bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong Collision Model for Energy Transfer in Systems of Oscillators
Authors: Hoare Michael
Published: January 2005

Transition probabilities are formulated for single quantized oscillators which interact with a similar heat bath such that vibrational energy is conserved and randomly distributed between collision partners. Explicit solutions have been obtained for the corresponding relaxation and mean-passage-time problem, and results for the latter are compared with both ``equilibrium'' behavior and the predictions of the Landau—Teller scheme. Deviations from the equilibrium hypothesis tend toward a well-defined limit as the level spacing decreases to zero but are effectively negligible except where dissociation occurs within about 10 collisions.

It is shown that the notion of random energy distribution leads to a ``principal relaxation time'' of two collision intervals, which seems likely to be a lower bound for realizable energy-transfer models.
Nitrogen Electric Quadrupole and Proton Magnetic Resonances in Thiourea
Authors: Smith David H. , Cotts R. M.
Published: January 2005

The nitrogen nuclear electric quadrupole coupling constants for the two nonequivalent thiourea molecules in the low-temperature phase of solid thiourea, SC(NH2)2, have been determined as a function of temperature between 4° and 169°K. At 77°K, the coupling constants and asymmetry parameters are, for Molecule (1) e2q1Q/h=3121.6 kc/sec and η1=0.3954, and for Molecule (2) e2q2Q/h=3099.6 kc/sec and η2=0.3930. The two highest-frequency transitions in each spectrum exhibit temperature dependences that follow Bayer's theory of electric-field gradient averaging by local oscillators. Zeeman studies place the x principal axis of the electric field gradient out of alignment with the C,N bond, the axis of symmetry in the NH2 group. Magnetic dipole perturbation coupling between nitrogen and hydrogen nuclei is zero in first order, and the second-order dipole coupling shifts the quadrupole resonance line near values of the Zeeman field, which make the proton Larmor frequency equal to a nitrogen quadrupole transition frequency. The energy-conserving 14N-proton mutual spin flips, which occur at these applied magnetic fields, make several cross-relaxation experiments possible. The temperature dependences of the proton spin—lattice relaxation times is characterized by that of thermally activated molecular reorientation at temperatures above the ferroelectric transition temperature, 169°K. Measured values of the activation energy and pre-exponential frequency factor are 10 kcal/mole and 7.5×1013 sec—1. This molecular reorientation inhibits measurement of the quadrupole coupling above 169°K. Nitrogen quadrupole-lattice relaxation times appear to be the same for all level transitions and to follow a T—2 temperature dependence between 8° and 165°K.
Linked-Cluster Theorem and Unitarity
Authors: Yaris Robert
Published: January 2005

It is shown that the linked-cluster theorem for nonperturbational treatments (previously demonstrated) follows from the principle of unitarity (conservation of probability). The reasons why unlinked clusters appear in CI calculations, but can be cancelled out of the results is also briefly discussed.
Collective Electronic States in Molecular Crystals
Authors: Krugler J. I. , Montgomery C. G. , McConnell H. M.
Published: January 2005

A theory of the collective electronic states of linear-chain molecular crystals is developed. The theory is applicable to cases where the intermolecular electronic interaction is so strong that the electronic structures of the molecules in the crystal lattice may be grossly different from the electronic structures of the isolated molecules. Strong intermolecular interactions due to (a) dispersion forces and (b) intermolecular charge transfer, are considered. Case (a) corresponds to an extension of the Davydov singlet exciton theory to cases where the first-order exciton bandwidth is comparable to, or greater than, the isolated-molecule excitation energy. New features emerge in this strong coupling region, such as low exciton excitation energies, and ferroelectric-type electronic polarization. Case (b) represents an extension of Mulliken's theory of intermolecular charge transfer to infinite chains of alternating donor and acceptor molecules. The cooperative aspects of the intermolecular charge transfer are included using a Hartree-like self-consistent field approximation. The energy gap for charge-carrying elementary excitations is calculated. The calculations are also applicable to the problem of intermolecular charge transfer and electrical conductivity in regular linear molecular chains of N molecules and N/2 mobile electrons.
Mössbauer Effect in the System SrFeO2.5–3.0
Authors: Gallagher P. K. , MacChesney J. B. , Buchanan D. N. E.
Published: January 2005

Mössbauer spectra were measured at 4°, 78°, and 300°K for the two end members and two intermediate samples of the system SrFeO2.5–3.0. Of primary interest is the spectrum of strontium ferrate (IV) which at 300°K consists of a single unsplit line having a full width at half-intensity of 0.39 mm/sec and an isomer shift relative to copper of —0.171 mm/sec. At 4° and 78°K the spectra consist of six lines with an ISCu of —0.079 mm/sec and an hfs of 331 and 290 kOe, respectively. There is no evidence of quadrupole splitting, consistent with the cubic perovskite structure. The spectra of the pure iron (III) compound are composed of two sets of six-line spectra having ISCu of +0.126 and —0.047 mm/sec and hfs of 489 and 407 kOe, respectively, at 300°K. By analogy with YIG, it was concluded that the structure should contain equivalent amounts of octahedrally and tetrahedrally coordinated iron sites. Subsequent structural analysis confirmed this conclusion and indicated that the phase is isomorphic with brownmillerite. The spectra of the intermediate compounds were found to be more complex and are discussed in terms of accompanying changes in stoichiometry and structure.
Methane—Tritium System. II. Kinetics of the Exchange Reaction
Authors: Kandel Richard J.
Published: January 2005

