bluuebunny/crossref_metadata_2025 huggingface dataset:
Germanium-Hydrogen-Lithium Center in α-Quartz
Authors: Weil John A.
Published: February 2004

A new center, denoted by GeHLi2, has been observed by EPR to be present in alpha-quartz containing germanium, after room temperature x irradiation. The spin Hamiltonian at 8909 MHz and 300°K has been measured, yielding the Zeeman splitting tensor ḡ and the hyperfine coupling tensors Ā (73Ge), Ā (1H), Ā (7Li1), and Ā (7Li2). From the principal values and axis directions, a model for the center of the form Ge3+H−(Li+)2 has been derived. This postulates germanium to be present substitutionally at a silicon site, with the hydride and two lithium ions occurring interstitially nearby. The unpaired electron is thought to be in a Ge orbital a(4s) + b(4p), with |a|2∼ 0.18 and |b|2 ∼ 0.35, with considerable spin density also at the hydrogen. The center may be formed from a diamagnetic precursor Ge2+(Li+)2 by reaction with a hydrogen atom.
Approximate Numerical Hartree—Fock Method for Molecular Calculations
Authors: Schwarz Karlheinz , Connolly John W. D.
Published: February 2004

Calculations are presented which show that the atomic orbitals which result from approximate numerical Hartree—Fock calculations (by the Xα method) are as close to the Hartree—Fock limit for atoms as are those calculated using a double-zeta basis. Arguments are given which show that the exchange is treated with sufficient accuracy by the Xα method. With the additional ``muffin-tin'' approximation, which is widely used in solid state calculations, the ``multiple scattering'' formalism can be used for molecules to solve this model Hamiltonian without any further approximation. The exchange is treated with sufficient accuracy, therefore this approach should give the electronic energies as well as the usual type of ab initio calculation, whenever the ``muffin-tin'' approximation is good, but with 2 or 3 orders of magnitude less computational time.
Spin—Spin Coupling in Magnetically Condensed Complexes. XII. The Ground State of Tetrakis (N, N′-dimethylglyoximato) dicopper (II)
Authors: Villa Juan F. , Hatfield William E.
Published: February 2004

The ground state of tetrakis (N, N′-dimethylglyoximato) dicopper (II) is shown to be of triplet multiplicity with the first excited state being a singlet, at 29.8 cm−1 higher in energy. EPR measurements confirm the existence of spin—spin interactions, and a value of D=0.0340 cm−1 was obtained from the half-field line, Hmin. The other g values obtained from the triplet state spectra were g∥ = 2.155, g⊥ = 2.122 and (g) = 2.134. Cryomagnetic measurements in the low-temperature range (4.2–55°K) in conjunction with a best fitting procedure yielded the following values for the magnetic parameters: 〈 g 〉 = 2.157, 2J = + 29.8 cm−1 and θ = −1.45°K. A superexchange mechanism via the σ orbitals of the –N–O– bridge is proposed to account for the experimental findings. This mechanism includes both intra-atomic direct exchange and interatomic electron transfer.
Low-Frequency Vibrational Light Scattering in Viscous Liquids
Authors: Shuker Reuben , Gammon Robert W.
Published: February 2004

The theory of Raman scattering from the vibrations of amorphous materials is applied to the spectra of B2O3 glass and its melt. Experimental evidence is obtained indicating that low frequency scattering in the melt liquid is also due to first order scattering from intermolecular vibrational states. The relationship among several scattering mechanisms in liquids is discussed.
Variational Methods in the Wave Operator Formalism. A Unified Treatment for Bound and Quasibound Electronic and Molecular States
Authors: Micha David A. , Brändas Erkki
Published: February 2004

The wave operator formalism of Löwdin, heretofore used to describe states belonging to the discrete energy spectrum, has been extended to unify the treatment of bound and quasibound (or decaying) states. The approach makes use of an arbitrary reference function that may be chosen to approximate the physical state at short distances. Real and complex eigenvalues are obtained, respectively, for bound and quasibound states from an implicit equation, valid for all coupling strengths. Resonance positions and linewidths are explicitly independent of energy. Variational principles of the Lippmann—Schwinger type are presented which apply to states with either bound-state or decay boundary conditions. Particular cases leading to minimization or maximization principles for real energies are discussed. The formalism is considered in connection with decaying electronic states of atoms and decaying molecular states.
On a Generalized Einstein Theory for the Thermodynamics of Planar Surfaces and Microcrystallites
Authors: Abraham Farid F. , Dave J. V.
Published: February 2004

We present a generalized Einstein theory to predict the thermodynamic properties of planar surfaces and microcrystallites which Nishioka et al. have obtained from numerical normal mode calculations. An important aspect of our model is that it identifies the important physical features governing the structure of the vibrational free energy as a function of microcrystallite size.
Efficient Monte Carlo Generation of Self-Avoiding Polymers
Authors: Jurs Peter C. , Reissner John E.
Published: February 2004

A new method for generating self-avoiding random polymers is described. Utilization of this method makes the total time spent on double occupancy checking during the development of a self-avoiding polymer, in principle, only linearly dependent on the length. To test the method, self-avoiding polymers of 14 to 200 bonds have been developed on the tetrahedral lattice by Monte Carlo techniques. Properties of the distribution of polymers obtained are presented, and these properties are shown to be consistent with previously reported results.
Cellular Method and the Calculation of Molecular Wavefunctions. II. Application to the Alkali Molecules
Authors: Fricker H. S.
Published: February 2004

