bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR Spectrum of 3-Chlorothietane, an Example of Complete NMR Spectral Analysis by Computer Techniques
Authors: Keller Warren D. , Lusebrink T. R. , Sederholm C. H.
Published: January 2005

The NMR spectrum of 3-chlorothietane has been analyzed by the use of three computer techniques. These are (1) spectral decomposition (DECOMP), (2) spectral assignment (ASSIGN), and (3) Swalen and Reilley's iterative programs (NMREN and NMRIT). DECOMP determines to a large extent the frequencies and intensities of all lines which make up an unresolved multiplet. ASSIGN finds all possible sets of energy levels which are consistent with the observed frequencies and intensities of the completely resolved spectrum. NMREN calculates each set of energy levels by making a least-squares fit on the assigned transition frequencies. NMRIT calculates, for each set of energy levels, the corresponding coupling constants and chemical shifts if they are real. Only one set of coupling constants and chemical shifts is consistent with the NMR spectrum of 3-chlorothietane. The chemical shifts and vicinal coupling constants are quite normal. The geminal coupling constant is −8.63 cps. There is a large long-range coupling constant across the ring of +3.12 cps. The other two long-range coupling constants are smaller and negative. The geminal and long-range coupling constants are compared with theoretical calculations.
Study of the Vapors of Liquid Lead and Bismuth
Authors: Kim Jang H. , Cosgarea Andrew
Published: January 2005

The total vapor pressure and mass loss per unit time of lead and bismuth vapor were determined by the torsion—Knudsen-effusion—recoil method.

The average molecular weight of bismuth was determined as a function of temperature assuming the presence of a monomer and dimer species. The bismuth vapor composition is approximately 65% Bi2 and 35% Bi in the temperature range of investigation, 850° to 950°K. The average molecular weight of bismuth vapor decreased with increasing temperature. Vapors of lead were found to be monatomic.

In addition, the heats of dissociation and vaporization have been determined.
Reliability of Variational Double-Perturbation Procedure for Molecules
Authors: Chen J. C. Y. , Ehrenson S.
Published: January 2005

The applicability of the variational double perturbation procedure is investigated for molecules in an attempt to improve expectation values of operators other than the energy. The particular case of the hydrogen molecule is examined since expectation values of high accuracy for operators besides the energy are available for direct comparison. Differences are shown to exist among various simple wavefunctions with respect to energy as well as to the other operators considered. The relative differences found appear to be understandable on the basis of differences in the regions of space emphasized by the particular operator and how well the wavefunction approximates electron distributions in these regions. In general, the procedure for molecules does not appear to be as reliable as for atoms, most likely because the functions generally employed are not adequate in these spatial regions. It is obvious that improvements in the functions based only upon the variational energy criterion will not suffice.
Spin—Rotation Interactions in Polyatomic Molecules
Authors: Gordon R. G.
Published: January 2005

Nuclear spins interact with the intramolecular magnetic fields produced by molecular rotation. This interaction broadens and sometimes splits the nuclear-resonance signal observed by molecular-beam techniques. A semiclassical calculation is given for the band shape of such a broadened nuclear-resonance spectrum. One interesting feature of the results is that a logarithmic singularity in the resonance shape may occur if two of the principal components of the spin—rotation tensor differ in sign. The calculated band shapes are compared with several experimental contours, including a spherical-top molecule (CH4), a symmetric-top molecule (C2H6), and an asymmetric rotor (C6H5F). Values of the spin—rotation constants along the principal axes of inertia are thus obtained for these molecules.
Electrical Properties of Some Charge-Transfer Complexes under High Pressure
Authors: Andersen T. N. , Wood D. W. , Livingston R. C. , Eyring H.
Published: January 2005

The electrical resistances of several polyaromatic—halogen intermolecular charge complexes (pyrene with varying concentrations of bromine, coronene with iodine, and perylene with bromine) were measured at pressures up to 80 kbar. Activation energies as a function of composition were measured for the pyrene·XBr2 samples, as were Seebeck coefficients and activation energies at varying pressures for one of the complexes. The resistance decrease with increasing pressure is interpreted as due to an increase in concentration of charge carriers. Possible states in which the charge carriers exist are discussed.
Sites for the Dehydrogenation of Formic Acid on Gold
Authors: Bhakta M. A. , Taylor H. Austin
Published: January 2005

The dehydrogenation of formic acid on gold in the pressure range 5–15 mm Hg and the temperature range 130° to 200°C follows the rate law: −dPM/dt=aPM/(1+bPM); a and b are constants and PM is the monomer pressure. On heating, the catalyst acquires enhanced activity for the dehydrogenation. The enhanced activity depends on the temperature to which it is heated, approaches a limiting value after about 40 h of heating and decays at an annealing temperature (130°C) by zero, first, second, or higher order in a manner similar to the extra electrical resistivity induced by quenching. The decay is a function of time alone at constant annealing temperature, the dehydrogenation of formic acid having no apparent effect. Repeated quenchings, however, leave the catalyst with a small, apparently irreversible, enhanced activity. A mechanism for the dehydrogenation is proposed and is analyzed in terms of the energy of activation of the constituent steps. The results indicate that surface terminations of dislocations, vicinal faces, and vacancies or other point defects are perhaps the catalytically active sites.
Light-Scattering Study of Tobacco Mosaic Virus Solutions When Subjected to Electric Fields
Authors: Jennings B. R. , Jerrard H. G.
Published: January 2005

