bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Approach to the Solvent Power of Water for Hydrocarbons; Urea as a Structure Breaker
Authors: Frank Henry S. , Franks Felix
Published: February 2004

The finding of Wetlaufer et al., that addition of urea to water increases the (mole fraction) solubility of hydrocarbon gases (except methane) while making them dissolve with a smaller evolution of heat, is interpreted as a primarily statistical phenomenon. For this purpose, it is treated in terms of a skeleton model in which not only is water represented as a two-species mixture of dense and bulky constituents but the dissolved hydrocarbon is represented as dissolving separately in these constituents, as if it were distributed between two phases, i.e., between a quasiclathrate solution in the bulky constituent and a quasilattice or “regular” solution in the dense one. Added urea is pictured as being able to enter only one of the solutions, the quasilattice one in the dense water, with the result that it acts as a structure breaker. A statistical-thermodynamic analysis of this model leads to equations for the chemical potentials and the partial molal enthalpies and entropies of the hydrocarbon and the urea solutes, and it is found that very simple assumptions suffice to give calculated values for log γ and L̄ of urea, in binary aqueous solutions, in good agreement with experiment. The choice of parameters to fit the results of the Wetlaufer transfer experiments (of hydrocarbon from water to urea-water) leads to calculated values for the partial molal enthalpies and entropies of the hydrocarbons in their hypothetical binary solutions in the bulky (quasiclathrate solution) and dense (quasilattice solution) waters and comparison of these quantities with properties of appropriate real physical systems makes them appear to be acceptable. One inference from this successful result is that the hypothesis of Frank and Evans, that the “extra” negativeness of the S̄2 for hydrocarbon gases in water arises from a structure shift in the latter, may not be unique, but that a similar effect might also arise from the fact that water received some of the hydrocarbon solute into a different type of environment from what it would find in a “normal” solvent.
Crystal Spectra of Tetracene and Rubrene under Pressure
Authors: Nakashima T. T. , Offen H. W.
Published: February 2004

Pressure-induced spectral shifts (0–20 kbar) are compared for the absorption and fluorescence of tetracene and rubrene as crystals or embedded in polystyrene matrices. At 20 kbar the red shift of the tetracene crystal absorption is two to three times larger than either the red shift of tetracene in polystyrene or rubrene in both crystal and solid-solution environments. The crystal shifts and increased Davydov splitting at high pressure are related to calculations on compressed anthracene by Rice and Jortner. The spectral shifts indicate that crystal-field effects are negligible for rubrene due to steric factors. Strong specific interactions in the excited state between the phenyl substituents of rubrene and the phenyl groups of polystyrene are indicated from the fluorescence spectra at atmospheric pressure. The influence of pressure on tetracene crystal luminescence can be described in terms of excitation-energy transfer to tetracene dimers at defects. High pressures enhance the transformation of excitation energy into heat, probably by increasing non-radiative excition trapping at imperfections.
Computational Procedure for the Close-Coupled Rotational Excitation Problem: Scattering of Diatomic Molecules by Atoms
Authors: Lester William A. , Bernstein R. B.
Published: February 2004

A computational procedure is described for the integration of the coupled differential equations and determination of the probability matrices required for the accurate evaluation of cross sections for rotational excitation of diatomic molecules. The Arthurs–Dalgarno theory of scattering of an atom by a rigid rotator is employed. The approach developed takes advantage of several of the computational schemes used in the field of electron–atom scattering, particularly those of Smith. The principal virtue of the present computational method is its capability of generating “exact” results to serve as standards against which to compare various approximations such as sudden, dominant coupling, and distorted wave.
Microwave Studies of Collision-Induced Transitions between Rotational Levels. IV. Steady-State Measurements in NH3
Authors: Oka Takeshi
Published: February 2004

The technique of high-power microwave double resonance has been applied to the study of collision-induced transitions between rotational levels of ammonia. The inversion doublets for selected J values have been “pumped” by high microwave power, and the increase of absorption in other inversion doublets have been observed. Because of the abundance and intensities of ammonia lines, a systematic choice of 18 four-level systems was possible. The observed results were analyzed by steady-state equations, and relative values of rate constants have been determined. The experiments and analysis have led to the following qualitative conclusions:

(i) Collision-induced transitions with dipole selection rules (ΔJ = 0, ± 1, parity + ↔ −) are “preferred.”

(ii) The ΔJ = 0 dipole-type transitions have much greater probability than the ΔJ = ± 1 dipole-type transitions for levels with J∼K, but they have probabilities of equal order of magnitude for levels with J≫K.

(iii) The ΔJ > 1 transitions have much smaller probabilities than the ΔJ = ± 1 transitions.

(iv) The ΔK ≠ 0 transitions have much smaller probabilities than the ΔK = 0 transitions.

