bluuebunny/crossref_metadata_2025 huggingface dataset:
Intrinsic Viscosity of a Once-Broken Rod
Authors: Yu Hyuk , Stockmayer Walter H.
Published: January 2005

The intrinsic viscosity theory of Kirkwood, Riseman, and Auer is applied to a molecular model of two long rods of equal length connected by a flexible joint. In the nondraining limit, the intrinsic viscosity of a solution of such molecules is predicted to be 15% lower than that for rigid rods of the same molecular weight, in good agreement with experimental results of Teramoto, Yamashita, and Fujita. This reduction in intrinsic viscosity is smaller than would be expected from the radius of gyration.
Valence States of Carbon in π-Electron Systems. I. Alternant-Hydrocarbon Ground States
Authors: Silverstone Harris J. , Joy Hubert W.
Published: January 2005

When the molecular wavefunction is described in part by molecular-orbital theory, new terms (Coulomb self-repulsion integrals) enter the valence-state energy over and above the classic valence-bond valence state of Van Vleck. Atomic orbitals for π-electron theory are obtained by minimizing the energy of carbon in a valence state appropriate for alternant-hydrocarbon ground states. The 2pπ orbital so obtained with a non-integral-n ``double'' basis, with a simple valence-bond σ wavefunction and a simple molecular-orbital π wavefunction, gives a one-center Coulomb repulsion integral 〈2pπ 2pπ | 1/r12 | 2pπ2pπ〉=12.38 eV, compared to the semiempirical value of ∼11 eV.
Atom—Molecule Kinetics Using ESR Detection. II. Results for D+H2→HD+H and H+D2→HD+D
Authors: Westenberg A. A. , de Haas N.
Published: January 2005

The wide temperature range, fast flow kinetic system with ESR atom detection described recently has been used to measure rate constants for the isotopic reactionsD+H2→HD+H,H+D2→HD+D,over the range 250°—750°K and 300°—750°K, respectively. The precision of the data at a given temperature is about ±5%, except at the lowest temperature in each case where it is ±8%. It is believed that this also represents the accuracy. In the range 450°—750°K both sets of data are Arrhenius linear and obey (cubic centimeters mole−1·second−1) k1=4.4×1013exp(−7610/RT);  k2=4.9×1013exp(−9390/RT).Interpretation of the linear portion is made in terms of absolute rate theory with no tunneling. A potential-energy surface constructed by fitting the experimental activation energies by the Sato method as described by Weston is in essential agreement with the latter's results for the H3 complex. The properties of the complex give pre-exponential factors in satisfactory agreement with experiment. The experimental ratio k1/k2 in the linear region is closely predicted simply by the limiting form using the ratio of collision frequencies and the zero-point energy difference between H2 and D2. It is shown that the data in the nonlinear region below 450°K give apparent ``tunnel corrections'' τ for the two reactions which are qualitatively of the form τ1<τ2, while all theories predict τ1>τ2.
Raman Spectrum of Potassium Tantalate
Authors: Nilsen W. G. , Skinner J. G.
Published: January 2005

The Raman spectrum of KTaO3 has been measured as a function of temperature from 300° to 8°K. An argon-ion laser was used as the illuminating source and the scattered light was analyzed with an in-tandem grating spectrometer. The spectrum consisted entirely of second-order Raman processes originating for the most part from the Brillouin zone boundary where the combined density of states tends to be very large. No first-order Raman spectra were observed, in agreement with the known selection rules for the cubic perovskite structure. The scattering tensor deduced from the observed spectra appeared to be largely if not entirely diagonal, but the magnitude and sign of the individual diagonal elements were not investigated. Further, the predominant structural features of the spectrum are due to combinations and overtones between transverse modes. Two rather weak longitudinal overtones were found and other similar two-phonon spectra might be hidden under other more intense spectra.
Vacuum-Ultraviolet Chemiluminescence in the Reaction of Atomic Oxygen with Acetylene
Authors: Marmo F. F. , Padur J. P. , Warneck P.
Published: January 2005

Vacuum-ultraviolet emission from the reaction of atomic oxygen with acetylene was investigated spectrographically and with photoionization detectors. The spectrum was observed at wavelengths above 1400 Å and consisted entirely of bands belonging to the fourth positive system of CO. At short wavelengths, the intensity declines rapidly, but radiation was detected with photoionization detectors filled with xylene (1425–1475 Å), NO (1100–1340 Å), and CS2 (1100–1260 Å). The high-energy limit of the emission is, correspondingly, greater than 226 kcal/mole or almost 10 eV. The dependence of the intensity on initial reactant and third-body concentrations was investigated and compared with similar concentration-dependence data for the intensity of the CH band at 4300 Å. The results show that the vacuum-ultraviolet CO emission cannot be produced by either third-body recombination of carbon and oxygen atoms or by the reaction of atomic oxygen with excited CH radicals in the A2Δ state. The reaction proposed by Becker and Bayes O+C2O→CO (A 1Π)+CO (X 1Σ)can explain the observed emission if it is assumed that a fraction of the reaction C2O radicals are vibrationally excited.
Paramagnetic Resonance Study of Liquids during Photolysis. IV. Free Radicals from Acetaldehyde, Diacetyl, and Acetoin
Authors: Zeldes Henry , Livingston Ralph
Published: January 2005

