bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotational Isomerization of Polymer Chains by Stretching
Authors: Abe Y. , Flory P. J.
Published: February 2004

A general theory is presented on the effect of elongation of a polymer chain on the apportionment of its bonds and bond sequences among various rotational isomeric states. The perturbation of the population of a state η is found to be proportional to 32[(r2 / 〈r2〉0) − 1][(〈rη;i2〉0 / 〈r2〉0) − 1], where r is the length of the chain vector, 〈r2〉0 is the mean square of r for the unperturbed chain, and 〈rη;i2〉0 is the same quantity subject to the condition that the bond i or bond sequence i is in the conformational state specified by η. The theory is limited to the range of moderate deformations; it is inapplicable for lengths r approaching full extension of the chain. Numerical calculations are presented for polymethylene chains and for syndiotactic vinyl polymers. The calculated effects are very small; unit increase in r2 / 〈r2〉0 generally alters the conformation population of a given state by no more than about one bond (or sequence) per chain. The length of the given conformation and its susceptibility to orientation by stretching are the main factors governing the effect. The connection with strain dichroism is discussed.
Microwave Spectra, Barriers to Internal Rotation, and Dipole Moments of cis- and trans-Propylene Phosphine
Authors: Bowers Michael T. , Beaudet Robert A. , Goldwhite Harold , Chan S.
Published: February 2004

The rotational spectra of cis- and trans-propylene phosphine have been observed in the region 8–35 GHz. The respective barriers of the cis and trans isomers were determined to be V3 = 3010 cal/mole and V3 = 3050 cal/mole. The dipole moments were measured to be μtotal = 1.28 and 1.29 D, respectively. The relative stability of the isomers was also estimated. The trans is favored by ΔF = 130 ± 30 cal/mole.
Systematic Determination of the Slater Parameters for the First Transition Elements
Authors: Anno Tosinobu , Teruya Hirohide
Published: February 2004

Slater's parameter Fk and Gk with k ≠O have been determined systematically from the experimental atomic energy levels for the neutral atoms and singly through triply positive ions of the first transition elements in their 3dn, 3dn−14s, 3dn−14p, 3dn−24s4p, and 3dn−24s2. configurations, by a least-squares procedure. A procedure of obtaining the semiempirical values of F0's, which have never been obtained from the data of atomic spectra, is given along the line suggested by Anno [J. Chem. Phys. 47, 5335 (1967)] involving the consideration of appropriate “electron-transfer reactions.” Data on ΔE, the energy change in the course of the electron-transfer reaction, are also given, which may be combined with Fk's and/or Gk's (k ≠ 0) to obtain F0's. Ideal correlation lines, which correlate a particular kind of Fk, Gk (k ≠ 0), or ΔE with the atomic number Z and/or electron configuration in ideal situations where no anomaly due such as to CI or misassignment were present, are discussed and are given in such a way that they are most consistent with the actual data obtained to facilitate the semiempirical MO calculations on the transition metal compounds, in which the metal atom has a fractional charge and a fractional population in each of its AO's. As far as possible, the semiempirical data obtained in the present work have been compared with the data obtained with the nonempirical Hartree–Fock calculations.
Mössbauer Study of 57Co Implanted in Diamond
Authors: de S. Barros F. , Hafemeister D. , Viccaro P. J.
Published: February 2004

A Mössbauer source of 57Co in diamond has been produced by implanting 57Co with an isotope separator directly into a diamond single crystal. The Mössbauer spectra taken at 80 and 300°K and in the [100] and [110] orientations displays two peaks of equal intensity. These two peaks can be interpreted as quadrupole splitting caused by the displacement of the iron interstitial from its site of tetrahedral symmetry.
Transient Nuclear Magnetic Resonance Studies of Dilute Copper-Base Alloys
Authors: Fromhold A. T.
Published: February 2004

Data are presented for the nuclear spin–spin and spin–lattice relaxation rates for the 63Cu and 65Cu resonances in dilute copper-base alloys with the following atomic percent of the solute metals: 0.1% Ag, 0.2% Ni, 0.25% Al, 0.25% Au, 0.4% Ni, 1.0% Ni, and 5.0% Ag. The data reflect the sizable electric field gradients due to local strains introduced by alloying and the spatial rearrangement of conduction-band electrons in the vicinity of individual solute atoms.
Environmental Effects on f–f Transitions. III. Spectral Intensities of Lanthanide Nitrate, Sulfate, and α-Picolinate Solutions
Authors: Bukietynska K. , Choppin G. R.
Published: February 2004

The environmental effects of nitrate, sulfate, and α-picolinate anions on f–f transitions of lanthanide ions in aqueous solution were investigated. For the α-picolinate complexes, LnP3, it was possible to apply the Judd–Ofelt method to the evaluation of the spectral changes. The Jλ parameters were larger than for the aquoion spectra with J2 showing the largest change. Results are presented for trivalent Pr, Nd, Sm, Dy, Ho, Er, and Tm.
Antiferroelectric Transitions in NH4H2PO4 and NH4H2AsO4 Studied by Infrared Absorption
Authors: Wiener E. , Levin S. , Pelah I.
Published: February 2004

