bluuebunny/crossref_metadata_2025 huggingface dataset:
Different Perturbed Uncoupled Hartree–Fock (PUCHF) Methods for Physical Properties. I. Theory and Dipole Polarizabilities
Authors: Tuan Debbie Fu-tai , Davidz Andreas
Published: February 2004

Two different kinds of uncoupled Hartree–Fock (UCHF) Methods, Method C1/2 and Method C0, for the calculation of second-order physical properties are proposed. They differ from Dalgarno's uncoupled Hartree–Fock method (Method C1) by including half of the self-potential or not including the self-potential at all. They are formulated with a zeroth-order many-electron Hamiltonian, and first-order correction of both methods can be obtained without knowledge of the second-order orbitals. This situation is similar to the case studied by Tuan and co-workers for Method C1. The dipole polarizabilities for the He and Be isoelectronic sequences have been calculated by the three UCHF methods, αUCHF = α0, by the three UCHF methods with the first-order perturbation correction (PUCHF methods), αPUCHF = α0 + α1, and by the geometric approximation based on these three PUCHF methods, αgeom = α0(1 − α1 / α0)−1. The significance of the difference in the self-potential is demonstrated by comparing the results with results from the coupled Hartree–Fock (CHF) method. Method C1/2, which included the intermediate amount of self-potential, gave the best comparison of α0, α0 + α1 and αgeom with αCHF. For the He isoelectronic sequence from Method C1/2, α0 differs from αCHF by 9.71%–2.26%, α0 + α1 differs from αCHF by 1.29%–0.08%, and αgeom differs from αCHF by 0.42%–0.03%. Errors in the Be isoelectronic sequence are larger than those in the He isoelectronic sequence. Explanations in terms of the restricted forms of the Hartree–Fock wavefunction and of the variational first-order orbitals are given. The relative computing times for the CHF method and the perturbed version of Method C1/2 are in the ratio of 5 to 1. It is suggested that for evaluating the physical properties of larger and complicated systems the geometric approximation based on the PUCHF Method C1/2 can replace the CHF method as a simple and accurate method.
Theory for Ion Cyclotron Resonance Absorption Line Shapes
Authors: Marshall Alan G.
Published: February 2004

Explicit expressions have been calculated for the ion cyclotron resonance (ICR) absorption line shapes for reactive and for unreactive ionic species, in terms of ionic mass and charge, applied rf electric field frequency and magnitude, observing magnetic field strength, and electric drift potentials in various parts of the ICR spectrometer cell. The calculations are based on a zero-pressure equation of motion for the velocity of a charged ion which moves under the influence of a static magnetic field perpendicular to a static electric field and a sinusoidal time-varying electric field. The zero-pressure equation is applied only during the time intervals between ion–molecule collisions, and the power absorption contribution from ions in a particular region of the analyzer region of the ICR spectrometer cell is computed. The relative number of ions in a given region of the ICR cell is determined from that set of ion current expressions which follow from a particular specified kinetic scheme. The power absorption contributions from all regions of the analyzer are then summed; the resultant power absorption expression reduces to a Lorentzian line shape for reactive ions in the limit of very large collision frequency. It is shown that any process which interrupts ion power absorption may contribute to the linewidth of the ion cyclotron resonance. Computer-generated absorption and derivative line shapes are displayed for some representative cases, and plots of calculated ICR absorption linewidth vs collision frequency are given for several line-shape models. The relation of the present work to other models for ICR line shape is extensively discussed.
Critical Examination of the Herzberg–Teller Theory
Authors: Sharf Benjamin
Published: February 2004

It is shown that the Herzberg–Teller (HT) theory for computing the intensity pattern of forbidden transitions is not generally valid. For forbidden transitions, the standard computation of changes of equilibrium configurations which makes use of the Franck–Condon overlap factors is thus not adequate, in general. It is shown that the HT and non-HT induced transition moments are usually of comparable magnitude. Interference effects between the HT and non-HT exchanged intensity are operative.
Molecular Motion in Liquids: Rotational and Translational Diffusion in Weakly Associated Systems
Authors: Rothschild Walter G.
Published: February 2004

Detailed characteristics of the rotational motion (jump angles and intermolecular torques) and of the translational motion (trapping times between molecular jumps) in the system chloroform–benzene have been obtained from infrared correlation functions and proton nuclear magnetic relaxation measurements at room temperature. For this, the band contour of a far-infrared parallel band of CDCl3 (362 cm−1) and a mid-infrared perpendicular band of CHCl3 (1219 cm−1) in benzene solutions were measured and Fourier-inverted. The nuclear magnetic experiments involved proton spin–lattice relaxation of benzene in CDCl3 as well as spin–echo self-diffusion measurements, evaluated on the basis of the Torrey model of intermolecular spin–lattice relaxation. The results indicate that the molecular moieties forming the weak complex do not perform librational motions (torsional oscillations) about some type of intermolecular bond, but behave essentially as “random rotators,” performing gaslike orientational jumps through average angles of 0.4–0.7 rad around their inertial axes. Likewise, the translational motion appears to be carried mainly by large-distance jumps (about 5 Å) of the molecular moieties and not by translational jumps of the complex as a whole. It is suggested that this picture holds generally for weak complexes and weakly nonideal liquids and solutions.
Molecular Orbital Correlations and Ion–Molecule Reaction Dynamics
Authors: Mahan Bruce H.
Published: February 2004

