bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Spectra of Os4+ in Single Cubic Crystals at 4.2°K
Authors: Dorain Paul B. , Patterson Howard H. , Jordan Peter C.
Published: February 2004

The optical spectra of Os4+ (5d4) in single cubic crystals of K2PtCl6, Cs2ZrCl6, Cs2HfCl6, and Rb2ZrCl6 at 4.2°K has been studied. The spectrum is characterized by very narrow lines in the region from 10 000–36 000 cm−1. Vibrational structure is observed which may be assigned to the ungerade modes of the OsCl62− complex in the lattice. A crystal-field analysis within the d4 manifold fits the observed ten electronic, 0–0 transitions with an rms deviation of 228 cm−1 for the parameters A = 0, B = 741, C = 1296, V = 22490, and λ5d = 2416 cm−1. The calculated molar magnetic susceptibility agrees with that found for concentrated crystals such as K2OsCl6 and Cs2OsCl6. The analysis of the electronic states was dependent upon a calculation of intensities for the t2g4 → t2g3eg transitions. The calculated results are given for a tetragonal distortion of the cubic field and are shown to qualitatively agree with the linewidth of the transitions. The calculated g values for all observed transitions are tabulated. Finally, several conclusions about the optical spectra of 5d systems are presented.
Intensities in Octahedral Complexes of 4d and 5d Transition-Metal Ions
Authors: Jordan Peter C. , Patterson Howard H. , Dorain Paul B.
Published: February 2004

The theory of the intensity of vibronically allowed electric dipole transitions for octahedral complexes is investigated. The calculation is carried out within the confines of ligand field theory and full account is taken of spin–orbit coupling. Of particular interest are those transitions which take place with a considerable change of internuclear configuration and which may be characterized as mainly involving a t2gn → t2gn−1eg transition. Certain selection rules are determined and an approximate two-parameter form is found for the intensity of the allowed transitions. This calculation is particularly useful as an aid in assigning transitions in regions where there are many possible states. Application is made to the low-temperature optical spectra of Os4+ and of Re4+ in single crystals of Cs2ZrCl6. The spectra of OsF6 are also discussed. Some predictions are made about the low-temperature optical spectra of W4+, Ir4+, and Pt4+ in single crystals of Cs2ZrCl6.
Variational Form of Van Vleck Degenerate Perturbation Theory with Particular Application to Electronic Structure Problems
Authors: Kirtman Bernard
Published: February 2004

The variational equivalent of Van Vleck degenerate perturbation theory is derived. As an example we treat the Stark effect for the 2s and 2p states of a hydrogenic atom. Other applications involving angular momentum degeneracy as well as electronic and nuclear permutation degeneracy are discussed. The existence of interchange theorems is also noted.
Interchange Theorems in Degenerate Perturbation Theory
Authors: Kirtman Bernard
Published: February 2004

We derive the equivalent of Dalgarno's interchange theorems for the case of exact or near degeneracy using Van Vleck perturbation theory. The application to excited states and to calculations based on our “distinguishable electron” method is discussed.
Triplet-Exciton Dynamics in Polyadenilic Acid
Authors: Sommer Bat-Sheva , Jortner Joshua
Published: February 2004

In this paper we present the results of a theoretical study of triplet exciton dynamics in single-strand polyadenilic acid. The triplet jump time was related to the intermolecular electron-exchange interactions, and to a semiempirical scattering time. Calculations of the intermolecular interactions were performed for five different structural models for the helical polymer. The theoretical results are consistent with the available experimental triplet energy-transfer data for this system, provided that the structure of single-strand polyadenilic acid is close to that of RNA 11. For this structural model the nearest-neighbor triplet-transfer integrals in polyadenilic acid are ∼ 0.5 cm−1, and the estimated triplet-exciton jump time is τj ∼ 10−9sec.
Hydrazine Decomposition in Glow Discharge
Authors: Logan E. F. , Marchello J. M.
Published: February 2004

Glow-discharge decomposition of pure hydrazine in a flow system was studied at an inlet temperature of 25°C for several currents and flow rates. The emission spectrum from 3000 to 6000 Å was observed. Stable products were analyzed using gas chromatography. An important characteristic of the decomposition is the observation of an initial threshold level of hydrazine decomposition. The principal feature of the proposed reaction mechanism is the use of competitive reactions involving the rupture of the N–H and N–N bonds.
ESR and ENDOR Studies of Ion Formation in X-Irradiated Thiodiglycollic Acid
Authors: Box Harold C. , Freund Harold G. , Budzinski Edwin E.
Published: February 2004

Single crystals of thiodiglycollic acid were irradiated at 4.2°K and examined by ESR and ENDOR spectroscopy. The paramagnetic absorption consists of two components which are attributed to positive and negative ions of thiodiglycollic acid. The negative ion is formed by electron attachment to an oxygen of the carboxyl group. The unpaired spin density is localized primarily on the carbon atom of the carboxyl group. The positive ion has its charge and unpaired spin density localized primarily on the sulfur atom.
Microwave Spectrum of Ethyl Isocyanide
Authors: Anderson Robert J. , Gwinn William D.
Published: February 2004

The microwave spectrum of ethyl isocyanide has been observed in the frequency range 8–36 GHz. The ground state and several excited vibrational states have been assigned. A small Coriolis effect is seen in two of the excited states. An upper limit on the quadrupole coupling constants of 0.5 MHz is determined. The dipole moment is found to be 4.01 ± 0.03 D. From splittings in the excited torsional state, the barrier to internal rotation is calculated to be 3650 cal/mole, and this is compared to the value for ethyl cyanide.
Crystal Field in Rare-Earth Trichlorides. III. Charge Penetration and Covalency Contributions in PrCl3
Authors: Ellis M. M. , Newman D. J.
Published: February 2004