A comparison of the observed results with values calculated by using Anderson's theory suggests that the probabilities of the ΔJ = ± 1 quadrupole-type transition (parity +↔ +) are the same order of magnitude as those of the corresponding dipole-type transitions.
Self-Diffusion Coefficient of Liquid Lithium
Authors: Murday J. S. , Cotts R. M.
Published: February 2004

The coefficient of self-diffusion of 7Li in liquid lithium has been measured with nuclear magnetic resonance. The diffusion coefficient was determined from observations of the dependence of the spin-echo signal upon the amplitude of a pulsed magnetic field gradient. It is found that at the melting point D = 6.8 ± 0.3 × 10−5cm2 / sec and (T / D) (dD / dT) = 2.8 ± 0.3. In terms of an activation model, D = 0.94 ± 0.4 × 10−3 exp [ − (2300 ± 300cal) / RT]cm2 / sec. Resultsare compared with the Cohen–Turnbull free-volume model and the Ascarelli–Paskin dense-gas model for liquid diffusion. From the free-volume model, the effective hardsphere diameter is determined for Li and, in addition, for Na and K as well. The results compare favorably with effective hard-sphere diameters determined from neutron-scattering data.
Refractive Index and the Lorentz–Lorenz Function for Gaseous and Liquid Argon, Including a Study of the Coexistence Curve near the Critical State
Authors: Teague R. K. , Pings C. J.
Published: February 2004

Measurements of the refractive index of gaseous and liquid argon at 5893 Å were carried out along the coexistence curve and along eight isotherms from 133° to 173°K and for pressures from 15 to 100 atm. The measurements were combined with existing density data in the literature in order to calculate values of the Lorentz–Lorenz function. The experiments included detailed studies of the critical region, and the observed values of the refractive index were used to define the shape of the gas–liquid coexistence curve near the critical state. The critical temperature is estimated to be 150.704 ± 0.015°K. Values of nc = 1.0859, Pc = 48.18 atm, and LLc = 4.200 cm3 / mole were also determined. The shape of the coexistence curve is often described in terms of a critical coefficient β, with ρl–ρg = A0′(Tc − T)β. By detailed statistical analysis of the refractive index data, including variation of Tc over a slight range, β was found to be 0.364 ± 0.007. This is within the uncertainty range of previous determinations, but seems clearly higher than the value of 0.313 ± 0.004 predicted for the three-dimensional lattice gas. Measurements of the refractive index on the coexistence curve outside the critical region yielded an average value of the Lorentz–Lorenz function of 4.152 cm3/mole for the gas; the average liquid value is 4.213 cm3/mole. The values of the Lorentz–Lorenz function on eight isotherms between 133° and 173°K show a peak near the critical density, but within the experimental uncertainty; except for such peaks, the Lorentz–Lorenz values along the isotherms lie within the range 4.16–4.26 cm3/mole. All available values for the Lorentz–Lorenz function for argon ranging through three states of matter and temperatures from 20° to 300°K fall within ±1.5% of 4.19 cm3/mole.
Consequences of Photoselection on the Intensity and Polarization of Luminescent Molecules
Authors: Kalantar A. H.
Published: February 2004

Optically excited luminescent molecules are often not randomly oriented if rotational relaxation times are slow compared to excited-state lifetimes, i.e., the molecules are photoselected. The properties of the emission are examined and applied to relative intensity measurements. Analysis of the emission intensity shows that relative intensity measurements (e.g., the ratio of fluorescence to phosphorescence quantum yields) are in error whenever the relation of the axes of absorption and emission changes. Analysis of the polarization of the emission shows how to recognize and avoid the errors and how to enhance the sensitivity of relative intensity determinations by suitable selection of the following variables: polarization of the exciting light, angle between the exciting and the emitted beams, and the polarization of the emitted light.
Torsion–Vibration–Rotation Interactions in Methanol. I. Millimeter Wave Spectrum
Authors: Lees R. M. , Baker J. G.
Published: February 2004

In a study of internal rotation in methanol, the millimeter wave spectra of CH3OH, CD3OH, and CH3OD have been investigated between 90 and 200 Gc/sec. In the analysis of the spectra, torsion–vibration–rotation interactions were treated as adjustable parameters in semiempirical formulas. Kivelson's formula for a-type ΔK = 0 transitions was tested over a wide range of quantum numbers. It reproduced the CH3OH and CD3OH spectra quite well, but the approximations used in the calculations appear to start breaking down for the larger asymmetry of CH3OD. For assignment of b-type ΔK = ± 1 transitions, a method was developed based on the wide spectral range of the millimeter wave spectrometer. Sufficient b-type data were obtained for CH3OH to permit a test of Kirtman's formula for origins of Q branches. Convergence difficulties in the Q-branch least-squares fit prompted a re-examination of the theory, which revealed an interesting linear relation coupling six of the parameters. This relation shows that for any molecule the torsional barrier terms V3 and V6, the two moments of inertia about the near-symmetry axis, and two of the adjustable interaction parameters cannot be independently determined from the spectrum of a single isotopic species. This casts some doubt on values previously reported for V6 in other molecules and adds further uncertainty to V3 determinations. The effective V3 obtained by ignoring torsion–vibration–rotation interactions was found to decrease slightly on deuteration, values of 375.6, 371.8, and 370.3 cm− 1 being obtained for CH3OH, CD3OH, and CH3OD, respectively. Although it is impossible to determine V6 unambiguously from the spectrum of CH3OH alone, a qualitative argument suggests that V6 lies between 0 and −0.8 cm−1. The geometry of the molecule has been completely determined from the experimental data.
Polymer Dynamics. IV. The Zero-Frequency Intrinsic Viscosity of Polymer Molecules with Hydrodynamic Interaction and Excluded Volume
Authors: Hearst J. E. , Beals E. , Harris R. A.
Published: February 2004

The theory and model of Harris and Hearst has been extended to approximately include the effect of hydrodynamic interaction and excluded volume. The results agree in both the coil and rigid-rod limits with existing theories and experiment. The absence of a linear dependence of [η] upon an appropriate power of the molecular weight introduces some doubt as to the validity of conventional methods of interpretation of viscosity data.
Method of Moments in the Collision Theory
Authors: Eu B. C.
Published: February 2004

