bluuebunny/crossref_metadata_2025 huggingface dataset:
Orbital Energy Spectra of Electrons in Chemisorption Bonds: O, S, Se on Ni(100)
Authors: Hagstrum H. D. , Becker G. E.
Published: February 2004

This work presents the first experimental determinations of orbital energy spectra of electrons in chemisorption bonds. Our method, ion neutralization spectroscopy, determines a transition density function which is essentially the local density of states in the surface region of the solid. For the particular surface formed by chemisorption of the chalcogens in ordered, surface-crystalline arrays on Ni(100), the local density of states includes a strong component from the orbital energy spectrum of the electrons in the bonds of the surface molecules formed from the adsorbate atom and Ni atoms presented by the substrate lattice. The orbital levels of electrons in the surface bonds are broadened resonances or virtual states in whose energy range local wavefunction magnitude and hence transition probability for ion neutralization are enhanced. These orbital energy spectra, coupled with measurement of work-function change on adsorption, suggest, in many instances, plausible identifications of local bonding structures. For the specific cases of O, S, or Se(≡X) adsorbed in c(2 × 2) or p(2 × 2) arrays on Ni(100), the following tentative conclusions are drawn. The S or Se adsorbed in the c(2 × 2) structure forms a local bridge-type Ni2X surface molecule in which the chalcogen is bridged across the diagonal of the (1 × 1) surface unit square Ni mesh. The orbital energy spectrum in this case shows three orbital peaks in the available energy range analogous to what is seen for the free H2X molecule having C2υ symmetry. The S or Se in the p(2 × 2) surface arrangement exhibits a simpler spectrum in the available energy range consistent with π-type bonding in a pyramidal Ni4X structure of C4υ local symmetry. Oxygen, on the other hand, in either c(2 × 2) or p(2 × 2) surface-crystal structures, produces a broad resonance whose displacement relative to the energy of the atomic p orbital shows O to be considerably more negatively charged in its structure than are S and Se in theirs. This result coupled with measurements of work-function change and thermal behavior points strongly to a reconstructed surface in which O replaces Ni in the topmost layer of the crystal.
Light Scattering by Coupling of Orientational Motion to Sound Waves in Liquids
Authors: Ben-Reuven A. , Gershon N. D.
Published: February 2004

The fine features in the Rayleigh wings of light scattered from various liquids, observed by Starunov, Tiganov, and Fabelinskii, and by Stegeman and Stoicheff, and associated with shear waves according to the Leontovich theory, are explained from a molecular correlation-function point of view, based on the Kubo–Zwanzig–Mori theory. These features are attributed to a “bottleneck” effect, in which the short-lived Brownian orientational motion (“tumbling”) is coupled to a long-lived (hydrodynamic) sound mode. Line-shape expressions and an estimate of the magnitude of the effect are given.
Spin–Orbit Coupling in Aromatic Hydrocarbons. Analysis of Nonradiative Transitions between Singlet and Triplet States in Benzene and Naphthalene
Authors: Henry Bryan R. , Siebrand Willem
Published: February 2004

Rate expressions for intersystem crossings in aromatic hydrocarbons are formulated by treating both the spin–orbit coupling and the nuclear kinetic-energy operators as perturbations causing the nonradiative transition. General expressions are derived for the corresponding matrix elements, which are shown to fall into three groups, corresponding to three different mechanisms. In the first, which is subject to an electronic orbital selection rule, the transition is caused by spin–orbit coupling only. In the second and third, spin–orbit coupling and vibronic coupling act together, namely, Herzberg–Teller vibronic coupling in the second, and diabatic (non-Born–Oppenheimer) coupling, caused by the nuclear momenta, in the third mechanism. It is shown that in aromatic hydrocarbons spin–orbit coupling between π states governs the second mechanism and spin–orbit coupling between π and σ states the third mechanism. The three mechanisms are distinguished by the effect of partial deuteration on the rate constant, which may or may not give rise to a position-dependent deuterium effect, and by the different rate constants associated with the three sublevels of the triplet state. From these observations and quantitative calculations of the spin–orbit and vibronic matrix elements in benzene and naphthalene, it is concluded that in naphthalene T1↝S0 is governed by the third mechanism, and that in benzene the first and second mechanism may play a role in S1↝T1 and T1↝S0, respectively.
Study of a Refined Model for Aqueous 1-1 Electrolytes
Authors: Ramanathan P. S. , Friedman Harold L.
Published: February 2004

The hypernetted-chain integral equation is used to calculate the ion–ion pair correlation functions and the thermodynamic properties of models for aqueous alkali halides based on an ion–ion pair potential function having four terms: the usual Coulomb term, a core repulsion term of order r−9, a well-known dielectric repulsion term of order r−4, and a “Gurney” term to represent the effect of the overlap of the structure-modified regions, “cospheres,” about the ions when the ions come close together. The only parameter in the potential which is adjusted to fit excess free energy data for solutions is the coefficient Aij of the Gurney term for the interaction of ions of species i and j. This is scaled so it represents the molar free energy change of water displaced from the cospheres when they overlap. The corresponding entropy change Sij and volume change Vij are adjusted to fit, respectively, heat of dilution and apparent molal volume data. Some thermodynamic problems in this fitting process, due to the underlying McMillan–Mayer theory, are considered in detail. Good agreement is obtained between computed model properties and experiment for various sets of these parameters. Detailed results are given for one consistent set of Aij, Sij, and Vij parameters for all the alkali halide solutions for which the required data are available. The Aij parameters are in the range from 100 to − 200 cal/mole. Since this is small compared to RT, the thermodynamic data for these solutions can be interpreted without assuming rigid hydration of any of the ions, a conclusion previously reached by Rasaiah from the study of quite different models. The trends in A+− with variation of species do seem to reflect hydration and structure-breaking effects in the solutions. The sign of S+− is paradoxical, also in agreement with Rasaiah's results, while V+− and S+− seem to be mutually consistent.
Quadrupole Coupling and Anisotropic Chemical Shifts in Some Manganese Carbonyls
Authors: Spiess H. W. , Sheline R. K.
Published: February 2004