Our previous calculation has been corrected by taking into account the electrostatic-charge-penetration contribution and extended by including the covalency contribution. These are particularly relevant in the calculation of the n = 6 parameters, which are now brought into reasonable agreement with experiment.
Geometry and Electronic Structure of Carbon Trioxide
Authors: Gimarc B. M. , Chou T. S.
Published: February 2004

The extended Hückel form of molecular-orbital theory, developed by Hoffmann, was used to calculate the molecular energy of CO3 in several different assumed geometries in an attempt to find the structure of lowest energy. Energy calculations were also carried out along assumed paths of dissociation of CO3 into CO+O2 and CO2+O fragments. Correlation diagrams showing how energy levels change with bond angle are given and discussed in relation to Walsh's rules for the geometry of AB3 type molecules. Results seem to favor a planar, isosceles triangular (C2υ) geometry for the structure of CO3.
Monte Carlo Study of Rings on the Tetrahedral Lattice
Authors: Kumbar Mahadevappa , Windwer Stanley
Published: February 2004

A Monte Carlo study of the configurational and statistical thermodynamic properties of ring systems generated on the tetrahedral lattice is presented. It is shown that the above parameters obtained are in close agreement with those found for open walks. It is suggested that a number of ratios of configurational parameters may be fruitful quantities for studying a variety of systems.
Ionic Conductivity in Single Crystals of Iodine: Ions in Iodine
Authors: Bargeman Derk , Kommandeur Jan
Published: February 2004

Doping of iodine single crystals with p-phenylenediamine (PPD) leads to paramagnetism and a considerable increase in the electrical conductivity of these crystals. From electron spin resonance (ESR) measurements on doped single crystals it follows that the paramagnetism results from the ionization of the PPD molecules. The concentration and temperature dependence of the ESR signal can be interpreted employing the theory of chemical equilibrium PPD+I2⇆PPD++I2−. The electrons donated to the lattice form I2− ions, which may move as ions through the lattice. The donor ionization energy of PPD is found to be 0.50 eV. The motion of the I2− ions does not lead to considerable conductivity. Two of these ions can cooperate, however, to form an I3− ion and an I− ion: 2I2−⇆I3−+I−. The I3− ion can be rapidly transported in a manner similar to the protons in ice I3−+I2→I2+I3−, while the I− ion formed stays behind in the hole left by the dissociated I2− ion. The rapid transfer process of the I3− ion leads to the conductivity in the iodine single crystals. The concentration and temperature dependence of this conductivity can be quantitatively understood on the basis of this mechanism. Plating and current-efficiency experiments have been carried out on polycrystalline samples of PPD-doped iodine to prove the ionic nature of the conductivity.
Solubility of Naphthalene in Compressed Ethane and Nitrous Oxide: The Correlation of Naphthalene–Gas Second Cross Virial Coefficients Using Pseudocritical Parameters
Authors: King A. D.
Published: February 2004

The solubility of naphthalene in compressed ethane and nitrous oxide has been measured over pressure ranges of 1–60 atm at temperatures ranging from 20°–68°C. Second cross virial coefficients representing naphthalene–gas pair interactions are evaluated from the data. It is shown that when allowance is made for the effect of quadrupole moment on the critical temperatures of quadrupolar gases, ordinary combining rules for pseudocritical parameters reduce naphthalene–gas cross virial coefficients involving five different gases to a single function of the reduced temperature. It is concluded from this that: (a) quadrupole–quadrupole interactions between naphthalene and quadrupolar gases are negligible in comparison to the dispersion forces involved; and (b) that equilibrium constants for formation of acid–base complexes of carbon dioxide and naphthalene are considerably smaller than thought previously.
Application of the Prigogine–Nicolis–Misguich Theory of Transport
Authors: Palyvos J. A. , Davis H. T. , Misguich J. , Nicolis G.
Published: February 2004

The transport theory of liquids presented by Prigogine, Nicolis, and Misguich (PNM) is compared to experiment. The theoretical formulas are written in reduced form and a generalized plot of the reduced shear viscosity is given. The truncated Lennard-Jones potential-energy model is used. The liquids studied are argon, krypton, and xenon. Along the vapor-pressure curve, the agreement between the observed and predicted temperature dependence of the shear viscosity is rather poor. In the same region agreement between the observed and predicted temperature dependence of the thermal conductivity and bulk viscosity is fairly good, although the available bulk-viscosity data are subject to rather large experimental uncertainties. The relative contributions of the strongly repulsive (hard-core) part and of the soft continuous (Lennard-Jones potential-energy) part of the molecular interactions are examined for the transport coefficients. It is observed that some of the computationally difficult terms are negligible. The PNM theory is compared to the Rice–Allnatt (RA) theory. It is concluded that where comparisons are possible the PNM theory agrees somewhat better with experiment than does the RA theory when the predictions of both theories are based on the same values for the pair-correlation function. An Erratum to a previous Note [J. Chem. Phys. 48, 951 (1968)] on the PNM theory is given in the Appendix.
Formaldehyde Molecule in a Gaussian Basis. One-Electron Properties
Authors: Dunning Thomas H. , Winter Nicholas W. , McKoy Vincent
Published: February 2004