The results of the light-scattering study are presented. Measurements made in the absence of an applied electric field gave size parameters and a molecular weight for this rodlike molecule which are in good agreement with results obtained by other workers. These are a molecular weight of 49.5×106 and a radius of gyration of 940(±28) Å corresponding to a length of 3200 Å and a diameter of about 150 Å. The sample was very monodisperse. The second osmotic virial coefficient was zero. The application of alternating electric fields to solutions of polar or electrically anisotropic molecules results in changes of the angular distribution of the intensity of the scattered light and the introduction of an alternating scattered intensity component of twice the frequency of the applied field. The way in which these effects can be used to determine the electrical characteristics of the molecules is described. The solutions were subjected to fields up to about 500 V cm−1 at frequencies up to 30 kc/sec, and it was found that the molecules possessed both a permanent dipole moment μ and electrical anisotropy β. The values obtained were μ=4.1×104 D and β=4.3×104 D and these are in agreement with previously reported values. Consideration of the frequency dependence of the intensity changes enabled a value for the rotary diffusion constant to be estimated.
Stark Effect and Hyperfine Splitting for Near-Degenerate Levels of an Asymmetric Rotor. Application to NO2Cl and NOBr
Authors: Eagle Donald F. , Weatherly T. L. , Williams Quitman
Published: January 2005

An approximate method is presented for calculating the Stark effect and hyperfine splitting of near-degenerate rotational levels of an asymmetric-top molecule. This method has been used to calculate the Stark effects for the 21→30 transition of NO2Cl and the 11→20 transition of NOBr. The results are compared with the measured spectra and are found to agree within experimental error. The dipole moments obtained are μ = 0.53 D for NO2Cl and μa = 1.80 D for NOBr. The component μb for NOBr cannot be determined from the spectrum.
Studies of Lithium Hydride Systems. II. Solid—Liquid Equilibrium in the Sodium Chloride—Lithium Hydride System
Authors: Johnson Carl E. , Wood Scott E. , Crouthamel Carl E.
Published: January 2005

Thermal analysis has been used to determine the temperature—composition solid—liquid equilibrium diagram for the lithium hydride—sodium chloride reciprocal system. A eutectic composition of 55.2 mole % lithium hydride was observed, melting at 565.7°C. No evidence for the formation of solid solutions was observed. The values of chemical potential of each component have been calculated along the equilibrium curves where the solutions are saturated with respect to the pure solids. The limiting slopes of the saturation curves are consistent with the interpretation that sodium chloride exists primarily as an un-ionized monomer when dissolved in lithium hydride and that lithium hydride also exists primarily as an un-ionized monomer when dissolved in sodium chloride.
Electron Spin Relaxation in Solvated Manganese(II) Ion Solutions
Authors: Garrett B. B. , Morgan L. O.
Published: January 2005

Electron spin resonance (ESR) spectra were obtained for solutions of manganese(II) perchlorate in dimethylformamide (DMF), diethylformamide (DEF), dimethylsulfoxide (DMSO), and water. Variation of line shape with solvent and temperature was obtained and interpreted at low temperatures in terms of a model in which solvent fluctuations about the solvated ion modulate the ligand field and relax the electron spin through spin—orbit interaction. Relaxation times for Δms=1 transitions of the S=52 system were calculated using a semiclassical density-matrix formalism. In DMF, DEF, and DMSO solutions another contribution to relaxation was observed at high temperatures which may be attributable to ligand exchange or to internal motion in the complex ion. The high-temperature process was not observed in aqueous manganese(II) solutions.
Properties of the Quartic Anharmonic Contribution to the Specific Heat of a Face-Centered Cubic Lattice
Authors: Overton W. C.
Published: January 2005

In this paper we study Maradudin's recent approximation to the complex many-body expression for the quartic anharmonic contribution F4 to the free energy of a face-centered cubic crystal. It turns out that one can calculate C4, the quartic anharmonic contribution to the specific heat corresponding to F4, almost exactly at any arbitrary temperature by use of the vibration spectrum, thus necessitating only a single summation over the Brillouin zone. The machine-calculated result is an accurately determined curve of C4/Char, where Char is the harmonic specific heat, for a lattice model chosen to represent copper. This curve shows structural features in the form of wiggles and in the discussion it is argued that the cubic anharmonic contribution C3/Char would not negate the structure of C4/Char in the total form of the anharmonic contribution to the specific heat (C3+C4)/Char. Consequently, the theoretical results are compared with the experimental specific heat of copper expressed in the form CL[T, V(0°K)]/Char, where CL denotes the experimental lattice specific heat remaining after the necessary thermodynamic corrections have been made. Certain features of the experimental curve agree with the structural features of C4/Char alone, despite the fact that C3/Char is not presently taken into account.
Electronic-Relaxation Processes in Acetone
Authors: Borkman Raymond F. , Kearns David R.
Published: January 2005

The emission properties of acetone and acetone-d6 have been studied in order to investigate the mechanisms for relaxation of electronic excitation. The results are summarized in Fig. 2 and Table I.

