bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature-dependent study of carbon-13 spin-lattice relaxation times in para -azoxyanisole-A nematic liquid crystal
Authors: Schwartz M. , Fagerness P. E. , Wang C. H. , Grant D. M.
Published: February 2004

The 13C spin-lattice relaxation times of both the ring and methyl carbons in the liquid crystal, p-azoxydianisole, are reported as a function of temperature on both sides of the clearing point. In marked contrast to earlier results on proton relaxation, the relaxation times were found to exhibit no noticeable discontinuity at the nematic-isotropic transition temperature. The results are explained by comparing the mechanisms influencing the carbon-13 T1's to those present for proton relaxation.
Molecular dynamics in the solid state: Mössbauer and Raman spectroscopy of (CH3)2SN(C5H7O2)2
Authors: Herber R. H. , Leahy M. F. , Hazony Y.
Published: February 2004

The 119Sn Mössbauer effect resonance has been measured for dimethyltin(IV) bis acetylacetonate over the temperature range 4.2≤T≤120°K, and isomer shift, quadrupole splitting, recoil-free fraction, and Gol'danskii-Karyagin asymmetry parameters have been obtained over this interval. The resultant values for fa and the asymmetry parameter have been compared with the corresponding room temperature data extracted from x-ray diffraction results and permit a detailed evaluation of the vibrational motion of the metal atom in this quasioctahedral compound. On the basis of the temperature dependence of fa, it is possible to assign the Raman active mode observed at 37 cm−1 for the neat solid to an intra-unit-cell vibration of the two molecules against each other, confirming the essentially monomeric nature of the solid in the covalent lattice. Results of Mössbauer experiments on frozen solutions of this compound in glassy matrices lead to the conclusion that major structural differences exist between the neat solid (as probed by x-ray diffraction) and the molecule in solution (as probed by dipole moment measurements) and suggest that the structural inferences drawn by earlier investigators may not be mutually inconsistent.
Electrodynamic interactions between curved parallel surfaces
Authors: Parsegian V. Adrian , Weiss George H.
Published: February 2004

We formulate the electrodynamic force between concentric spherical and cylindrical surfaces. The results, which do include the nonadditivity of forces, deviate from expressions for parallel planar surfaces when the radii R1 < R2 of surface curvature are comparable to surface separation l = R2 − R1. In the limit of l ≪ R1, the first correction factor for curvature goes linearly as (l/R1). In the opposite limit, R1 ≪ R2, the interaction between concentric bodies goes as l−3.
Negative ion-molecule reactions with atomic hydrogen in the gas phase at 296 °K
Authors: Howard Carleton J. , Fehsenfeld F. C. , McFarland M.
Published: February 2004

Gas phase reaction rates have been measured for the reactions of Cl−, I−, OH−, O2−, SF6, and some hydrates of Cl−, OH−, and O2− with atomic hydrogen in a flowing afterglow system at 296°K. In general, the reaction mechanism is associative detachment, X−+H→HX+e, and the rate constants are very large (∼ 10−9 cm3/sec). The reactivities of Cl−, OH−, and O2− are reduced by clustering with H2O. The reaction of I− with H is immeasurably slow, and SF6− reacts with H to form SF5− which does not react further.
Theoretical studies of H+H2 reactive scattering
Authors: Wolken George , Karplus Martin
Published: February 2004

The H + H2 reactive scattering problem was studied quantum mechanically in three dimensions by the close-coupling technique. The ground vibrational state and a set of up to seven rotational states were included in the basis for both the initial and the final channels. The interaction of the three particles was described by the Porter-Karplus surface in order to permit comparison with classical calculations. A method was developed for solving the sets of coupled integrodifferential equations that appear in the close-coupling approach to rearrangement scattering. Transition probabilities for reactions involving the 0, 1, 2 rotational states of H2 were calculated for relative kinetic energies from 0.20 to 0.50 eV. Differential cross sections were estimated for the 0→1 rotational transition. The results were compared with three-dimensional classical studies as well as other quantum mechanical results. A significantly lower threshold for reaction was obtained in the present work both with respect to the three-dimensional classical results and a distorted wave Born calculation for reactive scattering from the same surface.
Transfer of functional group electronic structure representation between molecules: Ethane from methane
Authors: Fink William H.
Published: February 2004

Previously developed analyses are coordinated into a viable scheme for effecting the transfer of electronic structure representation from one molecule to another. The scheme is sufficiently flexible to enable variational redetermination of portions of the electronic structure. Results are presented for a number of variants of transfer of methyl groups from methane to ethane. Comparison with the fully variational SCF calculation is made. The results are encouraging for expanding the scope of the approach.
Hopping of ions in ice
Authors: Chen Mou-Shan , Onsager Lars , Bonner Jill , Nagle John
Published: February 2004