Paramagnetic resonance spectra in solutions at room temperature were studied during irradiation with ultraviolet light. The radical CH3ĊOHCOCH3, the acetoin radical, was produced from diacetyl in the presence of good H-atom donors. Using p-dioxane as the donor, the radical produced from the donor was also seen. The acetoin radical and CH3ĊHOH were produced from acetaldehyde in the absence of a good H donor. By adding a good donor to acetaldehyde solutions, the yield of the acetoin radical was suppressed, and the radical produced from the H-atom donor appeared. Reasonable reactions are proposed. In nearly neutral aqueous solutions or in slightly alkaline isopropyl alcohol solution, the acetoin radical was converted to the anion CH3COCOCH3−. The parameters of the acetoin radical and of its anion were measured in a number of solutions. The radical CH3ĊHOH was produced from acetoin in a variety of solutions, showing that cleavage of the acetoin molecules takes place. The spectrum of the acetoin radical underwent striking changes as acid was added to the solution. Spectra were calculated for a simple, reasonable exchange scheme. Calculated and observed spectra agreed very well for a large range of acid concentrations.
Transfer of Fine Structure in Nuclear Magnetic Double Resonance
Authors: Freeman R. , Gestblom Bo
Published: January 2005

In a nuclear magnetic double-resonance experiment, irradiation of one of the X resonances of an AX spin system with a second rf field γXH2/2π≪| JAX | splits each connected A line into a doublet; if there is any fine structure on the X resonance due to coupling to some third group of nuclei Z, and if γXH2/2π≫| JXZ |, the same fine structure can be observed on the two components of the A doublets, except that the splitting is reduced by a factor of 2. Thus, under suitable conditions the double resonance process may be said to ``transfer'' fine structure splitting from the irradiated to the observed resonance. In cases where there is also fine structure present on the A resonance due to a small coupling JAZ, the transferred splitting combines with it to give a new splitting | JAZ+½JXZ | for progressively connected lines, or | JAZ—½JXZ | for regressively connected lines. This technique has been used to detect a very small long-range coupling (+0.05 Hz) in 3-bromothiophene-2-aldehyde, where it is usually obscured by magnet field inhomogeneity. A second application is the indirect determination of the magnitude and sign of the coupling between carbon-13 and deuterium in methyl-d3-acetylene, J(13C–C–D)=−1.5 Hz.
Molecular Structure of Cyclopropane from Its Proton NMR in a Nematic Solvent
Authors: Snyder Lawrence C. , Meiboom Saul
Published: January 2005

The proton nuclear magnetic resonance spectrum of cyclopropane has been measured in nematic p,p′-di-n-hexyloxyazoxybenzene. The spectrum has been analyzed by determining the parameters of a spin Hamiltonian which permit its computer simulation. Several ways to determine the structure of cyclopropane from the elements of the spin Hamiltonian are employed, with all giving very similar geometric parameters. With the assumption of D3h symmetry for cyclopropane, and a C–C bond length of 1.510 Å determined by electron diffraction, we are able to fit the NMR spectrum with a structure having a C–H bond length of 1.123 Å and an HCH angle of 114.4°, which are to be compared with the corresponding gas phase electron diffraction values of 1.089±0.003 Å and 115.1±1°. The anisotropic motion corresponds to the molecular plane tending to be parallel to the applied magnetic field. For indirect spin—spin couplings we find JHH(cis)=+9.5±1 Hz, JHH(trans)=+5.5±1 Hz, and a positive sign for JCH, the indirect coupling between 13C and a directly bonded proton. The effects on the observed spectrum of JHH(gem) and JCH′, the indirect coupling of carbon 13 to a proton on another carbon, are too small to permit their determination. The shortness we find of the C–C bond relative to the C–H bond length is interpreted as a result of molecular vibrations. It appears that the analysis of NMR in nematic media provides an important method of precise molecular structure determination.
Flash Pyrolysis and Kinetic Spectroscopy of Ammonium Perchlorate
Authors: Petrella R. V. , Spink T. L.
Published: January 2005

The flash pyrolysis of ammonium perchlorate has been studied by kinetic spectroscopy. The absorption spectra of OH, ClO2, ClO, NO, and NH are described, and the relative concentration of each is given for the period of 1000 μsec following the initial photoflash. A mechanism for the flash pyrolytic decomposition of ammonium perchlorate is given in terms of the spectra observed. The flash pyrolytic data support the evidence that the initial step in the decomposition of ammonium perchlorate leads to the formation of ammonia and anhydrous perchloric acid. Subsequent reactions consist of the high-temperature oxidation of ammonia by perchloric acid.
Study of ``Non-Fickian'' Diffusion Anomalies through Time Lags. I. Some Time-Dependent Anomalies
Authors: Petropoulos J. H. , Roussis P. P.
Published: January 2005

The importance of permeation time-lag measurements for the detection and study of ``anomalous'' diffusion in a simple way is discussed. Measurement of a total of four time-lag quantities is proposed and their properties investigated for time-dependent ``non-Fickian'' behavior, particularly in polymer—penetrant systems near and below the glass-transition temperature. Detailed calculations were carried out for this case, on the basis of the widely accepted view that the ``non-Fickian'' anomalies observed are due largely to reversible structural relaxation processes in the substrate. The predicted behavior of the time lag as a function of penetrant concentration exhibits certain general features, which should be of use for the identification of this kind of ``non-Fickian'' anomaly. Time-dependent ``non-Fickian'' anomalies in substrates, where immobilizing chemical reaction or diffusion into sinks can occur independently of a main ``Fickian'' diffusion process, have also been examined. Such anomalies appear to have no effect on any of the time-lag parameters considered here.
Study of ``Non-Fickian'' Diffusion Anomalies through Time Lags. II. Simpler Cases of Distance- and Time—Distance-Dependent Anomalies
Authors: Petropoulos J. H. , Roussis P. P.
Published: January 2005

