bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-Hartree-Fock assessment of reorganization effects in ionic states of acetylene
Authors: Chu San Yan , Ozkan Ilker , Goodman Lionel
Published: February 2004

Calculations on acetylene 2Πu and 2Πg ions and the 1Σg neutral ground state using a series of wavefunctions with increasing basis set size converge to an estimated Hartree-Fock vertical ionization energy near 10.0 eV and an estimated Hartree-Fock vertical electron affinity near −4.2 eV. The calculations reveal that the near-Hartree-Fock σ orbitals change strongly with the state of ionization leading to σ-electron energy errors (for transferring ground state σ orbitals to the ions) of − 4.5 eV for the cation and + 3.2 eV for the anion. Each carbon atom is calculated to lose only about 0.34 e upon π-electron ionization and to gain about 0.42 e on π-electron capture. Consequently there is poor transferability of the ground state HF σ core to the ionic states so that π-electron energy changes of + 3.2 eV for the cation and − 3.8 eV for the anion are incurred. The error incurred by transferring π orbitals from the ground state to the ions with frozen σ core is −0.8 eV for the cation and − 0.35 eV for the anion. The σ- and π-orbital reorganization effects largely cancel on going to the ions producing gross reorganization energy changes of − 1.3 eV in the cation and − 0.55 eV in the anion. Comparison with C(sp2)→C+ and ethylene π-electron ionization indicate that aside from extensive σ-π cancellation reorganization effects are not transferable between these species. At least double zeta level basis sets are necessary for physically meaningful descriptions of ionic processes.
Study of the electronic structure of molecules. XXII. Correlation energy corrections as a functional of the Hartree-Fock type density and its application to the homonuclear diatomic molecules of the second row atoms
Authors: Lie George C. , Clementi Enrico
Published: February 2004

A semiempirical functional of the Hartree-Fock type density, previously obtained for the Hartree-Fock atomic functions and applied with good success to the second row hydrides (in paper XXI of this series), is now applied to the molecules H2(X 1Σg+), Li2(X 1Σg+), Be2(1Σg+), B2(X 3Σg−), C2 (x1 Σg+), N2(X 1Σg+), O2(X 3Σg−), and F2(X 1Σg+). For each molecule the potential energy curve is computed from the repulsive region to large internuclear distances. In order to follow the dissociation to the correct limits, we have added to the Hartree-Fock configuration of each molecule those configurations which are needed for describing proper dissociation (HFPD functions). It is found that for certain molecules (Li2, B2, C2, and O2) there are configurations which contribute quite significantly in the bonding regions and must be added to the HFPD function to reach a proper reference state function as previously defined (see paper XXI). With our functional of the density applied to the HFPD functions, the calculated dissociation energies are, with the experimental values given in parentheses, 4.69 eV (4.75 eV), 0.65 eV (1.14 eV), 1.64 eV (3.0 eV), 3.48 eV (6.36 eV), 9.34 eV (9.91 eV), 3.75 eV (5.21 eV), and 1.37 eV (1.66 eV) for H2, Li2, B2, C2, N2, O2, and F2, respectively. More realistic dissociation energies are obtained for Li2 (1.03 eV), B2 (3.06 eV), C2 (5.21 eV), and O2 (4.64 eV) if we use the proper reference state functions. The Σg+1 state of Be2 arising from the ground state atoms is repulsive. The agreement with the experimental dissociation energy is satisfactory but not as good as what we have previously obtained for the second row hydrides. However, owing to the extreme simplicity of the method it appears in a preliminary way that the combination of a Hartree-Fock type function and the functional of its density (of the form that we have proposed) is capable of yielding sufficiently reliable results for very little computational and human effort. Since the parametrization of the density functional was made for the atomic systems and not changed in the molecular formation, our method does not suffer from the need of variation of parameters introduced ad hoc and differing from molecule to molecule.
Drift mobility of holes in phenanthrene single crystals
Authors: Sonnonstine T. J. , Hermann A. M.
Published: February 2004

The temperature dependence of drift mobilities of holes in single crystals of phenanthrene was measured in the range 203–353°K in three crystallographic directions. Below the anomaly temperature of 72°C, the mobility temperature dependences are consistent with the Munn and Siebrand slow-phonon hopping process in the b direction and the Munn and Siebrand slow-phonon coherent mode in the a and c′ directions. The drift mobility temperature dependences in crystals that have been cooled through the anomaly temperature in the presence of illumination and an electric field are consistent with the model of Spielberg et al., in which the hindered vibration of the 4,5 hydrogens introduces a new degree of freedom above 72°C.
Anisotropic thermal expansion of α-Pb(N3)2
Authors: Mauer F. A. , Hubbard C. R. , Hahn T. A.
Published: February 2004

The anisotropic expansion coefficients of orthorhombic αPb(N3)2 in the temperature range 102–423 K were determined by a single crystal x-ray method. The cell parameters and rms deviations at 298.2 K are a = 11.33344[17], b = 16.28277[37], and c = 6.64058[10] Å. The linear expansion coefficients change gradually from αa = 5.7 × 10−5, αb = 0.3 × 10−5, and αc = 1.4 × 10−5 K−1 at 112, to αa = 8 × 10−5, αb = 0.4 × 10−5, and αc = 2.0 × 10−5 K−1 at 412 K. The largest expansion is in the a direction, which is perpendicular to sheets of azide ions separated by lead atoms.
On the unimolecular isomerization of methyl isocyanide after hot tritium substitution
Authors: Steed C. J. , Harris H. H.
Published: February 2004

