bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Effects on Core-Electron Binding Energies in Iodine and Europium
Authors: Fadley C. S. , Hagstrom S. B. M. , Klein M. P. , Shirley D. A.
Published: February 2004

A theoretical and experimental study was made of the shift in atomic core-electron binding energies caused by the chemical environment. Two models are presented to account for these “chemical shifts.” The first uses an energy cycle to break the core-electron binding energies into a free-ion contribution and a classical Madelung energy contribution. The Madelung energy contributes a significant part of the binding-energy shift. It can, in principle, be evaluated rigorously although there is some ambiguity as to a surface correction. The reference level for binding energies must also be considered in comparing theory with experiment (or in comparing experimental shifts with one another). Electronic relaxation could also introduce errors of ∼1 eV in shift measurements. The second, more approximate, model consists of a “charged-shell” approximation for bonding electrons in atomic complexes. It gives semiquantitative estimates of shifts and demonstrates the relationship between bond polarity and core-electron binding energy shifts. These models indicate that several features of the free-ion state will be reflected also in chemical shifts. Free-ion Hartree–Fock calculations were made on F, Cl, Br, I, and Eu in several oxidation states. These indicate that the removal of a valence electron shifts the binding energies of all core levels by nearly equal amounts (10–20 eV). This shift decreases with increasing atomic number in a given chemical family. The removal of an inner “valence” electron (e.g., 4f in europium) gives rise to relatively large shifts (∼20 eV). These features were also found in the experimental chemical shifts. Chemical shifts were measured for iodine in KI, KIO3, and KIO4 and for europium in EuAl2 and Eu2O3, using the technique of photoelectron spectroscopy. Binding energies in iodine were found to increase by ∼0.8 eV per unit increase in oxidation number. A Madelung energy calculation indicates that this corresponds to a loss of ∼0.5 electronic charges from the valence shell per unit increase in oxidation state, and this value agrees approximately with previous results obtained from Mössbauer measurements. A shift of 10 eV was found between Eu2 + and Eu3 +. This very large shift is due largely to the loss of a full 4f electron in this change of oxidation state. With some refinements, the above technique could produce very useful information about bonding in ionic solids, in particular, allowing the determination of the charge on each atom. Their application to such problems as a determination of the oxidation states of metals in biological molecules seems even more promising.
Dynamic Viscoelastic Properties of Dilute Polyisobutylene Solutions
Authors: Sakanishi Akio
Published: February 2004

In order to examine the Rouse and the Zimm theories, measurements have been made on complex rigidity G* of very dilute solutions of polyisobutylene (Mυ = 1.76 × 106) by means of the torsional crystal method at high frequencies. The complex intrinsic rigidity, [G*] =  lim c→0 (G* − iωηs) / c, and the limiting relaxation time, (τp)0 =  lim c→0 Kp(η − ηs)M / cRT, have been obtained by extrapolation to zero concentration, where Kp is the pth relaxation time factor determined on the basis of the above theories. In benzene at the theta temperature, curves based upon the Zimm theory excellently represent the experimental plots of log[G*]M / RT vs logωηs[η]M / RT, in which (τ1)0 = 2.54 × 10− 5sec (nondraining). In cyclohexane at 15.0° and 30.0°C, the results are intermediate between the Rouse and the Zimm theories (partial draining). The draining effect seems to correlate with the excluded volume effect.
Interpretation of Mesophase Transitions
Authors: Torgalkar Anil , Porter Roger S. , Barrall Edward M. , Johnson Julian F.
Published: February 2004

New data have provided a means for quantitatively testing the statistical theory of Frenkel for explaining the pretransitional effects adjacent to first-order transitions in mesophase systems. This theory has been frequently suggested as a qualitative explanation for pretransitional changes in physical properties that occur within 10°C of mesophase–isotropic transitions. The one previous quantitative test used compressibility and volume expansion data on p-azoxyanisole, which forms a single mesophase of the nematic type. It was concluded that the Frankel theory was of limited applicability; that (a) the equations did not apply closely, within about l°C of the transition, and (b) did not apply to pretransition effects below the transition. Calculations made here using new data on p-azoxyanisole show, in contrast, that the Frenkel theory (a) applies well near the nematic–isotropic transition, (b) the theory may be applied equally well on both sides of the transition, (c) that asymmetrical pretransitional effects are accurately treated, and (d) in contrast to an earlier result, specific-heat anomalies near the transition are accurately predicted and differ by a factor of 2 from previous estimates.
Helical Parameters of a Macromolecule
Authors: Damiani A. , DeSantis P.
Published: February 2004

Relations between internal coordinates (bond angles, bond lengths, and rotation angles) and helical parameters of a linear macromolecule are reported. The formulas, completely valid in all cases, are derived on the basis of the eigenvalue–eigenvectors solutions of the Eyring-transformation matrix. The set of cylindrical coordinates of a right-handed α helix is reported as an example.
Sublimation Energy of Benzene
Authors: Sen Purnendranath , Basu Sadhan
Published: February 2004

Using a free-electron model for the π-electron system in benzene the electronic quadrupole moment has been calculated to be 26.29 × 10−26 esu which is in fair agreement with the experimental value of 34.86 × 10−26 esu. Considering the molecular interaction to be quadrupolar in origin for benzene crystal the sublimation energy was calculated to be 10.64 kcal/mole which is in good agreement with the experimental value of 10.67 kcal/mole.
Kinetics of Ionic Processes in the Radiolysis of Liquids. IV. Geminate Recombination of Ions
Authors: Williams Ffrancon
Published: February 2004