The antiferroelectric phase transition of NH4H2PO4 and NH4H2PO4, as well as of their deuterated analogs, were studied by observing the changes in the infrared absorption spectra (250–4000 cm−1) accompanying the phase transition. The behavior of the spectrum of NH4H2PO4 and ND4D2PO4 while approaching Tc suggests that the same hydrogen-dynamics mechanism is responsible for the phase transition in both cases, and that the fluctuating double-minimum-potential-well theory for the hydrogens applies here too. The differences observed at temperatures below Tc indicate a different final arrangement of the hydrogens in the antipolar phase. There are more PO4 lines in the NH4H2PO4 low-temperature spectrum, indicating that the hydrogens are arranged asymmetrically along the c axis, thus inducing an antiparallel dipole network. The ir absorption spectrum of a mixed crystal NH4H2(AsO4)0.95(PO4)0.05 was measured at different temperatures in order to check the validity of the site-group assignments in these crystals. The gradual reduction in the correlation field splitting on increasing the deuterium percentage in the antipolar phases of ND4D2PO4 compounds suggests a more distorted deuteron network. Possible assignment for the absorption peaks in both phases of NH4H2AsO4 and ND4D2AsO4 (60% D) are given.
Stability Conditions for the Solutions of the Hartree–Fock Equations for Atomic and Molecular Systems. II. Simple Open-Shell Case
Authors: Paldus J. , Čĺžzek J.
Published: February 2004

The stability conditions for the solutions of the Hartree–Fock equations for the simple open-shell case, i.e., closed shell with one extra electron, are derived. It is shown that only “doublet stability” is relevant is this simple open-shell case, the solutions being always “nondoublet unstable.” The doublet stability conditions are then derived using the mathematical methods of quantum field theory, namely, occupation number representation, Wick's theorem, and Feynman-like diagrams. In order to familiarize the reader with the use of these concepts they are first used to rederive the singlet and nonsinglet stability conditions for the closed-shell case. A general method of finding new Hartree–Fock solutions, in the case that the symmetry adapted Hartree–Fock solutions are unstable, is briefly discussed. The implications of the instability on the ground-state correlation energy calculations and on the excitation energy calculations using time-dependent Hartree–Fock theory are considered.
Mass Spectrometric Determination of the Dissociation Energies of LaAu, CeAu, PrAu, and NdAu and Predicted Stability of Gaseous Monoaurides of Electropositive Metals
Authors: Gingerich K. A. , Finkbeiner H. C.
Published: February 2004

The Knudsen-cell mass spectrometric method has been used to study the exchange reactions LnAu(g)+Au(g)=Ln(g)+Au2(g), where Ln stands for a lanthanide metal. For Ln=C, the third-law and second-law enthalphies ΔH0° in kilocalories per mole were obtained as 23.4 ± 0.4 and 22.5 ± 1.2, respectively. The third-law enthalphies, in kilocalories per mole, for Ln=La, Pr, and Nd resulted in 29.6 ± 1.0, 20.3 ± 0.6, and 16.4 ± 1.5, respectively. The third-law investigation of the exchange reactions CeAu(g)+Ln(g)=LnAu(g)+Ce(g) yielded the reaction enthalpies ΔH0° in kilocalories per mole of: − 3.8 ± 2.2 for Ln=La, + 3.1 ± 0.8 for Ln=Pr, and + 6.4 ± 1.5 for Ln=Nd. Combining the enthalphies of the first reaction with the known dissociation energy of Au2(g) and using the value obtained for D0°(CeAu) as a standard for the second exchange reaction, the following dissociation energies, D0°, in kilocalories per mole have been derived for the gaseous lanthanide auride molecules: LaAu, 79 ± 5; CeAu, 75.0 ± 3.5; PrAu, 72.5 ± 5; and NdAu, 69 ± 6. The corresponding standard heats of formation ΔHf,298° in kilocalories per mole of these gaseous intermetallic compounds are 111 ± 6, 113 ± 5, 99.7 ± 5.5, and 96.5 ± 6.5, respectively. The high values for the dissociation energies of LaAu, CeAu, PrAu, and NdAu are explained in terms of the Pauling model of a single covalent bond to which a significant extra ionic contribution is added. Using this model, the dissociation energies of the diatomic alkali, alkaline-earth, and rare-earth aurides have been calculated. These gaseous intermetallic compounds are expected to be intermediate in their ionic character to the corresponding iodides and hydrides.
Nature of the External Heavy-Atom Effect on Radiative and Nonradiative Singlet–Triplet Transitions
Authors: Giachino Gary G. , Kearns David R.
Published: February 2004

The nature of the external heavy-atom effect on radiative and nonradiative singlet–triplet transitions in aromatic hydrocarbons has been investigated experimentally and theoretically. From studies of the perturbed phosphorescence of aromatic hydrocarbons in rigid glass and mixed-crystal systems we conclude that:

(i) Radiative T1 ↔ S0 transitions are much more susceptible to a heavy-atom effect than are the corresponding radiationless transitions.

(ii) The enhancement of the radiative T1 ↔ S0 transitions is due to mixing of excited singlet states associated with the perturber molecule into the triplet state of the perturbed molecule.

(iii) The important pertuber states appear to be highly localized on the heavy atom rather than states which are essentially delocalized [e.g., (π, π*) states].

