bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation Energy, Ionization Potential, Electron Affinity, Dipole and Quadrupole Moments of Chlorine Monoxide (ClO, 2Π) from Ab Initio Molecular Orbital Calculations
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

Molecular self-consistent-field wavefunctions near the Hartree–Fock limit have been computed by the Roothaan expansion method for ClO(2Π), ClO+(3Σ), and ClO−(1Σ) at an internuclear separation of 1.570 Å. Combination of the computed total energies with estimates for the molecular extra correlation energies yielded values of < 2.9, 2.2 ± 0.5, and 11.2 ± 0.4 eV for the binding energy, vertical electron affinity, and vertical ionization potential, respectively, of ClO. The above results, and the computed dipole moment, 0.81 ± 0.16 D, are in satisfactory agreement with experimental data. In addition to the above properties, the dipole and quadrupole moments have been calculated for ClO+ and ClO−.
Calorimetric Study of Iodine Pentafluoride: Heat Capacity between 5 and 350°K, Enthalpy of Fusion and Vaporization, Standard Entropy of the Vapor, and Other Thermodynamic Properties
Authors: Osborne Darrell W. , Schreiner Felix , Selig Henry
Published: February 2004

The heat capacity of iodine pentafluoride has been measured by an adiabatic method between 5 and 350°K. The triple point of the compound is 282.553 ± 0.01°K and the enthalpy of fusion is ΔHfusion = 11222 ± 11 J mole−1. The vapor pressure measured between 283 and 378°K is represented by the equation: log10PmmHg = − 3090.14 / T − 6.96834 log10T + 29.02167. A determination of the vapor density at 330 and 372°K resulted in the values − 2813 and − 1232 cm3 mole−1, respectively, for the second virial coefficient B to be used with the equation of state PV = RT + BP. The enthalpy of vaporization at 330°K was calculated to be ΔHvap(330°K) = 39320 ± 200 J mole−1. At 298.15°K the standard state values of the thermodynamic functions obtained from the heat capacity data are: CP° = 174.7 ± 0.17 J °K−1·mole−1, S° = 224.85 ± 0.22 J °K−1·mole−1, (H° − H°0) = 37086 ± 37 J mole−1, and (G° − H°0) / T = − 100.47 ± 0.1 J °K−1·mole−1. The standard entropy of iodine pentafluoride vapor at 330°K calculated from calorimetric data is 347.53 ± 0.84 J °K−1·mole−1. The fundamental frequency ν9 was observed in the infrared spectrum of the gas at 189.0 ± 0.7 cm−1. To bring the standard entropy calculated from molecular data into agreement with the calorimetric value, the unobserved vibrational frequency ν5 must be 181 ± 20 cm−1. A revised calculation of the standard enthalpy, entropy, and Gibbs energy of formation of IF5 from the elements at 298.15°K yielded the values ΔHf° = − 881.99 ± 1.34kJ mole−1, ΔSf° = − 340.0 ± 0.6 J °K−1·mole−1, and ΔGf° = − 780.62 ± 1.35kJ mole−1.
Metastable Ions and Isotope Effects in the Mass Spectra of Methane and the Deuteromethanes
Authors: Hills Lorin P. , Vestal Marvin L. , Futrell Jean H.
Published: February 2004

A differentially pumped double-focusing mass spectrometer was suitably modified for the study of metastable ions and collision-induced metastables. At high resolution the same instrument easily resolved protonated and deuterated ions of the same nominal mass. Accordingly, metastable ions and isotope effects in the mass spectra of CH4, CH3D, CH2D2, and CD4 were reinvestigated with this instrument in order to resolve certain ambiguities in previous studies. All four protonated molecular ions exhibited hydrogen-loss metastables, while CD4+ exhibited a corresponding unimolecular elimination of a deuterium atom. In addition to these true metastables, essentially every conceivable collision-induced metastable decay process was also observed. The observed relative intensities and isotope effects in the normal spectra are rationalized with general statistical arguments and with more complete calculations using the quasiequilibrium theory of mass spectra. The behavior of the rates at threshold and their effect on methane metastable intensities are also discussed.
Electronic Spectra of Some Methyl Substituted Benzenes in a Rare-Gas Solid
Authors: Katz Benjamin , Brith Malka , Sharf Benjamin , Jortner Joshua
Published: February 2004

In this paper we present the results of an experimental study of the absorption spectrum of toluene, toluene-d8, para-xylene, and meta-xylene in solid krypton in the spectral region 2800–1800 Å. Our main results are:(a) The absorption spectrum of the first (2700 Å) π → π* transition is very sharp for all these matrix isolated molecules and resembles in detail the gas-phase spectrum. (b) The observed vibrational structure of the second (2200 Å) π → π* transition is consistent with the A1g1 → B1u1 assignment for this transition in the benzene molecule. (c) The vibrational structure of the third (1850 Å) π → π* transition was resolved. An electronic splitting of 350 cm−1 was observed in the third excited state of para-xylene, which results from lifting of the degeneracy of the corresponding E1u1 state of the benzene molecule.
Geometrical Aspects of the Penetrable-Sphere Model
Authors: Widom B.
Published: February 2004

It is shown that the potential energy of interaction in the penetrable-sphere model may be decomposed into negative two-body, four-body, ··· potentials corresponding to attractive forces among the molecules, and positive three-body, five-body, ··· potentials corresponding to repulsive forces. These and related aspects of the interaction energy imply, via the potential distribution theory, a number of inequalities among the thermodynamic functions of the model fluid. It is also shown that the interaction potential is a homogeneous function of the coordinates of the molecular centers and of the sphere radius, from which there follow two virial-like relations. The latter yield a geometric criterion for phase equilibrium in the model, as well as additional thermodynamic inequalities.
Role of Spin Symmetry Conversion in Nuclear Relaxation in Solids
Authors: Wallach Daniel
Published: February 2004