Single crystals of a number of manganese carbonyls were studied by broadline NMR at room temperature. In the pentacarbonylhalides, Mn(CO)5X, the 55Mn quadrupole coupling constants (e2qQ / h) are 13.86 MHz (X is Cl), 17.46 MHz (X is Br), and 19.85 MHz (X is I). The asymmetry parameters are only 0.024–0.043, indicating rather high symmetry of the molecules in the solid. The halogen NMR was also observed and analyzed to give values for the quadrupole coupling parameters; 35Cl: e2qQ / h = 36.07 MHz, 81Br: e2qQ / h = 226.7 MHz, 127I: e2qQ / h = 927 MHz with η values of 0.03–0.06. The z axes of the field-gradient tensor at the manganese sites were found to lie along the Mn–X bond. The anisotropic chemical shifts of 55Mn in these compounds and (C5H5)Mn(CO)3 were also determined. In the Mn(CO)5X series the shift anisotropy decreases in the order Cl>Br>I (σzz − σxx = 1.3‰, 1.2‰, 1.0‰). The z component of the shift tensor was found to be constant within the series, but different from the isotropic shift in Mn(CO)6+. The parameters were compared to the results of a recent MO calculation for this series.
Time-Dependent Perturbation Calculations Based on the Hydrodynamic Analogy to Quantum Mechanics
Authors: Weiner J. H. , Askar A.
Published: February 2004

A new formulation is presented for the problem of the time-dependent perturbation of bound states. It is based on the hydrodynamic analogy to quantum mechanics and leads to the physical picture of a continuum of particles which oscillate in the vicinity of their equilibrium positions under the influence of the perturbing field. The corresponding mathematical formulation involves a single partial differential equation which is second order in time and fourth order in the spatial coordinates. The procedure is applied to the time-dependent polarizability of the hydrogen atom in its ground state. It was possible to obtain an exact series solution which yields results in full agreement with those previously obtained by other methods.
Quantum Yield of Ozone Formation from Photolysis of the Oxygen Molecule at 1849 and 1931 Å
Authors: Washida Nobuaki , Mori Yuji , Tanaka Ikuzo
Published: February 2004

Photolysis of oxygen molecules at 1849 and 1931 Å has been studied. The quantum yield of ozone formation by decomposition of excited oxygen molecules is 2.0 at 1849 Å above 100 torr, and 0.3 at 1931 Å between 300 and 1300 torr. The present measurements of absorption coefficients of oxygen at 1849 and 1931 Å show that the 1849 Å line of mercury coincides with no rotational absorption line of υ′ = 8; on the other hand, the 1931 Å line coincides approximately with a rotational absorption line of υ′ = 4. The experimental results of quantum yield of ozone formation can be explained by the consideration that the direct transition from the ground state to the repulsive Πu3 state occurs at 1849 Å, and the transition to the rather stable rotational level of B 3Σu− occurs at 1931 Å.
Long-Range Intermolecular Forces using Gaussian Basis Functions. A Model Calculation
Authors: Singh T. R. , Meath William J.
Published: February 2004

The charge-induced dipole induction energy and the dipole–dipole dispersion energy for the ground state H–H+ and H–H interactions are used as model energies for investigating the feasibility of using Gaussian basis functions to calculate long-range intermolecular forces. The use of various types of Gaussian basis sets to represent the first-order wavefunction, Ψ(1), in the calculation of the interaction energies and the errors introduced into the calculations by using Gaussian representations of the exact zeroth-order wavefunctions for the isolated atoms are considered. Satisfactory long-range forces, at least for the simple interactions considered here, can be obtained by using small Gaussian basis sets to represent the interaction, that is Ψ(1), and/or the zeroth-order wavefunction.
Monte Carlo Calculations of Energy Partitioning and Isotope Effects in Reactions of Fluorine Atoms with H2, HD, and D2
Authors: Muckerman J. T.
Published: February 2004

A total of 16 000 three-dimensional classical trajectories on an optimized semiempirical potential energy surface were computed for collisions of F atoms with H2, HD, and D2. Analysis of the reactive trajectories indicates general agreement with results of infrared chemiluminescence and chemical laser studies with respect to the partitioning of the available energy among the translational, rotational, and vibrational degrees of freedom in the reaction products. Of particular interest is the calculated effect of reactant rotation on the reaction cross sections for all the isotropic systems, and on the intramolecular isotope effect in the reaction of F with HD. These phenomena have not as yet been seen experimentally.
Band Shape of Optical Rotatory Dispersion
Authors: Lin S. H.
Published: February 2004

The main object of this paper has been to show that the band shape of optical rotatory dispersion can be quantitatively interpreted by taking into account the radiation damping effect which removes the singularities associated with optical rotatory dispersion and by regarding the dispersion curve of optical rotation to consist of a series of lines that merge into a simple broad band. The strength of each individual line is to a large extent determined by the Franck–Condon factor. To illustrate this approach, an example has been given.
Charge-Transfer Excitation Produced in Collisions of He+ and N2+ with Alkali Atoms
Authors: Salop A. , Lorents D. C. , Peterson J. R.
Published: February 2004