The effects of intermolecular tunneling by protons in ice and other protonic semiconductors on thermodynamic and transport properties are estimated on the basis of an idealized model. The model involves a simple tight-binding Hamiltonian on the infinite-dimensional set of molecular configurations in the generally proton-bonded but otherwise disordered structure. The cycle-poor topology of the state set is approximated by that of a cycle-free Bethe lattice, i.e., an infinite, homogeneous Cayley tree. For coordination q and hopping matrix element V the distribution of energy levels is given by the function g(u) = g(E/V) = q[4(q − 1) − u2]1/2/2π(q2 − u2), where q = 3 for the set of hopping options available to an ion in ice. The thermal average of the group velocity v = [4(q − 1) − u2]1/2 V d / ℏ on the Bethe lattice with lattice spacings d determines a finite coefficient of diffusion in real three-dimensional space, where paths on the Bethe lattice are represented by random walks in 3 space with only a finite measure of correlation between the directions of successive steps. These results agree with recent computations by Minagawa and with the results of various parallel efforts in the theory of electron tunneling. Some questions of principle are resolved by an analysis of the corresponding eigenvalue problem for a symmetrically constructed finite Cayley tree, and an effective upper bound for the error incurred by disregarding cycles is obtained from a computation for a periodic graph in three dimensions. While the ionic mobilities in ice are not yet well known, even the greatest claimed values of about 0.075 cm2/V · sec are compatible with matrix elements somewhat smaller than 1 mV, which would entail tunneling corrections to the partition function for a hydrogen ion of less than 2% near the freezing point.
Measurements of hyperpolarizabilities for some halogenated methanes
Authors: Finn R. S. , Ward J. F.
Published: February 2004

dc Electric-field induced optical second-harmonic generation has been measured for CH4, CH3F, CH2F2, CHF3, CF4, CClF3, and CBrF3. For CH4 and CF4 the third order hyperpolarizability χ(−2ω; 0,ω,ω) is obtained directly. For the other (dipolar) molecules, a bond additivity estimate for χ(−2ω; 0,ω,ω) is used to extract the second order hyperpolarizability χ(−2ω;ω,ω).

Results are compared with various data from the literature: calculated hyperpolarizabilities, and measurements of optical harmonic generation, optical mixing and the Kerr effect. The degree of consistency of the experimental data with a bond additivity model is discussed.
Conformation of the −NH2 group in a single crystal of p-chloroaniline as determined by combined Zeeman effects on the 35Cl and 14N nuclear quadrupole resonances
Authors: Ambrosetti R. , Colligiani A. , Grigolini P. , Salvetti F.
Published: February 2004

The Zeeman effect on the nuclear quadrupole resonance of both 35Cl and 14N nuclei in a single crystal of p-chloroaniline has been studied at room temperature. A spectrometer was employed which was capable of working at the resonance frequency of either nucleus without altering the position of the crystal. Novel features of the spectrometer were both a frequency stabilizing apparatus working at the 14N resonance frequency and the attachment of an electronic computer for direct and accurate ``on-line'' determination of spectral parameters. The relative orientations of the electric field gradient tensors on both nuclei have been obtained. Furthermore, by studying the 14N linewidth dependence on the static magnetic field orientation, information has also been gained about the position of the −NH2 protons in the electric field gradient tensor principal axes mainframe. Some remarkable experimental results can be interpreted theoretically when the treatment of the magnetic dipole interaction between 14N and 1H in the −NH2 group is pushed beyond first order. Analogous information has been gained by also studying a single crystal of p-bromoaniline.
Effect of magnetic and electric fields on the transport properties of polyatomic gases. I. Formal theory
Authors: Viehland Larry A. , Curtiss C. F.
Published: February 2004

The changes in the coefficients of shear viscosity and thermal conductivity caused by a homogeneous external field are considered for a single-component, dilute gas of spin-zero, polyatomic molecules. The quantum mechanical equations for these Senftleben-Beenakker effects are solved by an iterative technique which is especially suited to a series of restricted distorted wave approximations to the transition matrix. In this manner more rigorous and more physical reasons are found for the dominance of certain terms in the expansions usually employed to solve such equations. The final expressions for the Senftleben-Beenakker effects are in terms of ``collision integrals'' which are greatly simplified by using group theoretical methods to completely and explicitly handle the m-type quantum numbers.
Effect of magnetic and electric fields on the transport properties of polyatomic gases. III. Mixed second order effect on the shear viscosity of rigid rotors in a magnetic field
Authors: Viehland Larry A. , Curtiss C. F.
Published: February 2004

The Senftleben-Beenakker effect on the shear viscosity coefficients of a rigid rotor in a homogeneous magnetic field is treated in detail. Quantum and classical limit equations, valid for any intermolecular potential with a given functional dependence upon the angles between colliding molecules, are presented for this effect. Experimental measurements of this effect should lead, through the equations presented, to detailed information about anisotropic intermolecular potentials. As an example, calculations using a crude intermolecular potential to represent N2 are in reasonable agreement with experiment. The Senftleben-Beenakker effect on shear viscosity is shown to be of mixed second order in the potential anisotropy.
ESR study of 13C hyperfine splittings for the single line radical produced in γ-irradiated single crystals of succinic acid
Authors: Yim Moon B. , Klinck Ross E.
Published: February 2004

ESR studies of γ-irradiated single crystals of succinic acid-d6 have enabled evaluation of 13C hyperfine splittings for the single line radical species. The data confirm the structure as HOOCCH2CH2C=O. Isotropic 13C hyperfine splittings of 131.8 and 47.7 G have been obtained for the carbonyl carbon and the adjacent methylene carbon. Spin density calculations show that the majority of the unpaired electron density is localized in the σ orbital arising from the rupture of a C–OH bond in the undamaged molecule.
Optical study of the site symmetry distribution in KBr:Sm2+
Authors: Sundberg Michael N. , Lauer Howard V. , Chilver Charles R. , Fong Francis K.
Published: February 2004