The rates of nuclear transitions in molecules which are able to rotate about a single axis in the solid are considered. Only the effects of intramolecular dipolar interactions are taken into account. In molecules with threefold or higher symmetry about the rotation axis, only transitions which alter the symmetry of the nuclear state can occur. In molecules with twofold symmetry, if the angle between the internuclear vector and the rotation axis is 90°, only transitions which retain the nuclear symmetry can occur. If that angle is not 90°, both nuclear transitions which alter and which conserve symmetry are allowed. The detailed mechanisms which cause these two types of nuclear transitions are similar.
Gaseous Self-Diffusion through a Porous Medium
Authors: Strieder William
Published: February 2004

The mean free path theory of self-diffusion of “tagged” molecules is formulated for arbitrary Knudsen number (mean free path to average pore diameter ratio) in terms of two coupled integral equations. A variational upper bound on the net rate of diffusion through a porous slab is derived. An upper bound on the diffusion rate is calculated for a model pore structure generated by randomly placed, freely overlapping, solid spheres.
Dynamic Polarization of 7Li Nuclei in Solution
Authors: Potenza J. A. , Linowski J. W.
Published: February 2004

Lithium dynamic nuclear polarization (DNP) parameters, obtained at 74 G, are reported for lithium salts in solvents containing OH groups. Observed 7Li NMR enhancements indicate that the most sensitive experimental variable governing the degree of scalar coupling is the choice of free radical. Of the five radicals used, only nitroxide radicals lead to appreciable scalar coupling. Lithium T1 measurements suggest clustering in the solutions with different radicals avoiding lithium-containing regions to different degrees. Only nitroxide radicals appear to compete effectively with ROH to solvate lithium.
Millimeter-Wave Spectrum and Structure of Hypofluorous Acid: HOF and DOF
Authors: Kim Hyunyong , Pearson Edwin F. , Appelman Evan H.
Published: February 2004

The microwave spectra of two isotopic species of hypofluorous acid, HOF and DOF, have been investigated. The values of the A0, B0, and C0 rotational constants are 590 000, 26 758.00, and 25 512.51 MHz for HOF and 316 800, 25 591.25, and 23 587.75 MHz for DOF. The structural parameters calculated with these rotational constants are: r(O–H) = 0.964 ± 0.01 Å, r(O–F) = 1.442 ± 0.001 Å, and > HOF = 97.2° ± 0.6° Centrifugal distortion analysis in the symmetric top approximation gave DJ and DJK values of 0.0934 and 2.417 MHz for HOF and 0.0775 and 1.745 MHz for DOF, respectively. The P6 distortion term was not significant.
Core Polarization of Ag2+ (4d9, 2D) by Electron Paramagnetic Resonance of Frozen Acid Solutions
Authors: McMillan J. A. , Munie G. C.
Published: February 2004

Electron paramagnetic resonance of divalent silver in frozen solutions of HNO3, HF, HClO4, H2SO4, and H3PO4 in various concentrations has been observed in the X band at 77°K. In all cases, an axial symmetry with g ∥ > g ⊥ indicates that the ground state of the silver ion is dx2−y2 with various admixtures of ligand orbitals. An interpretation of 49 spectra considering orbital admixture and electron localization gives for the core polarization extrapolated to unit electron density the value of −9.36±0.32 a.u. which compares very well with the theoretical value of −9 a.u. for divalent ions of the second transition series. Extrapolation to zero electron density supports the existence of an important contribution to the polarization due to the electron density localized in the ligands.
Liquid-Crystal Domains in a Longitudinal Electric Field
Authors: Williams R.
Published: February 2004

Domains have been observed in the nematic liquid crystal, MBBA, using samples of known orientation in a longitudinal electric field. The results are compared with the conduction-induced alignment model for the formation of domains.
Rotational Excitation of Ion—Molecule Reaction Products: Comparison of the Statistical Phase-Space Model with Experiment
Authors: Moran T. F. , Fullerton D. C.
Published: February 2004

The statistical phase-space theory of chemical reactions has been used to compute vibrational and rotational distributions of N 2*+ formed in thermal reactions of rare-gas ions with nitrogen. Recent spectroscopic data have been used to estimate the rotational and vibrational state populations of N 2*+ from these bimolecular interactions. Experimental product state distributions compare favorably with those computed from the statistical phase-space treatment for thermoneutral or slightly exothermic reactions; however, discrepancies are observed between theory and experiment for moderately exothermic reactions.
Measurement of the Viscosity of the Atomic Hydrogen
Authors: Cheng Dah Yu , Blackshear Perry L.
Published: February 2004

The viscosity of a mixture of atomic and molecular hydrogen was measured. The hydrogen gas was dissociated in a rf discharge tube and then pumped promptly through a straight tube with a 1-in. inside diameter. The ratio of pressure drops between dissociated and molecular hydrogen at constant mass flow in the test section gives the ratio of viscosities of dissociated and molecular hydrogen. The recombination rate of atomic hydrogen limits the high operating pressure of this experiment and the slip flow condition limits the low operating pressure. The apparatus is designed to conduct tests within these limits with a sufficiently wide range of atomic hydrogen concentrations. Apparatus design consideration and underlying theory are reported. Viscosities were measured at −72, 0, 56, and 100°C. Both 1% H2O content and extremely dry hydrogen were used. The analysis of the data yields the viscosity of atomic hydrogen and the mutual diffusion coefficient between H atoms and H2 molecules. Some averaged collision cross sections and interaction potentials between H–H2 were fitted.
Crossed-Beam Chemiluminescence Studies of Some Group IIa Metal Oxides
Authors: Jonah C. D. , Zare R. N. , Ottinger Ch.
Published: February 2004