(iv) It does not seem necessary to invoke charge-transfer interactions to account for the enhancement.
Ultrasonic Relaxation Studies in Aqueous Solutions of 2–2 Electrolytes
Authors: Bechtler A. , Breitschwerdt K. G. , Tamm K.
Published: February 2004

The ultrasonic absorption in aqueous solutions of a number of 2–2 electrolytes including the sulfates of the bivalent transition metal ions has been measured in the frequency range 105–109 Hz at temperatures between 5 and 50°C. Generally, three relaxations can be separated in this frequency range if the structural absorption of the electrolytic solution is properly taken into account. Relaxation times and corresponding maximum absorption per wavelength are allocated to the normal coordinates of a three-step association or dissociation mechanism. In order to be applicable to the new experimental results, the existing theory of the stepwise association had to be extended to a more general form. By means of suitable transformations the normal coordinates can then be expressed in terms of kinetic and thermodynamic parameters of the individual reaction steps. Values of the rate constants, equilibrium constants, reaction volumes, and activation energies calculated on the basis of the extended theory are presented for the individual reaction steps.
Electron Relaxation and Molecular Vibrations: Triatomic Systems of the First-Row Elements, the Methyl Radical, and Diazomethane and Ketene
Authors: Burdett Jeremy
Published: February 2004

The well-known second-order perturbation method is used to correlate the bond–bond interaction constants in ground and excited electronic states of triatomic systems of the first-row elements, and unusual force constants in diazomethane and ketene with the effect of electron relaxation. The third- and fourth-order perturbation schemes are used to determine qualitatively the contributions to the third- and fourth-order parts of the vibrational potential function of carbon dioxide, by the electron relaxation effect. The fourth-order theory is used to rationalize the negative anharmonicities observed in ketene, diazomethane, the methyl radical, and planar excited states of ammonia.
Dissociation Energies, Enthalpies of Formation, Ionization Potentials, and Dipole Moments of NS and NS+
Authors: O'Hare P. A. G.
Published: February 2004

A dissociation energy of 4.8 ± 0.25 eV at 0°K has been deduced for NS(2Π) from spectroscopic data in the literature; the corresponding value for ΔHf0°(NS) is 2.91 ± 0.26 eV. Recent experimental results for ΔHf°(NSF) from this Laboratory indicate ΔHf0°(NS+, 1Σ+) = 12.76 ± 0.10 eV, from which the ionization potential of NS, 9.85 ± 0.28 eV, is obtained. Hartree–Fock–Roothaan ab initio calculations for NS and NS+ yielded, respectively, first ionization potentials of 9.75 and 24.3 eV, dipole moments of 1.732 and 3.893 D, and, for D0° (NS), an approximate value of 5.2 eV.
Absolute Absorption Intensities of the Librational Modes of ClCN and BrCN
Authors: Friedrich H. Bruce
Published: February 2004

The absolute absorption intensities of the two infrared-active librational modes in crystalline ClCN and BrCN have been measured. The sums of the intensities of the two modes were 750 ± 90 and 800 ± 140 cm mM−1 for ClCN and BrCN, respectively. A dipolar coupling model was used to compute the expected intensities and the contributions of dipolar interactions to the frequencies of these lattice modes. The evaluation of the lattice sums in the direct or reciprocal lattice is discussed. The calculated intensities were 970 and 835 cm mM−1 for ClCN and BrCN, respectively.
Transport Properties of Polar–Quadrupolar Gas Mixtures
Authors: Singh Y. , Gupta A. Das
Published: February 2004

Collision integrals for polar–quadrupolar gas mixtures have been computed under two limiting approximations: (i) Collision integrals are calculated on the fixed relative orientations with a 12–6–4 potential model and then these values are averaged by giving equal weight to all orientations; (ii) the potential is “pre-averaged” over all orientations and then collision integrals are calculated. The former method is more appropriate for slow rotating molecules and the latter one for fast rotating molecules. The polar–quadrupolar interaction term in the potential energy of interaction between a polar and a quadrupolar molecule is found to contribute materially to the transport coefficients and must, therefore, be considered for calculating accurately the mixture properties. Combination rules for estimating unlike interactions are discussed briefly.
Transport and Equilibrium Properties of Polar Gases
Authors: Singh Y. , Gupta A. Das
Published: February 2004

A simple preaveraged 12–6–6 potential model has been used to explain the observed viscosity and diffusion coefficients of polar gases. Force parameters for several polar gases have been determined from the experimental values of viscosity at different temperatures and observed dipole moments. Experimental second virial coefficient data in conjunction with the force parameters determined from viscosity have been used to estimate the molecular quadrupole moments. The results for three polar molecules (NH3, SO2, and CH3OH) have been reported. It has been shown that while the transport properties of a polar gas can be adequately described by a potential function consisting of a L-J (12–6) part plus a contribution due to the dipole moment, the contribution of the higher multipoles to the second virial coefficient of the same gas is not negligible.
Rapid Method to Construct “True” Potential Curves of Diatomic Molecules
Authors: Vaidyan V. K. , Santaram C.
Published: February 2004

A rapid method to evaluate the classical turning points of vibrational levels for the electronic states of diatomic molecules whose energy terms can be represented adequately by a quadratic in (υ + 12) is discussed. The method is based on the fact that the internuclear distance “r” corresponding to energy “U” can be represented by an equation of the form y(r) = mx(U) + c, the equation of a straight line. The method is also extended to electronic states whose weye is not very large. To check the validity of these procedures potential energy curves are constructed for X 2Σ+, A 2Π3/2, and A 2Π1/2 states of CN; X 1Σg+ and A 3Σu+ states of N2; and 3Π0u+ state of 79Br81Br. All these values are compared with those obtained by RKRV method. In all cases the agreement is found to be satisfactory, with a deviation of less than 0.1% to RKRV values. Further, a method to check the validity of a Morse function for a particular electronic state is discussed, and a method to adjust the Morse function to represent the true curve is illustrated by considering the A 2Π3/2 state of CN.
Self-Diffusion of Iodide Ions into Ion-Exchange Resin Dowex 1 × 8
Authors: ̌Span J.
Published: February 2004