Numerous one-electron properties of the formaldehyde molecule have been calculated using Hartree–Fock–Roothaan wavefunctions obtained from three different basis sets: an unoptimized minimum basis set of Slater orbitals, a (73 / 2) Gaussian basis set, and a (95 / 3) Gaussian basis set. Comparison of the calculated and experimental values is made whenever possible, the agreement in most cases being satisfactory. Use of the more flexible Gaussian wavefunctions results in significant improvements in many of the properties. Consideration of the atoms shows that no appreciable error arises from the use of Gaussian orbitals as expansion functions for the solution of the Hartree–Fock equations. Even though the best wavefunction is near the (sp) limit, some properties (such as the dipole moment and forces) are still inadequately described. Such a basis set is just not sufficient to describe the polarizations of the atoms caused by molecular formation. Inclusion of d orbitals in the basis set should substantially improve such properties.
Vibrational Dynamics in Liquid Water: A New Interpretation of the Infrared Spectrum of the Liquid
Authors: Schiffer J. , Hornig D. F.
Published: February 2004

In comparing the infrared spectra of liquid water and simple hydrates, two anomalies are noted which are apparently inexplicable in terms of presently acceptable theories of the liquid. These anomalies are explained in terms of a Maxwellian distribution of collisional interactions between water molecules, which when put in quantitative form reveals (1) that most molecules in the liquid are highly distorted by collisional perturbations, and (2) that there is a broad distribution of distortion among the molecules in the liquid. When translated into vibrational dynamics, these concepts lead to a continuum distribution of ν1 and ν3 modes of varying distorted molecules. It is shown that in its stretching motion, liquid water behaves dynamically as a continuum of OH bond oscillators of different frequencies, demonstrating both weak inter- and intramolecular vibrational interactions. A new interpretation of the infrared spectrum of liquid water is given in terms of this model, and other spectral evidence is offered in support of it.
Microwave Spectrum, Barrier to Internal Rotation, Structural Information, and Quadrupole Coupling of 1-Chloro-1,1-difluoroethane
Authors: Graner Georges , Thomas Clarence
Published: February 2004

The microwave spectra of two isotopic species, CH3–CF2 35Cl and CH3–CF2 37Cl, have been investigated in the region 8–40 GHz. A partial determination of structure strongly suggests a shortening in C–C, C–F, and C–Cl distances compared to singly or doubly substituted fluoro- or chloroethanes. Vibrationally excited states were observed showing doublets due to the hindered internal rotation of the methyl group. An analysis of these doublets gives a barrier to internal rotation of 4400 ± 100 cal/mole. The chlorine quadrupole coupling tensor is nearly symmetric about the C–Cl bond. This implies a pitfall in the application of simple resonance theory to molecules of this type; with simple resonance theory the shortened C–Cl bond is explained in terms of considerable double-bond character for the C–Cl bond, which in turn would call for an asymmetric χ tensor.
Chain Shortening in Polymethylene Liquids
Authors: Schaufele R. F.
Published: February 2004

The longitudinal accordion motion of polymethylene chains has been studied for n = 5–36 liquids and solids via laser-vibrational scattering. Unlike the fully extended, trans chains of the solids, the abundance of the trans conformation in the liquids is vanishingly small for n ≥ 9, in favor of chain shortened forms. This is indicated by the variation of the primary accordion mode frequencies, which approach a limiting value. A gradual intensity dimunition and broadening of the primary longitudinal band, accompanied by an increase of continuum intensity, with increasing n, indicates an approach towards conformational randomness.
Computation of Statistical Complexions by the Method of Steepest Descent
Authors: Tou James C. , Lin S. H.
Published: February 2004

The approach of the steepest descent method to the calculation of the totality of states is extended to the cases of a collection of harmonic oscillators coupled with rigid rotors, and of a collection of anharmonic oscillators. The equations derived are applied to a selected model and to cyclopropane.
Emission Spectra of S2−, Se2−, and SeS− Ions in KI Crystals
Authors: Rolfe J.
Published: February 2004

Luminescence emission measurements made at 4.2°K on KI crystals containing the ions S2−, Se2−, and SeS− revealed characteristic banded emission spectra similar to that of O2−, though both emission and excitation occur at longer wavelengths. The SeS− emission was always accompanied by S2− and Se2− emissions, so the emission spectrum was computed from three spectra obtained by excitation wavelengths favoring S2−, SeS−, and Se2− emission, respectively. From the detailed isotopic structure observed in all emission spectra, the ground-state vibration constants ωe″ and ωe″xe″ were calculated, and also values of ν00, the origin of the vibrational band system.
Calculation of Matrix Elements for One-Dimensional Quantum-Mechanical Problems
Authors: Dickinson A. S. , Certain P. R.
Published: February 2004

A simple method proposed by Harris et al. using the techniques of transformation theory for the generation of the matrix elements of one-dimensional potential functions in a discrete, orthonormal basis is shown to be equivalent to Gaussian quadratures when the basis is constructed of orthogonal polynomials. The basis exp(inθ) on (− π, π) is also discussed.
Stress–Optical Coefficient of Polyethylene Networks
Authors: Nagai Kazuo
Published: February 2004