Optical excitation produced in collisions of He+ and N2+ with alkali atoms has been investigated using a crossed beam apparatus. Studies of the spectral radiation were made in the near uv and visible wavelength region for ion kinetic energies 50–1600 eV. For He+ on K and Rb, the spectra observed were identified primarily with excited alkali ions resulting from electron capture into the ground state of He. The relative weakness of near-resonant excitations and the generally small magnitude of the emission cross sections are explained by the fact that the active electron moves from a closed shell of K or Rb to the 1s shell of He; orbital overlap requires a close encounter in which the atoms are strongly perturbed. For N2+ on K, the predominant spectra are the bands of the second positive system in N2 resulting from electron capture into the excited C 3Πu states of N2. Emission cross sections were large (10−17–10−16 cm2) having energy dependence characteristic of near-resonant charge-transfer reactions and the population distribution of the various vibrational states corresponded to the Franck–Condon factors for transitions between N2+(X) and N2(C). These features arise because the outermost electron of the alkali moves to an excited orbital of N2 so that orbital overlap favors a transfer at large distances, a process in which the collision partners are only slightly perturbed.
Deactivation of Vibrationally Excited Carbon Dioxide (001) by Collisions with Carbon Monoxide
Authors: Rosser W. A. , Sharma R. D. , Gerry E. T.
Published: February 2004

The rate constants associated with the deactivation of vibrationally excited CO2*(001) by collisions with CO have been experimentally determined from 300 to 900°K by a laser fluorescence method. These reactions involving CO considered were CO2*(001)+CO⇆ lim k2k1CO2+CO*(υ = 1), CO2*(001)+CO→ lim kCOCO2(ν1, ν2)+CO, CO*(υ = 1)+CO2→ lim k4CO+CO2(ν1, ν2), where CO2(ν1, ν2) is an unidentified product state. Within experimental error the rate constant k1 increases linearly with temperature T(°K) from a value of 5.7 × 103 torr−1·sec−1 at room temperature to a value of 11.2 × 103 torr−1·sec−1 at 900°K. From 500 to 900°K the rate constant kCO(torr−1·seconds−1) varies with temperature as log10kCO = A − BT−1/3, with A = 6.61 and B = 31.6. From 300 to 500°K the measured values of kCO are greater than those corresponding to the cited relation. The rate constant k4 was found to be negligible compared to kCO. The probability per collision of vibrational energy transfer from CO2*(001) to CO(υ = 0) was computed by a theory involving long range forces. The calculated probabilities, using only multipolar interaction and only exponential repulsive interaction, are in equally good agreement with the probabilities deduced from measurement of R1, the transfer rate constant in the exothermic direction.
Microscopic Reversibility for Rates of Chemical Reactions Carried Out with Partial Resolution of the Product and Reactant States
Authors: Kinsey James L.
Published: February 2004

Applications of the principle of microscopic reversibility are considered for reaction rates measured in experiments that reveal some of the dependence on the rotational, vibrational, and/or translational states of the reactants or products. Each type of measurement establishes a characteristic set of quantum states for the reactants and products, suggesting that removal of trivial statistical factors (densities of states) from the data to retrieve a purely dynamical quantity ω̄(E), the state-to-state reaction rate suitably averaged over the initial and final sets of states at fixed total energy E. This quantity is fully symmetric with respect to the direction of the reaction—either the forward or reverse rate coefficient can be obtained by multiplying ω̄ with the proper density of final states. Thus ω̄ reflects the intrinsic probability of the process, disregarding the statistical bias introduced by the nature of the experiment itself. Methods of accurate computation of state densities appropriate to several kinds of detailed kinetic measurements currently feasible are given.
Laser Induced Fluorescence of ClO2
Authors: Sakurai Katsumi , Clark John , Broida H. P.
Published: February 2004

Fluorescence spectra of the A(2A2)–X(2B1) system of ClO2 excited by five visible Ar-ion laser lines (4579–4880 Å) have been observed over a wavelength region from near excitation to beyond 7000 Å. Approximately 60 fluorescence bands have been observed for each laser line excitation and about half of these bands have been assigned. Vibrational constants of the ground state have been calculated from observed band positions.
Time Derivatives of Entropy Production near Equilibrium
Authors: Yao S. J.
Published: February 2004

We have shown here that the first and second time derivatives of entropy production, for a near-equilibrium isolated system which consists of an open subsystem and a large particle reservoir, are alternate in sign.
Electron Paramagnetic Resonance of Electron Irradiated K3Rh(CN)6 in a KCl Lattice
Authors: Muniz R. P. A. , Vugman N. V. , Danon J.
Published: February 2004

Electron irradiation of the diamagnetic Rh(CN)63− ion in a KCl host lattice produces three paramagnetic species. EPR studies reveal that one of the species can be assigned as Rh(CN)4Cl24−, of D4h symmetry, 4d7 low spin configuration, arising from the trapping of an electron in a dz2 orbital followed by the substitution of two axial cyanides by chloride ions. The experimental data have been interpreted in terms of a spin Hamiltonian yielding the principal values of the g and hyperfine tensors as g‖ = 1.995, g⊥ = 2.297, A‖Rh = − 40.8 × 10−4cm−1, A⊥Rh = − 36.9 × 10−4cm−1, A‖Cl = + 27.8 × 10−4cm−1, A⊥Cl = + 12.4 × 10−4cm−1. Theoretical estimates of g values confirm this assignment. A semiempirical estimate of the unpaired electron density on the metal and ligands is presented.
Studies of Ferroelectric Solids by Magnetic Resonance. XVIII. Proton and Deuteron Resonance of Thiourea
Authors: O'Reilly D. E. , Peterson E. M. , Saffar Z. M. El
Published: February 2004