The scattering matrix elements for two-body collision problems are obtained in terms of reactance matrix elements which are in turn given in terms of solutions of moment problems. The reactance matrix elements obtained by this method are suitable for practical calculations. Nonsingular as well as optical potentials are used in this study and illustrative calculations are given. The phase shifts calculated with an attractive exponential potential by means of the first moment of symmetrized integral kernel gives a reasonable agreement with the exact phase shifts for the parameter chosen. General forms and computational prescriptions for a semiclassical optical phase shift and wavefunction are given. For an optical potential with a δ function as its imaginary part the first moment gives rigorous result. Optical phase shifts for this potential are calculated as a function of orbital angular momentum at a given kinetic energy. It is found that the imaginary part of the phase shift has a series of sharp spikes, which may render an explanation of the undulation at large angles of the differential elastic cross section of reactive systems. It is also shown that the optical phase shift obtained in this method reduces in high-energy limit to a form similar to that in the eikonal approximation.
Linewidth of the J = 12→32 Rotational Absorption in Nitric Oxide
Authors: French I. P. , Arnold T. E.
Published: February 2004

The linewidths and intensities of the 10 lines around 150 GHz (5 cm−1) corresponding to the J = 12→32 transition in nitric oxide have been measured with a Fabry–Perot resonator. Collisions are the dominant broadening mechanism at the pressures of interest in this study (0.2–2 torr), although Doppler and saturation broadening are seen at lower pressures. The measured self-broadening linewidth parameter, averaged over the various lines, is 2.82 MHz/torr. This gives a nitric oxide collision diameter of 5.26 Å, which compares with 3.53 Å from kinetic theory. Line broadening due to a number of atomic and molecular species has also been measured. Collision diameters again exceed kinetic theory ones. This is attributed to dipole–dipole, dipole–quadrupole, quadrupole–quadrupole, and dipole–induced-dipole interactions.
Studies on the Vibrational Spectrum of the SO4 = Ion in Crystalline M2′M″(SO4)2·6H2O (M′ = K or NH4 and M″ = Mg, Zn, Ni, or Co): Observations on the Symmetry of the Sulfate Ion in Crystals
Authors: Ananthanarayanan V.
Published: February 2004

Polarization studies on the Raman spectra of suitably oriented single crystals of the isomorphous M2′M″ (SO4)2·6H2O (M′ = K or NH4 and M″ = Mg, Zn, Ni, and Co) have been carried out to assign the symmetry species of the sulfate group frequencies. The theoretical principles underlying these experiments are briefly explained. Infrared absorption spectra of these sulfates have been recorded by the pressed-disk and mull techniques. Infrared reflection data from the literature are also collected and analyzed along with the other data. The results relating to the multiplicity of the SO4= frequencies are discussed in terms of the symmetry of the sulfate ion in these crystals.
Rigid Spheres Near Close Packing: Tunnel Model and a Lower Bound on the Partition Function
Authors: Rudd Walter G.
Published: February 2004

In the high-density limit, the Helmholtz free energy function for an assembly of N rigid spheres at temperature T has the asymptotic form lim τ→1 FN / NkBT ≃ 3 ln(σ / λ) − 3 ln(τ − 1) + C + ···, where kB is Boltzmann's constant, σ is the sphere diameter, λ the mean thermal de Broglie wavelength, and τ = V / V0 where V0 is the close-packed volume of the hard-sphere crystal whose bulk volume is V. The value of the constant C for the tunnel model in a face-centered cubic lattice is found to be C = 1.60145 ···, as compared with the single-particle free-volume cell value C = 1.5629 ···. In addition an upper bound for C in a face-centered lattice is calculated, with the result C3 < 3.5045···, a previous result being C3 < 3.6423···.
Electronic Zeeman Measurements on 1,4-Dibromonaphthalene
Authors: Castro George , Hochstrasser Robin M.
Published: February 2004

A summary of interpretive methods regarding high-field electronic Zeeman measurements is presented. The equations calculated for two active spin substates (zero field) of the lowest triplet state, are applied to 1,4-dibromonaphthalene crystal spectra.

The Zeeman spectra of the electronic and vibronic origins of the lowest triplet state have different polarization, but they have very similar Zeeman effects indicating similar spin-substate activity. The complete analysis enables us to show that the lowest triplet state is of species 3B2 which correlates with 3B2u in D2h. The vibronic origins are shown to arise by spin-orbit coupling with singlet states that are vibronically mixed with other singlet states.

Certain crystal-field effects are apparent in the spectra and those are discussed in relation to two suggested types of mixing; namely, intermolecular spin-orbit coupling, and intermolecular exchange coupling.
Solute-Solute Interactions in Aqueous Solutions
Authors: Kozak John J. , Knight William S. , Kauzmann Walter
Published: February 2004

