bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Transfer in the De-excitation of (H3+) by H2
Authors: Leventhal J. J. , Friedman L.
Published: February 2004

Proton transfer from H3+ to H2 has been investigated in a tandem mass-spectrometer system. Evidence for efficient de-excitation of H3+ in approximately one collision has been obtained by study of threshold for collision-induced dissociation of D3+ and reactions in the H3+–C2H2, H3+–C2H4, and H3+–CH4 systems. The results suggest a transfer mechanism which leaves behind as product an excited neutral hydrogen molecule containing most of the internal energy of the original triatomic molecular ion.
Complex Defects in CoO
Authors: Hed A. Z.
Published: February 2004

The isobaric electrical conductivity of CoO has been measured in the range 850°–1200°C, at oxygen pressures between 10−0.88–10−2.88 atm. From the slopes of the isobars it is concluded that the enthalpy of formation of some of the defects is negative, and these defects are therefore complex. It is suggested that the dominant complex defect consists of an interstitial Co cation and two Co vacancies.
Effect of Ligand-Field Terms in Approximate Molecular-Orbital Calculations on Metal Complexes
Authors: Canadine R. M. , Hillier I. H.
Published: February 2004

An approximate molecular-orbital scheme is developed and used to assess the contribution of ligand-field terms in calculations of the electronic structure of inorganic complexes. Comparative calculations on the MnO4− ion by this and other methods are presented, and it is shown that the self-consistent charge distribution, and hence the interpretation of the nature of the bonding, is critically dependent on the formalism of the off-diagonal elements.
Rodlike Model for a Polyelectrolyte Solution with Mono- and Divalent Counterions
Authors: Dolar D. , Peterlin A.
Published: February 2004

The charge distribution of simultaneously present mono- and divalent counterions and the degree of ion binding is calculated for the simplified rodlike model of polyelectrolyte solution without addition of low-molecular-weight electrolyte. Divalent ions concentrate much more than monovalent ions in the vicinity of the charged macromolecule and hence push the monovalent ions farther away. As a consequence, the degree of binding of divalent ions increases and that of monovalent ions decreases with increasing of the equivalent fraction of the other type of ions. This agrees with the dependence of the selectivity coefficient of ion exchange on the fraction of ionic species within the resin phase.
Dissociative Attachment of Electrons in Ammonia and Ammonia-d3
Authors: Sharp T. E. , Dowell J. T.
Published: February 2004

Cross sections for total negative ions and amino negative ions have been measured as a function of energy for dissociative attachment of electrons in the gases NH3 and ND3. Two peaks are observed, at 5.65 and 10.5 eV. Both peaks contain H−(D−) and NH2−). Small direct isotope effects were found, in negative ion production, except for H−/D− formation at 5.65 eV where the isotope effect was 1.0. The peak at 5.65 eV leads to products in their ground states. The corresponding potential-energy-vs-internuclear-distance (H–NH2) curve for NH3− may contain a hump or may merely have a shallow slope in the Franck–Condon region. The peak at 10.5 eV arises from a repulsive state of NH3−, and the amino fragment is formed in an excited state. Empirical trends in the isoelectronic series methane, ammonia, and water are identified.
Structure of the Alkali Hydroxides. IV. Interpretation of Vibration–Rotation Interactions in CsOH and RbOH and Refinement of Structures
Authors: Lide David R. , Matsumura Chi
Published: February 2004

A new formulation of the vibration–rotation interactions in linear triatomic molecules is developed for the purpose of explaining the anomalies found in the microwave spectra of CsOH and RbOH. This formulation, which explicitly takes into account the curvilinear nature of the motions, leads to a some-what different partitioning of the interaction constant α2 into harmonic and anharmonic contributions. The harmonic contribution resulting from direct averaging of the moment of inertia over the bending mode is found to dominate the α2 constant in most linear molecules, in contrast to the traditional treatment, which leads to a large anharmonic contribution. In the alkali hydroxides the harmonic and anharmonic parts are comparable in magnitude but of opposite sign; the resulting cancellation is responsible for the unusual vibrational dependence of Bυ in these molecules. The deuterium isotope shifts of Bυ are in excellent agreement with the predictions of this treatment. All of the microwave and infrared data on CsOH and RbOH are consistent with a reasonable force field, although uncertainties in the harmonic force constants prevent a quantitative determination of anharmonic constants. In the absence of contrary evidence, we conclude that the alkali hydroxides very probably have a linear equilibrium configuration. The equilibrium bond lengths in CsOH are estimated to be: rCsO. = 2.391 Å, rOH = 0.960 Å; in RbOH: rRbO = 2.301 Å, rOH = 0.957 Å.
Neutralization of Isolated Ion Pair in Polar Media. I. Theory for the Yield of Solvated Electrons
Authors: Mozumder A.
Published: February 2004

Motion of an isolated ion pair in a polar medium is described here through the Smoluchowski equation with a time-dependent dielectric constant. The time dependence is taken as appropriate to constant charge rather than to constant external field. Explicit solution of the problem is obtained in the framework of prescribed diffusion. This solution, in the infinite time limit, gives the escape probability. The yield of escaped electrons is identified with the solvated electron yield. Known yields in various polar media are used to calculate the respective thermalization distances and effective dielectrc constants. Dielectric relaxation time is explicitly used in the present formulation. Two diffusion constants are used, one prior and one after relaxation. Calculated results are compared with experiment. Physical concepts derived from the present model relate to thermalization length, effective dielectric constant, and diffusion–relaxation length.
Mössbauer Spectra of Tetrahedral Alkali Dithioferrates (III)
Authors: Raj Deo , Puri S. P.
Published: February 2004

