bluuebunny/crossref_metadata_2025 huggingface dataset:
Motion of Localized Triplet Excitons
Authors: Soos Zoltán G. , McConnell Harden M.
Published: January 2005

A theory is developed for exciton—phonon interactions in ionic molecular crystals showing triplet-exciton magnetic resonance. By using a simple model for the phonon Hamiltonian it is shown that the triplet excitons tend to be localized, or ``self-trapped,'' and to move in a diffusional manner.

The activation energy for diffusion is found to be essentially ½Λ, where Λ is the ``self-energy'' of the triplet exciton due to exciton—phonon interaction. It is suggested that the anomalous excess activation energy for exciton—exciton spin-exchange line broadening is ½Λ rather than the phonon-coupled exciton—exciton repulsion suggested previously. It is also shown that exciton creation and annihilation with the absorption and emission of phonons has no significant effect on the exciton magnetic resonance linewidths at low temperatures.
Motions of Molecules in Condensed Systems. XIV. Polarized Infrared Spectra of Single Crystals of Diborane
Authors: Freund Isaac , Halford Ralph S.
Published: January 2005

The polarized infrared spectra of single crystals of diborane as well as the spectra of the vapor and liquid are presented and analyzed. Evidence for the existence of three solid phases is discussed and the structure of the low-temperature form partially elucidated. This phase is found to be monoclinic with two or more molecules per primitive unit cell located on sites of symmetry no higher than Ci. Confirmatory evidence for Lord and Nielsen's assignment of ν9≈950 cm−1 and Smith and Mills' assignment of ν7≈850 cm−1 is presented. It is suggested that the strong electronic absorptions in the not-too-far ultraviolet are of B1u symmetry. Some indication of a special interaction in the solid state is found.
Photolysis of Cyclobutane at Photon Energies Below and Above the Ionization Energy
Authors: Doepker R. D. , Ausloos P.
Published: January 2005

The photolysis of cyclo-C4H8 and of cyclo-C4H8—cyclo-C4D8 mixtures has been investigated at 1470 and 1236 Å in the absence and presence of NO. In addition, a series of experiments carried out in which H2S was used as a free-radical interceptor in the photolysis of cyclo-C4D8 at 1236 Å. Approximately 90% of the observed products can be accounted for by the primary process: C4H8+hv→2C2H4. The extent to which the internally excited ethylene formed in this process will decompose further increases with diminishing pressure and wavelength.

The photolysis of cyclobutane has been investigated at energies above the ionization energy (I.E.=10.3 eV), using the argon resonance lines at 11.54 and 11.72 eV. It is shown that when NO is added to the system, cis-2-butene, trans-2-butene, and 1-butene are major products. These butenes are, however, not produced when NO (I.E.=9.25 eV) is replaced by O2 (I.E.=12.1 eV) and are only formed in trace amounts when no additives are present. It is suggested that the parent ion acquires the olefinic structure and undergoes charge exchange with NO.
Lifetime and Quenching of Anthracene Fluorescence in the Vapor Phase
Authors: Ware William R. , Cunningham Paul T.
Published: January 2005

The fluorescence lifetime and self-quenching of anthracene vapor has been examined as a function of temperature. The fluorescence lifetime in the absence of quenching is found to be 5.7±0.2 nsec and is independent of temperature over the range 200° to 300°C. This value, together with published Stern—Volmer constants is used to determine the quenching probability for quenchers such as O2 and NO. Probabilities considerably less than unity are obtained.

The second-order rate constant for self-quenching of anthracene vapor is found to have a negative temperature coefficient. The previously reported negative coefficient found in the Stern—Volmer constant for self-quenching can be explained by a temperature effect on the actual quenching process without resort to excimer decomposition.

Vapor-phase absorption and fluorescence spectra are reported. The oscillator strength and the quantum yield calculated from the actual and natural lifetimes are compared with corresponding values for solution.
Study of Electron Correlation in the H6 Ring, Using a Novel Approximation
Authors: Larson Everett G. , Thorson Walter R.
Published: January 2005

Studies on electron behavior in finite model systems provide information relevant to electrons in lattices. Approximate schemes for testing electron correlation may be tested by such model calculations. We report here the results of a study on the 1Γ1 ground state of the H6 hexagonal ring, using a novel type of wavefunction containing both valence bond and molecular orbital components. The method has a number of significant advantages and gives results as good as those of the simple alternant molecular orbital (AMO) method. Possible implications of these results for molecular and solid-state electron behavior are discussed briefly.
Light Scattering of Water, Deuterium Oxide, and Other Pure Liquids
Authors: Cohen Gerald , Eisenberg Henryk
Published: January 2005

The Rayleigh ratio and the Cabannes factor for water, deuterium oxide, and a number of other pure liquids were determined at 25°C, at angles of observation ranging from 30° to 150°, at 546 and 436 mμ. It was found that the Rayleigh ratio of water is substantially lower than the values reported in the literature; the values found by us Ru546(90)=0.865 10−6 cm−1, Ru436(90)=2.32 10−6 cm−1 for H2O, and Ru436(90)=0.843×10−6 cm−1, Ru436(90)=2.30 10−6 cm−1 for D2O are in excellent agreement with the predictions of the Einstein density-fluctuation theory, modified by the Cabannes anisotropy factor. The temperature dependence of the Rayleigh ratios for H2O and D2O is also satisfactorily predicted by the variation of the bulk parameters appearing in the Einstein—Cabannes equations. In contradistinction to such liquids as benzene, the Rayleigh ratios of H2O and D2O have a minimum, at about 22° and 28°C, respectively. No significant new information on the structure of water as a function of temperature can be derived from light-scattering experiments.
Luminescence Phenomena in Gamma-Irradiated Pure Alkane Glasses: Relaxation Mechanisms
Authors: Funabashi Koichi , Herley Patrick J. , Bueton Milton
Published: January 2005