An estimate is made of the dispersion in the recombination time for ions undergoing diffusive recombination from an initial separation distance r. Then, an elementary method is used to obtain the least distance of ionic approach for which the Nernst–Einstein relation describes the motion of the ions. The inclusion of these considerations does not seriously affect the dependence of recombination time on r3 for r values between 40 and 120 Å in liquids of low dielectric constant (ε ≈ 2) at 300°K.
Equilibrium Distribution of Droplets in the Theory of Nucleation
Authors: Lin J.
Published: February 2004

The equilibrium distribution of droplets in the theory of irreversible nucleation is derived by the method of grand canonical ensembles. It is found that if the free energy of the liquid drops is assigned a classical value in terms of the macroscopic surface tension, the distributions obtained are identical with the theory of Reiss and Katz.
l-Averaged Exchange Term in the Hartree-Fock Equations
Authors: Garrett W. R. , Mullins L. D.
Published: February 2004

A possible improvement of Slater's simplification of the Hartree–Fock equations was suggested by Harman, Callaway, and Acton wherein an averaged exchange potential was defined for each set of states having a common orbital angular momentum. In the present paper, such an averaging is performed on the Hartree–Fock equations, and the resulting equations are solved self-consistently. Comparisons are made between results obtained from the l-averaged exchange approximation, Slater's average, the free-electron exchange approximation, and the complete Hartree–Fock method. With very little increase in computational difficulty, the l-averaged exchange approximation yields results which are an improvement over Slater's average or the free-electron exchange approximation.
Light Scattering from Multicomponent Fluids
Authors: Blum L.
Published: February 2004

The spectrum of the light scattered by a multicomponent fluid is discussed using the thermodynamic approach originally suggested by Landau and Placzek. The structure of the central Rayleigh line is discussed for two particular cases; the infinitely dilute solution of rigid polymers and a binary mixture.
Impurity Effects in Ice
Authors: Seidensticker R. G. , Longini R. L.
Published: February 2004

The electrical effects of fluorine and nitrogen substituting for oxygen in ice may be described in terms of energy levels characteristic of various proton configurations. Hydrogen fluoride and ammonia are considered as protonic donors and acceptors in ice, analogous to electronic donors and acceptors in semiconductors. The appropriate configuration states are devised and the statistics of the proton population are derived. Interfacial states are included in the model and their interaction with the bulk population is considered qualitatively. Some parameters of the model are evaluated from published data.
Spin Delocalization and Vibrational–Electronic Interaction in the Toluene Ion–Radicals
Authors: Purins D. , Karplus M.
Published: February 2004

An analysis is made of the spin distribution and hyperfine splittings of the toluene anion and cation radicals. Considered are the importance and magnitude of the splitting of the benzene-ion degeneracy by the interaction between the ring and the methyl group, the effects of spin delocalization into the methyl group by different mechanisms, and the consequences of vibrational and thermal coupling of the near-degenerate levels. The spin delocalization mechanism in the toluene ions is shown to be in agreement with a perturbation model for the Ċ–B = A system (here Ċ corresponds to the aromatic ring). The vibronic calculation is based on an ASMO–CI treatment of the electronic energy levels and their variation with bond lengths and angles; an attempt is made to include all significant vibrational contributions. The previously neglected alteration of the neutral-molecule vibrational functions due to the addition or removal of a pi-electron is found to be of particular importance. Although the exact quantitative results are dependent on the electronic parameters, the lowest anion vibronic state consists of about 90% of the antisymmetric and 10% of the symmetric electronic state. Comparison of the calculated and experimental temperature dependence of the anion hyperfine splittings shows that the vibronic treatment gives reasonable results.
Electronic Structures of the Tris(acetylacetonato) Complexes of the Iron-Series Transition-Metal Ions. I. General Theory and Its Application to Simple Complexes
Authors: Hanazaki Ichiro , Hanazaki Fumie , Nagakura Saburo
Published: February 2004

A theoretical treatment of the π-electron structure of metal complexes containing organic unsaturated molecules as ligands is developed and applied to the tris(acetylacetonato) complexes of Al(III), Sc(III), and Co(III) ions. The π-electron structure of each complex is studied by considering the configuration interaction among various kinds of electron configurations obtained by putting π electrons in the 3dπ atomic orbitals of the central metal ion and in the π-molecular orbitals of three ligands which are obtained by the Pariser–Parr–Pople method in such a way as SCF MO's can be obtained under the electrostatic field of the central metal cation. The ground, locally excited, and metal–ligand charge-transfer configurations are taken for all the complexes. The theoretically obtained electronic transition energies and intensities are discussed in detail and are compared with the observed values. The present theoretical method including explicitly the electron interaction gives a satisfactory explanation of the electronic absorption bands observed with the complexes. In particular, the following results seem to be noticeable: (1) the magnitude of splitting of the locally excited band into the A2 and E components of the D3 symmetry can be predicted quantitatively; (2) the moderately strong absorption bands appearing in the visible region for cobalt complex can be assigned to the metal–ligand charge-transfer transition.
Electronic Structures of the Tris(acetylacetonato) Complexes of the Iron-Series Transition-Metal Ions. II. Complexes Containing Paramagnetic Metal Ions
Authors: Hanazaki Ichiro , Hanazaki Fumie , Nagakura Saburo
Published: February 2004

