bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Temperature on the Formation of Radicals by Hydrogen-Atom Bombardment
Authors: Henriksen Thormod
Published: February 2004

Thymine and dihydrothymine have been exposed at different temperatures to hydrogen atoms and the number of radicals induced has been measured by ESR spectroscopy. The results demonstrate that the sample temperature during exposure strongly influences the radical formation. In the present experiments the 5-thymyl radical is formed in both substances. In thymine a hydrogen atom is added to the ring whereas in dihydrothymine the radical is formed by a corresponding abstraction reaction. Both reactions seem to require temperatures above approximately 130°K. The yield of radicals was found to increase exponentially with the sample temperature during exposure. The apparent activation energy for the addition reaction was found to be approximately 1.2 kcal/mole whereas the abstraction reaction exhibited an activation energy of 2.5 kcal/mole.
Estimation of the Number of Self-Avoiding Lattice Polygons
Authors: Whittington S. G. , Valleau J. P.
Published: February 2004

This paper is concerned with the use of a capture–recapture technique for estimating population size. As an example of its application, some estimates have been made of the number of polygons weakly embeddable in the square lattice. The results support the conclusion that the probability of initial ring closure varies inversely as nθ, where n is the ring size and θ = 11 / 16.
Evaluation of Multicenter Integrals by Polished Brute-Force Techniques. II. Accuracy, Timing, Integral Values, and General Computational Considerations
Authors: Wahl Arnold C. , Land Robert H.
Published: February 2004

The analysis presented recently by the authors for the general evaluation of the multicenter electron-repulsion integrals 〈χa(1)χb*(1)(1 / r12)χc(2)χd*(2)〉 and the nuclear attraction integrals 〈χa(1)(1 / rc)χb*(1)〉 is briefly reviewed followed by a characterization of the method's accuracy, speed, and generality. Our method, which integrates a one-electron potential Vab with a one-electron charge distribution Ωcd, is operative on an IBM 360/75 computer for Slater-type orbitals with quantum numbers n ≤ 8,l ≤ n − 1,|m| ≤ l, arbitrary geometry, and scale factors. A precision of 10−6 hartree is routinely achieved at an average time per integral of between 100 and 200 msec depending upon the total number of integrals evaluated.
Hyperfine Coupling Constants and Covalency in Sandwich Complexes
Authors: Prins R.
Published: February 2004

An analysis of the isotropic proton hyperfine coupling constants of V(C5H5)2, Ni(C5H5)2, and Cr(C6H6)2+ is given. The unpaired electrons in the e1g* molecular orbitals in Ni(C5H5)2 are found to be rather strongly delocalized into the carbon 2pz–π framework of the ligands. In agreement with bonding theories this indicates that the interaction between the metal 3dxz and 3dyz orbitals and the ligand e1g–π molecular orbitals is very important for the chemical bonding in sandwich complexes. In Cr(C6H6)2+ and V(C5H5)2 the proton coupling constants are determined mainly by σ delocalization of the unpaired electron in the a1g(3dz2) orbital into the hydrogen 1s orbitals. In V(C5H5)2, also, delocalization into the ligand π framework is present and this is thought to be due to the e2g orbitals. It is concluded that the interaction of the metal 3dxy and 3dx2−y2 orbitals with the ligand e2g–π molecular orbitals is appreciable.
Microwave Absorption and Molecular Structure in Liquids. LXXIV. Dielectric Relaxation Mechanisms of Alkyl Ethers and Didodecyl Sulfide
Authors: Dasgupta S. , Abd-El-Nour K. N. , Smyth C. P.
Published: February 2004

The dielectric constants and losses of heptane solutions of ethyl, dihexyl, didodecyl, and dodecylmethyl ether and didodecyl sulfide have been measured at wavelengths of 0.2, 1.2, 3.2, 10.0, and 25.0 cm and 30 000 m at temperatures between 6° and 50° and used to calculate the dielectric relaxation times of the liquids. With one exception, the results for each liquid can be analyzed into a long relaxation time associated with rotational orientation of the molecule as a whole and a short relaxation time for dipole orientation by intramolecular motion. In the case of the small ethyl ether molecule, the difference between the size of the small molecule and those of its intramolecular polar groups is insufficient to permit any observable separation of relaxation processes. The considerable sizes of the atomic polarization values suggest contributions to infrared absorption by twisting around the C–C bonds.
Variational Treatment of Hydrodynamic Interaction in Polymers
Authors: Rotne Jens , Prager Stephen
Published: February 2004

It has recently been pointed out by several authors that the Kirkwood–Riseman diffusion tensor normally used to treat hydrodynamic interactions in polymer molecules is not necessarily positive definite, an unphysical behavior which results from the neglect of short-range contributions to the interaction between chain segments. The problem can be reformulated as a minimization of the rate at which energy is dissipated by the motion of the suspending fluid, and in this way we have obtained an approximate diffusion tensor which (1) is positive definite for all configurations of the polymer molecule, (2) approaches the Kirkwood–Riseman diffusion tensor at large separations between the interacting segments, and (3) can be written as the true diffusion tensor plus a positive definite correction. The last feature can be used to obtain variational bounds on relaxation times and sedimentation rates.
4f–5d
Excitation Energy of Tb3+ in Solids
Authors: Hoshina Teruhiko
Published: February 2004

Excitation spectra of the D45 → 7F emission of Tb3+ were measured in Sc(or In) BO3, and Y (or Gd) BO3, Y3Ga5O12, Sc (or Y) PO4, and Sc2 (or Y2) O3 at room temperature. The 4f–5d excitation band is discriminated from the host lattice excitation band by inspecting the concentration dependences of the excitation spectra. The energy and the shape of the 4f–5d excitation band are almost the same in the lattices with the same structure. The band splittings are related to the symmetry of the crystalline field acting on Tb3+. The 4f–5d excitation band is extremely enhanced by lowering temperature to 77°K.
Absolute Far-Infrared Absorption Intensities of α-Nitrogen
Authors: Louis Robert V. St. , Schnepp O.
Published: February 2004