It has been shown previously that gamma-irradiated pure 3-methylpentane glass at 77°K emits a characteristic luminescence according to a law which can be expressed as the sum of three first-order decays. In this new work on both 2-methylpentane and 3-methylpentane, it is shown: (1) that the two pentanes emit at 77°K, as nearly as can be established, in precisely the same fashion; (2) that the intensity of luminescence is decreased and the decay curve is flattened by permitting the glassy sample to relax at 77°K between vitrification and gamma irradiation; (3) that the decay law at both 77°K and 90°K is the sum of three first-order decay laws; (4) that the activation energies, as established by fixed-temperature measurements at those two temperatures, are all near 0.04 (±0.01) eV, but that the characteristic frequencies of the three laws vary by a factor of ∼102; (5) that, in addition to light which appears isothermally at 77°K and which is stimulated also by infrared irradiation, there is a glow portion which begins to appear only at temperatures near 100°K; (6) that while the long-wavelength portion of the luminescence spectrum is unaffected by the treatment to which the sample is subjected, there are significant changes in the shorter wavelength region on prolonged irradiation; (7) that at least two different kinds of electron traps are involved; (8) that chemical products are involved in the luminescence; and (9) that in gamma-sensitized luminescence as well as in radiation chemistry, radiolytic products play an important role in determination of the elementary processes responsible for the effects observed.
Solid-State Reactions of the Gold Dicyanide Ion in the Pressed-Disk Technique
Authors: Jones Llewellyn H. , Kressin Ivan K.
Published: January 2005

Infrared studies of pressed disks of KBr containing KAu (CN)2 and the species enriched in 13C and 15N show that solid solutions of Au (CN)2− in KBr are not formed as previously postulated but that the Au (CN)2− groups remain in clusters. Studies of KCl pressed disks containing small amounts of both KAu (CN)2 and KBr show that there is a specific interaction of Au (CN)2− with Br−, presumably with formation of Au (CN)2Br−2 perhaps as a polymeric chain. A similar interaction with I− occurs to a lesser extent.
Lattice Vibrations and Debye Temperatures of Copper and Aluminum
Authors: Varshni Y. P. , Shukla R. C.
Published: January 2005

Dynamical matrix elements have been presented for the axially symmetric model for cubic crystals, when interactions out to any neighbor are considered. The model has been applied to obtain the vibration spectra and Debye temperatures of copper and aluminum. In the case of copper, results have also been presented for the phonon-dispersion curves, vibration spectrum and Debye temperatures as obtained from the tensor-force model using White's atomic force constants. Comparison of the results with experimental data shows that the axially symmetric model gives rather poor results for Debye temperatures of Cu and Al.
Pyrolysis and Oxidation of Formaldehyde in Shock Waves
Authors: Gay I. D. , Glass G. P. , Kistiakowsky G. B. , Niki H.
Published: January 2005

The pyrolysis and oxidation of formaldehyde have been studied in shock waves by mass spectrometry and by ionization measurements over the temperature range 1400° to 2100°K. The pyrolysis shows first-order rate dependence with respect to both formaldehyde and inert gas after a temperature-dependent induction period. Experiments with formaldehyde-d2 show that the pyrolysis proceeds by a radical chain mechanism. The formation of the radical H3CO has been detected. The observed activation energy is 28±2.5 kcal/mole, which is surprisingly low; various mechanisms are suggested to explain this result.

The initial stage of the oxidation consists mainly of an oxygen-induced decomposition of formaldehyde into CO and H2, followed by branching chain oxidation of the H2 thus produced, as well as of remaining formaldehyde, and partial oxidation of the CO. Chemi-ionization is observed in the oxidation reaction, the species H3O+ and H3CO+ being the only ions detected. The total yield of ions is virtually independent of temperature. Very good agreement is obtained between measurements in reflected shock waves with the TOF mass spectrometer and in incident waves with a Langmuir probe. The mechanism of the oxidation reaction and of ion formation is discussed.
Narrow-Line Source for 119Sn Mössbauer Spectroscopy
Authors: Herber R. H. , Spijkerman J. J.
Published: January 2005

A dilute solution of metallic tin in palladium has been found to be useful as a source in 119mSn Mössbauer spectroscopy. A 3%-Sn−97%-Pd matrix has been studied in detail and gives rise to single-line resonance spectra with single-line absorbers (e.g., β-Sn, Mg2Sn, etc.). The zero-absorber-thickness extrapolated linewidth obtained with the Pd(Sn) source at 297°K and β-tin absorbers at 77°K was found to be 0.77±0.02 mm sec−1. The recoil-free fraction for the Pd(Sn) source is approximately 0.42 at 297°K. The observed Pd(Sn)–SnO2 isomer shift is 1.46±0.04 mm sec−1 at room temperature and the corresponding Pd(Sn)–Mg2Sn isomer shift is 0.35±0.02 mm sec−1. Palladium—tin matrices with up to ∼10% by weight of tin can be successfully used as narrow-line, large recoil-free fraction sources for Mössbauer spectroscopy at room temperature.
Spectral Shifts in the Absorption and Fluorescence of Pyrene under High Pressures
Authors: Offen H. W. , Eliason R. R.
Published: January 2005