The deuteron nuclear magnetic resonance of thiourea-d4 has been studied in the paraelectric Solid V at 300°K and above and in the ferroelectric Solid I at 120°K. The electric field gradient (EFG) tensors at 300°K demonstrate that the molecules are undergoing rapid 180° flip motion about the C–S bond as deduced earlier from proton second moments by Emsley and Smith. Complex deuteron spectra were observed at 120°K and fully analyzed. The quadrupolar coupling constant e2qQ / h and asymmetry parameter η for the inner and outer deuterons are inner:e2qQ / h = 212 ± 3 kHz,η = 0.154 ± 0.007,outer:e2qQ / h = 207 ± 3 kHz,η = 0.180 ± 0.016. The orientation of the principal coordinate systems of molecules 1 and 2 for the inner deuterons confirm the ferroelectric structure proposed by Goldsmith and White. The x and z principal axes of the outer deuterons deviate by about 10° from the plane defined by the heavy atoms. This appears to be due to an actual noncoplanarity of the outer N–D bonds with the plane of the molecule as indicated by earlier electron and neutron diffraction studies. Proton relaxation times T1 and T1ρ have been measured from 240 to 420°K. T1 reaches a minimum near 400°K and T1ρ a corresponding minimum near 270°K which are assigned to the 180° flip process. Near 330°K a secondary minimum in T1ρ is observed which is assigned to a ferroelectric mode process associated with Solid I. Below 290°K the deuteron resonance lines of the outer deuterons are observed to split into two components separated by 2.2 kHz. This splitting is ascribed to a slowing down of another motional process which involves a small change of the quadrupolar coupling constant due to a small change in the orientation of the outer N–D bonds.
Phase-Transfer Theory and Its Application to Long Chain Molecules: DNA
Authors: Tong B. Y. , Tong S. Y.
Published: February 2004

Phase-transfer theory is applied to study two unrelated phenomena in DNA molecule: (a) the electronic structure of DNA and (b) the helix–coil transition, also known as denaturation. It is shown from theory that some spectral lines and gaps are always there in all DNA molecules irrespective to the arrangements of the four fundamental groups: adenine (A), thymine (T), guanine (G), and cytosine (C). This explains the fact that optical spectroscopy shows a lot of over-all similarities in the various DNA molecules. To study the helix–coil transition, the usual Ising model is used with periodic boundary condition at the two infinite ends of the molecule. Exact and explicit expressions for the transitions are obtained for any periodically arranged molecule. An exact expression can also be written down for the random molecule, if the order of the A–T and G–C pairs can be specified. The width of the transition is shown to be the maximum in the 50% A–T pairs and 50% G–C pairs. Strong interactions between the neighboring pairs are indicated by the fact that steplike transition curves are not observed in experiments.
Vibrational Relaxation and Electronic Quenching of the C 3Πu (υ′ = 1) State of Nitrogen
Authors: Calo Joseph M. , Axtmann Robert C.
Published: February 2004

A molecular lifetime apparatus was used to study energy transfer processes of the C 3Πu state of nitrogen. Kinetic and luminosity measurements as a function of pressure indicate a cross section σ(3) = 2.5 ± 0.7 Å2 for vibrational relaxation of N2(C 3Πu)υ′=1 by ground-state nitrogen molecules. A useful result of the kinetic analysis is that although the observed lifetime (including quenching) decreases with υ′, vibrational relaxation reduces the gross C state luminescence decay to a single exponential, characteristic of the υ′ = 0 level. Natural radiative lifetimes and electronic quenching cross sections, σ(2), were determined for the υ′ = 0 and υ′ = 1 levels of the C state: υ′ = 0: τ = 40.5 ± 1.3 nsec and σ(2) = 1.98 ± 0.02 Å2; υ′ = 1: τ = 44.4 ± 1.4 nsec and σ(2) = 1.42 ± 0.71 Å2. Estimates of electronic and vibrational deactivation cross sections for the υ′ = 2 level are υ′ = 2: σ(2) = 3.9 ± 0.8 Å2and σ(3) = 1.6 ± 0.4 Å2. The efficiencies for excitation of the υ′ = 0 and υ′ = 1 levels by the secondary electronsproduced by fission fragments are in the ratio 1.0:0.44. It is argued that the C 3Πu(υ′ = 1) state deactivates in two ways through a common N4 intermediate, viz., C 3Πu(υ′ = 1) + X1Σg+(υ′ = 0) ± N4(C2υ)→ lim IB 3Πg(υ″ = ξ) + X 1Σg+(υ″ ≥ 0) → lim IIC 3Πu(υ″ = 0) + X 1Σg+(υ″ = 0) and that the strong vibrational relaxation is accounted for by a nonadiabatic mechanism originally proposed by Nikitin for vibrational relaxation of ground-state NO.
Absolute Oscillator Strengths for the CH+, CD+, and BH A 1Π–X 1Σ+ Transition
Authors: Smith William Hayden
Published: February 2004

Radiative lifetime measurements for the CH+(CD+) A 1Π state (70 ± 25 nsec) and for the BH A 1Π state (159 ± 16 nsec) are reported. Absolute oscillator strengths are computed using RKR Franck–Condon factors. Astrophysical implications of these data are indicated.
Electron Spin Resonance of the CN Molecule Trapped in Gamma-Ray Irradiated Potassium Cyanate
Authors: Owens Frank , Breslow Richard A. , Gilliam O. R.
Published: February 2004

Electron spin resonance (ESR) studies have been made on single crystals of potassium cyanate (KNCO) that have been irradiated with gamma rays at room temperature. Two ESR spectra resulted. One of these consisted of an S = 12 center displaying a three-line hyperfine structure. This spectra is assigned to a CN molecule. The molecule occupies two sites in the lattice in which the molecular axis is parallel to the [110] and the [11̄0] directions of the unit cell. The parameters of the spin Hamiltonian deduced from the spectra are | A‖ | = 5.0 ± 0.5 G, | A⊥ | = 2.3 ± 0.5 G, | Aiso | = 3.2 ± 0.5 G, and g⊥ = 1.999 ± .002. The g‖ is not determined.
EPR Linewidth Study of Vanadyl Complexes in Various Solvents
Authors: Angerman N. S. , Jordan R. B.
Published: February 2004