The absolute intensities of the translational lattice mode absorptions of α-N2 in the far infrared have been measured. The experimental values are smaller by a factor of 5 than the calculated intensities obtained from a quadrupole-induced mechanism theory. This discrepancy is discussed in terms of the model on which the theory was based. The intensity of the 50-cm−1 line was found to be temperature dependent and decreased gradually between 15°K and 35°K. No discrete absorption was observed for the β phase above 36°K. The 50-cm−1 line has a width smaller than 0.5 cm−1 and the 70-cm−1 line has a width of 6 cm−1. Evidence was found for a decrease of the frequency of the 50-cm−1 line as the phase transition temperature is approached.
Experimental Studies of Internal Field Effects on the Dielectric Properties of Anisole–Benzene and Other Mixtures
Authors: Kranbuehl David E. , Klug Dennis D. , Vaughan Worth E.
Published: February 2004

An equation derived by Cole, which relates the frequency-dependent complex dielectric permittivity to the molecular dipolar autocorrelation function, is compared to dielectric measurements reported in the literature. The dielectric behavior of binary polar mixtures agrees with that predicted by Cole's equation provided specific short-range interactions are absent. Measurements of the complex dielectric permittivity of anisole–benzene mixtures as a function of composition, wavelength, and temperature are reported. The anomalous dielectric behavior exhibited by this system is not due to internal field effects. Possible causes of the anomalies are discussed.
Photolysis of C3O2 in the Presence of CH3F at 1470 Å
Authors: Tschuikow-Roux E. , Kodama S.
Published: February 2004

Carbon suboxide (C3O2) has been photolyzed at the 1470-Å Xe resonance line at 25°C in the presence of CH3F, with and without added inert gases. The principal reaction products include acetylene, vinyl fluoride, CO, and CO2. The results are interpreted in terms of the participation of an electronically excited C2O (singlet) radical produced in the primary photochemical process. The energy of excitation of C2O is considerably higher than the reported Δ1, Σ1, and π3 excited states of C2O. A tentative estimate places the value at ∼ 3.1 eV above the ground-state C2O (3Σ).
Zero-Field Splittings in tris(Oxalatochromium) (III) Complexes
Authors: Kawasaki Yoshikane , Forster Leslie S.
Published: February 2004

The spin Hamiltonians of Cr(ox)33− in the crystalline hosts K3Al(ox)3·3H2O, (NH4)3Al(ox)3·2H2O, and Na3Al(ox)3·5H2O have been evaluated from ESR spectroscopy and compared with the Cr3+:NaMgAl(ox)3·9H2O results. The D parameter (0.72 ± 0.06 cm−1) is relatively insensitive to environment but E varies from zero to 0.1 cm−1. A comparison of the ESR and optical spectra indicates the need to include rhombic components in ligand field treatments of 2E and 4T2 splittings. The so-called monoclinic and heated Cr3+:NaMgAl(ox)3·9H2O forms behave identically in ESR and optical measurements.
Dielectric Studies. XXII. Interaction of Chloroform with Electron-Donor Molecules
Authors: Magee M. D. , Walker S.
Published: February 2004

The dielectric absorption of chloroform, acetone, diethylether, and triethylamine, each in cyclohexane, and mixtures of chloroform, respectively, with acetone, diethylether, and triethylamine in cyclohexane has been determined at up to five microwave frequencies at 25°C. The dielectric data have been analyzed to yield relaxation times and, where appropriate, dipole moments. The binary solutions are characterized by single relaxation times but the ternary mixtures show pronounced distribution parameters and, in general, a mean relaxation time significantly longer than those of the individual constituents. This is interpreted in terms of a contribution from a longer relaxation time due to a complex. A procedure for obtaining the equilibrium constant for hydrogen-bond formation of a 1:1 complex is given and yields values of the same order as those by other methods. A more detailed investigation and/or improved accuracy could yield more accurate equilibrium constants and also the dipole moments of the complexes.
Reaction of the Excited Oxygen Atoms (O1D2) with Isobutane
Authors: Paraskevopoulos G. , Cvetanović R. J.
Published: February 2004

Reaction of O1D2 atoms, formed by photolysis of N2O at 2139 Å, with isobutane has been studied in the gas phase at room temperature and at total pressures between 80 and 1250 torr. The major features of the reaction are similar to those observed previously in this Laboratory with propane. The excited atoms insert indiscriminately into the primary and tertiary CH bonds of isobutane. The “hot” butanols formed by insertion are stabilized at pressures much lower than those required for stabilization of “hot” propanols. The lifetimes of the “hot” butanols have been determined. The reaction mechanism is discussed.
Nuclear Spin Relaxation in Acetylene Gas
Authors: Ahn Myong-Ku , Johnson Charles S.
Published: February 2004

Proton spin–lattice relaxation times (T1) have been measured in acetylene gas between −50 °C and 19°C using a CAT for signal averaging. T1 was found to depend linearly on the number density ρ in the range of these measurements (0.1 to 0.9 amagat). The temperature dependence of the ratio T1/ρ indicates that the spin–rotational interaction provides the dominant relaxation mechanism. Cross sections for the transfer of angular momentum are presented.
Relaxation Theory for Modulation Excitation of Vibronic States
Authors: Schlag Edward W. , Yao S. J. , von Weyssenhoff Hanns
Published: February 2004