Chemiluminescence from a beam of Group IIa metals traversing a scattering chamber filled with NO2 or N2O gas has been studied as a function of wavelength and pressure. The Ba+NO 2 and the Ba, Sr, and Ca + N 2O chemiluminescent reactions are first order in both reactants while Ca + NO 2 and Sr+NO 2 are quadratic in the NO2 pressure. Cross sections for beam attenuation are about 90–170 Å2 for reactions with NO2 (consistent with an electron-jump model), while those for N2O are 15–30 Å2. For the Ba+NO 2 reaction, the chemiluminescence has been assigned to the BaO A 1Σ−X 1Σ band system. From the resolved rotational structure it is concluded that with higher v′ excitation, the J′ distribution is characterized by a lower rotational temperature. A lower bound of 131.5 kcal/mole is placed on D 0 °(BaO). For certain reactions the chemiluminescence is weakly polarized. A model involving the partitioning of angular momentum between the rotation and recoil angular momenta of the products is proposed to account for the degree of polarization of the chemiluminescence.
Electronic Spectroscopy of Maleimide and Its Isoelectronic Molecules. II. Maleic Anhydride and 4-Cyclopentene-3,5-dione
Authors: Seliskar Carl J. , McGlynn Seán P.
Published: February 2004

The electronic spectroscopy of maleic anhydride and 2,2-dimethyl-4-cyclopentene-3,5-dione have been investigated in the vapor and solution phases. Each of these molecules exhibits two low-intensity absorption bands in the region λ > 2300 Å which are assigned as 1Γππ*←1Γ1 transitions. Each molecule possesses a high-intensity absorption band at λ ≈ 2000 Å which is assigned as a 1Γππ*←1Γ1 transition. Neither molecule exhibits any significant luminescence intensity. Vibrational analyses of the absorption bands are discussed and vacuum ultraviolet spectra are also presented.
Nuclear Transverse Cross Relaxation in Liquids
Authors: Vold R. L. , Chan S. O.
Published: February 2004

Transverse nuclear magnetizations of chemically shifted nuclei are shown to be coupled by real damping factors or cross relaxation terms. It is shown theoretically and experimentally that this coupling leads to cases for which T2 is longer than T1. Consequences of cross relaxation relevant to Fourier transform spin-echo spectroscopy are discussed, and it is shown that spin-echo linewidths cannot in general be assigned to relaxation of specific nuclei.
Base Composition Dependence of DNA Hypochromism
Authors: Brown Ellen , Pysh E. S.
Published: February 2004

The low energy region hypochromicities of poly (dA) poly (dT) and poly (dG) poly (dC) were calculated to compare three coupling formalisms currently used to describe the electronic structure of polymers: first-order perturbation theory (FOPT), configuration interaction of singly excited monomer states (CI), and time dependent Hartree theory (TDH). Several scaled sets of monomer molecular orbitals, at the Hückel (HMO) and Pariser-Parr-Pople (PPP) levels, were used to describe the low energy transitions, and the Coulomb potential was represented with distributed monopoles. The HMO set fails to give the observed base composition dependence of hypochromism (HAT > HGC) for all three formalisms. The PPP sets give the correct order for all formalisms, and the difference between the experimental and calculated hypochromism converges to the same value in AT and GC helices as the power of the coupling theory increases (FOPT < CI < TDH), indicating a base independent contribution from solvent, backbone, and vacuum uv monomer states.
Mean Field Theory and Infinite Dimensionality in Widom—Rowlinson Model
Authors: Lie T. J.
Published: February 2004

It is known for the Ising model that the mean field theory describes exactly the limit of infinite dimensionality in the one-phase region. It is shown in this article that the same statement applies also to the Widom—Rowlinson model of penetrable cubes. This model has nonpairwise-additive, many-body interactions such as one finds in the ionic solution theory. Mayer's cluster expansion scheme is used to show that the equation of state in the limit of infinite dimensionality is identical to the mean field result.
Classical-Limit Green's Function (Fixed-Energy Propagator) and Classical Quantization of Nonseparable Systems
Authors: Miller William H.
Published: February 2004

On the basis of a classical-limit approximation for the Green's function, a classical quantum condition for general, nonseparable dynamical systems is obtained. Bound-state eigenvalues are seen to be associated with stable periodic trajectories, and quasibound (or metastable) states are related to unstable periodic trajectories. Application is made to ns2 states of the two-electron atom, and quite resaonable results are obtained for the energies of the 1s2 and 2s2 states of He and H−. An accurate value is also obtained for the lowest eigenvalue of three identical bosons (e.g., helium atoms) interacting through pair Morse potentials.
Analysis of Orientational Broadening of Raman Line Shapes
Authors: Bartoli F. J. , Litovitz T. A.
Published: February 2004