The theoretical method developed in Paper I is extensively applied to the tris(acetylacetonato) complexes containing paramagnetic metal ions such as Cr3+, Fe3+, and Ti3+. The results show that the present theoretical treatment is very useful in explaining the electronic structures and electronic absorption spectra of these complexes. Particularly the following two points may be emphasized: (1) Originally forbidden singlet–triplet π → π* transitions in the ligand are intensified by the mixing of the singlet and triplet states of the ligand through the transfer of the metal unpaired electron to the ligand π-electron system. This fact is shown to be important in explaining the electronic spectra of the Cr(acac)3 and Fe(acac)3 complexes containing paramagnetic metal ions. (2) Ti(acac)3 is shown to be peculiar because of the degeneracy of its ground configurations which is released by the configuration interaction. The band due to the transition between the split ground configurations is predicted to appear in the infrared region. Moreover, the transitions to triplet excited states in the ligand are shown to be intensified through the mixings with the interligand charge-transfer transitions and with some doubly excited transitions.
Detection of Vitrons in Pentachlorobiphenyl at 40 MHz and the High-Frequency Mechanical Properties of Chlorinated Biphenyls
Authors: Moore R. S. , McSkimin H. J. , Gieniewski C. , Andreatch P.
Published: February 2004

Measurements of the in-phase and quadrature components of the dynamic shear impedance were carried out on pentachlorobiphenyl (Aroclor 1254) at 40 MHz from 293° to 318°K using an ultrasonic reflectance technique. The minimum in a plot of the high-frequency limiting shear modulus G∞′ as a function of temperature predicted by Miles and attributed to the formation and breakup of vitrons, i.e., clusters, was not observed. This result is considered in light of other evidence for cluster formation. These measurements were compared with data of other workers at low frequencies for other homologs of the Aroclor series using a modified reduced variables procedure based on G∞′. Excellent superposition was found using this method. Data for the Aroclor series were also compared using a procedure based on the semiempirical equation developed by Lamb as well as in terms of the theories of Peterlin, Reinhold, and Thurston for high-frequency response. From the latter, estimates of h* ≥ 0.3,φ / f = 0, and 30 ≤ Z < 100 were obtained, where h* corresponds to the hydrodynamic interaction per segment, φ / f is the ratio of the internal to segmental friction coefficients, and Z is the number of segments.
Magnetic Resonance Lineshape and Chemical Shift of Molecules in Clathrates
Authors: McTague John P.
Published: February 2004

Proton magnetic resonance spectra of small molecules in hydroquinone clathrate cages have been observed. Despite the fact that diffusion is a very slow process in these systems, lines were sufficiently narrow (< 100 Hz) to observe separate resonances corresponding to chemically shifted protons. The observed line shape, which is not Lorentzian, has been related to anisotropic orientational probability of the enclathrated molecule within the crystalline potential. The degree of alignment found for H2S at room temperature is ∼ 6 × 10−4.
Crystal Structure of the Transition-Metal Molybdates and Tungstates. V. Paramagnetic Alpha-Nh2(MoO4)3
Authors: Jamieson P. B. , Abrahams S. C. , Bernstein J. L.
Published: February 2004

Paramagnetic α-Nd2(MoO4)3, prepared below the transition temperature of 960°C, crystallizes in a subtle variant of the scheelite structure. The lattice constants of the basic tetragonal unit cell are a = 5.298 ± 0.007 and c = 11.705 ± 0.023 Å, with space group I41/a and 43 of a Nd2(MoO4)3 formula per unit cell. The ordered distribution of two Nd atoms over every three available sites results in additional weak scattering corresponding to a monoclinic unit cell with a = 27.02, b = 11.705, and c = 11.85 Å, with β = 105.3°, space group C2. The integrated intensities of 2490 scheelitelike reflections within a reciprocal hemisphere of radius (sinθ) / λ = 1.02 Å−1 were measured with PEXRAD, of which 198 were independent and above background. Refinement of the atomic positions, assuming a statistical distribution of 23 Nd on each scheelite 4b site, resulted in an agreement factor between measured and calculated structure factors of 0.0375. Each Nd atom is dodecahedrally coordinated to eight oxygen atoms, with four Nd–O distances of 2.492 ± 0.010 Å and four others of 2.509 ± 0.011 Å. Each Mo atom occupies a tetrahedron of oxygen atoms, with four identical Mo−O distances of 1.800 ± 0.011 Å. An arrangement of Nd atoms and vacancies in the monoclinic cell giving a predicted scattering pattern in satisfactory agreement with observation is presented.
Matrix Infrared Spectrum and Bonding in the Dibromomethyl Radical
Authors: Carver T. Granville , Andrews Lester
Published: February 2004

Simultaneous condensation of bromoform and lithium atoms at high dilution in argon on a CsI window at 15°K produces new infrared absorptions which are assigned to lithium bromide and the dibromomethyl radical. The identity of dibromomethyl is confirmed by comparison of spectra obtained from HCBr3, DCBr3, and HCBr2Cl precursors reacting with lithium and sodium. These new absorptions are assigned to the antisymmetric H–C–Br bending and C–Br stretching modes and the symmetric C–Br vibration. The antisymmetric vibrational assignments are supported by product-rule and normal-coordinate calculations which give the potential constants F55 = 3.10 ± 0.10 mdyn/Å, F56 = 0.32 ± 0.01 mdyn/rad, and F66 = 0.50 ± 0.05 mdyn·Å/rad2, while the symmetric C–Br mode yields an approximate force constant F22 = 3.7 ± 0.4 mdyn/Å. The C–Br valence force constants for bromomethyl radicals exceed normal C–Br values, while electronic stabilization for these radicals is indicated by bond dissociation energies. Similar results for chloromethyl radicals, in contrast to fluoromethyl radicals, suggest that (p–d)π bonding between the free-radical carbon orbital and the d orbitals on chlorine and bromine might account for the stabilization of chloromethyl and bromomethyl radicals, which cannot occur for fluoromethyl radicals or molecules with completely satisfied valence.
Electrostatic Probe Studies of the Nitrogen Pink Afterglow
Authors: Chen Sin-Li , Goodings J. M.
Published: February 2004

