bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Spectrum of Methyl Difluoramine : Structure, Conformation, Dipole Moment, Barrier to Internal Rotation, and Quadrupole Coupling Constants of the Molecule
Authors: Pierce Louis , Hayes Robert G. , Beecher James F.
Published: January 2005

The microwave spectra of the common and three isotopic species of methyl difluoramine have been investigated from 8 to 27 Gc/sec. From an analysis of the rotational constants the following structural parameters are obtained:DCN1.449 ÅCH1.091 ÅNF1.413 Å∠NCHs110∘22′∠FNF100∘59′∠NCHa106∘14′∠CNF104∘38′∠HsCHa111∘45′∠HaCHa110∘15′.The conformation of the methyl group is such that the in-plane CH bond (CHs) is staggered with respect to the NF bonds. The methyl group is nearly symmetric and the NCH angles indicate the methyl group and its symmetry axis to be tilted away from the CN bond axis and towards the unshared electron pair by about 2.8°. Quadrupole hyperfine structure was resolved and analyzed for each of the four species. The quadrupole coupling constants of the common species are: χAA=6.45 Mc/sec, χBB=0.46 Mc/sec, χCC=−6.91 Mc/sec. A crude estimate of χBC (2.8±0.6 Mc/sec) is obtained by comparing data for the common and symmetric monodeutero species. The rotation of principal axes in going from one species to the other is 2°11′. A similar comparison of Stark effect data for the same two species makes it possible to determine uniquely the orientation of the dipole moment. The dipole moment is 2.57±0.03 D and it lies at an angle of 12°54′ with respect to the CN bond. No tunnel-effect splittings were resolved in the ground-vibrational state; however, such splittings were found in the first-excited torsional state and they yield the threefold symmetric part of the barrier to internal rotation as V3=4170 cal/mole. Using parameters based on reasonable notions of bonding in CH3NF2, the Townes and Dailey theory of quadrupole coupling is found to account satisfactorily, though approximately, for the observed coupling constants. Similar results are obtained for CD3ND2 and HNF2. The relationship of methyl group ``tilt'' to the problem of barriers to internal rotation is discussed.
Series Expansion for Two-Center Noninteger-n Overlap Integrals
Authors: Silverstone Harris J.
Published: January 2005

A series in the internuclear distance R is derived for the two-center overlap integral between noninteger-n Slater-type orbitals. There are in general two types of terms: R2N+λ and Rn1+n2+1+N, (N=0,1,2,···; λ = |l1—l2|, |l1—l2| + 1, ···, l1+l2). When n1+n2 is an integer while n1 and n2 are not integers, logarithmic terms arise. The series is for general values of n1, n2, l1, l2, m1, m2, ζ1, and ζ2, and it converges absolutely for R<∞.
Series Expansion for Two-Center Noninteger-n Coulomb Integrals
Authors: Silverstone Harris J.
Published: January 2005

A series in the internuclear distance R is derived for the two-center Coulomb integral between noninteger-n Slater-type charge distributions. There are in general two types of terms: R2N+λ and Rn1+n2+3+N, (N=0, 1, 2, ···; λ = |l1—l2|, |l1—l2| + 1, ···, l1+l2). Most of the coefficients are found from the coefficients of the overlap series by exploiting {∇2 (Coulomb integral) = −4π (overlap integral)}. When n1 and n2 are not integers but n1+n2 is, the series contains logarithmic terms. The series is for general values of n1, n2, l1, l2, m1, m2, ζ1, ζ2, and R, and it converges for R<∞.
Polarizability of an Argon Atom in Solid Argon
Authors: Keil Thomas H.
Published: January 2005

A calculation in the tight-binding approximation, of the static polarizability of an argon atom in solid argon is presented. A linear variational technique is used to estimate the polarizability. The results are given as a function of the lattice parameter. The predicted polarizability at the normal solid density at T = 0°K is about 6% less than the free-atom value. For an increase in density accessible to pressure measurements of the static dielectric constant, an additional decrease of 4% in the polarizability is predicted. The relevance of these results to an a priori calculation of an interatomic potential for solid argon is discussed.
Difference-Equation Model for Ionic Conductivity. I. Step Voltage Response
Authors: Kahn D. , Maycock J. Norman
Published: January 2005