The phosphorescence lifetime of acetone at 77°K in ether—IPA glass was 4×10−4 sec and the quantum yield for phosphorescence was ΦP=0.03±0.01. Deuteration of the acetone increased the phosphorescence lifetime to 1×10−3 sec and the quantum yield to ΦP=0.08±0.02. The phosphorescence of acetone was found to be quenched by the addition of pentene−2 to the rigid solution, but the fluorescence was unaffected. From the quenching data it is concluded that the excited-singlet→excited-triplet intersystem-crossing quantum yield is ΦIC=1.0±0.1, independent of temperature between 298° and 77°K. The intersystem-crossing rate constant is kIC=4×107 sec−1 and is not affected by deuteration. The excited triplet state is populated with nearly unit efficiency upon excitation of acetone to its lowest singlet state, and therefore the low phosphorescence yield, even in acetone-d6, indicates that radiationless transitions from the triplet state to the ground state are primarily responsible for determining the lifetime of the lowest triplet state.

A medium effect on the acetone phosphorescence lifetime at 77°K was observed; it was found to vary from 3×10−4 in glycerine solutions to 1×10−3 sec in crystalline acetone. The triplet-state lifetime in crystalline acetone decreased only slightly upon increasing the temperature to just below the melting point of crystalline acetone, but in the case of glycerine solutions, the triplet-state lifetime decreased by at least a factor of 10 in raising the temperature from 77° to 200°K, even though the glycerine remained quite solid. The fluorescence quantum yield in liquid solutions was found to be independent of solvent at 25°C.

The lifetime of the lowest (n, π*) singlet state of acetone is primarily determined by intersystem crossing to the lower-lying excited triplet state and is therefore τS=2.5×10−8 sec. The quantum yield for acetone fluorescence at room temperature was found to be ΦF=0.01±0.003. No deuterium effect on ΦF was observed and therefore it may be concluded that either there is no deuterium effect on the rate of internal conversion from the excited singlet state to the ground state, or, what is more likely, that internal conversion is much slower than intersystem crossing which is not affected by deuteration.

The fluorescence spectra of acetone and acetone-d6 were found to be identical under all conditions, as were the phosphorescence spectra of acetone and acetone-d6. The phosphorescence was found to be polarized perpendicular to the lowest singlet—singlet absorption, consistent with theoretical predictions.
Viscoelastic Relaxation and Non-Arrhenius Behavior in Diols
Authors: Kono R. , McDuffie G. E. , Litovitz T. A.
Published: January 2005

Ultrasonic shear relaxation data are reported for the associated liquid pentanediol−1,5 at frequencies between 13 and 470 Mc/sec. Reduction of the data indicates a relatively narrow distribution of relaxation times. Viscosity data are also reported on this liquid which show a slight but definite deviation from Arrhenius behavior (lnηs∝1/T). The shear data are compared to that for two other diols: 2-methyl pentanediol−2,4 and butanediol−1,3. In this comparison it is shown qualitatively that the width of the distribution of shear relaxation times increases as the temperature dependence of the average relaxation time deviates from the Arrhenius form. It is argued that the origin of both the non-Arrhenius character of the average shear relaxation time and the distribution of these times lie in cooperative molecular motion.
Isomer of 130I
Authors: Wilkey D. Dennis , Willard John E.
Published: January 2005

The existence of the isomer 130Im (9.2 min) has been established by the growth of the gamma-ray spectrum of the 130I ground state following neutron irradiation of 129I, and also by the incorporation of 130I into organic combination as a result of the isomeric transition of I2(130Im) dissolved in n-hexane. The isomer decays to the ground state by a highly converted isomeric transition with a 0.77 probability and to the 0.54-MeV level of 130Xe by beta emission with 0.23 probability. The cross-section ratio, σ(130Im)/σ(130I), for production of the isomers from 129I by pile neutrons is about 2.0. The fraction of the isomeric transition events which result in organic incorporation of the 130I daughter in solutions of I2(130Im) in n-hexane, or in solutions of RI(130Im) in ethyl iodide, is about 0.40.
One-Center-Expansion—Configuration-Interaction Studies on CH4 and NH3
Authors: Rutledge Ronald M. , Saturno Antony F.
Published: January 2005

One-center-expansion—configuration-interaction calculations have been extended to include higher-order spherical harmonics and extra radial factors. Calculations have also been made to study the prediction of nuclear geometry. Computations on CH4 using as a basis set the orthonormalized Slater atomic orbitals through l=8, yielded a ground-state energy of −39.94 a.u. Further, the inclusion of additional Schmidt orthogonalized radial factors gave much less improvement than the addition of higher spherical harmonics.

The calculations with basis orbitals through l=4 on NH3 failed to predict a nonplanar configuration of minimum energy except for the case where the basis set was truncated to include only orbitals through l=2. For the l=2 case NH3 was predicted to have a nonplanar geometry within one degree of the experimental value.
Equation of State, Grüneisen Constant, and Interatomic Forces
Authors: Kachhava C. M. , Saxena S. C.
Published: January 2005

The equation of state of solids and the Grüneisen constant are interrelated and these can further be explicitly expressed in terms of the parameters of the interatomic potential and other simple constants. Calculations have been performed in this paper for these quantities on the familiar Born and Born—Mayer potentials. In general, the results reported here on alkali halides exhibit a good qualitative agreement between theory and experiment. This, however, is encouraging in view of the simple and approximate nature of the theory.
Association of CN in an Expansion Wave
Authors: Bauer S. H. , Watt W. S.
Published: January 2005

The expansion wave generated by the simultaneous arrival of the ``contact'' surface and the reflected rarefaction wave was used for a direct kinetic study of a condensation process, the association of CN radicals generated by shocking C2N2/Ar mixtures to about 2000°K in the reflected-shock region. During the quenching-expansion phase the concentration of CN radicals decreases due to the concurrent chemical association and the lowering in total density. The CN concentration was followed spectrophotometrically at 3883 Å.