Studies of the short-duration nitrogen pink afterglow (PA) are reported for different electrostatic probe types (spherical and cylindrical) and materials (Pt and Au). Various collision-dominated probe theories were applied to determine the electron density Ne and temperature Te. Experimental radial distribution curves are presented for the parameters kTe, Ie / Ii (electron to ion current ratio), and Ne at various points in the PA. An apparent increase in the ion current caused by emission of electrons from the probe surface was found to correlate with the light emission intensity of the first negative bands of N2+. kTe was found to be about 1 eV upstream of the PA in the dark space, reaching a maximum of nearly 4.5 eV before decreasing again to 1 eV downstream. The maxima in the axial profiles through the PA of Te, the light emission intensity and the ion current coincide, while Ne (in the range 1–5 × 109 cm−3) shows its maximum a few milliseconds later. The effect of impurities on the PA was examined. The role played by electrons in the process of PA formation is discussed.
Laser Raman Spectra of Polymethacrylic Acid
Authors: Tobin Marvin C.
Published: February 2004

Laser-excited Raman spectra are reported for polymethacrylic acid as a solid, an aqueous gel, and a strongly alkaline aqueous gel. The spectrum of the neutral gel is identical with that of the solid, although alkalization produces some changes. The spectra are analyzed in terms of changes in chain configuration. Some of the Raman lines of the aqueous gel are highly polarized. The polarizations are used to make some frequency assignments.
Scattering of 3He, 4He, and the Hydrogenic Molecules from the (111) Plane of Ag
Authors: Palmer Robert L. , Saltsburg Howard , Smith Joe N.
Published: February 2004

Molecular beams of the isotopes of He and H have been reflected from the (111) plane of epitaxially grown Ag crystals. The spatial scattering distributions of 3He and 4He are compared with those of H2, HD, and D2 at various angles of incidence and primary beam temperatures from 80° to 1500°K. Deviations in the specularity of these gases are interpreted in terms of the exchange of rotational state energy of the diatomic species at the surface. Comparisons of number density and flux measurements indicate a significant dependence of the mean speed of the reflected beam on θr. It is proposed that this variation is also enhanced by the degree of rotational state interactions, which decreases with increasing beam temperature. Finally, it is suggested that the appearance of a truly specular component in these scattering distributions is related to an apparent surface roughness through the relation λ > h cosθi, where 0.8 Å < h < 1.7 Å.
Nuclear Spin–Lattice Relaxation in Aqueous Alkali-Metal Chloride Solutions
Authors: Woessner D. E. , Snowden B. S. , Ostroff A. G.
Published: February 2004

The concentration dependence of the viscosity-adjusted deuteron nuclear spin–lattice relaxation rates of solutions of alkali-metal chlorides in deuterium oxide indicates that viscosity is useful in normalizing the relaxation data. This normalization reveals changes in the relationship between the average molecular rotations and the viscosity, suggesting variations in the dynamic structure of the solutions with various ionic species and concentrations. This viscosity adjustment is not sensitive to the small changes which can be revealed by comparing the concentration dependence of the relaxation rates for the solute nuclei to that for the solvent nuclei. This comparison is shown for the LiCl solutions.
Compton Scattering Factors for Aspherical Free Atoms
Authors: Cromer Don T.
Published: February 2004

Incoherent scattering factors for all aspherical free atoms have been computed from numerical SCF Hartree–Fock wavefunctions. The complete Waller–Hartree theory with all exchange terms has been used.
Vibrational Spectra and Force Field of Ruthenium Tetroxide
Authors: Levin Ira W. , Abramowitz Stanley
Published: February 2004

Measurement of the infrared gas-phase spectrum of the ν3 vibration for RuO4 provides values for both the Coriolis zeta constant ζ3 and the isotopic frequency shift Δν3 for the 101Ru–102Ru exchange. These data, in addition to the vibrational amplitudes l(Ru–O) and l(O...O), serve as constraints in specifying unique force fields for the F2 symmetry species of RuO4. Agreement among the sets of force constants separately determined by the supplemental information confirms the potential function for this system.
Isotope Sieve for 4He vs 3He. The Low-Temperature Heat Capacity of SiO2 Glass before and after Contact with 4He and 3He
Authors: Hornung E. W. , Fisher R. A. , Brodale G. E. , Giauque W. F.
Published: February 2004