The differential equations for two-carrier charge transport with current blocking electrodes are discussed. An explicit difference equation analog to these quasilinear, parabolic, partial differential equations is obtained. It is shown that such a model is stable over a sufficient time period for a range of input parameters. The initial current obtained when a step voltage is applied to the crystal is shown to be the sum of two exponentials corresponding to the mobilities of the two vacancy species. The dependence of the initial decay constant on various parameters is obtained. In most instances the dependence does not agree with the predictions of a linearized theory. The dependence does agree with experimental results in all cases. The applicability of these results to the problem of electron diffusion is discussed.
Density Dependence of the Bulk Viscosity in Argon
Authors: Madigosky W. M.
Published: January 2005

The coefficient of ultrasonic attenuation in dense gaseous argon was measured as a function of frequency from 5 to 85 MHz, and as a function of density from 0.5 to 1.0 g/cm3 at −38.6°C. The attenuation was found to be in excess of that attributed to the shear viscosity and thermal conductivity and was ascribed to the existence of a significant bulk viscosity. The magnitude of the bulk viscosity was found to be less than the hard-sphere calculation of 53 the shear viscosity, and essentially proportional to the density squared. The results are in excellent agreement with the predictions of Gray and Rice and support the Rice—Allnatt approach to a theory of liquid transport properties.
Deuteron Nuclear Magnetic Resonance in Anthracene Crystals
Authors: Ellis David M. , Bjorkstam John L.
Published: January 2005

The room-temperature electric quadrupole coupling constants |eQΦzz/h| and asymmetry factors η=(Φxx—Φyy)/Φzz for deuterons in single-crystal anthracene-d10, have been determined. For all deuteron sites |eQΦzz/h| falls in the range 181±3 kc/sec, and η=0.064±0.013. |Φzz| > |Φyy| > |Φxx| are elements of the diagonalized electric-field-gradient tensors at the deuteron sites, with Q the deuteron electric quadrupole moment. Within experimental error, at each site Φzz is along the geometrical C—D bond, and Φyy is normal to the molecule plane.
Force Constants of Diatomic Molecules. I. A General Semitheoretical Approach
Authors: Empedocles Philip
Published: January 2005

A general method for calculating the quadratic, cubic, and quartic force constants of homonuclear diatomic molecules and binary hydrides is proposed. The scheme has been designed to be sufficiently simple for application to any molecule and represents an attempt to bridge the gap between atomic and molecular data. It uses as starting parameters only the orbital exponents and one-electron, one-center, kinetic-energy integrals for the united and separated atoms. A distorting operator is defined and used to generate functions of the molecular orbital type. A scaling property of wavefunctions along the three independent Cartesian axes is invoked to calculate a reasonably close approximation to the kinetic energy of the electrons and its derivatives with respect to the internuclear coordinate. The virial method is used to calculate the force constant from these quantities. The method is applied to the elements of the first and second periods.
Photolysis of Matrix-Isolated Dichlorine Monoxide: Infrared Spectra of ClClO and (ClO)2
Authors: Rochkind Mark M. , Pimentel George C.
Published: January 2005

In situ photolysis of matrix-isolated dichlorine monoxide, Cl2O, at 20°K, produced eight bands near 960 cm−1 and a quartet near 375 cm−1. Growth plots for the high-frequency features during photolysis show that three distinct molecules are produced. Oxygen and chlorine isotopic shifts indicate that ClClO, with a structure like those of the nitrosyl halides, is most probably responsible for absorptions between 962 and 952 cm−1 as well as for the 377–368-cm−1 quartet. In addition, bands at 982 and 945 cm−1 are attributed to (ClO)2, in which pairs of ClO molecules are weakly linked. Thus (ClO)2 resembles the nitric oxide dimer rather than H2O2 or O2F2. The observed frequencies indicate that the vibrational frequency of ClO itself is probably near 970 cm−1 rather than 853 cm−1 as deduced earlier from electronic spectra.
Simple Test of Unimolecular Reaction Theory
Authors: Lyon Richard K.
Published: January 2005

If a molecule undergoes a unimolecular isomerization among three virtually identical forms, and the isomerization is sequential at high pressures, then the isomerization will become direct as the pressure is decreased. This low-pressure selectivity shift can be calculated completely a priori from the Rice—Ramsperger—Kassel theory without any empirical information or assumptions concerning either the molecule or the transition state. As an example of such a system the isomerization of 1-proto-perdeuteriocyclopentadiene has been studied as a function of pressure. The observed low-pressure selectivity shift is in good agreement with the prediction.
Vacuum-Ultraviolet Photolysis of Acetylene in Inert Matrices. Spectroscopic Study of the Species C2
Authors: Milligan Dolphus E. , Jacox Marilyn E. , Abouaf-Marguin Luce
Published: January 2005