One method for the absolute measurement of rate constants for defined quantum states is to study their response to sharply defined pumping. Such an experiment is the observation of the relaxation process after excitation of selected vibronic levels with amplitude modulated light. The observation could either involve secondary absorption or radiative emission. A general stochastic theory is formulated here for these time-defined processes, in this case, undergoing vibronic relaxation and fluorescence emission. From the general transport matrix describing the relaxation problem via the master equation, the observables are an unambiguous consequence. The solution is given in a form suitable for direct computation. For this particular case, the theory predicts a phase angle in terms of a many-shot expansion, which is not restricted to exponential fluorescence decay.
Effects of Molecular Buffer Gases on the Cesium Hyperfine Frequency
Authors: Bernheim R. A. , Kohuth L. M.
Published: February 2004

The fractional pressure shifts of the cesium hyperfine interaction were measured to be (in units of 10−9/mm Hg): −116, for CH4, −95.7 for CHD3, −188 for C2H6, −282 for C3H8, −370 for C4H10, −305 for C2H4, and −671 for C3H6. The pressure shifts of the saturated hydrocarbons are understood as arising from the long-range dispersion part of the potential between a cesium atom and the buffer molecule. The shifts due to the unsaturated hydrocarbons indicate a contribution arising from transient charge transfer of the cesium valence electron into unoccupied molecular states. The effect of the molecular electric dipole moment upon the shift could not be ascertained.
Frequency Distribution and Neutron Scattering of Polyethylene Glycol Chain
Authors: Matsuura Hiroatsu , Miyazawa Tatsuo
Published: February 2004

Optical and acoustic branches of chain vibrations of polyethylene glycol were treated by the use of the intrachain force field previously refined. From dispersion curves (frequency versus phase difference), the frequency distribution weighted by squared amplitudes of hydrogen nuclei was calculated, and inelastic thermal-neutron scattering peaks in the region 600–200 cm−1 were assigned. Appreciable anisotropy in scattering is anticipated from the weighted frequency distribution.
Energy Transfer in Near-Resonant Molecular Collisions due to Long-Range Forces with Application to Transfer of Vibrational Energy from ν3 Mode of CO2 to N2
Authors: Sharma R. D. , Brau C. A.
Published: February 2004

The cross section for the near-resonant transfer of vibrational energy from CO2(001) to N2(0), CO2(001) + N2(0)→CO2(000) + N2(1) + ΔE, is calculated for the isotopes N214 (ΔE = 18 cm−1) and N215 (ΔE = 97 cm−1). The impact parameter (semi-classical) approximation is used, and it is assumed that the vibrational-energy transfer is caused by the interaction of the instantaneous CO2 dipole moment with the N2 quadrupole moment. When proper account is taken of the rotational motions of the molecules it is found that in collisions of CO2 with 14N2 only the low rotational levels of the CO2 and N2 molecules contribute to Reaction (1). In collisions of CO2 with 15N2, only those rotational levels contribute which undergo transitions cancelling most of the relatively large (97 cm−1) vibrational-resonance defect. For 14N2 below about 1000°K, where the cross section displays a negative temperature dependence, the results are in excellent qualitative and quantitative agreement with available experimental data, with no adjustable parameters in the theory. Above about 1000°K the experimental cross-section data display a positive temperature dependence indicating that some other mechanism becomes important there. For 15N2 the calculations are in good agreement with an experimental measurement at 300°K. Data at other temperatures are not presently available. The theoretical results indicate that the cross section for the vibrational-energy transfer should have maximum around 200°K. Below this temperature the higher rotational levels which dominate the energy-transfer process are unfavorably weighted in the Boltzmann distribution.
Ion–Molecule Reactions in Aromatic Systems. I. Secondary Ions and Reaction Rates in Benzene
Authors: Lifshitz Chava , Reuben Bryan G.
Published: February 2004

The reactions between benzene and the ions obtained by electron bombardment of benzene have been investigated in a pulsed ion source mass spectrometer. The major secondary ions were found to be C12H11, C12H10+, C12H9+, C12H8+, C11H7+, C10H9+, C10H8+, C10H7+, C9H7+, and C8H7+. Ionization-efficiency curves were measured for parent and product ions, employing the retarding potential difference (RPD) method. The parent ions leading to most of the product ions were identified. The secondary ions appear similar to ions formed by electron bombardment of biphenyl and related compounds. The ion–molecule reaction rate constants were evaluated for benzene and hexadeuterobenzene. The rate constants varied between 2% and 30% of the values predicted by the Stevenson–Gioumousis theory of ion–molecule reactions. Inverse isotope effects were observed for “condensation” reactions, while normal effects were obtained for most of the other reactions. Variation of the translational energy of the reactant ions in a conventional mass spectrometer caused the expected decrease in cross section with increasing energy. The ions formed by “condensation” processes were affected the most. The results are discussed in the light of the various existing theories of ion–molecule reactions. In ion–molecule reactions of this complexity, the low rate constants may be due to the interference of back reactions. The isotope effects agree qualitatively with prediction.
Paramagnetic Resonance of Room-Temperature-Stable V-Type Centers in γ-Irradidated Alkali Halide–Boron Oxide Glasses
Authors: Griscom D. L. , Taylor P. C. , Bray P. J.
Published: February 2004

