bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of the Transferability of Atomic Hartree-Fock Valence Shell Orbitals
Authors: Adams William H.
Published: February 2004

Two procedures by which atomic valence shell orbitals may be transferred between atoms have been studied numerically. The one procedure optimizes the overlap between transferred and true orbitals, and the second, the electronic energy calculated with the transferred orbitals. The two procedures give significantly different results. Both improve on the results obtained in a previous study.
Hot Atom Reactions in the HBr–Br2, DBr–Br2 Systems
Authors: White John M. , Su H. Y.
Published: February 2004

Reactions of photochemically generated hot hydrogen atoms have been studied in HBr–Br2 systems at 185 and 229 nm and in DBr–Br2 systems at 185 nm. Kinetic analysis furnishes k3/k2—the rate coefficient ratio for the reactions H*+Br2← lim 3HBr+Brand H*+HBr← lim 2H2+Br.At 185 nm for HBr, k3/k2=4.11± 0.16, while at 229 nm k3/k2=5.48± 0.22. For DBr at 185 nm the ratio is 5.07± 0.12. Complementary trajectory calculations have been performed on a semiempirical potential-energy surface. The results of these calculations suggest that the observed variations in k3/k2 arise primarily because the reaction cross section for Process (3) varies strongly with energy in the hot atom regime and is different for the HBr and DBr systems.
Electron Attachment and Compound Formation in Flames. V. Negative Ion Formation in Flames Containing Chromium and Potassium
Authors: Miller William J.
Published: February 2004

Application of several different experimental techniques (flame-ion mass spectrometry, microwave cavity resonance, electrostatic probe, and absorption spectrophotometry) reveals that addition of chromium to fuel-rich atmospheric-pressure H2/O2/N2 flames seeded with potassium results in formation of Cr-containing negative ions. The following reaction scheme, equilibrium constants, and enthalpy changes provide a satisfactory quantitative interpretation of the experimental results: e+HCrO3=CrO3−+H, Δ H0,1°=125± 40 kJ mole−1, H2+CrO3−=HCrO3−+ H, Δ H0,4°=78± 40 kJ mole−1 K1=2500 exp(−13 400/T) K4= 1.7  exp(−9900/T). Electron affinities for HCrO3 and CrO3 inferred from this data are 229 kJ mole−1 and 390 kJ mole−1, respectively.
Electronic Bonding of Cu2+ in Amorphous and Crystalline TeO2: EPR and Optical Spectra
Authors: Siegel I. , Jones E. P.
Published: February 2004

Electron paramagnetic resonance and optical spectra of Cu2+ ions doped into polymorphic TeO2 have been investigated. Spectra were obtained for the non-Zachariasen, octahedrally coordinated amorphous form and for the tetragonal crystalline form. The spectra were interpreted in terms of a molecular-orbital model of a Cu2+ ion in square-planar coordination to the oxygen ligands and compared to results obtained previously for amorphous and tetragonal GeO2. The properties of the dopant Cu2+ ions in the non-Zachariasen TeO2 glass were found to be similar to those of Cu2+ ions in the Zachariasen GeO2 glass. The Cu2+ ions were more covalently bonded in the TeO2 glass than in the TeO2 crystal and less covalently bonded in both forms of TeO2 than in the corresponding GeO2 polymorphs.
Nuclear Magnetic Resonance of Ferroelectric Lithium Ammonium Tartarate
Authors: Saffar Z. M. El , O'Reilly D. E. , Peterson E. M. , Flick Cathy
Published: February 2004

Lithium-7, proton, and deuterium NMR have been studied in lithium ammonium tartarate LiNH4C4O6H4· H2O (LAT) both above and below the ferroelectric-paraelectric transition temperature Tc (98°K). Complete rotation patterns have been obtained near 300°K for the 7Li, H, and D (of D2O) resonance. The hydrogen atoms of the water of hydration have been located in the unit cell, and are observed not to change position as the transition temperature is traversed. Likewise the 7Li NMR does not change significantly above and below Tc. The deuteron resonances of the ND4+ ion, however, change abruptly on traversing Tc in direct analogy to the behavior found in (ND4)2SO4. The spontaneous polarization computed from the distortion of the ND4+ ion determined by NMR accounts for 60% of the total polarization of LAT. Proton relaxation times are interpreted in terms of a relatively fast reorientation of the NH4+ tetrahedron about a twofold axis and relatively slow reorientation about a threefold axis. Evidence is presented to show that the rotation is coherent at low temperatures corresponding to quantum mechanical tunneling. It is proposed that the hydroxyl protons of the tartarate ions are undergoing motion between several inequivalent positions in the unit cell.
Hellmann-Feynman and Virial Theorems in the X α Method
Authors: Slater John C.
Published: February 2004

It is proved that the Xα method leads rigorously to the Hellmann-Feynman and virial theorems. The proof of the virial theorem is general, not limited to the scaling argument used in earlier discussions. These proofs hold only if α is a constant, independent of nuclear positions. If α has one value inside one atomic sphere, another in another sphere, there are small correction terms, so that if one wishes the theorems to be rigorously applicable, it is best to use the same α everywhere. Discussion of the van der Waals force indicates that the Xα method should give a satisfactory treatment of this force.
Spontaneous Predissociation in I2
Authors: Tellinghuisen Joel
Published: February 2004