We examine the application of molecular orbital correlation diagrams to ion–molecule collision processes. In situations where the reactant and product orbitals are few in number and well spaced in energy, the correlation diagrams give a clear picture of how the reactant electron configuration evolves to that of the products. The diagrams lead to a simple explanation of why the endothermic H2+(He, H)HeH+ and H2+(Ne, H)HeH+ reactions occur, whereas the exothermic processes He+(H2, H)HeH+ and Ne+(H2, H)NeH+ have undetectably small cross sections. Similarly, it is possible to use the diagrams to explain why the CO+(H2, H)HCO+ and N2+(H2, H)N2H+ reactions proceed by direct interaction mechanisms despite the substantial stability of the intermediate ions H2CO+ and N2H2+. Several other applications of the diagrams are discussed.
Distinguishable Electron Method (DEM) for Electronic Structure Calculations. II. Derivation of Accessible Correlation Expressions for Physical Properties and Application to the Polarizability of Two-Electron Atoms
Authors: Kirtman Bernard , Mowery Robert L.
Published: February 2004

The distinguishable electron method is extended to the calculation of physical properties other than the energy. Such calculations utilize accessible correlation expressions containing no correlated wavefunctions. It is shown that the necessary perturbation functions can be obtained from solutions of one-electron differential equations. For purposes of illustration, our method is applied to the polarizability of the helium sequence, starting with an open-shell screened nucleus initial approximation. Three different sets of optimized screening constants are employed. The best set—obtained by a new procedure which depends upon the property—yields polarizabilities that agree well with experiment and are superior to the perturbed coupled Hartree–Fock method.
Mode Expansion in Equilibrium Statistical Mechanics. III. Optimized Convergence and Application to Ionic Solution Theory
Authors: Andersen Hans C. , Chandler David
Published: February 2004

The mode expansion is an infinite series for the Helmholtz free energy of a system of classical particles with spherically symmetric interparticle potentials. A systematic procedure is presented for making the mode expansion converge as quickly as possible for particles whose potential includes a strong repulsion. This optimization procedure is physically related to the excluded volume effects produced by the repulsive forces. When the mode expansion is truncated after the one-mode term (the random phase approximation), the optimized result is related to the spherical model integral equation. The optimized mode expansion is applied to the restricted primitive model of aqueous 1–1 and 2–2 electrolyte solutions and compared with the results obtained from Monte Carlo calculations for salt concentrations up to 2M. The comparison indicates that in this concentration range, the optimized mode expansion converges fairly rapidly. Truncation of the expansion for the 1–1 electrolyte after the two-mode term yields values for the Helmholtz free energy, osmotic coefficient, and activity coefficients which are in almost perfect agreement with the Monte Carlo calculations up to 2M. Accurate values of the excess internal energy are also obtained. For 2–2 electrolytes, the convergence of the optimized mode expansion is not as rapid as that for 1–1 electrolytes. Even so, when truncated after the two-mode term, the optimized mode expansion for the 2–2 electrolyte predicts configurational energies which differ by at most 6% from the Monte Carlo results for concentrations between 0.5M and 2M.
Matrix-Isolation Raman and Infrared Spectra, Molecular Structure, and Force Constants for XeO3F2
Authors: Claassen Howard H. , Huston John L.
Published: February 2004

Both the Raman and the infrared spectra of low-temperature matrix-isolated molecules of XeO3F2 are reported. D3h symmetry for the molecules is indicated. The observed fundamental frequencies in cm−1 are 806.7 (a1′), 567.4 (a1′), 631.7 (a2″), 375.4 (a2″), 894 (e′), 318 (e′), 190 (e′), and 361 (e″). Force constants are reported in terms of the orbital valency force field assumption.
Collinear Collisions of an Atom and a Morse Oscillator: An Approximate Semiclassical Approach
Authors: Morse Robert I. , LaBrecque Rodney J.
Published: February 2004

The semiclassical treatment by Heidrich, Wilson, and Rapp of atom–harmonic oscillator collinear collisions with exponential and Morse repulsive potentials, is extended to include collisions, with the same potentials, between an atom and a Morse oscillator. The classical equations of motion for the Morse oscillator system lead to a differential equation which can be solved in the same form as the harmonic oscillator system by an iterative method. It is found that for vibrational transitions between low lying levels and for relative translational energies on the order of several oscillator quanta only one or two iterations are necessary for convergence to within a few percent. The results are compared with a calculation for harmonic oscillator systems.
Thermodynamics of Microcrystallites and Its Relation to Nucleation Theory
Authors: Abraham Farid F. , Dave J. V.
Published: February 2004

We develop a generalized Einstein model for calculating the thermodynamic properties of small crystalline clusters of atoms. The validity of the model is established through the molecular dynamics calculations by Dickey and Paskin and the numerical normal mode analysis by Burton for certain cluster packings. The rapid computational procedure and low computer storage requirements for our model calculations enable us to easily compute thermodynamic quantities for cluster configurations and sizes beyond those previously studied. Polyhedron cluster packings and “approximately spherical” cluster packings are used to generate clusters of various configurations. The Einstein theory is used to study the Helmholtz free energy, vibrational energy, and entropy for the various cluster configurations and for cluster sizes up to ∼ 1000 atoms. The model calculations are compared with the predictions based on the capillarity approximation used in nucleation theory. The simplicity of the method enables one to calculate the thermodynamic quantities for other types of systems.
Liquid Mixture Excess Properties and Gas Solubilities by the Hard-Sphere Model
Authors: Miller Reid C.
Published: February 2004