The rates of the reactions of CH4 with T2 to give, successively, CH3T, CH2T2, CHT3, and CT4, and of the reverse reactions of the tritiated molecules with protium were measured. Second-order rate constants were obtained from the data, and radiation yields were determined. The reactions were shown to follow two paths. Beta decay energy deposited in the tritium resulted in an exchange reaction in which approximately one exchange took place per ion pair formed. Energy initially deposited in the methane resulted in six exchanges per ion pair. Equilibrium constants were calculated from the steady-state concentrations and were shown to be close to the high-temperature, classical values. Hot atom, ion, and radical reactions are believed to play a predominant role in the exchange.
Nucleation and Crystal Growth in Chlorpromazine
Authors: Ehlers W. , Haneman D.
Published: January 2005

Chlorpromazine, a widely used tranquilizer drug, is difficult to purify by standard zone melting techniques due to its extreme supercooling, even to liquid-helium temperatures. It has been found that the liquefied material undergoes a transition to the glassy state at —30°C and that there is a maximum rate of nucleation of crystallites at —50°C, while the substance is in the glassy state. Crystal growth from these nuclei in the form of hexagonal platelets proceeds at a maximum rate at +31°C, in the liquid state. Using techniques based on these data, zone refining has been found to be a practical process.
Influence of Competitive Decomposition Processes on Ionization Efficiency Curves from Electron Impact
Authors: Lifshitz Chava , Long F. A.
Published: January 2005

The energy dependence of ionization efficiency by electron impact for polyatomic molecules is influenced by the entrance of decomposition processes. The observed yield of parent ion drops sharply at the energy onset of a high-yield decomposition process. Ionization efficiency curves for products from other decomposition processes are similarly effected. These effects are particularly apparent for decomposition processes with energy thresholds some volts above the parent ion appearance potential, and this is illustrated by data for the ionization efficiencies from the molecules NH3, C2H4, and C2F4. Perturbation from such competitive processes can result in erroneously high measured appearance potentials for the product ions.
Absolute Infrared Intensities of the Fundamental Absorption Bands in Solid CO2 and N2O
Authors: Yamada Haruka , Person Willis B.
Published: January 2005

Absolute infrared intensities of the fundamental vibrations of CO2 and N2O have been measured in polycrystalline solid films. The path length has been measured by observing interference fringes. In contrast with CS2, the results for the solid phase do not agree exactly with those predicted from the gas phase values, using only the simple ``field-effect'' correction. In particular the intensity in the solid is less than that in the gas phase for v1 and v3 of N2O and for v3 of CO2, whereas the ``field-effect'' predicts an increase in intensity. However, the observed changes in intensity are relatively small. The predicted frequency shifts also do not agree with the observed values, indicating that other effects are important. Bond moment parameters are presented. The bond moment μ is the same as in the gas phase, but the derivative, ∂μ/∂r, decreases by about 25%. Some incomplete studies of the intensities in mixed crystals of N2O and CO2 are presented.
Critical Solution Behavior in a Binary Mixture of Gaussian Molecules
Authors: Stillinger F. H. , Helfand E.
Published: January 2005

We have examined in detail the cluster expansion for the mixing free energy of molecules whose repulsive interactions give rise to Ursell—Mayer cluster bonds of Gaussian form. By choosing the Gaussian width for unlike molecular pairs in a binary solution to exceed a common width assignment for like pairs, the resultant positive mixing free energy can produce phase separation at sufficiently high over-all density. Using the exact evaluation technique for any Gaussian cluster integral of arbitrary complexity, the set of free-energy contributions involving clusters of up to five particles were calculated and treated as input in a Padé approximant to estimate the width-ratio-dependent critical density. In the large unlike-to-like width-ratio limit, only the relatively restricted class of clusters corresponding to ``bicolored'' graphs needs to be considered, and the free-energy calculation may be easily extended to eight-particle clusters. A Padé analysis of the second composition derivative of free energy (related to composition fluctuations and solution turbidity in the critical region) yields results at variance with simple solution theories, but of the same type that may by analogy be inferred from recent three-dimensional Ising model susceptibility numerical analyses. A list is appended of the multiply connected mixture graphs through five points and bicolored graphs through eight points.
Relative Stabilities of Weak Hydrogen Bonds to Nitrogen
Authors: Berkeley Peter J. , Hanna Melvin W.
Published: January 2005