The heat capacity of two samples of annealed SiO2 glass has been measured over the range 0.5°−4.2°K. The data for a solid cast cylinder are represented by C = 0.33T + 0.271T3 + 0.0220T5μgibbs / g. A hollow cylinder made from tubing gave the result C = 0.26T + 0.234T3 + 0.0165T5μgibbs / g. The heat capacity of each sample was also measured at 90 kG with no detectable change. It has been found that 4He can be sorbed by the glass at temperatures below 4.2°K and cannot be appreciably removed by long evacuation at 4.2°K. This effect has been studied in terms of the temporarily altered heat capacity after the glass has been exposed to liquid and gaseous 4He. Similar experiments with 3He indicate that it is not sorbed in SiO2 glass below 4.2°K, and exposure to liquid or gaseous 3He produces no change in heat capacity. It is suggested that SiO2 glass may be useful in separating 3He and 4He by selective sorption.
Chemiluminescent Reactions of He(23S) with Nitrogen, Oxygen, Carbon Monoxide, and Carbon Dioxide
Authors: Cher Mark , Hollingsworth C. S.
Published: February 2004

Rate coefficients for chemiluminescent reactions of excited helium with N2, O2, CO, and CO2 were determined by measuring the spatial dependence of visible emission in a flowing helium afterglow apparatus at pressures between 1 and 2 mm Hg. Rate coefficients are approximately proportional to the temperature over the range 305°–527°K. The magnitudes extrapolated to 300°K in units of 10−10 cm3 molecule−1·sec−1 are as follows: N2 = 1.0 ± 0.3, O2 = 3.3 ± 0.9, CO = 1.7 ± 0.5, CO2 = 7.9 ± 2.5. The relative concentration of metastable He(23S) was determined by optical absorption measurements as a function of total flow rate (or pressure). A close correlation exists between the resulting curve and the curves for the total emission intensity. These data provide strong evidence that Penning ionization by He(23S) atoms is a major process for populating the emitting states.
Determination of Electrolyte Apparent Molal Compressibilities at Infinite Dilution Using a High-Precision Ultrasonic Velocimeter
Authors: Garnsey R. , Boe R. J. , Mahoney R. , Litovitz T. A.
Published: February 2004

Using a newly designed high-stability sing-around circuit ultrasonic velocities in aqueous salt solutions down to concentrations of 2 × 10−4mole/liter have been measured. Adiabatic apparent molal compressibilities at infinite dilution, and where possible standard molal compressibilities, have been determined for some aqueous solutions of tetra-alkylammonium bromides, alkali-metal chlorides and sulfates, and MgSO4. The determination of these quantities from precise sound velocity, volumetric, and calorimetric measurements is discussed. The practice of obtaining φKs0 from empirical extrapolation of φKs data is shown to be unreliable and unnecessary.
Many-Body Corrections to Isotopic Volume Differences in Solid Neon
Authors: Brown J. S.
Published: February 2004

A calculation is presented of the effect of triple-dipole forces on the differences of volume of 20Ne and 22Ne lattices at 0°K in the quasiharmonic approximation.
Chlorine Hyperfine Interactions in π-Electron Radicals
Authors: Kohin Roger P.
Published: February 2004

Using data presented earlier, the complete anisotropic 35Cl hyperfine interaction tensor is evaluated for an α-chlorine in a π-electron radical for the first time. In CClHCOOH the tensor has an isotropic part aCl = + 3.7 G and anisotropic parts Bx = + 16.3 G, By = − 6.2 G, Bz = − 10.1 G. The x direction is normal to the radical plane while z is along the C–Cl bond. These values permit the following spin-density assignments in the various orbitals of the C–Cl fragment: ρCπ = + 0.78, ρClπ = + 0.15, ρClσ(3pz) = − 0.03, and ρClσ(3s) = + 0.002.
First-Order Phase Transitions in Multistranded Macromolecules
Authors: Applequist Jon
Published: February 2004

The theory of the helix–coil equilibrium in an n-stranded macromolecule is investigated under restrictions analogous to the matching case discussed in the preceding paper for two-stranded molecules. The problem is found to be formally identical to the two-strand case by showing that the probability of a looped state is proportional to k−a, where k is the number of links in each branch of the loop and a = 3(n − 1) / 2 for Gaussian chains. It follows that a first-order phase transition occurs at a critical value of the stability constant for n ≥ 3. Data bearing on the helix–coil transition in the three-stranded protein collagen are examined and found to suggest that a first-order phase transition would indeed occur under equilibrium conditions. The three-stranded polynucleotide complex formed from one stand of polyriboadenylic acid and two strands of polyribouridylic acid shows an apparent second-order transition. This is interpreted to mean that mismatching of strands occurs in this material.
NMR Spectra of Pyrophosphoryl Tetrafluoride and μ-Oxobis(thiophosphoryl Difluoride)
Authors: Hill William E. , Sharp D. W. A. , Colburn C. B.
Published: February 2004

The fluorine and phosphorus NMR spectra of pyrophosphoryl tetrafluoride and μ-oxobis (thiophosphoryl difluoride) have been examined under high resolution. The NMR spectra of these compounds have been analyzed as an AA′XX′A″A″′ system and the coupling constants have been determined.
Internal Excitation in Nonreactive Molecular Collisions: Resonance Widths in the Scattering of an Atom by a Rigid Rotor
Authors: Muckerman J. T.
Published: February 2004