Numerous glasses were prepared from mixtures of alkali halides and boron oxide and subjected to 60Co γ rays at room temperature; these were examined by ESR techniques at 9.1 and 35 GHz. The induced spectra can be divided into two categories: (1) a resonance due to boron–oxygen centers previously studied in alkali borate glasses, and (2) certain new resonances which are shown to be due to V-type centers (halogen2− molecule ions). The Cl2− species is stable at room temperature; its spin-Hamiltonian parameters determined by means of a computer simulation of the spectrum are: g‖ = 2.0042, g⊥ ≃ 2.035, A‖ = 100 G35–35, A⊥≃8 G35-35. Inclusion of small amounts of KCl or LiCl in borate glasses can result in nearly total suppression of the usual boron–oxygen-center resonance, i.e., the dissolved chloride ions prove to be the more efficient hole traps. The Br2− centers can also be formed, but less efficiently. The F2− centers are not produced in borate glasses which is consistent with other data which suggest that fluorine forms covalent bonds with boron in these materials.
Crystal Field in Rare-Earth Trichlorides. IV. Parameter Variations
Authors: Curtis M. M. , Newman D. J. , Stedman G. E.
Published: February 2004

Parameter variations are determined for changes in the ligand coordination angles and distances in Pr3+:LaCl3. Parameters for Sm3+ and Er3+ substituted in LaCl3 are also calculated. These results are used in conjunction with the superposition approximation to discuss the variation of parameters down the rare-earth series in the trichlorides and to predict values of the dynamic orbit–lattice parameters in PrCl3.
Microwave Spectrum and Ring-Puckering Vibration in 1,1-Difluorocyclobutane
Authors: Luntz Alan C.
Published: February 2004

The microwave spectrum of 1,1-difluorocyclobutane has been studied in the ground vibrational state and in six excited satellites of the ring-puckering vibration. Large perturbations to the rotational spectra were observed for the lowest two pairs of vibrational levels. Double-resonance experiments were used to help assign these nonrigid-rotor spectra. These perturbations resulted from the coupling of vibrational and rotational angular momentum and gave the separations between the pairs of levels as Δ01 = 0.0620975 cm−1 and Δ23 = 3.87 cm−1. From these splittings and the variation of effective rotational constants with vibrational state, the ring-puckering potential was determined as V(Q) = 6.184Q4 − 77.30Q2cm−1, where Q is a reduced hermonic-oscillator coordinate. This corresponds to a barrier of 241 ± 5 cm−1 to the planar configuration. Calculations of the ring-puckering potential energy and of the vibration-rotation kinetic energy were made from a computer program for a dynamical model of the vibration. The excellent agreement between the calculated and experimental results provides good confirmation for the description of the vibration given by the model.
Improved Bond-Stretching-Energy Curves from the Integral Hellmann–Feynman Method
Authors: Mazziotti Alexander , Lowe John P.
Published: February 2004

The connection between the local-energy concept and the integral Hellmann–Feynman (IHF) method is used to obtain an improved bond-stretching-energy curve from short one-center expansions of HeH+. An alternative method of analyzing the IHF method, based on spectral impurities, is developed. It is shown how this formalism also enables one to rationalize and predict IHF results. IHF calculations on single-center expansions for H2 are reported. It is concluded that, for single-center expansions (especially when centered at a nucleus), the IHF method is a very promising way to get improved bond-stretching energies.
Molecular Collisions. IX. Restricted Distorted-Wave Approximation for Rotational Excitation and Scattering of Diatomic Molecules
Authors: Curtiss C. F. , Bernstein R. B.
Published: February 2004

The general expression for rotational excitation and scattering cross sections for rigid diatomic molecules derived in Paper VIII is reduced to yield a restricted distorted-wave approximation, resulting in a relatively simple equation for the inelastic transition probabilities. The new expressions possess significant advantage over analogous ones of Davison and of Arthurs and Dalgarno due to the elimination of certain multiple summations. The results are, however, demonstrated to be identical by direct resummation methods. For a potential which is separable into a product of a radial and an angular function, the dependence of the transition probability upon the anisotropy parameters is given explicitly.
Behavior of the In-Plane g Tensor in Low-Symmetry d1 and d9 Systems with Application to Copper and Vanadyl Chelates
Authors: Hitchman M. A. , Olson C. D. , Belford R. L.
Published: February 2004

A general expression is developed for the orientations and magnitudes of the principal in-plane g values of low-symmetry d1 and d9 complexes considered as highly perturbed axial systems. The low-symmetry components of the ligand field cause participation of | 3z2 − r2〉 in the ground state and reorientation of the | xz〉, | yz〉 orbital set. The way in which these effects show up in the in-plane g ellipse is investigated for a number of possible bonding situations. A critical evaluation is made of the information which can be (and that which cannot be) obtained from the in-plane g values, and the observed g parameters from electron paramagnetic resonance of several copper and vanadyl chelates of Schiff's bases and ketoenolates are discussed in terms of the theory.
Vacuum-Ultraviolet Photochemistry. IX. Primary and Chain Processes in the Photolysis of Hydrogen Peroxide
Authors: Stief L. J. , DeCarlo V. J.
Published: February 2004

Evidence is presented for the occurrence of primary processes leading to the formation of both atomic and molecular hydrogen in the photolysis of H2O2 at 1236 Å. Formation of OH in a primary process probably occurs as well. The latter is apparently the sole process required to explain the results at 1470 and 2537 Å. Processes leading to the formation of O(1D) account for less than 1% of the photochemical decomposition. Chain processes leading to the formation of O2 but not H2 occur at 1236 Å. The possibilities considered are a free radical chain and an energy chain. It is shown that the results are more consistent with the occurrence of an energy chain involving atomic hydrogen and vibrationally excited OH radicals. Emission of OH A 2Σ+→X2II(0, 0) band at 3064 Å was observed during photolysis of H2O2 at 1236 and 1470 Å.
Molecular Three-Center Nuclear-Attraction Integrals via Ellipsoidal Coordinates
Authors: Roberts P. J.
Published: February 2004