Thermodynamic properties of binary liquid mixtures containing simple species are calculated with the hard-sphere model originally proposed by Longuet-Higgins and Widom. No liquid mixture data is used. The only mixture parameter employed is k12, the deviation parameter for the geometric-mean mixing rule for intermolecular energy parameters. Very encouraging agreement with experiment is observed for both close-boiling systems and for mixtures containing a supercritical solute. A calculational scheme for mixtures containing the quantum gases hydrogen and helium is also developed with the same model.
Raman Scattering Studies of Liquids and Glasses. I. Liquid and Supercooled Liquid Glycerol
Authors: Wang C. H. , Wright R. B.
Published: February 2004

The Raman scattering technique was used to investigate the low-lying intermolecular modes in liquid and vitreous glycerol from 65–353°K. It was found that while the integrated intensity of the polarized spectrum decreases with decreasing temperature, the depolarization ratio remains more or less constant (≅ 0.68). A large decrease in the scattering intensity occurs near the glass transition temperature. Considering that a normal mode of vibration is responsible for both the ir absorption and the Raman scattering, we have derived an expression which relates the absorption coefficient to the scattering power spectrum. The derivation was obtained with a similar technique used by Kubo and Tomita in their theory of magnetic resonance absorption and relaxation. The derived expression was used to calculate the ωχ″(ω) function (the absorption coefficient divided by the frequency ω) from the measured Raman spectrum. It was shown that the so obtained ωχ″(ω) curves can be fitted to within experimental uncertainty by a simple damped-harmonic oscillator function with a temperature-dependent damping constant. Except for a transition region at 260–280°K, the temperature behavior of the damping constant derived from the depolarized Raman spectrum can be described in terms of two activation energies. For the temperature region above 285°K, the activation energy corresponds to the hydrogen bond energy, and for the region below 280°K the activation energy is considered to arise from the anharmonicity in the hydrogen bond potential. The reason for the temperature insensitive Raman scattering cross section in vitreous materials is also given.
Limited Expansion Gaussian Lobe Orbitals in Ab Initio Studies of Atoms and Molecules
Authors: Grimmelmann Erik K. , Chesick John P.
Published: February 2004

Results of ab initio calculations for first-row atoms and ions and LCAO–MO calculations for methane, fluoromethane, difluoromethane, trifluoromethane, and ethylene are presented for basis sets consisting of groups of limited numbers of s-type Gaussians and simple Gaussian lobe p orbital representations. Parameters are presented for atoms and ions of elements beryllium through fluorine using a three-Gaussian 1s-core group, an additional Gaussian for the 2s orbital and a two-Gaussian lobe p orbital. When used in LCAO–MO calculations this atomic orbital representation appears to provide results for charge distributions, molecular geometries, valence shell MO energies, calculated HF dissociation energies, and excitation energies (for ethylene) comparable to results obtained using minimum STO basis sets. A method for isolating the core orbitals from the LCAO variation process is applied and discussed for the molecular calculations.
Effusion. VII. The Failure of Isotropy of a Gas in an Effusion Cell and the Transition Region
Authors: Wahlbeck P. G.
Published: February 2004

A theory with a molecular model is presented for the transition region between the molecular flow region and the hydrodynamic flow region for the effusion of gases through orifices. The theory has as its basis a parameter which is associated with the failure of isotropy of the gas within the effusion container and which is calculated from the solid angle subtended by the vacuum opening of the orifice at the collision site of gaseous molecules within the effusion cell. This leads to modification of the kinetic theory equations for the ideal orifice for both the angular number distributions and the orifice transmission factors; these modified equations agree well with available experimental data. For orifices with orifice walls, the solid angle subtended by the orifice wall becomes an important parameter because the probability that a molecule has its trajectory such that it collides with the orifice wall depends upon that solid angle. A modification of the Clausing theory for nonideal orifices appears to agree well with experimental angular distributions for the cylindrical orifice case. It should be possible to extend these calculations to other nonideal orifice shapes.
Estimates of Error Bounds of Gas Transport Properties. II. Polyatomic Gases
Authors: Monchick L.
Published: February 2004

It is shown that for the real part of certain gas transport properties a variation principle exists that involves a symmetric dissipative collision operator derived from the Waldmann–Snider collision operator. This allows the methods of the previous papers of this series to be applied to some polyatomic gas transport properties and, in particular, to develop error bound formulas.
Far-Infrared Spectrum and Normal Coordinate Analysis of α-Methanol
Authors: Wong P. T. T. , Whalley E.
Published: February 2004

The infrared spectra of α-methanol and α-methanol-d3 have been measured in the range 400–20 cm−1 at 100 and 150°K. Seven intermolecular vibrations are expected and were observed. The CH3 internal rotations were not observed. A normal coordinate analysis of the spectra has been made assuming that the potential energy has the symmetry C2h, that is, is independent of the position of the hydrogen atom in the hydrogen bond. The hydrogen-bond stretching force constant is 0.346 mdyn Å−1, which is about twice the value for the hydrogen bond in ice. This does not correlate well with the effect of hydrogen bonding on the OH stretching frequencies, nor with the dissociation energy of the dimers of methanol and water in the vapor. However, the heat of sublimation of methanol at 0°K indicates that about 8.5 kcal mole−1 are required to break the hydrogen bonds, compared with only 5.66 kcal mole−1 in ice, which is consistent with the higher force constant for methanol.
Spurious Dissociative Attachment Peaks from Inelastic Loss Reactions
Authors: Chantry P. J.
Published: February 2004