Mössbauer spectra were taken of a series of compounds with tetrahedrally coordinated (sp3) iron (III) having a general formula AFeS2, where A=Na, K, Rb, Cs, over a temperature range 77°–300° K. The molar susceptibilities were also examined over the same range of temperatures. The almost temperature independence of ΔEQ indicates that level separation is larger or ∼ kT. In contrast to the observations in the case of octahedral compounds, the increasing electronegativity of the cation increases the isomeric shift (I.S.) value. This is explained by the fact that the decreasing electronegativity of the cation increases the partial 4s character at iron in the compound. Furthermore, it is pointed out that the Walker, Wertheim, and Jaccarino (WWJ) plot is applicable to the compounds having tetrahedrally bonded (sp3) iron. The internal magnetic field in KFeS2 at − 28°C is considered to result not from any magnetic transition, but from relaxation effects, whereas in the case of Na, Rb, and Cs dithioferrates it has been averaged to zero.
Long Radiative Lifetimes of Small Molecules
Authors: Bixon Mordechai , Jortner Joshua
Published: February 2004

In this paper, we apply a theory of electronic relaxation in polyatomic molecules for the study of the anomalously long radiative lifetimes of NO2, CS2, and SO2. We have classified medium-size molecules which exhibit intramolecular vibronic coupling into two intermediate cases, which we call the sparse intermediate case and the dense intermediate case, characterized by low and high spacing of the vibronic levels relative to the radiative width. The radiative decay in the sparse intermediate case was considered in detail, taking advantage of the coarse level spacing and the extremely short intramolecular recurrence time encountered in this case. From our model calculations, we conclude that:

(a) in the sparse case, the radiative decay rate is characterized by a superposition of slowly varying exponentials;

(b) the mean radiative lifetime is expressed as a radiative lifetime calculated from the integrated oscillator strength and “diluted” by the number of states within the half-width of the manifold of coupled levels;

(c) no intramolecular electronic relaxation processes are encountered in this case;

(d) a qualitative interpretation of the complex molecular spectra is provided.
Molecular SCF Calculations for ScH3NH3 and TiH3F
Authors: Stevenson Philip E. , Lipscomb William N.
Published: February 2004

Exact minimum Slater basis sets have yielded LCAO–MO–SCF wavefunctions for the model compounds ScH3NH3 and TiH3F. The dative bond in ScH3NH3 has a small overlap population (0.11 electron) and a small charge transfer of only 0.12 electron from N into, primarily, 4pz and 3dz2 of Sc, but there are comparable redistributions among the orbitals of e symmetry as well. The charge on F in TiH3F is − 0.28e, and the Ti–F bond has overlap populations of 0.20e in bonding orbitals of a symmetry, and 0.18e in those of e symmetry. Changes on each H atom (attached to the metal) are − 0.28e in ScH3NH3 and − 0.30e in TiH3F.
Analytical Evaluation of Energy Eigenvalues for a Class of Anharmonic Oscillators
Authors: Handelsman Richard A. , Lew John S.
Published: February 2004

For the family of potentials V(x) = Axm + Bx2m, B > 0; m = 2, 4, 6, ···, this paper derives analytical expressions for eigenvalues of the one-dimensional time-independent Schrödinger equation. The required eigenvalues are first defined implicitly through the authors' form of the asymptotic expansion of the quantum condition given originally by Dunham. For the stated family of potentials, the integrals which appear in this expansion are evaluated in terms of hypergeometric functions, and expanded in series. A technique is then developed for reversion of the resulting series, by which the eigenvalues are given directly as an expansion in powers of two well-defined variables. This technique is used to exhibit 13 terms of the resulting series and is shown to yield as many terms as may be desired. A second-order approximation obtained from this double series is evaluated for the special potentials V(x) = Ax2 + Bx4 and V(x) = Bx2m with m = 2, 4, 6. Our analytical results, known in principle to be increasingly accurate for higher eigenvalues, are then compared with the numerical or seminumerical computations of other authors and found in practice to yield excellent agreement as low as the third and fourth eigenvalues.
Bimolecular Reaction of N2O with CO and the Recombination of O and CO as Studied in a Single-Pulse Shock Tube
Authors: Lin M. C. , Bauer S. H.
Published: February 2004

The reaction between N2O and CO was studied in a single-plus shock tube over the temperature range 1320°–2280°K, in mixtures of the reactants highly diluted with Ar. In the range of temperatures 1317°–1908°K the rate constant for the bimolecular reaction, N2O+CO→ lim 1N2+CO2, was found to be k1 = 1.1 × 1011exp(− 23 000 / RT) cm3mole−1·sec−1. From the rates of formation of CO2 above 1642°K, a constant for the nonradiative third-order recombination of O and CO was obtained (for the temperature range 1500°–3000°K), O+CO+Ar5→ lim 5CO2+Ar, k5 = 2.8 × 1012exp(+ 23 800 / RT) cm6mole−2·sec−1. The large negative activation energy so deduced is shown to be in full agreement with the low value for the activation energy previously observed for CO2 decomposition. An energy diagram was constructed on the basis of a recent CO flame study and results on the limiting high-pressure CO2 decomposition. The mechanisms for the radiative and the three-body recombination, and the dissociation of CO2, are discussed in terms of this energy diagram.
Nuclear Magnetic Relaxation Studies of Internal Rotations and Phase Transitions in Borohydrides of Lithium, Sodium, and Potassium
Authors: Tsang Tung , Farrar T. C.
Published: February 2004