Series of experiments were performed to show the influence of the concentration and flow rate of solution on the self-diffusion of the iodide ion into the ion-exchange resin Dowex 1 × 8. Using a model based on the concept of an effective diffusion layer with the nonlinear concentration profile, rate curves were calculated and compared with experimental results. Good fitting in the whole concentration and flow range is observed. Using the same model, concentration profiles in both solid and liquid phases for three different thicknesses of the diffusion layer were calculated.
Incorrect Dissociation of CO in the Restricted Hartree–Fock Approximation
Authors: Green Sheldon
Published: February 2004

A restricted Hartree–Fock calculation using a large Slater-type basis was performed on CO at six internuclear distances from Re = 2.132 to R = 10.0 a.u. Values for several one-electron operators are reported. Results are discussed in terms of the incorrect dissociation of the function due to symmetry restrictions.
NMR and Magnetic Susceptibility Measurements of a Series of Manganic Dithiocarbamates
Authors: Golding R. M. , Healy P. , Newman P. , Sinn E. , Tennant W. C. , White A. H.
Published: February 2004

The NMR and magnetic susceptibility results of a series of manganese (III) dithiocarbamates have been determined and interpreted using a model where the d4 ion is in a crystal field of octahedral symmetry: the ground electronic state is the E5 state. The true symmetry about the metal ions in dithiocarbamates differs somewhat from octahedral, and the implications of this are discussed. By comparing the NMR results for the iron (III) dithiocarbamate analogs we have shown that the extent of d-electron delocalization depends markedly on the transition metal ion. The variation of the isotropic proton hyperfine interaction constants along the alkyl chain, which reflects the electronic configuration of these complexes, also depends markedly on the transition metal ion.
Predissociations Induced by a Magnetic Field
Authors: Huo Winifred M.
Published: February 2004

A theoretical study of field-induced predissociations is presented. It is found that the rate of predissociation in general depends on the rotational quantum number. However, for several limiting cases the rotational dependence cancels out. The vibrational effect on predissociation is treated in the semiclassical approximation. Comparison is made with the recent experimental results on the magnetic quenching of iodine fluorescence by Degenkolb, Steinfeld, Wasserman, and Klemperer.
Protonic Conductivity in Imidazole Single Crystal
Authors: Kawada A. , McGhie A. R. , Labes M. M.
Published: February 2004

Imidazole single crystal has a highly anisotropic conductivity; the ratio of conductivity in the c and a crystallographic directions is ∼103. In the c crystallographic direction, the hydrogen bonded direction, protonic carriers are discharged as hydrogen at the negative electrode. The limiting conduction process is possibly due to L-defect injection and transport back down the hydrogen bonded chain after the proton is discharged. Conductivity in the a direction is probably electronic and extrinsic.
Asymptotic Solutions of the Time-Dependent Nernst–Planck Equations
Authors: MacGillivray A. D.
Published: February 2004

Some analytic solutions of the time-dependent Nernst–Planck equations are obtained for “voltage-clamp” boundary conditions. The solutions are in the form of asymptotic expansions, valid for small and large times and small voltage-clamp values.
Scheme for Sensitive Nuclear Double-Resonance Detection: Deuterium and 13C
Authors: Schwab M. , Hahn E. L.
Published: February 2004

An experiment which involves the participation of three nuclear spin species is carried out to accomplish sensitive double-resonance detection of nuclei. An ordered nuclear quadrupole spin system (A) is used to establish and monitor a metastable ordered state of a second abundant spin system (B). A double-resonance coupling is brought about between the B spin system and a third rare or weakly interacting system (C) to accomplish the detection of the C resonance. The usefulness of this scheme lies in the choice of an A system with a short spin–lattice relaxation time (T1A) and a B system with a long spin–lattice relaxation time (T1B). The choice of a long T1B increases the sensitivity of the experiment in that a long time is available during which effective nuclear dipole–dipole cross relaxation can occur between the B and C systems. With a short T1A, the cycling rate at which information is gathered to detect the C system is enhanced by a factor ∼T1B / T1A over that of the earlier two species double-resonance method. For increased sensitivity T1B can be chosen arbitrarily long, while for the purposes of an increased rate of data acquisition, T1A can be chosen arbitrarily short, thus producing an efficient double-resonance scheme. This scheme is applied to a 12% deuterium enriched sample of paradichlorobenzene. The nuclear quadrupole coupled Cl35 reservoir acts as the A system. The zero field nuclear quadrupole resonance system (at 34.78 mHz at 77°K) supplants the usual high field stabilized magnet and power supply required in an NMR double-resonance experiment. The B proton system has a zero field lifetime of 46 sec, and approximately a 1 h lifetime at 135 G. The C systems investigated are (1) deuterium and (2) the naturally abundant 13C nuclei in paradichlorobenzene. An analysis of double-resonance detection of I = 1 spin systems is given and shows that for a well resolved nuclear quadrupole asymmetry η splitting, a double resonance cannot be detected because of the nonsecular character or quenching of cross-relaxation interaction terms. The analysis is extended to include the unquenching effect of constant magnetic fields and the integer I > 1 quadrupole system is discussed. The observation of the 13C resonance is the first reported observation through the nuclear magnetic resonance techniques of the 1.1% naturally abundant 13C in a solid.
Electronic Structures of Polymers Using the Tight-Binding Approximation. I. Polyethylene by the Extended Hückel Method
Authors: Imamura Akira
Published: February 2004

The formulas for the electronic structure of the polymer were given in terms of the extended Hückel method by the use of the tight-binding approximation. Then, the electronic structure of polyethylene was calculated by means of these formulas to search for the most stable conformation. It was found that the fully extended all-trans state was the state of minimum energy which was in harmony with the experiments. Moreover, the charge distributions on polyethylene with various conformations were calculated and compared with those of n-propane, n-pentane, and n-heptane calculated by the extended Hückel method.
Quantum Mechanical Model of Three-Body Rearrangement Scattering. I. Formal Solution of the Helmholtz Equation on a Square
Authors: Robinson Peter D.
Published: February 2004