Study of the properties of the time-lag parameters defined in Part I is here extended to the case where the solubility (S) and thermodynamic diffusion (DT) coefficients are functions of position X in the direction of flow. Such studies permit the detection and, characterization of this type of ``non-Fickian'' diffusion behavior. This is still possible, though in a more limited way, when S and DT also depend on time. The properties of the time-lag parameters mentioned above have been investigated in some detail for cases amenable to analytical treatment; namely when S and DT are functions either of X alone or of both diffusant activity, a and X, provided that a, X are separable in the appropriate functions. Similarly, it is shown that when S and DT also depend on time t a limited study of both kinds of ``non-Fickian'' anomaly is possible, if a, t are separable from X in S(a, X, t), DT(a, X, t).
High-Pressure Mössbauer Studies on α-Fe2O3, FeTiO3, and FaO
Authors: Vaughan R. W. , Drickamer H. G.
Published: January 2005

The effect of pressure has been measured on the Mössbauer resonance of α-Fe2O3, FeTiO3, and FeO. The first two compounds have very similar structures but with ferric and ferrous iron, respectively. The ferrous iron shows a significant increase in electron density at the nucleus with pressure, while the electron density at the ferric nucleus is virtually independent of pressure. The direction of the quadrupole splitting in α-Fe2O3 changes sign at about 30 kbar. This may be associated with a Morin (spin—flip) transition which occurs at 260°K at 1 atm, or with a slight relocation of the iron ion in the unit cell, or with a combination thereof. Ferrous oxide, a nonstoichiometric material crystallizing in the fcc structure, partially transforms to a magnetic phase at about 50 kbar. The apparent change in isomer shift and quadrupole splitting with pressure indicates that the splitting is due to the defect structure.
Temperature Dependence of the Mössbauer Recoilless Fraction in Organotin Compounds
Authors: Stöckler H. A. , Sano H. , Herber R. H.
Published: January 2005

The temperature-dependent behavior of the Mössbauer effect recoil-free fraction associated with some organotin absorbers was investigated in the temperature range of 68° to 330°K. It was tentatively found that the recoil-free fraction of 119Sn in organotin compounds shows no systematic dependence on nearest-neighbor atom mass, ligand mass, molecular weight, coordination number with respect to the tin atom, macro or bulk chemical properties, isomer shift, or quadrupole splitting. The present investigation indicates, however, that a polymeric lattice structure which directly involves the 119Sn atom contributes significantly to a large recoil-free fraction.
Electron-Impact Studies of PbCl2, PbBr2, and PbClBr
Authors: Hastie J. W. , Bloom H. , Morrison J. D.
Published: January 2005

Using a quadrupole mass spectrometer, ionization efficiency curves have been obtained for both positive and negative ions resulting from the electron-impact ionization and dissociation of PbCl2, PbBr2, and PbClBr molecules. Both simple and ion-pair processes were identified. The values of the appearance potentials for the fragment ions indicate they are formed with little or no excess kinetic energy, hence the following ionization potential (I.P.) and electron affinity (E.A.) values were calculated: I.P. [PbCl2]=10.3, I.P. [PbBr2]=10.2, I.P. [PbClBr]=10.4, I.P. [PbCl]=7.5, I.P. [PbBr]=7.8, E.A. [PbCl]=1.0, and E.A. [PbBr]=0.9 eV. The accuracy is better than ±0.2 eV.
Studies of N4+ and N3+ Ion Formation in Nitrogen Using High-Pressure Mass Spectrometry
Authors: Asundi R. K. , Schulz G. J. , Chantry P. J.
Published: January 2005

The formation of the complex ions of nitrogen N4+ and N3+ has been studied at pressures up to 0.1 torr using a differentially pumped mass spectrometer and monoenergetic electron-beam techniques. The N4+ ion has an appearance potential of 15.0±0.1 eV, and exhibits a quadratic pressure dependence in the threshold region, consistent with the secondary reaction N2*+N2→N4++e. At electron energies greater than 17.5 eV, a cubic pressure dependence is observed, consistent with the secondary reaction N2++2N2→N4++N2. The reverse of this reaction has been shown to lead to an early onset of N2+ when a sufficiently large extraction field is used to impart the necessary kinetic energy to the N4+ ion. The N3+ ion has an appearance potential of 21.1±0.1 eV and exhibits a quadratic dependence at low pressures, consistent with the secondary reaction N2+(4Σu+)+N2→N3++N, proposed previously by Cermak and Herman. At higher pressures the N3+ pressure dependence deviates from quadratic due to the depopulation of the N2+(4Σu+) state. An analysis of this deviation in the N3+ pressure dependence provides an approximate estimate of the radiative lifetime of the N2+(4Σu+) of τ=8×10−6 sec and of the collisional destruction rate coefficient 〈QDv〉Av=2×10−9 cm3/sec.
Effect of Bond Formation on Electron Scattering Cross Sections for Molecules
Authors: Kohl D. A. , Bonham R. A.
Published: January 2005