Proton spin–lattice relaxation times, T1, have been measured as a function of temperature for KBH4, NaBH4, and LiBH4. For NaBH4 and KBH4, 23Na and 11B relaxation measurements were also made. In all cases, the magnetization recovery is approximately exponential. Correlation times, τc, derived from the T1 data were used to calculate activation energies, V, for BH4− ion reorientations. For the cubic phase of KBH4, V = 14.8 ± 0.4 kJ/mole (3.55 ± 0.1 kcal/mole) (± always refers to rms error) from measurements on proton and 11B. For NaBH4, V was found to be 11.2 ± 0.5 and 14.8 ± 0.7 kJ/mole (2.7 ± 0.1 and 3.5 ± 0.2 kcal/mole) for the high- (cubic) and low-temperature (tetragonal) phases; an anomaly in τc was observed at temperatures slightly below the phase transition, and may be interpreted as a relatively sudden change in V associated with the phase transition. In LiBH4, a rather broad minimum was observed for the proton T1 vs temperature; this has been interpreted as due to two inequivalent BH4− tetrahedra with activation energies of 20 ± 1 and 16 ± 1 kJ/mole (4.7 ± 0.3 and 3.8 ± 0.3 kcal/mole). The proton and 11B nuclei are relaxed by magnetic dipolar interactions, but quadrupolar fluctuations are the dominating relaxation mechanism for 23Na in the cubic phase of NaBH4.
Microwave Spectrum of Dimethylgermane
Authors: Thomas E. C. , Laurie Victor W.
Published: February 2004

The rotational spectrum of the five Ge isotopic species of dimethylgermane has been investigated in the region 8–35 GHz. All identified transitions were split into quartets by the internal rotation of the methyl groups. From the splittings a barrier V3 = 1182 cal/mole has been determined. Rotational constants for the A1A1 ground torsional state of the 74Ge species are A = 12 522.67 MHz, B = 5587.68 MHz, and C = 4264.57 MHz. No hyperfine structure due to the quadrupole moment of 73Ge was resolved giving upper limits | χaa | < 3.0 MHz, | χbb | < 3.6 MHz. Stark-effect measurements gave a dipole moment of 0.616 D. With assumption of the methyl-group dimensions, structural parameters for the heavy atoms were calculated to be: rCH = 1.083 Å (assumed), ∠HCH = 108.5° (assumed), rCGe = 1.950 ± 0.003 Å, ∠CGeC = 110.0 ± 0.5°. No tilt of the methyl groups was detected.
Ultrasonic Absorption in Aqueous Solutions of Dextran
Authors: Hawley S. A. , Dunn F.
Published: February 2004

The ultrasonic absorption measured in aqueous solutions of dextran (1–6 polyanhydroglucose) as a function of molecular weight (3.4 × 103–3.7 × 105) and frequency (3–195 MHz) reveals a relaxational behavior related to the calculated viscoelastic properties of free-draining random coils.
Ultraviolet Absorption Cross Sections for the Thallium Halide and Silver Halide Vapors
Authors: Davidovits P. , Bellisio J. A.
Published: February 2004

The ultraviolet cross sections for the thallium and silver halide vapors were measured in the region 2200–4500 Å. In the region of the main continua the cross sections are between 5 × 10−17 cm2 and 1 × 10−17 cm2. For the thallium halides the data revealed a new process consisting of two closely spaced absorptions. It is shown that this process may be due to transitions into states formed by interactions between excited atomic and ionic potentials. For the silver halides there is a significant continuum absorption on the long-wavelength side of the band structure. This indicates that there is a repulsive state below the bound excited state of the molecule.
Electron-Diffraction Structural Study of Polymeric Gaseous Hydrogen Fluoride
Authors: Janzen Jay , Bartell L. S.
Published: February 2004

Electron diffraction patterns with molecular interference features extending beyond s = 35 Å−1 were obtained for gaseous self-associated HF introduced under its own vapor pressure at −19° and at +22°C through a conventional nozzle system into a 40-kV electron beam. The diffraction patterns and their dependence on temperature are best explained with the hypothesis that the monomer and a puckered, cyclic hexamer were the only appreciable constituents of the scattering vapors. Mean FFF angles in the hexamer were found to be only about 104°, in contrast with the 120° angles reported for the infinite planar zigzag chains in crystalline HF at −125°C. This pucker may simply be a consequence of thermal bending of the extremely flexible ring. Indeed, the experimental radial distribution function is so smeared out by large ring-bending amplitudes that the data cannot distinguish between boatlike and chair conformations. It is likely that the free (HF)6 molecules sweep randomly through both conformations in their thermal undulations. At the two temperatures studied the hydrogen-bonded FF distances were 2.525 and 2.533 Å, with standard errors of 0.003 Å, in comparison with the solid-state result of 2.49 ± 0.01 Å. Corresponding FF amplitudes of vibration were 0.089 and 0.101 Å (±0.003 Å), respectively. Perhaps 70% at −19° and 45% at 22° of the hydrogen bonds were asymmetric with covalent FH distances 0.040 Å longer than those in the monomer molecules. The data suggest, however, that the remainder of the ring protons migrate a substantial distance off-axis to a more symmetrical disposition between the fluorines.
ESR Measurement of Quadrupole Coupling in N(SO3)22−
Authors: Close David M. , Rexroad Harvey N.
Published: February 2004