Existing lifetime data for the B[O+u(3II)] state of I2 are discussed in terms of the radiative and predissociative decay components. Franck-Condon calculations for the B→ 1u(1Π) predissociation show that the lifetimes and photodissociation yields are consistent with the location of the 1u(1II) state deduced independently from absorption measurements. The predissociative decay rate is negligible near v′ = 14, rises to a sharp peak at v′∼5 and a broader, weaker maximum around v′ = 26. Rotational predissociation may be significant for absorption within ∼20 Å of the B-state dissociation limit.
Magnetic Structure of ErAu2
Authors: Atoji Masao
Published: February 2004

The magnetic properties of ErAu2 having the tetragonal body-centered CaC2-type structure have been investigated at temperatures between 297 and 1.8°K by neutron diffraction experiments on powdered specimens. The onset of an incommensurate, transverse wave moment alignment (the α structure) occurs at 6.7°K. The α magnetization wave propagates along the a axis and is polarized in the b direction, all in the face-centered description. The α wavelength is 6.443 Å = 1.248 a and is temperature independent. At 4.0°K, a commensurate antiferromagnetic moment wave (the β structure) appears with the propagation direction parallel to the a axis. The β wavelength is equal to the a spacing. As regards the β moment components, the x ∥ a component is slightly larger than the y ∥ b component and the z ∥ c component is undetectably small. The composite configuration of the α and β waves delineates a distorted-fan modulation. In cooling, the α amplitude develops to 6.7 μB at 4°K, then decreases to 5.9 μB near 3°K, and retains 5.9 μB at 3>T>0° K. The β wave moments approximate the Brillouin magnetization with the extrapolated moments of 3.2 and 2.7 μB at 0°K for the x and y components, respectively. The maximum composite moment is 9.2 μB at 0°K, while the ordered moment of the free Er3+ ion is 9.0 μB.
Anisotropic Electron Spin Resonance Spectra of PCl2 and NCl2 in Low Temperature Matrices
Authors: Wei Michael S. , Current Jerry H. , Gendell Julien
Published: February 2004

Well-resolved ESR spectra of PCl2 were observed from the thermolysis (1000°C) of PCl3, in argon, krypton, xenon, and nitrogen matrices. Satisfactory computer simulated spectra were obtained using two slightly different interpretations. One assumed a rhombic g tensor and an axially symmetric phosphorus hyperfine tensor; gxx=2.0024, gyy=20011, gzz=1.9962; C∥(P)=293 G; C⊥(P)=± 30.5 G; C∥(Cl)=17.5 G; C⊥(Cl) <0.3 G. The other assumed an axial g tensor and a rhombic phosphorus hyperfine tensor; g∥ = 2.0024, g⊥ = 1.9986; Cxx(P)=293 G; Cyy(P)=± 39.0 G; Czz(P)=± 22.5 G; C∥(Cl)=17.5 G; C⊥(Cl)<0.3 G. In situ photolysis of PCl3 in argon produced a spectrum tentatively assigned to the asymmetric PClCl radical. The ESR spectrum due to NCl2 radicals was observed from a direct room temperature sprayon of NCl3 mixed with nitrogen or argon. Experiments using 15NCl3 were also performed. The following assignment was obtained: gxx=2.006, gyy=2.025, gzz=2.023; Cxx(14N)=40 G; Cyy(14N)=14 G; Czz(14N)=6 G; C∥ (Cl)=24 G; C⊥(Cl)=17 G. A discussion of the spin density distribution in the nitrogen and phosphorus dihalide radicals (NF2, NCl2, PF2, and PCl2) and of the electronic structure of these species using the available experimental data, atomic electronegativities, and the results of extended Hückel molecular orbital calculations is presented. Some information on the decomposition reactions of NCl3 was obtained. A test of the reference values of the atomic nuclear moment—valence electron spin coupling parameters is possible by using the total spin densities determined for these radicals. The reference values calculated by Hurd and Cooden are shown to be preferable.
Photoionization of Excited H2 Molecules
Authors: Cohn Arthur
Published: February 2004

The photoionization cross sections of the singly excited H2 states are calculated. The Coulomb approximation method utilizing the Temkin-Vasavada electron H2+ scattering phase shifts is used. Cross sections of ∼1–2 × 10−17 cm2 are found for all states at threshold, the same range as found for H(n=2) atoms.
Classical S-Matrix Theory of Reactive Tunneling: Linear H+H2 Collisions
Authors: George Thomas F. , Miller William H.
Published: February 2004

Complex-valued classical trajectories (computed by direct numerical integration of Hamilton's equations) are found for linear reaction collisions of H+H2→ H2+H (on the Porter-Karplus potential surface) at collision energies for which all ordinary real trajectories are nonreactive, and from such trajectories classical S-matrix elements are constructed. This analytically continued classical-limit theory is seen to be an accurate description of reactive tunneling for the H+H2 system. At each collision energy there is only one classical trajectory that contributes to the reaction, so that various features of the reaction dynamics are easily elucidated by looking specifically at this one trajectory. It is also shown how a Boltzmann average of the reaction probability can be carried out semiclassically, and this leads to an interesting relation between the imaginary part of the time increment of the complex-valued trajectory at a given energy and the absolute temperature at which this is the dominant energy in the Boltzmann average: Im(t2−t1)=−12ℏ /(kT). It is seen, for example, that for T ≲ 1000°K the dominant energy region is below the classical threshold, i.e., in the tunneling region.
Effect of Scavenger Competition on Hot Atom Chemistry. I. Correction to the Kinetic Theory
Authors: Malcolme-Lawes D. J.
Published: February 2004