A systematic investigation of orientational broadening of Raman vibrational lines is undertaken and measurements of line shapes are made for 19 liquids. The problem of separating orientational broadening from the intrinsic vibrational lineshape is discussed in detail and a method of analysis is presented. The advantages and limitations of this method are considered and compared to an earlier method proposed by Rakov [Tr. Fiz. Inst. Akad. Nauk SSSR 27, 111 (1964); Opt. Spectrosc. 7, 128 (1959)]. The intrinsic width is determined for each line studied and removed from the spectrum to give the orientational broadening. It is noted that the intrinsic line shape, measured from polarized Raman spectra, may be used to correct infrared vibrational spectra which suffer from the same problems. It is shown that neglect of intrinsic width can lead to significant errors in the interpretation of the infrared data.
Activation Energies of the Addition of O(3P) Atoms to Olefins
Authors: Atkinson R. , Cvetanović R. J.
Published: February 2004

Modulated generation of the ground electronic state oxygen atoms, O(3P), and phase-shift measurements have been used to determine the rates of O(3P) addition to ethylene, propylene, 1-butene, and isobutene in the temperature interval 25–200°C. Absolute values of the Arrhenius activation energies and pre-exponential factors have been determined and compared with the corresponding previous relative data from this laboratory and with other absolute measurements reported in the literature. Most of the experimental results are now seen to be mutually consistent. The apparently different previous conclusions regarding the activation energies of the O(3P) reactions with olefins based, respectively, on the relative and the absolute rate measurements can be reconciled in a simple manner. The rate constants and the Arrhenius parameters for the reaction of O(3P) atoms with NO have also been determined.
Random-Coil Dimensions and Dipole Moments of Vinyl Chloride Chains
Authors: Mark J. E.
Published: February 2004

A rotational isomeric state model with neighbor interactions is used to calculate mean-square unperturbed dimensions and dipole moments for vinyl chloride chains CH3–(CHCl–CH2–)xH having degrees of polymerization x ranging from 1 to 150 and stereochemical structures ranging from perfect syndiotacticity to perfect isotacticity. Conformational energies used in the calculation were those which had been established in an analysis based on the stereochemical equilibration of 2,4-dichloro-n-pentane by Flory and Williams. The calculations indicate that the dimensions of poly(vinyl chloride) chains of large x should decrease significantly with increasing isotacticity; this dependence of chain dimensions on stereochemical structure is the opposite of that calculated for vinyl chains having alkyl side groups, such as polypropylene. The dipole moments of poly(vinyl chloride) chains are also predicted to decrease with increasing isotacticity and both the dimensions and dipole moments are expected to decrease with increasing temperature, the largest dependence occurring in the case of perfectly syndiotactic chains. The marked differences in configurational characteristics of poly(vinyl chloride) and polypropylene chains are primarily due to the significant difference in size between Cl atoms and CH3 groups; the electrostatic interactions present in poly(vinyl chloride) chains are of relatively minor importance. The predicted results for large x are in good agreement with published experimental results on poly(vinyl chloride).
On a Mass Spectrometric Angular Distribution Study of the Effusion of the Potassium Chloride Vapor System from Cylindrical Orifices
Authors: Grimley Robert T. , Muenow D. W. , LaRue J. L.
Published: February 2004

A mass spectrometric investigation has been made of the angular number distributions of the KCl and K2Cl2 molecules effusing from cylindrical orifices with geometries of L/R = 1−4 at temperatures of 565, 585, and 605°C. It was found that the angular distributions for neither the KCl nor the K2Cl2 molecule agrees with the predictions of the classical Clausing model. The angular distribution of the monomer is more diffuse than predicted by theory, whereas the dimer distribution is more highly focused than the experimental monomer distribution or the theoretical distribution. For a given orifice geometry, progressive defocusing of both beams was observed as the temperature was increased. None of the presently proposed theoretical models is capable of predicting the experimental angular distributions. However, substantial evidence exists to suggest that dissociation of the dimer on the orifice walls is an important factor.
Study of Nonadiabatic Transitions in Triatomic Molecules
Authors: Jug Karl , Weyssenhoff Hanns von
Published: February 2004

Nonadiabatic coupling between electronic states in triatomic molecules has been studied with special consideration given to the possibility of internal conversion. Approximate calculations of electronic and vibrational coupling elements and density of states, which determine the transition probability, have been performed for H2O and some other molecules. The results suggest that the statistical model mechanism for large molecules should not be applied to triatomics. Under favorable conditions, e.g., sufficiently different shape or position of the two potential curves involved, strong coupling might occur which is large enough to explain anomalously long fluorescence lifetimes in small molecules. However, observations of lifetime lengthening of the first excited states of NO2 and SO2 cannot easily be explained because internal conversion through vibrational modes is symmetry forbidden. In this case, the role and relative importance of intersystem crossing and Renner—Teller coupling need further investigation.
Pair Distribution Function for a Gas of Hard Rods
Authors: Hubbard J. B. , Runnels L. K.
Published: February 2004

The pair distribution function is approximated to third order in the density expansion for a gas of long, thin rods. Zwanzig's model is used in which the molecules are rectangular parallelepipeds of length l and square cross section d2. The long molecular axes can point in only three mutually perpendicular directions. The distribution function coefficients are calculated exactly as functions of relative position and orientation in the limit l→ ∞, d→0, l2d→1. The potential of mean force is found to be positive at low density for perpendicular orientations and negative at low density for parallel orientations. It is proved that in the above limit, parallel orientations do not contribute to the pressure.
Semiclassical Transition Probabilities for Atom—Atomic-Oscillator Collisions with Morse Potential Interaction
Authors: LaBrecque R. J. , Morse R. I.
Published: February 2004

Semiclassical (ITFITS) calculations of the transition probabilities for a collinear collision of helium with a tungsten atomic oscillator are compared with quantum mechanical results and found to be in good agreement. The appreciable magnitude of multiple quantum transition probabilities is noted.
Diffusion of Impurity Ions in Ionic Crystals. Treatment of the Diffusion Equations for Concentration Dependent Diffusion Coefficients
Authors: Beniere François , Beniere Michelle , Chemla Marius
Published: February 2004