An experimental study of the electronic spectrum of pyrene under high pressures in polymer matrices, mixed crystals, and in the crystalline state is reported. Pyrene concentrations less than 10−2M in plastics show a red shift in the monomer fluorescence, which is slightly larger than that of the Lb absorption band. In plastic samples containing higher concentrations of pyrene the excimer fluorescence appears and reveals greatly reduced intensities upon compression and net spectral shifts, ranging in magnitude between +700 to −400 cm−1 at 25 kbar. The red shifts in the spectra of pyrene molecules in durene and fluorene host matrices are larger than in the plastics for the absorption bands, but comparable for the monomer fluorescence. Pyrene microcrystals show a red shift of ∼2100 cm−1 in the La band and ∼1500 cm−1 in the excimer fluorescence at 25 kbar.
Remarks on Excitation Transfer Between Unlike Molecules
Authors: Katsuura Kanji
Published: January 2005

Vibronic states of a ``dimer'' formed by two unlike molecules are studied. Criteria for strong coupling and weak coupling are examined. According to these criteria, the strong-coupling case, namely, the case where the adiabatic approximation is applicable to the entire system, is more important in a system of two unlike molecules than in a system of two identical molecules. In some systems of two unlike molecules the adiabatic approximation is applicable to the entire system even when the interaction between the two molecules is very weak. Unlike the vibronic states of a strongly coupled system of two identical molecules, in which electronic excitation is completely delocalized, the vibronic states of a strongly coupled system of two unlike molecules exhibit, to some extent, localization of electronic excitation on one of the molecules. Thus, in the latter case, the transition between the vibronic states of the entire system may result in the transfer of electronic excitation from one molecule to the other. The probability of such transition is estimated, and the relation to Forster's theory is discussed. It is shown that Forster's theory is valid only when the emission spectrum of an excitation donor molecule and the absorption spectrum of an excitation acceptor molecule overlap each other substantially.
Ternary Excess Enthalpies in Simple Reciprocal Fused-Salt Mixtures. II. The Systems Na+–Ag+–Cl−–NO3 and Na+–Ag+–Br−–NO3−
Authors: Meschel S. V. , Kleppa O. J.
Published: January 2005

Calorimetric measurements in the liquid range of these fused-salt systems at 350° are reported. These results, when compared with data for the binary systems involved, permit an evaluation of the ternary excess enthalpies. These quantities are compared with the predictions of the conformal ionic solution theory of Blander and Yosim and with quasichemical theory.

It is found that to a first approximation the excess enthalpies are in good agreement with quasichemical theory. Thus, the systems considered, for which the enthalpy change associated with the metathetical reactions is of the order of 15–20 kcal/mole, behave in a manner similar to that of the previously investigated system Na+–K+–Cl−–Br−.
Paramagnetic Resonance of Vanadium (II) in Ferroelectric Potassium Ferrocyanide
Authors: O'Reilly D. E. , Schacher G. E.
Published: January 2005

Electron paramagnetic resonance of ferroelectric potassium ferrocyanide trihydrate doped with divalent vanadium has been investigated in the temperature range −180° to 20°C. Below the ferroelectric Curie temperature (Tc=−26°C) the resonance line positions may be expressed by a spin Hamiltonian for which the fine-structure terms D and E are linearly dependent on the spontaneous polarization. Above Tc the spin Hamiltonian is independent of temperature, D is an order of magnitude smaller than at low temperatures, E=0, and the z principal axis lies in the crystal a—c plane.

An anomaly in the linewidth of the ±32→±12 satellite resonance lines is observed in the vicinity of the ferroelectric Curie temperature. With the applied magnetic field along the z principal axis, the linewidth decreases abruptly by a factor of 2 with increase in temperature through the phase transition.

Dielectric constant and spontaneous polarization data are reported which agree with values previously given by Waku. The temperature dependence of the electron resonance is attributed to noncubic components of the crystal-field potential at an iron site produced by the permanent dipole moments of aligned water molecules. Orientations of water molecules determined by NMR are used to calculate the fine-structure tensor including both quartet and doublet T2g excited states. A mechanism of the anomalous line broadening due to fluctuations of the spontaneous polarization is proposed. Effects of both long-range electrostatic and short-range hydrogen-bond interactions in the ferroelectric transition of KFCT are qualitatively discussed.
ESR Study of NO3 and NO2 Produced on uv Irradiation of HNO3 Solutions at 77°K
Authors: Hayon E. , Saito E.
Published: January 2005

The paramagnetic species produced on uv photolysis of nitric acid at 77°K were studied using electron spin resonance. The primary photochemical process HNO3→OH+NO2 is followed by OH+HNO3→H2O+NO3. Three species are observed. One species is a triplet and is characteristic of the NO2 spectrum. The second is a singlet in H14NO3 (g=2.018) and a nonfully resolved doublet in H15NO3. On the basis of its blue color, absorption spectrum, photodecomposition on irradiation in its wave bands, competitive elimination on addition of OH radical scavengers, and hyperfine structure it is identified as the NO3 radical. The third species (g=2.0075), is produced as a product of the photodecomposition of NO3, and is tentatively assigned to NO.
Dielectric Relaxation in Liquid Polypropylene Oxides
Authors: Baur M. E. , Stockmayer W. H.
Published: January 2005