Solute-solute interactions in aqueous solutions of nonelectrolytes are interpreted using both lattice and distribution function theories of the dissolved state. Experimental activity data of high precision can be obtained from the literature for aqueous solutions of many nonelectrolytes. If the logarithm of the solvent activity coefficient (γ1) is expressed as a power series in the mole fraction of the solute (x2), lnγ1 = Bx22 + Cx23 + ···, then the coefficients B and C can be determined analytically from the experimental measurements. Values of B were obtained for 52 aqueous mixtures; values of C were obtained for 39 of these mixtures. The solutes considered include aliphatic alcohols, amines, amides, ketones, fatty acids, amino acids, and sugars. In some cases, experimental data were available from which the temperature dependence of the quantities B and C could also be determined. The effect of solute size on the coefficients B and C was investigated using the lattice theories of Flory, Huggins, and Guggenheim and McGlashan. More detailed conclusions concerning solute-solute interactions can be drawn by using experimental activity data in conjunction with the McMillan-Mayer theory of solutions. The minimum attractive contributions to the second virial coefficient of the osmotic pressure were estimated for most of the systems studied in this paper. Pairwise attractions seem to increase with (1) increasing aliphatic chain length (from the temperature dependence of the coefficient B it is also found that pairwise association due to aliphatic chains increases with increasing temperature); (2) an increase in the number of solute functional groups capable of participating in hydrogen-bond formation; (3) increasing dipole moment of the solute molecule for a series of amino acids and peptides. The minimum attractive contributions to the third virial coefficient were determined and interpreted for 12 of the systems. Finally, the relative importance of pairwise versus triplet interactions in aqueous solution was investigated.
Nuclear-Spin Conversion and Vibration-Rotation Spectra of Methane in Solid Argon
Authors: Frayer Franklin H. , Ewing George E.
Published: February 2004

The ν3 and ν4 infrared spectra of methane in an argon matrix have been studied. The assignment of vibration-rotation features enables the methane rotational energies to be determined. The spacings of these levels, which are discussed in terms of crystal-field effects, suggest that methane is a hindered rotor in its solid matrix. The vibration-rotation features exhibit time-dependent absorption changes. These changes which are evidence of triplet →quintet nuclear-spin conversion that accompanies the J = 1→J = 0 rotational relaxation, follow first-order kinetics with a half-life of 90 min. The half-life is unchanged by addition of up to 1% N2 to the matrix but decreases to 3 min with only 0.2% O2. Two mechanisms are proposed which are in order of magnitude agreement of observed relaxation rates. In the absence of paramagnetic impurities, spin-spin interaction within the molecule mixes spin states and allows J = 1→J = 0 to relax into the crystal lattice. In the presence of O2 the spin states are mixed by the magnetic-field gradient which is set up across CH4.
Vibrational Spectra of Molten Salts. IV. Infrared Spectra of Metal Thiocyanate Solutions
Authors: Hester R. E. , Krishnan K.
Published: February 2004

Molten KSCN has been used as a solvent for the thiocyanates of Mg(II), Ca(II), Ba(II), Zn(II), Hg(II), and Pb(II), and for Cd(NO3)2, NiCl2, CoCl3, and CrCl3. Infrared spectra are reported for these solutions, with solute concentrations varying from 5 to 30 mole %. All spectra were obtained from systems just above their melting points, i.e., within the range 170°-200°C. Infrared bands characterizing complexation of SCN− by the metal ions have been observed and assigned. All the metals studied, with the exception only of Hg(II) and Pb(II), have been shown to bind through the nitrogen atom of SCN. Hg(II) and Pb(II) bind the sulfur atom. Relative metal-thiocyanate bond strengths in the complexes formed have been deduced from shifts in frequency from the pure KSCN values. Force-constant calculations have been made for the complexed thiocyanates.
Assignment of Excited Electronic States of the Benzyl Radical by the Method of Three-Step Photoselection
Authors: Johnson Philip M. , Albrecht A. C.
Published: February 2004

The assignments of three excited states of the benzyl radical and some of its methyl derivatives are obtained by a method which involves an extension of the usual photoselection technique. Rigid solutions at 77°K of the parent methylated benzenes are photolyzed with polarized light to give the corresponding benzyl radical (Step 1), the radical is then itself excited with polarized light (Step 2), and the polarized-radical emission is analyzed (Step 3). The theory of this three-step procedure is outlined and applied both qualitatively and quantitatively to the experimental results. Because of the known L1b assignment of the excited state associated with the parent molecule absorption, it is possible to determine the absolute polarization of the transitions in the benzyl radicals. Polarizations of the vibronic bands in the benzyl-radical emission independently confirm the results. The state assignments which follow (and which are based on a B22 ground state symmetry) fully disagree with the predictions of MO theories (slightly refined). On the other hand they confirm the predictions arising from unrefined valence-bond and composite systems calculations.
Structure of Aluminum Hydroxide Gel
Authors: Petz John I.
Published: February 2004

X-ray measurements of three aluminum hydroxide gels indicate that the Al3+ ion is coordinated by an octahedral arrangement of oxygen sites and the relationship between the remaining oxygens is essentially the same as in liquid water.
Interpretation of Relaxation Times in the “Electric-Field Effect on Critical Opalescence”
Authors: Cooper Martin J. , Mountain Raymond D.
Published: February 2004

The relaxation time characterizing the response of concentration fluctuations in a binary mixture to the application of an electric field is related to the free relaxation of concentration fluctuations. Examination of light scattered by such systems in the vicinity of the critical mixing point indicates that the change in the turbidity of the fluid with time can not be related to the diffusion coefficient as simply as is the change in the intensity with time of the light scattered through a given angle which is related to the diffusion coefficient D and change in the wave vector k by a factor exp ( − 2Dk2t).
Temperature Dependence of Crystalline Tetracene Fluorescence
Authors: Kazzaz A. A. , Zahlan A. B.
Published: February 2004

A 100-fold increase in the fluorescence emission of crystalline tetracene is observed on cooling from room temperature to 4°K. Phase transformations and lattice distortions are reflected in a drastic change of the emission spectra: the high-temperature modification has an emission that resembles closely tetracene dimer fluorescence while the low-temperature modification fluorescence is nearly a mirror image of the absorption spectrum. The changes in the quantum yields are interpreted on the basis of the Dexter–Fowler model which predicts a considerable difference in the rates of radiationless transitions from different vibronic states.
Microwave Spectra of Methylcyclopropanes. I. 2,2-Difluoro-1-Methylcyclopropane
Authors: Ford Robert G. , Beaudet Robert A.
Published: February 2004