The so-called second-order transitions in ESR spectra, which involve a change in both electron and nuclear spin, are sensitive to electric quadrupole coupling. The quadrupole interaction for 14N in N(SO3)22− was studied by observation of these transitions at 31.5 GHz in single crystals of γ-irradiated potassium aminedisulfonate. The resulting spectra can be explained assuming the principal axis system of the field-gradient tensor is the same as the hyperfine coupling tensor. The coupling constants then become e2Qqx′x′ = − 5.2 ± 1.4 MHz and e2Qqy′y′ = + 3.2 ± 1.0 MHz, where the x′ and y′ principal axes have direction cosines of (0.829, 0, 0.559) and (0, 1.0, 0) in an a* bc axis system.
Alternant Molecular Orbitals without Spin Projections
Authors: Musher Jeremy I.
Published: February 2004

A new method for utilizing different orbitals for different spins is proposed which obviates the procedures usually employed to project states of desired multiplicities out of a single determinantal function. The method, which calculates an approximation to a spatial eigenfunction of the Hamiltonian rather than to the total wavefunction itself, serves to simplify calculations not only for alternant molecular orbitals, but also for wavefunctions of the valence-bond and nonpaired spatial-orbital type.
Mössbauer-Effect Studies of Lattice Dynamic Anisotropy and Line Asymmetry in Semiconductor and Organometallic–Tin Compounds
Authors: Stöckler Hans A. , Sano Hirotoshi
Published: February 2004

The lattice dynamic anisotropy in double-layer molecules of stannous sulfide and dioctyltinoxide was investigated in the temperature range of 60°–320°K by observing the Karyagin effect in Mössbauer doublet spectra. It was found that in molecules with a two-dimensional polymeric network the motion of the Mössbauer atom is largest in the direction perpendicular to the plane of the extended layer and that the lattice dynamic anisotropy increases at higher temperatures. The “polymer effect” enhances the recoilless fraction by restricting the motion of the molecule in the direction of the polymer bonding. An analysis for the evaluation of absolute values of the recoilless fraction has been outlined. It was shown that stannous selenide is lattice dynamically and electronically isomorphous with stannous sulfide. The observed lattice dynamic anisotropy in both SnS and SnSe would contribute to the anisotropic semiconducting behavior in these materials. It was suggested that a rigid-body treatment as applied to a layer-type structure could be extended to include the motion of atoms on the surface of small particles. A Thirring expansion analysis was used to determine the frequency moment in the high-temperature limit for SnS.
Shock-Tube Studies of Sulfur Hexafluoride
Authors: Bott J. F. , Jacobs T. A.
Published: February 2004

Shock-tube kinetic studies of SF6 dissociation in argon have been made in the temperature range of 1650°–2050°K at pressures from 0.13–30 atm. Rate constants for the initial fragmentation of SF6 have been determined and have been found to be explainable in terms of classical unimolecular reaction kinetics. The analysis of the data in terms of the RRK theory yielded S = 6, λD = 0.25, E0 = 75.92 kcal/mole, and A = 1012.95sec−1 as the best values of the unimolecular parameters. The data did not rule out values of 5 to 7 for S or a factor of 2 range in λD with corresponding variations of about 4 kcal/mole in E0 and a factor of 3 in A. E0 = 75.92 kcal/mole represents the strength of the first S–F bond. Both ir and uv techniques were used to obtain the data.
New Scaled Atoms-in-Molecules Theory for Predicting Diatomic Potential-Energy Curves III. Refined Applications to the X 1Σg+ and E 1Σg+ States of H2
Authors: Ellison Frank O. , Slezak Jane A.
Published: February 2004

Scaled atoms-in-molecules theory is applied to the ground X 1Σg+ and first excited E 1Σg+ states of H2. Five basis functions are included, corresponding to 1s H + 1s H, 1S H− + H+, 1s H + 2s H, 1s H + 2p0H, and 2p+ H + 2p− H. Variational scaling parameters are introduced into the A- and B-atom eigenfunctions comprising each basis function; the ground and first excited state energy roots of the secular determinant are independently minimized with respect to these scaling parameters. For computing interatomic contributions to the energy and overlap matrix elements, three different approximations to the 1S H− ground-state eigenfunction are used. Scaled atoms-in-molecules theory in this approximation yields an H2 ground-state energy which is 6.5 kcal/mole above the exact result. An E 1Σg+ excited-state curve is obtained with the proper double minimum; the predicted energy at the outer minimum is almost exact, and at the inner minimum it is about 7.5 kcal/mole too high.
Rate Equations for Reactions at High Temperatures Involving Radical Intermediates: Consecutive-Parallel and Rice–Herzfeld Mechanisms
Authors: Houser T. J.
Published: February 2004

For complex reactions which produce, in the initial step, radical intermediates that attack the reactant in a subsequent step, the form of the rate equation will change as the reaction temperature increases. This is caused by a change in the relative rates of the individual steps in the mechanism due to differences in activation energies. A method has been developed for calculating the form of the rate equation at these higher temperatures for two mechanisms: a consecutive-parallel nonchain process and the Rice–Herzfeld chain reaction. The method is based on the elimination of time as the independent variable from the rate equations. It was calculated, for the consecutive-parallel mechanism, that the rate is a complex increasing function of the extent of reaction at temperatures high enough so that the steady-state assumption was not valid, i.e., the rate of the radical attack step was too slow compared to rate of radical production. Using this approach it was shown that significant deviations from steady state would be found in the case of methane pyrolysis at about 2200°K for concentrations below 10−6 mole/cm3. It was found for the Rice–Herzfeld mechanism that a shift from three-halves to first-order kinetics occurs as the temperature increases, although the concentrations of radicals in the transition temperature range would still be low enough not to invalidate the steady-state assumption. For acetaldehyde and dimethyl ether pyrolyses, these shifts would occur at about 1100° and 900°K, respectively.
Integral Equation Computations for Aqueous 1–1 Electrolytes. Accuracy of the Method
Authors: Rasaiah Jayendran C. , Friedman Harold L.
Published: February 2004