The ``image method'' described in the preceding paper [H. S. Fricker and P. W. Anderson, J. Chem. Phys. 55, 5028 (1971)] is used to calculate valence orbitals in Li2, Na2, K2, and NaLi for a Wigner-Seitz cellular potential. The Green's functions are obtained by the quantum defect method. We discuss the problems involved in generating basis functions from point sources, and describe a simple, partly variational matching procedure which yields eigenvalues accurate to about 0.001 Ry and excellent wave-functions. Although the method is much simpler than a conventional self-consistent calculation, it gives, as in the metals, a good description of the binding: We obtain equilibrium distances to better than 10%, binding energies and vibration frequencies to within 30% and, with an empirical ``Coulomb integral,'' reasonable excitation energies. But the importance of short-range and angular correlations and the absence of a model comparable with the free electron theory of metals, makes it difficult to calculate the remaining interactions from first principles.
Radius of Gyration of Macromolecules with Increasing Chain Stiffness and Excluded Volume
Authors: Kumbar Mahadevappa M.
Published: February 2004

The Rouse-Beuche spring model has been used to study the mean square radius of ring and chain molecules with increasing local chain stiffness and excluded volume. The mean square radius is represented by a three parameter equation, and it has been observed that both types of molecules obey the same exponent relation between the mean square radius and the molecular weight. The ratio of mean square radius of ring to chain molecules has been investigated, and it has been concluded that, for long chain molecules, this ratio behaves independently of local chain stiffness and slightly increases as the excluded volume parameter increases.
Carbon-13 Magnetic Resonance Studies on Charge-Transfer Complexes: Pyridine-Iodine
Authors: Larkindale J. P. , Simkin D. J.
Published: February 2004

Carbon-13 chemical-shift data on pyridine and its charge-transfer complex with iodine are presented. The Karplus-Pople theory of chemical shifts, together with CNDO/2-SCF MO calculations, is found to lead to good semiquantitative agreement with experiment. It is shown that both bond orders and electron density must be taken into account to obtain agreement with experiment. Carbon-13 shift measurements, like proton shift measurements, do not enable the amount of charge transfer to be estimated. Under the experimental conditions used, no estimate of the equilibrium constant could be obtained, but the shifts of the carbon atoms in the pure complex were estimated.
Perpendicular Band Contours and Vibrational Potential Function of the E′ Vibrations of AsF5
Authors: Hoskins L. C. , Perng C. N.
Published: February 2004

A computer program has been written that synthesizes the perpendicular band contours of symmetrictop molecules. This program was applied to the E′ vibrations of AsF5 and Coriolis constants were determined. The Coriolis constants and vibrational frequencies were then used to fit an E′ vibrational potential function. Two force fields were found, one of which has a normal coordinate which may explain the equivalence of the axial and equatorial fluorines in the NMR spectrum.
Determination of the Radial Distribution Function and the Direct Correlation Function of Spheres by X-Ray Small-Angle Scattering
Authors: Brady George W. , Gravatt C. C.
Published: February 2004

An experimental determination of the pair and direct correlation functions of polystyrene latex spheres in the high-density limit has been made. From these the pair potential for hard spheres has been calculated. The significance of the functions as they bear on the Percus—Vevick and the hypernetted chain approximation is discussed.
Bernal Model: A Simple Equilibrium Theory of Close-Packed Liquids
Authors: Caron Laurent G.
Published: February 2004

The Bernal model of a hard-sphere liquid is used in conjunction with an extension of the cell method to predict the behavior of liquid argon near melting. The entropy of disorder associated with the Bernal state is deduced. The model is found to be applicable to liquid metals.
Infrared Spectra of Polar Diatomic Molecules in Quadrupolar Condensed Solvents
Authors: Girardet C. , Robert D. , Galatry L.
Published: February 2004

The present paper is devoted to the computation of the infrared spectral properties of couples containing a polar and a quadrupolar molecule located at fixed distances which are permanently realized in condensed media. A study of the orientational quantum states of such couples using an asymptotic method is presented. This method is particularly suited when the angle dependent variation of the total interaction energy is large compared with the rotational energy of the free molecules. Then, a detailed quantitative description of the spectra of such couples is given and is compared to experimental data concerning the infrared spectra of dilute solutions of HCl in the solid, liquid, and highly compressed gases N2, CO, CO2 and CS2. The binary model used to build the theoretical spectra appears to be well suited to describe many detailed features of the experimental data. A discussion is then given to help in the understanding of why the concept of molecular couple used to approach the spectral properties of the condensed phases is apparently able to give a fairly consistent description of the observed profiles of the considered media.
Calculation of the Infrared Spectrum of SF4 Using CNDO /2 Techniques
Authors: Levin Ira W.
Published: February 2004

Raman spectra of polycrystalline SF4 at liquid-nitrogen temperatures are discussed and an alternative to several recent vibrational assignments is suggested. Approximate sets of normal coordinate vectors are established for each of three possible frequency assignments. Relative infrared intensities for gas-phase SF4 are then calculated for each vibrational assignment using the approximate normal coordinates and a set of dipole derivatives, ∂P/∂Sj, computed by the CNDO/2 method. Comparisons between the sets of observed and calculated relative intensities for the gas phase indicate that the general intensity trends of the experimental data are reproduced by the semiempirical dipole derivatives. For SF4, the calculation is moderately sensitive to differences in the vibrational assignment, particularly, for the b1 and b2 stretching vibrations. The appealing application of utilizing semiempirical quantum mechanical techniques toward designating vibrational assignments is discussed.
CNDO Calculation of Dipole-Moment Derivatives and Infrared Intensities of BF3
Authors: Bruns Roy , Person Willis B.
Published: February 2004