Total differential scattering cross sections were obtained experimentally for molecular hydrogen, nitrogen, and oxygen. The cross section for helium was also measured and compared with a calculated cross section to calibrate the apparatus. The calculation of the binding energy from the data was carried out and compared with previous results. It was found that the scattering method with presently available experimental and theoretical techniques cannot give values comparable in accuracy to other methods for obtaining the binding energy itself but it is useful as a test of scattering theory. The binding energy obtained for hydrogen was in good agreement with the spectroscopic value. The binding energies which were obtained for nitrogen and oxygen were considerably higher than the accepted values. The experimental uncertainties were quite large but even so the results suggest that there may be significant deviations from the simple theory. Information about the molecular densities was obtained which may serve as a useful check of theoretically calculated wavefunctions. The data were not sufficiently accurate and numerical methods have not been developed to a point where quantitative calculations of the electron densities could be made from the experimental data. The relevant theoretical quantities needed for comparison with experiment are not yet available. Qualitative arguments indicate the observed intensities are consistent with what is known about the effect of binding on molecules.
Mass-Spectrometric Study of Ions in Xe, Kr, Ar, Ne at Pressures up to 40 torr: Termolecular Formation of the Rare-Gas Molecular Ions. Bond Dissociation Energy of Ar2+ and Ne2+
Authors: Kebarle P. , Haynes R. M. , Searles S. K.
Published: January 2005

The positive ions obtained from alpha-particle irradiation of the rare gases Xe, Kr, Ar, Ne were studied in the pressure range 5–40 torr. In all cases both the rare-gas molecular ion R2+ and the atomic ion R+ could be observed. The R2+/R+ ratio could be decreased by the addition of gases which react with R2+ and R+ through charge transfer. This technique led to a determination of the rate constant for the termolecular reaction R++2R→R2++R. The rate constant for argon is 6×10−32 cm6 atom−2·sec−1. The ratio of Hornbeck—Molnar ionization to direct ionization in Ar was found equal to 0.4. Xe2+ is a major ion in Kr (at 20 torr) containing 10 ppm xenon. The kinetics of the efficient formation of Xe2+ is examined. It is concluded that Xe2+ is formed by Kr2++Xe→KrXe++Kr followed by KrXe++Xe→Xe2++Kr. The rate constants for these two reactions are estimated at 10−10 cm3 molecule−1·sec−1. Both reactions must be exothermic. A schematic representation of the energies of formation of the Kr, Xe, homo- and heteronuclear ions is given. Changes in the charge-transfer spectrum of ethylene with change of the concentration ratio of R2+ and R+ are used to derive the ethylene charge-transfer spectrum due to R+ and R2+. The charge-transfer spectrum with R+ is in agreement with that obtained from experiments using low pressures and near-thermal velocity R+. The charge-transfer spectrum due to R2+ is used in conjunction with the breakdown graph of ethylene to obtain the recombination energy R.E. of R2+. The bond dissociation energy of R2+ is then estimated from D(R+—R)=I.P.(R)—R.E.(R2+). Values between 1.5–2 eV are obtained for the dissociation energies of Ar2+ and Ne2+.
Rotational Isomerism in Haloacetones. II. Iodoacetone
Authors: Cook Bobby R. , Crowder G. A.
Published: January 2005

Infrared spectra for the vapor, liquid, and solid states of iodoacetone, and for solutions of iodoacetone were obtained. There are two rotational isomers present in approximately equal concentrations in the liquid state, but the less polar form is present in excess in the vapor. The more polar form is present in excess in the solid. Assignment of some of the fundamentals was made.
Evaluation of the Equilibrium Constant for the N2O4 (g)=2NO2 (g) Reaction at 298.16°K from Light-Transmission Measurements
Authors: Harris Louis , Churney Kenneth L.
Published: January 2005

The absorption coefficient of NO2 (g) has been found to be both temperature and pressure dependent for the temperature range 299.71° to 376.52°K and pressures from 2 to 5 cm Hg, for the 5461-Å mercury ``line''. The equilibrium constants for the reaction N2O4 (g)=2NO2 (g), at the temperatures 299.71°, 303.70°, and 308.89°K, have been evaluated by combining precise transmittance measurements for the 5461-Å mercury line with the known vapor pressures of solid N2O4. ΔG°298.16 for the above change in state has been found to be 1.151±0.004 kcal/mole, which, when combined with the known value of ΔS°298.16, gives ΔH°298.16=13.640±0.100 kcal/mole.
Microwave Spectrum of IOF5
Authors: Pierce Stephen B. , Cornwell C. D.
Published: January 2005

The microwave spectrum of iodenyl pentafluoride IOF5 shows it to be a symmetric rotor with C4v symmetry. Rotational constants are B(I16OF5) =2131.09±0.01 Mc/sec and B(I18OF5) =2073.15±0.02 Mc/sec. The iodine nuclear quadrupole coupling constant is +552.9±0.6 Mc/sec, and the molecular dipole moment is 1.08±0.10 D. The coupling constant is discussed in terms of a simple molecular-orbital model.
Gas-Phase Electron Resonance Spectrum of ClO
Authors: Carrington Alan , Dyer Paul N. , Levy Donald H.
Published: January 2005

The electron resonance spectrum of ClO in the gas phase is described, and the theoretical analysis is discussed in detail. As a result of this analysis, values of the following molecular constants are obtained. The fine-structure constant A = − 282±9 cm−1, the rotational constant B0=0.622±0.001 cm−1 (for 35Cl16O), the 35Cl nuclear hyperfine constant h = 111±2 Mc/sec, and the 35Cl quadrupole coupling constant e2Qq=−88±6 Mc/sec. Corresponding values of the 37Cl hyperfine constants are also obtained. The results are discussed in terms of the expected ground-state electron configuration of the radical.
Electrical, Magnetic, and Superconducting Properties of Copper Disulfide
Authors: Munson Ronald A. , DeSorbo Warren , Kouvel J. S.
Published: January 2005