The stress–optical coefficient of polyethylene networks is calculated on the basis of a theory previously developed, and results are compared with experimental data recently reported by Gent and Vickroy. Observed temperature coefficients of ΔΓ, the optical anisotropy of Kuhn's random link (an equivalent to the stress–optical coefficient) for unswollen samples, are much larger than those calculated using acceptable values of EG, the energy of the gauche conformation, relative to that of the trans. It is concluded that observed temperature coefficients should include some contributions other than those implied in the theory, i.e., those arising from the conformational change with temperature. Data on samples swollen in decalin (about half those for unswollen samples) are better fitted with the theory, yielding values of the effective C–C bond anisotropy, Δαe = (α1 − α2)C–C − 2(α1 − α2)C–H, in satisfactory agreement with those from other sources. Here, α1 − α2 is the anisotropic bond polarizability. The short-range orientational order among polymer-chain segments in concentrated solutions and in the molten state is proposed to be a mechanism responsible for the abnormally large ΔΓ and its temperature coefficient observed for unswollen samples. The author's previous view supporting Denbigh's bond polarizabilities is abandoned. The possibility of negative Δαe, recently suggested by Murrell and Musgrave, is denied.
Vibrational Bending and Stretching Frequencies for C4, C5 and C6
Authors: Sanborn Russell H.
Published: February 2004

A correlation of electronic structure, developed from molecular-orbital considerations, with bending force constants for 15 linear molecular species containing carbon, nitrogen, and oxygen has produced estimates for the average bending force constants of C4, C5 and C6. These force constants are used to estimate a set of vibrational energy levels for each species to be used in calculations of the thermodynamic functions.
Formation of the Triplet State of Naphthalene in the Pulse Radiolysis of Gaseous Mixtures of Benzene and Naphthalene
Authors: Nishikawa Masaru , Sauer Myran C.
Published: February 2004

A significant yield of the lowest triplet state of naphthalene is observed when 1.9 atm benzene containing small amounts of naphthalene is pulse irradiated in the gas phase at 120°C. The yield is independent of naphthalene concentration from 0.3 mole % to at least 3 mole %. Electron scavengers (SF6 and CCl4) decrease the yield by 70%, as does a positive-ion scavenger, triethylamine. This 70% is thought to originate by neutralization of C10H8+ by C10H8−. The other 30% of the triplet yield is thought to originate from benzene (3B1u) formed directly by the irradiation of the benzene vapor. Naphthalene was found to be 34 ± 4, 38 ± 4, and 18 ± 2 times more efficient in accepting energy from the benzene triplet than trans-butene-2, cyclohexene, and nitromethane, respectively. Similar results were obtained using 1.3 atm argon as the main gas, with about 3 mole % benzene and about 3 × 10−3 mole % naphthalene present at 25°C. In this case, the naphthalene triplet was formed after the pulse, and kinetic analyses of the curves as a function of naphthalene concentration allowed an evaluation of the benzene (3B1u) decay constant of 1.3 × 105 sec−1 at 18 torr benzene (which decreases with increasing benzene pressure) and of the rate constant for energy transfer from benzene (3B1u) to naphthalene of (3.0 ± 0.5) × 1011 liter mole−1·sec−1. Naphthalene was found to be 20 ± 3 times more efficient than trans-butene-2 in accepting energy from triplet benzene.
Vibrational Bandwidths in Liquid Water
Authors: Wall Theodore T.
Published: February 2004

The Raman stretching bands of HDO in liquid water are Fourier transformed to a time axis and it is concluded that both hindered rotatory and hindered translatory motions play a role in giving these bands the observed width. Long time diffusions are not evident in the transformed spectral functions.
Vacuum-Ultraviolet Photolysis of N2O. IV. Deactivation of N(2D)
Authors: Black G. , Slanger T. G. , St. John G. A. , Young R. A.
Published: February 2004

The NO(β) emission (B 2II→X 2II) observed during photolysis of N2O at 1470 Å is due to a chemiluminescent reaction between N(2D) and N2O. Transient measurements of this emission are analyzed to give the rate coefficients for removal of N(2D) by several simple molecules. Photolysis at 1236 Å also produces NO(B 2Π), and the decay curves can be analyzed to give the same rate coefficients as observed at 1470 Å, although there is evidence that an additional NO(B 2Π) production mechanism is involved. Quenching coefficients are also tabulated for N2(A 3Σ) and O(1S), two other species investigated by the same technique.
Crystal-Field-Induced Configuration Interaction in the Configuration (l1 + l2)n
Authors: Armstrong Lloyd
Published: February 2004

Effective operators are obtained which reproduce, to second order in perturbation theory, the effects of crystal-field-induced configuration interaction on the energy levels of the configuration (l1 + l2)n. Techniques of second quantization are used to carry out the calculation. Many effects of the configuration interaction are found to be absorbed by the first-order crystal-field terms. The results are discussed in relation to similar calculations made of the structure of the configuration ln by Rajnak and Wybourne.
Magnetoviscosity of Magnetic Colloids
Authors: McTague John P.
Published: February 2004

We have observed that the viscosity of a dilute (≈ 1015 particles cm−3) colloidal suspension of single domain ferromagnetic particles is a marked function of both the magnitude and direction of an externally applied magnetic field. For particles with dimensions of a few hundred angstroms, the viscosity saturates in a field of order 1 kG. The additional viscosity is greater by a factor of 2 for the field parallel to the flow than with it perpendicular. This magnetoviscous effect is qualitatively accounted for by the hindrance to particle rotation caused by the magnetic torque.
Viscosity of Magnetic Suspensions
Authors: Hall W. F. , Busenberg S. N.
Published: February 2004