The equations for the diffusion of divalent ions into alkali halide crystals have been investigated for the case where the thermally produced vacancies and the vacancies added by the impurity are both to be taken into account. The concentration dependence on the diffusion coefficient is then given by D(C)=Dsα C[1+(1+2β/C2)(1+4β/C2)−1/2,where Ds, α, and β are constants at constant temperature. Fick's second law is numerically treated for the initial conditions of the thin deposited layer. The diffusion profiles calculated for trial values of the specific activity of 45Ca are in good agreement with the experimental profiles of diffusion of Ca+ + into NaCl single crystals.
Optical Spectra of Orientationally Disordered Crystals. IV. Effects of Short-Range Correlation of Orientations
Authors: Klug D. D. , Whalley E.
Published: February 2004

The infrared spectrum of an orientationally disordered crystal in which there is a short-range correlation in the dipole moment derivatives with respect to the internal coordinates is discussed theoretically, and equations of general validity are derived. Numerical discussions are given of the spectrum of a linear chain, a square planar array, and a simple cubic array of molecules in which the short-range correlation is describable by a single parameter.
On Solvophobic Interaction
Authors: Wilhelm Emmerich , Battino Rubin
Published: February 2004

An extended version of the scaled particle theory is used to calculate various thermodynamic functions pertaining to the solubility of gases in liquids. In particular, the Gibbs free energy of cavity formation Ḡc is determined for several solvent—gas systems. The usefulness of this quantity as a practical and relatively simple guide for comparing solvophobic interaction in various media is discussed.
Background Polarization in the Dipole Theory of Molecular Exciton States
Authors: Philpott Michael R.
Published: February 2004

The influence of high-lying states on the energy and intensity of lower exciton levels is considered using a theory which is exact in the dipole and single-particle approximations.
On a Shock-Tube Study of CO2–CO Vibrational Energy Transfer
Authors: Seery D. J.
Published: February 2004

The rate of vibrational energy transfer from CO2(001) to CO(v=1) has been measured from 730 to 2325°K using a shock tube. Time-resolved measurements were made of the infrared emission from the CO(v=1) level as it approached equilibrium following shock heating. These measurements were then used as input in a model calculation to obtain the rates for the CO2–CO energy-transfer reaction. The data indicate that energy transfer from CO2 to CO is slightly more efficient than transfer from CO2 to N2 in spite of the 10-fold increase in the energy defect for CO.
Mixed Magnetic and Electric Dipole Transition in s-Triazine
Authors: Hochstrasser Robin M. , Lin T. S. , Zewail Ahmed H.
Published: February 2004

We have shown that the radiation pattern for absorption to the lowest energy excited singlet state of s-triazine corresponds to that of a mixed electric and magnetic dipole transition. This was done by demonstrating, for the first time with an organic, the classic procedure of obtaining absorption coefficients for different k, ε̂, and Ĥ for a uniaxial arrangement of molecules. We find the 30 014 cm−1 transition of s-triazine to be 26% magnetic and 74% electric dipole, hence the state symmetry is 1E in the crystal field, and 1E″ in the free molecule (D3h).
Proton Spin Relaxation and Molecular Motion in Liquid Thiophene
Authors: Kitchlew Anup , Rao B. D. Nageswara
Published: February 2004

Proton spin relaxation and molecular motion in liquid thiophene are studied in the temperature range 300–550°K by measuring spin—lattice relaxation time, T1, and the coefficient of self-diffusion, D, using spin—echo technique. The value of T1 varies from 24.0 sec at 300°K to 72.0 sec at 550°K with a maximum of 94.0 sec at 490°K. The value of D varies from 2.4× 10−5cm2/sec at 300°K to 38.0× 10−5cm2/sec at 550°K. These results have been analyzed in terms of three relaxation mechanisms: inter and intramolecular dipolar interactions and spin—rotation interactions. The analysis shows that (i) the rotational diffusion constant perpendicular to the plane of the molecule varies from 0.21× 1011sec−1 at 300°K to 3.5× 1011sec−1 at 550°K and obeys an Arrhenius equation up to 500°K with an activation energy 3.2 kcal/mole, (ii) the value of the angular velocity correlation time varies from 1.4× 10−14sec at 300°K to 10.8× 10−14sec at 550°K. An estimate of the spin—rotation interaction constant gives 13TrC≲ 1.0 kHz. The reorientational motion is found to be diffusional up to about 480°K.
Senftleben-Beenakker Effects and the Thermomagnetic Torque in Time-Varying Fields
Authors: Roden Wm. S. , Moraal H. , McCourt F. R.
Published: February 2004

Detailed derivations of the expressions describing the Senftleben-Beenakker effects in collinear static and alternating magnetic fields are given. In addition, an expression for the thermomagnetic torque in rarefied polyatomic gases is derived. Numerical calculations have been made for the torque phenomenon in nitric oxide under various conditions and the results compared with experiment. In particular, a value of −49.3 has been found for the effective g factor for NO, to be compared with values of −47.4 obtained from Senftleben data and −48.2 obtained from molecular beam magnetic resonance data.
Upper Bounds on Solutions of the Poisson—Boltzmann Equation near the Limit of Infinite Dilution
Authors: MacGillivray A. D.
Published: February 2004