Peaks in the electron energy dependence of negative ion production are usually the direct result of dissociative attachment reactions of the type e+XY→XY*−→X−+Y. Each such peak is related to a particular intermediate molecular negative ion state XY*− and provides an approximate estimate of the energy of that state in the Frank–Condon region. A dissociative attachment peak may, however, be accompanied by a smaller “partner” peak at a higher electron energy at which an inelastic energy loss collision leaves the electron with an energy at which subsequent dissociative attachment can occur. Thus the separation of the partner peak from the main dissociative attachment peak equals the most probable energy loss. A peak in the production of O− from O2 at 15 eV, observed previously, but not satisfactorily explained, has been studied experimentally and is shown to arise from the above described reaction sequence involving the loss of ∼ 8.4-eV energy by excitation of the B 3Σu− dissociation continuum. Satisfactory correlation of the observations with published energy loss spectra is demonstrated and the expected quadratic pressure dependence of the signal is confirmed. In addition a technique is described whereby the energy of the electrons directly responsible for the ion production is measured even though it differs from that of the primary electron beam. On the basis of the present observations it is concluded that in the region of 15 eV essentially all of the energy loss occurs through the 8.4-eV process, and the inelastic cross sections of Hake and Phelps are appropriately re-apportioned. Peaks in the production of O− from N2O in the region of 7–15-eV beam energy are shown to have a quadratic pressure dependence and are ascribed to the same general mechanism. Correlations with known energy losses are, however, less satisfactory than in the O2 case. Possible reasons for this are suggested. Peaks in O− production from CO at 16 and 18.3 eV arise from excitation of the A 3π and A 1π states. The relative magnitudes of these two excitation cross sections apparently changes dramatically with increasing electron energy. Two peaks in O− production from NO, at 14.2 and 15 eV, are similarly correlated with known energy losses and the first of these peaks ascribed to excitation of the c 2π and/or the D 2Σ+ state.
Photosensitized Dehydrogenation of Crystalline Durene: Mechanism of Duryl Radical Formation
Authors: Migirdicyan Eva
Published: February 2004

The photosensitized dehydrogenation of durene doped with 2,4,5-trimethylbenzaldehyde and naphthalene-d8 gives rise to duryl (2,4,5-trimethylbenzyl) radicals. The rate of production of these radicals was studied as a function of the guest, of photolyzing light intensity, and of temperature. The experimental data show that the mechanism of radical formation is dependent upon the nature of the particular guest involved. In naphthalene-d8/durene mixed crystals, duryl radical is probably formed by a stepwise biphotonic absorption process involving the first triplet state of the guest as an intermediate. The results show that radical formation is not responsible for the temperature dependence of the naphthalene-d8 phosphorescence lifetime in durene host at T > 220°K. In 2,4,5-trimethylbenzaldehyde/durene mixtures, the formation of duryl radical is a monophotonic process, and the over-all reaction is the hydrogen abstraction of aromatic carbonyl compounds with a lowest nπ* triplet state, a process which has been extensively studied in liquid solutions. However, the use of the solid state together with low temperature techniques has revealed the intervention of a new transient species as a precursor to matrix dehydrogenation.
Degenerate Excited State in the Structure of B2O3
Authors: Leidecker H. W. , Simmons J. H. , Litovitz T. A. , Macedo P. B.
Published: February 2004

A degenerate excited state is essential to the description of structural rearrangements which account for the relaxational heat capacity, thermal expansion, and compressibility of vitreous B2O3. These relaxational responses cannot be simultaneously described by a two-state model, or by any model involving a single ordering parameter, as shown by the magnitude of the Prigogine—Defay ratio (π≠1). The apparent two-state behavior of the temperature derivatives, Δα and Δcp, and failure of a two-state model to predict a sufficiently large compressibility (pressure derivative), suggest an analysis of structural rearrangements in vitreous B2O3 in terms of a single ground state and a twofold degenerate excited state which is characterized by different volumes.
Hyperfine Interaction, Chemical Bonding, and Isotope Effect in ZnH, CdH, and HgH Molecules
Authors: Knight Lon B. , Weltner William
Published: February 2004

ESR spectra of ZnH, CdH, HgH, and HgD molecules in their ground Σ+2 states were measured while trapped in solid argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with H, D, 111,113Cd, and 199,201Hg nuclei were observed. Coefficients of approximate LCAO wavefunctions are derived from these magnetic parameters and correlated with chemical bonding trends in the series and with the limiting united-atom model. Replacing H by D in HgH causes an increase of spin density on Hg and a decrease in g∇. This is shown to be largely due to the small decrease in interatomic distance and is discussed relative to other spectroscopic observations.
Ion—Molecule Reactions in an O2+–H2O System
Authors: Fehsenfeld F. C. , Mosesman M. , Ferguson E. E.
Published: February 2004

A sequence of reactions which occur in ionized O2–H2O mixtures has been studied with the following results: O2++H2O+M→ O2+·H2O+M,   k=0.9, 2.8, and 2.0×10−28 cm6 sec−1 for M=He, N2, and Ar, O4++H2O→O2+·H2O+O2,   k=2.2×10−9 cm3 sec−1,  O2+·H2O+H2O→H3O+·OH+O2,   k=1.9×10−9 cm3 sec−1, → H3O++OH+O2,   k≤ 3× 10−10 cm3 sec−1, H3O+·OH+H2O→H3O+·H2O+OH,   k=3×10−9 cm3 sec−1. The measurements were made at 295°K in a flowing afterglow system, operated in both fixed and variable reaction length modes. The results indicate that D(O2+·H2O)〉D(O2+·O2), D(H3O+·H2O)≳D(H3O+·OH).
Ion—Molecule Reactions in NO+–H2O System
Authors: Fehsenfeld F. C. , Mosesman M. , Ferguson E. E.
Published: February 2004