The 4.2 °K narrow line fluorescence of KBr:Sm2+ arising from 5D0→7FJ transitions have been investigated in terms of Zeeman anisotropy fluorescence analysis, lifetime measurements, and Zeeman polarization determinations. There is a strong resemblance between the optical properties of the KBr:Sm2+ system and those of the previously investigated KCl:Sm2+ system. As in KCl:Sm2+, the dominant site is the nearest-neighbor (nn) C2v Sm2+–K+ vacancy pair. A few additional lines attributable to the second nn C4v pair have been found in KBr:Sm2+. The present findings support the earlier conclusion that alkali halide crystals doped with divalent cations are usually characterized by a distribution of the first few nn ion defect pairs.
Correlation holes and wavefunctions for the 1S, 1P°, and 3P° states of Be, B+, and C2+
Authors: Tatewaki Hiroshi , Tanaka Kiyoshi
Published: February 2004

``Average'' pair distribution functions, P(r12), are calculated both from the Hartree-Fork (HF) and configuration interaction (CI) wavefunctions for the 1P°, 3P°, and 1S states of Be, B+, and C2+. The average electronic separation, , and interelectronic interaction energy, , are also obtained from the CI and HF wavefunctions. Reflecting the difference of the degree of correlation (between the CI and HF wavefunctions), the CI wavefunctions give a larger interelectronic distance than the HF wavefunctions except for the 1P° state of Be. For Be 1P°, the CI wavefunction reduces the average electronic separation in comparison with the HF wavefunction; this contradicts the general idea that the calculated electron pair distribution function for a CI wavefunction is more spread out than for the HF counterpart. This reduction of  is discussed in connection with the fact that the 2p orbital obtained by the HF calculation in Be 1P° is much more diffuse that that in the other states and that the 2p electron distribution is contracted by the CI calculation. Apart from Be 1P°, the difference between the two functions, P(r12), calculated from the CI and HF wavefunctions, gives a shallower correlation hole for 3P° than for 1P° and 1S. This is because in the HF calculation the Pauli principle keeps the L-shell electrons apart in the triplet state.
Electron paramagnetic resonance of 239Pu3+ and 243Am4+ in CeO2 and of 241Pu3+ in ThO2
Authors: Kolbe W. , Edelstein N. , Finch C. B. , Abraham M. M.
Published: February 2004

The g values of the 5f5 ions Pu3+ and Am4+ in CeO2 cubic symmetry sites have been measured by EPR techniques and found to be 1.333 ± 0.001 and 1.3120 ± 0.0005, respectively. For the case of Pu3+, the cubic crystal field parameters were calculated and compared with those previously obtained for other fluorite-structure lattices. The EPR spectrum was also observed for 241Pu in ThO2 and the ratio of the magnetic moments 241μI/239μI determined to be 3.52 ± 0.06.
New set of rules of the Slater type on the screening constants and the effective principal quantum numbers
Authors: Sakai Yoshiko , Anno Tosinobu
Published: February 2004

The screening constants (si→j's) and the effective principal quantum numbers (ni's) have been re-examined for the atoms and the ions with electron configurations of the 1s22sm2pn (m=0, 1, 2; n=0, 1, ⋯ , 6) type. The method used is to derive the expression of the total energy of the 1s22sm2pn atom in its average of the configuration in terms of si→j's and ni's by using the virial theorem and to fit this expression to the experimental or the Hartree-Fock (HF) values of the total energies of various 1s22sm2pn atoms. As the basis AO's, both the hydrogenic AO (HAO) and the (single) Slater-type AO (STO) have been tried. The orthogonalized HAO (OHAO) and the orthogonalized STO (OSTO) have also been tried. These minimal basis AO's, in which the orbital exponents are determined with the ``new Slater rules'' thus derived, are compared with the HF AO's to see to what extent we are able to resemble minimal basis AO's to the correspondong HF AO's. It is concluded that the OSTO can behave reasonably closely to the HF AO as far as the 1s and the 2s orbital are concerned. As for the 2p AO, it is found that a minimal basis AO of the Slater type cannot approximate the HF AO, no matter what value of the orbital exponent is taken. The occurence of the nonintegral value of the effective quantum number is discussed and a concept called orbital contraction factor is proposed.
Systematic determination of the double ζ type 2p atomic orbitals for the atoms and the ions of the first-row elements
Authors: Sakai Yoshiko , Anno Tosinobu
Published: February 2004

A double ζ type 2p atomic orbital, whose radial part R 2pdouble is a linear combination of two Slater-type 2p functions R2p(ζ1) and R 2p(ζ2) [R 2pdouble = c1R 2p(ζ1) + c2R 2p(ζ2)], is constructed for each of the neutral atoms, singly negative ions, and the singly and doubly positive ions of the first-row elements. The orbital exponents ζ1 and ζ2 and the expansion coefficients c1 and c2 are determined by a least-squares method with a criterion that our double ζ type 2p function gives an over-all optimum reproduction of the Hartree-Fock (HF) values of the one- and the two-electron integrals involving 2p AO only. Not only the ground configurations but also the excited configurations of the type 1s22sm2pn are treated, although only the average of each of the configurations is treated. Remarkable regularities are found for ζ1, ζ2, c1, and c2, although those of the negative ions behave differently, and formulas are obtained for these parameters from the analysis of such regularities. It is demonstrated that the formulas thus obtained work very well. Finally, two sets of the screening constants and the orbital contraction factors are obtained from the configurational dependence of ζ1 and ζ2, which may be explained as those for the outer and the inner parts of the double ζ type 2p function.
3
B
1-1A1 transition of SO2 gas. II. Radiative lifetime and radiationless processes
Authors: Strickler S. J. , Vikesland John P. , Bier H. D.
Published: February 2004