The Bunker formulation of RRKM theory is used to investigate the yields of CH2TCN and CH2TNC after the substitution of tritium for hydrogen on methyl isocyanide. To rationalize experimental data, large amounts of rotational energy are required at the last collision where either the rate coefficients for the forward and reverse reactions are comparable to the mean free time. This would imply either that the substitution reaction produces even larger amounts of rotational excitation than was previously expected (by typically occurring at larger impact parameters) or that rotational energy is not transferred to collision partners as effectively as in collisions near thermal energy.
Dissociative excitation of CO by electron impact: Translational spectroscopy of long-lived high-Rydberg fragment atoms
Authors: Smyth Kermit C. , Schiavone James A. , Freund Robert S.
Published: February 2004

Carbon and oxygen atoms in long-lived high-Rydberg states have been produced by the electron impact dissociative excitation of CO. The observed time-of-flight distributions and excitation functions reveal seven dissociation processes; appearance potentials and dissociation limits have been determined for each of them. For the slowest high-Rydberg fragments the excitation function exhibits sharp, resonancelike structure near threshold. These data are analyzed by the core-ion model of high-Rydberg dissociation, in which the Rydberg electron acts as a spectator to the dissociation process. The observed dissociation limits involve high-Rydberg atomic fragments with ground state ion cores. Available data on the dissociative states of CO+ and CO++ and on the kinetic energy distributions for C+ and O+ measured by dissociative ionization experiments are discussed and compared to the high-Rydberg results.
Raman study of ferric chloride solutions and hydrated melts
Authors: Sharma Shiv Kumar
Published: February 2004

A Raman study of ferric chloride hexadydrate (FCHH) in 11.5M HCl solutions has shown the presence of tetrahedral FeCl4− ion as the most prominent species. An appreciable concentration of a polymeric species, which is composed of higher chloroferrate groups of the type FeCl5 · H2O, and a small concentration of lower chloro-aquoferrate complex ion of the type Fe(H2O)4Cl2+ are also present in the solutions. The saturation of FCHH-11.5M HCl solution with dry HCl is observed to convert both the polymeric species and the lower chloro-aquoferrate ions into FeCl4− ions. In hydrated ferric chloride melts the most prominent species exists in the form of tetrahedral FeCl4− ion along with an appreciable concentration of Fe(H2O)4Cl2+ ion. Hydrated ferric chloride melts saturated with LiCl or dry HCl gas, contains only FeCl4− ions. In the case of moderately acidic (≤ 6M HCl) ferric chloride solutions Raman evidence has revealed the presence of a polymeric species along with significant concentrations of lower chloro-aquoferrate complexes. For neutral ferric chloride solutions evidence indicates that the most prominent species exists in the form of a polymeric species with structural characteristics similar to those observed in moderately acidic solutions. It has been proposed that these polymeric species are composed of randomly oriented higher chloroferrate groups of the type FeCl5 · H2O and FeCl6. Higher stability of the polymeric species in the neutral solutions has been attributed to the presence of a strong hydration layer around the polymeric species.
Semiclassical theory for low-energy molecular collisions II. Atomic exchange reactions
Authors: Ritchie Burke
Published: February 2004

A form of semiclassical theory of molecular collisions, previously formulated and applied to H+, H2 vibrational excitation in I, is applied to H, H2 atomic exchange. The formulation involves separation of the potential into two parts, a ``trajectory'' potential along which only elastic scattering can occur and ``coupling'' potential which can produce inelastic or reactive scattering. The first part is chosen such that the classical two-body central force formulas apply. This determines the coupling potential in the parameters, the classical trajectory R (t), and the classical deflection function θ(t). The time-dependent Schrödinger equation is then solved to produce the reactive probabilities. The problem is formulated in a coordinate system in which initial and final scattering coordinates are constrained to remain the same throughout the reaction. This procedure produces asymptotic momentum transfer or ``recoil'' factors of the form exp[(i/ℏ)μν · R] which multiply the vibrational-rotational wavefunctions, but it preserves orthogonality in the scattering wavefunctions and permits the coupled equations in the two-state approximation to be approximately decoupled in the symmetric process. Calculations are carried out to illustrate effect of trajectory on reaction probabilities.
Magnetic circular dichroism of manganese pentacarbonyl halides
Authors: Gall C. , Butler I. S. , Simkin David
Published: February 2004

The absorption spectra and MCD have been obtained for Mn(CO)5X (X=Cl, Br, and I) in the region of the 370 to 420 nm absorption band of these complexes. The MCD consists primarily of a positive A term, consistent with the assignment of (1A1 → 1E) for this band found in the literature. In addition, both the dipole strength (D), and the ratio (A/D), change regularly in going down the series Cl, Br, I, which provides evidence that the orbitals involved in this transition are e[π, x] → b1[σ*, 3dx2−y2] as given in the MO treatment of Fenske and De Kock [Inorg. Chem. 9, 1053 (1970)], rather than b2[π*, 3dxy] → e[π*, CO(5) suggested in an earlier work by Gray et al.
Nuclear magnetic relaxation in molten salts. II. Spin-lattice relaxation time of 7Li in lithium nitrate and its mixtures with potassium nitrate
Authors: Harold-Smith Duane
Published: February 2004