The computations described earlier [J. Chem. Phys. 48, 2742 (1968)] have been carried out for a variety of primitive-model parameters representative of aqueous 1–1 electrolyte solutions at 25°C. A number of tests, some new, have been applied to assess the accuracy of the results. One test involves a square-mound model, for which some results are also given. The hypernetted-chain equation is found to be quite satisfactory for these models up to 1M electrolyte concentration.
Electronic Relaxation in Large Molecules
Authors: Bixon Mordechai , Jortner Joshua
Published: February 2004

In this paper we consider the problem of the radiative decay of electronically excited states of a large molecule. We have considered both intramolecular vibronic coupling and the interaction with the radiation field. Compound states for a system of decaying indistinguishable levels are constructed using the Fano method. General expressions for the radiative decay rate are derived and applied for the statistical limit of intramolecular vibronic coupling. On a time scale shorter than a typical intramolecular recurrence time the radiative decay is exponential, and the reciprocal lifetime consists of independent contributions of radiative and nonradiative components. The experimental implications of these results for large and medium-size molecules are discussed.
On the Motion of Aerosols in Nonuniform Gases. I
Authors: Loyalka S. K.
Published: February 2004

The use of a variational approach for solving the problem of the motion of aerosol particles in nonuniform gases, at all rarefactions, is proposed. In particular, explicit variational formulations are given for the frictional drag and the force in diffusiophoresis.
Test of Combining Rules for Intermolecular Distances. Potential Function Constants from Second Virial Coefficients
Authors: Good Robert J. , Hope Christopher J.
Published: February 2004

A new combining rule for equilibrium distances in intermolecular potential functions, d12 = (d11d22)1/2, is tested by means of experimental second virial coefficients of gas mixtures. It is found to be superior to the Lorentz “arithmetic mean” rule.
Statistical Mechanics for Long Semiflexible Molecules: A Model for the Nematic Mesophase
Authors: Wulf Alexander , De Rocco Andrew G.
Published: February 2004

A model system for long semiflexible rods is introduced to investigate the nematic mesophase. The free energy is separated into two parts F = F″ + Δ, where F″ represents a fully aligned, hard system and Δ a correction which in our case is evaluated by the counting technique of DiMarzio extended to the case of nonrigid rods. F″ may be estimated by a variety of techniques. We find several interesting features: (1) for both rigid and flexible cases the anisotropic phase undergoes a second transition at still higher densities to what we take to be the solid phase; (2) for the flexible case sensible values of length-to-breadth ratio and flexibility give the isotropic–anisotropic transition at liquid densities and with Δρ / ρ̄ ∼ 0(1%) in keeping with experiment and in marked contrast to all available results for strictly rigid systems; (3) for a given temperature there is a lower bound to the stiffness energy (associated with making a bend) required for the existence of an isotropic–anisotropic transition. In the present model this energy has the value kT log 2.
Natural Abundance Carbon-13 Partially Relaxed Fourier Transform Nuclear Magnetic Resonance Spectra of Complex Molecules
Authors: Allerhand Adam , Doddrell David , Komoroski Richard
Published: February 2004

Proton-decoupled partially relaxed Fourier transform (PRFT) NMR of carbon-13 in natural abundance was used to determine spin–lattice relaxation times (T1) of individual carbons in solutions of cholesteryl chloride, sucrose, and adenosine 5′-monophosphate (AMP) at 15.08 MHz and 42°C. With the exception of a few side-chain groups, all protonated carbons have T1 values of less than 1 sec. Some side-chain carbons on cholesteryl chloride show evidence of internal reorientation and have relaxation times of up to 2 sec. Nonprotonated carbons have T1 values in the range 2–8 sec. These relaxation times are sufficiently short to make ordinary Fourier transform NMR a very sensitive technique in the study of complex molecules without the need for spin-echo refocusing schemes. Integrated intensities and nuclear Overhauser enhancements prove that, except for two of the three nonprotonated carbons in AMP, all 13C nuclei in these compounds relax mainly through 13C–1H dipolar interactions. Measured T1 values of protonated carbons were used to determine rotational correlation times. The ring backbone of 1M cholesteryl chloride in CCl4 reorients isotropically with a correlation time of 9 × 10−11 sec. Methyl groups directly attached to the backbone show evidence of internal motion with a correlation time ≲ 5 × 10−12 sec. A comparison of T1 values on the side group attached at C-17 indicates that the effect of internal motion is greatest for carbons near the free end. The two rings in sucrose behave as a single rigid entity reorienting isotropically with correlation times of 7 × 10−11 and 3 × 10−10 sec for 0.5M and 2M aqueous solutions, respectively. There is evidence for internal reorientation of the CH2OH side chains, with a correlation time much longer than that of methyl groups in cholesteryl chloride. The adenine group of 1M aqueous AMP is more restricted in its rotational motion than the sugar moiety. It appears that PRFT NMR spectra will be a useful addition to the arsenal of spectrochemical techniques. Relaxation times measured from PRFT spectra can be used in assignments. Furthermore, resonances that are unresolved in the normal spectrum, can be separated in PRFT spectra if the overlapping peaks arise from carbons with appreciably different T1 values.
Moment Analysis of Magnetic Circular Dichroism: Diamagnetic Molecular Solutions
Authors: Stephens P. J. , Mowery R. L. , Schatz P. N.
Published: February 2004