The following reaction sequence which occurs in ionized NO–H2O or air—H2O mixtures has been studied: NO++H2O+M→NO+(H2O)+M, NO+(H2O)+H2O+M→NO+(H2O)2+M, NO+(H2O)2+H2O+M→NO+(H2O)3+M, NO+(H2O)3+H2O→H3O+(H2O)2+HNO2. The measurements were made at 295°K in a flowing afterglow system, and reactions were measured for M = He, Ar, and N2.
Ion Cyclotron Resonance Power Absorption: Collision Frequencies for CO2+, N2+, and H3+ Ions in Their Parent Gases
Authors: Huntress W. T.
Published: February 2004

The complete solution for the equation of motion of an ion in the ICR cell is shown to give results for the instantaneous power absorption in excellent agreement with experiment at all pressures. The instantaneous power absorption at resonance initially increases linearly with time, and at high pressures levels off to a constant value at saturation where the energy gained by ions from the rf electric field is equal to the energy dissipated in collisions. An expression is also derived for the average kinetic energy of an ion at saturation in the steady-state limit. Pulsed ICR techniques are used to obtain the instantaneous power absorption curves for N2+, CO2+, and H3+ ions in their parent gases as a function of pressure, from which are calculated the momentum transfer rate constants k, and the dependence of the rate constants on ion kinetic energy. At 293°K, k(N2+)=k(CO2+)=0.67×10−9 cm3 molecule−1· sec−1, and k(H3+)=1.09×10−9 cm3 molecule−1· sec−1. For N2+ ions in N2 and CO2+ ions in CO2, the rate constants are both significantly greater than that predicted by polarization theory and both rate constants increase significantly with increasing ion kinetic energy. This behavior is most likely a consequence of long-range resonant charge transfer outside the orbiting impact parameter.
CO(a 3Π), Its Production, Detection, Deactivation, and Radiative Lifetime
Authors: Slanger T. G. , Black G.
Published: February 2004

This paper describes the first reported observation of the CO Cameron bands (a 3Π→X 1Σ+) produced from CO through photon absorption processes. The technique depends on quasiresonance fluorescence processes involving d 3Δ↔X 1Σ+ and a′ 3Σ+↔X 1Σ+ transitions and subsequent radiation from these triplet levels to the a 3Π state. From experiments in which the exciting lamp is pulsed, time decay measurements permit evaluation of the quenching rate constants for CO(a 3Π) by CO, NO, O2, H2, and CO2. The radiative lifetime of CO(a 3Π) has been obtained by use of the quenching rate constants, the intensities of the a 3Π populating transitions, and the Cameron band intensities, and it has an average value of 4.4±1.1 msec. Transfer of electronic energy takes place from CO(a 3Π) to NO, resulting in production of two radiating states, NO(A 2Σ) and NO (B 2Π), with approximate efficiencies of 23% and 10%, respectively. Either of these may be used as a monitor of the CO(a 3Π) state. Quenching of CO(a 3Π) by N2 leads to production of N2(A 3Σu+), but rate constants will have to be evaluated as a function of the degree of CO(a 3Π) vibrational excitation.
ESR Study of an Interstitially Trapped Copper Ion in a Crystal of L-Alanine
Authors: Wilkinson Bob A. , Miyagawa Ichiro
Published: February 2004

It has been found that copper ions are trapped interstitially in crystals of L-alanine grown from a solution containing copper chloride. The ESR absorption, which was studied at 9 and 23 GHz, showed a superhyperfine structure from a single 14N, suggesting that the Cu2+ is bonded to a single nitrogen atom. This result is in contrast to the case of copper chelate compounds of amino acids in which the Cu2+ is bonded to a pair of nitrogen atoms, in addition to a pair of oxygen atoms. The g tensor, the hfs tensor, and the 14N super-hfs tensor were determined, and the possible position of the Cu2+ ion in the crystal was discussed. The tensors showed no evidence of temperature dependence between room temperature and 4.2°K.
Self-Consistent Molecular Orbital Methods. X. Molecular Orbital Studies of Excited States with Minimal and Extended Basis Sets
Authors: Bene Janet E. Del , Ditchfield R. , Pople J. A.
Published: February 2004

Molecular orbital theory is applied to the excited states of a group of small molecules. Vertical transition energies are calculated using minimal and extended basis sets both with and without configuration interaction between singly excited states. The separate effects of extending the basis set and including CI are examined, and an evaluation of the over-all performance at each level is made by comparing calculated results with experimental values. Minimal basis calculations with limited CI are found to describe adequately n→π* transition energies. Although triplet π→π* energies are reasonably described at this level, an extended basis set is necessary to obtain even a moderate approximation to singlet π→π* energies.
Entropy and Molecular Correlation Functions in Open Systems. I. Derivation
Authors: Raveché Harold J.
Published: February 2004

A method is presented for obtaining an expression for the entropy in terms of molecular correlation functions defined in the grand canonical ensemble. The procedure is for a system of a single molecular species whose dynamics are determined by classical equations of motion. The entropy is obtained as a sum of two different classes of functions each involving the correlations between n-tuples of molecules. One class contains logarithmic terms similar to those obtained for the closed system; the other class involves isothermal activity derivatives of potentials of mean force. The latter terms, which are moments of the correlations between disjoint sets of molecules, can make appreciable contributions to the entropy. The method leads to results similar to those obtained from a different procedure by Nettleton and Green. The expression for the entropy is obtained and properties of the results are discussed for a simple fluid system.
Isoelectronic Molecules. III. First- and Second-Order Physical Properties for Systems of N-Interacting Electrons
Authors: Saturno Antony F. , Laurenzi Bernard J.
Published: February 2004