It is shown that relaxation time measurements can be used to study small structural changes in molten salt mixtures by NMR, even when chemical shifts are vanishingly small. The temperature dependence of the spin-lattice relaxation time of 7Li in pure lithium nitrate is compared with the quasilattice random flight model, and the correlation time τc is obtained. The correlation time is then combined with measurements of the 7Li relaxation time in (lithium/potassium) nitrate mixtures to obtain the composition dependence of the electric field gradient at the lithium nucleus and the lithium-anion distance. The results of relaxation time, chemical shift, and infrared measurements are compared.
Electron spin resonance spectra of V2+, Mn2+, and Ni2+ in single crystals of CsMgBr3 and CsMgI3
Authors: McPherson G. L. , Koch R. C. , Stucky G. D.
Published: February 2004

The electron spin resonance spectra of V2+, Mn2+, and Ni2+ doped into single crystals of CsMgBr3 and CsMgI3 have been studied at room and liquid nitrogen temperatures. The host lattices adopt the CsNiCl3 structure in which the basic structural feature is a linear array of [MX6]4− octahedra sharing faces. The site symmetry of the Mg2+ ion in this type of lattice is D3d, and the spectra can be described by an axial spin Hamiltonian. Well developed superhyperfine structure resulting from coupling with the bromine and iodine nuclei is observed in a number of the spectra at certain crystal orientations. The g values obtained for V2+ in CsMgI3 (g∥≃ g⊥≃ 2.04) are unusually large for a d3 ion and may be indicative of considerable metal to ligand delocalization. The spin Hamiltonian parameters for V2+, Mn2+, and Ni2+ in CsMgBr3 and CsMgI3, and the variation of the parameters from lattice to lattice is discussed.
An EPR study of W5+ in a recently discovered triclinic tungsten bronze, Na0.33WO3
Authors: Mollet H. F. , Gerstein B. C.
Published: February 2004

A single crystal EPR study of W5+ in triclinic Na0.33WO3, a recently discovered compound, has been carried out at about 15 K and 9.2 MHz. The EPR spectrum consists of two strong resonances and several weaker resonances whose relative intensities are sample-dependent. The total W5+ concentration is approximately 1000 at. ppm. The principal g-tensor components and the 183W hyperfine splitting constants for the two strong resonances are |g1|=1.695±0.003, |g2|=1.659±0.003, |g3|=1.636±0.003 [|A2|≃(61±8)×10−4 cm−1] and |g1|=1.676±0.002, |g2|=1.630±0.002, |g3|=1.593±0.002 [|A3|≃(52±4)×10−4 cm−1] for resonance 1 and resonance 2, respectively. The hyperfine splitting constants could only be determined in a few orientations because of either lack of resolution or interference of weaker resonances. It is proposed that the observed resonances are due to different W5+ point defects in the Na0.33WO3 host. This work represents the first evidence of W5+ in the tungsten bronzes.
Isomer shift of 57mFe in ferric-hemin
Authors: Moutsos P. , Adams J. G. , Sharma R. R.
Published: February 2004

The isomer shift of 57mFe in ferric-porphyrin chloride (hemin) has been estimated from the electron charge density at the iron nucleus obtained in the framework of a rather idealized model of an Fe3+ ion overlapping with the orbitals of neighboring atoms. The constants appearing in the expression for the isomer shift have been taken from the modifications of the previous analysis of the isomer shift of 57mFe in Fe2O3 and several rare-earth iron garnets. Using the structure parameters (which indicate the off-plane displacement equal to 0.475 Å of the iron atom from the porphyrin plane) as determined by Koenig, the calculated value of the isomer shift for 57mFe in ferric-hemin is found to be 1.26 mm/sec (including relativistic effects) with respect to stainless steel, in reasonable agreement with the Mössbauer experimental result of about 0.50 mm/sec observed by Bearden et al., by Gonser and Grant, and by Shulman and Wertheim. The isomer shift has also been obtained for two other available sets of structure parameters for the purposes of comparison. The results have been discussed in view of the approximations used.
Measurement of vibrational-vibrational exchange rates for excited vibrational levels (2≤v≤4) in hydrogen fluoride gas
Authors: Osgood R. M. , Sackett P. B. , Javan A.
Published: February 2004

A measurement of the total decay rate (due to both V-V and V-T processes) of the second, third, and fourth vibrational levels in vibrationally cold hydrogen fluoride gas is described. The measured endothermic rate constants are 8×105, 1.6×106, and 1.4×106 sec−1 · torr−1, respectively. It is argued that the major contribution of each of these decay rates is from the process HF(ν = n)+HF(ν = 0)→ HF(ν = n − 1) + HF(ν = 1) where n = 2,3, and 4. The technique used in these measurements is a novel variation of the method of laser induced fluorescence. It involves exciting the first; first and second; or first, second, and third vibrational levels of HF via multiband laser optical pumping. Collisional population of the level of interest then occurs through the reverse of the above vibrational exchange process. An analysis using rate equations shows that the rise rate of the population of a given level is governed by the forward rate of the above process. It is also shown theoretically and experimentally that in the pressure regime where diffusion is unimportant the decay rate of level ν = n is n times that of ν = 1. This result is shown to be a result of the existence of a vibrational exchange equilibrium at a relatively low vibrational temperature. If the pressure is sufficiently low so that the diffusion time across the original radius of excitation is comparable to the decay time of the population of the nth level, it is found that the decay rate of that level is not n times that of ν = 1. This phenomenon which is termed ``vibrational temperature'' diffusion is given a brief experimental and theoretical description.
Spin and bonding properties and optical spectra of octahedral transition metal complexes using the multiple scattering Xα method
Authors: Larsson Sven , Connolly John W. D.
Published: February 2004