The method of moments enables more rigorous analysis of magnetic circular dichroism data than rigid shift models. Moment analysis is here applied to magnetic circular dichroism measurements on room temperature solutions of MnO4−, CrO42−, PdCl42−, SbCl6−, Ni(CN)42−, Fe(CN)64−, triphenylene, and coronene. Qualitative conclusions previously reached on the basis of rigid shift models are shown to be very little affected. More accurate values for the magnetic moments of degenerate excited state manifolds are obtained. The new data for Fe(CN)64− support the assignment of the 47 000 cm−1 absorption band to an intramolecular, t2g → t1u metal-to-ligand transition.
Ab Initio Potential Surfaces of BeH2+
Authors: Poshusta R. D. , Klint D. W. , Liberles A.
Published: February 2004

The potential surface of the BeH2+ molecular ion in C2υ geometries is computed by two ab initio methods: self-consistent-field (SCF) theory and valence bond configuration interaction (VBCI). Both calculations predict this ion to be weakly bound in a A12 state. A bound excited state of B22 symmetry is also predicted. According to SCF theory, the A12 state has a binding energy relative to H2 and (1s22s)2S Be+ of 0.19 eV, a BeH distance of 4.43 bohr, and a HBeH angle of 19.9°. The B22 state has a binding energy relative to H2 and (1s22p)2P Be+ of 3.2 eV, a BeH distance of 2.63 bohr, and a HBeH angle of 73.1°. SCF theory also gives an approximate ionization energy for BeH2 of about 9.71 eV. According to the VBCI calculation, the A12 state has a binding energy of 0.11 eV, a BeH distance of 4.16 bohr, and a HBeH angle of 20.5°, while the B22 state has a binding energy of 2.74 eV, a BeH distance of 2.76 bohr, and a HBeH angle of 93°. These ab initio results plus some experimental data for related ions strongly indicate that BeH2+ exists in two stable states which should be observable in mass spectrometers.
Kinetic Theory of Multicomponent Dense Fluid Mixtures of Rigid Spheres
Authors: Tham M. K. , Gubbins K. E.
Published: February 2004

The Enskog theory of dense, rigid-sphere fluids is extended to the multicomponent case. Equations obtained for the transport coefficients reduce to Thorne's equations in the special case of two components. The theory is used to predict the effect of the various independent variables on the isothermal diffusion coefficients for a ternary rigid-sphere mixture. It is found that coupling can be important if the constituents have significantly different rigid-sphere diameters. The special case of a ternary mixture with one component dilute is also considered. Many of the trends observed for rigid-sphere mixtures are in agreement with experimental observations for mixtures of real fluids.
Role of Kinetic Energy in the Franck–Condon Principle
Authors: Mulliken Robert S.
Published: February 2004

During an electronic transition in a molecule the nuclear positions and momenta (hence kinetic energies) both tend to remain fixed according to the Franck principle. According to the quantum mechanical Franck–Condon principle, the most probable changes in vibrational quantum numbers or nuclear energy conform to the Franck principle. As usually implemented, it is assumed that the most probable nuclear-energy transitions are approximately at frequencies corresponding to the R values (R = internuclear distance) of classical turning points of the nuclear motion, where the classical kinetic energy is zero. It is shown here for some model diatomic cases that, in transitions to or from a bound state with enough vibrational energy, an equally strong maximum of transition probability as a function of frequency can occur classically corresponding to R values where the nuclei in the initial state have maximum kinetic energy. Quantum mechanically, this means for example that in such cases, transitions to states of the final-state continuum with considerable kinetic energy can have a relatively high probability if the potential curves of the two electronic states differ strongly in a suitable way. Formulas for the “fluctuation intervals” between diffraction maxima in the intensity structure of the continuum are derived. Applications to the observed emission spectrum of the iodine molecule are made in an accompanying paper.
Reverse Deuteration Effect. Interference Effects in Nonradiative Decay
Authors: Sharf Benjamin
Published: February 2004

Interference effects between S1 → T1 and S1 → T2 intersystem crossing processes are considered. A reverse deuteration effect might be exhibited by S1 → T1 and S1 → T2 nonradiative decays.
Shape of a Random-Flight Chain
Authors: Šolc Karel
Published: February 2004

An analysis is made of the distribution function and its moments for a linear combination of three randomly chosen orthogonal components of the so-called radius of gyration of an unrestricted random-flight chain, and certain averages of moments are obtained of the three-dimensional distribution W (L12L22L32), where L1 ≤ L2 ≤ L3 are the orthogonal components of the radius of gyration along the principal axes of inertia of the chain. The strong departures of the chain shape from spherical symmetry indicated by these results are confirmed and complemented by Monte Carlo studies of unrestricted random walks on a simple cubic lattice. A surprisingly high ratio of principal components is found for chains with 50 and 100 bonds, 〈L32〉: 〈L22〉: 〈L12〉 ≃ 11.7:2.7:1.
Magnetic Resonance Line Shapes in Solids. II. Molecular Motion in Methyl Chloroform and Methyl Trichlorosilane
Authors: McIntyre H. Michael , Johnson Charles S.
Published: February 2004