The physical properties of copper disulfide are correlated with those of the disulfides of the transition elements manganese through nickel, all of which have the pyrite structure, by the consideration of the effect of the anion crystal field upon the d-electron energy levels. Copper disulfide shows a weak paramagnetism which appears to follow a Curie—Weiss law below 100°K with a small localized moment, μeff2=0.34 μB2, and a paramagnetic Curie temperature equal to −25°. It is a metallic conductor with a specific resistivity of 2×10−3 Ω·cm at room temperature. The superconducting transition temperature is 1.56°±0.04°K.
Absolute Measurements of Elastic Cross Section for Small-Angle Scattering of Electrons from N2 and O2
Authors: Fink M. , Kessler J.
Published: January 2005

Absolute elastic cross sections are measured by electron scattering for N2 and O2 at 37 and 60 kV. (The angle range was 5 to 70 mrad.) The comparison between the measurements and the theory (atomic independent model) gives fairly good agreement for angles larger than 30 mrad. For smaller angles considerable deviations are found. Two qualitative arguments are given to show that these differences are due to chemical binding in these diatomic molecules.
Interpretation of Experimentally Determined Growth Rates of Ice Crystals in Supercooled Water
Authors: Pruppacher H. R.
Published: January 2005

The results of recent measurements of the growth rate of dendritic ice single crystals along the basal plane in supercooled water are presented. These results are discussed in the light of the theory of Bolling and Tiller for a heat-flow controlled-growth mechanism and in the light of the molecular kinetic theory developed by Cahn. It was found that the growth rate of ice dendrites in supercooled water cannot completely be understood on the basis of a heat-flow controlled-growth mechanism but has to be explained on the basis of the combined mechanisms of heat dissipation and molecular-growth kinetics. Our analysis of the growth kinetics showed that at bath supercoolings between 0° and 9°C the growth rate of ice dendrites varied with the square of the interface supercooling in accordance with a growth mechanism which involves the advance of a diffuse interface by a lateral motion of steps originating at screw dislocations. At bath supercoolings larger than 9°C the growth rate varied linearally with the interface supercooling in accordance with a continuous-growth mechanism by which the surface advances normal to itself without the need of steps. The deviations from this behavior made evident by some of the experimental results are explained in terms of a reduction of the growth rate of individual ice dendrites as a consequence of their thermal interaction.
High-Pressure Decomposition of Some Titanate Spinels
Authors: Akimoto S. , Syono Y.
Published: January 2005

The stability of titanate spinels has been investigated at high pressures and high temperatures with the aid of tetrahedral anvil-type and piston-cylinder-type high-pressure apparatus. Decomposition of titanate spinels M2TiO4 (M=Mg2+, Fe2+, and Co2+) to MTiO3 with ilmenite structure plus MO with sodium chloride structure has been found to occur. Equilibrium phase boundaries of these reactions are determined as P(kbar)=−18+0.019T(°C) for Mg2TiO4→MgTiO3+MgO; P(kbar)=11+0.025T(°C) for Fe2TiO4→FeTiO3+``FeO''; and P(kbar)=−9+0.035T(°C) for Co2TiO4→CoTiO3+CoO. It is suggested that similar decomposition of silicate spinels may occur in a lower mantle of the earth.
Paramagnetic Resonance of the Triplet State of Tetramethylpyrazine
Authors: Vincent James S.
Published: January 2005

EPR measurements are reported for solid solutions of tetramethylpyrazine (TMP) in durene under ultraviolet irradiation at 77°K. The fine structure of the paramagnetic resonance spectrum observed at 9.2 and 35 GHz may be described by the spin Hamiltonian H=gβH·S+DSz2+E(Sx2−Sy2) in which S=1, D/hc=±0.0990±0.0005 cm−1, E/hc=±0.0043±0.0007 cm−1, and g(isotropic) =2.003±0.001. No hyperfine structure is observed in crystals doped with either normal TMP or perdeuterated TMP. The triplet emission spectrum is also reported for TMP measured in an argon and a hydrocarbon matrix at 4.2°K. The 0–0 band of the T→S emission of TMP is at 26 050±30 cm−1 in both matrices. The emission decay constant is 0.41±0.03 sec in both matrices at 4.2°K. The EPR measurements and the emission studies indicate that the lowest triplet state of TMP is of π—π* character. This is in contrast with the known n—π* character of the triplet state of the parent compound pyrazine.
Microwave Spectral Linewidth of OCS Molecule Due to Molecular Collisions
Authors: Krishnaji  , Srivastava Shyam Lal
Published: January 2005

A double-modulation microwave spectrograph has been used to determine the width of j 1→2 line of OCS molecule at different pressures due to collisions with the following perturbers: carbonyl sulfide, argon, oxygen, air, methyl bromide, and water vapor. Experimental linewidth parameters for OCS–OCS, OCS–Ar, OCS–O2, and OCS–N2 molecular collisions are interpreted using Anderson—Tsao—Curnutte theory for the mixed-interactions case. The molecular quadrupole moments of OCS, O2, and N2 are found to be 2.0±2.0, 2.0±0.2, and 5.0±0.5 D·Å, respectively.
Compton Scattering Factors for Spherically Symmetric Free Atoms
Authors: Cromer Don T. , Mann Joseph B.
Published: January 2005

Incoherent scattering factors for all spherically symmetric free atoms have been computed from numerical SCF Hartree—Fock wavefunctions. The complete Waller—Hartree theory with all exchange terms has been used.
Factor Group Splitting and Zeeman Splitting of the Lowest Triplet State of Phenazine
Authors: Clarke Richard H. , Hochstrasser Robin M.
Published: January 2005

The T1←S0 transition of the phenazine crystal is studied in polarized light, and in high magnetic fields, with the crystals at 4.2°K. A factor group splitting of 4 cm−1 is observed in the 0, 0 band. The two components have the same polarization—predominantly along the b axis. The polarization, relative intensity, and Zeeman spectra are used to assign the plus and minus factor group states in association with a crystal symmetry adapted spin—orbital coupling theory.