Enthalpies of formation are reported for the weak complexes formed between nitrogen bases and chloroform. These thermodynamic data are obtained from the temperature variation of equilibrium constants determined from NMR dilution-shift measurements. The value of —ΔH0 for an amine—chloroform complex is 50% greater than that for a nitrile—chloroform complex. This is the trend of basicity with respect to hybridization that is experimentally observed in organic chemistry. This trend is described in terms of a semiclassical model for weak hydrogen bonds, consisting of two effects. These are the classical electrostatic attractive energy and the quantum mechanical overlap repulsion energy. Examination of the electrostatic energy shows that it alone cannot be responsible for the different energies of the amine and nitrile complexes. The repulsive overlap energy is proportional to the square of the overlap integral times an average ionization potential. The overlap integrals for the nitrile and the amine are not significantly different, but the ionization potential of an amine is significantly lower than that of a nitrile. These facts explain the 0.3-Å longer hydrogen-bond length for the nitrile (compared with the amine) calculated previously. Such a difference in bond lengths, in turn, gives rise to differences in the electrostatic energies closely corresponding to the observed differences in ΔH0's.
Electronic States of Benzene by Photoselection. The Polarization of Luminescence in Benzene, Perdeuterobenzene, and Perchlorobenzene
Authors: Russell P. G. , Albrecht A. C.
Published: January 2005

The polarization of fluorescence and phosphorescence of benzene (φH), perdeuterobenzene (PDB), and perchlorobenzene (PCB) (phosphorescence only) excited in rigid solutions at 77°K is studied in detail. Excitation is achieved in the first absorption band of each molecule using polarized 2537-Å mercury radiation. The absorption bands and all emission bands (except the phosphorescence of PCB) are highly structured and of a forbidden type of electronic transition. The unstructured phosphorescence of PCB is also interpreted as an electronically (as well as spin) forbidden transition. The polarization of emission is found to be significantly constant over the entire band of each emission after sufficient experimental control is achieved. Precautions against depolarization effects due to concentration depolarization and rotational relaxation are taken. Both effects are found under extreme conditions. The polarization data are converted to intrinsic molecular transition moments. The fluorescences agree with the 100% in-plane transition required of a 1B2u assignment in D6h symmetry. The fractional transition moments of the phosphorescences are mixed with the out-of-plane component dominant but less so in the order PDB, φH, PCB. The wavelength-independent but mixed polarization is at first contradictory, but in fact is due to the fineness of the zero-field splitting of the triplet components. These data have already been used to demonstrate that the triplet state achieves suitable singlet character by vibronic coupling in the triplet manifold to triplet states which spin-orbit couple to dipole allowed singlet states. Although the lifetime of the phosphorescence of PCB is shortened by more than 2500-fold, the polarization properties are significantly little changed. The heavy atom effect does not appear to disrupt the mechanism for mixing singlet into triplet proposed for φH. This raises interesting questions regarding the importance of σσ* states and the one- and two-electron components of the spin—orbit coupling operator. The triplet-state assignment is 3B1u (D6h) for φH and PDB and 3A2u (D3d) for PCB.
Study of Two-Center Integrals Useful in Calculations on Molecular Structure. V. General Methods for Diatomic Integrals Applicable to Digital Computers
Authors: Wahl Arnold C. , Cade Paul E. , Roothaan C. C. J.
Published: January 2005

The calculation of the electronic structure of atomic and molecular systems involves the determination of a number of integrals over the electronic coordinates. These calculations are feasible only by the use of high-speed, large-memory digital computers.

This discussion is based on a culmination of experience obtained in this laboratory with regard to methods useful in the evaluation of two-center integrals by means of digital computers. The ground work for this paper, in terms of the analysis employed, is given in a series of papers by Roothaan, Ruedenberg, and Jaunzemis, but significant changes have evolved which offer considerable improvements and more economical calculations. The analysis presented here is especially the result of efforts to take full advantage of the capabilities of present digital computers. The methods advocated here are thought to be near optimal to a completely reliable and automatic computation of the electronic integrals in question with the desired accuracy. A not insignificant aspect of the methods given here is that an approach was sought which is unfailingly reliable and accurate regardless of the AO's involved in the integrals and at the same time as economical as possible.
Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment
Authors: Marcus R. A.
Published: January 2005

In its usual form activated complex theory assumes a quasiequilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced. The new equation for the transmission coefficient contains internal centrifugal terms. The fourth assumption can also be weakened and a rotational interaction included in the formalism. In applications of the rate equation use can be made of the recent finding that in the immediate vicinity of a saddle point or a minimum, a potential energy surface can be imitated in some major topographical respects by a surface permitting separation of variables. The separated wave equation for the reaction coordinate is then curvilinear because of the usual curvature of the path of steepest ascent to the saddle point. Calculations of transmission coefficients and rates can be made and compared with those obtainable from the usual one-dimensional Cartesian-like calculations on the one hand and with some based on the numerical integration of the n-dimensional Schrödinger equation on the other. An application to a common three-center problem is discussed.
Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment
Authors: Marcus R. A.
Published: January 2005

In its usual classical form, activated-complex theory assumes a particular expression for the kinetic energy of the reacting system, one being associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic-energy expression. A rate equation of the customary form is obtained: krate=(kT/h)exp[−(F‡−Fr)/kT], where F‡ is the free energy of a system constrained to exist on a hypersurface in n-dimensional space and Fr is the free energy of the reactants. The usual derivation is then reinterpreted, in terms of geodesic normal coordinates, to be somewhat more general than it appears.