The effect of scavenger reactivity in a hot reaction zone is considered using the model and symbolism of the kinetic theory of hot atom reactions. Expressions are derived which enable the extent of scavenger interference to be estimated from experimental scavenger curves, and a simple method of correcting available kinetic theory parameters is given.
Effect of Scavenger Competition on Hot Atom Chemistry. II. Computer Simulation
Authors: Malcolme-Lawes D. J.
Published: February 2004

A computer model is used to simulate the effect of varying amounts of scavenger competition in a hot atom system consisting of reactant, inert moderator, and scavenger. The results are analyzed in terms of the kinetic theory of hot atom reactions. The scavenger corrected kinetic theory is tested and is shown to yield adequately corrected kinetic parameters.
Integral Equation Approach to Bound State Atomic Systems. Preliminary Studies of Helium and Hydrogen
Authors: Cooper W. Grant , Kouri Donald J.
Published: February 2004

The Sams-Kouri method for noniteratively solving integral equations is used to solve the integral form of Schrödinger's equation for He such that the Hartree-Fock approximation is avoided and the inclusion of nuclear motion is straightforward. An exact formalism is presented which requires the solution to coupled integral equations, and the method for generalizing to many electron atoms is indicated. Calculations are reported for a single integral equation approximation to He which illustrates the essential features of the method. The energy value obtained is approximately 85% of the total binding energy. Calculations for the H atom are given so comparisons with an exactly soluble atomic problem can be made, and the energy values for the ground and first three excited states are in excellent agreement with the exact values. Excited state calculations are found to be no more difficult than those for the ground state.
Absorption Spectra of Pure Liquid Benzene in the Ultraviolet Region
Authors: Inagaki Takashi
Published: February 2004

Absorption spectra of pure liquid benzene were measured at several temperatures from room temperature to just below the freezing point of benzene, in the wavelength region 3000–1670 Å. Because of the very large absorption coefficient of benzene in this region, the transmission measurements were made with the samples prepared as thin films. Three absorption bands of quite different intensities were observed, corresponding to the π – π* singlet transitions well known in the vapor phase spectra. The spectra obtained are compared with those in the vapor and solid phases.
On the WKB Approximation in Time-Dependent Scattering Theory Including Rearrangement Processes
Authors: Eu Byung Chan
Published: February 2004

The classical correspondence of the S matrix for scattering processes is examined with a view to obtain the classical approximation and also to clarify the nature of the approximations required for the classical formula. In this discussion the Schrödinger equation in the momentum representation is employed instead of the usual coordinate representation in order to provide a more direct route to the classical limit of the S matrix. The S matrix thus obtained essentially corresponds to the WKB approximation, and, with a further approximation, leads to Miller's expression except for a multiplicative factor and an additional phase which are in general not equal to 1 and 0, respectively. The classical limit is also discussed in terms of Wigner-Moyal phase space distribution function, and when the classical limit of this function is taken, an additional factor and phase appear in the S matrix.
Radiation Abstraction of Hydrogen Atoms in Single Crystals of Thymine
Authors: Dulčić A. , Herak J. N.
Published: February 2004

Single crystals of both thymine monohydrate and anhydrous thymine were irradiated at 77°K and the radicals induced were analyzed with ESR spectroscopy. The radical species, formed by abstraction of a hydrogen atom from nitrogen, was studied in detail. Molecular orbital calculations suggest that the abstraction takes place from N(1). The nitrogen and the methyl proton coupling tensors are identical in both crystal systems. The ĝ tensor is axially symmetric (g∥ =2.0032, g⊥ =2.0064) with the axis of symmetry perpendicular to the ring plane. The differences between deuterated and undeuterated thymine monohydrate crystals are also discussed.
On the Configurational Statistics of Ethylene-Propylene Copolymers
Authors: Mark J. E.
Published: February 2004

Mean-square unperturbed dimensions 〈 r2〉0 and their temperature coefficient d ln〈 r2〉0/dT have been calculated for ethylene-propylene copolymers by means of the rotational isomeric state theory of chain molecules. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of polyethylene and polypropylene, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the propylene sequences. It is shown that 〈 r2 〉0 and d ln〈 r2〉0/dT for these copolymer chains should be most sensitive to chemical sequence distribution in the case where propylene sequences are highly isotactic in stereochemical structure. Calculations carried out using values of these variables thought to be appropriate for ethylene-propylene polymers experimentally investigated give values of d ln〈 r2〉0/dT which are in good agreement, in general, with those obtained from previously published force-temperature measurements on elongated networks of ethylene-propylene chains.
Dielectric and Mechanical Response of Ice Ih Single Crystals and Its Interpretation
Authors: von Hippel A. , Mykolajewycz R. , Runck A. H. , Westphal W. B.
Published: February 2004