Upper bounds on solutions of the nonlinear Poisson—Boltzmann equation are obtained. The relationship of these bounds with certain assumptions in Manning's limiting law theory for polyelectrolytes is discussed. In particular, it is shown that Manning's condensation assumption may be dropped without changing the important consequences of his theory.
Molecular Rotational Zeeman Effect in Thioformaldehyde
Authors: Rock S. L. , Flygare W. H.
Published: February 2004

The high-field rotational Zeeman effect has been observed in thioformaldehyde. The magnetic susceptibility anisotropies are 2 χaa − χbb − χcc = 52.3 ± 1.1 (× 10−6 erg/G2 · mole) and 2 χbb − χaa − χcc = −5.1 ± 0.7. The molecular g values with uniquely determined signs are gaa = −5.2602 ± 0.0068, gbb = −0.1337 ± 0.0004, and gcc = −0.0239 ± 0.0004. c is the out-of-plane axis and the a axis is the dipole axis. gaa represents the largest molecular g value yet measured. Use of these five Zeeman parameters and the known structure gives the molecular quadrupole moments: Qaa = 3.0± 0.7 (× 10−26 esu · cm2), Qbb = −2.4 ± 0.5, Qcc = −0.6 ± 1.1; the diagonal elements of the paramagnetic susceptibility tensor: χaap = 45.8 ± 0.3 (× 10−6 erg/G2 · mole), χbbp = 88.3 ± 0.6, χccp = 82.6 ± 0.6; and the anisotropies in the second moments of the electronic charge distribution. By estimating the out-of-plane second moment of the electronic charge distribution as 〈 c2 〉 = 4.6 ± 0.4 (× 10−16 cm2) using free atom values, we have evaluated the remaining individual second moments of the electronic charge distribution to be 〈 a2 〉 = 21.1 ± 0.6 (× 10−16 cm2) and 〈 b2 〉 = 6.6 ± 0.5. The diagonal elements of the diamagnetic and total magnetic susceptibility tensor also follow from the above estimation of 〈 c2 〉 and are χaad = −47.5 ± 2.5 (× 10−6 erg/G2 · mole), χbbd = −109.1 ± 3.0, χccd = −117.6 ± 3.4, χaa = −1.7 ± 2.5, χbb = −20.8 ± 3.1, and χcc = −35.0 ± 3.5, giving the bulk magnetic susceptibility as χ = 13 (χaa + χbb + χcc) = −19.2 ± 1.8 (× 10−6 erg/G2 · mole. These values are then compared to those of the oxygen analog, formaldehyde, and trends in this pair are compared to several other previously studied oxygen-sulfur analogs.
INDO and MINDO/2 Crystal Orbital Study of Polyacetylene, Polyethylene, and Polyglycine
Authors: Beveridge David L. , Jano Issam , Ladik Janos
Published: February 2004

Approximate valence electron self-consistent field crystal orbital calculations using INDO and MINDO/2 parameters are described for polyacetylene, polyethylene, and polyglycine in a planar and α-helical conformation. The electronic energy band structure and electronic charge distribution are discussed and compared with previous theoretical calculations and available experimental results.
Electrohydrodynamic Instabilities in Some Nematic Azoxy Compounds with Dielectric Anisotropies of Different Sign
Authors: DE Jeu W. H. , Gerritsma C. J.
Published: February 2004

Electrohydrodynamic instabilities are observed in planar slabs of nematic azoxy compounds with values for Δ ε = ε∥ − ε⊥ between −0.2 and +0.2. Above a threshold voltage for negative Δε the well-known cellular domain pattern is found. For positive Δε a reorientation only is observed in the nematic phase. However, for dc fields at the same voltage, cellular flow is present in the isotropic phase. Moreover, in this case domains can be introduced by a magnetic field H ⊥ E. These different effects cannot be explained by considering stability criteria only. A discussion is given in which the orientating torques of the field on the nematic determine whether an instability leads to domains or not.
Laser Excited Emission Spectroscopy of Azulene in the Gas Phase
Authors: Huppert Dan , Jortner Joshua , Rentzepis Peter M.
Published: February 2004

In this paper we present the results of an experimental study of the radiative decay of the two lowest singlet states S1 and S2 of the azulene molecule in the gas phase excited by a Q switched ruby laser (14 400 cm−1) and by its second harmonic (28 800 cm−1). Spectroscopic information has been obtained concerning the energy resolved spectra of the S1 → S0 and of the S2 → S1 emission. The quantum yield data for the S1 → S0 decay led to an estimate of the nonradiative decay time of S1. The branching ratio between the S2 → S0 and the S2 → S1 emissions was utilized for the evaluation of the S2 → S1 radiative decay time. The study of the consecutive two photon S0 → S1 → S2 excitation leads to an estimate of the S1 → S2 absorption cross section near the electronic origins of the two excited states. The decay characteristics of the lowest excited singlet state of the ``isolated'' azulene molecule confirm the theoretical prediction concerning nonradiative electronic relaxation in the statistical limit.
Solutions of Master Equations and Related Random Walks on Quenched Linear Chains
Authors: Lakatos-Lindenberg Katja , Hemenger Richard P. , Pearlstein Robert M.
Published: February 2004