The dielectric properties of undiluted liquid atactic polypropyleneoxide have been studied as functions of temperature and molecular weight. The principal dispersion occurs at essentially the same frequency for all molecular weights at a given temperature, but at ower frequencies there is a small secondary loss peak that depends strongly on molecular weight. This secondary dispersion is shown to result from relaxation of a ``cumulative'' dipole, about 0.18 D per monomer unit, whose resultant magnitude depends on the long-range conformation of the chain molecule. Experimental relaxation times for the secondary dispersion agree well with predictions based on Rouse—Bueche—Zimm theory. The main dispersion shifts with temperature according to the WLF equation.
Preparation of Single-Phase Crystals of Compounds with Extremely Small Existence Regions
Authors: Albers W.
Published: January 2005

A method is described for the preparation of thermodynamically stable single crystals. The method can be used to eliminate small amounts of precipitate in a single crystal without an extensive knowledge of the phase diagram.
Magnetic Behavior of Gadolinium Sulfate Octahydrate at Low Temperatures
Authors: Levy Peter M.
Published: January 2005

The energy levels of the ground state of gadolinium in gadolinium sulfate octahydrate, determined by recent paramagnetic resonance experiments, are used to calculate the contribution from the crystalline field to the magnetic susceptibility. When Onsager's formula is used to account for the magnetic interaction between the Gd3+ ions, we find that the calculated susceptibility from ½° to 4°K agrees to within 1% with the susceptibility determined from experiments on adiabatic demagnetization.
Thermal Stability: An Extension of Frank-Kamenetsky's Theory
Authors: Steggerda J. J.
Published: January 2005

An exothermic reaction, proceeding in a reaction mass, may give an explosion or thermal equilibria depending upon the magnitude of the number δ. Frank-Kamenetsky's original criterion for thermal explosion is δ>3.32. Extended calculations have shown that a more detailed consideration of the situation is possible. In a spherical reaction mass, thermal explosion may be induced by a foreign heat source when δ>1.66.
Local Equilibrium Approach to Transport Processes in Dense Media
Authors: Prigogine I. , Nicolis G. , Misguich J.
Published: January 2005

The viscosity and thermal conductivity of a dense medium is studied. A model is constructed in which the singlet distribution function remains in local equilibrium whereas the doublet distribution function deviates from its local equilibrium value. It is this deviation of the pair function which accounts for the potential contributions to the transport of momentum and energy in the dense fluid. An integral equation is deduced for that part of the correlation function relevant to these transport coefficients and an approximate solution is sketched. Finally this approximation is briefly discussed in connection with some other approaches to transport processes in liquids. Numerical results for the evaluation of the approximate expression for the viscosity coefficient will be published in due course.
Vibrational—Rotational Angular-Momentum Coupling in Spherical-Top Molecules. II. General Zeta Sums
Authors: McDowell Robin S.
Published: January 2005

General Coriolis zeta sums are derived for all molecules belonging to tetrahedral, octahedral, and icosahedral point groups. For all infrared-active species, the zeta sum is given by ∑ ζi=m0+12(δr+δg+1)m−12(δr+2), where m0=1 or 0 depending on whether or not a central atom is present; m is the number of sets of equivalent nuclei on threefold or higher symmetry axes, but not on all symmetry elements; δr=1 or 0 depending on whether or not the rigid rotations belong to the infrared-active representation; and δg=1 for Point Group Th and zero for all other point groups. Several related matters are considered, including the definition of the signs of individual zetas. The application of these zeta sums to the analysis of vibrational spectra is treated briefly, especially with regard to the contours of unresolved bands.
Thermal Decomposition of 2,3-Dimethylbutane in a Single-Pulse Shock Tube
Authors: Tsang Wing
Published: January 2005

2,3-Dimethylbutane has been pyrolyzed in a single-pulse shock tube. The initial steps appear to involve the breaking of carbon—carbon bonds. At about 1100°K the decomposition mechanism is as follows:[Complex chemical formula]The Arrhenius parameters for the bond-breaking steps are k1=1016.1exp(−76 000/RT)sec−1k2=1016.6exp(−81 100/RT)sec−1.  (1000∘−1200∘K)
13C Nuclear Magnetic Resonance Spectroscopy. VI. Azines and Methyl Azines
Authors: Lauterbur Paul C.
Published: January 2005

The 13C nuclear magnetic resonance spectra of the six known unsubstituted azines, pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, and s-tetrazine have been obtained, as well as those of some of their methyl derivatives. The carbon shieldings have been compared with those calculated theoretically, and estimates of the effects of π and σ electron densities and of bond orders are attempted. Reasonably good agreement between theory and experiment is obtained if the σ bonds between carbon and nitrogen are assumed to be very slightly polar.
Spin Delocalization in Mixed Tetrahedral Ni II Complexes
Authors: Eaton D. R. , Phillips W. D.
Published: January 2005

