bluuebunny/crossref_metadata_2025 huggingface dataset:
Deuterium Quadrupole Coupling in Formyl Fluoride
Authors: Kukolich Stephen G.
Published: February 2004

The 101–000 rotational transition in HFCO and DFCO was recorded with a beam maser spectrometer. Hyperfine structure due to the deuterium quadrupole coupling was observed for DFCO. Analysis of the spectrum yielded the deuterium quadrupole coupling strength along the D–C bond direction of eqQ = 205. ± 4. kHz. This rotational transition had not been reported previously for DFCO. A comparison of deuterium quadrupole coupling strengths with force constants along the H–C bond is made according to the theory of Salem.
Analysis of Dielectric Dispersion Data
Authors: Dannhauser Walter
Published: February 2004

Assuming superposition of arbitrary numbers of dispersions, a method of resolving them is presented. A restriction of the method is that the lowest-frequency dispersion follows the Debye equation. Apparent violations of superposition which have been reported may be due to errors in the analysis of data. The method is illustrated with simulated data which suggests that a skewed-arc dispersion may be resolved, within the usual experimental error, into closely overlapping Debye-type dispersions.
Ion–Molecule Reactions of CH4–CD4 Mixtures at High Pressures
Authors: Chong Shuang-Ling , Franklin J. L.
Published: February 2004

Ion–molecule reactions in mixtures of CH4 and CD4 at pressures up to about 0.65 torr have been carried out in a single ion source of a quadrupole mass filter. From the isotope distribution in the ethyl ions, it is evident that randomization occurs in the complex of methyl ions with methane. There is no evidence for reaction of ethyl ion with methane. Similarly, methane ions react with methane to form CH5+, CH4D+, CD4H+, and CD5+. The ratios of products are very nearly what would be expected from reactions of methane ion with methane rather than from transfer of protons and deuterons from methanium ion. H and D atoms appear to be transferred at equal rates but deuterons are transferred at only about six-tenths the rate of transfer of protons.
Cation Diffusion and Conductivity in Solid Electrolytes. II. Mathematical Analyses
Authors: Kikuchi Ryoichi , Sato Hiroshi
Published: February 2004

This paper constitutes Paper II of the series and presents theoretical analysis and supplements the results shown in Paper I. Equilibrium properties of the layer in which Na ions exist in β- and β″-alumina are analyzed using the cluster variation method. Diffusion coefficients and ionic conductivities of Na ions in these two substances are derived using the path probability method.
Exciton Superexchange, Resonance Pairs, and Complete Exciton Band Structure of B12u Naphthalene
Authors: Hong Hwei-Kwan , Kopelman Raoul
Published: February 2004

A method for the determination of complete exciton band structures in molecular crystals is given. Pairwise exciton interactions are derived from resonance-pair data using an exciton “superexchange” approach. Koster and Slater's impurity cluster formulation is found to be applicable to nontrivial interchange symmetry systems, within the “restricted Frenkel–Davydov” theory. The derivation starts from the recent general formulation for isotopically mixed crystals of arbitrary concentrations. The resonance pair states are given by the second-order self-energy of the mixed crystal Green's function. General symmetry arguments and moment sum rules have been worked out for resonance pairs. It is demonstrated for naphthalene-h8 resonance pairs in naphthalene-d8 that superexchange corrections are not only inevitable for the B12u pair states but that they can also be utilized to assign experimental pairwise interactions to definite crystal directions, i.e., specific pairs. The naphthalene first singlet excited state 0–0 vibronic exciton band is successfully described by the “restricted Frenkel–Davydov” dispersion relation: ε(k±) =  ∑ e Meexp(ik·Re ±  ∑ i Miexp(ik·Ri), where e = a, b, c, (a + c) and i = 12(a + b), [12(a + b) + c]. Three sets of M's that are consistent with all resonance-pair and monomer mixed crystal data are tabulated. The only one consistent with a multipole expansion gives for the Me's and Mi's, respectively, − 0.6, − 3.9, − 3.7, 6.1, and 18.0, 2.0 cm−1. This point multipole expansion is safely limited to nonnearest-neighbor interactions and truncated beyond transition octopoles (Q31c = 7 and Q33c = 72 Å3). The translational shift is − 4.5 ± 4 cm−1, and the hot-band density-of-states function has been independently reproduced from the mixed crystal data, indicating that exciton–phonon coupling is small. The results are compared with ab initio calculations and new criteria for theoretical computations are suggested.
Relaxation Experiments in Binary Mixtures of Kneser Liquids
Authors: Hunter J. L. , Davenport J. M. , Sette D.
Published: February 2004

Relaxation curves have been obtained for appropriate mole concentrations of most of the binary mixtures formed from the following Kneser liquids: CS2, CH2Cl2, CH2Br2, C6H6, and CCl4, and relaxation frequencies found as a function of concentration of constituent molecules. The CS2=CH2Cl system, in particular, has been studied in detail, and it has been found possible to predict the absorption as a function of frequency and concentration from a general formula which contains relaxation strengths and relaxation frequencies of the two pure components, and the two cross terms involving the reaction rates of the unlike molecules with each other.
Nonempirical LCAO–MO–SCF Study of the Energy Surface for Linear HeH2+
Authors: Brown Peter J. , Hayes Edward F.
Published: February 2004