Dipole-moment derivatives, ∂p/∂Sj, have been calculated (according to the method of Segal and Klein) for the infrared-active symmetry species of BF3, using approximate wavefunctions from the CNDO/2 procedure of Pople and Segal. The results agree fairly closely with the experimental values determined by McKean. In an attempt to understand the calculated ∂ p/∂ Sj values more fully, we have analyzed them in terms of derivatives (∂ μ/∂ rk) with respect to the generalized internal coordinates, rk. The latter calculated derivatives have been further analyzed in order to deduce the magnitudes of the different factors contributing to the values of ∂ μ/∂ rk. Comparison is made with corresponding values from the related F2CO molecule.
Valence-Bond Studies of AH2 Molecules. I. BeH2
Authors: Maclagan Robert G. A. R. , Schnuelle Gary W.
Published: February 2004

The valence-bond method is discussed and is compared with the molecular-orbital SCF method from a computational standpoint. A procedure is outlined for performing valence-bond calculations making use of the Prosser and Hagstrom biorthogonalization technique to evaluate the cofactors required when evaluating the energy using Löwdin's formula. A minimal basis set (STO) valence-bond calculation on BeH2 including all possible configurations which do not involve excitation of the Be 1s electrons is reported. This is compared with a molecular-orbital calculation using the same basis set. A valence-bond wavefunction neglecting ionic configurations is shown to give an energy better than the molecular-orbital wavefunction and almost as good as a ``full'' valence-bond calculation. The perfect pairing and Craig and Thirunamachandran's resonance approximation are examined. A scheme for performing semiempirical valence-bond calculations analogous to the Pople—Santry—Segal CNDO/2 MO method is described. Ionic configurations cannot be neglected in this ZDO approximation, but this is not a serious limitation. The method is very simple computationally. Hybrid and localized orbitals can be used.
Applicability of SCF Theory to Some Open-Shell States of CO, N2, and O2
Authors: Rose John B. , McKoy Vincent
Published: February 2004

By working with the real functions π x and π y instead of π + and π −, we show how to express the SCF Hamiltonians for the Σ states of the configurations (π u)3 (π g), (π u)3(π g)3, and (1π)3 (2π) of diatomic molecules in terms of the Coulomb and exchange operators only. With these results, we have used conventional SCF programs to solve for the wavefunctions of many interesting states of N2, O2, and CO, e.g., the B 3Σu− state of O2. For many states, the SCF results are in good agreement with experiment. However, SCF theory runs into serious trouble if electron correlation is important in determining the relative locations of excited states.
Localized Orbitals for Polyatomic Systems. II. Open Shell Case
Authors: Schlosser Herbert
Published: February 2004

We present a generalization of the Adams—Gilbert approach for constructing localized Hartree—Fock (HF) orbitals from the closed shell single Slater determinant case to the case where one has several open shells of different symmetry in addition to closed shells of electrons. Our starting point is the open shell HF formalism discussed by Roothaan and Huzinaga. We then apply appropriate localization operators to construct the localized AG orbitals, and also develop the resulting equations in powers of the overlap. Finally, we present several perturbation-iteration schemes for solving the open shell Adams—Gilbert equations, and comment on pseudopotential methods for construction of localized orbitals.
Phosphorescence Enhancement in Phenyl-Substituted Methanes
Authors: Watson Fred H. , El-Bayoumi M. Ashraf
Published: February 2004

Experimental evidence is presented which shows that the natural phosphorescence lifetimes, τP°, decrease with increased phenylation in the molecular series: toluene, diphenylmethane, triphenylmethane. This indicates that a spin—orbit enhancement mechanism is operative. Natural fluorescence lifetime data support the exciton molecular model for diphenylmethane and triphenylmethane and show that the phenyl groups have little electronic overlap. The experimentally observed natural fluorescence lifetimes, τ F°, at 77°K suggest that the exciton levels have similar transition moments with small forbidden character for the low-energy component. The dramatic enhancement of phosphorescence in the series is due to several factors, namely, an increase in intersystem crossing rate constant kisc, an increase in phosphorescence rate constant kP, and a decrease in radiationless triplet decay constant kP′. Although the electronic overlap is small enough for the exciton model to be a valid approximation to explain singlet absorption intensities and fluorescence lifetimes, the overlap must be taken into consideration to account for the enhancement of spin—orbit coupling down the series. The molecular geometry of diphenylmethane consistent with the fluorescence lifetime data and the observed exciton splitting is described.
Determination of Proton Affinity from the Kinetics of Proton Transfer Reactions. I. Relative Proton Affinities
Authors: Roche A. E. , Sutton M. M. , Bohme D. K. , Schiff H. I.
Published: February 2004

A study of the kinetics of selected proton transfer reactions proceeding in a flowing afterglow at 300°K has led to the proton affinity order PA(CO) > PA(N2O) > PA(CH4) > PA(CO2) > PA(NO) > PA(N2) > PA(H2) > PA(O2) > PA(Ar) and the order PA(CH4) > PA(CF4) > PA(N2). A comparison of these orders with established values for proton affinity reported in the literature has led to the following proton affinity limits: 3.4 eV<PA(Ar) <4.2 eV; 4.9 eV<PA(N2) <5.5 eV; 5.5 eV<PA(N2O) <6.1 eV; and 4.9 eV<PA(CF4) <5.5 eV. In most cases these limits represent a considerable improvement over previously available information on proton affinities.
Vibration-to-Vibration Energy Transfer in Hydrogen Bromide Mixtures
Authors: Chen Hao-Lin
Published: February 2004