Spin-polarized multiple scattering calculations using scaled local exchange are performed for the following octahedral clusters: TiF63−, CrF63−, CrCl63−, MnF62−, MnF64−, FeF63−, NiF62−, NiF64−, and NiCl64−. Good agreement is obtained with EPR and NMR measurements of transferred hyperfine interactions. fσ is found to be larger than fπ even for the d3 systems. For the optical spectrum the method predicts the shift quite well when Cl is substituted for F.
Field dependence of nuclear magnetic relaxation of 207Pb in aqueous Pb(ClO4)2
Authors: Hawk Roger M. , Sharp Robert R.
Published: February 2004

Nuclear magnetic relaxation times of the 207Pb resonance have been measured as a function of temperature and concentration at field strengths of 16.9, 11.7, and 6.56 kG in aqueous Pb(ClO4)2. Longitudinal relaxation is composed of spin-rotation, chemical shift anisotropy, and dipolar contributions in a 3.5M solution, while spin-rotation strongly dominates the relaxation at all temperatures between the melting and boiling points in a 1.15M solution. T2 accurately equals T1 at 1.15M, as is expected for a dominant spin-rotation interaction, but is 20–30% shorter in the 3.5M solution, possibly due to a minor relaxation component arising from scalar coupling to naturally abundant H217O. Chemical shifts of 207Pb have also been measured in aqueous Pb(ClO4)2 and Pb(NO3)2. The chemical shift and relaxation data show that ClO4− penetrates the Pb+2 hydration sphere at concentrations above about 2M, but no effects of such penetration are seen at lower concentration.
Formation and decay of dual fluorescences in p-dimethylaminobenzonitrile
Authors: Struve W. S. , Rentzepis P M.
Published: February 2004

We have studied by the methods of picosecond spectroscopy the fluorescence risetimes of the S1→S0 and S2→S0 emissions of p-dimethylaminobenzonitrile in several polar solvents of increasing viscosity at 25 and −78°C to determine the relaxation dynamics controlling their kinetics. Vibronic relaxation resulting from interaction with the solvent as a dissipative medium appears to precede the S1→S0 fluorescence. An earlier hypothesis that the S2→S0 emission follows a modified Debye theory of viscosity-controlled solvent reorganization is not completely supported by our data, though solvent viscosity does appear to influence the relaxation dynamics. Available data do not distinguish between intramolecular − N(CH3)2 rotation and nonviscosity limited solvent reorgainization as leading to S2→S0 emission, whose decay lifetime was determined to be ∼ 1 nsec.
Improved simulation of liquid water by molecular dynamics
Authors: Stillinger Frank H. , Rahman Aneesur
Published: February 2004

Molecular dynamics calculations on a classical model for liquid water have been carried out at mass density 1 g/cm3 and at four temperatures. The effective pair potential employed is based on a four-charge model for each molecule and represents a modification of the prior ``BNS'' interaction. Results for molecular structure and thermodynamic properties indicate that the modification improves the fidelity of the molecular dynamics simulation. In particular, the present version leads to a density maximum near 27°C for the liquid in coexistence with its vapor and to molecular distribution functions in better agreement with x-ray scattering experiments.
Vibronic effects in the 7000 Å state of azulene
Authors: Small G. J. , Kusserow S.
Published: February 2004

Vibronic perturbations in the 7000 Å S1(B1) ← S0(A1) absorption system of azulene due to a large number of b1 vibrations have been identified. The total induced oscillator strength for this transition is 1.2×10−3 while the allowed oscillator strength is 7.8×10−3. Accurate intensities for the b1 vibronic origins relative to the allowed origin are reported. Calculations are presented which indicate that the two most probable coupling routes for the vibronic interactions (intensity) involve the second excited 1A1 state (S4) and the ground state, S0. The latter route exists due to the large change in permanent dipole moment between S0 and S1, ∼ 2 D. Assignments for all 12 of the excited state a1 fundamentals (excluding CH) are given. The differences between the 7000 Å 1B1 ← 1A1 and 3500 Å 1A1 ← 1A1 absorption systems are discussed in relation to the anomalous fluorescence behavior of azulene.
Time-resolved thermal lensing studies of laser-induced translational energy fluctuations in CD4, SO2, and OCS
Authors: Siebert D. R. , Grabiner F. R. , Flynn G. W.
Published: February 2004

Translational energy changes caused by nonresonant vibration-vibration (V-V) and vibration → translation/rotation (V → T/R) processes have been studied in laser-excited CD4, SO2, and OCS by the time-resolved thermal lensing technique. Kinetic cooling has been observed in CD4 and SO2, indicating the contribution of endothermic collisional processes to the vibrational relaxation of these molecules. Varying amplitude of the cooling observed in CD4 has been attributed to rotational relaxation effects. A generalized spectrophone effect has been observed in mixtures of laser-excited CH3F with CH3Cl. The sensitivity of the thermal lens to very weak absorption is discussed with regard to possible trace impurity detection. A discussion of the effects of acoustic phenomena is also presented.
Thermal ion emission from some transition metal carbides heated on graphite filament
Authors: Sasaki Noriaki , Kubo Kenji , Asano Mitsuru
Published: February 2004

Thermal ion emissions from the carbides of Ti, Zr, Hf, V, Nb, and Mo heated on graphite filament have been studied by means of the mass spectrometric single filament surface ionization technique. With Ti–C, Zr–C, Hf–C, V–C, and Nb–C systems dicarbide ions and with Mo–C system monocarbide ions were identified, respectively, in addition to the corresponding metal ions. Abundance ratios MC2+(g)/M+(g) and heats of vaporization of some ionic species were determined, and heats of vaporization of neutral species were also derived.
High temperature enthalpies and related thermodynamic functions of the trifluorides of Sc, Ce, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb
Authors: Spedding F. H. , Beaudry B. J. , Henderson D. C. , Moorman J.
Published: February 2004