Normally, rotation—vibration interaction is neglected, as in the above derivation, although not in treatments of some special reactions in the literature for which the centrifugal potential is important. A derivation is given which includes the influence of this centrifugal potential but which omits Coriolis effects.
Density Matrix Description of Coupled Spin Systems in the Presence of Two Strong Oscillatory Fields
Authors: Barfield Michael , Baldeschwieler John D.
Published: January 2005

A density matrix description of coupled spin systems in the presence of two strong rf fields is given following a relaxation matrix formalism. The irradiating rf field, H2, has significant effects on the population distribution in a spin system even though the frequency of H2 is not close to a resonance frequency of the system. Signal frequencies and intensities calculated in the limit of large amplitudes of the observing field H1 with ω2 off resonance and ω1 saturating only a single line are compared with experimental proton—fluorine field-sweep nuclear magnetic double resonance spectra of CHFCl2 and CH2F2. Apart from relaxation effects, the most important factor affecting the saturated intensities is the mixing of the pure states by H2.
Far-Infrared Spectra of Cyanuric Acid, Uracil, and Diketopiperazine
Authors: Shimanouchi Takehiko , Harada Issei
Published: January 2005

The far-infrared spectra of cyanuric acid, uracil, and diketopiperazine were measured in the region from 300 to 90 cm—1. The GF matrix method was applied to the analysis of lattice vibrations. The translational lattice vibrations were assigned to some of the observed bands. The force constants of hydrogen bonds were obtained.
Kerr Effect in Flexible Polymers
Authors: Dows David A.
Published: January 2005

A theory of the Kerr effect in flexible polymers is presented, which relates the electro-optical birefringence to details of the polymer structure. Previous interpretations of the data are criticized. It is shown in particular that the Kerr effect should be quite sensitive to rotational hindering in the polymer molecule. The theory is applied to several model polymers and order-of-magnitude agreement with data for polyvinyl halides is obtained.
Relaxation of a Lorentz Gas with a Repulsive r—s Force Law
Authors: Oser Hansjörg , Shuler Kurt E. , Weiss George H.
Published: January 2005

The relaxation of a Lorentz gas (dilute light particle subsystem in a heavy particle heat bath) has been studied for a repulsive r—s central force law interaction between the light and heavy particles. The Fokker—Planck equation for the velocity distribution functions of the light particle subsystem has been solved numerically for s=5, 9, 13, 21, and ∞ for various initial conditions. The dependence of the rate of relaxation and of the form of the time-dependent velocity distribution function on the force law parameter s is discussed in light of the above results.
Effect of Pressure on the Viscosity and Dielectric Relaxation Time in Glycerol
Authors: McDuffie G. E. , Kelly M. V.
Published: January 2005

Dielectric relaxation and viscosity data are presented for glycerol as a function of pressure and temperature. Viscosity data are given over a temperature range +10°C to —10°C and over a pressure range of atmospheric to 4000 kg/cm2. Dielectric data are given at —6.7°C over the same pressure range. The form of the pressure dependence of the dielectric relaxation time appears to be Arrhenius and that of the viscosity is approximately Arrhenius. However, the pressure dependences of the dielectric time and the viscosity are significantly different, the ratio of ηs to τD varying by approximately two over the pressure range studied. The pressure dependence of ηs and τD were examined according to both the free volume theory of Williams, Landel, and Ferry (WLF) and the hole theory of Eyring. Both theories fail to give the proper pressure dependence of the data. When the WLF theory is applied to the data, the resulting form of the pressure dependence of ηs is incorrect. Although the hole theory of Eyring predicts the correct form of the pressure dependence, a strongly temperature-dependent hole volume, with a negative temperature coefficient of expansion, is needed to fit the experimental data.
Many-Electron Theory of Atoms and Molecules. IV. Be Atom and Its Ions
Authors: Tuan D. F. , Si̇nanoğlu O.
Published: January 2005

The many-electron theory is used and the correlation energy of Be is obtained as —2.567 eV, 99.87% of the experimental value. The theory gives each of the pair correlations as a separate minimum. The intershell correlations of 1s22s Li-like and 1s22s2 Be-like ions are given for 3≤Z≤12 using the ``pair-aufbau'' theory. The environmental effects of additional electrons on the correlation energy of a given subshell are obtained explicitly. The correlation energy ε(1s2) is reduced by 4.5×10—2 eV in going from Be2+ ion to the 1s2 core of Be+ and by 4.7×10—2 eV from Be2+ to Be core. The corresponding changes in the 1s2 parts of the Hartree—Fock energies are 5.7×10—4 eV and 17.5×10—4 eV. In this way the errors involved in the ``neglect of inner shells'' in calculating chemical or spectroscopic properties from outer electrons alone can be examined in detail.
Many-Electron Theory of Atoms and Molecules. V. First-Row Atoms and Their Ions
Authors: McKoy V. , Si̇nanoğlu O.
Published: January 2005