The laser-excited vibrational fluorescence technique has been used to determine the rate constants for vibration-to-vibration energy transfer from HBr to other molecules in gaseous mixtures. Cross sections at room temperature have been found: σHBr–N2 = (1.78 ± 0.17) × 10−2 Å2,σHBr–CO = (5.5 ± 0.3) × 10−2 Å2,σD2–HBr = (9.10 ± 0.96) × 10−3 Å2,σHBr–O2 ≤ (9.3 ± 0.6) × 10−4 Å2. The cross section for vibration-to-rotation or translation energy transfer between HBr and D2 has also been determined as σHBr–D2 = (0.96 ± 0.1) × 10−4 Å2. The dependence of cross section on V → V energy level differences is about the same magnitude as in the analogous HCl systems but considerably larger than it is in other diatomic—diatomic systems. Strong intermolecular forces and larger amplitudes of hydrogen atom stretching vibration are likely to be the dominant reason for the observed phenomena.
Statistical Mechanics of Systems with Internal Constraints: Rubber Elasticity
Authors: Freed Karl F.
Published: February 2004

The general formulation of the statistical mechanical description of systems with internal constraints is recast into a form in which the ensemble average is written as a summation over the initial and final microscopic states of the system. The functional integral formulation previously developed to treat polymer networks is generalized to include these permanent constraints. The statistical mechanics of rubber elasticity is considered using a simple model in which the cross linkages are taken to be permanent topological constraints on the polymer network; these linkages are taken to be at the same places along the chains in both the initial and the deformed states. Entanglements are ignored, and the elasticity of this ``phantom'' network is obtained by using a variational principle for the free energy. The analog of the average affine deformation of the network is obtained as a variational result of the calculation. The elastic modulus obtained is in agreement with Flory's theory; however, the present statistical mechanical formulation is capable of also considering the effects of interactions between different polymer chains, chain stiffness, etc., and closed circuits in the polymer network.
Absolute Reaction Rate Constants and Chemical Reaction Cross Sections of Bimolecular Reactions
Authors: Lin S. H. , Lau K. H. , Eyring H.
Published: February 2004

Detailed specific rate constants of bimolecular reactions have been derived from the viewpoint of the absolute reaction rate theory, and the corresponding reaction cross sections have been obtained. The energy dependence of the reaction cross sections of the absolute reaction rate theory in the high energy range has been discussed, and it has been shown that the cross sections of the absolute reaction rate theory converge as the energy approaches infinity, if the effect of the exclusion of the disallowed states is properly taken into account.
Radial Electron–Electron Distributions and the Coulomb Hole for Be
Authors: Benesch Robert , Smith Vedene H.
Published: February 2004

Individual radial electron–electron distribution functions, Pi(r12)'s, are defined in terms of the eigen-functions (the natural geminals, NG's) of the spin-free 2-matrix, P(2)(r1, r2 | r1′, r2′). The total radial electron–electron distribution function, P0(r12), is defined in terms of P(2). It is demonstrated that the structure of individual two-particle eigenfunctions can easily be determined from the corresponding Pi(r12). Distributions are obtained for the S1 ground state of the Be atom by numerical Fourier transformation of x-ray intensity values. The natural spin geminal (NSG) analysis by Barnett and Shull of Weiss' configuration interaction (CI) wavefunction is used for the determination of correlated Pi(r12)'s, while the 2-matrix analysis of Clementi's Restricted Hartree–Fock (RHF) function is employed in the evaluation of independent particle model (IPM) Pi(r12)'s. The correlated and RHF P0(r12)'s are compared with that obtained from a two-configuration wavefunction of Watson, which takes into account the near degeneracy of 2s and 2p orbitals. By subtracting the RHF from the Weiss P0(r12), a description of the Coulomb hole function, Δ(r12), is obtained for the S1 Be ground state. A measure of the Fermi correlation may be obtained with Pi(r12)'s constructed from those S1 and S3 RHF geminals which involve the spatially symmetric or the spatially antisymmetric combination of 1s and 2s orbitals.
Trajectory Surface Hopping Approach to Nonadiabatic Molecular Collisions: The Reaction of H+ with D2
Authors: Tully John C. , Preston Richard K.
Published: February 2004

An extension of the classical trajectory approach is proposed that may be useful in treating many types of nonadiabatic molecular collisions. Nuclei are assumed to move classically on a single potential energy surface until an avoided surface crossing or other region of large nonadiabatic coupling is reached. At such points the trajectory is split into two branches, each of which follows a different potential surface. The validity of this model as applied to the HD2+ system is assessed by numerical integration of the appropriate semiclassical equations. A 3d “trajectory surface hopping” treatment of the reaction of H+ with D2 at a collision energy of 4 eV is reported. The excellent agreement with experiment is an encouraging indication of the potential usefulness of this approach.
Anisotropic Intermolecular Force Effects in Spectra of H2– and D2–Rare-Gas Complexes
Authors: McKellar A. R. W. , Welsh H. L.
Published: February 2004