The results were reduced in three ways: (A) unidirectional association to C2N2 in the presence of a third body, (B) relaxation to the local equilibrium via a three-body process, and (C) bimolecular reaction with C2N2 and CmNm polymers (formed during the heating process) to produce higher polymers. The data show that at the onset of quenching, the removal of CN was sluggish. This is attributed to failure to attain equilibrium in the preparation of the sample. After ≈200 μsec the data were best fitted by the third mechanism. This conclusion is in agreement with results obtained by another method and is supported by a reaction scheme which accounts for the formation and decay of CN in the presence of CmNm species. For a 2% initial concentration of C2N2, an average polymer number of ≈10 was indicated.
Detection of Radiation Damage in Anthracene Crystals by Space-Charge-Limited Current Measurements
Authors: Weisz S. Z. , Cobas Amador , Richardson Paul E. , Szmant H. Harry , Trester Seymour
Published: January 2005

It is shown that hole traps are induced in anthracene crystals by irradiating the crystals with either gamma or x rays. These traps are detected by measuring the steady-state current—voltage characteristic of the crystal in the space-charge-limited current region. A modified type of Kallmann—Pope cell employing a sodium sulfate solution as one electrode and sodium iodide—iodine solution as the hole injecting electrode was used. After irradiating the crystals with gamma rays or x rays, part of the current—voltage curve shows a square-law dependence and the current saturation occurs at higher voltages than in the nonirradiated crystals. By applying space-charge-limited current theory and interpreting the voltage at which the departure from the square law occurs as the trap-filled-limit voltage for the induced deep traps, the density of these traps can be estimated. Using this calculated density it is found that one deep trap is created for every 45 keV of incident energy absorbed in the crystal.
Theory of the Origin of the Internal-Rotation Barrier in the Ethane Molecule. II
Authors: Wyatt Robert E. , Parr Robert G.
Published: January 2005

In the previous paper, the total energy difference ΔW hindering internal rotation in the ethane molecule was shown to comprise a nuclear—nuclear repulsion energy difference plus an electronic energy change ΔE, which may be computed from the integral Hellmann—Feynman formula, ΔE=∫ρES(1)H′(1)dv(1). Here ρES(1) is the first-order spinless transition density between the eclipsed and staggered states, and H′(1) is the difference between the one-electron electron-nuclear attraction operators for the two forms. It was shown how ρES(1) and H′(1) both could be expanded in Fourier series in the electronic azimuthal angle φ about the CC axis, so that ΔE becomes the sum of contributions from successive Fourier components of the transition density.

In the present paper this analysis is continued. The threefold and ninefold components of ρES(1) are accurately computed from the LCAO—SCF wavefunctions of Pitzer and Lipscomb, thus eliminating several mathematical approximations made in the previous paper. The threefold contribution to the rotation barrier is found to be ΔE3≈−2.4 kcal/mole, the ninefold contribution ΔE9≈0.0 kcal/mole. The net barrier is ΔW≈2.4 kcal/mole. Contributions to ΔE3 from localized and corresponding orbital expansions of ρES(1) are evaluated, and contour maps are given of ρ3(r,θ) and ρ3(r,θ)A3(r,θ) over the whole molecule. From the orbital analyses and the density maps, the following conclusions are drawn: (1) The CC and carbon iS orbitals contribute insignificantly to ΔE. (2) Most of ΔE arises from CH orbitals. (3) The quantity ΔE can be interpreted as mainly arising from regions around protons; regions near the CC axis are unimportant. (4) The effects of changes of localized orbitals on rotation are probably not negligible, but their precise evaluation is particularly difficult.

The Pitzer—Lipscomb energy difference, 3.3 kcal/mole, is different from the integral Hellmann—Feynman result. A method for bringing the two methods into concordance is described, and it is reasoned that if this were carried through the common result would probably be very near the experimental value, 2.9 kcal/mole.

Various other theoretical questions are discussed, and a number of suggestions are made for further research on the internal-rotation problem.
Nuclear Magnetic Relaxation of Polymer Solutions. Side-Chain Motion
Authors: Ullman Robert
Published: January 2005

In this paper, the magnetic relaxation of nuclei of spin ½ which are attached to polymer molecules is calculated. The computation is based on the idea that the relaxation process is a consequence of magneticdipole interaction between spins attached to the same segment. The particular point of this paper is to treat the relaxation as a consequence of the relative motion of the spins with respect to the polymer segment to which they are attached. The polymer segment, itself, undergoes a complicated Brownian motion which has been analyzed in a previous paper in terms of the Zimm—Rouse model of chain macromolecules.
Valence Force Field of CX3YZ2 and the Vibrational Spectra of CF3NO2, CCl3NO2, and CBr3NO2
Authors: Castelli Alex , Palm Ann , Alexander Chester
Published: January 2005