The effect of an external magnetic field on the viscosity of a dilute suspension of magnetized particles is calculated to first order in the volume fraction of solution occupied by the particles. The steady-state motion of the particles under the influence of the external field is derived through an unusual application of Stokes' theorem to the equations of motion.
New Method for Constructing Wavefunctions for Bound States and Scattering
Authors: Gordon Roy G.
Published: February 2004

A new method is developed for integrating coupled differential equations arising in bound state and scattering problems in quantum mechanics. The wavefunctions are easily constructed in piecewise analytic form, to any prescribed accuracy.
Proton Pseudopotential Form Factor
Authors: Phillips J. C. , Pollack R.
Published: February 2004

Dielectric screening theory is used to discuss the ion core form factor of a proton. The Coulomb potential is too strong near r = 0 to be treated by dielectric techniques, but a pseudopotential can be constructed which is finite at r = 0. This form factor can be used to construct electromechanical molecular models.
Substitutional Diffusion in an Ordered System
Authors: Kikuchi Ryoichi , Sato Hiroshi
Published: February 2004

A general treatment of the atomic diffusion in alloys is given using the path probability method with an approximation taking a pair of lattice points as the basic cluster. Diffusion coefficients for ternary alloys for any degree of order by vacancy mechanism are given. The equations are then simplified by regarding the third atomic species as the isotope of the second atomic species. The theory then gives the isotope diffusion coefficient in binary alloys as functions of the degree of order and of the composition; this diffusion coefficient corresponds directly to the experimental results, and they are compared. The specific importance of the correlation effect in the multicomponent system is emphasized. The calculation of the required physical quantities, the degree of long-range order, short-range order, the distribution of the vacancies, etc., in the equilibrium state in ternary alloys with vacancies are also given in the Appendices.
Electronic Structure and Geometry of NO2+ and NO2−
Authors: Pfeiffer Gary V. , Allen Leland C.
Published: February 2004

The electronic structure of NO2+ and NO2− has been investigated as a function of angle by means of ab initio MO LCAO SCF wavefunctions. Atomic orbitals used in the basis set are close to free-atom Hartree–Fock solutions. Several excited states, in addition to the ground states, have been obtained for the two ions. Total energies, population analyses, and one-electron orbital energies vs angle (Walsh diagrams) have been computed to aid interpretation of the wavefunctions. It turns out that the dramatic change in geometry from NO2+ (linear) to NO2− (bent, 115.4°) can be understood by the occupancy and shape of a single orbital, the 6a1 in NO2−. Our results contribute to the establishment of a firm mathematical and numerical foundation of Walsh's rules and diagrams. The present calculations also serve to substantiate and extend previous wavefunctions for these important chemical species.
Information on the Exciton Band Structure of the 1B2u State of Crystalline Naphthalene from the Variation of Energy Denominators Method
Authors: Hanson D. M. , Kopelman R. , Robinson G. W.
Published: February 2004

Perturbation shifts of guest levels in isotopic mixed crystals of naphthalene have been determined. These data verify that the density function for exciton states is almost symmetric over the entire exciton band of the first singlet state. This result agrees with the entire band structure as observed in band-to-band transitions and disagrees with the band structure calculated from the octopole model for the inter-molecular interaction. The transition energies of guest levels also disagree with a model for the exciton splitting involving configuration interaction with charge transfer states. A possible source of the exciton splitting is suggested, and the available data for evaluating theoretical descriptions are outlined.
Translational Diffusion Constant of a Random Coil
Authors: Broersma Sybrand
Published: February 2004

The translational diffusion constant D for a random coil (or thread) of length L, wire diameter d, and end-to-end distance R (rms) is given by D = (kT / 3πη0L)[log(A / d) + 2(8 / 3π)1/2(L / A)1/2 − 1.0], where A = R2 / L. The diffusion constant for a coil subject to internal repulsive forces has also been calculated from its geometry.
Energy Surface and Generalized Oscillator Strength of the A″1 Rydberg State of H2O
Authors: Miller K. J. , Mielczarek S. R. , Krauss M.
Published: February 2004

The energies and wavefunctions of the lowest singlet and triplet Rybderg states in H2O were calculated in the expansion basis self-consistent-field procedure for a single configuration. A portion of the energy surface of the A″1 Rydberg state for an HOH angle of 105° was determined that shows the asymmetric dissociation of this state into ground-state H(2S) and OH(2Π) fragments. The energy along the reaction coordinate is almost separable into a repulsion depending only on the center-of-mass separation and an attractive potential that depends only on the OH internuclear separation. For the C2υ conformation a large basis set was used to approach the Hartree–Fock limit. Using these functions a minimum was calculated in the generalized oscillator strength for the A11→B11 transition as a function of the momentum transfer function or the electron scattering angle. This behavior was then confirmed experimentally for an energy loss of 7.4 eV with an incident electron energy of 500 eV. Such a minimum is a general characteristic of Rydberg transitions and is not an essentially molecular phenomena. The good agreement between experiment and theory indicates a reasonable fit to the Rydberg wavefunction by the approximate Hartree–Fock calculation.
Vibrational Spectra and Structure of S4N4 and S2N2
Authors: Bragin J. , Evans M. V.
Published: February 2004