After a short introduction of the status quo and of the experimental distinction between continuous distributions of relaxation time and discrete spectra, it is shown that in our best Ice Ih single crystals seven discrete relaxation spectra can be identified in the frequency range from 8 × 10−3 to 105 Hz. The experimental determination of the molecular origin of these ``standard'' spectra is the main theme of our investigation. Evidence is provided by the magnitude and temperature dependence of the relaxation times τ and polarization contributions Δ κ′ of the various spectra and the influence of imperfections, multicrystallinity, and of HF doping on these characteristics. Spectrum 3, representing the normal volume polarization of ice, can be explained satisfactorily by the dipole moments inscribed by field-directed diffusion of Bjerrum L, D defects into the proton memory system; destruction of the single crystal produces a cheaper L-D supply, reduction of the diffusion distance, and a new spectrum 3A of internal boundary conduction. The correlation claimed between mechanical and electrical relaxation by L-, D-defect action seems erroneous: Mechanical losses and basal glide appear to originate from the formation of Frenkel defect pairs and dislocation transfer. Spectra 0–2 stem from imperfections, spectra 4–6 from charge carriers avoiding the antipolarization memory of the ice and causing space-charge polarization. The action of HF on polarization and conduction of ice single crystals, as seen by our discrete dielectric spectra analysis, is very different from that previously believed and reported. It is tentatively analyzed for spectra 1–4; mechanical and diffusion effects are also considered. The work is being extended to transconduction and electrode phenomena.
Far Infrared Spectra of Ring Compounds. X. Hindered Pseudorotation in Six-Membered Rings: Estimation of the Barrier Height for Half-Chair Inversion in Dioxene and 2,3-Dihydropyran
Authors: Lord R. C. , Rounds T. C. , Ueda Toyotoshi
Published: February 2004

High-resolution far-infrared spectra of 1,4-dioxene (I) and 2,3-dihydropyran (II) have been determined. The spectra are divided into three principal regions associated with the twisting mode, the bending mode, and difference tones between the two. Analysis of the data was made in terms of the two-dimensional potential function, V(β, τ), of Ikeda and Lord [J. Chem. Phys. 56, 4450 (1972)]. The results for dioxene are: V (β, τ) in cm−1=−4580β2−19059τ2+835.5β4+13280τ4+15422β2τ2, and for dihydropyran are: V (β, τ) in cm−1=−4447β2−15526τ2+851.4β4+9783τ4+12738β2τ2. To the extent that these potential functions can be extrapolated reliably beyond the immediate neighborhood of the potential minimum, they imply that the most stable conformation is a twisted (half-chair) form with the respective twist angles 48.54° (I) and 51.04° (I), and barriers to planarity of 6838 cm−1 (I) and 6160 cm−1 (II). A metastable bent form appears to exist at 561 (I) and 352 cm−1 (II), respectively, above the energy minimum in the twisted conformation, with barriers to conversion from the twisted form of 2890 (I) and 2940 cm−1 (II).
Moment Theory Bounds for the Second-Order Optical Properties of Atoms and Molecules
Authors: Langhoff P. W.
Published: February 2004

A variety of oscillator-strength-distribution frequency moments are employed in conjunction with theorems from the theory of moments to construct bounded estimates for the dynamic polarizabilities and related optical properties of atoms and diatomic molecules. This technique circumvents the explicit construction of an accurate approximation to the dipole oscillator-strength distribution appearing in the Kramers-Heisenberg formula, and relates the dispersive optical properties of a system to the simpler frequency moments of its excitation spectrum. The bounds obtained follow from the theory of Tchebycheff systems of functions, although the Stieltjes nature of the polarizability insures that various other related formalisms, including the theory of Padé approximants, Gaussian quadratures, variational principles, and linear programming methods, can also be employed in their construction. Illustrative applications of the moment technique are given for the ground states of atoms and diatomic molecules employing oscillator-strength sum-rule moments, which can be determined from the ground state wavefunction of the system, and negative-even-integer (Cauchy) moments, determined from both theoretical and semi-empirical procedures. Highly accurate bounds for the refractivities, Verdet coefficients, and Rayleigh scattering cross sections of atomic and molecular hydrogen and helium are obtained using a small number of sum-rule moments and the static value of the polarizability. The sum-rule moment bounds obtained for the optical properties of the heavier inert gases, which exhibit more structured and complex dipole excitation spectra, are somewhat weaker than those for the smaller systems, although the mean values of the bounds are generally in good agreement with experiment. The long wavelength Faraday rotation data for neon appears to be somewhat anomalous, however. Theoretical and semiempirical Cauchy moments for the polarizability components of diatomic hydrogen, nitrogen, and oxygen are employed in the construction of Cauchy moment bounds. The theoretical results for molecular hydrogen, in the time-dependent Hartree-Fock approximation, are in good agreement with previous theoretical determinations of the dispersion in hydrogen, and the semiempirical results aid in the interpretation of uv Rayleigh scattering measurements for molecular hydrogen and nitrogen. Comparisons of the Cauchy moment bounds for the molecular Verdet coefficients with measured Faraday rotation data shows that all three diatomic gases satisfy the ``modified'' Becquerel formula. The ease with which bounds for the second-order optical properties of atoms and molecules can be constructed when the required frequency moments are available suggests that the moment technique should be one of continuing interest, with extensions of the approach to additional linear and nonlinear optical susceptibilities expected to be similarly rewarding.
Variable Trap Problem in Isotopic Mixed Crystals of s-Triazine
Authors: Fischer Gad
Published: February 2004

Theoretical treatments of isotopic mixed crystals, in general, have assumed that the intermolecular interactions are equal and that the problem can be reduced to a consideration of the free molecule excitation energies. It is shown that for the isotopic s-triazines the intermolecular interactions are different and that now it is necessary to consider a trap depth which is both concentration and distribution dependent. This has necessitated a modification of the existing theories. Experimental results have been obtained over the entire concentration range for the s-triazined-0/s-triazined-3 mixed crystal system, and the results have been qualitatively explained in terms of a concentration dependent trap depth.
Interaction of Sound with Gas Phase Reactions
Authors: Gilbert Robert G. , Hahn Hong-sup , Ortoleva Peter J. , Ross John
Published: February 2004