Four separate but related contributions to the theory of quenched stochastic processes in one dimension are presented. First, Green's functions are derived for Laplace transformed master equations (here described in the language of, but not restricted to, hopping excitons) on finite chains with either periodic or free-end boundary conditions, and with either a disruptive (substitutional impurity) or a nondisruptive quencher. We solve these problems in spectral form for short-range quenching with arbitrary quencher location and quenching rate parameter Qo. Second, the analogous random walk situations are treated. The solution of the generating function (finite-difference analog of the Laplace transform) equation is identical to that of the Laplace-transformed master equation with a disruptive quencher, but not with a nondisruptive quencher. Unlike the master equation case, slowly damped oscillations of the random walk chain excitation function can exist. Other differences also exist and are discussed; these occur at short times, with large concentration of quenchers, or in the presence of uniform decay processes like fluorescence. Third, the spectral solutions of the master equations are applied to provide a closed analytical expression for the lowest moment of the chain excitation function on a particular chain in the presence of fluorescence, and to demonstrate the existence of an inflection point in the excitation function of an open chain excited and quenched at opposite ends. Fourth, we apply the coherent potential approximation to the master equation that describes a uniformly excited, randomly and nondisruptively quenched infinite chain. A closed analytic expression is obtained for the lowest moment of the excitation function in the absence of fluorescence, and is compared with previously obtained expressions for infinite chains with periodic nondisruptive quenchers or random disruptive quenchers. Finally, we discuss briefly the possibility of applying our results to the problem of metal-ion quenching of the phosphorescence of polyriboadenylic acid.
Experimental Determination of the Repulsive Potentials between K+ Ions and Rare-Gas Atoms
Authors: Inouye H. , Kita S.
Published: February 2004

Integral elastic scattering cross sections have been measured by the attenuation method for potassium ions with an energy selected in the range of 500–4000 eV scattered by room-temperature He, Ne, Ar, and Kr atoms through effective laboratory angles greater than 5×10−3 rad. The repulsive potentials have been derived from the measured values of the cross sections with allowance for the density distribution across the beam in the collision chamber. The potentials are well represented by the following expressions: He:    V(r) = 1110 exp(−4.15r)    for    1.23 < r < 1.77,Ne:    V(r) = 4910 exp(−4.40r)    for    1.55 < r < 2.04,Ar:    V(r) = 2920 exp(−3.46r)    for    1.79 < r < 2.43, and Kr:    V(r) = 6420 exp(−3.69r)    for    1.92 < r < 1.53, where V(r) is in electron volts and r in angstroms.
On Singlet-Triplet Transitions Induced by Exchange with Paramagnetic Molecules and the Intermolecular Coupling of Spin Angular Momenta
Authors: Chiu Ying-Nan
Published: February 2004

The theoretical basis of the singlet-triplet transition mechanism by exchange coupling with neighboring paramagnetic molecules is examined. Attention is drawn to the two implicit assumptions of this exchange coupling model: (1) the validity of ``perfect'' permutational exchange of electrons between the neighboring molecules, and (2) the validity of the conservation of total spin angular momentum of the two neighboring molecules. With respect to the first assumption, it is found that the finiteness (vs perfection) of exchange overlap has not been sufficiently allowed for in the conventional (electrostatic) exchange mixing of allowed singlet and charge-transfer states and in the conventional transitions only among the composite states of the same total spin angular momentum (e.g., triplet← triplet). It is derived that there exists a direct transition moment (between the two molecules) weighted by overlap integrals, which may not be much smaller than the allowed transition moment weighted by (the indirect) exchange mixing coefficients, and which may exhibit interference effect with the latter. It is pointed out that if exchange energy is finite and spin interactions are sizable, transitions to other states of different spin multiplicities (e.g., singlet← triplet and quintet← triplet), which are not split sufficiently far apart, may contribute to intensity through spin interactions. With respect to the second assumption, it is shown that the small but finite spin interactions, especially interelectronic spin interactions, which do not commute with the assertedly conserved total angular momentum S2, have not been accounted for. A comprehensive formalism is developed to treat simultaneously exchange interaction along with spin interactions and to provide for various ranges of their relative magnitudes. These spin interactions are also shown to exhibit interference effects with the exchange interaction in the total intensity expression. All transitions, including Δ S ≠ 0 and Δ MS ≠ 0,, are considered. Matrix elements of the direct transition, of the exchange mixing of allowed singlet and charge-transfer states, and of the spin-orbit, spin-other-orbit, and spin-spin interactions are computed for general molecular orbitals and for the case of three and four electrons. The commutation and noncommutation of spin operators with S2 are traced to permutation symmetry and are treated by isomorphism to C3v (for three electrons) and Td (for four electrons) point groups. Irreducible representations of the linear as well as quadratic forms of spin and orbital operators and their interaction tensors are derived. Their relationship to spin eigenfunctions of given permutational symmetries is discussed.
Summation of Pairwise Potentials in Gas-Surface Interaction Calculations
Authors: Cabrera Nicolás , Goodman Frank O.
Published: February 2004

A model is presented from which the over-all gas-surface interaction may be calculated, in simple closed form, from direct summation of microscopic, pairwise, gas atom-solid atom interactions. A formula is derived for the Fourier components of the gas-surface interaction potential which results from summation of the general pairwise potential over all lattice sites; for the special case of the Yukawa pairwise potential, the results are exponential functions of the distance of a gas atom from the solid surface. In this way, empirical over-all gas-surface interaction laws of the exponential type are related to more basic, but still empirical, pairwise interactions. The system He-LiF is considered as an illustration of the work.
On the Correlation between EPR and Positron Annihilation Measurements on γ-Irradiated Acetyl Methionine
Authors: Eldrup M. , Lund-Thomsen E. , Mogensen O.
Published: February 2004