The high temperature enthalpies of high purity ScF3, CeF3, SmF3, GdF3 (redetermined), TbF3, DyF3, ErF3, TmF3, and YbF3 were measured from 100 to 1600°C and EuF3 from 100 to 975°C. The thermal data for the other fluorides in the rare earth series were reported earlier from this laboratory. The heat capacity, enthalpies of transition and fusion, and related thermodynamic functions were calculated. The smoothed values of H°T−H°298.15, Cp, S°T−S°298.15, and −(F°T−H°298.15)/T are tabulated at 100° intervals. The melting points, transition temperatures, and lattice parameters of the high purity fluorides prepared in this study were determined.
In-out decomposition for inelastic collisions as subdynamics. II. Scattering matrix and approximation methods
Authors: Shipsey Edward J.
Published: February 2004

The work of a previous paper is extended. The scattering matrix is expressed in an explicitly unitary form by means of the subdynamics relations. A procedure is given such that a wide variety of approximations can yield a unitary scattering matrix.
Approximate spin projection of three-component UHF wavefunctions: The states of the pentachlorocyclopentadienyl cation and the croconate dianion, C5O52−
Authors: Phillips Donald H. , Schug John C.
Published: February 2004

The approximate spin projection method of Amos et al. is extended to handle UHF wavefunctions having three significant components of differing multiplicity. An expression is given for the energy after single annihilation which differs from that of Amos and Hall. The new expression reproduces the results obtained from a previous exact calculation for which the weights and energies of the components are known. The extended approximate projection method is applied to the pi-electron UHF wavefunctions for the ground states of the pentachlorocyclopentadienyl cation and the croconate dianion, C5O52−. The results indicate a triplet ground state for the former and a singlet ground state for the latter, in agreement with experimental ESR susceptibility measurements for these molecular ions. C5Cl5+ cannot be treated by restricted Hartree-Fock theory due to its open-shell ground state. Incorrect results are obtained for the croconate dianion if restricted Hartree-Fock theory and singly excited configuration interactions are utilized.
Molecular rotation in liquid and solid carbon tetrachloride
Authors: O'Reilly D. E. , Peterson E. M. , Scheie C. E.
Published: February 2004

Spin-spin relaxation times of chlorine-35 have been measured in CCl4 from below the melting point (250°K) to near the gas-liquid critical point (556°K). From density and compressibility data, the scaled particle theory, and activation energies, values of the mean work required to create a molecular vacancy are computed. Theoretical pre-exponential factors and volumes of activation for self-diffusion are evaluated and compared with recent data. By means of a modified Hubbard relationship and a hindered rotation model values of the rotational correlation time are evaluated and compared with experiment. Arguments are presented to indicate that the extended J-diffusion model does not apply to liquid carbon tetrachoride.
Anisotropic proton hyperfine interaction in the electron spin resonance spectra of the n-propyl and n-butyl radicals in an argon matrix at 4.2 K
Authors: McDowell C. A. , Shimokoshi K.
Published: February 2004

The electron spin resonance spectra of the n-propyl and n-butyl radicals have been measured in an argon matrix at 4.2 K. The radicals were produced in situ by photolysis of the corresponding iodides. The spectra have been analyzed fully and the analysis confirmed by comparison with simulated spectra obtained by a comprehensive computer program. From comparison of the simulated spectra and the experimental ones the following hyperfine interactions and g tensors have been obtained: A1α=29.2± 0.05 G; A2α=17.0± 0.05 G; A3α=20.1± 0.05 G; A⊥β=37.3± 0.05 G; A∥β=34.0± 0.05 G; Aisoα=22.1± 0.05 G; Aisoβ=35.10± 0.05 G; g1 = 2.0030, g2 = 2.0033, and g3 = 2.0025. The parameters for both radicals were the same within our experimental errors. By analysis of the linewidths observed for the β-proton couplings we show that at 4.2 K the methylene group in these radicals is undergoing restricted reorientation or tunneling rather than classical free rotation. Modified Bloch equations for the two site case were used to estimate the correlation time for the reorientation or tunneling. We were also able to determine the equilibrium configuration of the radicals. The correlation times for reorientation of the β protons of both radicals were found to be the same within experimental error and to be equal to τ = 6 × 10−10 sec at 4.2 K. This fast correlation time is attributed to extensive quantum mechanical tunneling occurring at 4.2 K.
Infrared and visible photon upconversion in LaCl3:Pr3+ (Nd3+)
Authors: Zalucha Denis J. , Sell Jeffrey A. , Fong Francis K.
Published: February 2004

Investigation of the optical properties of single crystals of LaCl3 containing 1% Pr3+ and traces of N d3+ impurity has revealed several upconversion processes in which laser excitation results in the emission of photons of higher energy than that of the pump photons. The fluorescence upconversion flux dependences and decay times are analyzed in terms of two mechanisms: (1) a sequential two-photon excitation process in which the initially excited ion decays to a lower excited level before the absorption of a second photon sends it to a higher excited level and (2) an energy transfer upconversion (ETU) process in which two nearby ions in excited states undergo an annihilation interaction resulting in one ion in a higher excited state and the other in a lower state. The time dependence of the upconverted fluorescence is derived from transient rate equations for the ETU process under a square wave excitation and the derivation is found to be in good agreement with the experimental data. Upconverted fluorescence resulting from infrared quantum counter action is also observed when the sample is in double resonance with a laser excitation source and a broad-band (1.15–4 μ) infrared source.
Determination of the proton chemical shielding tensor in anhydrous α-oxalic acid by multiple pulse NMR
Authors: Van Hecke P. , Weaver J. C. , Neff B. L. , Waugh J. S.
Published: February 2004