Reaction and sound propagation are coupled in ideal gas phase reactions which have a difference in the sums of stoichiometric coefficients of reactants and products, or which have a pressure-dependent rate coefficient. Numerical and approximate analytical (WKB-type) solutions are obtained for the hydro-dynamic equations which take into account this coupling and which describe the spatial and temporal variations in density, velocity and concentration for an isothermal system far from equilibrium. Specific results are given for a unimolecular reaction of the type A → B+C, where sound is shown to be amplified in both high and low pressure regions, with an accompanying change in frequency; the system is unstable to small perturbations. Possible applications include a new method for the determination of rate coefficients by acoustic means.
Monte Carlo Calculation of ESR Line Shapes in the Slow Motional Region
Authors: Pedersen J. Boiden
Published: February 2004

The ESR line shape in the slow modulation region is calculated from the Kubo-Anderson theory by using a Monte Carlo technique for averaging the relaxation function. The problem of spurious peaks is solved by the means of a window technique. It is explicitly shown how to sample the relaxation function. The method is applied to axially symmetric and asymmetric secular g tensor and pseudosecular terms modulated by isotropic rotational diffusion. Other interactions, e.g., nonsecular terms, as well as other types of modulation may be included.
Model for the Repulsive Elastic Scattering of Atoms by Solid Surfaces
Authors: Goodman Frank O. , Liu William S. , Cabrera Nicolás
Published: February 2004

A model is developed, enabling the intensities of diffracted beams to be calculated in closed form, starting from a pairwise (Yukawa-type) interaction law between a gas atom and a solid atom. The treatment is more satisfying than most previous treatments, which calculate the diffracted intensities as functions of empirical parameters describing the over-all gas-solid interaction, without reference to the microscopic (pairwise) interaction. The model is illustrated by an application to the He–LiF system.
Lattice Dynamics of M2XY6 Hexabromometallates: Cs2UBr6
Authors: Chodos Steven L.
Published: February 2004

A seven parameter model based on a modified Urey-Bradley potential with long range Coulomb terms is used to describe the lattice dynamics of M2XY6 compounds. Optical data are used to evaluate the force constants for the case of Cs2UBr6. The model is to be used as a starting point for a comprehensive calculation of the vibronic structure of Cs2UBr6.
Raman Spectra of Matrix Isolated Molecules: Application to the Force Field for CCl4
Authors: Levin Ira W. , Harris W. C.
Published: February 2004

Small isotopic frequency shift information, if precisely determined, provides an effective constraint on intramolecular force fields. The Raman spectrum of the ν4 mode of matrix isolated CCl4 exhibits a splitting pattern which is interpreted in terms of the chlorine isotope effect. These data are employed in assigning approximate limits to the crucial stretch-bend interaction force constant (F34). This force field is compared to potential functions derived by other investigators in which F34 is fixed by mean square amplitude information and relative Raman intensities. The Raman matrix spectra of CCl4 were recorded with a general purpose cryostat which was designed for use with a Cary Model 81 spectrophotometer equipped with an argon ion laser source. Spectra were obtained from samples with dilutions of CCl4 in argon in mole ratios of 1:400 to 1:600.
Natural Bifurcation Coordinates for Three-Dimensional Chemical Reactions
Authors: Harms Susan H. , Wyatt Robert E.
Published: February 2004

Three-dimensional atom-diatom collisions which can lead to two possible rearrangement products are considered under the restraint of near-linear intermediates. A coordinate system (natural bifurcation coordinates) is introduced to provide for smooth internal rotation of the system in the region of reaction path bifurcation; thus systems are allowed to ``wobble'' from one reaction path to the other. For both two- and three-dimensional reactions, the Hamiltonian operator is derived from the classical kinetic energy.
Systematics in the Electronic Spectra of Nucleoside Derivatives
Authors: Inskeep Warren H. , Miles Daniel W. , Eyring Henry
Published: February 2004

In order to calculate accurately the orientation of the sugar relative to the base in the pyrimidine nucleosides from circular dichroism data, the localized nature of the electronic transitions in both the sugar and the base have been exploited. Within the matrix formalism of the theory of optical activity, the sugar is treated by the bond exciton theory without the resonance assumption. The chromophore is treated by a semiempirical self-consistent field calculation from which the delocalization of each transition is extracted and then compared with the results of the bond exciton treatment. In three bands, there is excellent support for the SCF CI result, and these three are then used to draw conclusions regarding the molecular geometry. The one-electron effect on the pyrimidine nucleoside circular dichroism is shown to be small. The manner in which transitions are localized in the various chromophores is then used as a basis for a systematical discussion of various nucleoside spectral properties.
Electron Spin Resonance and Electron Nuclear Double Resonance Studies of DL-Serine. II. Identification of Free Radicals Produced in the Range 153–340°K
Authors: Castleman B. W. , Moulton Grace C.
Published: February 2004

Single crystals of x-irradiated DL-serine, deuterated DL-serine, and α-D-1-DL-serine have been examined in the temperature range 77–340°K using ESR and ENDOR techniques. Six of the radical species observed are identified and the mechanisms by which these species are formed are discussed. The initial species produced at 77°K are the anion and cation radicals which decay through inter- and intramolecular processes and finally form two stable radicals at room temperature.
Implementing the SAAP Formalism. II. Simultaneous Eigenfunctions of L2 and S2 by Direct Diagonalization
Authors: Salmon W. I. , Ruedenberg Klaus
Published: February 2004