Solutions of the Helmholtz equation (∂2 / ∂x2 + ∂2 / ∂y2 + k2 + 1)Ψ = 0 describing a simple scattering process in an L-shaped region are studied. To obtain the correct expansion for ψ(x, y) on the square corner of the L shape when k = 1, it is found necessary to replace terms sinkx siny and sinx sinky by sinx siny and (x cosx siny–y cosy sinx). Terms similar to the latter have been neglected by previous authors and spurious resonances found in consequence.
EPR Studies on Trapped Species Produced by Tritium β Particles in Alkaline and Acid Ices at 77°K
Authors: Hase Hirotomo , Kevan Larry
Published: February 2004

EPR studies were performed on 60Co γ-irradiated 6M and 10M NaOH and 11M H2SO4 frozen solutions at 77°K and on similar frozen solutions which were tritiated with T2O. The yield of trapped species was always larger in the γ-irradiated systems than the corresponding yield in β-irradiated systems. The γ / β yield ratios were in semiquantitative agreement with similar ratios in liquid solutions. This is discussed in terms of different mean linear energy transfer for tritium β and 60Co γ radiation. Paramagnetic relaxation studies versus radiation dose were carried out on the tritiated systems and compared with previous results on γ-irradiated systems. For trapped H atoms in acid ice a spatially uniform distribution was found for both β and γ radiolysis. Trapped electrons in alkaline ice show a nonuniform distribution for γ radiolysis characterized by a finite spur radius. The distribution is also nonuniform in β radiolysis, but the average spur radius is larger. Surprisingly, the local concentration of trapped electrons appears smaller in β compared to γ radiolysis. A greater fraction of overlapping spurs in β radiolysis can account for these results.
Phase Velocity and Attenuation of Hypersound in Water of Different Isotopic Constitution
Authors: Shaham-Bronstein J. , Sarid D. , Low W.
Published: February 2004

Measurements of the phase velocity and the attenuation of sound in H2O16, D2O16, and H2O18 at 4.2 and 0.9 GHz, respectively, are reported. Spontaneous Brillouin scattering techniques and an injected phonon technique were employed. The phase velocities of D2O16 and H2O18 are very similar; classical theories cannot explain the experimental results. The values of α/f2, the attenuation α divided by the frequency squared, are higher for H2O18 and D2O than for H2O16.
Pulse Radiolysis Studies. XVI. Kinetics of the Reaction of Gaseous Hydrogen Atoms with Molecular Oxygen by Fast Lyman-α Absorption Spectrophotometry
Authors: Bishop W. P. , Dorfman Leon M.
Published: February 2004

The pulse radiolysis method has been used to produce ground-state hydrogen atoms in gaseous hydrogen and has been combined with fast Lyman-α absorption spectrophotometry to observe these atoms directly with microsecond time resolution. The technique has been used to study the kinetics of the reaction H + O2 + M = HO2 + M, where M is H2. The rate constant for this reaction was found to have the value (1.7 ± 0.4) × 1010M−2·sec−1 at 298°K. This value, together with earlier data for Ar as third body, gives kH2 / kAr = 2.0 at 298°K for the ratio of the efficiencies of H2 and Ar as third body in this reaction.
Photoemission of Electrons from Tellurium into Sulfur Single Crystals
Authors: Williams R. , Sinencio F. Sanchez
Published: February 2004

Measurements have been made of the photoemission of electrons from tellurium into sulfur single crystals. The quantum yield as a function of photon energy has an exponential form that has not previously been reported for internal photoemission. A part of the spectrum at higher energies has a different form. The exponential part of the spectrum is interpreted on the basis of the hopping model for electron conductivity in sulfur. Capture of a photoexcited electron by a sulfur molecule in the crystal is believed to be the decisive step in the process. The form of the photoemission spectrum at higher energies may be related to the conduction band that has recently been reported for sulfur.
Magnetic Properties and Molecular Quadrupole Tensor of the Water Molecule by Beam-Maser Zeeman Spectroscopy
Authors: Verhoeven J. , Dymanus A.
Published: February 2004

The hyperfine and Zeeman components of the 3–2–22 and 43–51 transitions of D2O, the 22−21 transition of HDO, and the 6−5−5−1 transition of H2O have been measured with a beam-maser Zeeman spectrometer. This allowed determination of the elements of the magnetic moment tensor Ggg and of the anisotropic part of the magnetic susceptibility tensor (χgg–χAv) for D2O. The best fit results are (for χgg–χAv in 10−8kHZ G−2): Gaa = 0.32530(10), Gbb = 0.36009(22), Gcc = 0.32513(15), χaa–χAv = 3.88(20), χbb–χAv = − 1.66(40), χcc–χAv = − 2.23(30). From these values the elements of the molecular quadrupole moment tensor for D2O have been determined (in 10−26 esu·cm): θaa = 2.72(2), θbb = − 0.32(3), θcc = −2.40(2). The sign of the molecular electric dipole moment and the validity of the isotopic invariance of the electronic charge distribution have been investigated by comparing the molecular magnetic moments of D2O, HDO, and H2O. The obtained experimental values for several one-electron properties are in fair agreement with recent accurate ab initio calculations.
Theoretical Studies of Hot-Atom Reactions. II. Yields for Exchange Reactions of Hot Tritium Atoms with Hydrogen and Deuterium Molecules: Simple Models for Nonreactive Scattering
Authors: Porter R. N. , Kunt Sinan
Published: February 2004