Multiple pulse line-narrowing methods have been used to determine the proton chemical shielding tensors in a single crystal of anhydrous α-oxalic acid. The results indicate approximate axial symmetry of the chemical shift about the nominal hydrogen bond directions with the largest shielding occurring when the external field is parallel to the hydrogen bond.
Electron spin resonance of γ-irradiated alkyl phosphates: The C2H5 radical in magnesium diethyl phosphate (MgDEP)
Authors: Bernhard W. A. , Ezra F. S.
Published: February 2004

The major free radical product trapped at 77°K in γ-irradiated magnesium diethyl phosphate [((C2H5O)2PO2)2Mg] is the ethyl radical. The following principal values for the α and β proton hyperfine tensors were determined from ESR data obtained at the Q band: Axα=15.9, Ayα=20.6, Azα=25.5; and Axβ=26.0, Ayβ=26.5, Azβ = 27.6± 0.5 G. Significant reorientation of the ethyl radical occurs upon cleavage of the carbon oxygen bond. The assymetry in the α hyperfine tensor has been interpreted in terms of a twofold potential barrier to the rotation of the methylene group. Hindrance to the rotation of the methyl group, relative to the methylene, is apparent from differential line broadening within the spectrum at 77°K.
Electron spin resonance of γ-irradiated alkyl phosphates: The CH3ĊHOP(O)2OC2H5− radical in magnesium diethyl phosphate (MgDEP)
Authors: Ezra F. S. , Bernhard W. A.
Published: February 2004

The free radical species observed by ESR after γ irradiation of magnesium diethyl phosphate (MgDEP) at 77°K and annealing to 160°K is CḢ3CHOP(O)2OC2H5−. The radical structure has been determined by deuterium and 13C substitution in polycrystalline samples and by a single crystal analysis. Hyperfine principal values for the α hydrogen, β hydrogen, and phosphorous nuclei are: (AzH α = − 7.3 G, ‖ to C–H bond; AxHα = − 15.8 G, ‖ to p orbital; AyHα ∼ − 27.5 G), (AzHβ = 25.2 G, ‖ to C–C bond; AyHβ = 22.2 G; AxHβ = 22.8 G), and (AyP = 4.7 G, ‖ to p orbital; AzP = 6.1 G, ∼ ‖ to C ⋯ P direction; AxP = 2.8 G). From the temperature dependency of the phosphorous hyperfine coupling and the single crystal analysis, it is concluded that the predominant mechanism for transfer of spin to the phosphorous is hyperconjugation.
Absolute differential cross sections of elastically scattered electrons. V. O2 and CO2 at 500, 400, and 300 eV
Authors: Bromberg J. Philip
Published: February 2004

Absolute differential cross sections of electrons elastically scattered by O2 and CO2 were measured at energies of 500, 400, and 300 eV over the angular range of 2° to 40°. In both cases the cross sections become independent of the momentum change in the limit of small momentum change, and polarizabilities were calculated.
Influence of intramolecularly compensated dipoles upon collision absorption in liquids
Authors: Dasgupta S. , Smyth C. P.
Published: February 2004

Measurements of dielectric constant and dielectric loss at 0.22, 1.25, 3.22, and 10.00 cm have been made upon benzene, hexafluorobenzene, an equimolar mixture of benzene and hexafluorobenzene, a dilute solution of hexachlorobenzene in benzene, and hexane, dodecane, and octadecane. The very small sizes of the dielectric losses observed in this frequency region, where loss due to the rotational orientation of dipolar molecules of this size should be at or near a maximum, indicates the absence of any appreciable permanent molecular dipole moment. The increase of the loss values with increasing frequency in this region indicates that, as already established for benzene, they form the low-frequency tail of a very-far-infrared absorption band for each liquid. The absorption presumably arises from the small temporary dipole moments induced by molecular collisions. It is found that the absorption coefficients are increased by the presence of mutually opposing and compensating permanent dipoles and of π electrons in the molecules.
High pressure laser Raman study of the dissociation of aqueous bisulfate ion
Authors: Davis A. R. , Adams W. A. , McGuire M. J.
Published: February 2004

A three-window optical cell has been designed and built to study the effects of pressure on the Raman spectra of corrosive liquids, gases, and solutions. The technique has been used to probe the effect of pressure on the dissociation of bisulfate ion in aqueous media. The relative changes of the dissociation constant with pressure are found to be in agreement with the results of high pressure conductivity measurements.
Molecular Zeeman effect in methyl fluoride
Authors: Norris C. L. , Pearson E. F. , Flygare W. H.
Published: February 2004

Several rotational transitions in CH3F were observed at high magnetic fields to give the molecular g values of g⊥=−0.062 ± 0.002 and g∥=0.265±0.008, the magnetic susceptibility anisotropy of χ⊥−χ=(8.5 ± 0.6)× 10−6 erg/G2· mole, and molecular quadrupole moment along the C3 axis of Q∥ = (0.4 ± 1.0) × 10−2 6 esu · cm2. The value of g∥ in CH3F is compared to other molecules. The remaining Zeeman parameters are listed and discussed in light of the electronic structure.
Energy limits in chemiluminescent, atom transfer reactions: Bond dissociation energy of NaF
Authors: Ham David O.
Published: February 2004