The correlation energies of the 1s22s2 inner cores of the first-row atoms B, C, ···, Ne are found to be very different from those of the corresponding four-electron Be-like ions, B+ to Ne6+, due to the exclusion effects of the outer 2p electrons. Whereas the 2s2 correlation, ε(2s2), in the 1s22s2 ions increases from —1.13 eV in Be to —3.2 eV in Ne6+, the 2s2 correlation in the neutral atoms decreases from —1.13 eV in Be to —0.27 eV in Ne. The many-electron theory was used for the nonempirical 2s2 calculations and included the use of the r12 coordinate. With these theoretical ε(2s2) values the correlation of a 2p electron with the 1s22s2 inner core is found to be large, ∼—1 eV. Also the 2p2 correlation comes out about —1 eV. The results show that core energies will, in general, depend strongly on the state and number of the outer-shell electrons and that intershell correlation interactions may be appreciable. Implications for π-electron systems and the ligand-field theory of inorganic complexes are discussed.
Scattering of High-Velocity Neutral Particles. XIII. Ar–CH4; A Test of the Peripheral-Force Approximation
Authors: Mason E. A. , Amdur I.
Published: January 2005

Collision cross sections have been measured for argon atoms with energies between 700 and 2100 eV, scattered in room-temperature methane. The results have been analyzed to obtain the average potential between an argon atom and a methane molecule, 〈V(r)〉Av=936/r7.85eV,  2.31 Å≤r≤2.66 Å.This result has been used as a test of combination-rule approximations by comparing it with the average potential calculated from previous measurements on He–CH4, He–He, and Ar–Ar. The peripheral-force approximation gives consistent relations among the experimental results for these systems.
Amino Wagging and Inversion in Methylamines
Authors: Tsuboi Masamichi , Hirakawa Akiko Y. , Ino Takamitsu , Sasaki Tadahiro , Tamagake Keietsu
Published: January 2005

Fine structures have been observed of the amino-wagging bands at 780 cm—1 of CH314NH2, at 776 cm—1 of CH315NH2, at 625 cm—1 of CH314ND2, and at 689 cm—1 of CH314NHD. For each vibration—rotation line an appreciable inversion splitting is observed. There is a marked coupling found between the inversion and the internal rotation; and the amount of the inversion splitting of each absorption line depends greatly upon the internal rotation quantum number σ (=0, +1, or —1) and the over-all rotation quantum number K of the state in question. A hypothetical inversion splitting when the coupling were absent is estimated to be 31.6 cm—1 for the first excited state of the amino-wagging vibration of CH314NH2.
Role of Electrostatic Energy Barriers in the Expansion of Lamellar Crystals
Authors: Hurst C. A. , Jordine E. St. A.
Published: January 2005

The method of Fourier transforms has been used in the investigation of the electrical forces between the platelets of the montmorillonite crystal. The potential-energy curve, as a function of the distance 2D between the platelets, is shown to have two turning points. The one with the smaller value of D is a minimum and is therefore a point of stable equilibrium, while the one with the larger value of D is a maximum and is a point of unstable equilibrium. For small separations of the platelets the potential energy is positive and increases with decreasing separation, while at large separations the potential energy is negative and decreases linearly with increasing separation. The foregoing is shown to be in complete accord with accumulated experimental findings over the years. Physically, the basis of the shape of the energy curve is that at small separations the repulsive ion—solvent and ion-image forces prevail whereas at intermediate distances the attractive surface-ion terms become important; finally the surface—surface terms dominate at larger distances.

It is also shown that by suitable expansions the Fourier transform method can be used to generate the required sets of electrostatic images developed in an earlier work by the optical analog.
Vibrational Spectra and Molecular Structure of Bicyclo[1.1.0]butane
Authors: Haller Ivan , Srinivasan R.
Published: January 2005

The infrared and Raman spectra of bicyclo[1.1.0]butane and the infrared spectrum of its deuterated analogue were observed. The rotational structure of some infrared bands were partially resolved. If the numerical values occurring in cyclopropane and its derivatives are adopted for the related structural parameters of bicyclobutane, the spectrum is found consistent with a C2v structure with an angle between the planes of the rings of 126°±3° and a bridgehead C–C distance of 1.54±0.02 Å. A complete assignment of the fundamental vibrational frequencies of the light isotope is given.
Theory of Heats of Mixing of Certain Charge-Unsymmetrical Fused Salts
Authors: Davis H. Ted
Published: January 2005

A theory is presented for the thermodynamic mixing properties of certain charge-unsymmetrical fused salt mixtures of the type (P+—Qz+)X—. The analysis is based upon the work of Reiss, Katz, and Kleppa who showed that for charge-symmetrical molten-salt mixtures many of the thermodynamic properties of mixing could be understood in terms of a model ionic melt consisting of rigid impenetrable ions interacting with a Coulomb potential. The predicted form of the heat of mixing agrees with the experimental data of Kleppa et al. on the alkali-nitrate—alkaline-earth nitrate mixtures.
X-Ray Diffraction Measurements of Silver during Slow Heating to the Melting Point
Authors: Beaman D. R. , Balluffi R. W. , Simmons R. O.
Published: January 2005