The infrared spectrum of solid S4N4 has been recorded to a low-frequency limit of 50 cm−1, the Raman spectrum re-examined, and depolarization ratios of the most intense spectral lines obtained. The 12 observed vibrational fundamentals of tetrasulfur tetranitride have been fit by means of a valence force field in which 10 independent parameters were adjusted. The calculated frequencies are in good agreement with the experimental data and a complete vibrational assignment is proposed based in part on the results of the computations. A discussion of the computed potential field in relation to the molecular structure of S4N4 is included. The infrared spectrum of solid S2N2 at − 80°C has been obtained to a low-frequency limit of 50 cm−1. Five vibrational frequencies have been observed. The molecule was subjected to vibrational analysis based on D2h symmetry. The results of the computations were used in assigning five vibrational fundamentals.
Some Diabatic (Quasistationary) States of Small Diatomic Systems—Projected Atomic Orbitals
Authors: O'Malley Thomas F.
Published: February 2004

It has been recognized, both from experiment and from theory, that the diatomic potential curves followed by colliding atoms are frequently not those of the conventional stationary adiabatic states. The actual states, which have been named “diabatic,” are most easily understood as adiabatic states which are quasistationary rather than stationary. In the work reported here, several methods (those of Holoeien, Lipsky–Russek, and Feshbach), which were developed for atoms, are applied in an exploratory manner to calculate quasistationary electronic states of some small diatomic systems. The potential-energy curves calculated are those for H2(1Σg,u) and also HeH+(1Σ), He2+(2Σg), and He2(3Πu). It was found that the method of Holoeien and of Lipsky and Russek, when applied to molecules, gave results which were satisfactory and physical for all R's, and generally superior to that of Feshbach. A new and simpler method, using projected atomic orbitals in a valence-bond wavefunction, was also developed. Aside from their direct usefulness for simple processes such as differential elastic scattering and symmetric charge transfer (a numerical application is made to double charge transfer in H–H+ collisions), these diabatic states each form the nucleus of a quasiadiabatic representation of the electronic Hamiltonian, from which inelastic, charge-changing, and rearrangement collisions involving these systems can be calculated most directly and precisely.
Effect of Deuteration on the Fluorescent Lifetime of Liquid Benzene
Authors: Helman W. P.
Published: February 2004

Decay times of neat benzene C6H6 and C6D6 fluorescence excited by 250-nm light are, respectively, 27 and 32 nsec at 25°C. Measurements made over the range of temperature 5°–35°C both of the pure benzenes and of solutions in cyclohexanes C6H12 and C6D12 show that the solvent is without effect on the measured rates, that at a particular temperature benzene monomer and excimer have the same rate of de-excitation (corresponding to lifetimes of 28 nsec for C6H6 at 25°C and 33 nsec for C6D6 at 22°C), and that the activation energy for internal conversion of monomer in both cases (on certain stipulated assumptions) is 0.28 eV within limits of experimental error. The reduction, by deuterium substitution, in the rate of de-excitation from the monomer is less than the reduction in the rate from excimer and the rate for benzene excimer is indicated to be independent of temperature in the range studied.
Analysis of The Most Probable Path Description of Irreversible Processes
Authors: Wilson Hugh R. , Rice Stuart A.
Published: February 2004

The Kikuchi path probability method in irreversible statistical mechanics is examined in order to determine its relation to a quantum-mechanical description of irreversible processes. This is accomplished by exhibiting the connection between the Kikuchi theory and the Van Hove form of the master equation. The most probable path assumption, central to Kikuchi's work, is then analyzed and its range of validity discussed.
Conductivity and Mössbauer Measurements in Doped Ice
Authors: Pelah I. , Ruby S. L.
Published: February 2004

Measurements have been made on the recoilless (NGR) absorption of Sn4+ ions in 0.2M SnCl4 frozen aqueous solutions (FAS) as a function of time and temperature. These reproduce most of the effects, including the anomalous transient disappearance of the Mössbauer effect, seen by previous workers using Fe2+ and Fe3+ ions in FAS. The electrical conductivity of the SnCl4 FAS was also measured, and found to “follow” the NGR results very closely, despite the great differences in the fundamental mechanisms of these two phenomenon. There is evidence for melting of part of the FAS above 200°K.
Chlorine Nuclear Quadrupole Resonance in ErCl3 and Some Similar Chlorides
Authors: Carlson E. H. , Adams H. S.
Published: February 2004

In ErCl3 at 4.2°K the 35Cl NQR frequencies are 4.4566 ± 0.0002 and 4.5157 ± 0.0002 MHz and the asymmetry parameters η are 0.53 ± 0.02 and 0.52 ± 0.03 for the eightfold and fourfold sites, respectively. The electric field gradient xx principal axis at each site is within 4° of the bisector of the Er–Cl–Er angle. The above results are analyzed in a “bond-switching” scheme. We report also the 35Cl NQR frequencies in the trichlorides of Y, Dy, Ho, Tm, Yb, La, and U. The adequacy of the point-change model as the primary source of the electric field gradient in these ionic crystals is tested.
Energy Dependence of the Elastic Total Collision Cross Section of Identical Molecules: 4He
Authors: Dondi M. G. , Scoles G. , Torello F. , Pauly H.
Published: February 2004

The velocity dependence of the total collision cross section for velocity-selected molecular beams of 4He scattered by 4He at 2°K has been measured. Undulations due to the quantum statistics have been resolved between 650 and 1200 m sec−1. Results are compared with exact and approximate calculations and the sensitivity of this effect to potential parameters is discussed. Finally we show the possibility to extract from the data the absolute value of the total collision cross section independently from scattering centers density measurements.
Optimized Gaussian Basis SCF Wavefunctions for First-Row Atoms
Authors: Whitman Donald R. , Hornback Charles J.
Published: February 2004