The microwave spectrum of 2,2-difluoro-1-methylcyclopropane was observed in the range 8-38 gHz. The ground and first excited methyl torsional states were assigned, and a barrier of 2260 ± 150 cal/mole was obtained from the splittings in the first excited torsional state. The dipole moment was measured and found to be μA = 2.03 ± 0.03 D, μB = 1.19 ± 0.04 D, μC = 0.31 ± 0.07 D, and μtotal = 2.37 ± 0.05 D. The barrier to internal rotation in this molecule is compared to barriers in similar molecules.
Studies of Xenon Chlorides and Other Xenon Compounds by the Mössbauer Effect in 129Xe
Authors: Perlow G. J. , Perlow M. R.
Published: February 2004

The compounds XeCl2 and XeCl4 have been made in the beta decay of ICl2− and ICl4− containing radioactive 129I. The electric quadrupole interaction in the 39.6-keV excited state of the 129Xe nucleus is employed to study these substances by the Mössbauer effect. The decay products are compared with XeF2 and XeF4 and with the parent ions. It is shown that the decays ICl2−→XeCl2 and ICl4−→XeCl4 both result in the recall of 0.2 electrons per bond from each ligand to the central atom. In the xenon halides the charges per fluorine are − 0.72 and per chlorine are − 0.5. The assumption of pure pσ bonding in the xenon halides is tested by the isomer shifts. With its aid the shifts can be calibrated by the quadrupole couplings. A shielding constant obtained from Hartree-Fock calculations by Wilson is then used to relate p-electron to s-electron transfer, which is next employed to examine the charges on the xenon atom in XeO4 and XeO6−4. The former is prepared in beta decay, the latter equivalently either in beta decay or in bulk. It is shown that directed sp3d2 hybrid bonds for XeO6−4 are inconsistent with the measured isomer shift. The recoilless fractions and linewidths are tabulated for a number of xenon compounds.
Capture Radius for Ion Recombination
Authors: Parks Eric K.
Published: February 2004

An expression for the capture radius defined by Thomson for three-body ion recombination is derived for arbitrary ion and neutral masses. The recombination rate constants calculated from this expression for a variety of systems are compared with the available experimental data. It is found that use of the rigorously calculated capture radius seriously underestimates the recombination rate constant.
Far-Infrared Spectra of Ring Compounds. III. Spectrum, Structure, and Ring-Puckering Potential of Silacyclobutane
Authors: Laane Jaan , Lord R. C.
Published: February 2004

The infrared spectra of gaseous silacyclobutane and silacyclobutane-1, 1-d2 have been recorded in the range 24-300 cm−1. Both molecules show the complicated vibrational fine structure expected from a double-minimum potential for the ring-puckering vibration. The absorption maxima of silacyclobutane were fitted to a potential of the form V = a (x4 − bx2), where x is the ring-puckering coordinate. The potential barrier is calculated as 440 ± 3 cm−1, and the dihedral angle of the puckered ring as 35.9 ± 2°. The spectrum of silacyclobutane-1, 1-d2 can be interpreted with the same potential function but the quantitative agreement with observed levels above the barrier is less accurate. The discrepancy is ascribed to interaction between the ring-puckering mode and the SiD2 rocking vibration.
E↔
2
A
2
4
Transition in Cr3+:K3Co(CN)6 Crystals
Authors: Condrate Robert A. , Forster Leslie S.
Published: February 2004

Analysis of the Cr(III) E↔2A24 spectrum in Cr3+ doped K3Co(CN)6 crystals indicates a E2 splitting of 49 cm−1. The very weak 0-0 lines are consistent with a centrosymmetric complex and a magnetic dipole transition. The measured lifetime exceeds 100 msec, greater by a factor of 10 than the lifetime computed from the absorption spectrum.
Adsorption Energy and Isotherms of Ions at the Electrode
Authors: Hurwitz H. D.
Published: February 2004

A general approach to the theory of ionic adsorption at the mercury electrode (mobile adsorption) is given. An explicit expression of the excess free energy of adsorption is derived on the basis of the method of cluster expansion as indicated by Buff and Stillinger provided that the following assumptions are made: (1) pure electrostatic coupling between diffuse layer ions and adions, (2) adsorbed solvent effects defined in terms of a local dielectric constant. At low ionic coverage of the electrode surface a simplified version of the adsorption isotherm is suggested. In this case a hard-core model is used to describe steric effects between adions, and a model of distribution at the surface is further assumed that serves to bring out, respectively, the cavity field effect, the atmosphere effect, and reordering of particles upon adsorption. The resulting isotherm of adsorption is then compared to experimental data concerning chloride adsorption. At large coverages the hexagonal lattice approximation for ionic adsorption is shortly discussed.
Transition from Branching-Chain Kinetics to Partial Equilibrium in the Combustion of Lean Hydrogen-Oxygen Mixtures in Shock Waves
Authors: Gardiner W. C. , Morinaga K. , Ripley D. L. , Takeyama T.
Published: February 2004

Concentration profiles of the OH radical in the shock-initiated combustion of lean hydrogen-oxygen-argon mixtures at low pressures (∼0.3 atm) and temperatures (∼1400°K) are found to exhibit pronounced spikes prior to attainment of partial equilibrium. It is shown that this effect is not encompassed within the accepted mechanism for the H2–O2 reaction. Possible reconciliations are presented and discussed.
Spectroscopic Studies of Ruthenium(II) Complexes. Assignment of the Luminescence
Authors: Klassen D. M. , Crosby G. A.
Published: February 2004