Formulas are presented for a series expansion method for molecular three-center nuclear-attraction integrals, using a modified Laplace expansion due to Sack. It is shown how to extend the technique to two-electron-exchange integrals and to one type of three-center electron-repulsion integral. Electronic integrations are conducted in ellipsoidal coordinates using two centers as foci. The auxiliary functions arising from the analysis of the nuclear-attraction integrals are simpler than those occurring with conventional expansion methods.
Collisional–Radiative Electron–Ion Recombination Rate in Rare-Gas Plasmas
Authors: Chen C. J.
Published: February 2004

The minimum de-excitation rate of a recombining electron in the atom is calculated by using Gryzinski's formulation for the electron–atom collision process and Bates and Damgaard's Coulomb approximation for the radiative transition probability. The calculated minimum rate is taken to be the electron–ion collisional–radiative recombination rate. The electron–ion recombination rates are measured in a decaying plasma produced by a transient discharge. The comparison between the theoretical calculations and experimental results for five rare-gas (He, Ne, Ar, Kr, and Xe) plasmas is presented.
Temperature Coefficient of Hypersonic Sound and Relaxation Parameters for Some Liquids
Authors: Eastman D. P. , Hollinger A. , Kenemuth J. , Rank D. H.
Published: February 2004

The spontaneous Brillouin effect has been used to determine the variation of sound speed with temperature in the temperature range of − 30° to + 160°C above the relaxation frequencies in dibromomethane, dichloromethane, and carbon disulfide, below any relaxation frequency of acetone and nitrobenzene, and in the region of dispersion in chloroform, carbon tetrachloride, benzene, and acetic acid. In some cases the speeds have been corrected for dispersion. The temperature coefficient of sound and the parameters that characterize the relaxation have been evaluated and compared with other determinations. The sound speeds as a function of temperature have also been measured in water and five viscous liquids; 1-octanol, ethylene glycol, aniline, glycerol, and pentachlorobiphenyl. A simplified form of the Isakovich–Chaban theory involving a single temperature-dependent relaxation time has been used to predict the dispersion in glycerol and pentachlorobiphenyl and the amplitude absorption coefficient in glycerol from ultrasonic data. The predicted speeds are in quantitative agreement with the measured values. The observed amplitude absorption coefficient is shifted to higher temperature as the more complete theory of Isakovich and Chaban would predict.
Electrical Conductivity of Silver Bromide Membranes and the Diffuse Double Layer
Authors: Hall J. E. , Bruner L. J.
Published: February 2004

Electrical impedance measurements have been made on a system consisting of an AgBr membrane separating identical aqueous solutions of AgNO3. Metallic silver electrodes immersed in the solutions complete a cell for dc resistance measurements related to the transport of Ag+ ions through the membrane/solution system. Measurements have been made at solute concentrations between 4.0 × 10−4N and 1.0N and at temperatures ranging from 20°–180°C, with pressurization of the conductance cell. The results obtained are interpreted in terms of a theoretical description which treats the specific resistance of the membrane as a sum of two parts, one of which is simply related to the resistivity of AgBr in bulk. The other component arises from the formation of diffuse double layers at the membrane/solution interfaces. Analysis of the data in terms of this theory permits the evaluation of K + , the partition coefficient for Ag+ ions, which is equal to the ratio of the concentration of Ag+ ions in the aqueous solutions at the isoelectric point to the concentration of Ag+ interstitial ions in bulk AgBr. The concentration of Ag+ ions in aqueous solution at the isoelectric point ciso is also determined. It is found that K+ = 7.4 × 10−9exp(0.97 eV/kT), and ciso = 4.2 × 10−6exp(0.46 eV/kT) g·mole/liter, where T is the absolute temperature, and k, the Boltzmann constant, is equal to 8.61×10−5 eV/°K. Our values for ciso are higher than those reported by other authors working with freshly prepared sols and with systems similar to that employed in this study. These discrepancies are attributed to aging effects and to differing experimental conditions.
Light Scattering from Chemically Reactive Fluids. II. Case with Diffusion
Authors: Blum Lesser , Salsburg Zevi W.
Published: February 2004

The thermodynamic approach for light scattering developed in a previous paper is extended to include the diffusion process. The results for zero angle are the same as stated before [B. J. Berne and H. L. Frisch, J. Chem. Phys. 47, 3675 (1967); L. Blum and Z. W. Salsburg, ibid. 48, 2292 (1968)], that is, the only remaining contribution to the central Rayleigh line is due to the chemical reactions.
Dipole Moments of the Excited States of Azulene
Authors: Hochstrasser Robin M. , Noe Lewis J.
Published: February 2004

The splitting of spectral lines by an electric field, in the accepted sense, is dependent on the interaction of the field with degenerate states. However, molecular crystals having no degenerate molecular states can be subject to a linear Stark mixing due to the interaction of the field with the inequivalent molecules in the unit cell. In a dilute mixed crystal where the guest–guest interactions are vanishingly small, the resultant splitting of spectral lines, ΔS = EGΔμ, is directly proportional to the field strength E, a geometrical factor G, and the change in dipole moment Δμ between the ground and excited states. The substitutional solid of azulene in naphthalene was chosen to demonstrate this effect. The dipole moments of the first and second singlet states of azulene have geen determined and are −0.42 and −0.31 D, respectively.
Electronic, Vibrational, and Zeeman Spectra of Triplet NO2
Authors: Hochstrasser Robin M. , Marchetti Alfred P.
Published: February 2004