The nonempirical LCAO–SCF–MO method using a contracted Gaussian basis is used to generate a potential energy surface for the ground state of the linear HeH2+ system. Recently, Chupka, Berkowitz, and Russell reported that even above threshold the cross sections for the reaction H2++He=HeH++H, are strongly dependent on the vibrational state of the H2+ ion. Examination of the calculated potential-energy surface for this reaction reveals that the energy barrier for this reaction occurs very late in the exit channel. This result, coupled with the work of Polanyi and Wong on the effect of the position of the potential-energy barrier, suggests that this late energy barrier is the reason that vibrational energy is much more effective than translational energy in causing this reaction. Another interesting feature of the calculated potential energy surface is the presence of a minimum corresponding to a HeH2+ complex. Investigation of the energy of this complex as a function of He–H–H bond angle demonstrates that the 180° form is the most stable.
Collisional Quenching of Metastable Hydrogen Atoms
Authors: Slocomb C. A. , Miller W. H. , Schaefer H. F.
Published: February 2004

Quenching of metastable hydrogen atoms by low energy collisions with atoms and molecules is considered, the actual process being H(2s)+X→H(2p)+X. The Born approximation, with long-range multipole–multipole interactions, is used to describe collisions of H(2s) with molecules, and simple formulas for the cross section result. Collisions with spherically symmetric species (i.e., rare gas atoms) are treated in the adiabatic approximation, and the process is seen to be formally identical to symmetric charge transfer. Numerical results for collisional quenching by helium, based on accurately computed potential curves, are presented.
Reactions of Hydrogen and Deuterium Atoms Formed in the Photolysis of Methane and Perdeuterated Methane at 123.6 nm
Authors: Hellner Lucette , Masanet Jeannine , Vermeil Catherine
Published: February 2004

The photolysis of methane and perdeuterated methane has been carried out at 123.6 nm, in the presence of interceptors (deuterium in the case of methane, and hydrogen in the case of deuterated methane). The hydrogen and deuterium atoms formed are statistically in thermal equilibrium with the reaction medium; it follows that the photodissociation into CH3 and H has a probability close to zero at 123.6 nm. In addition, it is confirmed that CH4 and CD4 have different photolytic behaviors insofar as the quantum yields of hydrogen and deuterium are concerned, with φH > φD.
Far-Infrared Collision-Induced Absorption in CO2. II. Pressure Dependence in the Gas Phase and Absorption in the Liquid
Authors: Birnbaum G. , Ho W. , Rosenberg A.
Published: February 2004

The pressure dependence of the collision-induced spectrum in CO2 at room temperature in the frequency region 7–250 cm−1 is measured throughout this region as a function of density, ρa, from 0–85 amagat. At each frequency the density variation of the absorption is fitted by α(ν, ρa) = ρa2α2(ν) + ρa3α3(ν) to obtain values of α2(ν) and α3(ν). The coefficient α2(ν) and its temperature dependence is discussed in the previous paper of this series. The coefficient α3(ν) is negative in sign and has a band shape considerably sharper than that found for α2(ν). The Kramers–Kronig integral π−2∫α3(ν)ν−2dν is in reasonable agreement with the theoretical value of the third dielectric virial coefficient. Absorption in liquid CO2 is measured at 0°C and compared with the band spectrum obtained in the gas phase at the same temperature. The peak intensity in the liquid spectrum occurs at a frequency 25 cm−1 higher than in the gas phase. The integrated intensity ρa−2∫α(ν)dν in the liquid is 3.2 ± 0.1 × 10−4 cm−2·amagat−2, whereas that for the low density gas is 5.11 ± 0.20 × 10−3 cm−2·amagat−2.
Radial Distribution Functions and Superficial Quantities for Rigid Sphere Fluids; Method of “Point” Chemical Potential Using Scaled Particle Theory
Authors: Harris S. J. , Tully-Smith D. M.
Published: February 2004

The radial distribution of rigid spheres of diameter a about a single fixed solute rigid sphere of diameter b was calculated using the method of “point” chemical potential and effective local density, together with results from the scaled particle theory of rigid sphere fluids. This method, which avoids the superposition approximation, gives rise to a nonlinear integral equation which was solved numerically for various values of b in the interval a ≤ b < ∞ and for intermediate fluid densities. An apparent freezing transition was observed; the density required for this transition was a minimum for b = ∞ and increased as b was decreased. The superficial density of matter referred to the surface of radius r = (a + b) / 2, Γr*, was found, using these distribution functions, to be small and positive. Knowledge of Γr* allowed the unambiguous location of the equimolecular Gibbs dividing surface.
Interpretation of Molecular-Beam Radiofrequency ortho–para Transitions in Methane
Authors: Hougen Jon T.
Published: February 2004

A modified formalism, involving primarily changes in certain group-theoretical arguments, is presented for the data leading to the recent report that the splitting between the two inversion levels of methane has been resolved.
Optical Selection Studies of Radiationless Decay in an Isolated Large Molecule
Authors: Nitzan Abraham , Jortner Joshua
Published: February 2004