Absorption and emission spectra of nine (4d)6 ruthenium(II) complexes dissolved in rigid glasses are reported. Tris(bipyridine), tris(o-phenanthroline), bis(tripyridine), and a series of cis-substituted bis(bipyridine) complexes of ruthenium(II) were synthesized. The cis substituents were cyanide, ethylenediamine, pyridine, oxalate, and chloride chosen for their order in the spectrochemical series. On the basis of the structures of the emission spectra, their energy relationships with charge-transfer absorption bands, and the lack of correlation between the energies of emission and predictions from crystal-field theory, it is proposed that the intense luminescence observed from all the complexes under excitation by ultraviolet light is charge transfer in nature.
Percus-Yevick Isotherm for the Exp-6 Intermolecular Potential
Authors: Curé J. C. , Babb S. E.
Published: February 2004

The Percus-Yevick equation has been solved by numerical integration for the 55°C isotherm of argon. The results are compared with calculations using the Lennard-Jones potential, both for the Percus-Yevick equation and for Monte Carlo calculations. Agreement is fair, with the L-J potential being superior in some regions and inferior in others. All of these calculations are compared with experiment with poor results. By dropping the value of α to 13.7, significantly better agreement with high-density experiments is obtained, at the expense of worse second-virial coefficients.
Surface Ionization. III. The First Ionization Potentials of the Lanthanides
Authors: Hertel G. R.
Published: February 2004

The surface ionization comparison technique was used to measure the first ionization potentials of the lanthanide elements. Values obtained were La, 5.55 ± 0.05 eV; Ce, 5.54 ± 0.06; Pr, 5.40 ± 0.05; Nd, 5.49 ± 0.05; Sm, 5.61 ± 0.05; Eu, 5.64 ± 0.05; Gd, 6.16 ± 0.05; Tb, 5.89 ± 0.04; Dy, 5.82 ± 0.03; Ho, 5.89 ± 0.03; Er, 5.95 ± 0.03; Tm, 6.03 ± 0.04; Yb, 6.04 ± 0.04; and Lu, 5.32 ± 0.05. The IP of Pm is estimated to be 5.55 eV. The reference element used was silver. A tabulation of all known reported values is included, and comparisons are made. Agreement is generally good.
4000-8000-Å Emission from Far-Ultraviolet Photolysis of N2O, NO, NO2, CO, CO2, and O2
Authors: Young R. A. , Black G. , Slanger T. G.
Published: February 2004

Luminescence has been observed in the 4000-8000-Å region during the uv photolysis of a number of simple gases with Ar, Kr, and Xe resonance lamps. CO and NO photolyzed at 1470 Å give fluorescence spectra, emission being produced from the d3Δυ = 7 state of CO and from a number of little-known upper states of NO. CO2 photolysis gives the 5577-Å line of O(1S) at all wavelengths from 1048 to 1470 Å; at the longer wavelengths the O(1S) is formed in a secondary process, as there is insufficient energy available during the initial dissociation. The N2O photolysis produces the N2 first positive bands, the NO β bands, and O(1S), depending on the photolyzing wavelength. In O2 photolysis, the only emitting species is O2(b1Σg+), presumably formed during O(1D) deactivation.
Theoretical Description of Periodically Pulsed Nuclear Magnetic Double Resonance
Authors: Gordon Sidney L.
Published: February 2004

Periodically pulsed nuclear magnetic double resonance is described by the Bloch equations for a single nucleus of spin 12, and by the density matrix master equation for AmXn spin systems. In this experiment, the observing rf field H1 and the strong rf field H2 are periodically pulsed so that H1 is on when H2 is off, and off when H2 is on. The H1 and H2 pulse intervals are each equal to τ seconds. The Bloch-equation description illustrates the basic features of the experiment in terms of the macroscopic moment. This description provides a physical model for the production of double-resonance signals in the limit of short τ. The density-matrix analysis separates into two parts: the production of population changes by H2; and the production of detected signals by H1. The formalism is illustrated by the AX2 system, 1, 1, 2-trichloroethane. Theoretical and experimental frequency-sweep spectra are compared for values of τ ranging from 1.25 to 0.0315 sec. The spectra are dynamic in the sense that the detector output is periodic in time with a period of 2τ. The theoretical spectra are computed by assuming that the nuclear spin system is in a quasisteady state, and that the recorder pen swings between the maximum and minimum values of the detector output. The population changes caused by H2 are complicated functions of τ. When τ = 1.25 sec, the spectra approximate periodically pulsed single resonance with the inclusion of the nuclear Overhauser effect. When τ = 0.0315 sec, the spectra approximate steady-state double resonance corresponding to H1 and H2 having one-half their amplitudes. The spectra for intermediate values of τ are complicated, and display a variety of unusual spectral features.
Heat Capacity of Silver Iodide. I. Experiments on Annealed Samples
Authors: Perrott C. M. , Fletcher N. H.
Published: February 2004

The heat capacity of silver iodide has been measured over the range 50°–400°C using an adiabatic calorimeter, the design of which is discussed. Below about 150°C the behavior of the β form is normal and it transforms to the α form at this temperature with latent heat 1.5 ± 0.1 kcal/mole. If the sample is stoichiometric, the α form has an anomalously high specific heat Cυ, ranging from 18 cal/mole·°C at 150°C to 26 cal/mole·°C at 400°C. If the sample deviates from stoichiometry by as little as 1 mole % in either direction, then its specific heat is normal at 12 cal/mole·°C from 150° to 400°C. An interpretation of these results in terms of lattice disorder is suggested.
Intrinsic Viscosity of Wormlike Chains with Excluded-Volume Effects
Authors: Sharp Phillip , Bloomfield Victor A.
Published: February 2004