Spectra of H2–Ar, H2–Kr, and H2–Xe Van der Waals complexes, accompanying the Q1(0), S1(0), Q1(1), and S1(1) transitions of the pressure-induced fundamental absorption band of hydrogen, have been studied in a path length of 165 m at temperatures in the range 85–158°K. At the low total gas densities used, 1–2 amagat, the lifetimes of the complexes were sufficiently long to show a great deal of new detail in the spectra. The R and P branches (δl = ± 1, where l is the angular momentum of the complex) accompanying the overlap-induced Q1(0) transitions, could be analyzed on a nonrigid rotation model to give Lennard-Jones ε and Σ parameters for the molecular pairs. The spectra accompanying the quadrupole-induced S1(0), Q1(1), and S1(1) transitions show T and N (δl = ± 3) as well as P and R branches, and many of the lines are split by the anisotropy of the intermolecular forces. The splitting is qualitatively in agreement with a model with loose coupling between J, the angular momentum of the H2 molecule, and 1. Well-resolved spectra of D2–Ar, D2–Kr, and D2–Xe complexes accompanying the S1(0) transition of deuterium were also obtained; these show more bound states than the H2–rare-gas spectra and anisotropic interaction effects are evident. The H2–N2 complex shows a spectrum with a diffuse structure not previously observed.
Combined SCF and CI Calculations for the Low-Lying Rydberg and Valence Excited States of Ethylene
Authors: Buenker Robert J. , Peyerimhoff Sigrid D. , Kammer Wolf Ekkehard
Published: February 2004

A series of nonempirical SCF–MO and CI calculations is carried out for the excited states of ethylene. In the usual manner the SCF treatment itself is seen to underestimate vertical transition energies from the closed-shell ground state to open-shell excited states by about 1 eV; an exception is noted, however, in the case of the π → π* singlet–singlet species. A CI(PCMO) treatment, which employs the SCF MO's of a given parent configuration as basis for its own CI expansion, is quite successful in balancing the correlation error, obtaining excellent agreement with experimental transition energies to valence and Rydberg states alike; a possible exception is found in the case of the π → π* singlet–singlet excitation for which the calculated value of 8.32 eV overestimates the location of the V ← N absorption maximum by 0.7 eV. The variational π* MO of the SCF wavefunction for the upper-state singlet is quite diffuse, but it is argued that this fact is not inconsistent with the known experimental data for the V ← N band system. Since the calculated state is found to correlate with a valence species for antiplanar ethylene, its diffuse character in the planar geometry does not imply that its potential surface should resemble that of a Rydberg state; in addition, its charge density contours emphasize that it should not be associated with a pure Rydberg species even in the planar conformation. The change in character with relative rotation of the methylene groups suggests that the electronic transition moment must be considered explicitly in the theoretical treatment of the intensity distribution in the V ← N bands, and also indicates that the probability of nonvertical transitions to partially rotated structures may well be greater than that of the vertical excitation.
Self-Consistent Perturbation Theory of Nuclear Spin-Coupling Constants: Application to Couplings Involving Carbon and Fluorine
Authors: Blizzard A. C. , Santry D. P.
Published: February 2004

A self-consistent perturbation theory is presented which permits efficient calculation of the contact, orbital, and dipolar contributions to nuclear spin coupling. The theory is applied with the INDO molecular orbital method to a number of couplings involving carbon and fluorine. The usually neglected orbital and dipolar terms are found to be very important in FF and CF coupling, and the orbital interaction plays a significant role in certain CC couplings. Generally good agreement is obtained between theory and experiment with the exception that the incorrect sign is obtained for cis JFF. The value of JCF in difluoroacetic acid is predicted to be − 235 Hz.
Excitation of Parity-Forbidden Transitions in H2 by Energetic Electrons
Authors: Ford Lewis , Browne J. C.
Published: February 2004

The cross sections for energetic electron excitation of the parity-forbidden X 1Σg+ → E, F 1Σg+ transitions are calculated in the Born approximation. The intensities for these forbidden transitions are predicted to be comparable to the intensities of the allowed X 1Σg+ → C 1Πu and X 1Σg+ → B 1Σu+ transitions for scattering angles as small as 0.75° for 34-keV electrons.
Molecular Orbital Model for Antimony Luminescent Centers in Fluorophosphate
Authors: Soules T. F. , Davis T. S. , Kreidler E. R.
Published: February 2004

A detailed semiempirical molecular orbital description of the low-lying excited states of the antimony luminescent center in fluorophosphate is presented. The MO model is used to interpret both the excitation and emission spectra. Good agreement with experiment is found. The model also explains differences in the characteristics of the excitation and emission spectra which are observed when the phosphor is prepared in the presence or absence of charge-compensating oxygen.
Continued Factorization Method for van der Waals Interactions
Authors: Tang K. T.
Published: February 2004

A continued factorization procedure is introduced to telescope the infinite series of the dynamic polarizability into a finite sum. The effective oscillator strengths can also be continually factorized. Both the upper and the lower bounds of the dynamical polarizability can be obtained from expressions identical in form. A single change of the last effective excitation energy of the continually factorized series turns it from an upper to a lower bound. The rest of the effective excitation energies are the natural resonance frequencies of the system. When the continued factorized series is substituted into the Casimir–Polder formula, we obtained the usual London formula for the van der Waals force with finite number of terms. Expressed in terms of oscillator strength sums and the natural resonance frequencies, all quantities in the London formula are given in closed forms. While it has the same formal structure of the Padé approximant method, the present method eliminates the entire process of constructing the approximant and gives tighter bounds.
Magnetic Susceptibility of Yb3+ in an Octahedral Environment
Authors: Karraker D. G.
Published: February 2004