Proton magnetic resonance spectra of a number of paramagnetic Ni II chelates of the type NiL1L2 where L1 and L2 are different aminotroponeimine ligands have been examined. The proton resonances show large hyperfine contact interaction shifts due to delocalization of spin density from the metal to the ligand by dπ—pπ bonding. In the series of mixed chelates the amount of spin density delocalized to the different ligands varies markedly. Comparison with the spectra of the symmetric chelates shows that one ligand of each of the mixed chelates gains in spin density at the expense of the other ligand. The effect has been found to depend on the electron withdrawing or donating properties of the ligand substituents. The results for a number of ligands containing substituted phenyl groups have been correlated with the Hammett σ parameters. Two possible interpretations of these results are discussed, one proposed by Lin and Orgel and the other suggested by Jaffe's ideas of competitive π bonding in tetrahedral complexes. The latter is preferred for the Ni II aminotroponeimineates.
Gaussian-Transform Method for Molecular Integrals. II. Evaluation of Molecular Properties
Authors: Kern C. W. , Karplus M.
Published: January 2005

The Gaussian-transform approach to the evaluation of multicenter molecular integrals is developed for one- and two-electron coordinate operators averaged over a wavefunction which is constructed from one-electron orbitals composed of exponential basis sets. The general method is outlined and applied to a number of electric- and magnetic-interaction operators. Formulas for these operators are given not only for exponential orbitals but also for Gaussian orbitals, which enter at an intermediate stage in the treatment of the exponential case. The complete analysis, supported by numerical data gathered from test programs, serves to demonstrate that the Gaussian-transform method represents a possible approach to the determination of polyatomic wavefunctions and their properties.
Calculation of Absolute Raman Intensities of A1 Modes of Molecules and Ions from a Delta-Function Potential Model
Authors: Long Thomas Veach , Plane Robert A.
Published: January 2005

A delta-function potential model of molecular binding is used to derive an expression for α∥b, the parallel component of the molecular polarizability from the region of a chemical bond, and ∂ᾱ/∂r, the derivative of the mean molecular polarizability with respect to a change in a bond length for the A1 stretching modes of diatomic and polyatomic molecules and ions. The final expression is ∂ᾱ/∂r=23(gσ/Za0)12nr3, in which g is the delta-function strength; Z, the effective nuclear charge; σ, the Pauling covalent bond character; a0, the Bohr radius; n, the number of electrons in the bond region; and r is the equilibrium internuclear distance. There is shown to be good agreement between calculated and experimental values of both α∥b and ∂ᾱ/∂r.
Vibrational Relaxation of Methane
Authors: Richards L. Willard , Sigafoos David H.
Published: January 2005

When methane gas is heated in an incident shock wave, its absorption of the 1470-Å xenon resonance radiation increases to a higher equilibrium value at a rate which is associated with the rate of vibrational relaxation. Some values of the absorption coefficient k from I/I0= exp(—kx) at thermal equilibrium taken from a smoothed curve are: 1.2 cm−1 at 650°K, 10 at 1000, 47 at 1500, and 95 at 2000. In the temperature range from 740° to 1600°K, the vibrational relaxation time of a 1:9 methane—argon mixture was observed to be exp(−5.8+55 T−⅓) μsec·atm, and it was exp(−5.4+45 T−⅓) μsec·atm for a 1:1 methane—argon mixture. From these results, a relaxation time of exp(−5.4+40 T−⅓) μsec·atm was calculated for pure methane, which agrees with room-temperature ultrasonic data, and a relaxation time of exp(−6.2+61 T−⅓) μsec·atm was calculated for a trace of methane in argon. A comparison is made with data for the relaxation time of oxygen containing small amounts of methane.
Structure of Sodium Aluminogermanate Melts with Na2O/Al2O3 Ratio Equal to Unity
Authors: Riebling E. F.
Published: January 2005

The viscosities and densities of a series of ternary sodium aluminogermanate melts with the Na2O/Al2O3 ratio equal to unity have been determined for temperatures between 1200° and 1500°C. The viscosity and expansion coefficient evidence suggests that aluminum (III) takes part in network formation in the form of AlO4 tetrahedra. The molar-volume data can best be interpreted in terms of a model that involves GeO4 and AlO4 tetrahedra as well as v̄Na2O increase that is positively related to the Al2O3 content. Crystal-structure and binary-melt data were used to suggest likely coordination-polyhedra types and partial molar volumes for the models discussed.
Vibrational Energy Transfer in High-Energy Collisions
Authors: Treanor Charles E.
Published: January 2005

Time-dependent wavefunctions are used to evaluate the exact transition probabilities for a forced harmonic oscillator. The forcing is represented by a time-dependent potential, where this potential has a linear dependence on the oscillator coordinate. The results are compared with available numerical solutions for a harmonic oscillator forced with a potential which has an exponential dependence on the oscillator coordinate. The comparison is made for the collision of an N2 molecule with another particle, and it is found that although the results for the two cases are similar, the linear potential gives higher values for the multiquantum transitions. It is then shown that time-dependent wavefunctions which contain the corresponding classical motion as a parameter provide a good set of functions for a perturbation calculation. The energy transfer to these oscillating wavefunctions is always identical to the energy transfer to the classical oscillator. Thus the perturbation value of the energy transfer represents the difference between the classical and the quantum-mechanical result. It is shown that this value, which is zero for the linear forcing potential, is very small for higher-order potentials, even at high velocity of impact. This demonstrates that classical calculations can be used to obtain the energy transfer in molecular collisions at high temperature.
Verification of the Kuhn—Thomas Sum Rule in the Framework of Some Recent Polarizability Theories for Molecular Aggregates
Authors: Thiéry Jean
Published: January 2005