Optimum atomic Gaussian-type-function bases for self-consistent-field calculations are reported for B, C, N, O, and F, with from two to eight s functions and from one to four p functions. Orbital energies and coefficients are presented for the (3s1p), (5s2p), and (7s3p) bases for each atom, and the functions are shown to yield lower atomic energies than previously proposed Gaussian bases of the same size.
Microwave Spectrum of 2-Methylfuran
Authors: Norris Wilfred G. , Krisher Lawrence C.
Published: February 2004

The pure rotational spectrum of 2-methylfuran has been measured in the range 12 000–33 000 MHz. Analysis, using a fourth-order perturbation treatment, of internal rotation A–E doublet splittings gives a barrier of 1190 cal/mole. The spectrum for an excited vibrational state has been assigned, and exhibits essentially the same internal barrier.
Theory of a Helix-to-Coil Transition in a Triple-Stranded Macromolecule
Authors: Goldstein Byron , DeLisi Charles
Published: February 2004

The theory of the helix-to-coil transition for a triple-stranded macromolecule in solution is discussed for the case in which the triple helix “melts” directly into three single strands. Assumptions are made which permit the use of the method of sequence generating functions for the three-stranded case. The ring weighting function is derived and a secular equation for the partition function is obtained. The fraction of bonds intact as a function of temperature is then calculated. The results are compared to available experimental data.
Proton Magnetic Resonance Studies of Methanol Solutions of Mn2+, Cu2+, Fe2+, and Fe3+
Authors: Breivogel F. W.
Published: February 2004

The transverse relaxation times have been measured for the solvent protons in methanol solutions of Mn2+, Cu2+, Fe2+, and Fe3+. From the temperature dependence of the relaxation times the rates and activation parameters have been determined for the exchange of solvent molecules between the first coordination sphere of the metal ion and the bulk solvent. The kinetic parameters k1 (seconds−1 at 25°C), ΔH† (kilocalories), and ΔS† (entropy units) are 3.7 × 105, 6.2, and − 12 for Mn2+; 108, 10, and 13 for Cu2+; 5.0 × 104, 12.0, and 3 for Fe2+; and 5.1 × 103, 10.1, and − 8 for Fe3+. A coordination number of 6 was assumed in making the calculations. For all of the divalent ions the OH and CH3 protons exchanged at the same rate. For the divalent metal-ion complexes the contact shifts were measured and discussed in terms of the electron delocalization mechanisms.
Optical and Photoelectron Spectra of Small Rings. III. The Saturated Three-Membered Rings
Authors: Basch Harold , Robin M. B. , Kuebler N. A. , Baker Clive , Turner D. W.
Published: February 2004

The electronic states of cyclopropane, ethylene oxide, ethylenimine, and diaziridine were investigated using gas-phase and condensed-phase vacuum ultraviolet spectroscopy, photoelectron spectroscopy, and Gaussian orbital self-consistent field calculations. Correlation of the gas-phase and condensed-phase optical spectra of cyclopropane with the first band in its photoelectron spectrum confirms the presence of Rydberg transitions in the optical spectrum involving excitation of an electron from the 3e′ sigma level. The valence shell spectrum of cyclopropane is complex but is dominated by two very strong A11′ → 1E′, σ → σ*, excitations. The Rydberg spectrum of ethylene oxide is reassigned to include the two absorptions in the 55 000–65 000-cm−1 region, all bands originating from the 2b2π orbital, while its valence shell spectrum is closely related to that of cyclopropane. Similar but less conclusive results were obtained for ethylenimine. Virtual orbital calculations of σ → σ* excitation energies gave results uniformly too high by about 3 eV, but calculated dipole velocity oscillator strengths seem to agree closely with experiment. Comparison of photoelectron spectra and the Koopmans' theorem ionization potentials of the first six levels of the three-membered rings showed that the calculated values are too high by 8% and that reorganization and correlation energy corrections improve the agreement markedly.
Isotopic Exchange between Oxygen and Carbon Monoxide in Shock Waves
Authors: Garnett S. H. , Kistiakowsky G. B. , O'Grady B. V.
Published: February 2004

The isotopic exchange reaction between 18O2 and CO has been studied in a shock tube coupled to a time-of-flight mass spectrometer, over the temperature range 1700°–2600°K, using very dilute CO+O2 mixtures in neon. The rate is found to increase with time. Auxiliary studies of the 16O2–18O2 exchange reaction and of the 18O2–C16O exchange reaction induced by nitrous oxide pyrolysis have demonstrated that this exchange occurs via an atomic mechanism. The rates of O-atom attack on O2 and CO are found to be almost equal over the temperature range studied. Using the known rate of N2O decomposition, at 1820°K the calculated rate constants for these two reactions are 11. × 10−12 and 6.6 × 10−12 cm3/molecule·sec, respectively, in excellent agreement with the extrapolations of the low-temperature values in the literature. The reaction producing O atoms in the absence of N2O is equal order in both O2 and CO but the over-all order is uncertain. The observed activation energy of the initiation process is less than that suggested in the literature. Oxygen-atom concentrations which are a factor of 30 greater than calculated from the literature values of the rate coefficients of the reaction CO+O2→CO2+O indicate that some chain multiplication process, possibly involving trace impurities, is occuring.
Vibrational Energy Distribution through Chemical Laser Studies. I. Fluorine Atoms plus Hydrogen or Methane
Authors: Parker John H. , Pimentel George C.
Published: February 2004