Measurements of the x-ray lattice parameter, the Bragg diffraction peak intensity, and the diffraction peak width were made during the very slow quasiequilibrium heating of high purity silver (99.999+% pure) to the point where melting was observed. Back-reflection measurements were made using a 〈;422〉 reflection from a small homogeneously heated single crystal region under conditions allowing continuous visual observation of the x-rayed region. A specially developed technique allowed several thousand meassurements to be made in a temperature interval starting about 4°C below the onset of melting. Normal lattice expansion (to within ±Δa/a=3.8×10—6) was observed to within at least a few thousandths of a degree (°C) of the temperature at which melting was first clearly detected visually. The half-width of the Bragg peak remained constant over this range. A 50% decrease in intensity, however, was observed starting about 0.08°C below the point at which melting was first observed. This result was attributed to the gradual onset of two-phase alloy melting which was not immediately detected visually. This was consistent with chemical analysis which revealed the presence of sufficient impurities (mainly ∼1 ppm oxygen) to have produced a two-phase melting range between solidus and liquidus of the order of a tenth of a degree (°C). It was generally concluded that there was no evidence from the x-ray measurements of any anomalous lattice behavior (premelting phenomena) in silver at temperatures as close to the solidus absolute temperature as a few parts per million (or possibly less). This was consistent with the expected first-order nature of the transition.
Chemical Shifts and Pi-Electron Densities in Substituted Benzenes
Authors: Wu T. K. , Dailey B. P.
Published: January 2005

The theoretical values of the proton, carbon, and fluorine chemical shifts of the substituted benzenes with a variety of substituents have been calculated and compared with the experimentally observed chemical shifts. It is found that the para shieldings, as assumed, are primarily determined by the pi-electron density variations induced by the substituents. However, at ortho and meta positions, factors other than pi-electron densities become important in contributing to the observed shieldings. In disubstituted benzenes, it appears that the proposed additivity relationship of the substituent effects may be a combined effect of at least two separate additive mechanisms, one of which is from the pi-electron variation; both, however, contribute to the shieldings to an approximately equal extent.
Spin—Orbit Coupling Constant of Nitric Oxide. Determination from Fundamental and Satellite Band Origins
Authors: James Thomas C. , Thibault Robert J.
Published: January 2005

Precise measurements of the band origins of the 2Π½—2Π½ and ∏212−∏212 subbands of the fundamental of nitric oxide and of the band origin of the 1–0 ∏212−∏212 satellite band provides accurate values for the spin—orbit coupling constants A0 and A1 for the v=0 and v=1 vibrational levels. The values obtained are A0=123.160 cm—1 and A1=122.911 cm—1. When these results are combined with the results of Olman, McNelis, and Hause, precise values of A2 and A3 are also obtained. They are A2=122.658 cm—1 and A3=122.360 cm—1. Causes for the discrepancy in A values calculated from other investigators' results are discussed. Certain discrepancies in rotational constants obtained from this and other infrared studies are pointed out and briefly discussed.
Quartic Oscillator as a Basis for Energy Level Calculations of Some Anharmonic Oscillators
Authors: Chan Sunney I. , Stelman David , Thompson Larry E.
Published: January 2005

A variational treatment facilitating accurate energy level calculations for the mixed harmonic—quartic oscillator within the frameworks of both the harmonic oscillator and the quartic oscillator representations is formulated. The usefulness of the quartic oscillator as a basis for such calculations is examined in detail. It is shown that the quartic oscillator representation yields significantly better energies than the conventional harmonic oscillator representation even for moderate quartic anharmonicities. The first 10 energy levels, expectation values of x2, x4, and some transition moments are presented over the range of anharmonicities from the pure harmonic oscillator to the pure quartic oscillator.
On the Excited Electronic States of Isotactic Polystyrene and Polyvinylnaphthalene
Authors: Vala Martin T. , Silbey Robert , Rice Stuart A. , Jortner Joshua
Published: January 2005

A detailed theoretical analysis of the band structure and Davydov splittings in the p and β bands of isotactic polystyrene and polyvinylnaphthalene has been undertaken. It is shown that singlet band splittings are large and have different symmetry characteristics from those of crystalline benzene and naphthalene. The triplet bandwidths are, however, very small. The rate of triplet—triplet annihilation is shown to be considerably less than that characteristic of a monomeric aromatic crystal such as anthracene or naphthalene and therefore phosphorescence from the pure polymer is a distinct possibility. The role of aperiodic potentials on the bandwidths is briefly discussed.
Appearance Potentials of the Fragment Ions from CF3I
Authors: Dorman F. H.
Published: January 2005

The ionization-efficiency curves for the parent and fragment ions from CF3I have been examined using Morrison's second differential method. Accurate appearance potentials can be obtained only for some ions, i.e., CF3I+=10.5±0.1 eV, CF3+=11.5±0.1 eV, and I+=13.4±0.1 eV, but not for the ions CF2I+, CF2+, and CF+ by this or any other method.