A modification of the equation given by Strickler and Berg is derived for calculating from spectroscopic data the radiative lifetime of a molecule whose transition moment varies with configuration. Using this equation, the radiative rate constant of the 3B1 state of SO2 is calculated to be 79 ± 5 sec−1. The decay rate of this state is reported as a function of pressure at 30°C. The rate constant for quenching by ground state SO2 is found to be (4.52 ± 0.18) × 108 1 mole−1 · sec−1. The decay rate extrapolated to zero pressure is found to be (1.12 ± 0.20) × 103 sec−1. Comparison with the radiative rate constant shows that only about 7% of the triplet molecules emit, and the rest undergo some pressure independent nonradiative process.
Segregation in alkali halide crystallization from aqueous solutions
Authors: Rosenberger F. , Riveros H. G.
Published: February 2004

Segregation from solutions and melts is compared theoretically. It is shown from thermodynamic arguments that equilibrium solution segregation is more effective. Segregation coefficients k0 are calculated for aqueous alkali halide systems, based upon theoretical heat of dissolution values (solid solution) and solubility data (liquid solution). Good agreement with experimental values is obtained over a range of 1 > k0 > 10−4. A critical discussion of the available experimental data and limitation of the thermodynamic theory in terms of off-equilibrium phenomena is given.
Computer simulation of (n, γ) recoil damage in hexahalorhenate crystals
Authors: Robinson Mark T. , Rössler K. , Torrens Ian M.
Published: February 2004

A comprehensive computer program, originally written to simulate radiation damage in metals, has been applied to a study of recoil damage following (n, γ) activation of the halogen ligands in crystals of K2[ReCl6], K2[ReBr6], and their mixtures. Calculations were made of the retention of radiohalogen in the complex anions and of the primary retention of the radiohalogens in their own original ions, both quantities as functions of the initial recoil energy. Assuming a volume for the spontaneous recombination of vacancies and interstitials containing about 50 halogen sites, good agreement is achieved between the calculations and recent experiments in the pure crystals. The retention was found to be independent of recoil energy, a result which appears to be quite general. Failure of the calculations to account for the very low retention of radiochlorine in dilute solutions of K2[ReCl6] in K2[ReBr6] is attributed to difficulties of energy accomodation between nearly thermal Cl recoils and the host crystal.
Temperature dependence of the diffusion and accommodation coefficients in nitrous oxide and carbon dioxide excited into the (00°1) vibrational level
Authors: Doyennette L. , Margottin-Maclou M. , Gueguen H. , Carion A. , Henry L.
Published: February 2004

We have studied the temperature dependence of the relaxation rates in nitrous oxide and carbon dioxide excited into the (00°1) level by absorption of the radiation of a Q-switched laser. The relaxation constant β has been determined by measuring the decay time of the fluorescence emitted by the gas. Measurements were performed in the temperature range between room temperature up to 1000 °K and at gas pressures low enough to determine the diffusion coefficient of the excited molecules and their wall-deexcitation probability versus temperature.
Field-dependent relaxation and absolute nuclear shielding of 207Pb in liquid PbCl4
Authors: Hawk Roger M. , Sharp Robert R.
Published: February 2004

Relaxation times T1 and T2 of 207Pb in liquid PbCl4 have been studied for the purpose of establishing an absolute nuclear shielding scale for lead. T1 has been decomposed into scalar and spin-rotation contributions using variable temperature measurements at the two field strengths 6.59 and 16.90 kG. T2 is much shorter than T1 and is strongly dominated by scalar coupling to chlorine. Knowledge of the scalar contributions to T1 and T2 determines the halogen relaxation times (τ35 = 7.15 μsec at 25°C), the lead-chlorine coupling constant [(J(207Pb−35Cl) = 705 Hz)], and the reorientational correlation time (τθ = 1.72 × 10−11 sec at 25°C). A correlation time τJ for the angular momentum vector has been computed using J diffusion theory, but the value obtained appears to be too short (0.8–2.9 × 10−14 sec) to be meaningful in terms of classical diffusion of rigid molecules. Nevertheless, the known range of 207Pb chemical shifts places an absolute upper limit on τJ of 6 × 10−14 sec at 263°K. The physical significance of such short correlation times is discussed, and it is concluded that τJ probably describes collision-induced distortions in the molecular structure. Experimental values of the spin-rotation contribution to (T1)−1 are used in conjunction with estimated values of τJ to compute limiting values for the spin-rotation constant that place limits on the paramagnetic part of the magnetic shielding constant. A shielding scale previously deduced from optical pumping data is discussed, and a source of possibly substantial error in this scale is pointed out.
Temperature dependence of vibrational relaxation in the HF, DF, HF–CO2, and DF–CO2 systems
Authors: Lucht Roy A. , Cool Terrill A.
Published: February 2004