The lowest triplet state is assigned as 3B2u in agreement with theoretical predictions.
Study of Energy Transfer from Sb3+, Bi3+, Ce3+ to Sm3+, Eu3+, Tb3+, Dy3+
Authors: Blasse G. , Bril A.
Published: January 2005

Energy transfer from the sensitizers (S) Sb3+, Bi3+, or Ce3+ to the activators (A) Sm3+, Eu3+, Tb3+, or Dy3+ has been studied in four different host lattices, viz., YOCl, YBO3, YAl3B4O12, and YPO4. The efficiency of the energy transfer in these systems varies markedly. This is the case even for a given combination of S and A in different host lattices. In most, but not all, cases SS energy transfer is also important. The SA energy transfer is probably nonradiative and occurs mainly by exchange interaction if the S emission band overlaps only 4f−4f absorption bands of A, but by electric multipole—multipole interaction, if the S emission band overlaps allowed absorption bands of A. Taking these ideas and the energy overlap of S emission and S absorption or S emission and A absorption into account, it is possible to explain the results in a qualitative way. If, however, the energy difference between the state S* (excited) +A and the state consisting of the ions S++A− is relatively small, no energy transfer by exchange is observed.
Theory of Molecular Polarizabilities
Authors: McLean A. D. , Yoshimine M.
Published: January 2005

Buckingham's theory of the interaction between a polarizable charge distribution and an external electric field is presented and extended in a unified way. Transformations of components of the molecular polarizability tensors under change of the coordinate origin are derived. Relationships between tensor components in systems of axial and spherical symmetry are given.
Geometry of Ozone and Azide Ion in Ground and Certain Excited States
Authors: Peyerimhoff Sigrid D. , Buenker Robert J.
Published: January 2005

A series of ab initio SCF MO calculations for ground and various closed-shell excited states of O3 and N3− have been carried out with a view toward investigating relationships between the geometries of these states. The calculations give quantitative verification to many of the assumptions made in previous empirical theories dealing with this subject and enlarge the scope of former quantitative schemes to include more quantitative predictions relative to steepness of potential surfaces of molecular states. Thus it is shown that the calculated SCF total energy surfaces of both O3 and N3− can be compared quite concisely in terms of a small number of differentiating orbital-energy curves.
Kinetics of the Two-Body Radiative Association of Atoms
Authors: Palmer Howard B.
Published: January 2005

A treatment of radiative association of atoms based on equilibrium statistical mechanics is presented for the case where colliding atoms enter the repulsive region of an excited state and radiatively stabilize by undergoing electronic transition to the ground state. The final rate expression is the same as that derived from scattering theory when the potential is pure repulsive. The equilibrium treatment seems to have some advantages, for this special interaction, and may actually be somewhat more general than at first appears to be the case.
Physical Clusters, Surface Tension, and Critical Phenomena
Authors: Stillinger Frank H.
Published: January 2005

A physical-cluster theory of condensation and critical phenomena is developed in which primary emphasis is placed on collective modes of oscillation of clusters under the restoring force of their surface tension. A procedure is advocated for self-consistent inclusion of surface mode interaction leading to a nonlinear integral equation whose solution yields a wavelength-dependent surface tension. An explicit expression is derived for the physical-cluster-size distribution near condensation, and from it follows prediction of critical exponents δ (critical isotherm degree), γ′ (initial compressibility below Tc), ν′ (correlation length), and η (deviation from Ornstein—Zernike pair distribution at the critical point), in terms of the phenomenological coexistence curve (β) and surface tension (σ) exponents, as well as a parameter v, which is not directly measureable. The predictions are not consistent with the so-called ``scaling laws,'' except for special v values that seem experimentally unacceptable. Reasons are listed indicating fundamental differences between the critical phenomena in lattice gases enjoying high current theoretical fashionability, and continuum fluid models. For a range of v values, the physical cluster theory predictions agree well with experiment. Appendices are devoted to an interfacial fluctuation theorem, and to an outline of the present physical-cluster theory in two dimensions.
Weak-Coupling Theory of the Vibrational Structure of Molecular Exciton States
Authors: Philpott M. R.
Published: January 2005

The weak-coupling theory of molecular exciton states is extended to include the interaction of a vibronic (vibrational—electronic) exciton with its dissociated states in which vibrational and vibronic excitations occur on different sites. Only nondegenerate electronic states of the free molecule are considered. The spirit of the weak-coupling limit is rigorously adhered to in that no approximations are made concerning the nature of the molecular potential-energy surfaces. Analogy with exciton trapping by impurities leads to the notion of vibrational capture by vibronic excitons. There are also correlated or secondary capture states in which the vibrational exciton follows the vibronic exciton at a fixed distance as it moves through the crystal. Expressions containing the frequency shifts and Franck—Condon factors of the isolated molecule as parameters are derived for the energy and intensity of the capture state. In two special models the effects of large frequency shift and equal Franck—Condon factors are treated. For a linear chain with nearest-neighbor interactions, explicit formulas are derived for the transition probability and compression of the exciton band due to coupling with dissociated states.
Paramagnetic Resonance Study of NO2 in Irradiated KNO3 at 4°K
Authors: Holmberg Robert W. , Livingston Ralph
Published: January 2005