The semiclassical formalism for molecular aggregates, presented by Nesbet, is compared to the corresponding classical treatment of DeVoe. A development of the first theory allows the determination of the complex polarizability tensor representing a given electronic transition. Another development allows the computation of the energy absorbed by a molecular aggregate. This energy expression is of quadratic form with respect to the incident field, which permits the definition of a tensorial extinction coefficient and a tensorial oscillator strength. The same results are obtained with the theory of DeVoe. The preceding tensors are calculated for an aggregate of two nonidentical molecules (each molecule is assumed to be represented by only one polarizability). A special class of spatial configurations of the molecules of an aggregate is found, for which the tensorial oscillator strength remains invariant. The scalar oscillator strength is invariant whatever the aggregate spatial configuration is. These results show that the Kuhn—Thomas sum rule is verified in this particular case (a molecular dimer) of two electrons coupled by Coulombic forces.
Analysis of the Nuclear Overhauser Effect in the Difluoroethylenes
Authors: Kuhlmann Karl F. , Baldeschwieler John D.
Published: January 2005

Analysis of the nuclear Overhauser effect observed in proton double resonance is used to determine the probability of relaxation between spin states of different symmetry in the three difluoroethylene isomers. The probability of relaxation between states of A and B symmetry is much greater for CH2CF2 than for either cis- or trans-CHFCHF. This indication of an appreciable A to B transition probability in CH2CF2 provides some detailed information on the symmetry properties of the interactions responsible for nuclear relaxation. A qualitative comparison of the Overhauser effects in these three molecules indicates that the fluorine spin—rotation interaction is probably responsible for the A to B relaxation in CH2CF2, but further experiments are suggested to test this hypothesis.

The relaxation equations for these spin systems are solved for steady-state and transient behavior using transition probabilities given by assuming relaxation by randomly varying isotropic local fields. Overhauser effects and the transient recovery of the spin systems from the steady state in the presence of an irradiating rf field to thermal equilibrium are used to estimate quantitative proton, fluorine, and A to B relaxation rates.
On the Theory of Electron-Transfer Reactions. VI. Unified Treatment for Homogeneous and Electrode Reactions
Authors: Marcus R. A.
Published: January 2005

A unified theory of homogeneous and electrochemical electron-transfer rates is developed using statistical mechanics. The treatment is a generalization of earlier papers of this series and is concerned with seeking a fairly broad basis for the quantitative correlations among chemical and electrochemical rate constants predicted in these earlier papers. The atomic motions inside the inner coordination shell of each reactant are treated as vibrations. The motions outside are treated by the ``particle description,'' which emphasizes the functional dependence of potential energy and free energy on molecular properties and which avoids, thereby, some unnecessary assumptions about the molecular interactions.
Infrared Absorption by Symmetrical NO3 Free Radical in the Gas Phase
Authors: Cramarossa Francesco , Johnston H. S.
Published: January 2005

A new infrared absorption band between 1325 and 1375 cm−1 has been observed in the N2O5–O3 system at low pressure in an 80-m path-length cell. In such systems the presence of the symmetrical NO3 free radical is well known in terms of its visible absorption spectrum, which varies in the unusual way of Kss[N2O5]13[O3]13. The new infrared band lies at a frequency just below that for the antisymmetric stretch of the symmetrical planar nitrate ion; the absorption optical density varies as [N2O5]13[O3]13; and the new absorption has been assigned to the symmetrical NO3 free radical.
On the Relaxation Effect in the Limiting Conductance of Electrolytes
Authors: Résibois P. , Hasselle-Schuermans N.
Published: January 2005

The theory of the relaxation effect in electrolytes developed by Davis and one of the authors (P.R.) is improved by taking into account the interaction of the solvent with the ions. This is made possible if we assume that the ions have a large mass (M) with respect to the solvent molecules (m), in which case the recent developments of the microscopic theory of Brownian motion may be used. We show that the results of the classical theory of Onsager—Debye—Falkenhagen are recovered provided that the following conditions are satisfied: (m/M)«1, (e2C⅓/D0kT)«1, in such a way that (e2C/D0)«ζ2/M where ζ is the friction coefficient of the fluid. We also discuss the connection between the various statistical-mechanical approaches which have been proposed recently for discussing this problem.
Single-Crystal X-Ray Diffraction Study of β-Diborane
Authors: Smith H. Warren , Lipscomb William N.
Published: January 2005

The crystal structure of the β phase of B2H6 is monoclinic, in the space group P21/n, and the unit cell contains two molecules and has parameters a=4.40, b=5.72, c=6.50, and γ=105.1°. The value of R=Σ ||F0 |−| Fc|| /Σ|F0|=0.042 for the 86 independent diffraction maxima, obtained at −190°C by use of counter methods from a single crystal in an arbitrary orientation.
Microwave Spectrum of Methyl Vinyl Ketone
Authors: Foster Peter D. , Rao V. M. , Curl R. F.
Published: January 2005

The rotational spectrum of CH3COCHCH2 has been studied in the region 7–33 Gc/sec. Both a- and b-type transitions have been assigned. The barrier to internal rotation of the methyl group has been found to be 1250±20 cal/mole. The electric dipole moment has been found to be 3.16±0.05 D. The observed spectrum is consistent with a planar configuration in which the two double bonds are trans with respect to each other.
Bulk Photoconductivity of p-Chloranil Crystals
Authors: Reucroft P. J. , Rudyj O. N. , Salomon R. E. , Labes M. M.
Published: January 2005