Results of calculations of hot-atom yields and isotope effects for T atoms in H2 and D2 are reported for a variety of compositions. Use is made of the integral reaction probability formalism, quasiclassical reaction cross sections, and three simplified models for nonreactive scattering which preserve the energy independence of the average logarithmic energy loss. Theoretically predicted isotope effects are in good agreement with both high-energy T-recoil and low-energy photodissociation experiments for unmoderated systems. Anisotropic nonreactive scattering models give theoretical results generally in better agreement with experiment than does an isotropic model. The detailed energy and composition dependence of the hot-atom yield is examined and the errors incurred in the use of hot-atom kinetic theory are quantitatively analyzed. The kinetic-theory prediction that the high-moderator isotope effect is given by the ratio of the reactivity integrals and that the value is independent of the moderating mechanism is verified by results of the general theory for both 4He- and Ar-moderated systems. Explanation of discrepancies between the theoretical and experimental isotope effects in the high-energy limit for Ar-moderated systems appears to require calculations which make fuller use of the general integral reaction probability formalism.
Curve-Crossing Calculations for Ion-Pair Formation by Oxygen Incident on Alkalies
Authors: van den Bos J.
Published: February 2004

The Landau–Zener–Stueckelberg approximation has been applied to the process of forming a singly negative oxygen ion and a positive alkali ion by oxygen incident on one of the alkalies Na, K, Rb, or Cs. A central-field potential model with an adjustable parameter is used to produce the wavefunctions with eigenenergy as close as possible to the experimental value. The impact parameter method has been used to calculate cross sections for oxygen kinetic energies from 20 eV to 10 keV.
Photochemistry of Aromatic Olefins. I. Photochemical cis–trans Isomerization of 1-Phenyl-2-butene
Authors: Nakagawa C. S. , Sigal P.
Published: February 2004

The photochemical cis–trans isomerization of 1-phenyl-2-butene has been studied. The isomerization takes place through both intermolecular and intramolecular energy transfer from the phenyl to the olefin groups. Both singlet–singlet and triplet–triplet energy transfer processes are operative in the system. The rates of intramolecular energy transfer are obtained as 1 × 106 sec−1 for singlet–singlet and 2 × 106 sec−1 for triplet–triplet. The intersystem crossover yield of the phenyl moiety is calculated to be 0.65 or less.
Adsorption of Oxygen on the (110) Plane of Tungsten
Authors: Kohrt Carl , Gomer Robert
Published: February 2004

The sticking coefficients and desorption kinetics of oxygen on a (110) tungsten crystal have been investigated by a step desorption/reflection technique. Sticking coefficients follow a generalized Kisliuk model, if allowance for reflection on first impact with the surface is made. Unlike CO on (110) W, reflection of O2 is appreciable and appears to have an activation energy of 0.6 kcal, with respect to substrate temperature. Desorption follows first-order kinetics and has an activation energy of ∼ 92 kcal. The process is complex, however, as shown by the variation in pre-exponential with surface treatment. A mechanism involving the formation and subsequent decomposition of two distinct surface oxide phases is postulated and shown to fit the experimental results. On the basis of this mechanism the observed activation energy corresponds to the process oxide→mobile adsorbed O, and it is shown that this implies an upper limit of 126 kcal for the heat of adsorption of O atoms on (110) W.
Exact Treatment of the Long-Range Dipole–Dipole Interaction between Two Helium Atoms
Authors: Alexander Millard H.
Published: February 2004

We present a new expression for the long-range dipole–dipole interaction coefficient in terms of a polarizabilitylike response function. Using certain results of Schwartz, we are able to evaluate this coefficient in the case of the interaction between two helium atoms and, by careful error analysis, to set accurate error bounds to this quantity. We obtain C6 = 1.4605 ± 0.0025.
Electron Paramagnetic Resonance Studies of a Viscous Nematic Liquid Crystal
Authors: Fryburg G. C. , Gelerinter E.
Published: February 2004

We have studied the order as a function of temperature in the liquid crystal bis(4′-n-octyloxybenzal)-2-chloro-1,4-phenylenediamine using vanadyl acetylacetonate as a paramagnetic probe. The order found in the upper part of the mesophase (105–179°C) was normal. However, in the lower part of the mesophase (40–105°C) the order found was much higher than ordinarily observed, approaching complete alignment near the melting point. In addition, the EPR lines assumed an unusual shape in this lower temperature region. The observations were accounted for by assuming the liquid crystal was too viscous to allow free tumbling of the probe molecules, and by developing a new model in which a spatial rather than a temporal average was performed. Supporting evidence for the validity of the assumption was obtained experimentally by demonstrating that the liquid crystal had an unusually long response time for reorientation in the magnetic field.
Theoretical Interpretation of the Electron Scattering Spectrum of CO2
Authors: Claydon Charles R. , Segal Gerald A. , Taylor Howard S.
Published: February 2004

A theoretical study of processes observed in electron–CO2 scattering experiments is presented. Potential curves for CO2− are calculated to determine which scattering processes proceed through formation of short-lived negative molecule–ion compound states. The four dissociative attachment processes occurring below 20-eV incident energy are shown to result from four different electronic states of CO2−. Vibrational excitation of CO2 in the 3.0–4.5-eV incident energy range is shown to proceed through compound-state formation. The calculated energies of the compound states are shown to agree with the absorption spectra of CO2− trapped in crystalline solids. The inelastic scattering below 3.0 eV is shown to be nonresonant and of a direct nature. For this process the leading term in the angular dependence of the cross section is determined by dipole selection rules, which leads to strong forward peaking. For small-angle scattering the cross section is shown to be about 10−16 − 10−17 cm2 in magnitude. Further, the discussion on direct vibrational excitation cross sections will generally be valid for other nonpolar molecules with infrared-active vibrational modes.
Luminescence of Systems Containing Hydroxyl Ion
Authors: Maria H. J. , McGlynn S. P.
Published: February 2004