The lowest-energy singlet–triplet transition of NO2− has been studied in emission and absorption in single crystals of NaNO2 at 4.2°K. The space symmetry of the lowest triplet state at 18 959 cm−1 is shown to be B13. This assignment is in agreement with molecular orbital predictions. The spin-state substructure of the B13 level has been studied using the Zeeman effect, and it is shown that the main portion of the transition (f ∼ 8 × 10−8) (3B1←1A1) arises because of the electric-dipole activity of the |Tz〉 spin state. The observed spectrum is therefore mainly of type B2←A1, which is consistent with the polarization measurements. A small fraction of the intensity is induced by a b2 vibration (ν3′ = 1170 cm−1), and for that portion the |Ty〉 spin states of each vibronic level carry the electric-dipole intensity, possibly by virtue of a vibronic spin–orbit coupling mechanism. The assignments are confirmed by calculations of the spin–orbit matrix elements which suggest that a low-energy B21(π2→π3*) state is spin–orbit coupled to the B13 state. The absorption and emission Franck–Condon factors for the prominent angle bending mode (ν2′ = 644; ν2″ = 828 cm−1) gave an indication that the ONO angle opens by ∼15° on excitation to the B13 state. The fact that the NO2− emits only very weakly from the B13 state following excitation into the B11 state, while the emission from the B13 state is ∼ 7 times stronger when excitation is to the A21 state, is discussed in some detail, with special emphasis on the nature of radiationless transitions in solids.
Nucleation on Gaseous Ions
Authors: Russell Kenneth C.
Published: February 2004

The homogeneous nucleation theory of Lothe and Pound is extended to condensation on ions. A rate equation is derived that gives the frequency of droplet formation on an attenuated concentration of gaseous ions in supersaturated unary vapors. This treatment predicts little catalytic effect of ions in contrast to the classical theories of Volmer and of Becker and Doering, which predict condensation on ions at supersaturations substantially below those needed for homogeneous nucleation. The predictions of classical theory and of the present treatment are compared with Scharrer's cloud-chamber measurements of homogeneous, positive-ion, and negative-ion rain limits in a number of fluids. Neither theory predicts the different catalytic potencies of positive and negative ions. The homogeneous rain limits in CHCl3, C6H6, CCl4, and C6H5Cl are in good agreement with the Lothe–Pound theory, and the catalytic effect of ions is small or nil, in agreement with the present treatment. Classical theory correctly predicts only the homogeneous rain limit in H2O and homogeneous and positive-ion limits in C2H5OH.
Diffraction and Spectroscopic Studies of the Cobaltic Acid System HCoC2–DCoO2
Authors: Delaplane Robert G. , Ibers James A. , Ferraro John R. , Rush John J.
Published: February 2004

Cobaltic acid, HCoO2, and deuterated cobaltic acid, DCoO2, have been prepared and studied by x-ray and neutron-diffraction techniques, and by infrared spectroscopy and cold-neutron scattering. The materials crystallize in apparent space group D3d5–R<3¯m of the trigonal system with three molecules in a hexagonal cell of dimensions: HCoO2, a = 2.851(1), c = 13.150(5) Å; DCoO2, a = 2.854(1), c = 13.354(5) Å. The O–O distance, as determined by neutron-powder studies, of HCoCO2 is 2.50(2) Å. On this basis and the fact that there are three O–H–O bonds along the c direction, the O–D–O distance is 2.57(2) Å. Hence, the isotope effect here is as large as in the system HCrO2–DCrO2. Infrared studies at room temperature and at − 195°C over the region 70–4000 cm−1 may be interpreted in terms of an effectively symmetric O–H–O bond and an effectively asymmetric O–D–O bond. Although the neutron inelastic scattering measurements are not inconsistent with this interpretation, there is a band centered at 264 cm−1 in the neutron spectrum for HCoC2, which is not observed in the infrared spectrum. Model calculations, based on a two-dimensional potential function in which the asymmetric stretching frequency is coupled to the symmetric stretching frequency, were unsuccessful owing to the magnitude of the coupling term required to account for the very large isotope effect.
Alternative Approach to the Cluster Theory of Imperfect Gases and Condensation
Authors: Alexandrowicz Z.
Published: February 2004

The expansion of the density and pressure in terms of power series of activity, with cluster integrals as coefficients, is derived with the help of a new method. Rather than expanding at once the entire configurational partition function (3N-dimensional volume) the expansion here is applied to a quantity constituting the logarithmic increment of the partition function per molecule (three-dimensional volume). The expansion of this quantity is then recursively used to derive the thermodynamic functions for the system. Formulated in terms of “mathematical” clusters the method leads to a series expansion that, so long as such series converge, remains equivalent to the famous result of Mayer's theory. However, as the series become divergent (which presumably corresponds to condensation) the expansion cannot be anymore reduced to Mayer's series. When formulated in terms of “physical” clusters the present method permits to derive an expansion that duly allows for physical cluster integrals being mutually exclusive. The result is similar to the corrected version of the Frenkel–Band theory, as derived by Stillinger with a different method, the similarity breaking down, however, as the series become divergent. Another expansion, in terms of “modified clusters” and which proceeds via differentiation and reintegration with respect to β( = 1/kT) and which might prove to be of advantage in discussing condensation, is also derived on the basis of the present method.
Crystal Spectra of Hexaurea Complexes. II. Absorption and Emission in Crystals Containing the Hexaurea Chromium (III) Ion
Authors: Dingle R.
Published: February 2004

Absorption and emission bands have been observed in crystals containing the hexaurea chromium(III) ion. The moderately sharp features in the region 14 160–14 250 cm−1 have been examined in some detail in the temperature range 1.5°–300°K. A broad emission band has been seen at 12 300 cm−1 and is considered to be the T2g4 → 4A2g transition. Detailed radiative lifetime and quantum efficiency measurements lead to a proposal that includes the possible identification of the (0,0) T2g4(Oh) transition.
Thermodynamics of Rare-Earth–Carbon Systems. I. The Cerium–Carbon System
Authors: Balducci G. , Capalbi A. , De Maria G. , Guido M.
Published: February 2004