It is shown that the theory presented in II can be extended to systems of interacting electrons as well, and consequently, isoelectronic species continue to show a systematic variation of their physical properties with nuclear charge.
Theory of Molecular Interactions. II. Molecular Orbital Studies of HF Polymers Using a Minimal Slater-Type Basis
Authors: Bene Janet E. Del , Pople J. A.
Published: February 2004

Ab initio minimal bais LCAO SCF molecular orbital calculations have been performed to determine the energies and configurations of small groups of HF molecules. An intermolecular potential which spans the complete range of possible relative orientations for the dimer is presented. The predicted equilibrium form of the dimer is found, together with estimates of the intermolecular force constants. For polymers (HF)n, from n=3 to n=6, cyclic structures are found to be most stable. The hydrogen bond energies in these polymers deviate considerably from additivity.
Structural Comparison of Indene and Indenyl Using Electron Diffraction
Authors: Southern J. F. , Schäfer Lothar , Brendhaugen K. , Seip H. M.
Published: February 2004

The structure of indene, C9H8, was studied by electron diffraction for the sake of a comparison to the results previously obtained for indenyl. The mean C–C bond distance is the same (1.415 Å±0.01) for both molecules. The C–C bond distance range of indene (0.17 Å±0.02), however, is considerably larger than in the radical (0.09 Å). A structure is proposed for indene which, in view of the large number of independent parameters, must be considered as a nonunique solution of the electron diffraction pattern.
On the 1795-Å Transition of 2-Methylpropene (Isobutene)
Authors: McDiarmid Ruth
Published: February 2004

The absorption system originating around 1795 Å in isobutene has been studied in the parent compound and in three symmetrically deuterated isomers. Progressions are observed in the C=C stretch, –CH3 symmetric deformation, =CH2 deformation, =CH2 torsion, and =CH3 torsion vibrational modes. Sequences are observed in the =CH3 torsion and once in the =CH2 torsion. The ground- and upper-state methyl torsional potentials are calculated. The origin is tentatively identified as a false origin. The molecule is deduced to have undergone an extensive electronic change in the upper state. The transition is most probably A23py(σ*cc, b2)←π(px, b1).
Data by NMR and Representations of Self-Diffusion Coefficients in Carbon Tetrafluoride and the Determination of Intermolecular Force Constants
Authors: Khoury Fouad , Kobayashi Riki
Published: February 2004

Self-diffusion coefficients were measured by the pulsed nuclear magnetic resonance method for pure carbon tetrafluoride for the conditions −30 to 75°C and 20–440 atm. As predicted by the dilute gas theory, the density—diffusivity product (ρD) versus density (ρ) at constant temperature was found to be almost constant up to a reduced density of about 0.4, above which ρD started decreasing sharply. Based on the corresponding states principle, three semiempirical representations for the data were developed and compared. The low-density data were used, along with previously published second virial coefficient data, to evaluate intermolecular force constants for the Lennard-Jones (6–12) potential and the modified Buckingham (6-exp) potential.
Oxidation and Reduction of Amino Acids by Ionizing Radiation
Authors: Box Harold C. , Budzinski Edwin E.
Published: February 2004

The effects of ionizing radiation on the amino acids β-alanine and ε-aminocaproic acid were studied in single crystals irradiated at 4.2°K. The paramagnetic species resulting from radiation-induced oxidation and reduction processes were investigated using electron spin resonance and electron—nuclear double-resonance (ENDOR) spectroscopy. The reduced species is a free radical formed by the addition of an electron to the carbonyl oxygen of the carboxyl group. The ENDOR measurements indicate the oxidation product is a free radical derived from oxidized amino acid by the dissociation of CO2.
ENDOR Studies in Molecular Crystals. I. Glutaric Acid at 4.2°K
Authors: Kwiram Alvin L.
Published: February 2004

Two stable free radicals are formed in glutaric acid crystals on x irradiation. Ultraviolet illumination preferentially destroys one of these. Detailed ESR measurements are presented for the remaining radical and both radicals are studied by the ENDOR technique. Procedures for recovering the hyperfine tensor from the ENDOR data are presented. The contributions of the SxIx and SyIy terms are calculated to second order in the perturbation. The angular dependence of the anisotropic β-proton hyperfine interaction is calculated, and the results are compared with the observed behavior.
ESR of Exchange Coupled Cr3+ Ions in Phosphate Glass
Authors: Fournier J. T. , Landry R. J. , Bartram R. H.
Published: February 2004

A study of the ESR spectrum of a phosphate glass heavily doped with Cr2O3 is reported. The spectrum is attributed to exchange coupled Cr3+ ion pairs and is interpreted with reference to a spin Hamiltonian containing isotropic exchange, Zeeman, and fine structure terms. From the temperature dependence of the ESR intensity, it is inferred that the coupling is antiferromagnetic with an average coupling constant J=24±2 cm−1. The effects of fine structure interactions on the lineshape and breadth of the glass spectrum are considered, and the magnitudes of the fine structure parameters are estimated from the observed linewidths and dependence of the lineshape on microwave frequency. It is found that the fine structure constants are distributed in the range from 0.03 to 0.3 cm−1. The majority of the pairs are characterized by values near the lower end of the range, but the higher values are required to account for the absorption in the wings of the line.
Calculation of Chemical Reaction Rates by Variational Methods
Authors: Crawford Oakley H.
Published: February 2004