The laser excited fluorescence method has been employed to determine rate constants for V → V, R and V → R, T relaxation HF(ν = 1) and DF(ν = 1) by CO2 over the temperature range from 295 to 670°K. The self-deactivation rates for HF(ν = 1) and DF(ν = 1) by ground state molecules and the rate of V → V, R transfer from HF(ν = 1) and DF(ν = 1) to the CO2 (00°1) state exhibit a marked decrease with increasing temperature. The results provide additional evidence for the conversion of the large vibrational energy defects of the present systems into rotational motion of the hydrogen halide under the influence of a sizable attractive intermolecular potential well.
Attachment of slow (<1 eV) electrons to O2 in very high pressures of nitrogen, ethylene, and ethane
Authors: Goans R. E. , Christophorou L. G.
Published: February 2004

The results of a recent study on the capture of slow (<1 eV) electrons by O2 embedded in very high pressures of nitrogen (up to 27 500 torr), ethylene (up to 17 000 torr), and ethane (up to 17 500 torr) are presented and discussed. Large changes have been observed in both the magnitude and the energy dependence of the attachment rate (and cross section) with increasing density of these three media. At sufficiently low pressures (≲ 1500 torr for N2; ≲ 2500 torr for C2H4; ≲ 3500 torr for C2H6), low-energy electron attachment to O2 can be treated approximately as a three-body process. However, as the density of each medium increases, each affects the capture process differently, demonstrating the profound effect and importance of the environment on the electron attachment process. Electron capture mechanisms and reaction schemes consistent with the observed dependences of the attachment rates on the density of each medium are presented and discussed. The high-pressure data on O2 in C2H4 and N2 have been successfully related to ``liquid-state'' behavior. From the O2, C2H4 data an autoionization lifetime equal to ∼2 × 10−12 sec has been estimated for O2−*.
Isotopic reactive systems H+Cl2 and D+Cl2. A quantum mechanical treatment of the collinear arrangement
Authors: Baer Michael
Published: February 2004

An exact quantum mechanical study is performed of the collinear reactive systems H+Cl2 and D+Cl2. The surface applied in this work is a LEPS potential surface originally employed by Polanyi and co-workers. The main results are (i) a strong population inversion is found, the most populated levels being ν = 4 for the HCl product and ν = 5 for DCl; (ii) the initial vibrational state has very little influence on the rate of the reaction but strongly affects the final vibrational distribution of the product; (iii) the two isotopic systems behave very similarly (as a function of relative energy); (iv) at all points where there is classical trajectory data there is a broad agreement with the quantum results.
EPR of MnxMg1−x(HCOO)2·2H2O: A two-dimensional magnetic lattice
Authors: Shia L. , Kokoszka G.
Published: February 2004

A room temperature EPR study of a single crystal of Mn(HCOO)2 · 2H2O revealed an angular dependence which has been largely associated with anisotropic exchange. Diluted crystals of (Mn)ix(Mg)1−x(HCOO)2 · 2H2O with x = 0.88 and 0.65 have also been studied by room temperature EPR and the linewidth exhibited a concentration dependence. The linewidth was nearly isotropic for the x = 0.65 crystal. These results are related to the low temperature behavior of this material and the loss of long range order in the mixed metal system for x less than about 0.60. In addition a few low temperature EPR data points for polycrystalline samples of the same compositions suggested no strong temperature dependence to the linewidth. This tentatively rules out a major contribution to the linewidth form antisymmetrical exchange.
Dependence of the intensity of the absorption bands of Eu3+ in solution upon the anions present
Authors: Chrysochoos John
Published: February 2004

The narrow and very weak absorption bands of Eu3+ in solution at 526 nm and 579 nm associated with the transitions 7F0 → 5D1 and 7F0 → 5D0, respectively, are accompanied by red-shifted broad bands. The red shift depends upon the anion present and it is independent of the solvent. In the case of EuCl3 the red shift was found to be 335±2 cm−1 whereas in the case of Eu(NO3)3 a red shift of 366±2 cm−1 was observed. The intensity of the broad bands is solvent dependent and it increases as the dielectric constant of the solvent decreases. These bands are attributed to the nonionized rare-earth salts, i.e., > Eu–Cl and/or > Eu–NO3. On the other hand, the intensity of the narrow band at 526 nm is almost unchanged despite the changes in the intensity of the broad band. Since the intensity of the band at 526 nm, which is associated with Eu3+, ought to decrease as the intensity of the broad band increases, the lack of change may be attributed to an enhancement of the appropriate oscillator strength due to vibronic effects associated with such species as > Eu–Cl and/or > Eu–NO3.
Degenerate RS perturbation theory
Authors: Hirschfelder Joseph O. , Certain Phillip R.
Published: February 2004