The dose dependence of the relative EPR signal intensity and positron lifetime spectrum was measured for γ-irradiated acetyl methionine in the dose range from 0 to 30 Mrad. Angular correlation measurements were performed for the doses 0 and 30 Mrad. The result of the irradiation was the creation of EPR centers and inhibition of positronium formation. For one sample, irradiated with a dose of 30 Mrad, EPR and positron lifetime spectra were followed over a period of 50 days after the irradiation. The inhibiting effect and the EPR signal intensity decreased with time. No simple correlation could be established between the number of EPR centers and the positron annihilation data, but other possible explanations are discussed.
Exchange Interactions between Pairs of Differing Magnetic Spins in Heteropoly Complexes
Authors: Baker L. C. W. , Baker V. E. S. , Wasfi S. H. , Candela G. A. , Kahn A. H.
Published: February 2004

Coupled pairs of differing magnetic spins in tungsto-heteropoly complexes have been investigated by studying the magnetic susceptibility over the temperature range 2–300°K. The two sites of the magnetic ions are surrounded by oxygen ions in octahedral and tetrahedral coordinations with one oxygen ion in common. The ions studied were Co2+, Co3+, and Fe3+ in a total of six combinations on the two sites, offering a unique set of symmetries and ions for examining super-exchange effects. A closed form for the susceptibility has been obtained on assuming the spin Hamiltonian H=β (g1S1+g2S2)· H-JS1· S2, allowing for the possibility of g1≠ g2, S1≠ S2. Fitted values of J/k range from −6 to −70°K depending on the combinations of ions. The experimental agreement with the spin Hamiltonian for all cases studied is satisfactory for this system.
Calculation of Hyperfine Coupling Constants in Inorganic Radicals
Authors: McCain Douglas C. , Palke William E.
Published: February 2004

Hyperfine coupling constants have been calculated for the well-known radicals HCO, NO2, NF2, ClO2, and CF3 as well as a large number of related species. An SCF Hartree-Fock-type approach was used with a minimum basis set of Slater-type orbitals to obtain MO coefficients of the singly occupied orbital. Some of the coupling constants were obtained directly from the ab initio calculations; others were estimated by use of semiempirical relations. Comparison with experimental data shows fair agreement. In addition, the structures of NF2, O3+,O3−, O3, and CF3 were computed.
Hydrogen Bonds in H3Co(CN)6 and D3Co(CN)6. Model Calculations
Authors: Güdel H. U.
Published: February 2004

The ion [H1C1N1HN2C2H2]+ was chosen as a model for the shortest known N–H–N hydrogen bonds in H3Co(CN)6. Ab initio calculations with two basis sets of different size were used to evaluate the total energy of the electronic ground state of the model system for different H–N2 distances. Assuming linear hydrogen bonds, one-dimensional potential energy wells for the hydrogen atom were obtained. Inclusion of 2p-type polarization basis functions for the hydrogen bridge atom H was found to be essential. The validity of the chosen model was tested by comparing the results with experimental properties of H3Co(CN)6 and D3Co(CN)6. The vibrational behavior of hydrogen and deuterium atoms, respectively, in the model potential was investigated. Transitions ν=0→ ν=1 were compared with observed absorption bands in the infrared spectra and mean-square amplitudes of vibration with the corresponding quantities derived from Debye-Waller factors of neutron diffraction experiments. Since in both cases the agreement was good, the model was supposed to be useful for the description of the hydrogen bonds in H3Co(CN)6 and D3Co(CN)6. The potential energy well was found to be of the double-minimum type. The barrier, however, is so low that the vibrational ground state lies below the top of the barrier in D3Co(CN)6 and at about the same height as the top in H3Co(CN)6. Excited vibrational levels all lie above the barrier in both compounds. It may, therefore, be called a borderline case between a single-minimum and a double-minimum type potential.
Dielectric Relaxation Mechanism in Some Alkanethiols. II
Authors: Krishnaji  , Agarwal Vinod K. , Kumar Pradip
Published: February 2004

Dielectric constant and dielectric loss (ε′ and ε″) of four liquid alkanethiols have been measured at four microwave frequencies at 0, 20, 40, and 60°C. The normalized plots of ε′/(ε0−ε∞) vs (ε′−ε∞)/(ε0−ε∞) for all four liquids are skewed arcs. The characteristic relaxation time (τ0) and empirical parameter (β) have been calculated from these plots. The dielectric behavior of alkanethiols is more like alkyl halides than alcohols. The main mechanism which is responsible for asymmetric distribution of relaxation time in the liquid state appears to be multiple relaxation processes.
Liquid-Vapor Argon Isotope Fractionation from the Triple Point to the Critical Point. Mean Laplacian of the Intermolecular Potential in Liquid Argon
Authors: Phillips James T. , Linderstrom-Lang Carl U. , Bigeleisen Jacob
Published: February 2004

The statistical thermodynamic treatment of the equilibrium between a nonideal liquid mixture of isotopes and a vapor phase is extended to include isotope effects on the equation of state of the gas. The result is particularly simple when the isotopic partition functions in a given phase are compared at the same molar volume. The isotope fractionation factor α for 36Ar/40Ar between liquid and vapor has been measured from the triple point to the critical temperature. The results are compared with previous vapor pressure data, which cover the range 84–102°K. Although the agreement is within twice the statistical scatter of the present data, the present results for the lnα are systematically 5% lower than calculations from vapor pressure data. It is shown that T2 lnα is a linear function of (ρc−ρg), the density difference between the liquid and vapor, in the range 84–120°K. The fractionation factor approaches zero at the critical temperature with a nonclassical critical index equal to 0.42±0.02.〈∇2 Uc〉/ρc in liquid argon is derived from the experimental fractionation data and calculations of 〈 ∇2Ug〉/ρg for a number of potential functions for gaseous argon.