In this paper we present the results of a theoretical study of the nonradiative decay probability of a single vibronic level of a large isolated molecule. Utilizing Feynman's operator techniques, we were able to derive a theoretical expression of the dependence of the electronic relaxation rate on the excess vibrational energy in the excited electronic state for a “harmonic molecule” which is characterized by displaced potential surfaces. For a large effective electronic energy gap the nonradiative decay probability increases with increasing excess vibrational energy, while for a small energy gap the nonradiative decay in higher vibronic levels may be retarded. Our rough numerical calculations are found to be consistent with recent experimental data on optical selection studies in the isolated benzene molecule.
Nucleation of Voids in Materials Supersaturated with Vacancies and Interstitials
Authors: Katz Joseph L. , Wiedersich Hartmut
Published: February 2004

High-energy radiation simultaneously produces vacancies and interstitials in crystalline materials and, therefore, both types of defects are supersaturated during irradiation. The nucleation of defect precipitates under this circumstance is fundamentally different from the usual nucleation problem because of the competing effects of interstitials and vacancies on the size distribution of precipitate embryos. The rate of homogeneous nucleation of voids in such a material in which interstitials as well as vacancies are supersaturated is derived in this paper. It is shown that the thermodynamically derivable void embryo size distribution n0(x) (that is, the distribution which is in equilibrium with a given vacancy supersaturation) is in equilibrium with interstitials only when the latter are in equilibrium with the vacancies, i.e., when the interstitials are undersaturated to the same extent as the vacancies are supersaturated. The constrained distribution of voids n(x) (that is, when the interstitials are also supersaturated) is determined by the kinetics of incorporation of vacancies and interstitials into the embryos. Explicit expressions are given for n(x) in terms of kinetic parameters and n0(x). The rate of nucleation is then derived from n(x) along the lines of classical nucleation theory. The procedure developed here can readily be applied to the nucleation of other types of defect precipitates such as dislocation loops. A useful parameter to characterize the effect of excess interstitials on the nucleation of voids is the ratio of the rates at which interstitials and vacancies arrive at and are incorporated into void embryos. At a constant vacancy supersaturation, as this arrival rate ratio increases from essentially zero (i.e., interstitials in equilibrium with vacancies) the nucleation rate decreases and the size of the critical nucleus increases. Thus, to obtain a given rate of nucleation, increasingly larger supersaturations are required as the arrival rate ratio increases. The calculated changes are gradual at lower values of this ratio but become so drastic as the ratio approaches one that no nucleation of voids is then possible. As in classical nucleation theory, the rate of nucleation increases very rapidly with increases in supersaturation. This rapid increase of rate is obtained for all arrival rate ratios. We find that the supersaturations of defects which occur during irradiation in a high flux of energetic neutrons or ions are sufficient for readily observable nucleation rates for voids at intermediate temperatures but insufficient at high temperatures.
Electron Pair Correlation: Products of N(N − 1) / 2 Geminals for N Electrons
Authors: Silver David M.
Published: February 2004

The use of an antisymmetrized product of an N-electron spin eigenfunction and N(N − 1) / 2 geminals to form an N-electron, correlated wavefunction is proposed for atoms and molecules. This approach is more general than previous geminal-product schemes in that the wavefunction explicitly contains a different geminal for each of the pair interactions present in the system. By describing the geminals in terms of bilinear orbital expansions, the formalism remains quite tractable. The example of three pairs of electrons is used to exhibit explicit expressions for density matrices, energy and variational equations which hold for any desired choice of spin and orbital angular momentum state.
ESR Studies of Cu, Ag, and Au Atoms Isolated in Rare-Gas Matrices
Authors: Kasai Paul H. , McLeod D.
Published: February 2004

Electron spin resonance spectra were observed on Cu, Ag, and Au atoms isolated in Ne, Ar, Kr, and Xe matrices at ∼ 4°K. The hyperfine coupling constants and the g values were determined and examined for the matrix effect. With xenon matrices a superhyperfine structure with magnetic xenon nuclei was partially resolved, and by means of computer simulation, it was shown that these atoms are substitutionally incorporated within the Xe lattice. Also an evidence for atom-vacancy pairing was observed for Cu in Ne matrix.
Dissociative Excitation of Vacuum Ultraviolet Emission Features by Electron Impact on Molecular Gases. I. H2 and O2
Authors: Mumma M. J. , Zipf E. C.
Published: February 2004

The Hi(2p1 2P → 1s1 2S) 1215.67 Å-Lyman-alpha line and the Oi(3s1 3S0 → 2p4 3P) 1302.17, 1304.87, 1306.04-Å multiplet have been excited by electrons impacting on H2 and O2, respectively. Their excitation cross sections have been measured over the energy range from threshold to 350 eV. The cross section for dissociative excitation of Lyman alpha has a peak value of 1.23 × 10−17 cm2 ± 11%, while the cross section for the Oi 1300-Å multiplet has a maximum value of 3.8 × 10−18 cm2 ± 17%. The cross section for dissociative excitation of the Oi(3s1 1P0 → 2p4 1S) 1217.6-Å line is 1.5 × 10−19 cm2 ± 24% at 100 eV.
On the Molecular Theory of Dielectric Polarization in Rigid-Dipole Fluids
Authors: Ramshaw John D.
Published: February 2004