The magnetic susceptibility of Yb3+ in Cs2NaYbCl6 was measured from 2.5 to 100°K and showed Curie–Weiss temperature dependence from 2.5 to 20°K (μeff = 2.46 μB, θ = 0.95°C) and from 45 to 100°K (μeff = 4.47 μB, θ = 70°C), with a transitional region from 20–45°K. From a comparison of the experimental results with theoretical results for a J = 7 / 2 ion in an octahedral field, the two crystalline field levels observed were identified as a Γ6 ground level, and a Γ8 level about 60 cm−1 higher. The energy separation between the Γ6 and Γ8 levels and a ratio of the crystalline field parameters − b4 / b6 derived from other measurements were employed to deduce − b4 = 4.85–4.95 and b6 ≈ 0.05 − 0.002 cm−1. From these parameters, a Γ7 level at ∼ 160 cm−1 is predicted. A covalent contribution to the Γ6 ground level is considered.
Simplification of the General Quartic Force Field of Linear Triatomic Molecules
Authors: Smith D. Foss , Overend John
Published: February 2004

A model for the anharmonic interaction force constants of polyatomic molecules, previously advanced by Machida and Overend, has been tested for CO2, CS2, OCS, N2O, and HCN. The parameters of the model have been determined by least squares adjustment to the experimental spectroscopic data, and the results are compared with those found previously with the general quartic force field. The model reduces the number of parameters in the force field of the symmetric molecules from 12 to 7 and the number of parameters in the force field of the unsymmetric XYZ molecules from 19 to 11.
Motional Correlation Time in the Electron Spin Relaxation of S6 Spin State Ions in Solution
Authors: Burlamacchi L.
Published: February 2004

The electron spin resonance (ESR) linewidth of Mn2+ and Fe3+ ions was measured as a function of temperature in various solvents which can reach high viscosity coefficients before solidification. With increasing correlation time, fast-motion narrowing is no longer verified and the linewidth passes through a maximum value corresponding to ω0τc = 1. Evaluation of τc allows a quantitative check of the zero-field splitting relaxation process. It has been found that modulation of the zero-field splitting in most cases is not the only effective process in relaxing the spin system, even at room temperature. Evaluation of the hydrodynamical radii for Debye tumbling of the complexes gives results which are always smaller than expected. However, the dependence of the correlation time on the size of the complex strongly suggests that rotation of the zero-field splitting tensor is responsible for the line broadening.
Infrared Spectrum of Gaseous CF2 by Rapid Scan Spectroscopy
Authors: Lefohn Allen S. , Pimentel George C.
Published: February 2004

Gaseous CF2 was produced through flash photolysis of CF2Br2, and its infrared spectrum was recorded using a rapid scan infrared spectrometer (500-μsec scan time). The absorption at 1112 cm−1 was recorded at higher resolution, 1 cm−1, than used earlier and the previously postulated PQR band contour was corroborated. Another absorption near 1224 cm−1 was detected for the first time in the gas-phase spectrum and with sufficient resolution to reveal rotational structure. Several sharp features can be assigned as Q-branch transitions in a perpendicular band of a slightly asymmetric top. This shows unambiguously that this band is due to ν1. Two detailed assignments are almost equally plausible, one placing the band center at 1224 ± 1.5 cm−1 and the other placing it at 1229 ± 1.5 cm−1. Both assignments give A″ − 12(B″ + C″) = 2.62 cm−1 and A′ − 12(B′ + C′) = 2.60 cm−1, in acceptable agreement with the microwave value, 2.56 cm−1. The assignments for the transient absorptions at 1112 ± 1.5 cm−1 and at 1224 (or 1229) ± 1.5 cm−1 as ν3 and ν1, respectively, of CF2 are definitively established. Thus ν1 lies at a higher frequency than ν3, as is also true for NF2 and OF2.
Direct Numerical Solution to the Charge Exchange Problem. I
Authors: Leventhal Lance , Rotenberg Manuel
Published: February 2004

In light of the capabilities of modern digital computers the question of direct numerical solution of the time-dependent Schrödinger equation is raised. It is found that solutions are feasible for the one-electron charge transfer problem. Detailed algorithms are given, and a discussion of the errors committed when reducing quantum mechanical operators to numerical operators is presented. Examples of charge transfer are given in the form of contour plots for collisions in one and two dimensions.
Studies of OH− and OD− Ions in Magnesium Oxide. I. Distribution and Annealing of Hydroxyl and Deuteroxyl Ions
Authors: Henderson B. , Sibley W. A.
Published: February 2004

The infrared absorption and x-ray stimulated luminescence of magnesium oxide crystals containing OH− and OD− ions are reported. We find that the ratio ν(OH)− / ν(OD−) ≈ 1.35 determined from ir absorption data is very close to the expected theoretical value for pure stretching frequencies of the OH− and OD− ions. Comparison of the OH− and OD− spectra allows an unequivocal identification of the origin of three of the OD− bands. In particular a band at 2727 cm−1 is shown to be due to Mg(OD)2 precipitates, whereas the 2444.7- and 2455.5-cm−1 bands are due to the associate centers OD−[+ +] and OD−[+ +]O2−M3+. (In these linear systems [+ +] represents a cation vacancy, and M3+ represents a trivalent cation.) The effect of annealing treatments in the range 570–1500°K is discussed in the light of the distribution of OH− and OD− in the MgO lattice. Preliminary data on OH− absorption in CaO are also reported. The luminescence spectra from molecules of Mg(OH)2 and Mg(OD)2 in MgO are reported, and the associated fine structure is described as due to local vibrations of the molecule. The electronic states involved in the transition are not known.
Different Perturbed Uncoupled Hartree–Fock (PUCHF) Methods for Physical Properties. II. Dipole Shielding Factors
Authors: Tuan Debbie Fu-tai , Davidz Andreas
Published: February 2004