Approximate methods are employed in an attempt to reproduce the exact dependence of the widths of subexcitation resonances upon energy and the asymmetry (coupling) parameter in the scattering of an atom by a rigid rotor. Two approximation procedures are investigated. One is based on the “distortion” approximation to the resonance energies. It is shown that, except for cases of extremely weak coupling, this approximation is quite unsatisfactory. The other procedure, an extension of the “adiabatic” approximation to the resonance energies, is computationally as simple as the first method in that it does not require the numerical differentiation of the adiabatic wavefunctions. Agreement with the exact widths is quite good, suggesting that the approximation should be of considerable value in predicting whether or not a given resonance might be observable.
Electron Spin Relaxation in the N,N′-Dimethylpyrazine Cation Radical
Authors: Ahn Myong-Ku , Johnson Charles S.
Published: February 2004

Line shapes in the ESR spectrum of the N,N′-dimethylpyrazine cation radical have been studied from 20° to −80°C, and an analysis has been carried out using the relaxation matrix theory. It turns out that anisotropic dipole and g-tensor interactions provide the major relaxation mechanisms. Classical dipole tensor components have been calculated for all of the magnetic nuclei, and it is shown that the hyperfine splitting constants for the nitrogen nuclei and the methyl protons are positive. Partially resolved second-order structure is observed in some of the lines and a linewidth correction has been introduced to take this into account. Spin relaxation resulting from modulation of the isotropic dipole interactions through contact with the counter ion is discussed on the basis of an electrostatic model and a steric model. The predictions of the steric model are the most acceptable, but neither has been confirmed experimentally.
Triplet States in Mixed Molecular Crystals
Authors: Sommer Bat-Sheva , Jortner Joshua
Published: February 2004

Triplet exciton density of states functions were calculated for crystalline naphthalene and benzene, and the off-diagonal matrix elements of the Green's function were obtained for crystalline naphthalene, using theoretical intermolecular electron-exchange terms. These results were then applied for the study of triplet states in doped molecular crystals, using the one-particle Green's function method. The localized impurity, the impurity pair, and the general impurity problem were considered. The experimental implications of these results concerning the absorption and emission spectra and energy-trapping effects in dilute mixed crystals were considered.
Replacement Free Energy in the Thermodynamics of Small Systems
Authors: Abraham Farid F. , Canosa José
Published: February 2004

The object of this study is to present an analysis of the origin and calculation of the replacement free energy in the thermodynamics of small systems. An exact expression is obtained for the replacement free energy of a one-dimensional “crystal” with free ends.
Potential-Energy Surfaces of CH3+ and CH3−
Authors: Kari R. E. , Csizmadia I. G.
Published: February 2004

The possibility of decribing accurate Hartree–Fock energy surfaces for CH3+ and CH3− is discussed. The effect of the inclusion of a d-Gaussian-type function (GTF) on the potential-energy surface is studied using basis sets composed of 52 and 58 GTF.
Multiple-Quantum Transitions in Nuclear Magnetic Resonance of Strongly Coupled AA′BB′ Spin Systems
Authors: Bucci P. , Ceccarelli G. , Veracini C. A.
Published: February 2004

The nuclear magnetic resonance multiple-quantum spectra of thiophene and o-dichlorobenzene have been determined and analyzed. Yatsiv's theory, in spite of the fact that in the present cases simplifying assumptions are not fulfilled, correctly predicts frequencies, frequency shifts, and rf field amplitudes for maximum signal. A single less restrictive assumption is proposed which leads to the same conclusions as Yatsiv's. The intensities observed for MQ transitions are weaker than those predicted and the disagreement increases with the number of quanta involved.
NMR Doublet Splitting in Aqueous Montmorillonite Gels
Authors: Woessner D. E. , Snowden B. S.
Published: February 2004

Doublet splitting in the NMR spectrum of montmorillonite clay–water systems arises from the preferred orientation of water molecules on clay gels. The small magnitude of the doublet splitting compared to that expected for motionless molecules indicates dynamic preferential orientation of the water in the clay–water systems. The fact that the doublet splitting is observed for the D2O–clay gels at all temperatures but only for the H2O–clay gels at low temperatures and relatively small water content suggests the importance of hydrogen exchange in the observation of the H2O doublet. Hydrogen exchange “washes out” the proton doublet but not the deuteron doublet. The reason for this is the difference in the proton and deuteron nuclear spin interactions which give rise to the doublet.
Electron Paramagnetic Resonance Studies of the Triplet State of Coumarin and Related Compounds
Authors: Graber D. R. , Grimes M. W. , Haug A.
Published: February 2004

Electron paramagnetic resonance and optical experiments have been performed on the lowest photoexcited triplet state of coumarin and structurally related molecules which were randomly oriented in a rigid matrix at 77°K. The fine structure of the paramagnetic resonance spectrum of coumarin measured at 9.2 GHz can be described by the spin Hamiltonian H = gβH·S − (XSx2 + YSy2 + ZSz2) with the zero-field-splitting energies X = 0.0094 cm−1, Y = 0.0680 cm−1, and Z = 0.0774 cm−1, assuming an isotropic g value. These zero field splitting energies and a phosphorescence lifetime of 0.54 sec indicate that the lowest triplet state of coumarin is of a π–π* character.
Fluorescence of Benzene Vapor at Low Pressures
Authors: Parmenter C. S. , White Anne H.
Published: February 2004