A fluorescence of alkali halide single crystals doped with the corresponding alkali hydroxide has been observed and is attributed to the A 2Σ+ → X 2Π emission of a photoproduced hydroxyl radical. A phosphorescence of systems containing the hydroxide ion has also been noted at λ ∼ 400 mμ and is attributed to a Σ−4 → X 2Π emission of the OH radical. Photoprocesses in systems containing the OH− ion, as well as in aqueous systems containing certain salts and acids, are discussed in a qualitative way.
Hydrogen Bonding of H2+ to the He Atom: Energy Surface for Linear HeH2+
Authors: Edmiston C. , Doolittle J. , Murphy K. , Tang K. C. , Willson W.
Published: February 2004

Using pseudonatural orbitals as a basis for the superposition of configurations (SOC), we have calculated the adiabatic potential energy surfaces for linear HeHH+ and HHeH+. Except for the different basis set of Gaussian functions used, these calculations were carried out identically to one reported earlier for linear H3. It is found that HeHH+ has a potential energy minimum ∼ 5 kcal deep for RHeH ≅ 2.0 a.u., and RHH ≅ 2.0 a.u. This “hydrogen bonding” effect is given by the Hartree–Fock results and is little changed by SOC. HHeH+ is found to have a high potential energy barrier of ∼ 25 kcal for the symmetric complex, RHHe = RHeH ≅ 2.1 a.u.
Raman Scattering in Crystalline Polyethylene
Authors: Boerio F. J. , Koenig J. L.
Published: February 2004

The Raman scattering in crystalline polyethylene, deuterated polyethylene, and n-paraffins has been investigated as a function of temperature. Crystal-field splitting of the A1G methylene bending mode observed at room temperature increases at − 160°C in both polyethylene and deuterated polyethylene. No splitting of the B2G skeletal stretching mode and the B3G methylene twisting modes in polyethylene is observed at room temperature, but the two components of the space group fundamental are resolved at − 160°C. Similarly, splitting of the B2G methylene wagging mode in deuterated polyethylene is observed at − 160°C but not at room temperature. The observed crystal-field splittings are discussed in terms of splittings calculated from repulsive forces between hydrogen atoms on neighboring chains in the polyethylene crystal.
Electric Dipole Moment of SiO and GeO
Authors: Raymonda John W. , Muenter John S. , Klemperer William A.
Published: February 2004

The molecular beam electric resonance spectra of SiO and GeO have been measured. The electric dipole moments (in Debye) of SiO and GeO in the lower vibrational states are: VSiO28GeO7403.09823.282413.11783.303223.13723.323933.1574 The difference between observed and calculated dipole moment is quite similar in CO and SiO.
Fine Structure and Dipole Moment of Metastable a3Π Carbon Monoxide
Authors: Stern Richard C. , Gammon Richard H. , Lesk Michael E. , Freund Robert S. , Klemperer William A.
Published: February 2004

The radio-frequency spectrum of the first four (υ = 0–3) vibrational states of the a 3Π metastable state of 12C16O has been measured in molecular beam electric resonance from 0 to 500 MHz. Lambda doubling transitions have been observed in J = 2–7 of Ω = 2, and in J = 1 and 2 of Ω = 1 at zero electric and magnetic field and as a function of electric field. An exhaustive reanalysis of a 3Π optical data is presented, in which the spin–orbit, rotational, spin–spin dipole–dipole, and potential-energy parameters have been accurately determined. Together with parameters determined from the rf spectrum, the resulting set of fine structure parameters predicts the complete lambda doubling spectrum to better than 1 in 104 for J = 0–50, υ = 0–3. The predicted frequencies below 5 GHz are tabulated for possible radio-astronomical measurement of a 3Π CO. The Stark effect allows the a 3Π dipole moment to be determined to an absolute accuracy of 2 in 104, and the small dependence upon spin–orbit, vibrational, and rotational state has been accurately measured.
Dipole Transition Moments of Chromate Ion
Authors: Tandon S. P. , Surana S. S. L.
Published: February 2004

A LCAO–MO parametric calculation of chromate ion in terms of a single quantity β, the ligand mixing coefficient, has been carried out. The values of both dipole length (QtheoretL) and dipole velocity (QtheoretV) transition moments for A11 → 1T2 (t1 → 2e) transition of the chromate ion have been computed as functions of ligand mixing coefficient on the bases of Slater-type of orbitals (STO's) and more exact AO's formed by combination of 2p STO's with double-ζ3d AO's which duplicate as nearly as possible the SCF AO's. The contribution of charge transfer integral (Q1) and one-center (Q2) and two-center (Q3) ligand integrals to the transition moments as functions of β have also been estimated. Whereas QtheoretV is sensitive, QtheoretL is insensitive to change in the 3d radial function. The dipole transition moments are in better agreement with the experimental value when the Richardson's orbitals are used instead of STO's. The use of dipole velocity operator leads to better results than that of dipole length operator. As a by-product based on simplifying assumptions, the chromate ion appears to possess less π bonding than the permanganate ion.
Electron Paramagnetic Resonance of Dipyridyl-Coordinated Ag2+(4d9)
Authors: Halpern T. , McKoskey Susan M. , McMillan J. A.
Published: February 2004