The temperature dependences of the EPR linewidths for vanadyl acetylacetonate, VO(acac)2, have been measured in ethanol, n-propanol, isopropanol, n-butanol, t-butanol, trifluoroethanol, and trichloroethanol. A similar study has been carried out on vandayl trifluoroacetylacetonate, VO(tfac)2, in methanol and the solvated vanadyl ion, VO2+, in water. The EPR linewidths have been measured at 25°C for VO2+ in dimethyl sulfoxide, trimethyl phosphate, acetonitrile, N ,N-dimethylformamide, and methanol. The results are interpreted in terms of the theory proposed by Kivelson et al. to obtain rotational correlation times (τR) for the various systems. The results generally conform to the predictions of the modified Debye theory, in that τR and solvent visocity show the expected temperature dependence. Only VO(tfac)2 in methanol appears to be anomalous in this respect. A detailed analysis has shown that one of the parameters (γ) in Kivelson's expression for the linewidths is less sensitive to experimental error and therefore best suited for calculations of τR. The results indicate that at low temperature some mechanism in addition to spin–rotational relaxation is contributing to the “residual” linewidth.
Spectroscopic Determination of the Pseudorotation Barrier in Selenacyclopentane
Authors: Green W. H. , Harvey A. B. , Greenhouse J. A.
Published: February 2004

The infrared and Raman spectra of selenacyclopentane have been studied. A series of far-infrared absorption peaks is interpreted to indicate that the five-membered ring molecule has a large barrier to pseudorotation. The derived potential function is V(φ) in cm−1 = − (1795.4 / 2)[1 − cos(2φ)] + (13.45 / 2) × [1 − cos(4φ)] − (86.19 / 2)[1 − cos(6φ)] with the pseudorotation constant B = 1.55 cm−1. Evidence that the molecule has a twisted (c2) configuration in its lowest few vibrational states has been obtained.
Electron Paramagnetic Resonance of V2+, Mn2+, Fe3+, and Optical Spectra of V3+ in Blue Zoisite, Ca2Al3Si3O12(OH)
Authors: Tsang Tung , Ghose Subrata
Published: February 2004

Electron paramagnetic resonance and optical absorption spectra have been used to clarify the local environments of transition metal ions and their distributions among various Al and Ca sites in a gem quality zoisite crystal from Tanzania. The EPR spectra due to Mn2+, Fe3+, and two types of V2+ have been interpreted by the spin Hamiltonian βH·g·S + I·A·S + D[Sz2 − 13S(S + 1)] + E(Sx2 − Sy2) in the principal axes system x, y, z. The Mn2+ ions occupy one of the Ca sites, probably Ca(1), with point group symmetry m; g = 2.003 ± 0.005 and | A | = (85 ± 2) × 10−4cm−1, both isotropic, and also | D | = (103 ± 5) × 10−4cm−1, | E | = (34 ± 2) × 10−4cm−1, in general agreement with other oxides and hydrates. Highly anisotropic hyperfine and small zero-field splittings (| D | < 0.014 cm−1) are observed for V2+, which is the opposite of the usual situation. One of the two types of V2+ apparently occupies the same site as Mn2+; the other V2+ ion is in a general position, and probably occupies a double minima potential around the Ca(2) site. The Fe3+ ions occupy the AlII site since the point group symmetry is m; the principal axes, however, are displaced approximately 45° from the NMR axes of 27Al. Apparently, the local environment changes when Al3+ ions are replaced by Fe3+. For Fe3+, we found | D | = 0.14 ± 0.03 cm−1 and | E | ∼ 0.1 | D |. The optical absorption of V3+ and the trichroism of the zoisite single crystal are consistent with the two types of Al3+ site symmetries, with crystal field parameters Dq = 1850 and 1400 cm−1 at AlI and AlII sites.
Far-Infrared Absorption Spectra of Mercurous Halides
Authors: Ōsaka Toshiaki
Published: February 2004

The absorption spectra of mercurous halides Hg2X2 (X=Cl, Br, and I) were measured at 300 and 90°K in the wavenumber region 400–10 cm−1. Besides the two strong bands observed previously for each mercurous halide, some weak bands were found at 371, 310, and 156 cm−1 for chloride, at 310, 223, 156, and 113 cm−1 for bromide, and at 112 cm−1 for iodide. By use of a simple crystalline lattice model, the observed infrared spectra of halides together with the Raman spectra reported already could reasonably be explained. New assignments for the spectra are proposed and some force constants are determined.
Noniterative Solutions of Integral Equations for Scattering. V. Auxiliary T(kj) Matrix Formalism
Authors: Hayes Edward F. , Kouri Donald J.
Published: February 2004

The homogeneous integral solution method is used to develop a scheme for direct computation of the T matrix. The method involves calculation of auxiliary matrices T(kj) in terms of which the true T matrix is obtained. The auxiliary T(kj) matrices can be obtained by solving either integral or first-order linear non-homogeneous differential equations. The relationship of calculations based on these equations to those based on the wavefunction integral equations is discussed. Numerical studies of the general behavior of the homogeneous integral solution procedure are presented. These studies deal with rotationally inelastic collisions of an atom and a rigid rotator interacting via a Morse-type potential. An investigation of some higher-order numerical schemes for solving the integral and differential equations for the auxiliary matrices and the integral equations for the wavefunction is reported. The results indicate that the use of higher-order procedures such as the Runge–Kutta method or Simpson's quadrature scheme permit one to use step sizes 5–10 times larger than those required with the trapezoidal quadrature scheme (or equivalently, the uncorrected Euler method for the differential equation) to achieve a given accuracy. The role of the potential function is studied by a comparison of the | T |2 matrix elements for Lennard-Jones (12–6) and Morse potentials having the same well depth, curvature, and equilibrium position. In addition, hybrid potentials constructed by splicing together Morse and Lennard-Jones potentials are studied. The results indicate that, at the energy considered, the long-range portion of the potential has a dominant effect on the elastic and inelastic scattering.
Microwave Spectrum, Structure, and Dipole Moment of Cyclopropylphosphine
Authors: Dinsmore Lee A. , Britt Chester O. , Boggs James E.
Published: February 2004