The kinetic energy of the fragment ions near their threshold has been determined using a retardation method.
Inelastic Molecular Collisions with a Lennard-Jones (12–6) Interaction Energy
Authors: Shin Hyung Kyu
Published: January 2005

Vibrational energy transfer is discussed for a Lennard-Jones intermolecular interaction energy by use of the WKB semiclassical wavefunctions, from the point of view of the effect of an attractive term in the interaction energy. The effect is found to be very important in controlling the over-all magnitude of the de-excitation probability per unit time. An expression for fitting a Lennard-Jones potential to an exponential potential is derived by comparing the leading terms in the exponent of the perturbation integral.
On Spin Relaxation
Authors: Fulton Robert L.
Published: January 2005

A rigorous formulation of spin relaxation which allows physical insight into the nature of the relaxation process, allows higher-order approximations than hitherto made to be easily formulated and which gives a starting point for a discussion of long correlation times is given. Two approximations are considered in turn, both based on the shortness of the correlation time for the heat bath. One is shown to lead to the usual density matrix formulation, the other to the method of Argyres and Kelley. The explicit solutions of the resulting equations are found in the case of a constant magnetic field plus a perpendicular rotating field when the heat bath displays two-dimensional rotational symmetry. The differences between the two approximations are noted, giving a limit on the validity of both. The effect of initial correlation between the heat bath and spin is incorporated into the theory.
Integral Hellmann—Feynman Theorem
Authors: Kim Ho Jing , Parr Robert G.
Published: January 2005

In the Born—Oppenheimer approximation, it is shown that for any molecular isoelectronic process the total energy change, excluding nuclear kinetic energy, is given by the formula ΔW=ΔVnn+ ∫ ρ(1)H′(1)dτ(1).Here ΔVnn is the nuclear—nuclear repulsion-energy change, and H′ is the change in the one-electron nuclear—electron attraction operator. The function ρ(1) is the normalized transition density for the change, the integral over Electrons 2 through N of the product of the initial and final electronic wavefunctions, multiplied by N and divided by the overlap integral between the initial and final wavefunctions. For infinitesimal changes, it is demonstrated that this theorem reduces to the conventional Hellmann—Feynman theorem.

A corresponding differential equation and its equivalent variational principle are derived. Use of approximate wavefunctions in the several formulas is discussed, and various possible applications of the theorem are indicated. The theorem is shown to provide a rigorous basis for a pseudoclassical theory of molecular vibrations, and shown to indicate why electron-correlation effects ordinarily do not control molecular deformation.
Stress-Induced Migration and Partial Molar Volume of Sodium Ions in Glass
Authors: Weber Neill , Goldstein Martin
Published: January 2005

The partial free energy Ḡi of a chemical species is altered by pressure according to the relation dḠi=V̄idP, where Vi is the partial molar volume. In a glass sheet under a bending stress, there is a gradient of hydrostatic pressure (as well as shear) through the sheet, tending to drive the mobile Na ions from regions of compression to regions of tension, and equilibrium will be reached when the space-charge buildup balances the driving force of the pressure gradient. The initial current prior to space-charge limitation was measured in a soda-lime—silica glass sheet, and the partial volume of the Na ion in this glass calculated to be 2.2 Å3. This figure is surprisingly high, about ⅗ of the cation volume. A naive calculation attributing the volume change to electrostrictive effects gives reasonable agreement with this result, but further experiments are needed to test this explanation.
Normal Vibrations of the Polymer Molecules of Helical Conformation. IV. Polyethylene Oxide and Polyethylene-d4 Oxide
Authors: Yoshihara Toshio , Tadokoro Hiroyuki , Murahashi Shunsuke
Published: January 2005

Polarized infrared spectra of polyethylene oxide (PEO), —(CH2CH2O)n— and PEO-d4, —(CD2CD2O)n—, have been measured in the region from 4000 to 80 cm—1. The spectra of PEO at various temperatures (about —130°, 20°, 65°, and 80°C) were also observed, and splittings of some perpendicular bands were found at the low temperature. The selection rules for the PEO molecule are derived under the factor group D(4π/7). The normal vibrations of PEO and PEO-d4 are calculated for the Raman-active A1 symmetry species, the infrared-active A2 species, and the Raman- and infrared-active E1 species, by use of the GF matrix method with the Urey—Bradley force field taking into account the torsional displacement coordinates of the skeleton. The results show fairly good agreement between the observed and calculated frequencies, and give strong support to the 72 helix conformation proposed by the authors previously. The assignments of the bands are given and discussed.
Nuclear Relaxation in Coupled Spin Systems
Authors: Noggle Joseph H.
Published: January 2005

The density-matrix theory of relaxation for coupled spin systems in the liquid state is reviewed and equations are derived for the calculation of nuclear Overhauser effects and free decay. The theory is applied to the results of saturation-recovery experiments on 2,3-dibromothiophene (CS2 solution). The equations derived and the experimental method are in principle applicable for coupled spin systems with any number of spins. The saturation-recovery experiment proved capable of separating the contributions of internal and external dipole interactions to the relaxation of the protons in 2,3-dibromothiophene. The rotational correlation time for internal dipole—dipole relaxation was measured to be τc=(2.2±0.2)×10−12 sec.