A molecular theory is developed for the polarization P(r) produced by a weak position-dependent external electric field E0(r) in a finite fluid system, of arbitrary shape, composed of rigid polar molecules. The theory differs from earlier work in that no assumption is made concerning the form of the electrostatic constitutive relation. [The usual assumption in this regard is that P(r) = (ε − 1)E(r) / 4π, where E(r) is the total Maxwell electric field. The “dielectric constant” ε is well defined only if the relation between P(r) and E(r) is in fact one of constant local proportionality.] The result of the present theory is a non-local relation between P(r) and the external field E0(r). The contribution to P(r1) produced by E0(r2) (r1 ≠ r2) is determined by the orientational correlation which exists in zero applied field between two representative dipoles located at r1 and r2. In principle this result may be used to investigate the conditions under which the dielectric constant is well defined, a question of considerable interest but one which has received little attention. The probable existence of long-range orientational correlations in polar fluids unfortunately precludes at present such an investigation for dense fluids, although for dilute gases the investigation can proceed by means of a density expansion. In this way it is demonstrated that the dielectric constant is well defined at least to second order in the density. This demonstration provides some insight into the connection between long-range dipolar effects on the macroscopic and molecular levels. It also yields automatically expressions for the first and second “dielectric virial coefficients”; these expressions agree with results obtained by previous workers under the assumption that the dielectric constant is well defined.
High-Resolution Infrared Spectra of ν5 and ν3 + ν6 of CH3I
Authors: Matsuura Hiroatsu , Overend John
Published: February 2004

The infrared spectra of the ν5 and ν3 + ν6 bands of CH3I have been measured with a resolution of about 0.03 cm−1. The excited states of these bands form a Fermi diad and, from the analysis of about 600 lines in the spectra, the matrix element of the Fermi-resonance operator was determined. From this the cubic normal-coordinate force constant k356 was found to be 29.40 cm−1. In addition to the Fermi resonance, a further perturbation due to an x-y-type Coriolis resonance between the states | υ5 = 1 〉 and | υ3 = 1, υ6 = 1 〉 was discovered and analyzed.
Self-Consistent-Field Study of the Series XeFn, n = 2, 4, 6
Authors: Basch Harold , Moskowitz J. W. , Hollister C. , Hankin D.
Published: February 2004

An ab initio self-consistent-field computation has been performed on the series XeF2, XeF4, and XeF6 in a basis of contracted Gaussian functions. The charge distribution, photoelectron and optical spectrum, and one-electron properties are discussed and compared with available experimental results.
Ordered Proton Configuration in Ice II, from Single-Crystal Neutron Diffraction
Authors: Kamb Barclay , Hamilton Walter C. , LaPlaca Sam J. , Prakash Anand
Published: February 2004

D2O ice II has a fully deuteron-ordered structure in which two crystallographically independent types of water molecule form a tetrahedrally linked network of H bonds, with the deuterons lying near but not on the O···O centerlines. Orientation of the molecules is nearly, but not exactly, symmetrical in the donor O···O···O angles. The D–O–D angles (average, 105.4°) do not differ significantly from the angle in D2O vapor (104.5°) although the corresponding O···O···O angles are smaller (average, 93.8°). Agreement between D–O–D and O···O···O angles is improved about 6° (on average) by a distortion of the bond network, from symmetry R3̄c to R3̄. The approach to a match between D–O–D and O···O···O angles is only partly responsible for the existence of proton ordering in ice II. Twinning of R3̄ individuals is established by variations in certain diffraction intensities from crystal to crystal. Mean O–D bond length (0.98 Å) is slightly longer than in the vapor (0.957 Å). Variations among the individual O–D distances (range 0.95–0.01 Å) do not correlate with the H-bonded O···O distances (range 2.77–2.84 Å) and hence are probably not significant.
A Theory of Molecules in Molecules. I
Authors: von Niessen W.
Published: February 2004

A theory of molecules in molecules is presented in which the wavefunction of a molecule is constructed from the wavefunctions of possible molecular fragments. In the formalism of the Hartree–Fock–Roothaan theory further approximations are introduced. In the formation of the new molecule from the molecular fragments the effects of the interaction on the charge distribution are regarded as important only in the molecular parts neighboring each other, but neglected in the other parts, which are regarded as unperturbed. The localized molecular orbitals constituting the wavefunctions of the fragments can therefore be transferred unaltered, if they lie outside the region of interaction, or are redetermined with the help of the variational principle. Our aim is to construct the wavefunction of a large molecule from the wavefunctions of two (or few) large fragments and in this way save in the computational time. No approximations in the Hamilton operator or in the integrals are made in the first formulation, but some approximations are required in the treatment of the orthogonality problem inherent in a theory of molecules in molecules. In a restricted form (calculation of only two modified orbitals) the theory is applied to determine the potential energy curve of two hydrogen fluoride molecules along the reaction coordinate FH–HF. A comparison with exact SCF–MO calculations demonstrates that good results are obtained for intermolecular distances larger than one atomic unit. On the basis of this justification the theory is generalized and reformulated. An arbitrary number of orbitals can be modified, where the orbitals are an expansion only over a subset of the total set of basis functions. This approach gives a high flexibility in the calculation of approximate wavefunctions.
Determination of Hyperfine Constants and Nuclear Shielding in Methyl Fluoride and Comparison with Other Molecules
Authors: Wofsy S. C. , Muenter J. S. , Klemperer W.
Published: February 2004