Atomic emissions from the reactions M2 + X → MX + M* have been observed for the systems which produce MX = NaF, NaCl, NaBr, KCl, and KBr. Energy limits in these reactions are also discussed which yield lower limits on values of D00(MX) and a value of D00(NAF)=123 ± 3 kcal/mole is recommended. Arguments are presented in support of previous chemiluminescence determinations of bond energy limits.
HF infrared chemiluminescence, energy partitioning, and D(H–GeH3) from the reaction of F atoms with germane
Authors: Kim K. C. , Setser D. W. , Bogan C. M.
Published: February 2004

The infrared emission intensities from the reaction F+GeH4 have been used to measure the energy partitioned to the HF product. The experiments were conducted in a cold-walled reactor with various flow rates of GeH4 and fluorine atom source (discharged SF6 or CF4). Based on the highest observed HF vibrational-rotational level, D(H–GeH3) was estimated as ≤78 kcal mole−1. The initial relative vibrational populations were N(ν = 1): N(ν = 2): N(ν = 3): N(ν = 4): N(ν = 5) = 0.10:0.18:0.29:0.41: 0.02. Based upon D(H–GeH3) = 78 kcal mole−1, the mean fractional conversion of energy into HF vibrational energy was 0.58. The rotational distributions extend to quite high J levels; after correction for some rotational relaxation the mean fractional conversion to HF rotational energy was estimated as 0.12.
Study of the electron gas approximation
Authors: Kim Yung Sik , Gordon Roy G.
Published: February 2004

We test the applicability to atoms of the uniform electron gas energy expression in terms of the local atomic electron density. By using the known atomic electron densities obtained from an independent method (Hartree-Fock) for the density in the electron gas energy expression, we calculate some atomic energies, one-electron energies, and atomic ionization potentials and compare the results with the Hartree-Fock energy values. We calculate the local kinetic energy and exchange energy densities in Hartree-Fock atoms, and compare these results with the corresponding electron gas energy densities. We suggest a simple correction to the electron gas energy to be used for systems not paired in spin, and test this correction. We examine the effect of the finiteness of the atoms by treating a uniform electron gas with a finite number of electrons.
Oscillations in chemical systems. IV. Limit cycle behavior in a model of a real chemical reaction
Authors: Field Richard J. , Noyes Richard M.
Published: February 2004

The chemical mechanism of Field, Körös, and Noyes for the oscillatory Belousov reaction has been generalized by a model composed of five steps involving three independent chemical intermediates. The behavior of the resulting differential equations has been examined numerically, and it has been shown that the system traces a stable closed trajectory in three dimensional phase space. The same trajectory is attained from other phase points and even from the point corresponding to steady state solution of the differential equations. The model appears to exhibit limit cycle behavior. By stiffly coupling the concentrations of two of the intermediates, the limit cycle model can be simplified to a system described by two independent variables; this coupled system is amenable to analysis by theoretical techniques already developed for such systems.
Calculated long-range interactions and low energy scattering of Ar–H
Authors: Wagner Albert F. , Das G. , Wahl Arnold C.
Published: February 2004

The long-range interaction potential in Ar–H is evaluated through the use of the multi-configuration-self-consistent-field (MCSCF) method. The values of C6 and C8 obtained by analysis of the dispersion terms in this potential agree with previous calculations and estimates. The potential is used to calculate the total elastic cross sections for low energy hydrogen-argon scattering. These results support only one of the two conflicting experimental measurements reported in the literature.
On the deuteron quadrupole coupling constant in hydrogen bonded solids
Authors: Goren Shaul D.
Published: February 2004

Deuteron quadrupole coupling constants were calculated for the water dimer at different O–D bond length and different O–D ⋯ O angles. The results are used for the interpretation of the deuteron quadrupole coupling constants in hydrogen bonded solids.
Study of dielectric relaxation in alkyl acetates
Authors: Srivastava G. P. , Mathur P. C. , Krishna
Published: February 2004

The relaxation time and distribution parameter of methyl, ethyl, n-propyl, n-butyl, and amyl acetates have been determined, as a function of temperature, by measuring the dielectric constant and loss at 250 kHz, 9.00, 19.14, 29.7, and 38.7 GHz. The relaxation time is found to increase from methyl to amyl acetate and the effect of chain length on the relaxation time has been estimated after normalizing for the viscosity variation of different polar liquids. The distribution parameter for all these molecules has been calculated and is found to increase with the chain length. The energy parameters for dielectric relaxation and viscosity processes have been estimated. Entropy of activation is found to be negative for all the molecules.
On the estimate of the three-body contribution to time-correlation functions for transport coefficients. I
Authors: Eu Byung Chan
Published: February 2004

In this series of papers we investigate the three-body contribution to the quantum mechanical self-diffusion coefficient for a two-dimensional fluid with a view to resolving the question of its divergence. In this paper (Part I) we examine the approximate three-body contribution W 12(ε)R 0(ε)W 13(ε)R 0(ε)W 12≡W B especially with regard to its behavior in the vincinity of ε=0. We find through careful analysis that with reasonable bounds, the same as those assumed for W ij(ε) in the literature, the estimate of the approximate three-body contribution W B is bounded with respect to ε as ε→0 in a cut plane. That is, there is no logε divergence of the three-body contribution. In the literature the logε divergence of the three-body contribution has been attributed to the appearance of the logarithmic denisty dependence of transport coefficients. It is discussed in the paper that the light of the cluster expansion method previously developed by the author based on Zwanzig's theory regarding time-correlation functions for transport coefficients, the nonexistence of such logε dependence of the three-body contribution implies that the logarithmic density dependence of transport coefficients is mathematically unfounded.
Application of the time-dependent Ising model to chain motions
Authors: Isbister D. J. , McQuarrie D. A.
Published: February 2004