The bulk-photoconductivity properties of substituted p-benzoquinone crystals with particular reference to p-chloranil (tetrachloro-p-benzoquinone), are presented and discussed. While photocurrents excited by light in the fundamental absorption region of p-chloranil can probably be considered in terms of exciton processes involving the crystal absorption spectrum, ``anomalous'' photocurrent regions occurring below the main absorption edge can be more reasonably discussed in terms of impurity-sensitized photocarrier production. A possible mechanism for this sensitization is presented.
Theory of Helium Dissolution in Uranium Dioxide. I. Interatomic Forces in Uranium Dioxide
Authors: Olander Donald R.
Published: January 2005

Knowledge of the nature of the interatomic forces in uranium dioxide is required for theoretical treatment of phenomena such as radiation damage, adsorption, and gas solubility. The van der Waals and repulsive forces are of particular interest, for these interactions govern the behavior of neutral species in the crystal. The Kirkwood—Müller expression for the coefficients of the 1/rn dispersion forces were employed, and the form of the repulsive potentials was taken from the delta-function model of Mason and Vanderslice. The two disposable parameters in the repulsive potentials were evaluated from data on the atomic properties of the constituent ions and the lattice constant and compressibility of UO2. The calculated cohesive energy of the UO2 lattice was in very good agreement with the value obtained from a conventional Born—Haber cycle.
Molar Volume of Solid Parahydrogen along the Melting Line
Authors: Dwyer Robert F. , Cook Gerhard A. , Berwaldt Oren E. , Nevins Hugh E.
Published: January 2005

The molar volume (Vs) of solid parahydrogen along the melting line up to a temperature of about 24°K and a pressure of about 400 atm has been determined by two independent methods: direct measurement and computation from the heat of fusion and change in volume during melting. Results obtained by the two methods agree with each other within about ±0.2%; they are both referred to below as ``experimental.'' The empirical linear equation Vs=27.1788–0.283044 T reproduces the experimental results with a mean deviation of about 0.15%.
Electron-Diffraction Analysis of the Dielectric Structure of Anthracene
Authors: Yamaguchi S.
Published: January 2005

An electron beam was utilized for charging a dielectric object and for observing the diffraction pattern from it. Analysis of the pattern obtained permits one to see that anthracene molecules are oriented parallel to the c axis of a monoclinic lattice. The electron wavelength fluctuation method (0.0332–0.0380 Å) was applied for the present analysis.
Vector Coupling Coefficients for Atomic Self-Consistent-Field (SCF) Calculations
Authors: Malli Gulzari L. , Olive J. P.
Published: January 2005

General formulas are derived for the vector-coupling coefficients useful in atomic self-consistent-field (SCF) calculations. Tables of these coefficients for all the states arising from atomic configurations consisting of any combination of s, p, and d shells and for a single f shell have been prepared and are available for atomic SCF calculations.
Simple Orbitals for Molecular One-Layer Puffs
Authors: Dvořáček Zbyněk , Horák Zdeněk
Published: January 2005

The radial wave equation of an electron in a spherically symmetrical field[Complex chemical formula](potential field of a molecular one-layer puff) is solved. For this purpose the outer part of the radial function (r≥ρ) is approximated by the asymptotic expansion of the Whittaker function Wk, l+½(y). To improve the accuracy a converging factor is used. A comparison is done with existing exact or approximate calculations on phantom-center puffs (q0=0). The results are satisfactory for energies and wavefunctions as well. The influence of the choice of origin on the orbital energy in homonuclear diatomics is discussed. In ``non-phantom-'' center puffs (q0≠0), assuming the bare-nuclei approach, many inner radial wavefunctions (r≤ρ) were found hydrogenic to a very good approximation.
On the Dielectric Dispersion of Polyelectrolytes, with Application to DNA
Authors: Pollak M.
Published: January 2005

It has been reported in the literature that dielectric relaxation times measured in a DNA solution are orders of magnitude too large to be consistent with a Maxwell—Wagner mechanism. It has thus been concluded that the dielectric dispersion is associated with the rotation of molecules. It is shown in this paper that this conclusion is based on the use of an expression for the relaxation time which is not applicable to the case of highly elongated molecules. An expression is given which is appropriate to the case of a Maxwell—Wagner mechanism for highly elongated polyelectrolyte molecules. It yields a value for the relaxation time which compares well with the experimental results reported in literature.

Results of experiments on the anisotropy of the relaxation times in a flowing solution of DNA are reported. These results indicate clearly that the dielectric dispersion is indeed due to a Maxwell—Wagner mechanism.
Measurement of Inelastic Energy Loss in some Noble-Gas Ion—Atom Collisions at Kiloelectron-Volt Energies
Authors: Flinchbaugh David E.
Published: January 2005

Large-angle collisions of Ne+ ions with Ar and Ne atoms, and protons with argon, were investigated, and the inelastic energy loss Q was measured as a function of incident energy, scattering angles, and state of ionization following the collision. Measurements for the Ne+-on-Ar case were made at 3-, 6-, 12-, and 25-keV incident energies, and both the recoil target particles and the scattered incident particles were studied at several angles between 15° and 85° with respect to the incident beam. The Ne+-on-Ne and H+-on-Ar data were taken at 25 keV over the same angular range. The kinetic energies and scattering angles were accurately measured, and this, together with the energy and momentum conservation equations, allowed determination of the inelastic energy.