A concise, systematic procedure is given for determining the Rayleigh-Schrödinger energies and wavefunctions of degenerate states to arbitrarily high orders even when the degeneracies of the various states are resolved in arbitrary orders. The procedure is expressed in terms of an iterative cycle in which the energy through the (2n + 1)th order is expressed in terms of the partially determined wavefunction through the n th order. Both a direct and an operator derivation are given. The two approaches are equivalent and can be transcribed into each other. The direct approach deals with the wavefunctions (without the use of formal operators) and has the advantage that it resembles the usual treatment of nondegenerate perturbations and maintains close contact with the basic physics. In the operator approach, the wavefunctions are expressed in terms of infinite order operators which are determined by the successive resolution of the space of the zeroth-order functions. The operator treatment has some similarity to that of Choi (1969), but it is more closely related to that of either Hirschfelder (1969) or Silverstone-Holloway (1971). The operator expressions are useful for: double perturbations, expectation values of physical properties, and problems involving finite dimensional Hilbert space (for example, wavefunctions approximated by linear basis sets). The use of variational principles for degenerate perturbation problems is discussed.
Infrared spectra and structure of some matrix-isolated lanthanide and actinide oxides
Authors: Gabelnick S. D. , Reedy G. T. , Chasanov M. G.
Published: February 2004

The midinfrared spectra of the oxides of Ce, Pr, Sm, Eu, Tb, and Th have been obtained by vaporizing the solid oxides and trapping the vapor species in argon matrices. On the basis of oxygen-18 isotope shifts, a linear structure has been determined for PrO2, and nonlinear structures for CeO2, TbO2, and ThO2. Values of ωe and ωeχe have been determined for the monoxides of Pr, Eu, Tb, and Th from the small deviations between the observed and the theoretical harmonic isotope shifts.
Mass spectrometric study of the gaseous gallium monocyanide
Authors: Guido M. , Gigli G.
Published: February 2004

Using the mass spectrometric and double oven technique, the gallium cyanide molecule was identified and its atomization energy was determined: D0° (GaCN)=312.5 ± 1.4 kcal/mole. Upper limits for the atomization energies of GaN(g) and Ga2N(g) also were established.
Kinetic theory and rheology of dilute solutions of flexible macromolecules. I. Steady state behavior
Authors: Armstrong Robert C.
Published: February 2004

For a dilute solution of macromolecules idealized as elastic dumbbells with Brownian motion, expressions are obtained giving the stress tensor in terms of rate-of-strain tensors for an arbitrary, steady, homogeneous flow. The rheological equations of state are fit into a retarded motion expansion. For dumbbells with arbitrary, nonlinear, elastic connectors, the result is given up through terms of second-order. Stress tensor equations for two specific models, Hookean dumbbells and finitely extendible non-linear elastic (FENE) dumbbells, are given up through terms of third order.
Kinetic theory and rheology of dilute solutions of flexible macromolecules. II. Linear viscoelasticity
Authors: Armstrong Robert C.
Published: February 2004

For an arbitrary, time-dependent, homogeneous flow, an expression is obtained for the stress tensor describing the behavior of a dilute solution of macromolecules idealized as elastic dumbbells with Brownian motion. The result is given in terms of the relaxation modulus from linear viscoelasticity. The general relaxation modulus found for an arbitrary, nonlinear, elastic dumbbell is specialized to that for a finitely extendible nonlinear elastic (FENE) dumbbell. Good agreement is found when the result is compared with Warner's numerical calculations for the FENE dumbbell.
High-temperature series for the B-site spinel and diamond lattices and the question of universality
Authors: Lambeth David N. , Lee M. Howard , Stanley H. Eugene
Published: February 2004

The high-temperature series for the two-spin correlation functions on both the B-site spinel and diamond lattices have been calculated through tenth order for the Hamiltonian, H=−JΣ〈 ij 〉 Σα=1n(n≤ D) SiαSjα. Here Siα is the αth component of the D-dimensional classical spin and we define n as the spin space symmetry parameter. By  we limit the first summation to nearest-neighbor pairs of sites i and j on the lattice. The spin space symmetry parameter n is ≤D. We consider all six models resulting from D=1–3. Our analysis of the high-temperature series indicates that while the exponent estimates for the more loosely packed diamond lattice (q=4) indicate agreement with the universality hypothesis, the B-site spinel lattice (q=6) series are not yet displaying their critical behavior. Some conjectures concerning this peculiarity of the series for the two lattices are made.
Raman scattering in antiferroelectric ammonium dihydrogen arsenate
Authors: Leung R. C. , Lowndes R. P. , Tornberg N. E.
Published: February 2004

Light scattering measurements of the Raman active modes of vibration in the range 10–4000 cm−1 are reported for the paraelectric phase of NH4H2AsO4 in the temperature range 220–295 K. Through examination of these spectra we have identified the protonic, transverse optic, internal, and O–H–O valence vibrations and determined their symmetries.
Ion-molecule reaction rates in Ar at 296°K
Authors: Liu Wei-cheng F. , Conway D. C.
Published: February 2004

The rate constant k1 for the reaction Ar+(2P3/2) + 2Ar→Ar2+ + Ar was found to be (2.07±0.20)×10−31 cm6/sec at 296°K. The reaction was studied in a drift tube at pressures reduced to 0°C (P0) of 1.414–3 torr. Ions effused from the drift tube and were counted with a TOF mass spectrometer. It was found that Ar+ in the 2P1/2 state does not form Ar2+ at room temperature. This fact appears to have been neglected in previous determinations of k1. Corrections were made for the collision-induced transition Ar+(2P1/2) → Ar+(2P3/2), where k2 is the rate constant, and for side reactions with impurities. From experiments at P0=6 and 9 torr it was found that k2,Ar≤1.5×10−15 cc/sec. However, recent experiments indicate k2,Ar<4×10−16 cc/sec, so most of the transitions were caused by collisions with an impurity in the Ar.
Determination of relative rates for oxygen atom-hydrocarbon reactions by reduction of oxygen atom, nitric oxide chemiluminescence
Authors: McClenny William A.
Published: February 2004