Line shape and spin–lattice relaxation measurements are reported for methyl chloroform and methyl trichlorosilane. Spectra in the line shape transition region for CH3CCl3 are compared with exact line shape calculations by means of the apparent second moments to obtain 4.3 ± 0.2 kcal/mole for the energy of activation for methyl rotation. Proton T1 measurements at 30 MHz give activation energies of 3.7 kcal/mole for CH3CCl3 and 1.3 kcal/mole for CH3SiCl3, but the relaxation mechanisms are not completely understood. It is argued that the CH3CCl3 molecule rotates as a unit above 110°K. Line shapes and relaxation rates have also been determined for CH3CCl3 and CH3SiCl3 in perchloropropene glass where resolution is greatly enhanced in order to search for the effects of tunneling. The T1 measurements above 77°K indicate relatively free molecular motion and distinctly non-Arrhenius behavior. The spectra of these systems at 4.2°K are characteristic of rigid and rapidly rotating methyl groups for CH3CCl3 and CH3SiCl3, respectively. These results are consistent with the calculations of Apaydin and Clough for low and high tunneling frequencies but their line shapes for intermediate frequencies have not been confirmed.
Magnetothermodynamics of CuK2(SO4)2·6H2O. IV. Magnetic Moment, Heat Capacity, Entropy from 0.4 to 4.2°K with Fields to 90 kG along the α Magnetic Axis
Authors: Giauque W. F. , Brodale G. E. , Hornung E. W. , Fisher R. A.
Published: February 2004

This is a continuation of our magnetothermodynamic measurements on a 3.913-cm-diam spherical single crystal of CuK2(SO4)2·6H2O. The magnetic moment and heat capacity have been measured over the range 0.4–4.2°K, with fields of 0, 0.5, 1.0, 2.5, 5, 10, 15, 25, 40, 65, and 90 kG directed along the α magnetic axis. At 0.5°K the magnetic moment reached limiting values at fields in the range 40–90 kG. Mα(limit) = Mα(sat) + χαH = 6405 − 2.22 × 10−4HG·cm3/mole, where χα is the temperature-independent susceptibility (diamagnetic), and 6405 G·cm3/mole is the saturation value of the temperature-dependent paramagnetic system. Thus gα = 2.294. This may be compared with our previously measured gβ = 2.237 (corrected) and gγ = 2.071. No evidence of magnetic hysteresis was observed at temperatures above 0.4°K. Calorimetric measurements near magnetic saturation in the range 40–90 kG and magnetic susceptibility measurements near zero field each indicated weak ferromagnetic (presumably dipolar) interactions. The heat capacities at 90, 65, and 40 kG each approached zero, establishing a zero of entropy for the electron and lattice systems. This reference, in combination with 27 isentropes which crossed the isoerstedic heat capacity series, established the entropy throughout the experimental region. The total experimental electronic entropy was found to be 1.379 gibbs/mole compared with R ln2 = 1.3775 gibbs/mole. Smoothed values of the heat capacity, entropy, magnetic moment, enthalpy, internal energy, differential isothermal magnetic susceptibility, differential isoerstedic temperature coefficient of magnetic moment, and the isothermal work of magnetization are tabulated. The data will be utilized as a reference for establishing thermodynamic temperatures and other properties at temperatures below 0.5°K by means of isentropes to those temperatures.
New Selection Rule, Illustrated by Collision Cross Section Studies on the B 1Σ+ ← X 1Σ+ and the C 1Σ+ ← X 1Σ+ Transitions in Carbon Monoxide at Kinetic Energies of 300, 400, and 500 eV
Authors: Skerbele Ausma , Lassettre Edwin N.
Published: February 2004

Generalized oscillator strengths have been determined at 300, 400, and 500 eV for the two transitions B 1Σ+ ← X 1Σ+ and C 1Σ+ ← X 1Σ+ in carbon monoxide. The Born approximation does not hold accurately for either transition. The largest deviations (percentage wise) are found for the first of the above transitions and the trend of oscillator strength with momentum change (of the colliding electron) is very different from anything previously observed. This abnormal behavior is also found in relative intensity measurements done at low kinetic energies (to 23 eV). These transitions were studied because recent experimental and theoretical investigations [J. Chem. Phys. 53, 3801, 3806 (1970)] indicated that deviations from the Born approximation at high kinetic energies are subject to a selection rule; the deviations are maximum when term symbols are the same in ground and excited states. Previous experimental tests have been done only on forbidden transitions. The experiments reported in the present paper show that the deviations also occur for allowed transitions in which term symbols are the same in ground and excited states. Previous experiments are also reconsidered with a view to testing the selection rule hypothesis.
Photoexcitation of Hydrated Electrons Using a Q-Switched Ruby Laser
Authors: Kenney-Wallace Geraldine , Walker David C.
Published: February 2004

The lifetime of the photoexcited state of the hydrated electron in liquid water at room temperature is shown to be less than 6 × 10−12 sec following photoexcitation at 694 nm, a wavelength very close to λmax. This has implications concerning the nature of the optical transition involved and may suggest that the absorption band is a photoionisation efficiency profile rather than an electronic transition to a bound excited state. The absorbance of hydrated electrons (produced by uv flash photolysis) was measured at very high light fluxes using a Q-switched ruby laser under conditions where cryptocyanine and methylene blue solutions showed marked nonlinear absorption due to saturation of optical transitions. Whereas the dye solutions showed diminished absorbance and a shortening of the laser pulse at high light intensities, hydrated electrons gave identical absorbance at all intensities, varied over 7 orders of magnitude, up to 200 photons per hydrated electron per cm2 of the light beam.
Core Polarization of Cu2+(3d9, 2D) from Electron Paramagnetic Resonance of Cupric Pyridine Monocarboxylates
Authors: McMillan J. A. , Dixon N. S. , Halpern T.
Published: February 2004