The average value of the inelastic energy loss Q̄ is plotted vs recoil angle φ or vs scattering angle θ and a separate curve is obtained for each incident energy. However, when the various Q̄ values are plotted vs the calculated distance of closest approach r0, a universal curve is obtained for each ion—atom combination. The data points in each of the three cases studied appeared to fit best a curve giving Q̄ as a function of r0 to an inverse power. The protons especially showed deep penetration into the argon electron shell structure. Values of Q̄n, where n denotes the charge state of the collision product detected, are presented at each of several angles at each energy studied.
Energy Transfer between Triplet States in a Viscous Medium
Authors: Smaller B. , Avery E. C. , Remko J. R.
Published: January 2005

The mechanism of energy transfer between triplet states of aromatic molecules has been studied using deuterated phenanthrene as donor and deuterated naphthalene as acceptor. The investigation reveals that at high viscosities the transfer rate constant kt can be accounted for in terms of an electron exchange interaction and becomes diffusion controlled as the viscosity η is decreased and molecular motion becomes appreciable. The results covering viscosities above 104 P are in good agreement with a Debye diffusion-controlled collision reaction, ktη=const. The interaction is probably electron exchange in nature with range Rc≈20 Å. The relative magnitudes of Rc and r̄ = 〈r2〉½ determine the characteristics of the energy-transfer phenomenon.
Rigid Disks at High Density
Authors: Stillinger Frank H. , Salsburg Zevi W. , Kornegay Robert L.
Published: January 2005

A technique is developed for estimating the rigid-disk partition function near close packing, by evaluating the specific free-energy contributions from correlated motion of larger and larger sets of contiguous particles. In terms of the reduced density θ=A0/A (A0 is the close-packed value of the closed system's area A), the theory leads to an asymptotic series in the limit θ→1 for the Helmholtz free energy per particle, divided by kT, of the form: F/NkT∼2ln(λ/a)−2ln(θ−1−1)+C+D(θ−1−1)+···,in which C and D are appropriate numerical constants, λ is the mean thermal de Broglie wavelength, and a the disk diameter. It is shown that lattice defects cannot contribute to the above asymptotic series. The constant C is expressed as an infinite series whose leading term is the single-particle free area result [— ln (√3/2)], and whose successive terms account for high-compression cooperative motions involving ascending numbers of particles. An approximate value for C is obtained by computing all contributions for four or fewer correlated disks, with a resulting slight decrease below the free area value. The calculated C may be utilized along with machine-computed rigid-disk pressures on both fluid and solid isotherm branches to locate accurately the first-order phase transition by means of a Maxwell double tangent construction.

Some concluding remarks are directed to application of the present method to rigid spheres in three dimensions, where the high density stable crystal structure could be established by suitable extension of the present formalism.
Electronic Structure of SrO
Authors: Kaufman M. , Wharton L. , Klemperer W.
Published: January 2005

Molecular-beam electric-resonance spectra of SrO are measured in the rf and microwave regions. The microwave transitions are induced with a frequency-broadened klystron, greatly reducing the time needed to search for resonances. Rf-microwave double resonance is used to establish the vibrational assignment of the rf spectra from the known assignment of the microwave spectra. The dipole moment and rotation constant of 88Sr16O in the lowest two vibrational states are: μ0=8.900 D, μ1=8.874 D, B0=0.33688 cm−1, and B1=0.33469 cm−1. These rotation constants show that this 1Σ state is identical with the lower state of three optical-emission systems of SrO. With the aid of a molecular-beam magnetic-deflection experiment, it is shown that this state is almost certainly the ground electronic state of SrO. The evidence indicating triplet ground or low-lying states in SrO and the other alkaline-earth oxides is reviewed, and it is concluded that in no alkaline-earth oxide has a triplet ground state been established. SrO has the largest percent ionic character, μ/er, yet observed for any diatomic molecule. The dipole-moment function μ(r) of SrO differs considerably from that of BaO and cannot be explained by a model of two polarizable ions. A description of the bonding in the alkaline-earth oxides can be obtained from comparisons of recent SCF calculations on LiF and BeO.
Pressure-Induced Phase Transitions in Triplet-Exciton Crystals
Authors: Merkl A. W. , Hughes R. C. , Berliner L. J. , McConnell H. M.
Published: January 2005

The pressure dependence of the exchange-narrowed triplet-exciton magnetic resonance in (φ3PCH3)+-(TCNQ)2− and (φ3AsCH3)+(TCNQ)2− has been observed at 170 Mc/sec in the ranges 1–9 kbar, and 220°—362°K. Pressure-induced phase transitions in these salts are reported. The observed p—T phase diagram for (φ3AsCH3)+(TCNQ)2− can be explained remarkably well in terms of an elementary theory of non-interacting triplet excitons.
On the Optical Rotary Dispersion of Polymers
Authors: Harris Robert A.
Published: January 2005

The ``time-dependent Hartree'' method is used to obtain the optical rotary power of a polymer. The resulting equation for the susceptibilities are solved by a normal mode method in both the weak and strong coupling limit. First-order perturbation theory gives in a very simple way the Moffit—Kirkwood—Fitts equation. The time-dependent Hartree approximation is shown to satisfy both the f-sum rule, and the rotational-strengths sum rule. The susceptibilities of the polymer in an optically inactive medium are formally obtained, and a cumulant expansion is suggested. The relation of the time-dependent Hartree approximation to the classical theory of macroscopic electrodynamics and to exciton theory is discussed. The nature of the approximations used in the theory is discussed, as well as their range of validity.