Relative rates of reaction between oxygen atoms and hydrocarbons have been determined at 25°C ± 5°C. With reference to isobutene, the relative rates for ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, 1,3 butadiene, and 3-methylbutene-1 are: 0.042 ± 0.010, 0.20 ± 0.05, 0.18 ± 0.07, 0.79 ± 0.25, 1.25 ± 0.35, 0.96 ± 0.35, and 0.22 ± 0.05. Hydrocarbons and oxygen atoms are mixed prior to detection of the oxygen atoms by their chemiluminescent reaction with nitric oxide. The chemiluminescent signal is simply related to the product of the gas-phase contact time, the hydrocarbon concentration, and the reaction rate constant for the oxygen atom-hydrocarbon reaction. With an oxygen atom concentration of approximately 107 cm−3 at a system pressure of 10 torr, olefinic hydrocarbon concentrations as low as 1.0 parts-per-million are used to establish the relative rates.
X-ray photoelectron spectroscopy of tetraphenylporphin and phthalocyanine
Authors: Niwa Yoshio , Kobayashi Hiroshi , Tsuchiya Toshikazu
Published: February 2004

The x-ray photoelectron spectra of tetraphenylporphin, phthalocyanine and their copper complexes were measured. The copper complexes show a single nitrogen 1s photoline, whereas the metal free bases give rise to a doublet nitrogen 1s photoline. The central pyrrole and aza nitrogens in the metal free bases could be identified, whereas the central and meso-bridging aza nitrogens in phthalocyanine could not be discriminated. Each of the central two protons in the metal free bases is localized on one of the central four porphinato nitrogens. The shifts in N 1s binding energy observed in the present work could be reproduced by the shifts in the charge density on nitrogen obtained for the bonded structure by an extended Hückel molecular orbital calculation.
Lattice vibrations in chlorobenzenes: Experimental dispersion curves for β-paradichlorobenzene by neutron scattering
Authors: Reynolds P. A. , Kjems J. K. , White J. W.
Published: February 2004

Lattice vibrational dispersion curves for the ``intermolecular'' modes in the triclinic, one molecule per unit cell β phase of p-C6D4Cl2 and p-C6H4Cl2 have been obtained by inelastic neutron scattering. The deuterated sample was investigated at 295 and at 90°K and a linear extrapolation to 0°K was applied in order to correct for anharmonic effects. Calculations based on the atom-atom model for van der Waals' interaction and on general potential parameters for the aromatic compounds agree reasonably well with the experimental observations. There is no substantial improvement in fit obtained either by consideration of electrostatic forces or by further anisotropy in the dispersion forces not described in the atom-atom model. Anharmonic effects are shown to be large, but the dominant features in the temperature variation of frequencies are describable by a quasiharmonic model.
Spatial switching in chemical reactions with heterogeneous catalysis
Authors: Shymko R. M. , Glass Leon
Published: February 2004

The qualitative properties of chemical systems with localized (heterogeneous) catalysts can depend on the relative locations of the catalysts. By considering some simple chemical systems with two catalytic sites it is shown that the number and the stability of steady states and cycles changes with intercatalytic separation. These examples indicate that geometrical considerations must be explicitly considered when analyzing the dynamics of highly structured (e.g., biological) systems.
Lifetime of electronically excited NO2: Evidence for a short-lived state
Authors: Solarz Richard , Levy Donald H.
Published: February 2004

The lifetime of one spin component of the 524 rotational level of some vibrational level of B2 symmetry of the 2B2 electronic state of NO2 has been measured by observing the linewidth of the microwave-optical double resonance spectrum of that state. The lifetime determined from the zero power, zero pressure linewidth extrapolation is less than 3.39 ± 0.36 μsec and is over an order of magnitude shorter than that usually measured in NO2. This indicates that at least some electronically excited levels of NO2 have lifetimes approaching those calculated from the integrated absorption coefficient.
Interaction potential between two rigid HF molecules
Authors: Yarkony David R. , O'Neil Stephen V. , Schaefer Henry F. , Baskin Craig P. , Bender Charles F.
Published: February 2004

As a prelude to the study of energy transfer in the HF–HF system, the potential energy surface for the interaction of two rigid HF molecules has been calculated within the ab initio self-consistent-field framework. An H(4s 1p/2s 1p), F(9s 5p 1d/4s 2p 1d) basis set of contracted Gaussian function was employed. The number of unique points on the surface is greatly reduced by symmetry, and only 294 points were required to give a fairly complete description of the four-dimensional surface. Parts of the surface are illustrated by a series of contour maps. Some preliminary attempts to fit the surface to an analytic form are described. The equilibrium geometry of (HF)2 is predicted.
Molecular dynamics of one-dimensional hard rods
Authors: Bishop Marvin , Berne Bruce J.
Published: February 2004

The validity of computer experiments is tested by comparisons between exact one-dimensional hard-rod calculations and molecular dynamics experiments with 1000 hard rods. The computer results are shown to agree with exact values of the pressure, pair-correlation function, velocity autocorrelation function, and the diffusion coefficient.
Theoretical studies in photoelectron spectroscopy: Use of angular distribution data to deduce molecular orbital parameters
Authors: Ritchie Burke
Published: February 2004