The microwave spectra of three isotopic species of cyclopropylphosphine have been analyzed. The conformation of the molecule is the symmetric one allowing maximum interaction of the lone pair electrons of phosphorus with the intra-annular orbitals of the cyclopropyl ring. A structure compatible with the observed moments of inertia yields, along with other parameters, a C–P bond distance of 1.834 Å, distinctly shorter than that observed in other organic phosphine derivatives. The dipole moment is found to be 1.16 D.
Absolute Rate of the Reaction H+H2S
Authors: Kurylo Michael J. , Peterson Norman C. , Braun Walter
Published: February 2004

Flash photolysis coupled with resonance fluorescence of Lyman-α radiation at 121.6 nm has been used to investigate the rate of reaction of H atoms with H2S over the temperature range 190–464°K. Conditions were chosen under which atom–radical and radical–radical reactions were unimportant and only the H-atom–H2S reaction occurred. The rate constant thus obtained can be expressed as k1 = (1.29 ± 0.15) × 10−11exp[− (1709 ± 60) / 1.987T] cm3molecule−1·sec−1. Comparison of the Arrhenius A factor with that predicted by entropy considerations suggests a somewhat loose activated complex, but not as loose as expected on the basis of the exothermicity of the H+H2S reaction.
Nuclear Magnetic Resonance Study of Li3P Powder
Authors: Ossman G. W. , Silvidi A. A.
Published: February 2004

NMR spectra of lithium phosphide were obtained. The coupling constant for site 1 is 68.5 ± 3.0 kc/sec and for site 2 it is 16.0 kc/sec (upper limit). Asymmetry parameters are zero. Measured coupling constants are inconsistent with a pure ionic or a pure covalent model but are consistent with both Suchet's model and the Z2 = + 1 model, implying a degree of covalent bonding. Temperature studies show abrupt linewidth narrowing between roughly − 60 and 0°C. The narrowing is attributed to diffusion of the lithium ions.
Faraday Effect in Molecules
Authors: Chang Tai Yup
Published: February 2004

An expression for the Verdet constant appropriate for quantitative calculation is derived using double perturbation theory. This expression is used to calculate the Verdet constant for molecular hydrogen within the uncoupled Hartree–Fock approximation. This approximation turns out to underestimate the Verdet constant by a factor of about 2 for most of the range of wavelength considered.
Relative Rate Constants for Reactions of O(1D) Atoms Generated by Flash Photolysis of Ozone
Authors: Scott P. M. , Cvetanović R. J.
Published: February 2004

In view of the large disparities in the values of some rates of destruction of the excited (singlet) oxygen atoms O(1D), flash plotolysis of ozone in the presence of excess nitrous oxide has been used as an alternative source of O(1D) atoms to measure relative rates of their reaction with a number of added gases. The values obtained for SF6, He, CO2, Xe, neopentane, and N2O are consistent with the earlier results from this laboratory obtained using entirely different sources of O(1D) atoms. The relative rates of O(1D) reactions with H2O vapor and O2 have also been determined and the values obtained are compared with the data in the literature.
Anomalous Specific Heat of Sodium Trihydrogen Selenite—An Associated Combinatorial Problem
Authors: Abraham Douglas B. , Lieb Elliott H.
Published: February 2004

This paper presents the exact solution of a lattice statistical problem posed by Makita and Miki in their theory of the anomalous specific heat of the ferroelectric sodium trihydrogen selenite. We conclude with a comparison of the experimental and calculated entropies.
Effect of the Solvent on the ESR Parameters of Copper Acetylacetonate
Authors: Adato I. , Eliezer I.
Published: February 2004

The study of the ESR spectra parameters of Cu(Acac)2 in different solvents shows that the anisotropy of the nuclear hyperfine interaction tensor varies with changes in solvent. The effect is most clearly exhibited by the parameter A⊥. A correlation is obtained between the spectral data and the nature of the solvent ligand. The results are in agreement with the empirical parameters DII,I of Selbin and DN of Gutmann. Our empirical parameter is also a moderately sensitive one for ranking solvents.
Symmetry Coordinates, Harmonic Force Field, and Mean Amplitudes for Light and Heavy Dibenzene Chromium
Authors: Cyvin S. J. , Brunvoll J. , Schäfer Lothar
Published: February 2004

The molecular vibrations of dibenzene chromium are analyzed in terms of the eclipsed 25 atomic model of symmetry D6h with planar ligands. A complete set of symmetry coordinates is constructed and based almost entirely on conventional types of valence coordinates. A harmonic force field is given, and is used to calculate the vibrational frequencies, mean amplitudes of vibration, and perpendicular amplitude correction coefficients for (C6H6)2Cr and (C6D6)2Cr.
Self-Diffusion, Spin-Lattice Relaxation, and Density of SF6 near the Critical Point
Authors: Tison J. K. , Hunt E. R.
Published: February 2004