The intrinsic viscosity [η] as a function of molecular weight M has been calculated for the Kratky-Porod wormlike chain, taking into account excluded-volume effects. The Peterlin theory of intrinsic viscosity was used for the calculation. The result for high molecular weights can be written [η] + bη′ ( 1 + β′M − (1 + ε) / 2)M2ε = KηM(1 + 3ε) / 2, where ε is an excluded-volume parameter. The Kuhn statistical segment length for native double-standard NaDNA in 0.195M [Na+] is found to be 542 Å, in fair agreement with, but somewhat lower than, the values found by other techniques. The hydrodynamic diameter of the double helix is evaluated as 79–82 Å, which is substantially higher than the value found from sedimentation coefficient measurements, and which appears physically unreasonable. Comparison with other theories of the intrinsic viscosity of wormlike coils, neglecting excluded-volume effects, is made. The value of the Mandelkern-Flory-Scheraga parameter β has been calculated as 2.87 × 106, higher by about 25% than the experimental value. β is found to depend only on excluded volume and not an persistence length.
Direct Observation of the Entire Exciton Band of the First Excited Singlet States of Crystalline Benzene and Naphthalene
Authors: Colson S. D. , Hanson D. M. , Kopelman R. , Robinson G. W.
Published: February 2004

The density-of-states functions for the exciton bands of the first excited singlet states of crystalline benzene and naphthalene have been determined experimentally. The experimental density functions were derived from spectral data involving exciton-band↔exciton-band transitions. The experimental results for naphthalene have been compared with calculations based on the octopole model. Using a Frenkel dispersion relation and various sets of coupling constants, density functions have been calculated and compared with the experimental results. For benzene these calculations show that the “optically forbidden” Au component lies between 37 815 and 37 875 cm−1. From the temperature dependence of transitions, phonon contributions have been estimated. It is found that the experimentally derived density function is temperature independent below ∼30°K.
EPR Spectra of Mn2+in Chloride, Bromide, and Iodide Host Compounds
Authors: Breivogel F. W. , Sarkissian Vernon
Published: February 2004

The EPR spectra have been obtained for Mn2+ fourfold coordinated in Cs2ZnCl4, K2ZnCl4, K2HgCl4, K2ZnBr4, and K2ZnI4; sixfold coordinated in NaCl, and KCl; and eightfold coordinated in CsCl. Large distortions from cubic symmetry were observed in CsCl. Variations in the manganese nuclear hyperfine splitting are discussed in terms of the nature of the ligand, changes in the manganese–ligand separation, and changes in the manganese coordination number. The effects of the changes in the coordination number have not been determined previously because concomitant changes in the internuclear distance usually have an opposite, and frequently larger, effect.
Crystal Structure of AgI at 3 kbar
Authors: Moore M. J. , Kasper J. S.
Published: February 2004

The nature of the atomic arrangement in the phase of AgI existing at pressures between 3 and 4 kbar has been deduced from x-ray diffraction studies with a diamond-anvil apparatus. The unit cell is either tetragonal or pseudotetragonal and contains a total of 4 atoms at 000, 12120, 120z, 012z̄ with z = 0.3. The calculated density is 6.19 g/cm3. While it is not possible to determine directly the site preferences of Ag and I, certain distributions are suggested by a simple displacive mechanism of producing the 3-kbar phase from the zincblende structure existing at room temperature and 1 atm pressure. The relationship of the new structure to that of the rock-salt structure existing between 4 and 100 kbar is also discussed.
ESR Study of Intramolecular Spin Exchange Effects on the Hyperfine Interaction in 2,2′-Dinitrobiphenyl Ether and Sulfide Radical Anions
Authors: Gupta R. K. , Narasimhan P. T.
Published: February 2004

Studies have been made on the intramolecular spin exchange effects in the ESR spectra of the radical anions of 2,2′-dinitrobiphenyl ether and sulfide obtained by alkali-metal reduction in tetrahydrofuran (THF) solution which was later diluted with dimethylformamide (DMF) to eliminate metal coupling effects. The spectra obtained show evidence for rapid spin exchange in the sulfide case whereas the exchange frequency in the ether case is of the order of the hyperfine splittings.
Optically Active Lattice Vibrations in Wurtzite-Type Crystals of Zinc Oxide and Cadmium Sulfide
Authors: Tsuboi Masamichi , Wada Akiyoshi
Published: February 2004

By the use of a set of equations previously derived by Tsuboi and a set of Raman data recently published by Damen, Porto, and Tell, a set of reasonable values of force constants in the wurtzite-type ZnO and CdS crystals has been obtained. It was shown that, in the infrared-active A1- and E1-type vibrations, an appreciable amount of electrostatic force is involved besides the short-range interatomic forces through the chemical bonds. Such an electrostatic force is considered to be caused by a macroscopic polarization due to an in-phase displacement of the ions in the crystal in question, and this should not be involved in the infrared-inactive E2-type vibrations. The amount of this particular electrostatic force has also been estimated.
Crystal Structure of the Transition-Metal Molybdates and Tungstates. IV. Paramagnetic CuMoO4
Authors: Abrahams S. C. , Bernstein J. L. , Jamieson P. B.
Published: February 2004