Variational methods for calculating chemical reaction rates are derived using Kohn's approach, and are tested on collinear H+H2 collisions. It is suggested that these methods show promise for treating simple reactions in their complete dimensionality.
Method for Finding the Equation of State of Liquid Metals
Authors: Jones Hilary D.
Published: February 2004

A variational method due to Mansoori and Canfield for finding the equation of state of a liquid has been extended to the case where atoms have a pair potential whose Fourier transform is known analytically. The method is used to calculate thermodynamic properties of sodium. The results are in good agreement with experiment.
Low-Temperature Magnetic Behavior of Several Oxides of Gadolinium
Authors: Miller A. E. , Jelinek F. J. , Gschneidner K. A. , Gerstein B. C.
Published: February 2004

The low-temperature magnetic susceptibility, 1–6°K, of the monoclinic and cubic, stoichiometric, and substoichiometric Gd2O3 phases are reported. The magnetic transformation temperatures have been determined and those of the substoichiometric phases probably give rise to the specific heat peaks observed in Gd metal containing appreciable amounts of oxygen.
Error Bounds to Expectation Values
Authors: Mazziotti Alexander
Published: February 2004

Upper and lower bounds to a true expectation value, P, are given by (Eμ L−Ẽ)/μ≤P≤(Ẽ−Eλ L)/λ, where Ẽ is the variationally minimized energy for the system of interest and Eμ L, Eλ L are lower bounds to the energies associated with reference Hamiltonians, Hλμ=H± λμP̂, with λ,μ〉0. These bounds are unique in that they are skewed about the approximate expectation value P̃, and because their application is not limited to positive definite operators. Approximate formulas, dU2λ /dλ (the derivative of variance with respect to parameter λ in Hλ) and 〈 ψ̃| P̂(H−Ẽ) |ψ̃ 〉 (where { ψ̃} is an approximate wavefunction) are shown to give the correct sign of an expectation value error.
Nuclear Spin—Lattice Relaxation in Ortho—Para Mixtures of Solid and Liquid Deuterium
Authors: Wang Richard , Smith M. , White David
Published: February 2004

A comprehensive study of the nuclear spin—lattice relaxation in the hexagonal close packed phase of solid deuterium and the liquid is presented. All of the measurements covering the temperature range 2.5–20.3°K and for para concentration 2%–94% were carried out using a pulsed technique, the pulse sequence being saturation −τ—90° at 8.0 MHz. It is shown that all of the experimental data can be accounted for on the basis of a kinetic model which assumes three principal relaxation mechanisms for the transfer of spin energy to the lattice from the two spin systems I=1, J=1 (para-D2) and I=2, J=0 (ortho-D2). These are (1) the modulation of the intramolecular spin—spin interactions by the anisotropic electric quadrupolar intermolecular interactions which represents the most important process for the direct relaxation of para-D2, (2) the intermolecular spin—spin interaction modulated by the self-diffusion in the solid or liquid which represents the only direct process for relaxation of the ortho-D2, and (3) the adiabatic cross relaxation between the two spin systems, the indirect process for the relaxation of the ortho-D2 dependent on the extent of coupling between the two different spins. This varies from the extreme of strong coupling in the rigid solid, where the self-diffusion is negligible, to weak coupling in the high-temperature solid and liquid where thermal motion is significant. A quantitative explanation of the experimental results for the hexagonal close packed solid is given in terms of existing theories for the mechanisms mentioned above. For the rigid solid regime (up to approximately 14°K), where the relaxation is determined entirely by the first mechanism, this requires that an effective electric quadrupole coupling constant in the solid of from 0.55 to 0.62Γ 0 be the coupling constant for the isolated pair. In the diffusion dominated regime, 14°K to the triple point all three mechanisms play an important role. Excellent agreement between theory and experiment is obtained for the same Γ eff, a self-diffusion coefficient D0=9.05× 10−2cm2/sec and an activation energy Ea=667 cal/mole, except for solids of very low para concentration. For the latter D0=2.0× 10−2cm2/sec and Ea=608 cal/mole. The theory predicts the observed frequency dependence of the spin—lattice relaxation in the diffusion-dominated regime. In the liquid state a spin—lattice relaxation time can be separately identified for each spin system. Whereas the para-D2 (I=1, J=1) results can be accounted for on a model which assumes mechanism (1) modified by the thermal motion in the liquid, no simple explanation is possible for the ortho-D2 data.
Green's Function for the Hydrogen Molecular Ion H2+
Authors: Laurenzi Bernard J.
Published: February 2004

The exact Green's function for the one-electron, two-center molecule H2+ has been found. It is a remarkably mild generalization of the well-known Green's function for the atom He+.
Chemistry of Nuclear Recoil 18F Atoms. IV. Hot F-to-HF and F-to-F2 Abstraction in CH3CF3
Authors: Parks Norris J. , Krohn Kenneth A. , Root John W.
Published: February 2004