We have measured the self-diffusion coefficient D and the 19F spin–lattice relaxation time T1 of SF6 along the liquid–vapor coexistence curve and several isochores using nuclear magnetic resonance. The density was also measured in the same samples. The samples were purified and mass spectrographically analyzed to be pure to 0.01%. The density values are interpreted in terms of the critical index β which is found to be 0.337 ± 0.012. The results of the self-diffusion and relaxation time measurements show no anomalous behavior in the critical region. The spin–rotation interaction appears to be the predominant relaxation mechanism in the range of our measurements. From the measured values of D and T1, both the linear momentum and angular momentum correlation times can be evaluated. The ratio of these times is a measure of the effectiveness of a collision in producing a change in the angular momentum of a molecule.
EPR Investigation of Irradiated Strontium and Zinc Acetate Single Crystals
Authors: Tolles W. M. , Sanders R. A. , Gisch R. G.
Published: February 2004

X-ray irradiation of strontium acetate hemihydrate produces CH3CȮ22− and not the methyl radical as in other acetates. At higher temperatures this spectrum is replaced with two magnetically distinct ·CH2CO2− radicals. In the presence of the propionate ion, further reaction proceeds at about − 30°C to yield one rotamer of one magnetically distinct CH3ĊHCO2− radical. The ratio of propionate/acetate damage at room temperature is found to be 700:1 in strontium acetate, indicating some mechanism for the delocalization of the damage. This same reaction with a substituted propionate ion occurs in zinc acetate with a ratio of 20:1. The coupling tensors for all species are presented.
Ultraslow Hydrogen Motion in KH2PO4 and NaH3(SeO3)2 Type Crystals
Authors: Blinc R. , Pirš J.
Published: February 2004

Ultraslow reorientational motions of the H2PO4 and H2SeO3 groups have been studied in KH2PO4, RbH2PO4, CsH2PO4, LiH3(SeO3)2, NaH3(SeO3)2, KH3(SeO3)2, and CsH3(SeO3)2 by dipolar and rotating frame proton spin–lattice relaxation measurements. The measured values of the reorientational correlation times change from about 10−3 sec at room temperature to about 10−5 sec at 100°C. The activation energies for the hindered rotation of the H2PO4, respectively, H2SeO3 groups are controlled by the size of the cation rather than by the strength of the O–H···O bonds, and vary from 0.4 to 1.4 eV. In contrast to the case of ice this slow reorientational process dominates the dc protonic conductivity of both the KH2PO4 and the NaH3(SeO3)2 group of hydrogen bonded crystals.
Semiclassical Theory of Vibrational Excitation for Diatomic Molecules with Conserved Collision Energy
Authors: Hansen C. Frederick , Pearson Walter E.
Published: February 2004

The semiclassical method for calculating collision induced vibrational transitions in diatomic molecules is extended to account for conservation of energy. Asymmetric distortions of the collision perturbation are found to have little effect on the transition probability, but symmetric distortions, associated with energy transiently stored in vibrational modes at the collision turning point, decrease the transition probability by factors of about 1.5 to 2. This correction does not significantly change the interaction potentials deduced from vibrational relaxation data.
Irreversible Statistical Mechanics of Polymer Chains. II. Viscosity
Authors: Iwata Kazuyoshi
Published: February 2004

The Fokker–Planck diffusion equation derived in the previous paper is applied to Erpenbeck–Kirkwood theory on the viscosity of polymer solutions. The Newtonian viscosity for ring polymers is given by ηN = 2ckT ∑ σ = 1N τσ / (1 + iωτσ), where τσ is the relaxation time, c is the number of polymers in unit volume, and kT has the usual meaning. Without hydrodynamic interactions among monomer units, the relaxation time is given by τσ = γσ2 / 2Dσ, where γσ and Dσ are, respectively, the expansion parameter and the diffusion constant in regard to the normal coordinate Qσ. With hydrodynamic interactions, the relaxation time is modified as τσ′ = τσ(1 + kTT̃σ / Dσ), where T̃σ is the σth eigenvalue of Kirkwood–Riseman tensor.
Absolute Generalized Oscillator Strengths for Four Electronic Transitions in Carbon Monoxide
Authors: Lassettre Edwin N. , Skerbele Ausma
Published: February 2004

Generalized oscillator strengths have been measured for the υ′ = 2 level of the fourth positive bands of carbon monoxide by comparing inelastically and elastically scattered electrons at 300-, 400-, and 500-eV kinetic energy and using the elastic collision cross sections measured by Bromberg [J. Chem. Phys. 52, 1243 (1970)]. Extrapolation to zero momentum change gives f0 = 0.0429. From relative intensity measurements, the limiting oscillator strengths of the levels from υ′ = 0–12 have also been determined. From zero angle spectra, the limiting oscillator strengths for transitions to the B 1Σ+, C 1Σ+, and E 1Π states have been determined. The values are 0.0153 ± 0.0014, 0.163 ± 0.015, and 0.094 ± 0.009, respectively; υ′ = 0 in each case. Relative intensities in the fourth positive bands have also been determined (and redetermined) at various angles and kinetic energies. Possible variation in relative intensities with scattering angle is discussed. A possible reason is given for the large discrepancy (a factor of 2) between the oscillator strength obtained for the entire fourth positive bands from electron impact and from lifetime measurements by other investigators.
ESR of the BO Molecule in Inert Matrices: A Case of Extreme Preferential Orientation
Authors: Knight Lon B. , Easley Warren C. , Weltner William
Published: February 2004

The BO molecule has been trapped in neon and argon matrices at 4°K in its ground Σ2 state and investigated by ESR spectroscopy. It is trapped in only one site in solid neon and is highly oriented with respect to the sapphire surface of condensation. The neon spectra indicate that BO molecules lie in vertical planes perpendicular to the surface and an analysis of their distribution within the planes places them preferentially either perpendicular or parallel to the surface. The derived magnetic parameters in neon are g‖ = 2.0012(3), g⊥ = 2.0015(3), A‖(11B) = 1018(1) MHz, A⊥(11B) = 1034(1) MHz. A‖ < A⊥ implies that the dipolar nuclear hf coupling is negative, a unique condition in diatomics. It is shown that it may be accounted for by including the effects of AO's centered on oxygen in the dipolar interaction at the boron nucleus.
Classical Oscillator Model for Electric Quadrupole Transitions
Authors: Freedhoff Helen S.
Published: February 2004