The molecular-beam electric resonance spectrum of methyl fluoride (CH3F) was measured in several rotational states. From analysis of the spectra the hyperfine structure of the molecule was determined. The hyperfine constants are (kilohertz): ζα=0.8±1.5, ζβ=14.66±0.7 for the spin—rotation interactions of the hydrogen nuclei, and cα=4.0±1.9, cβ=−51.1±1.3 for the spin—rotation at the fluorine. These results are combined with nuclear shielding data to calculate contributions to shielding and the electrostatic potential at the nucleus. Quantitative comparison is made with other molecules.
Theory of Light Scattering from Fluctuations of Membranes and Monolayers
Authors: Kramer Lorenz
Published: February 2004

General linear viscoelastic response relations are used to obtain the long-wavelength fluctuations of a thin membrane separating two viscous fluids. The intensity and spectrum of coherent light scattered inelastically from thermal fluctuations are calculated. It is found that the intensity is large enough to allow measurements on black membranes. Our theory includes clean surfaces, interfaces, and insoluble monolayers as special cases.
Microwave Spectrum of Iodostannane, SnH3I
Authors: Wolf Stephen N. , Krisher Lawrence C. , Gsell Ray A.
Published: February 2004

The pure rotational spectra of seven isotopic species of the chemically unstable symmetric top molecule iodostannane, SnH3I, have been measured in the region 28.3–31.6 GHz, using a microwave spectrometer. Each transition (J→J+1) exhibited a complex K structure due to quadrupole coupling and centrifugal distortion. A quadrupole coupling constant eQq=−1273±8 MHz and centrifugal distortion constant DJK=0.0041±0.0003 MHz were obtained from the analysis. Rotational spectra of vibrational excited states were observed for the most abundant isotopic species.
Comparisons of Dispersion Force Bounding Methods with Applications to Anisotropic Interactions
Authors: Langhoff P. W. , Gordon R. G. , Karplus M.
Published: February 2004

Comparisons and applications are made of the various procedures which have been devised recently for obtaining bounds to dispersion force coefficients. Particular attention is given to the methods based on approximate Gaussian quadratures and on Padé approximants, both of which require oscillator-strength sum rule values for their implementation. The equivalence of the bounds obtained from the two procedures, when identical input information is employed, is demonstrated to all orders, and the improvements that can result from the introduction of additional information, in the form of experimental transition frequencies and other sum rules, is investigated in the course of numerical applications. Comparisons with alternative bounding methods, such as those based on variational principles and related inner projection techniques, show that these procedures, which can also employ sum rule values for their implementation, are similar to the Gaussian quadrature and Padé methods and provide identical results if the same input information is employed. There also exists a second class of procedures which provides bounding inter-relations directly among the dispersion force coefficients, without reference to sum rule values, thus forming a useful complement to the former procedures. Numerical applications to molecular hydrogen, nitrogen, and oxygen, and the inert gases and alkali atoms, using both theoretical and semiempirical sum rule values, indicate that the bounding procedures can provide anisotropic dispersion force estimates of greater accuracy than those which can currently be extracted from rotational relaxation and related experiments. Comparison with more approximate methods for estimating the anisotropies in dispersion interactions, based on static polarizability anisotropies, serves to delineate the limits of accuracy of such approximations. The polarizability anisotropy approximation is found to provide overestimates in every case.
Method for Estimating Excess Kinetic Energy of Ionization Products in a Pulsed Ion Source
Authors: Platzner I. , Levin G. , Klein F. S.
Published: February 2004

The decay of thermal ions, produced in the pulsed ion source of a 60° magnetic sector mass spectrometer, was investigated and compared with calculations. The increased ion decay observed for several positive and negative ions is attributed to kinetic energy in excess of their ambient thermal energy. The dependence of the method on experimental conditions and particle collision effect is briefly discussed.
Three-Body Quantum Correction to the Free Energy of a Simple Liquid and the Role of Pair and Triplet Potentials in Isotopic Distillation
Authors: Present R. D. , Chen Chimin T.
Published: February 2004

The lowest-order quantum correction to the partition function and free energy of a simple dense fluid is generalized to take account of many-body forces. The three-body quantum correction is calculated using the triple-dipole potential for the nonadditive interaction, assuming the superposition approximation for the triplet correlation function, and taking the pair correlation functions from x ray and neutron diffraction experiments. In the case of liquid Ar near the triple point, the three-body correction is small enough to be neglected in connection with isotopic distillation experiments. These experiments provide values for 〈 ∇2U 〉, where U is the total interaction energy of the molecules in the liquid, and the results can be used in conjunction with experimental radial distribution functions to test empirical pair potentials u(r) for the Ar—Ar interaction. Several forms of u(r) are investigated and the Barker—Pompe, Kingston, and (exp-6) potentials are found to give the best results for 〈 ∇2U〉. The values of 〈 ∇2U 〉 test the repulsive region of the potential and are much less sensitive to the form of u(r) than is the vapor pressure of the liquid near the triple point. The vapor-pressure and isotopic-distillation tests are compared.
Theory of Fluorescence Depolarization by Anisotropic Brownian Rotations. Discontinuous Distribution Approach
Authors: Weber Gregorio
Published: February 2004