Cupric picolinate, nicotinate, and isonicotinate, diluted in the corresponding zinc or cadmium compounds, were observed for paramagnetic resonance in polycrystalline samples, at liquid-nitrogen temperature. The axial character of the magnetic spectra, sometimes with a slight orthorhombic distortion, added to a strong g anisotropy, facilitates the interpretation. All compounds exhibit well-resolved hyperfine structure with the copper nuclei and with the nitrogen nuclei of the ligands. In all three cases the ground state of the cupric ion is dx2−y2 with various degrees of covalency. The polarization of the core, extrapolated to total localization in the metal ion, agrees with theoretical estimates within 30%.
Optical and Magnetic Studies of Tripositive Thulium in Octahydrated Sulfate Crystals
Authors: Karlow E. A. , Gruber J. B.
Published: February 2004

The optical absorption spectra of single-crystal Tm2(SO4)3 · 8H2O and Tm3+ in Y2(SO4)3 · 8H2O have been studied in the range from 2500 to 8000 Å at 4.2 and 77°K. Nine [SL]-J levels were identified including 3P2,1,0, 1I6, 1D2, 1G4, 3F2,3,4. The vibronic, electronic, and temperature-dependent absorption lines of these multiplets were identified and tabulated. The spectra were studied as a function of magnetic field strength and as a function of orientation in the magnetic field. Zeeman absorption, paraelectric resonance, and zero-magnetic field optical absorption spectra all indicate a nearly accidental degeneracy in the ground state of tripositive thulium in the octahydrated sulfate salts. The magnetic moment was found to lie in the rectangular plane formed by the crystal's macroscopic habit and inclined at an angle of 46° with respect to the crystal's major habit direction. The crystalline lattice of these salts was found to possess magnetically inequivalent sites. The optical spectra arising from thulium ions in both sites are indistinguishable, but the application of an external magnetic field revealed that the local ionic magnetic moments in these two kinds of sites are inclined at a relative angle of approximately 60°. The observed splitting factor for thulium ions in both sites was found to be 13.4 Lorentz units. The principle features of the magnetic properties of these salts were confirmed by anisotropic paramagnetic susceptibility measurements.
Irradiation Damage and Semiconducting Properties of CdF2:Eu
Authors: Tzalmona A. , Pershan P. S.
Published: February 2004

Thermoluminescence data have been used to unravel the fluorescence spectrum of Eu3+ in the insulating CdF2 · host. Optical absorption and EPR measurements of semiconducting CdF2:Eu are the bases of a model of this semiconductor.
Crystal Structure and Ring Puckering in 1,1-Cyclobutanedicarboxylic Acid
Authors: Soltzberg Leonard , Margulis T. N.
Published: February 2004

A three-dimensional x-ray structure determination has been carried out on a crystal of 1,1-cyclobutanedicarboxylic acid (C6H8O4) at room temperature. An unusual electron density distribution for one carbon atom in the cyclobutane ring suggests a dynamic inversion of the ring conformation. The structure was determined by direct methods from 928 nonzero diffractometer data and refined to R=0.05. The monoclinic unit cell is in space group P21/c with Z=4. Measured density is 1.36 g/cc; calculated density is 1.37 g/cc. Unit cell dimensions are: a=6.128, b=10.536, c=11.005 Å and β=99.78°.
Structure Study of Liquid Neon by Neutron Diffraction
Authors: de Graaf L. A. , Mozer B.
Published: February 2004

Neutron-diffraction measurements with high statistical accuracy were performed on liquid neon at 35.05°K and at three different densities. The structure factors S(κ), measured to momentum transfers κ of 13.2 Å−1, show a density-dependent structure well beyond 6 Å−1. The data have been used to calculate the radial distribution functions g(r), the direct correlation functions c(r), and effective interatomic potentials.
Semiclassical Theory of Vibrationally Inelastic Scattering in Three Dimensions
Authors: Wartell M. A. , Cross R. J.
Published: February 2004

A hierarchy of semiclassical approximations is derived to treat vibrationally inelastic scattering in three dimensions. The radial wavefunctions of the coupled Schrödinger equations for the combined vibrationally and rotationally inelastic scattering are expressed in terms of the radial wavefunctions for elastic scattering from a spherically symmetric potential to ``remove'' the elastic scattering from the problem. The rotationally inelastic scattering is diagonalized using the sudden approximation. The orbital angular momentum is diagonalized using a classical action-angle transformation. The result is a simple set of coupled differential equations—one for each vibrational state. For small changes in relative energy we obtain the coupled equations for a time-dependent perturbation acting along a single classical trajectory. If the energy changes can be neglected, the sudden approximation for the vibrationally inelastic scattering is obtained. For large changes in energy a multitrajectory method is developed which uses a separate trajectory for each vibrational state. Using the sudden approximation, vibrationally inelastic transition probabilities are calculated for He+ H2 as a function of molecular orientations and impact parameters. Orientation-averaged cross sections cannot be obtained from collinear trajectories by a simple steric factor independent of energy and the specific transition. It is also shown that, in the sudden limit, the orientation-averaged differential cross section is approximately equal to the differential cross section for the orientation-averaged potential.
Predictive Theory of Coion Transport Accompanying Particle-Diffusion-Controlled Ion Exchange
Authors: Spalding Gary E.
Published: February 2004

A complete numerical solution of the Nernst—Planck equations is presented in order to assess the influence of coion transport on particle-diffusion-controlled ion exchange. The theory is applied to the conversion of a H-saturated resin membrane to a Na-saturated membrane when the former is immersed in infinite, well-stirred, 0.1 and 1.0M NaCl solutions. The reverse conversions are also considered. The numerical solution explicitly accounts for the effects of coion transport on the ion-exchange process, and its predictions are consistent with observations already in the literature.