A classical oscillator model for electric quadrupole transitions is presented, analogous to the Lorentz oscillator model for electric dipole transitions. The model allows one to describe classically the processes of spontaneous emission, scattering, and absorption, taking into account the force of radiative reaction. Transition probabilities, spectra, and the dielectric dyadic of a material due to quadrupole transitions are calculated. All quantities agree completely with the corresponding quantities obtained quantum mechanically.
129I Mössbauer Effect in Several Charge-Transfer Complexes of Iodine
Authors: Ichiba S. , Sakai H. , Negita H. , Maeda Y.
Published: February 2004

The Mössbauer effect of the 27.8-keV transition in 129I has been studied in the iodine complexes I2·phenazine, I2·acridine, and I2·hexamethylenetetramine. The Mössbauer spectrum of the I2·phenazine complex has shown only one chemical species of iodine, whereas those of the other complexes have shown the existence of two species of bridging and terminal iodine. From the Mössbauer parameters such as the isomer shift, quadrupole coupling constant, and asymmetry parameter, the electron distribution on the iodine atoms in the complexes was calculated. In the I2·phenazine complex, 0.09e− is transferred to the iodine atom from the phenazine molecule. In the I2·acridine and I2·hexamethylenetetramine complexes, the charges on the bridging iodine atoms are decreased and those on the terminal atoms are increased. In the later complex, a net charge of 0.08e− is transferred to the iodine molecule through the nitrogen atom from the hexamethylenetetramine molecule.
ESR Study of an Acetylenic Radical in Two Host Crystals. X-Irradiated Methyl-2-Nonynoate Trapped in Urea and Perhydrotriphenylene Inclusion Crystals
Authors: Birrell G. Bruce , Lai Allen A. , Griffith O. Hayes
Published: February 2004

Single crystals of methyl-2-nonynoate–urea and methyl-2-nonynoate–perhydrotriphenylene inclusion compounds were x irradiated at 77°K and investigated by ESR at room temperature. The stable radical observed in both inclusion crystals is CH3(CH2)4CH–C≡C–CO2CH3. This radical exists in quite different conformations in the two host crystals. All spectra are well resolved and agree with computer-simulated spectra. A table of proton coupling constants and g values is given.
Estimate of Potential Surface for K–Cl–Cl
Authors: Nyeland Carl , Ross John
Published: February 2004

An estimate of the potential surface of the system (K–Cl–Cl) has been made by first considering the configuration (K+, Cl2−) in a perturbation and variation treatment, and then considering with the aid of a number of approximations the combination of ionic and neutral terms (K, Cl2), (KCl, Cl).
Atomic and Molecular Calculations with the Pseudopotential Method. VIII Two-Valence-Electron Photoionization Cross Sections
Authors: McGinn George
Published: February 2004

A two-electron pseudopotential method is used to evaluate wavefunctions for the two-valence-electron systems: Li−, Be, B+, C+2, Mg, Al+, and Si+2 in the ns2S1 ground state and the nsεp 1P continuum states. For the ground state and the continuum states of all the systems treated a Hartree–Fock wavefunction is used. In addition, for the ground states of the Be isoelectronic sequence a Hylleraas-type correlated wavefunction for the two-valence electrons with the following number of variational parameters is used: Li− 6 and 15 parameters; Be 6 and 20 parameters; and B+ and C+2 6 parameters. Using these wavefunctions the photoionization cross section for the ns2−nsεp transition is evaluated in both the dipole length and the dipole velocity forms for all systems. Previous calculated values, mostly for Be, are also discussed.
On the Diffusion Coefficient of Triplet Excitons in Anthracene
Authors: Hoesterey D. C. , Robinson G. W.
Published: February 2004

The experimental data of Williams and Adolf on the diffusion of triplet excitons in crystalline anthracene are analyzed within the framework of a theory which properly accounts for the diffusion of the excitons during the time of the measurement. The effect of this diffusion is to make the maximum of the delayed fluorescence appear at a longer exciting wavelength than that predicted by the theory that was used to analyze the data. It appears as if the data are consistent with a diffusion constant in the c′ direction of 1.6 × 10−5 cm1/sec, a reduction of about a factor of three from the reported value, and consistent with the value reported by Ern [V. Ern, Phys. Rev. Letters, 22, 343 (1969)].
Mössbauer Spectra and Magnetic Susceptibility of Neptunium Tetrachloride below 85°K
Authors: Stone J. A. , Jones E. R.
Published: February 2004

Magnetic properties of NpCl4 were studied from 2.6 to 8.5°K, with the Mössbauer resonance of the 59.54-keV γ ray in 237Np, and with magnetic susceptibility measurements from 4.3 to 43°K using a vibrating-sample magnetometer at applied fields of 50 to 10 000 Oe. A ferromagnetic transition was found at 6.7 ± 0.1°K. Above the Curie temperature, NpCl4 obeys the Curie–Weiss law χ = C / (T − θ) with θ equal to 6.9°K, giving an effective moment of 3.08 μB. The Mössbauer data define the temperature dependence of the hyperfine fields in NpCl4. The behavior of the magnetic hyperfine field at the Np nucleus parallels that of the magnetization in the ferromagnetic region, giving an extrapolated H(0) of 3000 kOe. In the paramagnetic region only a small temperature-independent quadrupole splitting was observed.