The paramagnetic resonance spectrum of NO2 has been studied at 4°K in gamma-irradiated single crystals of KNO3. The g and hyperfine parameters are essentially the same as those for NO2 in NaNO2 but substantially different than those in KNO3 at 77°K, indicating that thermal motion at 77°K is frozen out at the lower temperature.
Effect of Pressure on the Mössbauer Resonance in Potassium Ferrocyanide, Potassium Ferricyanide, and Insoluble Prussian Blue
Authors: Champion A. R. , Drickamer H. G.
Published: January 2005

The effect of pressure to 200 kbar has been measured on the Mössbauer resonance in potassium ferrocyanide, potassium ferricyanide, and insoluble Prussian blue. The ferrocyanide exhibits a decrease of isomer shift with pressure large compared with typical high-spin ionic ferrous compounds. The ferricyanide exhibits an initial shift with pressure twice as large as the ferrous material. These large changes can be associated with changes in ``back donation'' and in 4s admixture in the binding. The ferricyanide reduces to ferrous compound with increasing pressure, paralleling to behavior of many high-spin ferric compounds. As in the case of the high-spin material, the phenomenon reverses with decreasing pressure. Near 50 kbar a first-order phase transition occurs which apperantly relieves the internal compression of the ferricyanide ion. It is accompanied by an increase in the isomer shift of the ferric ion and the pressure-induced ferrous ion as well as a decrease in the quadrupole splitting of the former. It is also accompanied by a large decrease in the percentage of Fe2+ ion present. This definitely relates the reversible reduction of ferric iron to overlap of the wavefunctions of metal and ligand. Insoluble Prussion blue contains high-spin ferric ion and low-spin ferrous ion. This compound also shows a reversible reduction of high-spin ferric ion with increasing pressure.
Elastic Electron Scattering Amplitudes for Neutral Atoms Calculated Using the Partial Wave Method at 10, 40, 70, and 100 kV for Z = 1 to Z = 54
Authors: Cox H. L. , Bonham R. A.
Published: January 2005

Elastic electron scattering amplitudes for neutral atoms were calculated using the partial wave expansion method for 10-, 40-, 70-, and 100-kV incident electrons. The partial wave phase shifts were calculated by numerical intergration using the phase amplitude method until the results converged to values obtained using the WKBJ and first Born approxmations, which were then used in the remainder of the partial wave sum.

The static potential field of the target atoms was represented by an analytical expression involving a sum of Yukawa terms. Potential field parameters for the expression were obtained by a least-squares fit of the radial electron distribution function, D (r), using Hartree—Fock and relativistic wavefunctions for all the neutral atoms from Z=1 to Z=54. For the smaller atoms from Z=1 to Z=21, Clementi Hartree—Fock wavefunctions were used and for the atoms from Z=22 to 54 Liberman—Waber—Cromer D (r) curves calculated using the Dirac Hamiltonian incorporating a j—j coupling scheme and the Slater ⅔ approximation in the exchange potential were used.
Far-Infrared Torsional Vibration Spectra of One-, Two-, and Three-(CX3) Top Molecules
Authors: Möller K. D. , De Meo A. R. , Smith D. R. , London L. H.
Published: January 2005

The far-infrared torsional vibration spectra in the 350–40-cm−1 spectral region are reported for the gaseous state of the following compounds: Ethyl chloride, propylene, deuterated ethyl bromide, 2-chloropropane, 2-bromopropane, 2-iodopropane, dimethylamine, deuterated dimethylamine, dimethyl ether, deuterated dimethyl ether, 2,2-difluoropropane, deuterated acetone, hexafluoroacetone, trimethylamine, tertiary butyl cyanide, and tertiary butyl acetylene. Using absorption bands assigned to torsional vibrations, the height of the potential barrier for internal rotation is calculated and compared to the available microwave data.
Approximate Theory of the Expansion of a Linear Polymer Chain in Nonideal Solvent
Authors: Fujita H. , Okita K. , Norisuye T.
Published: January 2005

A new rigorous expression is derived for the partition function of a linear polymer chain with its end-to-end distance fixed to a specified value R, subject to the condition that the interaction of a pair of chain segments is of a short-range nature and characterized by the binary cluster integral β. Starting with this expression and estimating the total number of segmental collisions in such a chain by use of the approximation of uniform distribution of segments and of the ellipsoid approximation to the over-all shape of the molecule, an approximate closed expression for α(z) is obtained, where α is the expansion factor of the molecule defined in terms of the statistical average of R2, and z is the familiar parameter characterizing the strength of excluded-volume effect. It is shown that the well-known α5 equation of Flory as well as the α3 equation of Kurata, Stockmayer, and Roig correspond to two extreme cases of the present theory. In the region of α3 up to about 3, the derived equation for α3 gives a curve which nearly coincides with that predicted by the equation of Ptitsyn, but beyond this, the latter yields α3 which increases more rapidly with increasing z. In the limit of large z, the present equation approaches the asymptotic form α5=2.630z, and thus it belongs to the fifth-power type as does the Flory equation.
Inorganic Radicals Trapped in Glasses at Room Temperature. IV. Silver Radicals in Metaphosphate Glass
Authors: Feldmann T. , Treinin A.
Published: January 2005

The effect of x irradiation on silver-activated metaphosphate glass was investigated. The optical and ESR absorptions were measured and assigned to Ag2+, Ag2+ and Ag0. Their optical bands have maxima at 275, 315, and 365 mμ, respectively. The silver atoms, stable at 77°K, show little chemical interaction with the matrix. A new color center which belongs to the base glass has been identified. It results from the reaction of electrons with the phosphate polymers and exhibits a large hyperfine coupling. Its nature is discussed.
ESR of Cyclic Radicals CnHn: Relationship of Total Splitting to Parameters of the Colpa—Bolton and Giacometti—Nordio—Pavan Equations
Authors: Vincow Gershon
Published: January 2005