In this paper, we generalize to molecules devoid of symmetry the phenomenological treatment of depolarization of the fluorescence by the Brownian rotations of a spherical molecule due to Spencer and Weber. There are six ways in which a system of orthogonal coordinates rigidly bound to the molecule may be made to coincide with the laboratory coordinates. The transitions between these permissible orientations gives rise to a system of six differential equations of transport, the solution of which entails that of a differential equation of sixth order. However, because of the equivalence of some of the rotations as regards the depolarizing effects, on account of the symmetry conditions, the solution of a differential equation of third order is only necessary. Consequently, after an instantaneous light pulse, a polarized component of the fluorescence will show a maximum of three exponential decays and the difference of parallel and perpendicular components a maximum of only two decays. The steady-state fluorescence polarization from a completely assymetric molecule is given by a simple expression containing as only parameters a mean rotational rate, the variance of three orthogonal rates of rotation, and an average of these rates weighted according to their angles with the emission oscillator. A qualitative comparison of this treatment with previous theories of depolarization that make use of classical rotary diffusion theory shows that the former is better suited to an intuitive understanding of the phenomena and to experimental usage.
On Convergence Difficulties in the Iterative Hartree—Fock Procedure
Authors: Koutecký Jaroslav , Bonačić Vlasta
Published: February 2004

Different procedures for solving the nonlinear Hartree—Fock problem are analyzed. The classical iterative procedure involving recalculation of the one-electron density matrix in each step does not depend only on local properties of the one-electron density matrix in the previous step. Convergence difficulties arising from this fact are exhibited and analyzed for a diatomic molecule. There can result oscillation of atomic charges for larger internuclear distances. The resulting bond-order matrix does not correspond to any extremum of the expectation value of the Hamiltonian. Illustrative numerical examples are presented. Calculations for the PPP model of polyatomic chains show that the same effect can occur even for configurations slightly different from equilibrium ones.
Pulsed Laser Emission Chemically Pumped by the Chain Reaction between Hydrogen and Fluorine
Authors: Hess LaVerne D.
Published: February 2004

The chain reaction between hydrogen and fluorine mixed with helium has been successfully employed to generate laser emission from HF. Chemical reaction was initiated by flash photolysis of the reagents premixed at room temperature. Evidence for participation of the ``hot'' reaction, H ·+F2→HF*+F ·, in the laser pumping mechanism is presented. Approximately 7% of the laser radiation from this system is at wavelengths longer than 3.04 μ indicating that the large exothermicity of the ``hot'' reaction is not temporarily stored as population inversion between high vibrational levels of newly formed HF. Power and energy outputs up to 18 W/cc and 0.5 mJ/cc have been measured from dilute mixtures (40:1) at total pressures of 130 torr. Small-signal gains of 3%/cm, chemical efficiencies of ∼1%, and pulses having durations up to 140 μsec were observed. Computer calculations of reaction times are in good agreement with the pulse durations observed for a variety of experimental conditions.
Interaction of Electrons and Holes in a Molecular Crystal
Authors: Hug Gordon , Berry R. Stephen
Published: February 2004

A classical electrostatic model is used to compute the energy of an anthracene crystal containing an electron and a hole, each localized on specific sites. The calculation is carried out for a large number of sites and gives the effective potential hypersurface of interaction of the charges. The model includes real, finite charge distributions and anisotropic polarizabilities and is carried out to terms in induced-dipole—induced-dipole interactions, which are quite significant. The energy of the charge-transfer state is estimated as 3.84 eV, 0.39 eV above the experimental value. The model gives the energy of two infinitely separated charges as 5.77 eV, 1.85 eV above the reported threshold for intrinsic photoconduction. The energy of (dressed) charge—charge interaction is non-Coulombic for charges in different a, b planes, but is Coulombic if both charges lie in the same a, b plane, in which case the computed effective dielectric constant in the a, b plane is 1.25.
Optical Spectrum and Magnetic Properties of Er3+ in CaWO4
Authors: Enrique Bernal G.
Published: February 2004

The polarized optical spectrum of Er3+ in calcium tungstate at 4.2 and 77°K is reported. Radial integrals and spin-orbit coupling parameter derived from fitting the position of the centers of gravity of the J manifolds in intermediate coupling are F2=423.89 cm−1, F4=67.995 cm−1, F6=6.667 cm−1, ζ=2377 cm−1. A first-order crystal field calculation based on the intermediate coupling states of the free ion is shown to account very satisfactorily for the optical spectrum, paramagnetic resonance, and magnetic hyperfine structure when using 〈 r−3〉 and the nuclear moment measured by atomic beam triple magnetic resonance. The agreement between the experimental and calculated crystalline quantum numbers is encouraging since they were not forced to fit in the calculation. Also, the fact that the 〈 r−3〉 values obtained for a truly free erbium atom can be used for the case of the ion in a crystalline host indicates that the 4f wavefunctions are little affected by the surroundings. The values of the crystal field parameters obtained from fitting the optical spectrum are: C20= 231±7 cm−1,   C40= −90±2 cm−1,   C60= −0.6±0.5 cm−1, C44=±(852±18) cm−1,   C64=±(396±5) cm−1,   B6−4=±(75±12) cm−1. The above parameters predict the Stark splittings of the 53 states up to 25 000 cm−1 with an rms deviation of 4.4 cm−1. The calculated g factors are g∥c(Z1)=1.21, g ⊥c(Z1)=8.45, g∥c(Z2)=3.65, g ⊥c(Z2)=7.03; the corresponding measured values are 1.247, 8.38, 3.42, and 6.98, respectively. The calculated and measured values of the hyperfine structure constants are: Acalc167= 41.61×10−4 cm−1, Ameas167= (42.5±0.5)×10−4 cm−1, Bcalc167= 290.60×10−4 cm−1, Bmeas167= (293±3)×10−4 cm−1.
Rotatory Sense and Pitch of Cholesteric Liquid Crystals
Authors: Leder Lewis Beebe
Published: February 2004