We present formulas for the differential cross section for ejection of energetic molecular photoelectrons. The cross section has been factorized into a radial and angular part. The angular part has been evaluated by use of standard angular momentum algebra, while the radial part requires explicit expressions for each partial wave component of the initial molecular orbital (which must be in the form of a single-center partial wave expansion) and for each partial wave of the photoelectron. We assume a parametrized form for the initial molecular orbital, and we calculate the photoelectron wavefunction by consecutive use of the distorted-wave-Born and Coulomb-Born approximations. This is a perturbative form, valid to O(k−2) in the asymptotic region of the wavefunction, where in atomic units k is the velocity of the photoelectron. The theory provides the means to invert angular distribution data, if available, to determine the parameters of the initial molecular orbital. Or, if this orbital is known, the theory provides an accurate high energy limit to test low energy theories or to normalize relative cross section measurements. We calculate the cross section for photoionization of H2+ from states of different symmetries as a function of internuclear distance. We indicate how the method can be extended to more complicated molecules.
Calculation of high energy elastic electron-molecule scattering cross sections with CNDO wavefunctions
Authors: Szabo Attila , Ostlund Neil S.
Published: February 2004

Differential cross sections for the elastic scattering of electrons from H2 are calculated within the Born approximation using molecular wavefunctions of different sophistication to determine the sensitivity of the cross sections to the quality of the wavefunction. An approximation to the molecular form factors based on the use of CNDO wavefunctions, which incorporates the distortion of the charge density upon the formation of the molecule without the necessity of calculating two center integrals, is used to calculate differential cross sections for electron scattering from CO, N2, NH3, H2O, and CH4 as a function of momentum transfer. For CO and N2 the CNDO calculations are in good agreement with results obtained using ab initio minimal basis wavefunctions and evaluating all integrals. The CNDO calculation describes the recently measured cross sections for NH3 much better than the method based on the independent atom approximation.
Spur reaction model of positronium formation
Authors: Mogensen O. E.
Published: February 2004

A new model of positronium (Ps) formation is proposed. Positronium is assumed to be formed by a reaction between a positron and an electron in the positron spur. Ps formation must compete with electron-ion recombination and electron or positron reactions with solvent molecules and scavenger impurities. It is also influenced by electron and positron solvation. The model correlates the measured Ps formation probabilities with the spur electron properties determined in radiation chemistry. The predictions of the model are shown to be in good agreement with experimental results for liquids and solids.
A modification of the Herzberg-Teller expansion for vibronic coupling
Authors: Roche Michel , Jaffé H. H.
Published: February 2004

First-order perturbation theory is used to obtain approximate Born-Oppenheimer wavefunctions, the zeroth-order wavefunctions being of the SCF LCAO MO CI type, with atomic orbitals ``following'' the nuclei. A practical determination of these functions within a CNDO/S scheme is presented. The intensities of forbidden transitions of formaldehyde and benzene are calculated with these functions and a comparison is made with previously reported results obtained by the conventional Herzberg-Teller expansion.
Correlation functions of classical fluids. III. The method of partition function variation applied to the chemical potential: Cases of PY and HNC2
Authors: Lee Lloyd L.
Published: February 2004

By adopting the formalism of inhomogeneous systems, a variational expansion of the partition function as a functional of the singlet density is developed. Its successive derivatives are given in terms of correlation functions of increasing orders. A theorem is proven relating the inhomogeneous partition function caused by a source particle to that of the homogeneous medium, from which a general expression for the chemical potential μ is obtained as an infinite series in integrals involving correlation functions of all orders. This series is truncated or resummed by considering three approximate theories on correlation functions: the Percus-Yevick approximation (PY), the hypernetted chain (HNC) approximation, and its extension HNC2. New expressions for μ in PY and HNC2 are given, while the results for HNC check with the formula given by Morita. To render our results on HNC2 open to the HNC2 distribution functions of Verlet and Levesque, we have generalized the Ornstein-Zernike relation to third order correlation functions, called OZ3. Four alternative forms are obtained, two of which, first derived here, are of much simpler form. The convolution form of Wu-Chien of the third order distribution function can be neatly summarized in light of OZ3 and is compared with other approximations. The μ formula for PY is found to be valid at low densities due to the convergence property. Examination of the hard sphere case shows that it is applicable to medium densities of ρd3 up to 0.5.
Electron spin resonance studies of irradiated succinamic acid. I. Triclinic single crystals
Authors: Straw D. C. , Moulton Grace C.
Published: February 2004

The products formed by x-irradiation of single crystals of triclinic succinamic acid have been studied by electron spin resonance in the temperature range from 77° to 300°K. The primary product observed at 77°K is the oxidation radical, CONH2CH2ĊH2, (I), formed by decarboxylation. The two α-hydrogens in I are exchanging rapidly and are equivalent at all orientations. Radical I decays by either an intermolecular or an intramolecular process to give two other products, CONH2CH2ĊHCOOH (II) or CONH2ĊHCH3 (III), respectively. Both II and III are stable at room temperature, however, III predominates in crystals irradiated at 300°K, whereas II predominates in crystals irradiated at 77°K and warmed to 300°K.