The paramagnetic resonance spectrum of solid [Ag dipy2] S2O8 and its solution in nitric acid have been observed at 77°K. The frozen solution exhibits silver hyperfine and nitrogen superhyperfine structure. Due to a strong axial g anisotropy it is possible to determine the principal values of the hyperfine interaction tensors. With these values it is found that the hole in the silver d shell is highly delocalized. Wavefunctions for the unpaired electron are calculated on the basis of the experimental results. Exchange narrowing in the solid wipes out the hyperfine structure.
Microwave Spectrum of Fluoroacetone
Authors: Saegebarth Ellen , Krisher Lawrence C.
Published: February 2004

The microwave spectrum of fluoroacetone has been studied in the region 18–35 GHz, and transitions arising from one rotamer have been assigned. This rotamer has all the heavy atoms in a plane with the fluorine and oxygen atoms trans to one another. The rotational constants are A = 8658.06, B = 4021.64, and C = 2845.12 MHz, which give Ia + Ib − Ic = 6.406 amu·Å2. Stark effect measurements give the dipole-moment components: μa = 0.907 ± 0.020 D, μb = 0.76 ± 0.05 D, μ = 1.18 ± 0.05 D. Satellite lines arising from excited states of both the methyl and CH2F torsions have been identified. The splittings of the rotational lines into A and E components have been analyzed using as a model a rigid methyl group attached to a rigid framework. This treatment gives a barrier to internal rotation of the methyl group of 1488 ± 30 cal/mole for the ground state and 1467 ± 30 cal/mole for the first excited methyl state. A model which takes into account coupling of the −CH3 and −CH2F torsional vibrations is also considered.
Theory of Penning Ionization. I. Atoms
Authors: Miller William H.
Published: February 2004

The theory of Penning ionization (PI) and related associative ionization (AI) is developed and examined in a classical, semiclassical, and quantum mechanical framework, the correspondence between the several descriptions being explicitly deduced; formulas for total cross sections for PI and AI, angular distributions for PI, and the distribution of energies of the ionized electron are presented. The possibility of anomalous structure is seen to appear in the energy distribution of the ejected electrons if the difference between the A*–B and A–B+ potential curves has a local extremum as a function of internuclear distance. Classically, this appears as an infinity in the distribution of electron energies, but the quantum mechanical expressions are reduced to obtain a uniformly valid approximation; the transition region through the classical infinity is characterized by an Airy function.
Stark Spectroscopy of NH3 ν2 Band by 10-μ CO2 and N2O Lasers
Authors: Shimizu Fujio
Published: February 2004

The Stark spectrum of the ν2 band of 14NH3 is studied using CO2 and N2O lasers equipped with a grating for the laser line selection. About 100 coincidences between NH3 lines of J≤7 and the laser lines are obtained. The NH3 line positions relative to the laser lines are calculated using the data for the dipole moment obtained by the same experiment.
K+, Na+, and Li+ Desorption from Oxygenated Tungsten
Authors: Daley Howard L. , Yahiku Arthur Y. , Perel Julius
Published: February 2004

The desorption times for K+, Na+, and Li+ from continuously oxygenated tungsten have been measured in the 1000–1500°K temperature range using an ac modulation technique. Under conditions of low alkali-metal coverage on the surface, the experimentally derived values of desorption energy (l) and zero intercept (τ0) in the Arrhenius expression τ = τ0exp(l / kT) sec are K+: l = 1.5 eV; τ0 = 2 × 10−10sec, Na+: l = 1.6 eV; τ0 = 7 × 10−10sec, Li+: l = 2.2 eV; τ0 = 2 × 10−10sec. Alteractions of the surface using an oxygen spray produced noticeable effects, particularly for K+.
Molecular Beam Kinetics: The Differential Cross Section of the Reaction Cl+Br2
Authors: Blais N. C. , Cross J. B.
Published: February 2004

The chemical reaction Cl+Br2 was studied using a crossed molecular beam apparatus. Measurements of the distribution of BrCl emitted from the reaction volume as a function of angle from the parent beams were made. The velocity distribution of BrCl was also measured at six angles, widely spaced over the angular distribution. Analysis of the data in center-of-mass coordinates reveals that the product is scattered sharply in the direction of the initial chlorine-atom velocity (forward). After scattering, about 75% of the total energy is in the BrCl internal modes. However, the distribution of this fraction is a function of the center-of-mass angle at which BrCl is scattered; the distribution broadens with increasing scattering angle. A compilation of trajectory calculations of one trial potential, simulating a near stripping model, shows a reasonably good fit to the experimental center-of-mass distributions. We conclude that the forces acting on the departing bromine atom are small at all distances.
Triplet-State Electron Spin Resonance of the Aromatic Amino Acids and Proteins
Authors: Zuclich Joseph
Published: February 2004

Electron spin resonance spectra have been observed in irradiated glassy solutions of the aromatic amino acids and related molecules. The zero-field splitting parameters of the amino acids (in cm−1) were found to be: tryptophan, D = 0.0984, E = 0.0410; tyrosine, D = 0.1301, E = 0.0558; tyrosinate ion, D = 0.1080, E = 0.0540; phenylalanine, D = 0.1475, E = 0.0439. The technique of magnetophotoselection was applied to determine the relative orientations between the principal magnetic axes and the first two electronic transition moments of tryptophan, tyrosine, and the tyrosinate ion. The Δm = 2 signals associated with tyrosine and tryptophan have been observed in a number of irradiated frozen protein solutions. In the case of ovalbumin the Δm = 1 spectrum of the tryptophan residues was observed. In every case, the protein triplet signals appeared to be identical to those of the free amino acids.