The gaseous phase in thermodynamic equilibrium with the condensed cerium–carbon system has been investigated by means of the combined Knudsen-cell–mass-spectrometric technique in the temperature range 1990°–2300°K. In addition to cerium atoms, the gaseous carbide molecules CeC2 and CeC4 were identified and their partial pressures measured. Using this information, the following dissociation and atomization energies were derived: D0° = 162 ± 2 kcal/mole for the Ce–C2 bond energy in CeC2; ΔH0° = 304.5 ± 1.5 kcal/mole for the atomization energy of CeC2; ΔH0° = 609 ± 5 kcal/mole for the atomization energy of CeC4. A heat of formation for the solid cerium dicarbide was also obtained.
Microwave Spectrum and Structure of Bicyclo[1.1.0]butane
Authors: Cox Kent W. , Harmony Marlin D. , Nelson Gordon , Wiberg K. B.
Published: February 2004

The microwave spectra of four isotopic species of bicyclo[1.1.0] butane have been investigated and the rotational constants of each species have been determined. Combining these data with those of the previously studied normal isotopic species, a complete set of structural parameters have been found. These include C1–C3 = 1.497 Å, C3–C4 = 1.498 Å, C3–C6 = 1.071 Å, C–H (methylene) = 1.093 Å, ∠C1C3H6 = 128°22′, dihedral angle, α, between cyclopropane rings = 121°40′, ∠HCH = 115°34′. These results are discussed with regard to the electronic structure of the molecule.
Pairwise Trapping of Radicals in Irradiated n-Hydrocarbons and Related Compounds as Studied by Electron Spin Resonance
Authors: Iwasaki Machio , Ichikawa Takahisa , Ohmori Toshio
Published: February 2004

The ESR signals due to the radical pairs were found in n-hydrocarbons γ irradiated at 77°K. Besides the spectra due to the ΔMs = 2 transition, ΔMs = 1 spectra were also found on the tail of the predominant spectra of isolated radicals. The ΔMs = 1 spectra of the radical pairs show nearly the same hyperfine splitting as that of the ΔMs = 2 spectra. From the analysis of the ΔMs = 1 spectra, the separation d‖ due to the zero-field splitting was determined to be 292 G from which the distance of the paired radicals was estimated to be 5.75 Å. The radical pairs are probably in the form of two alkyl radicals on the adjacent hydrocarbon chains. The value of 5.75 Å is consistent with the intercarbon distance between the adjacent chains aligned along the direction of the crystalline b axis. A glassy hydrocarbon such as squalane also gave the ΔMs = 2 spectrum but did not give the hyperfine lines on the tail of the ΔMs = 1 spectrum as is the case of high polymers. In addition, the effect of aditives and substituents was also investigated together with some other related compounds and the mechanism of the pairwise formation of radicals was discussed.
Single-Crystal Magnetic Studies on Copper Calcium Acetate Hexahydrate
Authors: Gregson A. K. , Mitra S.
Published: February 2004

Magnetic susceptibility, anisotropy, and EPR of single crystals of copper calcium acetate hexahydrate have been studied down to about 90°K. The average moment, anisotropy, and g values of the dodecahedrally coordinated copper ion are observed to be similar to those reported for octahedrally and tetrahedrally coordinated copper compounds. The metal–ligand bond is almost “ionic.” The data over the complete range of temperature can be fitted very well with Fisher's model of one-dimensional antiferromagnetism, which is consistent with the detailed structure of the crystal.
Mössbauer Studies of Iodine Bond Hybridization in Iodomethanes
Authors: Ehrlich Benjamin S. , Kaplan Morton
Published: February 2004

The Mössbauer effect of the 57.6 keV transition in 127I has been used to investigate the iodine bonding in CH3I, CH2I2, CHI3, and CI4 at 4.2°K. The data unambiguously imply the existence of a small amount of s hybridization in the iodine bonding orbitals. This hybridization increases approximately linearly through the series from ∼0% in CI4 to ∼8% in CH3I. The ionic character of the C–I bond also increases from CI4 to CH3I. The results are compared with several semiempirical predictions based on iodine NQR data. Separate experiments using the Mössbauer effect of the 27.8-keV transition in 129I have yielded consistent results in a CH129I3 absorber.
Rotational Spectra of Substituted Diazirines. II. Methyldiazirine
Authors: Scharpen LeRoy H. , Wollrab James E. , Ames Donald P. , Merritt James A.
Published: February 2004

Ground-state rotational spectra of HCH3CN2 and HCD3CN2 have been assigned, and the structural parameters obtained by least-squares fitting the observed moments are r(CN) = 1.481 ± 0.01 Å, r(CC) = 1.501 ± 0.01 Å, r(NN) = 1.235 ± 0.005 Å, and ∢N2CC = 122.3 ± 0.6°. The internal rotation splittings for HCH3CN2 and HCD3CN2 yield barriers of 773.9 and 770.4 ± 1.0 cal/mole, respectively. The quadrupole coupling constants χaa, χbb, and χcc are + 0.48 ± 0.8, − 2.53 ± 0.4, and + 2.05 ± 0.4 MHz for HCH3CN2 and 0.20 ± 0.8, − 2.36 ± 0.4, and + 2.16 ± 0.4 MHz for HCD3CN2. Analysis of the Stark effect give a dipole moment of 2.03 ± 0.07 D for HCH3CN2 and 2.02 ± 0.07 D for HCD3CN2.
ESR Study of l-Alanine-1-13C Irradiated at Low Temperatures
Authors: Sinclair James , Hanna Melvin W.
Published: February 2004