Cholesteryl compounds can be either right-handed or left-handed cholesteric liquid crystals. It is shown that the cholesteryl skeleton is effectively right handed, and that additions at the 3β-carbon of the first ring tend to reduce the right handedness, i.e., increase the pitch. This effect can be expressed as 1/λ0=1/np=7.5d−15.6, where d is a distance measured in the direction of the 3β-carbon bond direction. For d>2.08 Å the liquid crystals become left handed, and the pitch now decreases with increasing distance d.
Further Significance of the Pariser Method for Evaluation of the One-Center Electron Repulsion Integral
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2004

There is a difference between the nonempirical and the semiempirical value of the one-center electron repulsion integral, even if correct recognition is made of the atomic species for which the semiempirical value of the integral is determined with consideration of an electron-transfer reaction according to Pariser. This difference has been analyzed for the integral which represents the average interaction of a pair of 2p electrons within an atom. It is shown that the main source of the difference is the failure of the usual nonempirical determination of the integral in considering properly the reorganization of the electrons occuring in the course of the electron-transfer reaction. The correlation energy is shown to have only minor contribution to this difference.
Application of Rayleigh—Schrödinger Perturbation Theory to the Hydrogen Atom. II
Authors: Gray B. F.
Published: February 2004

Various unsuccessful attempts to treat the hydrogen atom problem by perturbation theory, starting from a free particle as the unperturbed state, are examined. Calculations in closed form are presented, confirming the incorrect results but throwing light on the reasons for the failure, which occurs in spite of the fact that convergent power series expansions in the perturbation parameter exist, and of course are known explicitly. The failure is shown to be essentially due to nonuniform convergence at the point where the boundary conditions are applied, and furthermore this failure occurs for a wide class of potentials besides the Coulomb. Previous methods of avoiding this difficulty for the Coulomb potential are shown not to be of general validity.
Field Adsorption of Inert-Gas Atoms
Authors: Tsong Tien Tzou , Müller Erwin W.
Published: February 2004

A variational calculation shows that inert-gas atoms can only be adsorbed above protruding surface atoms, but not on flat metal planes or at surface lattice sites. The calculation also yields the effective polarizability of a helium atom near a metal plane. The inert-gas atoms are adsorbed at the apex of metal surface atoms by a field-induced dipole—dipole interaction. A statistical consideration expresses the probability of field adsorption in terms of experimental parameters. Preliminary atom-probe data on the temperature and field dependence of image gas adsorption agree with the theoretical results.
Model for Neutralization and Scavenging of Charges in Irradiated Dielectric Liquids. I. Evolution of the Neutralization Process in Multiple Ion-Pair Cases
Authors: Mozumder A.
Published: February 2004

A diffusion model has been constructed for calculating the survival probability, as a function of time, against neutralization in multiple ion-pair cases in irradiated dielectric liquids. Such situations are generated by the absorption of a substantial amount of energy in a relatively small region. The geometry of the region is taken as spherical for energy deposit 〈 500 eV and as cylindrical if energy deposit is ≥ 500 eV. The infinite-time limit of the so-calculated survival probability gives the probability of escaping charge neutralization which is calculated and compared with two experiments. The agreement is satisfactory. The mutual electrostatic interaction between the charges is considered through a screened field within the framework of prescribed diffusion. The relevant Smoluchowski equation is then integrated in time to give the desired survival probability. Special considerations, as described in the text, are necessary at long time limits. The results are compared between the two geometries used here and also with earlier work on isolated ion pair.
Dielectric Studies. XXX. Complex Formation and Intramolecular Hydrogen Bond Fission in ortho-Substituted Phenols
Authors: Magee M. D. , Walker S.
Published: February 2004

Dielectric constant and loss factors of o-nitrophenol, o-chlorophenol, guaiacol, 2,6-di-tert-butylphenol (DTBP), and 2,4-dinitrophenetole in p-xylene and o-nitrophenol in cyclohexane, each solution containing a specified mole fraction of a powerful electron donor molecule, 1,4-diazabicyclo-2,2,2-octane (DBO), have been determined at four or five microwave frequencies at 25°C. Consistent analyses into contributions from two Debye terms could not be obtained for any of the solutions except that of DTBP. The mean relaxation times, distribution coefficients, and dipole moments all show considerable changes compared with solutions of the same molecules not containing any DBO. The solutions of 2,4-dinitrophenetole and DTBP are exceptions. The data can be explained by complexing of the DBO with the phenols via a hydrogen bond involving the hydroxyl hydrogen. Since the intermolecular hydrogen bond competes with the DBO for the hydrogen of the hydroxyl group a significant amount of complexing must correspond to rupture of a proportion of intramolecular hydrogen bonds even in the case of the o-nitrophenol. The absence of complexing with 2,4-dinitrophenetole, a highly polar molecule, shows that dipolar interactions are not important. Only weak interaction seems to occur with DTBP and DBO, and this may be attributed to the bulky tert-butyl groups shielding the phenolic proton.
Microwave Spectrum, Barrier to Internal Rotation, and Dipole Moment of cis-3-Pentene-1-yne
Authors: Ford Robert G. , Beaudet Robert A.
Published: February 2004