Sets of valence-type potential-energy constants for CF3NO2, CCl3NO2, and CBr3NO2 were determined by using a minimum of 98% agreement between each calculated and observed vibrational frequency as a criterion, by imposing constraints inferred from data on other molecules and by maintaining a consistency expected from the related nature of these three molecules. C2v symmetry was used to factor the secular equations. The sensitivity of the potential energy constants to variations in the structure of the CNO2 framework is examined. The applicability of a previously proposed relationship between the electronegativity of the CX3 group, changes in the ONO angle and the strengths and s-orbital character of the NO bonds is examined. An empirical relationship, Δω=74.0ε, is suggested by the behavior of the NO2 symmetric deformation frequency with changes in the electronegativity of the halogen atoms.
Molecular Structures of Gaseous Hexabromo- and ortho-Dibromobenzene as Determined by Electron Diffraction
Authors: Strand Tor G.
Published: January 2005

The molecular structures of hexabromo- and ortho-dibromobenzene have been studied by least-squares refinements based on gaseous electron-diffraction intensity data. The equilibrium conformation of ortho-dibromobenzene is found to be planar with C2v symmetry and with an angle of 63.6°±0.5° between the two carbon—bromine bonds. For hexabromobenzene, the ortho-bromine—bromine distance indicates a distorted structure possessing S6 symmetry with every second bromine atom above and below the plane of the benzene ring. The other bromine—bromine and the nonbonded carbon—bromine distances, however, are in better agreement with a planar and undistorted configuration. Possible structures of this molecule are discussed in the text. The most important molecular parameters and estimated standard deviations are listed in Table IV.

Accurate partial-wave scattering factors for the atomic scattering of 40-keV electrons have been applied in some refinements. The results are compared with the results obtained using scattering factors according to the first Born approximation, and a better agreement with the experimental data is observed for the former scattering factors.
Electrical Properties of Cobalt Monoxide
Authors: Fisher Bertina , Tannhauser D. S.
Published: January 2005

The electrical conductivity of polycrystalline CoO1+x was measured as a function of temperature and partial pressure of oxygen, P(O2). The range of temperature was 900°—1450°C and the range of partial pressure was 1 − 10−12 atm. The plot of the conductivity against partial pressure of oxygen gave two distinct regions: Region A, where the conductivity is proportional to P(O2)¼, and Region B, where the conductivity is proportional to P(O2)⅙. From these results, together with considerations of ionic radii, we concluded that the dominant defects in CoO1+x at high temperatures are cation vacancies, with the majority being singly ionized in Region A and doubly ionized in Region B.

A combination of gravimetric and electrical measurements showed that the mobility of the holes contributed by these vacancies rises exponentially with temperature. The activation energy of mobility is Eu=0.3 eV. At 1350°C, the mobility is about 0.4 cm2 V−1·sec−1. These values are discussed in terms of polaron theory.

The sum of the enthalpy of formation of a neutral vacancy and the first ionization energy is Δhv+E1=0.56 eV. The second ionization energy was measured separately and found to be E2=0.65 eV. A rough estimate of the first ionization energy gives E1≅0.45 eV.

Analysis of Seebeck-coefficient measurements performed in the same range of temperature and oxygen pressure is consistent with the results of the conductivity measurements regarding the sign and number of charge carriers. The term Ap, the so-called heat of transport, was calculated on the assumption that p0, the molar concentration of available states for charge carriers, is about 1. This assumption gave negative values for Ap. The term dAp/d(kT)−1, which is independent of the value of p0, is about 0.24 eV in Range A, and 0.54 eV in Range B. The value of dAp/d(kT)−1 in range A is close to Eμ, as the theory suggests.

The resistivity of quenched samples of CoO1+x was measured at temperatures below 70°C for different x. Above the Néel temperature (tN≅19°C) the activation energy of the conductivity is ½E1+Eμ≅0.5 eV in a wide range of concentrations. This value is consistent with E1 and Eμ evaluated at high temperatures. At very low deviations from stoichiometry the activation energy increases, due perhaps to the appearance of electrons donated by interstitial cobalt atoms. Below the Néel temperature the activation energy ε decreases by about 0.1 eV, the difference between ε(t>tN) and ε(t<tN) depending on the departure from stoichiometry. This decrease is not understood.

The appendix contains a slight correction to the phase diagram that was previously published. This correction is due to a more refined analysis of the data.
Electron Spin Resonance Study of Radical Pairs Trapped in X-Irradiated Single Crystals of Dimethylglyoxime-O,O-d2, Glyoxime, and Methylglyoxime at Liquid-Nitrogen Temperature
Authors: Kurita Yukio , Kashiwagi Michio
Published: January 2005

The ESR spectra of x-irradiated single crystals of dimethylglyoxime-O,O-d2, glyoxime, and methylglyoxime have been measured at 77°K. An analysis of the spectra reveals the presence of radical pairs R1—CR2NȮ···R1—CR2NȮ , where R1=C(CH3)NOD and R2=CH3 for dimethylglyoxime-d2 (the average distance between the unpaired electrons R=5.4 Å), R1=CHNOH and R2=H for glyoxime (R≦4.8 Å), and R1=CHNOH and R2=CH3 for methylglyoxime (R≦5.2 Å). Radical pairs decay in dimethylglyoxime faster than in dimethylglyoxime-d2. The fact shows that the iminoxy radicals CR1NOH–CR2NȮ diffuse by hydrogen-atom abstraction from nearby hydroxyl groups.
Selection Rules for R-Center Absorption
Authors: Kennedy Larry Z.
Published: January 2005