The ESR spectra of l-alanine-1-13C, x irradiated at low temperatures (T < 150°K), have been examined. The spectra have been interpreted in terms of a carboxyl radical similar to those postulated for other irradiated organic acids. From the values of the 13C hyperfine tensor it has been confirmed that the unpaired electron is essentially a 22pπ-type electron located primarily on the carboxyl carbon and that this spin density interacts with the α proton. From the magnitude of the isotropic 13C hyperfine splitting it is found that the RCO2− structure is bent about 8° from planarity. The stable room-temperature fragment in irradiated l-alanine-1-13C exhibits essentially isotropic 13C splittings of 12.8 G.
Vibrational Spectra and Molecular Potential Fields of Mercurous Chloride, Bromide, and Iodide
Authors: Durig J. R. , Lau K. K. , Nagarajan G. , Walker M. , Bragin J.
Published: February 2004

The Raman and infrared spectra of solid mercurous chloride, bromide, and iodide have been recorded and the vibrational fundamentals assigned on the basis of D∞h molecular symmetry. Normal modes were found at 279, 250, 169, 107, and 42 cm−1 for the chloride, 220, 184, 136, 71, and 37 cm−1 for the bromide, and at 194, 138, 113, 49, and 31 cm−1 for the iodide. The potential fields of the molecules have been analyzed assuming the most general valence forces. The potential constants and normal modes are described and discussed in terms of the assignments. The mixing of the Hg–Hg and the Hg–X stretching modes is considered in detail.
Isotherms of Argon to 10 000 bars and 400° C
Authors: Robertson S. L. , Babb S. E. , Scott Gene J.
Published: February 2004

Isothermal measurements of the density of argon have been carried to pressures of 10 000 bars and temperatures to 400°C. The data are presented, and the results compared with other workers.
Collisions of Monoenergetic Electrons with NO2: Possible Lower Limits to Electron Affinities of O2 and NO
Authors: Stockdale J. A. D. , Compton R. N. , Hurst G. S. , Reinhardt P. W.
Published: February 2004

The yields of O−, NO−, and O2− ions produced by dissociative attachment of electrons to NO2 have been studied as a function of the electron energy from 0 to 6 eV. A modulated retarding-potential-difference technique permitted electron-energy resolution of approximately 0.1 eV. The measured appearance potentials for NO− and O2− were found to be consistent with an electron affinity of ≥0.65 eV for NO and ≥1.1 eV for O2. These lower limit measurements to the electron affinities of O2 and NO are discussed in relation to previous studies of electron attachment to these molecules.
Ketene in a Gaussian Basis: LCAO–MO–SCF Wavefunction, One-Electron Properties, and Electron-Density Maps
Authors: Letcher John H. , Unland Mark L. , Van Wazer John R.
Published: February 2004

An SCF calculation of the wavefunction for ketene is presented. The basis functions are a (73/73/3) uncontracted set of Gaussian 1s and 2p orbitals. Energy components, population analysis, one-electron properties, and density maps are presented and discussed. A main conclusion is that, opposite to formaldehyde, the total contribution of π orbitals to the radial extent of the charge density in the out-of-plane direction in ketene is greater than the total contribution of the σ orbitals. Both second moments of charge and density maps support this conclusion.
Statistical Thermodynamics of Polymer Solutions. VII. The Triple-Contact Contribution to Pairwise Interactions of Linear Chains Differing in Molecular Weight
Authors: Tagami Yukiko , Casassa Edward F.
Published: February 2004

The influence on the osmotic second virial coefficient of configurations with three contacts between pairs of chain segments has been calculated, in part analytically and in part numerically, for a bimolecular cluster of linear polymer chains chemically alike but unequal in degree of polymerization. All classes of contributing chain configurations are included—those with three intermolecular contacts, and those with two intermolecular contacts and one intramolecular contact. The new calculations indicate the need for minor quantitative revision of results published earlier for the special case of triple-contact interactions between two identical chains.
One-Electron Properties of Near-Hartree–Fock Wavefunctions. II. HCHO, CO
Authors: Neumann D. B. , Moskowitz J. W.
Published: February 2004

The results of Hartree–Fock level self-consistent-field molecular orbital calculations using contracted Gaussian basis sets are reported for the ground states of the formaldehyde and carbon monoxide molecules. The best computed wavefunctions are shown to have total energies, at most, 0.05 a.u. from their Hartree–Fock limits. A large number of one-electron properties were computed from the wavefunctions. Results for the carbon monoxide molecule are in excellent agreement with the Slater basis Hartree–Fock results of Huo [J. Chem. Phys. 43, 624 (1965)]. For formaldehyde the calculated molecular properties are in good agreement with experiment. Our best estimates for several of the properties in HCHO are: dipole moment, μz = 2.82 D; quadrupole moment, θaa = 0.0056 × 10−26 esu·cm2, θbb = 0.250 × 10−26esu·cm2, θcc = − 0.256 × 10−26esu·cm2; diamagnetic shielding at the proton, σaad(H) = 92.63 ppm, σbbd(H) = 94.68 ppm, σabd(H) = 52.80 ppm, σccd(H) = 147.13 ppm, and σAvd(H) = 111.48 ppm; diamagnetic shielding at 13C, σaad(C) = 288.50 ppm, σbbd(C) = 355.34 ppm, σccd(C) = 371.60 ppm, and σAvd(C) = 338.48 ppm, diamagnetic susceptibilities, χaad = − 27.99, χbbd = − 54.19, χccd = − 61.53, and χAvd = − 47.91 emu/mole; deuteron quadrupole coupling constants, (eqQ/h)AA = 172.4 kc/sec, (eqQ/h)BB = − 87.22 kc/sec, and (eqQ/h)CC = − 85.21 kc/sec; 17O quadrupole coupling constants, (eqQ/h)aa = − 2.28 Mc/sec, (eqQ/h)bb = 12.8 Mc/sec, and (eqQ/h)cc = −10.5 Mc/sec.