The time-dependent Ising formalism developed by Glauber is applied to cooperative rotameric transitions in polymer chains. The Laplace transform of the time-delayed autocorrelation function for an ``isolated dipolar segment'' is given analytically as a function of chain length N and investigated for large N. It is found that Glauber's exact result for infinite N can be extracted and the difference becomes meaningful only for small N less than 28.
van der Waals potentials and crystal energies of ionic compounds
Authors: Ladd M. F. C.
Published: February 2004

A modification of Mayer's calculation of the constants of the van der Waals potential in ionic compounds is presented. Its applicability is demonstrated with respect to the energetically well defined alkali-metal halides, and an extension to compounds of the rutile structure is discussed.
The hydrated proton H+(H2O)n. II. A spectroscopic study and normal coordinate treatment of the oxonium ions H3O+ and D3O+
Authors: Basile L. J. , LaBonville P. , Ferraro J. R. , Williams J. M.
Published: February 2004

A spectroscopic study and a normal coordinate treatment (NCT) of the oxonium ions H3O+ and D3O+ in solid H3O+CH3C6H4SO3− and D3O+CH3C6H4SO3− were made. Neutron diffraction studies indicated a pyramidal, C3ν symmetry for the oxonium ions. Based on this symmetry, the observed frequencies for H3O+ and D3O+ were assigned and a NCT attempted using the general valence force field and the Urey-Bradley force field. Comparison of the fundamental vibrations in various oxonium compounds was made. It was demonstrated that a relationship between the OH stretching frequencies in H3O+ and D3O+ ions vs R (the O⋯O distance) exists, as well as a relationship between the stretching frequency shift (Δνs) and R. The failure of past investigators to recognize this trend may have contributed to the confusion regarding the assignments. This is the first confirmation of such a trend existing in oxonium compounds. It is suggested that the stretching mode frequencies in H3O+ and D3O+ are dependent on R. When Rx-y is greater than the X–H⋯Y van der Waals radius sum, the asymmetric stretching vibration (ν3,e) is at higher frequency than the symmetric stretching vibration (ν1,a1); where Rx-y is less, the stretching mode frequencies are inverted.
Recursion analysis of the configurational-coordinate model for equal force constants
Authors: Struck C. W. , Fonger W. H.
Published: February 2004

For transitions between two offset oscillators with equal force constants, the optical band shapes are described by the distribution Wpu giving the probability that the optical transition is accompanied by the generation of pu phonons. For the Condon approximation and for thermal equilibrium among the initial-oscillator vibrational levels, Wpu is shown through the Manneback recursion formulas for the overlap integrals to satisfy the recursion formula S0vWpu+1+ puWpu −S0<1+m>vWpu−1 =0. S0 and v are offset and temperature parameters, respectively. From this Wpu recursion formula, the moments of the Wpu distribution, its approximate forms, its exact expression, and numerical values are obtained in simple ways.
Calculated linewidths for CH4 broadened by N2 and O2
Authors: Tejwani G. D. T. , Fox K.
Published: February 2004

The Anderson-Tsao-Curnutte theory of collision-broadened spectral lines, as extended by Tejwani for octopolar interactions, has been used to compute linewidths for methane broadened by molecular nitrogen and oxygen. Widths of vibration-rotation lines in the infrared-active fundamental bands ν2, ν3, and ν4; the combination bands ν2 + ν3 and ν3 + ν4; and the overtone bands 2ν3, 2ν4, and 3ν3 have been calculated for the symmetry species A, E, and F separately, and for a large range of the total angular momentum quantum number J. The effect of the dipole moment of CH4 due to vibration-rotation interactions was considered. The temperature dependence of the linewidths has been obtained for 210°K ≤ T ≤ 300°K. These results were used to compute corresponding air-broadened linewidths. It has been shown that the calculated linewidths depend significantly on the magnitude of the octopole moment for methane.
Quantum mechanics of transfer reactions
Authors: Carbonell R. G. , Kostin M. D.
Published: February 2004

A method that takes into account both tunneling and transitions is presented for calculating the rate constant for transfer reactions. An exothermic proton transfer reaction with a large energy of activation is considered, and the rate constant is computed as a function of temperature. It is found that at high temperatures the Arrhenius plot for the rate constant is nearly linear, but at low temperatures, where quantum effects become especially important, the plot is nonlinear.
Electrical transport properties of single crystal rare-earth sesquisulfides
Authors: Taher S. M. A. , Gruber John B. , Olsen L. C.
Published: February 2004

Electrical transport properties of semiconducting single crystal Nd2S3, Gd2S3, and Dy2S3 (Th3P4, bcc structure) have been investigated between 80 and 300°K. Electrical resistivity (ρ), Hall coefficient (RH), and thermoelectric power (α), all measured as a function of temperature, are reported for several single-crystal samples of each compound. The crystals are black degenerate n-type semiconductors owing to slight excess rare earth over R2S3 stoichiometry. To interpret the data over this temperature range where the samples display extrinsic semiconducting behavior, we have considered a parabolic band model combined with different scattering mechanisms. The scattering mechanisms include acoustical phonon scattering, alloy scattering, and charged impurity scattering. Above 150°K for the Nd2S3 samples and above 200°K for the Gd2S3 and Dy2S3 samples, the data seem to suggest that a parabolic band model with alloy scattering appears possible. These conclusions appear reasonable in light of the known excess rare earth found in each sample investigated having the Th3P4 defect structure.