New hot abstraction reaction channels have been demonstrated for nuclear recoil 18F atoms reacting with fluorocarbon substrates. Hot F-to-HF abstraction in CH3CF3 is a very efficient process with an absolute hot yield of 51%±3%. Hot F-to-F2 reactions also occur, but with much lower efficiencies. The F-to-F2 absolute hot yields in CH3CF3, C2F6, and C3F6 are 5.4%±0.3%, 6.9%±0.8%, and 11.7%±0.5%, respectively. In good agreement with theoretical expectations, translational excitation appears to be much more effective as a driving force for the exoergic F-to-HF process in comparison with the endoergic F-to-F2 process. The Arrhenius activation energy for thermal F-to-HF abstraction in CH3CF3 is at least 2.1±0.1 kcal/mole larger than the value associated with the thermal 18F-atom pi-addition process in C3F6.
Electron Spin Resonance Spectra of RSO2 Radicals Formed by the X Radiolysis of Sulfones
Authors: Geoffroy M. , Lucken E. A. C.
Published: February 2004

X irradiation of single crystals of dibenzyl sulfone yields the PhCH2S·O2 radical while irradiation of PhSO2CH2COOH, PhSO2CH3, and PhSO2Ph yields the PhS·O2 radical. The principal values of the g and 33S hyperfine coupling tensors were measured (PhCH2S·O2: g=2.0027, 2.0056, 2.0094; A33S=96.3, 63.4, 56.2 G; PhS·O2: g=2.0023, 2.0051, 2.0072; A33S=107.1, 71.3, 71.3 G) and are discussed in terms of the electronic structure of these species. In PhSO2CH2COOH a further radical, g=1.89, 1.98, 2.04, is observed at low temperatures and is probably a trapped electron.
Electron Affinities of Halogen Diatomic Molecules as Determined by Endoergic Charge Transfer
Authors: Chupka W. A. , Berkowitz J. , Gutman David
Published: February 2004

Ion-pair formation by photon absorption at threshold wavelengths has been used to prepare I−, Br−, and F− ions with approximately room-temperature thermal energies, as verified by retarding-potential measurements. The primary ions were accelerated and their reactions with halogen molecules studied at laboratory kinetic energies from 0.0 to about 4.0 eV. Thresholds were determined for endoergic reactions of the type X−+Y2→X+Y2 −, where X may be the same as Y. At least two reactions were used in determining each electron affinity. The agreement was good in all cases. The values of electron affinity obtained are 3.08±0.1 eV for F2, 2.38±0.1 eV for Cl2, 2.51±0.1 eV for Br2, and 2.58±0.1 eV for I2. Interhalogen molecular ions such as IBr− were also observed, and measurement of the threshold for formation gave the value 2.7±0.2 eV for the electron affinity of IBr. The retarding-potential measurements of F− from F2 strongly support a value for the dissociation energy of F2 in the neighborhood of 1.6 eV.
Electron Affinities of O2, O3, NO, NO2, NO3 by Endothermic Charge Transfer
Authors: Berkowitz J. , Chupka W. A. , Gutman David
Published: February 2004

Lower limits to the electron affinities of the molecules O2, O3, NO, and NO2 have been measured by determining the thresholds for endothermic charge transfer from I− to the corresponding molecules. The technique involves formation of I− by photoion-pair formation and measurement of the intensity of the product ion as a function of the energy available in the collision. The lower limits obtained are O2, 0.48 eV; O3, 1.96 eV; NO, 0.09 eV; and NO2, 2.04 eV. The threshold for the reaction I−+HNO3→NO3 −+HI has also been measured, and provides a lower limit to Δ H f0○(NO3 −). When combined with the best current estimate of ΔH f0○(NO3), it yields E.A. (NO3)≥2.48 eV.
Ion-Impact Energy-Loss Spectrum of Oxygen
Authors: Moore John H.
Published: February 2004

Electronic transitions in the oxygen molecule arising from ion—molecule collisions have been studied by measuring the kinetic energy lost by 100 eV–4 keV H+, H2+, and He+ inelastically scattered from O2. The 7–9-eV region of the energy-loss spectrum is strongly collision-energy dependent. The broad feature ordinarily identified as the Schumann—Runge continuum appears to be the result of at least two different transitions. A peak corresponding to the optically forbidden Herzberg continuum (A 3Σu+←X 3Σg −) is observed in all of the ion-impact spectra. Triplet—singlet transitions into the a 1Δg and b 1Σg+ states are the most intense features of the H2+− and He+−impact spectra. Cross sections for the above-mentioned processes exceed 10−17 cm2.
Excited State Symmetry Assignment Through Polarized Two-Photon Absorption Studies of Fluids
Authors: McClain W. M.
Published: February 2004

We consider the effect of molecular symmetry on the two-photon absorption constants of a randomly oriented sample of molecules. It is shown that a complete polarization study of an allowed two-photon transition of a fluid generally yields enough information to permit an unequivocal identification of the symmetry species of the excited state. Ambiguities occur in only a few cases. Thus, oriented molecule studies for symmetry assignment will be largely unnecessary in two-photon molecular spectroscopy. Symmetry assignment rules are given for all of the 32 crystallographic point groups and for the two groups of linear molecules. It is shown that certain transitions, which are allowed for two photons of different energies, are forbidden for two photons of the same energy. The application of this formalism to Raman scattering problems is discussed.
Photoelectron Spectra of F2O and Cl2O
Authors: Cornford A. B. , Frost D. C. , Herring F. G. , McDowell C. A.
Published: February 2004

The valence ionization potentials of F2O and Cl2O have been determined by photoelectron spectrometry, and the results are compared with the predictions of ab initio and approximate LCAO SCF calculations. The first PES band shows vibrational structure which is assigned to ν1 for F2O, and to both ν1 and ν2 for (Cl2O). These frequencies all show slight increases over the corresponding values for the ground states of the neutral molecules.