A procedure is described for generating simultaneous atomic eigenfunctions of S2, Sz, L2, Lz as linear combinations of spin-adapted antisymmetrized products of atomic orbitals. The resulting functions are of the Serber type, i.e., they also are eigenfunctions of all geminal pair-spin operators. Flow diagrams for computer programs are given and running times are quoted.
Asymptotic Behavior of the Green-Kubo Integrands in Binary Mixtures
Authors: Pomeau Y.
Published: February 2004

In binary mixtures, as in monatomic fluids, the time dependent Green-Kubo autocorrelation functions decrease as t−d/2 for large times (d = dimensionality ≥ 3). In 3d binary mixtures, the space dependent auto-correlation functions decrease at large distances as R−4 for the diffusion and thermodiffusion coefficients and as R−7/2 for the shear and bulk viscosity and heat conductivity.
Hyperfine Structure Constants of Chlorine Monofluoride
Authors: Davis Richard E. , Muenter J. S.
Published: February 2004

The radio frequency spectrum of 35ClF has been observed in the J=1 and J=2 rotational states of the ground vibrational state using molecular beam electric resonance spectroscopy. The results are: eqQ(Cl)=−145 782.11(9) kHz, μ=0.8881(2) D, CCl=+21.615(9) kHz, CF=−22.67(3) kHz. JClF=+1.005(54) kHz. The value for the fluorine spin rotation constant is used to calculate the high frequency term of the magnetic shielding at the fluorine nucleus, σHF = + 61.7 ppm.
Statistical Mechanics of Wormlike Chains. I. Asymptotic Behavior
Authors: Gobush William , Yamakawa Hiromi , Stockmayer W. H. , Magee W. S.
Published: February 2004

The asymptotic form of the bivariate probability distribution describing both the position and the unit tangent vector at the endpoint of a continuous wormlike chain is obtained to terms of O(t−2), where t is the ratio of the total contour length to a statistical segment length. The method of solution utilizes operational algebra developed to solve the Liouville equation.
Statistical Mechanics of Wormlike Chains. II. Excluded Volume Effects
Authors: Yamakawa Hiromi , Stockmayer W. H.
Published: February 2004

The mean-square end-to-end distance and the second virial coefficient are evaluated for stiff chains with excluded volume. The calculation is based on a wire-bead model whose backbone in the unperturbed state obeys wormlike-chain statistics. In order to establish the necessary distribution functions, results derived in the second Daniels approximation in the previous paper are used, and suitable extrapolations from the coil region to the high-stiffness (low temperature) limit are made. The ring closure probability in this limit is also derived by applying a variation principle to a functional-integral representation of the partition function in terms of the bending elastic energy of the chain. The result is used for the first-order perturbation calculation of the mean-square end-to-end distance. Evaluation of the second virial coefficient is carried out in the double-contact approximation. The interpenetration function ψ is also calculated in an approximate fashion, and is shown to be appreciably smaller than for the coil limit over the ordinary range of interest for typical stiff chains. This result is consistent with experimental data for cellulose nitrates.
Shoulder of Optical Absorption Spectrum of the Trapped Electron in Gamma-Irradiated Crystalline Ice
Authors: Kawabata Keisuke , Okabe Shigeru , Taniguchi Setsuo
Published: February 2004

Precise measurements of the absorption spectrum and its differential of the trapped electron in crystalline ice were made. The absorption spectrum, due to a single kind of trap, has a shoulder around 5000–5600 Å, suggesting that it is composed of at least two components.
Pulse Radiolysis of Liquids at High Pressures. III. Hydrated-Electron Reactions Not Controlled by Diffusion
Authors: Hentz Robert R. , Farhataziz  , Hansen Earl M.
Published: February 2004

Specific rates of the reactions of eaq− with hydrogen ion, formamide, acetamide, acetoxime, benzyl alcohol, and 2-chloroethanol have been measured by pulse radiolysis at 29°C and six pressures from atmospheric to 6.4 kbar. The specific rates increase monotonically with increase in pressure to 6.4 kbar except that for the H3O+ reaction for which there is no further significant increase above ∼3.5 kbar. Results for the H3O+ reaction are consistent with that reaction not being diffusion controlled. The activation volume of each reaction increases with increase in pressure. Such a result is attributed to a decrease in cavity volume of the electron with increase in pressure. Activation volumes, in units of milliliters per mole, at 1 atm and 29°C are −2.7, −10.3, −7.0, −9.5, −9.3, and −8.2 for the reactions with H3O+, formamide, acetamide, acetoxime, benzyl alcohol, and 2-chloroethanol, respectively. Interpretation of the activation volumes gives a partial molal volume of 7 ml mole−1 and, with an electrostriction volume of 3 ml mole−1, a cavity volume of 10 ml mole−1 for the electron in water at 1 atm and 29°C. A previous estimate of V̄(eaq−) = 0 ml mole−1, based on study of competitive reactions of eaq− by γ radiolysis at high pressures, is reconciled with the value of V̄(eaq−) = 7 ml mole−1.
Influence of Attractive Forces on the Quantum-Mechanical Transition Probabilities for Atom-Diatomic Oscillator Collisions
Authors: Roberts R. E. , Diestler D. J.
Published: February 2004