The microwave spectrum of cis-3-pentene-1-yne has been observed in the region 8–38 gHz. The barrier to internal rotation of the methyl group was found to be 1140 cal/mole from splittings of the rotational transitions. The rotational constants are A=11790.60 MHz, B=3388.17 MHz, C=2672.20 MHz. The total dipole moment is 0.78D.
Perturbation Theory for Nonuniform Fluids: Surface Tension
Authors: Toxvaerd So/ren
Published: February 2004

The Barker—Henderson perturbation theory for uniform fluids is extended to include nonuniform fluids. The surface tension for a Lennard-Jones fluid is calculated by minimizing the free energy in the surface layer. Comparison with the corresponding experimentally obtained values of surface tension for argon shows that excellent agreement is obtained in the case of a Lennard-Jones 12–6 fluid with values of the potential parameters determined from the second virial coefficient.
Gas-Phase Recombination of Hydrogen. A Comparison between Theory and Experiment
Authors: Shui Ven H. , Appleton John P.
Published: February 2004

The modified phase-space theory of reaction rates has been used to calculate the three-body recombination and dissociation rate coefficients of hydrogen in the presence of H2, He, Ar, and Xe collision partners. The theoretical predictions, which rely on semiempirically derived interatomic potential information, are shown to be in excellent agreement with the measured rate coefficients over wide temperature ranges.
Excited-State Intermolecular Interactions Involving Paramagnetic Molecules: Effect of Spin—Spin and Spin—Orbit Interactions on the Quenching of Triplets
Authors: Kearns David R. , Stone A. J.
Published: February 2004

The effects of spin-spin interactions on the rate constants, kq, for the quenching of excited triplet-state molecules by molecular oxygen and NO have been examined. Depending upon the strength of the electrostatic interactions between the excited triplet-state molecule and molecular oxygen, kq may vary from kd, the diffusion-controlled value, down to kd/9. In agreement with experimental observations, oxygen is predicted to be a better triplet-state quencher than is NO. The analysis also suggests that through application of sufficiently high magnetic fields, it should be possible to observe changes in the quenching constant and that this effect could be used to obtain information about the nature of the electrostatic interactions which are present in the collision complex between the excited triplet-state molecule and paramagnetic quenchers.
Isotope Effects in the Photoionization Yields and in the Absorption Cross Sections for Methanol, Ethanol, Methyl Bromide, and Ethyl Bromide
Authors: Person James C. , Nicole Paul P.
Published: February 2004

The values of the absorption cross section σ and the photoionization yield η (the probability that photon absorption produces ionization) have been experimentally determined for CH3OH and CD3OD, C2H5OH and C2D5OD, CH3Br and CD3Br, and C2H5Br and C2D5Br at various photon energies in the energy range of 9.97–11.78, 10.32–11.78, 10.08–11.78, and 9.97–11.78 eV, respectively. In each case, there is increased ionization for the deuterated molecule over a part of the energy range studied. This increase is seen in the values of both η and the photoionization cross section, σi(σi=η σ), and it is discussed as evidence for the competitive preionization of intermediate states. The effects of methyl substitution on σ and σi are also discussed, and ionization potentials are reported for each gas.
Liquid Metal Equation of State Based on Scaling
Authors: Grover Richard
Published: February 2004

Experimental data on the equation of state of liquid metals are summarized to show that a corrected entropy of melting can be taken as a constant for all metals and that the specific heat in the liquid has a universal dependence on the ratio of the temperature to the melting temperature. From these correlations, together with the Lindemann law for melting, an approximate equation of state for liquid metals is developed.
Hulthén Transform Functions for the Excited States of Two-Electron Atoms
Authors: Gruninger John
Published: February 2004

Hulthén functions are used to approximate the 2p and 3d orbitals of the lowest 1P, 3P, 1D, and 3D states of helium and to approximate the 2p orbitals of the lowest 3P states of the two-electron ions of Li, Be, and B. The orbital approximations and energies of the singlet states obtained using Hulthén 1p and 2d functions are identical to those obtained by Chong from minimal basis Slater 2p and 3d functions. The Hulthén 1p functions differ significantly from the Slater 2p functions only for the 3P states. The energies obtained for the 3P states are lower than those obtained from the minimal basis Slater functions. Using the new results for the 1P and 3P states of He, a term separation of 0.0087 a.u. is obtained. This value is in close agreement with the Hartree—Fock value of 0.0088 a.u.
Some Applications of Time-Dependent Rate Constant Theory to Radiation Chemistry
Authors: Schwarz Harold A.
Published: February 2004

It is well known that rate constants for diffusion-limited reactions decrease with time after the start of an experiment, an effect due to the time required to establish a diffusion gradient of each reactant around the other. It is pointed out that slow reactions between ions also exhibit a time dependence because a finite time is required to establish the Boltzmann distribution of each type of ion around the other. The latter effect appears as an increase of rate constant with time for reactions between ions of opposite charge and a decrease for ions of similar charge. These time dependent effects are applied to the picosecond pulse radiolysis results of Wolff et al. on electron formation and decay in acetone and acid solutions, and to some competition experiments of Czapski and Peled. Effects attributed by them to reactions of a precursor of the hydrated electron are shown to be similar to expected consequences of time-dependent phenomena of the hydrated electron itself.