The theory of correlations among the interactions of two (or more) spins with external spins is discussed. The external interactions of the two protons on 2,3-dibromothiophene were found to be 75% correlated.
Electron Spin Resonance Studies of γ- and X-Ray-Irradiated Zeolites
Authors: Kasai Paul H.
Published: January 2005

Electron spin resonance studies have revealed the formation of superoxide ions O2− attached to the zeolitic cations when the Type Y zeolites (Linde's) are irradiated by γ and x rays in the presence of oxygen. A second unique color center was found when Na–Y zeolite was irradiated in vacuum. This center is attributed to an electron trapped within a large cavity shared among four Na+ ions.
Excited Electronic States of Crystalline Benzene
Authors: Silbey Robert , Rice Stuart A. , Jortner Joshua
Published: January 2005

In the present paper, the excited electronic states of crystalline benzene are examined with the use of exciton theory. Ion-pair exciton states are considered and it is shown that these may play a considerable role in determining the observed spectra. Their effect on the lowest triplet state is also considered. The results of the analysis are in agreement with the available experimental data and are also consistent with the analysis of the spectrum of crystalline naphthalene.
Effect of Environment on the Unimolecular Decay of the Triplet State
Authors: Ladner S. Jules , Becker Ralph S.
Published: January 2005

Lifetimes and relative quantum yields of phosphorescence were measured over the temperature range −10° to −196°C for solutions of palladium (II) mesoporphyrin IX, dimethyl ester, and ρ-phenylbenzophenone in methylphthalylethylglycolate. The observed variation in the rate constants for the unimolecular decay of the triplet state coupled with the changes in the relative quantum yields of phosphorescence provide conclusive evidence in favor of a viscosity influence on the unimolecular decay processes. Employing values of the activation energy for internal degradation of the triplet state in the range of those reported in the literature, and other information, the total rate constants are divided into the individual ones. The changes in the individual rate constants for the radiative and nonradiative processes are presented and discussed. In the cases studied, the probability of internal degradation from the triplet state decreases with increasing viscosity. However, the probability for the radiative process decreases for palladium porphyrin but increases for ρ-phenylbenzophenone with increasing viscosity.
Investigation of Triplet-State Energy Transfer and Triplet—Triplet Annihilation in Organic Single Crystals by Magnetic Resonance and Emission Spectra: Diphenyl Host
Authors: Hirota Noboru
Published: January 2005

Temperature and concentration dependence of the decays of the paramagnetic resonance signals from various guest molecules in their triplet states were studied extensively in diphenyl and diphenyl-d10 host. Temperature-dependent and -independent delayed fluorescence spectra of the various guest molecules and their lifetimes were also studied. The observations are discussed in terms of three types of triplet-state energy transfer and triplet—triplet annihilation. The rates of transfer and activation energies were determined for the temperature-dependent part of the triplet-state energy transfer. The rates are discussed in connection with the triplet exciton interaction in single diphenyl crystals.
Charge-Transfer Exciton State and Energy Levels in Tetracene Crystal
Authors: Pope Martin , Burgos José , Giachino Joseph
Published: January 2005

An experimental study of the double-quantum external photoelectric effect in tetracene reveals evidence of an exciton state of energy 2.9 eV different from the normal exciton. This mobile, bulk-generated state is considered to be a charge-transfer (CT) exciton and is most efficiently produced at an energy ≥Ec=3.7 eV. We associate Ec with the lower edge of a relatively broad upper conductivity band. Presumably, there are other conducting states Ec′ such that ECT<Ec′<Ec. The calculated value for the polarization energy of the free electron in the crystal, Pe=Ic—Ec=1.6 eV, where Ic is the threshold energy for external electron emission. This is the same as the polarization energy of the positive hole Ph=Ig—Ic, where Ig is the ionization energy of the tetracene molecule. The electron affinity of the isolated molecule must be less than 0.8 eV. The diffusion length of the charge-transfer exciton is less than 5000 Å.
Molecular Orbital Theory for Octahedral and Tetrahedral Metal Complexes
Authors: Basch Harold , Viste Arlen , Gray Harry B.
Published: January 2005

Self-consistent charge and configuration (SCCC) molecular orbital calculations are reported for 32 selected octahedral and tetrahedral first-row transition-metal complexes containing halide and chalcogenide ligands. It is found that for the range of metal oxidation states II through IV, Fσ, chosen to fit the experimental Δ, is a function of only the metal atomic number for constant Fπ. In the range of formal metal oxidation numbers V through VII, Fσ is also a function of oxidation number.

Calculated and observed trends in covalency, Δ values, and first L→M charge-transfer energies are compared. The conclusion is drawn that the molecular orbital method, in its present formulation, gives a reasonable account of the ground states and low excited states in simple metal complexes.
Diatomic Forces and Force Constants. I. Errors in the Hellmann—Feynman Method
Authors: Benston Margaret Lowe , Kirtman Bernard
Published: January 2005

Diatomic forces and force constants can be calculated from the Hellmann—Feynman (H—F) theorem and its derivatives but this theorem omits terms which do not vanish, in general, unless the wavefunction is exact. Using common approximate valence bond and molecular orbital wavefunctions for H2, of both the scaled and unscaled type, we have evaluated the terms which are omitted in this manner. In each case the total theoretical force and the force constants were determined as well. We note that the H—F theorem, when used with approximate wavefunctions, can assume a variety of inequivalent forms depending upon the set of electronic coordinates held constant during differentiation. Two such forms are studied in detail, namely the virial and electrostatic theorems. Various equivalent expressions for the quadratic and cubic force constants (k2 and k3) are developed by taking the first two derivatives of these theorems. Some of our expressions are new and one, in particular, has immediate computational advantages. A new approximation for k3 is tested and the implications of our study for the perturbation treatment of force constants is noted.