The total splitting of the ESR proton hyperfine spectra of the cyclic π-electron radicals, CnHn, is investigated. Theoretical expressions for the total splitting are derived in terms of the parameters of the Colpa—Bolton (CB) and Giacometti—Nordio—Pavan (GNP) extensions of McConnell's relationship. The application of these equations to the experimental results for radicals CnHn is discussed. The application of the CB and GNP correlations to the calculation of the proton splittings for alkyl-substituted CnHn radicals is also discussed.
Energy-Moment Methods in Quantum Mechanics
Authors: Delos J. B. , Blinder S. M.
Published: January 2005

Three quantum-mechanical computational techniques based on energy moments, μk= ∫ dqψ*(q)Hkψ(q), and semimoments, νk(q′)=[Hkψ(q)]q=q′, are formulated. The μ method, which employs the μk, is connected to the method of moments in probability theory, to the variational method, and to eigenvalue spectroscopy. The ν and λ methods, which employ semimoments, are related to local energy methods using one and several configuration points, respectively. An Nth-order calculation, requiring 2N moments or semimoments, yields N approximate eigenvalues and eigenfunctions. In accordance with a conjectured convergence criterion, exact eigenstates are approached in the limit N→∞. From quantities obtained in a moments calculation, a lower bound on the ground-state eigenvalue can also be determined using a refinement of Weinstein's criterion. A computational method for generating moments and semimoments is given and the μ method is applied to the linear harmonic oscillator.
Transport Properties of Polar-Gas Mixtures. I. Viscosities of Ammonia—Methylamine Mixtures
Authors: Burch L. G. , Raw C. J. G.
Published: January 2005

The viscosity coefficients of ammonia, methylamine, and binary mixtures of these gases have been measured in the temperature range 0°—400°C using a capillary transpiration method. The Stockmayer intermolecular potential parameters for the pure gases have been determined, and the mixture results are discussed in terms of the kinetic-theory expressions for the mixture viscosities using the empirical combining rules for the potential parameters. The experimental viscosity results have also been used to estimate diffusion coefficients in the pure gases (self-diffusion) and in the mixtures by several different procedures.
Viscosity of Helium and Nitrogen and their Mixtures at Low Temperatures and Elevated Pressures
Authors: Kao James T. F. , Kobayashi Riki
Published: January 2005

Experimental viscosity data have been determined for the helium—nitrogen system for five approximately equally spaced compositions at 50°C over the pressure range from 10 to 500 atm, nine compositions at 0°C from 10 to 500 atm, seven compositions at −50°C from 10 to 400 atm, and five compositions at −90°C from 10 to 200 atm. The maximum probable error of the calculated viscosity data is 0.137%. Most of the data taken cover hitherto uncharted regions of pressure, temperature, and compositions. Both maximum and minimum viscosity of gas mixtures at some isothermal—isobaric conditions have been observed. To the authors' knowledge the phenomenon of minimum isobaric—isothermal viscosity is reported for the first time in nonpolar mixtures. Within the experimental accuracy of this study, it has been found that the temperature-independent residual-viscosity concept holds for a fixed composition only on an approximate basis. The residual viscosities of helium, nitrogen, and their mixtures show about 0.5% spread with temperature from 50.00° to −90.00°C at constant density.
Gas-Phase Photolysis of Ethyl Iodide at 2537 and 2288 Å. Reactions of Hot Ethyl Radicals with Added Hydrocarbons
Authors: Rebbert R. E. , Ausloos P.
Published: January 2005

The photolysis of C2H5I and C2D5I have been investigated at 2537 and 2288 Å in the presence of thermal alkyl radical scavengers such as O2 or I2. The ethane (quantum yields at 2537 Å: φC2H6=0.82×10−3, φC2D6=0.29×10−3) formed in such mixtures can be entirely ascribed to abstraction of an H (or D) atom by a ``hot'' ethyl radical formed in the primary dissociation of ethyl iodide. The differences in quantum yield between C2H6 and C2D6 are in part ascribed to a difference in the partitioning of the excess energy (∼30–40 kcal) carried over from the primary process into vibrational and translational modes. When C2D5I or C2H5I is photolyzed in the presence of a cyclo-C6H12–cyclo-C6D12–O2 mixture (1:1:0.1), or of a cyclohexane-1,1,2,2,3,3,-d6–O2 mixture, the relative probability for abstraction of an H atom vs that for abstraction of a D atom (πH/πD) is equal to 1.5±0.1. The latter value shows little dependence on a change in wavelength and is also not affected when unreactive gases are added to the reaction mixtures. The added gases do, however, reduce the probability of the abstraction process. For instance, the probability of reaction with cyclohexane by a ``hot'' C2D5* radical is reduced 50% after one collision with carbon dioxide, the most efficient quencher used. The relative quenching probability of the ``hot'' C2D5* radical by different additives is as follows: He−0.50; Ne−0.62; N2−1.00; and CO2−1.51.

When C2H5I is photolyzed at 2537 Å in the presence of CD3CH2CD3, CH3CD2CH3, or CD3CH2CH2CD3 it shows that the relative probability per atom for the abstraction of a primary compared to a secondary H atom in a hydrocrabon molecule by a hot ethyl radical is 1:4.5. Moreover, the quantum yield for ethane formation at 2537 Å per secondary hydrogen atom for a series of cycloalkanes and normal alkanes is 0.32±0.07×10−3.