A recent observation that apparent vibronic fine structure in the R2 absorption band of the R center in alkali halide crystals corresponds energetically to certain lattice phonons at the Brillioun zone boundary is considered in the light of possible selection rules for optical absorption. A perturbation calculation is employed. The selection rules found are not inconsistent with the lattice-phonon interpretation, but they do not characterize or allow identification of the fine structure.
Atomic Structure and Correlation in Liquid Binaries by X-Ray and Neutron Diffraction with Application to NaK
Authors: Henninger E. H. , Buschert R. C. , Heaton LeRoy
Published: January 2005

For a liquid or amorphous binary three independent diffraction patterns are required to completely characterize the atomic structure, including the correlation of the two atom types. However if the distribution of atomic density is the same about either atom type only two patterns are required. This two-pattern method, as developed by Keating, was applied to 50 at. % liquid sodium—potassium using x-ray and neutron diffraction. The results indicated a very nearly random mixing of atom types, but further analysis of the data showed that the assumption of identical distributions about the Na and K atoms is invalid. Indeed, consideration of the factors which may determine the liquid structure makes this assumption highly questionable for most binaries. A new method of combining the x-ray and neutron-diffraction patterns was developed which can yield qualitative information on the correlation and serve as a test for theoretical structural models. The new approach utilizes the ratio of the two weighted atomic distributions obtained separately from the x-ray and neutron patterns. For the 50% NaK system the neutron pattern alone gives the true atomic distribution with nearest-neighbor concentrations at 4.4, 7.7, and 11.2 Å, and the comparison with the x-ray distribution indicates that at the first three nearest-neighbor distances a given atom tends to be paired with atoms of the opposite type, with some concentration of Na–Na pairs at 5.0 Å and K–K pairs at 6 to 7 Å.
Primary Processes in Ozone Photolysis
Authors: DeMore W. B. , Raper O. F.
Published: January 2005

The photolysis of O3 dissolved in liquid Ar at 87°K has been studied at 2537 Å and at wavelengths near 3130 Å. Quantum yields of O3 photodecomposition were determined for O3 concentrations ranging from 5×10−4 to 0.3 mole/liter at 2537 Å and 0.03 to 0.67 mole/liter at 3130 Å. Disappearance of O3 is attributed to the reactions O3→ lim φIabsO2+O(1D),O(1D)+O3→2O2,where Φ is the quantum yield of O(1D) formation at a given wavelength. The limiting photodecomposition quantum yield at high O3 concentration is about 2 at 2537 Å and about ½ at 3130 Å.

Quantum yields were also determined at several wavelengths in the interval 2970 to 3340 Å for the photo-exchange reaction O3+36O2→52O3+O2.

The foregoing studies, together with previous work, show that the O(1D) quantum yield in O3 photolysis is unity below 3000 Å but falls to a value of 0.4±0.15 in the 3130-Å region. The exchange experiments show that the total quantum yield of atomic oxygen, including O(1D) and O(3P), retains a constant value of unity throughout the wavelength range studied, with onset of O(3P) formation occurring at 3000 Å.

From these results the rate of O(1D) production in the lower atmosphere is calculated to be 1.2±0.5 pphm/h (pphm is parts per hundred million), based on an assumed O3 concentration of 10 pphm and a solar zenith angle of 45°.
Electron Correlation and the Nuclear Spin—Spin Coupling Constant. I. An Alternant Molecular Orbital Description of Nuclear Spin—Spin Coupling
Authors: Barfield Michael
Published: January 2005

A theoretical description of contact nuclear spin—spin coupling is presented in terms of the density-matrix formalism and the approximation of an ``average excitation energy''. For a molecular system in a singlet state the density of spin coupling is proportional to the difference between the correlation functions for electrons of the same and opposite spins. Application of the one-parameter alternant molecular orbital (AMO) method, which includes both types of correlation in an easily visualizable manner, yields expressions for the density of spin coupling in alternant systems of 2n electrons. In the case of directly bonded systems of two electrons, correlation between electrons of antiparallel spins make a significant contribution to the coupling constant. Coupling constants between nuclei separated by two and three bonds are examined by the AMO expressions in the tight-binding approximation. In contrast to the single-determinant results, a long-range spin correlation is implicit in the AMO description and depending on whether the nuclei are in the same or different subsets of the alternant system, this term alternates in sign.
LCAO—MO–SCF Calculations on LiH Using Gaussian Basis Set
Authors: Csizmadia I. G.
Published: January 2005

A series of calculations was carried out on LiH using Gaussian-type functions (GTF) to approximate the Hartree—Fock (HF) molecular orbitals in an LCAO expansion. Scaled orbital exponents on Li and optimized exponents on H were used. The calculated values approached the Hartree—Fock limit asymptotically very well. These encouraging results certainly justify the recent use of GTF's on small organic molecules.
Temperature-Independent Factor in Isotopic Rate-Constant Ratios
Authors: Gatz Carole R.
Published: January 2005

A general expression is given for the temperature-independent factor (TIF) in isotopic rate-constant ratios, in terms of the reaction coordinate (a linear combination of internal displacement coordinates) and the G matrix for the transition state. Values of TIF for some three-center carbon models are given for reaction coordinates that include simultaneous changes in bond angle and bond lengths.
Theoretical Transition Probabilities
Authors: La Paglia S. R. , Sinanoğlu Oktay
Published: January 2005

The contribution to the intensity of atomic and molecular electronic transitions beyond the Hartree—Fock, or independent-particle model, is examined by means of ``many-electron theory'' (MET). The contribution is of first order in the wavefunctions of the combining states.