The dipole shielding factors for the He and Be isoelectronic sequences have been calculated by the three uncoupled Hartree–Fock (UCHF) methods, γUCHF = γ0, by the three UCHF methods with the first-order perturbation correction (PUCHF methods), γPUCHF = γ0 + γ1, and by the geometric approximation based on the three PUCHF methods, γgeom = γ0(1 − γ1 / γ0)−1. The significance of the different amounts of self-potential included in the three PUCHF methods is demonstrated by comparing the results with results from coupled Hartree–Fock (CHF) calculations and the theoretical values. For the He isoelectronic sequence the PUCHF Method C1/2 is considered to be the best. The range of error of γ0 compared with γCHF is 0.14%–0.49%. The range of error of γ0 + γ1 or of γgeom compared with γCHF is 0.01%–0.13%. Larger errors in the Be series are attributed to the restricted forms of the Hartree–Fock wavefunction and the variational first-order orbitals.
ESR Study of X-Ray Irradiated Crystals of Copper Acetate Monohydrate
Authors: Kawamori Asako , Miyagawa Ichiro
Published: February 2004

Two single crystals of copper acetate monohydrate were irradiated by x rays at 80° and 290°K, respectively. In the paramagnetic centers produced at both temperatures, a single copper nucleus was found to contribute to the hyperfine structure. Spin Hamiltonian parameters of 63Cu of the center produced at 80° were determined to be gz = 2.364, gx = 2.047, gy = 2.086, Az = − 126.8, Ax = 32.1, Ay = − 11.3, and Q = 7.3, and those for the center produced at 290°K to be gz = 2.387, gx = 2.069, gy = 2.062, Az = − 131.4, | Ax | = 7.0, | Ay | = 5.0, and Q = 9.0, the A and Q tensors being given in units of 10−4 cm−1. The result was compared with that of zinc-doped copper acetate and was interpreted in terms of molecular orbitals between copper and acetate oxygens. A small mixing of the dz2 orbital to the ground dx2−y2 orbital was shown to account for the large anisotropies of both the g tensor and A tensor for the sample irradiated at 80°K. The paramagnetic center produced at 80°K was converted irreversibly at about 150°K to another species, which was found to be identical to that produced at 290°K.
Compressibility of 18 Molecular Organic Solids to 45 kbar
Authors: Vaidya S. N. , Kennedy G. C.
Published: February 2004

New compressibility data on 18 organic solids are reported. Measurements on a number of these solids have been made for the first time. Compressibilities up to 45 kbar were determined by observing piston displacement in a static high-pressure apparatus. Related compounds show a progressive decrease in compressibility with increase in molecular volume.
Reaction of Hydrogen Atoms with C2H4 and C2D4
Authors: Penzhorn R. D. , Darwent B. de B.
Published: February 2004

A study of the photolysis of HI in the presence of C2H4 and C2D4 was carried out at low conversions, in the presence of large pressures of moderator, and at various temperatures. In the experiments with C2D4 the formation of small percentage of HD was detected and it was found that the HD/H2 ratio provides a very sensitive test of the presence of hot reactions. The observed rate of hydrogen formation was used to evaluate the ratio of rate constants for the following reactions: H+HI→H2+I, H+C2H4or C2D4→C2H5or C2D4H. The Arrhenius parameters for k2 / k1 were found to be 0.30 exp(− 845 / RT) and, using the previously determined value for k1, we find k2 = 6.9 ± 0.7 × 1011cm3mole−1·sec−1. This value is based actually on the value of k for H+I2 as determined by Sullivan and extrapolated to our conditions. C2D4 has been found to react about 10% faster than C2H4.
Lyman-Alpha Emission Induced by the Collisions of Electrons with Molecular Hydrogen
Authors: Kauppila W. E. , Teubner P. J. O. , Fite W. L. , Girnius R. J.
Published: February 2004

The ratio of electron-impact cross sections of atomic and molecular hydrogen for production of uv radiation detected by an oxygen-filtered iodine-vapor-filled photon counter has been precisely measured in a modulated beam experiment. Using a filter 1.67 cm long with an oxygen pressure of 1 atm, the ratio of cross sections at 100 eV was found to be 4.05 ± 0.07. Using the known cross section for production of Lyman-alpha radiation from the hydrogen atom, the cross section for molecular radiation received by the detector was determined to be 1.48 (± 0.05) × 10−17 cm2.
Multiconfiguration Wavefunctions for the Water Molecule
Authors: Schaefer Henry F. , Bender Charles F.
Published: February 2004