Paramagnetic CuMoO4 is triclinic, space group P1̄, with lattice constants a = 9.903 ± 0.028, b = 6.783 ± 0.015, c = 8.359 ± 0.0019 Å, α = 101.08° ± 0.20°, β = 96.88° ± 0.20°, and γ = 107.05° ± 0.20° at 298°K, with six formula weights in the unit cell. The integrated intensities of 6310 reflections within a reciprocal hemisphere of radius (sinθ) / λ = 1.02 Å−1 were measured with PEXRAD; of these, 3081 were independent and significantly above background. The atomic arrangement is similar to that in ZnMoO4 but with corresponding atoms displaced by as much as 0.4 Å. Refinement by the method of least squares gave a final agreement factor between measured and calculated structure factors of 0.064. Two of the independent copper atoms occupy axially distorted octahedra of oxygen atoms; the four short Cu–O bond distances in each octahedron range between 1.933 ± 0.010 and 1.980 ± 0.012 Å, with an average value of 1.953 Å. The axial Cu–O bonds range in length between 2.213 ± 0.012 and 2.619 ± 0.011 Å, with an average value of 2.364 Å. The third copper atom occupies a distorted tetragonal pyramidal arrangement of oxygen atoms, with basal Cu–O distances ranging from 1.894 ± 0.013 to 1.985 ± 0.010 Å, the average being 1.928 Å; the apical Cu–O bond length is 2.341 ± 0.009 Å. The three independent molybdenum atoms are surrounded by somewhat distorted oxygen tetrahedra with Mo–O distances varying between 1.701 ± 0.010 and 1.862 ± 0.008 Å, the average being 1.772 Å. All atoms in CuMoO4 vibrate with significant thermal anisotropy.
Radiationless Transitions and Molecular Quantum Beats
Authors: Jortner Joshua , Berry R. Stephen
Published: February 2004

Radiationless transitions in isolated molecules are examined from the point of view of the breakdown of the Born–Oppenheimer approximation and the nature of the decay of coherently excited states. The problem of intramolecular vibronic coupling between zero-order Born–Oppenheimer states in an isolated molecule seems amenable now to a new approach both in terms of interpretation and of experimental investigation. We have classified molecules exhibiting vibronic mixing into two extreme cases, which we call the resonant case and the statistical case, characterized by low and high densities of molecular eigenstates, respectively. We have then considered the coherent excitation of these states and derived general expressions for photon counting rates and for the integrated intensity. Quantum beat signals can be investigated to analyze close-lying molecular eigenstates in the resonance limit. In the statistical limit the interference effects within a manifold of close-lying states are manifested by a radiationless decay process. An analysis of the radiationless decay times and the quantum yields is given.
Oxidation of Ethylene by the Photolysis of NO2 at 25°C
Authors: Jaffe Sigmund , Keith James
Published: February 2004

Ethylene was irradiated at 3660 Å in the presence of NO2 at 25°C. Quantum yields were determined as a function of ethylene pressure, NO2 pressure, and the total pressure (using N2). The quantum yields for NO2 dissociation increased as a function of (C2H4) and approached a value greater than 2. The main features of the proposed mechanism are the addition of oxygen atoms to ethylene producing an energy-rich intermediate which dissociates into CH3 and CHO. This is followed by rapid reaction of the radicals with NO2 to produce the stable products.
Spin–Orbit Coupling in Some Positive Ions of Cr, Mn, and Fe
Authors: Fisk C. , Valdemoro C. , Fraga S.
Published: February 2004

The spin–orbit splitting factors for various terms of positive ions of Cr, Mn, and Fe have been evaluated from existing analytical Hartree–Fock functions. The agreement with the experimental values, whenever available, is satisfactory.
Evaluation of Knudsen Measurements of the Sublimation of Manganese(II) Selenide
Authors: Wiedemeier Heribert , Goyette William J.
Published: February 2004

Knudsen effusion measurements have been carried out with stoichiometric MnSe over a temperature range from 1414°–1628°K, and a pressure range from 10−6−10− 4 atm. Two differently prepared samples and two different molybdenum effusion cells were used in four independent runs, representing a total of 40 vapor pressure measurements. The results are concordant and demonstrate that MnSe vaporizes congruently in this range. The calculational technique for the evaluation of the Knudsen data is based on the general reaction MnSe(s) = Mn(g) + 12(1 − α)Se2(g) + αSe(g). The calculated mean value for the degree of dissociation α is 0.45 and for the third-law heat of reaction 140.6 ± 2.5 kcal/mole at 298°K, in good agreement with the corresponding second-law value of 143.2 ± 3 kcal/mole. The heat of formation of MnSe(s) is found to be −37.4 ± 2.5 kcal/mole.
Bare-Nucleus Perturbation Theory: Excited States of Hydrogen Molecule
Authors: Goodisman Jerry
Published: February 2004

Ground and excited Σ+ states of R = 1.4a0 are treated by perturbation theory. The full interelectronic repulsion is taken as the perturbation, and the energy of each of nine states is calculated through third order. The equation for the first-order wavefunction is treated by the Hylleraas variational principle, using a linear variational function including up to 30 James–Coolidge basis functions. Comparisons with conventional linear variational calculations using the same basis functions, and with related calculations of other workers, are given. The perturbation results are in most cases superior to variation, especially when small basis sets are used, but it is noted that the inadequacy of the present basis set for excited states leads to slow convergence of the energies of both methods with addition of basis functions. The bare-nucleus Hamiltonian also becomes a worse starting point for higher states because of electronic shielding, as evidenced by slower convergence of the perturbation energy series. For the five states of the three lowest configurations, however, accuracy to about 1 kcal is obtained.