MET analysis of the off-diagonal matrix element for the transition probability in the frozen-core approximation yields physically interesting expressions which are applied to atomic and molecular examples. Considerable improvement in calculated atomic (e.g., Be resonance transition) and molecular (e.g., π—π* transitions) intensities are obtained when analysis shows that ground-state ``hole pairs'' are strongly scattered into the orbital sea of the excited state.

The uses of energies and operators in the calculation of electronic intensities is also examined. The relation between the expectation values of operators ∇ and r which replaces the widely used off-diagonal hypervirial theorem in the absence of exact wavefunctions is given.
Many-Electron Theory of Nonclosed-Shell Atoms and Molecules. I. Orbital Wavefunction and Perturbation Theory
Authors: Silverstone Harris J. , Sinanoğlu Oktay
Published: January 2005

A theory of electron correlation in nonclosed-shell states, such as excited states of atoms and molecules, triplet states, free radicals, and transient species, is developed. A general (multiconfiguration) restricted Hartree—Fock (GRHF) wavefunction is taken as the starting point. When near degeneracies are not strong enough to cause large orbital and charge deformations, Roothaan-type restricted Hartree—Fock (RHF) open-shell orbital theories are used. The first-order Schrödinger equation with RHF as the zeroth-order wavefunction is solved. Various correlation processes (near-degeneracy-type internal correlations, semi-internal pair correlations in which only one electron is ejected out of the Hartree—Fock sea, external pair correlations as in closed shells, and spin and symmetry orbital average polarization effects) are obtained in a form separated from one another. The second-order energy also includes ``cross-pair correlation effects,'' an open-shell phenomenon that need be taken into account in the evaluation of electronic spectral levels and stability of open-shell systems. The first-order solution yields the main open-shell correlation processes, which are generalized to the variational theory in II with means for evaluation of the separate effects.
Delayed Ionization of Excited Phenanthrene and Anthracene in Solution
Authors: Kawada Allan , Jarnagin R. C.
Published: January 2005

The delayed ionization of excited states of phenanthrene and anthracene was observed in tetrahydrofuran solution. The measured photocurrent rose, attained a maximum, and decayed in time very long compared to flash duration. No currents were observable in hexane solution and current response was quenched on admission of O2 to the tetrahydrofuran solutions. The observed time dependence, dependence on flash intensity, and wavelength dependence are consistent with an interpretation based on 3B1 excitation via intersystem conversion from excited 1A1 and the subsequent interaction of two 3B1 molecules to yield current carriers.
Hugoniot Equations of State of Several Unreacted Explosives
Authors: Coleburn N. L. , Liddiard T. P.
Published: January 2005

Plane shock-wave compressions and an optical method were used to obtain the unreacted equations of state of 11 explosives and propellants for pressures up to 90 kbar. Measurements of the transit times of weak shock waves (∼100 bar) yielded longitudinal sound-wave velocities.
Heterogeneous Nucleation of Alkali Halide Crystals from Solution
Authors: Upreti M. C. , Walton A. G.
Published: January 2005

The epitaxial nucleation of KCl, KBr, KI, NH4I, RbCl, and RbBr from solution onto mica substrates at various temperatures has been examined. Critical supersaturations, produced by cooling the substrate thermoelectrically, were found to be sensitive to lattice matching and saturation temperature. The critical supersaturation decreased with increase in saturation temperature and increased with decrease in lattice match between substrate and deposit. Experimental results conform semiquantitatively to a modified two-dimensional nucleation equation. Apart from the lattice matching and saturation temperature, adsorption energy, surface diffusion and the lattice energy of the crystal deposit are believed to play an important part in heterogeneous nucleation. Hence surface-active sites, where ions are bound strongly, favor nucleation. Materials of high lattice energy are not readily nucleated even if matching with the substrate is perfect.
Temperature Dependence of ESR Linewidths of Some Nitrobenzene Anion Radicals
Authors: Millett Francis , Harriman John E.
Published: January 2005

Electron spin resonance spectra of anion radicals of nitrobenzene and p-nitrobenzoic acid in dimethylformamide and of p-nitrophenol in dimethylformamide and acetonitrile have been obtained over a range of temperatures. Linewidths have been measured and the variations among them are discussed in terms of the Freed—Fraenkel theory. It is concluded that the anisotropy of molecular tumbling must be considered for these systems, but a complete analysis has not been made.
Radiationless Deactivation of the Fluorescent State of Substituted Anthracenes
Authors: Bennett R. G. , McCartin P. J.
Published: January 2005

Radiationless deactivation of the fluorescent state of substituted anthracenes has been studied by measuring the temperature dependence of both the triplet yield and the absolute fluorescence lifetime. It is concluded that in those derivatives which show a significant variation of fluorescence yield with temperature, radiationless deactivation proceeds entirely by intersystem crossing. The existence of triplet states which are approximately degenerate with the fluorescent state in anthracene derivatives has been demonstrated experimentally. A tentative explanation is offered for the influence of temperature and substitution on the fluorescence behavior of substituted anthracenes.
59Co Nuclear Electric Quadrupole Coupling in a Single Crystal of Co(en)3Cl3·3H2O
Authors: Scott B. A. , Bernheim R. A.
Published: January 2005