A new method is described for determining the energy distribution among the product vibrational energy levels in an exothermic reaction. By careful control of the rotational temperature in the UF6–H2(D2) and UF6–CH4(CD4) chemical laser systems, one can obtain conditions for which two hydrogen fluoride vibration–rotation transitions initiate simultaneously and with the same gain. From the relationship between relative gain, rotational temperature, and the vibrational populations, an accurate value can be determined for the ratio of the populations Nυ / Nυ−1 of the two states involved in the first transition to reach laser threshold. This ratio equals kυ/kυ−1 after vibrational deactivation has been taken into account. This technique has yielded the following rate-constant ratios:F + H2→limυHFυ† + H, k2 / k1∼5.5 F + D2→limυDFυ† + D, k3 / k2∼1.6. The significant observations are that the rate-constant ratios are all above unity, the hydrogen and methane values are very close to each other, and the DF ratios are much closer to unity than their HF counterparts.
Raman Studies of Molecular Motion in Condensed Oxygen
Authors: Cahill J. E. , Leroi G. E.
Published: February 2004

Raman scattering has been observed from both the external and internal motions of the molecules in each of the four condensed phases of oxygen. The stretching vibration gives rise to a sharp band at 1552.5 cm−1 in each phase. Weak wings occur at the base of this band in the γ and liquid phases. Librational lattice modes are observed at 44 and 79 cm−1 in the α phase and at ∼ 50 cm−1 in the β phase. The intensities of these bands relative to that of the internal fundamental are in reasonable agreement with those expected from the oriented gas model. In γ- and liquid oxygen, the external motion gives rise to strong wings on the Rayleigh line. Estimates of the mean-square torsional amplitude and the torque acting on the molecule have been made from the observed low-frequency spectra, and indicate that the torsional motion is highly hindered in each phase. The root-mean-square torsional amplitude increases from an average of 9° in the α phase to 18° in the liquid.
Matrix Isolation Studies of Group-IV Oxides. I. Infrared Spectra and Structures of SiO, Si2O2, and Si3O3
Authors: Anderson J. S. , Ogden J. S.
Published: February 2004

The matrix isolation of silicon monoxide vapor leads to the formation of at least three distinct species: SiO, Si2O2, and Si3O3. Infrared absorptions for these molecules are observed at 1223.9 cm−1 (Si16O); 804.7, 766.3 cm−1 (Si216O2); 972.6, 631.5, 312.0 cm−1 (Si316O3). Equations are given for the in-plane vibrations of the X2Y2(Vh) ring and the X3Y3(D3h) ring, and using 18O substitution, it is shown that these respective models account for the observed ir absorptions of Si2O2 and Si3O3. Estimates are given for the molecular dimensions of Si2O2 (rSi–O = 1.71 Å, ∠OSiO = 87°) and Si3O3 (RSi–O = 1.70 Å, ∠OSiO = 100°), and for their unobserved vibration frequencies. The reaction SiO + Si2O2 → Si3O3 is observed during diffusion studies, and a lower limit obtained for the mean bond energy in Si3O3 of ∼104 kcal/mole.
Polarized Crystal Spectra of CoF2 and Co0.06Zn0.94F2
Authors: Zimring Lois Jacobs , Stout J. W.
Published: February 2004

Polarized spectra of oriented single-crystal CoF2 and Co0.06Zn0.94F2 are presented in the range 5000–25 000 cm−1 at 298, 77, and 20.4°K. Molar extinction coefficients and oscillator strengths are calculated. The spectra of CoF2 and of dilute Co2+ in ZnF2 are very similar. The principal bands are identified as transitions from the T1g4 (4F) ground level to T2g4 (4F), A2g4 (4F), and T1g4 (4P) levels. A value of Dq = 715 cm−1 is obtained. A sharp electric dipole line, 10 cm−1 wide, is seen at 22 768 cm−1 in CoF2 at 20.4°K.
Hydrogen Bond Studies. XXXVII. The Crystal Structure of Sulfuric Acid Dihydrate (H3O+)2SO42−
Authors: Taesler Inger , Olovsson Ivar
Published: February 2004

The crystal structure of H2SO4·2H2O has been determined from three-dimensional single-crystal x-ray data recorded at −190°C. The crystals are monoclinic, space group C2 / c, with 12 formula units in a cell with the dimensions: a = 13.008, b = 7.979, c = 14.881, and β = 101.60°. The structure consists of H3O+ and SO42− ions. Each of the three independent H3O+ ions is hydrogen bonded to three different SO42− ions (0···0 distances, 2.520–2.590 Å) is such a way that a three-dimensional hydrogen-bond pattern is formed. The average S–O distance in the sulfate ion is 1.474 Å.
Two-Channel Model for Electron Transfer in Ion–Molecule Collisions
Authors: North G. R. , Leventhal J. J.
Published: February 2004

A phenomenological model based on competition between charge-transfer and atomic-rearrangement (chemical reaction) channels is used to calculate the charge exchange cross section for Ar+–H2 collisions below 1000 eV. The energy dependence of the calculated cross section is in good agreement with recent data.
Solvation of the Titanous Ion in Aqueous and Methanol Solutions
Authors: Chmelnick A. M. , Fiat D.
Published: February 2004

The solvation of the titanous ion in aqueous and methanol solutions has been studied by means of proton, deuteron, and oxygen-17 magnetic resonance. Kinetic parameters for the exchange reaction of the solvent molecules between the coordination sphere and the bulk, hyperfine coupling constants, and relaxation times of the unpaired electron of the titanous ion have been determined. Attempts to interpret the results in view of the uniqueness of the titanous ion among the ions of the first transition-metal series have also been made.