Numerically exact quantum-mechanical transition probabilities for the collinear collision between an atom and a diatomic oscillator interacting via a strongly attractive Morse potential are compared with those obtained in various simple perturbation approximations. It is concluded that many of the improved perturbation approximations which work well for purely repulsive interactions are also quantitatively accurate for Morse interactions having deeply attractive wells. A simple distorted wave correction factor, derived, for example, via second-order perturbation theory, yields quite accurate transition probabilities, even for very small reduced collision energies (Ecoll/D=0.05) where attractive forces dominate in determining the dynamics of the collision. Furthermore, when the perturbation limit is no longer applicable, the so-called exponential approximation provides a viable method for calculating both direct and multiquantum transition probabilities.
Some Theoretical Results for the Photochemical Decomposition of Large Molecules
Authors: Kay Kenneth G. , Rice Stuart A.
Published: February 2004

The expressions describing photochemical dissociation derived by Rice, McLaughlin, and Jortner are evaluated analytically for molecules satisfying Γ ≫ ε (1+r) and for times t ≪ ℏ / ε, where Γ is the width of the initial state due to interaction with an intermediate manifold, ε is the level spacing of the manifold, and r is essentially the ratio of the manifold level widths to ε. Excitation is found to decay exponentially from the initial state with rate Γ / [(1+r) ℏ]. In contrast to the behavior originally perdicted, the decay is found to be nonsequential, and a constant ratio, equal to r, is maintained between the populations of the continuum and the manifold. The results should be applicable to large molecules having a single decomposition mode.
Lattice Model for Biaxial Liquid Crystals
Authors: Shih Chuen-Shyr , Alben Richard
Published: February 2004

The possibility that the repulsive interaction between platelike molecules might give rise to biaxial liquid crystal order is examined by considering a molecular-field lattice model in which molecules are represented by rectangular plates. We find that plates which are neither very square nor very rodlike in shape may exist in a phase characterized by biaxial long-range order in the orientation of the plates. This biaxial phase occurs at high pressure. At some lower pressure the biaxial phase undergoes a second order phase transition to a uniaxial phase. At a still lower pressure the uniaxial phase undergoes a transition to an isotropic phase. This last phase transition is usually first order in that there are discontinuities in the density and the orientational order in going through the transition. However the size of the discontinuities depend strongly on the shape of the plates. For example for plates of length 6 and width approximately 2.22 and thickness 1, the discontinuities are zero, and the transition is accidentally second order. The discontinuities at this uniaxial-isotropic transition are always very small for plates which have the potential to give rise to a biaxial phase. This last result is shown to have a direct physical basis which should transcend the limitations imposed by the approximate nature of our calculation. Thus we conclude that for real substances likely to have biaxial phases of the type we have studied, the value of the nematic order parameter at the nematic-isotropic transition should be much lower than for other nematic liquid crystals.
Vibrational Spectrum and Force Field of Xenon Tetroxide
Authors: McDowell Robin S. , Asprey Larned B.
Published: February 2004

Infrared and Raman spectra are reported for Xe16O4 and Xe18O4 vapor. The infrared band contours are analyzed to give values for the Coriolis constants and the xenon isotopic frequency shift, and anharmonicity corrections are estimated for the fundamental frequencies. General quadratic force constants are calculated, using as constraints the O16–18O and Xe129–132Xe frequency shifts and the Coriolis constants. The force field is significantly different from those of RuO4 and OsO4. Valence stretching force constants are fr=6.40 ± 0.10 mdyn/Å and frr=−0.08 ± 0.04 mdyn/Å; the negative value of the interaction constant frr indicates that the bonding differs appreciably from that in the transition metal tetroxides. Standard-state thermodynamic functions for XeO4 vapor are calculated for the temperature range 250–400°K.
Theoretical Interpretation of the Optical and Electron Scattering Spectra of Polyatomic Molecules. III. N2O and the Discovery of Resonant Phenomena in the B Region at 6.8 eV
Authors: Chutjian Ara , Segal Gerald A.
Published: February 2004

Energies and parts of potential surfaces are calculated for the first eleven excited electronic states of nitrous oxide; the states within ten electron volts of the ground state. The assignment of the energies and symmetries of these states which is carried out with the aid of semiempirical INDO calculations, is shown to be consistent with all available optical absorption spectra, electron scattering data, and with photolysis and photosensitization experiments. The weak, diffuse vibrational bands in the 6.8 eV B region have been interpreted as resonant interaction between the continuum levels of the 1 1II state and bound vibrational levels of the underlying 1Σ− state. The mixing is made electronically allowed through bending in the excited states. Supporting experimental and theoretical evidence for this assignment are given, and experiments are suggested to confirm several of the other assignments made.
Measurement of the Quadrupole Coupling Constant and Asymmetry Parameter of the Ring Deuterons in Several Deuterated Benzene Derivatives
Authors: Barnes R. G. , Bloom J. W.
Published: February 2004

Measurements are reported of the magnitude and asymmetry of the ring deuteron quadrupole coupling tensor in several simple deuterated benzene derivatives, i.e., benzene, toluene, ethylbenzene, as well as naphthalene, pyridine, and cyclohexane, using polycrystalline specimens at 77°K and in a magnetic field strength of 24 kOe. The e2qQ/h and η values obtained are: benzene, 180.7 ± 1.5 kHz, 0.041 ± 0.007; toluene, 179.9 ± 1.7 kHz, 0.056 ± 0.002; ethylbenzene, 177.8 ± 2.2 kHz, 0.063 ± 0.003; pyridine, 178.0 ± 1.2 kHz, 0.039 ± 0.006; cyclohexane, 173.7 ± 1.7 kHz, ≤ 0.01; naphthalene, 176.7 ± 1.5 kHz, 0.053 ± 0.005.
Formation of Calcium Ions by Charge Transfer
Authors: Rutherford J. A. , Mathis R. F. , Turner B. R. , Vroom D. A.
Published: February 2004