The nuclear electric quadrupole coupling constant of 59Co in a single crystal of the racemic Co(en)3Cl3·3H2O was determined to be 2.63 Mc/sec from the splitting of the 59Co nuclear magnetic resonance spectrum. The sign of the coupling constant is probably negative from considerations of the contribution of the lattice to the electric-field gradient, assuming a point-charge model, together with the very small distortion of the Co(en)33+ complex observed in x-ray diffraction studies.
Line-Shape Analysis in EPR Spectra of Nb(IV) Complexes in Solutions and Glasses
Authors: Lardon M. , Günthard Hs. H.
Published: January 2005

The EPR spectra of a Nb (IV) complex in alcoholic liquid and solid solution are investigated between 293° and 77°K. The spectra exhibit hyperfine structure originating from interaction of one single 4d electron with the central Nb(I=92) nucleus. At 77°K the spectra show a complicated appearance. In order to analyze the observed spectra a formula for the line shape is derived by assuming a Lorentzian shape function, axial symmetry of both the g and a tensor, and completely randomized orientation of the complexes. With the correct transition probabilities and a certain approximation for the resonance field a closed expression for the line shape of a single hyperfine structure line is given, which readily lends itself to numerical calculation. By use of a computer program the components of the g and a tensor are determined for three different alcohols, methanol, ethanol, and isopropanol, as solvents (see Table IV). It is shown that satisfactory agreement between observed and calculated spectra can only be obtained if anisotropy of the Lorentzian line-shape parameter is assumed besides the well-known dependence of this parameter on the magnetic quantum number m.
Kinetics of Unimolecular Breakdown. IV. The Linear Chain
Authors: Levine R. D.
Published: January 2005

The time evolution of a system characterized by a Hückel Hamiltonian is studied. The model employed is that of electron (or excitation) transfer in a linear chain. Exact solutions are obtained for Green's function, rate and transition functions, the lifetime, and the master equation for the transfer.
Kinetics of Unimolecular Breakdown. V. Mass-Spectral Patterns
Authors: Levine R. D.
Published: January 2005

The measurement of mass-spectral patterns is discussed as a foundation for a formal theory. The formalism is developed in close correspondence with experimental information and concepts. The Morrison technique is discussed and expressions are derived for all measured quantities in terms of the matrix elements of relevant transition operators.

Rearrangement processes are discussed and isotope retention ratios are predicted in agreement with experiment.
Electron Spin Resonance of the Radical Ions of an Isomeric Alternant and Nonalternant Aromatic Hydrocarbon
Authors: Lewis I. C. , Singer L. S.
Published: January 2005

Electron spin resonance (ESR) spectra have been obtained for the negative ions of the nonalternant aromatic hydrocarbon Δ9,9′-bifluorene, and for its even alternant structural isomer, dibenzo(a,c)triphenylene. Coupling constants have been determined and compared with those obtained for the positive ions and with spin densities calculated from Hückel molecular orbital (HMO) theory.
Calculation of the Barrier to Internal Rotation of Ethane
Authors: Goodisman Jerry
Published: January 2005

It is proposed to calculate the barrier to internal rotation from the torque on a CH3 top when the molecule is in an intermediate rotational configuration, rather than from the energies of the staggered and eclipsed forms. Advantages of this approach, which requires only an approximation to the electronic distribution for this one configuration, are discussed. Three easily derived approximate molecular orbital functions for ethane yield barriers between 0.7 and 2.1 kcal/mole.
Effect of Beam Temperature on the Heterogeneous Nucleation of Zinc from the Vapor
Authors: Ruth V. , Moazed K. L. , Hirth J. P.
Published: January 2005

The effect of the vapor temperature on the nucleation of zinc from the vapor phase onto substrates of mica, lithium fluoride, and Pyrex glass was investigated with a double-Knudsen-cell technique. There was some effect of beam temperature on the critical supersaturation for nucleation on all three substrates. For the glass substrate the critical supersaturation was determined as a function of beam temperature and was found to agree well with earlier measurements by Hudson if the model of disk-shaped nuclei is assumed. The results indicated that the thermal accommodation coefficient for zinc on Pyrex is aT=0.78 in the range 600°—800°K.
Quantum Statistical Mechanics of Isotope Effects. II. The Surface Tension and Internal Energy
Authors: Deutch J. M. , Kinsey J. L. , Oppenheim I.
Published: January 2005

The thermodynamic properties of a system with given intermolecular potential, including first quantum corrections, are shown to be identical to those for a classical system with an effective intermolecular potential. This technique, together with a statistical-thermodynamic derivation of a molecular expression for the surface tension, enables one to calculate the classical and the first-quantum-corrected surface tension. The first quantum corrections are utilized to discuss the difference in the thermodynamic properties of isotopes. The agreement between the experimental and theoretical difference in surface tension of H2 and D2 is excellent. It has been found that the major difference is due to the difference in density along the vapor—liquid equilibrium line. The effect is similar though not as pronounced in the case of the energy of vaporization.