental values of the entropy of C3. Three basis sets were used, with (4s2p), (4s2p1d), and (4s3p1d) centered on each carbon atom. Both self-consistent-field (SCF) and configuration interaction (CI) (656 configurations) calculations were carried out with the smallest basis. The CI wavefunctions were obtained by a method which may be viewed as an extension of the pseudonatural orbital technique of Edmiston and Krauss. Using the smallest basis, both SCF and CI calculations yield ``normal'' bending frequencies, ∼320 cm−1. It is concluded that electron correlation has little effect on the bending frequency. The larger (4s2p1d) and (4s3p1d) basis SCF calculations yield much smaller bending frequencies, the latter being 69 cm−1, in good agreement with the unusually low experimental value of Gausset, Herzberg, Lagerqvist, and Rosen. The bending potential is predicted to be quite anharmonic. These results are discussed qualitatively in terms of a Walsh diagram and the importance of d orbitals by symmetry considerations.
Valence Bond Calculations of Spin Density Distribution in Benzyl Radical
Authors: Raimondi Mario , Simonetta Massimo , Tantardini Gian Franco
Published: February 2004

The a priori valence bond method in the σ-π approximation has been applied to benzyl radical with inclusion of an increasing number of ionic structures. When all structures are included, the hyperfine coupling constants calculated from spin densities through the McConnell relationship are in excellent agreement with experimental results. Comparison with other theoretical results is also included.
Lowest Singlet State of p-Chloroaniline in Pure and Mixed Crystals
Authors: Marchetti Alfred P.
Published: February 2004

The lowest 1B2 state of p-chloroaniline has been examined in neat and mixed crystals at 4.2°K. The coupling of the p-chloroaniline electronic state to host phonon modes varies greatly depending on the host. Weak coupling has been observed for a durene host, and stronger coupling with the excitation of pseudolocal phonon modes has been observed with a biphenyl host. The change in dipole moment on excitation to the 1B2 state was +1.26 D. In the neat-crystal spectra large vibronic effects, not present in the mixed-crystal spectra, have been found. These effects, along with a strong depolarization of the vibrational bands in the spectra, indicate a possible vibronic interaction among the factor group states.