The intensity and spectral distribution of fluorescence from the first excited singlet state (1B2u) of benzene in the pressure range 0.05–7 × 10−5 torr has been studied by monitoring a number of prominent bands. Fluorescence was excited by Hg 2537-Å radiation. At pressures below 0.01 torr, the intensity of every band monitored is directly proportional to benzene pressure. This indicates that both the quantum yield and the spectrum of benzene fluorescence are invariant in this pressure domain, at least to within the 10% scatter of the data. The constant quantum yield is estimated to be near 0.4 so that significant non-radiative relaxation occurs. These pressures extend by more than two orders of magnitude into the low-pressure region where hard-sphere collisions cannot effect relaxation of B2u1 molecules. The implications of these data with respect to radiationless relaxation processes in isolated molecules are discussed. Collision-induced relaxation (probably vibrational relaxation) of some of the B2u1 benzene vibronic states excited by Hg 2537-Å absorption can be observed at 0.05 torr, and this has been studied in pure benzene and in mixtures of benzene and CO. The efficiency of ground-state benzene in depopulating these states is about one in two hard-sphere collisions. CO is about half as effective. The rate of vibrational relaxation by CO is seen to differ among the several excited states populated by Hg 2537-Å absorption.
Molecular Distortions and the Phosphorescence of Benzene
Authors: Nieman G. C.
Published: February 2004

The relative intensities of the members of a progression (Franck–Condon factors) can be used to determine changes in molecular geometry upon electronic excitation. A detailed examination of the normal coordinates shows that for benzene and similar species only one vibrational mode (ν1, ∼990 cm−1) is expected to form progressions, even for deuterated benzenes having many totally symmetric vibrations which, according to group theory, might be expected to form progressions. For a D2h distorted benzene a second coordinate (ν8, ∼1600 cm−1) is expected to form progressions. The phosphorescence of all isotopically substituted benzenes has only one main progression frequency (950–990 cm−1), while the dominant progressions for the methylbenzenes involve the 1600-cm−1 mode. Quantitative calculations show that in the lowest triplet state of benzene the difference between long and short bonds is less than 0.01 Å, while for toluene a value of ∼0.07 Å is found.
Shock-Wave Study of Vibrational Energy Exchange between Diatomic Molecules
Authors: Sato Yukinori , Tsuchiya Soji , Kuratani Kenji
Published: February 2004

The relaxation equation of the vibrational energy for a mixture of two diatomic gases is solved under the condition of Landau–Teller, considering the translation–vibration energy transfer (T–V) processes as well as the vibrational energy exchange (V–V) process. The solution shows that the relaxation of each of the component molecules proceeds as if it has two relaxation times. At the starting point of the relaxation process, both of the components begin to relax with their respective T–V relaxation rates, and then, the relaxation rate of one component, which has a smaller T–V relaxation time, decreases gradually, while the rate of the other component increases. Finally, both the components relax with the same rate toward their equilibrium states. The extent of coupling between the T–V processes of the two components is determined by the rate of the V–V process and by the concentration of two species in the mixture. Based on the preceding analysis, the vibrational relaxations of CO in CO–N2, CO–C2, CO–D2, and CO–H2 mixtures diluted in Ar are observed by the infrared emission of the CO fundamental behind shock waves, and the V–V collision probabilities are determined. The results agree with the SSH theory except in the case of CO–H2 collision. Theoretical calculation using the Morse-type potential is also discussed for the near-resonant V–V process between CO and N2.
Theoretical Justification of the Apparently Anomalous Low-Energy Behavior of Some Ion–Molecule Reactions
Authors: Kaufman Joyce J. , Koski Walter S.
Published: February 2004

It is generally observed that cross sections for exothermic ion–molecule reactions decrease with increasing ion kinetic energies indicating a negligible activation energy. An important exception to this behavior is exhibited by the exothermic reaction O++N2→NO++N, the cross section of which goes through a maximum as a function of ion energies. A study of the pertinent potential-energy curves, taking into account the proper symmetry- and spin-allowed combinations of the reactants and products, shows the origin of the apparently anomalous behavior of this reaction.
Crystal Spectra of Hexaurea Complexes. III. Optical and Magnetic Properties of Crystals Containing the Hexaurea Vanadium (III) Ion
Authors: Dingle R. , McCarthy P. J. , Ballhausen C. J.
Published: February 2004

Low-temperature polarized crystal spectra of the [V(urea)6]3+ ion are presented and discussed. In many ways they closely resemble those seen in V3+/Al2O3. The ground-state splitting of A23 has been established by both optical and magnetic means and is reported as 6.0 ± 0.5 cm−1. The source of spectral intensity is almost entirely due to the influence of the static, odd crystal field.
Additive Coloration of Sodium Chloride
Authors: Maurer Robert J.
Published: February 2004

The formation of F centers in sodium chloride by reaction of the salt with a metal depends on the free energy of formation of the metal chloride. The observed relative effectiveness of the alkaline-earth metals and cadmium is explained in this manner. In equilibrium, an electrostatic potential difference exists between the interiors of the metal and the crystal.
Effect of Temperature in Gas Electron Diffraction. III. The Temperature Dependence of the First Four Moments of a Morse Oscillator
Authors: Ng E. W. , Su L. S. , Bonham R. A.
Published: February 2004

The effect of temperature on the first four moments of a Morse oscillator is investigated over the temperature range of 10°–1500°K. Numerical calculations are carried out for parameters of the I2 molecule. An expression of the Morse oscillator in a power series of the displacement coordinate is used to calculate the moments by both a variational and a perturbational approach. A classical calculation is also carried out for comparison. It is concluded that a potential with quadratic, cubic, and quartic terms can yield moments at about the 1% accuracy level up to 800°K, while that including the fifth- and sixth-power terms yields moments at the same accuracy level up to 1000°K. Applications of results to gas electron diffraction are discussed.
Intrinsic Viscosity of Polyelectrolytes
Authors: Imai Satoshi
Published: February 2004