Charge transfer cross sections have been measured in the energy range from 1 to 500 eV for nine common atmospheric ions in collision with neutral calcium atoms. The ions studied are O+, N+, N2+, NO+, O2+, H2O+, H3O+, N2O+, and Ca+. In all cases the cross sections are found to be large indicating near resonant processes. Mechanisms consistent with this observation are given. Extrapolation of the measured cross sections to thermal energies has also been carried out.
Formation of Iron Ions by Charge Transfer
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2004

Reactions of iron atoms with common atmospheric ions have been studied in the energy range from 2 to 500 eV. The ions considered are H+, O+, N+, N2+, NO+, O2+, H2O+, and H3O+. With the exception of one proton transfer reaction, all of the processes studied involved charge transfer. All but one of the charge transfer reactions were found to have large cross sections over the total energy range and probably proceed by near resonant energy paths. Where possible the measured cross sections have been extrapolated to thermal energies.
Electron-Spin Resonance Studies of Crystal Field Parameters in Mn2+: LiNbO3
Authors: Rexford D. G. , Kim Y. M.
Published: February 2004

ESR studies were performed on a single crystal of ferroelectric LiNbO3 doped with manganese. Mn2+ in an axially symmetric site is described by the spin Hamiltonian [H=gβ H·S+B20D20+B40040+B43043+(B43043)*+AS·I]. Values for B43(B43=0, B43I=17 G) reported here, have not been reported previously. By examining the temperature dependence of B43 and B40 a value for the fractional change in the optical parameter Dq[(1/Dq)(∂Dq/∂T)=−3.5 × 10−3 °C−1] has been calculated. A discussion of the temperature dependence of B20 is also given.
Crossed Beam Collision Mechanics: Reactions of Ca, Sr, and Ba with HI and Limits on D° for CaI, SrI, and BaI
Authors: Mims Charles A. , Lin Shen-Maw , Herm Ronald R.
Published: February 2004

Angular distributions of MI (M=Ca, Sr, or Ba) products scattered from crossed beams of HI and M are reported and compared with derived expressions for the angular distributions of the velocities of the center-of-mass. These comparisons indicate that the reaction threshold relative kinetic energies, E*, are 5, 4, and 2.5 kcal/mole for the Ca, Sr, and Ba+HI reactions, respectively. Energy conservation and these measured E* values establish rigorous lower bounds for D0°(MI) of 64 (CaI), 65 (SrI), and 66 (BaI) kcal/mole.
Comparison of Calculated Chain-Length Dependence of the Anisotropy and Depolarization Ratio in n-Alkane Gases with Measurements of the Laser Light Scattering by Photon Counting
Authors: Aval Ghaffar M. , Rowell Robert L. , Barrett Joseph J.
Published: February 2004

Theoretical optical anisotropy and depolarization ratio calculations of n-alkanes are critically reviewed. New depolarization ratio measurements on gaseous n-alkanes are reported from a new method employing a continuously rotating analyzer, an argon ion laser, and photon counting electronics. The experimental and theoretical depolarization ratios are compared. The experiments show an increase of depolarization ratio with increasing number of C–C bonds in contrast to the theoretical results which show a general decrease of depolarization ratio. A new formula for depolarization ratio calculation of ethane which is a nonlinear symmetric top molecule is suggested. This formula reduces ethane's theoretical depolarization ratio by 25%. Our measurements suggest nonzero depolarization ratios for the spherical molecules methane and neopentane in contrast to the theoretical predictions. Possible sources of errors are discussed.
Son et Lumière or the Optoacoustic Effect in Multilevel Systems
Authors: Bauer Hans-Jörg
Published: February 2004

The theory of the periodically driven as well as of the pulse spectrophone is given for a gas with an arbitrary number of collisional excitation and de-excitation reactions. The basic kinetic quantities are the rate constants which provide the most simple means of comparison with other experimental methods. No use is made of the methods of irreversible thermodynamics, but the approach is closely related to that theoretical concept. A matrix notation is used throughout since it provides the least complicated expressions and so eliminates possible sources of algebraic errors as well as programming errors in the case of numerical evaluations. Compared to the two-level theory no additional assumptions are made. A link to the wealth of theoretical information available for the acoustic relaxation experiment is installed, especially for the case of mixtures of harmonic oscillators. The results are compared to those obtained by other means and examples are given.
Vibrational Relaxation of Hydrogen
Authors: Hopkins Barbara M. , Chen Hao-Lin
Published: February 2004

The rates of vibrational relaxation of D2 and HD have been studied by laser-induced vibrational fluorescence technique. The relaxation times of D2/HCl, HD/HCl, D2/H2/HCl, and D2/HD/HCl mixtures at 296°K show cross sections of V → T, R energy transfer as σD2–D2=1.4 ± 0.1 × 10−22 cm2,σD2–H2=1.4 ± 0.1 × 10−21 cm2,σD2–HD=8.2 ± 1.0 × 10−22 cm2,σHD–HD=6.9 ± 0.8 × 10−22 cm2,σHCl–D2=4.0 ± 0.4 × 10−21 cm2,σHCl–HD=1.7 ± 0.2 × 10−20 cm2.Cross section for V → V energy transfer from HCl to HD as σHCl–HDv → v=2.0 ± 0.2 × 10−20 cm2.Comparison of vibrational relaxation rates among hydrogen isotopes and direct correlation between high temperature shock tube results and room temperature data reveal the importance of both rotational and translational motion in the process of vibrational energy transfer of hydrogen.