Configuration-interaction (CI) wavefunctions have been calculated for H2O using basis sets ranging from minimum Slater-type orbital to Dunning's 4s2p1d contracted Gaussian oxygen set and 2s1p set on the two hydrogen atoms. An iterative natural orbital procedure is used throughout. Three different types of CI functions are examined: (1) first natural configuration (FNC) plus single and double excitations to other valence orbitals; (2) the first-order wavefunction; (3) FNC plus all singly and doubly excited configurations, holding the 1a1 orbital doubly occupied. It is found that correlation effects seen in the minimum basis set calculation continue to dominate in CI (2) as the size of the basis is increased. The importance of different orbitals and configurations is discussed in light of the occupation numbers and wavefunctions. The most extensive calculation includes 1027 1A1 configurations and yields a total energy of − 76.2418 hartree, corresponding to slightly more than 50% of the correlation energy of the water molecule. Our most accurate first-order wavefunction yielded a dissociation energy of 8.2 eV, with respect to two exact hydrogen atoms and a very accurate O-atom wavefunction of the same general form. For comparison the SCF dissociation energy of H2O is 6.8 eV, and the experimental value 10.1 eV.
Accurate SCF Calculation for Ammonia and Its Inversion Motion
Authors: Stevens Richard M.
Published: February 2004

A series of SCF calculations for the ammonia molecule in various gemoetries have been performed, using large basis sets of STO's. It is found that the height of the inversion barrier can be accurately predicted in the Hartree–Fock approximation, but that the basis set must be close to complete. Our largest calculations are in excellent agreement with previously reported calculations using Gaussian basis orbitals. A potential curve has been computed for the inversion motion using a near-Hartree–Fock basis set. The computed spectrum is in qualitative agreement with experiment; quantitative accuracy is not obtained, probably because the computed NH bond distance is too short.
Infrared and Raman Spectra of Substituted Hydrazines. III Symmetrical Dimethylhydrazine
Authors: Durig J. R. , Harris W. C.
Published: February 2004

The infrared spectra of gaseous, liquid, and polycrystalline symmetrical dimethylhydrazine and its deuterium analogs have been recorded from 70–4000 cm−1. The Raman spectra of the liquid and solid samples have also been recorded and depolarization values have been measured. A comparison of the infrared and Raman spectra of the respective compounds indicates that the liquid phase consists of approximately a 69:31% mixture of gauche conformers. An assignment of the observed frequencies based on band positions, relative intensities, and isotopic shifts is presented for both molecular conformations. Although the torsional fundamentals were observed for the molecules in both the gaseous and crystalline states, the bands observed for the solids were more clearly defined and were thus employed for the barrier height calculations. The threefold methyl rotational barrier is calculated to be approximately 3.3 kcal/mole, whereas the magnitude of the barrier hindering internal rotation about the N–N bond is estimated to be 5.0 kcal/mole.
Aromatic Solute Molecular Ion and Triplet State Formation in Polystyrene and Polymethylmethacrylate
Authors: Siegel Seymour , Stewart Thomas
Published: February 2004

Solutions of naphthalene-d8 and N,N,N′,N′ tetramethyl-p-phenylenediamine (TMPD), singly and in combination, in polystyrene (PS) and polymethylmethacrylate (PMMA) were irradiated by 1.9-MeV electrons at 86°K. The irradiation pulse had a half-width of 0.7 sec. Examination of the absorption spectra of samples immediately after the irradiation pulse indicated that solute triplet state molecules and positive ion molecules were produced, with TMPD as the solute in both polymer hosts. With naphthalene, positive ions were observed only in PMMA, whereas triplet state molecules were observed in both polymers. Analysis of the data from the mixed solute samples indicates that the presence of 0.05M TMPD captures all of the mobile positive charge, even when the naphthalene concentration is as high as 0.2M. Surprisingly, the production of naphthalene triplet state molecules is only slightly affected by the presence of TMPD. Charge migration or delocalization over appreciable distances occurs in both polymers. The radiation yields of triplets and ions in the two polymers are discussed and compared. PMMA is just as effective as PS in producing triplet excited states of the aromatic solute in terms of limiting yields at high solute concentration, but the concentration dependence is different in the two polymers. From an analysis of the G values of the various transient species as functions of the solute concentration and temperatures and by comparisons with published work performed with nanosecond and microsecond electron pulses, deductions are made with regard to charge capture and migration in these systems. The implications of these deductions with regard to primary radiation mechanisms are discussed.
Theoretical Investigation of the Electronic Structure and Properties of N3−, N3, and N3+
Authors: Archibald Timothy W. , Sabin John R.
Published: February 2004

An ab initio LCAO MO SCF calculation using a Gaussian basis was carried out on N3−, N3, and N3+. From the results of the calculation, some of the physical and electronic properties of these species are discussed and compared to experiment where possible.
ESR Study of the Effects of Alkali Metal Substitution on the Radical Species Produced and the Stereospecific Formation of Radicals in Irradiated Carboxylic Acids
Authors: Toriyama Kazumi , Muto Hachizo , Iwasaki Machio
Published: February 2004

A remarkable difference has been found in the radical species produced when the alkali metal was changed from potassium to sodium in irradiated single crystals of acid salts of maleic acids. The room temperature stable species in an irradiated single crystal of potassium hydrogen maleate was previously found to be the symmetrical delocalized π radical formed by removal of the acidic proton. In contrast to this result, the stable species found in sodium hydrogen maleate was the radical formed by the addition of hydrogen to the double bond. Furthermore, it has been found that the addition takes place selectively to one of the two vinylene carbon atoms, as is unexpected from the symmetrical structure of the hydrogen maleate ion. A similar difference was also observed in the unstable species at 77°K. The potassium crystal gave the symmetrical σ radical formed by removal of the acidic proton while the sodium crystal gave the unsymmetrical σ radical. Here again the unpaired electron is selectively located in one of the two COO groups. These results indicate that the formation of radicals in crystalline solids is strongly affected by the surrounding crystalline field, since the sodium crystal is known to have a different crystal structure with hydrated water.