The intrinsic viscosity and expansion factor of polyelectrolyte have been calculated by using the Debye–Hückel approximation to the potential of mean force between segments. The results obtained are compared with experiments by Takahashi and Nagasawa.
Linear Homogeneous Constrained Variation Procedure for Molecular Wavefunctions
Authors: Weber Thomas A. , Handy N. C.
Published: February 2004

A method is described for the determination of wavefunctions which are subject to linear homogeneous constraints. This variational procedure obtains such wavefunctions directly from the solution of a standard eigenvector-type problem and, unlike previously proposed methods for handling these constraints, does not depend upon any iterative calculation.
Hyperpolarizability of Helical Polymer Molecules and the Sampling of the ir-Active Optical Phonon Dispersion Curves
Authors: Fanconi Bruno , Peticolas Warner L.
Published: February 2004

The selection rules for the inelastic three-photon scattering of light by helical molecules is obtained from group theoretical analysis. It is shown that the dispersion curve (frequency vs wave vector) for ir-active optical phonons may be sampled at four points throughout the Brillouin zone by measuring the frequency of the scattered light as a function of the polarization of both the incident (laser) and the scattered light provided that proper orientation of the laser light relative to the helix axis is maintained.
EPR Spectrum of Fe3+ in Synthetic Brown Quartz
Authors: Matarrese L. M. , Wells J. S. , Peterson R. L.
Published: February 2004

A detailed description is given of the EPR spectrum of Fe3+ in synthetic brown quartz (the so-called I center, presumed to be interstitial). There are three equally populated sites differing only in the orientation of their principal axes, which coincide with the three twofold axes of quartz. The values of the Hamiltonian parameters that fit the data best are: g = 2.0039, C20(≡D) = 734.3G, C22[≡(61 / 2 / 2)| E |] = 401.7G, C40 = 2.52G, C44 = 1.40G, where the Clm are the coefficients of the Racah operators in the Hamiltonian. Lobes of the V22, V42, and V44 parts of the crystal-field potential point 0.7°, 29.5°, and 26.8°, respectively, from the optic axis of quartz. The occurrence of irregular off-axis extrema of the line positions when the magnetic field is directed in the vicinity of the optic axis precludes the assignment of magnetic axes of the paramagnetic center in the usual way. All features of the spectrum are predicted accurately by computer calculations based on the derived Hamiltonian. Although the data are not conclusive evidence, they are believed to be more consistent with an assignment of the I center to a substitutional site.
Uncoupled Hartree–Fock Calculations of the Ring-Current Contribution to the Magnetic Susceptibilities of Conjugated Molecules
Authors: Amos A. T. , Roberts H. G. Ff.
Published: February 2004

Uncoupled Hartree–Fock perturbation theory is used to compute the ring-current contributions to the magnetic susceptibilities of several conjugated hydrocarbons. In the usual form of the perturbation theory this leads to an origin dependent result, but when corrections are included this origin dependence is removed. The final results agree very well with those calculated using the more complicated coupled Hartree–Fock method, and, when empirical values are used for the local contributions to the susceptibility, the theoretical values for the components, the mean value, and the anisotropy of the susceptibility are in excellent agreement with experiment.
Asymptotic Evaluation of WKB Matrix Elements
Authors: Pack Russell T , Dahler John S.
Published: February 2004

A procedure is given for the analytic asymptotic evaluation of certain integrals which arise in the quantum-mechanical theory of inelastic molecular collisions. The integrals are evaluated using WKB wavefunctions and the saddle-point method. The method is equivalent to Landau's but is considerably more transparent and is easily applied to vibrational and rotational transitions for which there is no crossing of potential-energy surfaces, as well as to electronic transitions near a crossing point. The special case of resonance collisions is discussed, and the method is illustrated with an example.
Experimental Verification of the Dusty-Gas Theory for Thermal Transpiration through Porous Media
Authors: Hopfinger E. J. , Altman M.
Published: February 2004

For complete comparison of the dusty-gas theory for thermal transpiration through porous media with experimental results, isothermal permeability measurements as well as a knowledge of the geometric properties of the porous media are needed in addition to the thermal transpiration measurements. Such measurements were made for several gases on five porous ceramics and two Millipore filters under a variety of conditions, and steady-state results of a net flow that equals 0 and results of a net flow that does not equal 0 were compared with the theory. Good agreement was found to exist in the range of a pore diameter to molecular mean-free-path ratio de / λ < 10. The coefficients appearing in the equations can all be determined from independent experiments; for a quantitative prediction of transpiration results it is, however, necessary to adjust the porosity–tortuosity factor appearing in the coefficient which arises from the termal-diffusion term. This porosity–tortuosity factor was found to be more closely represented by ε / q2 rather than ε / q.
Vibrational Spectra of Group IIB Halides. II. The Halides of Cadmium and Mercury
Authors: Loewenschuss A. , Ron A. , Schnepp O.
Published: February 2004

The infrared spectra of the vapors of all cadmium and mercury halides were studied at low temperatures by matrix isolation. The spectra are classified into four absorption regions recorded in the 800–35-cm−1 range. The highest and lowest frequencies are assigned to the antisymmetric stretching mode and the doubly degenerate bending modes, respectively, of the MX2 molecules. The nature of the bonding in the molecule is discussed and statistically calculated entropy values are compared with corresponding values obtained from thermochemical measurements.