The vacuum-ultraviolet photolysis of acetylene isolated in Ar, Ne, and N2 matrices at 4° and at 14°K is shown to lead to the appearance of a number of visible-ultraviolet absorption bands which may be assigned to the species C2, as well as to an 1848 cm−1 infrared absorption assigned, with the aid of isotopic substitution studies, to the free radical HC2. The (0, 0) band of the Mulliken system of C2 is observed with great intensity at 2382 Å (Ar matrix) or at 2323 Å (Ne matrix) and the (2, 0), (3, 0), and (4, 0) bands of the Phillips system of C2 are observed in an Ar matrix at 8700, 7675, and 6880 Å, respectively, indicating that the x 1Σg+ state of C2 is the ground state of this species not only in the gas phase but also in the matrix. Features assigned by previous workers to the Swan transition of triplet C2 appear at 5206 and 4725 Å. A third member of the progression, not previously observed, appears at 4334 Å. Experiments utilizing C2D2 and C2H2 (58% 13C) support the assignment of these features to C2. The 5206-Å band system decreases in intensity and finally disappears when the sample is subjected to radiation of wavelength near 2500 Å. Problems associated with the assignment of these features are discussed, and a possible mechanism for their photolytic destruction is suggested.
Near-Molecular Hartree—Fock Wavefunction for CH3−
Authors: Kari R. E. , Csizmadia I. G.
Published: January 2005

Ab initio LCAO—MO—SCF calculations have been performed on CH3− with a C–H bond length of 1.95 Bohr atomic units, using Gaussian-type functions (GTF) as the basis set. By successive increases in the size (N) of the basis set of GTF (N = 12, 20, 28, 36, 40) it was possible to approach the estimated molecular Hartree—Fock limit within 0.06 Hartree atomic units. The best calculated total energy was −39.4798 hartrees. The Hartree—Fock limit has been estimated to be −39.535 hartrees for the equilibrium C–H distance, and as high as −39.501 hartrees for the above C–H separation. The variation of the geometry of CH3− indicated that the molecule is pyramidal in its ground state, with the HCH angle approximately equal to 115°. The inversion-barrier height is estimated to be 1.22 kcal/mole. The charge distribution, as deduced from Mulliken's population analysis, was such that there was approximately 1.099 negative charge on the carbon atom and 0.033 positive charge on each of the three hydrogen atoms. Due to its symmetry, the planar molecule possessed zero dipole moment but it assumed finite values in pyramidal conformations. The total electron density as well as the near-Hartree—Fock molecular-orbital densities are presented in the form of contour maps. Within the framework of a single Slater determinantal wavefunction, estimation for the energy values of some of the low-lying electronic excited states of CH3− have been made.
Some Thermodynamics of Photochemical Systems
Authors: Ross Robert T.
Published: January 2005

A limit on the thermodynamic potential difference between the ground and excited states of any photochemical system is established by evaluating the potential difference at which the rate of photon absorption and emission are equal; the relationship between absorption and emission is given by a Planck-law relation, provided that there is thermal equilibrium between the sublevels of each electronic band. The actual potential developed may be evaluated if the quantum yield of luminescence is known. The maximum amount of power storage obtainable is evaluated by lowering the potential difference until the product of the potential difference and the fraction of the quanta retained is maximized. The history and applications of the Planck-law relation between absorption and emission spectra are discussed briefly, and applications of the potential difference calculation are mentioned.
Long-Wavelength, Infrared-Active Fundamental for Uranium, Neptunium, and Plutonium Hexafluorides
Authors: Frlec Boris , Claassen Howard H.
Published: January 2005

The long-wavelength, infrared-active fundamentals, ν4, have been observed for uranium, neptunium, and plutonium hexafluorides at 186.2, 198.6, and 206.0 cm−1, respectively. The corresponding values predicted earlier from combination bands were 184, 198, and 203 cm−1. From the P—R branch separations Coriolis zeta constants have been calculated for these bands.
Microwave Spectrum and Rotational Isomerism of Ethyl Formate
Authors: Riveros José M. , Wilson E. Bright
Published: January 2005

The microwave spectrum of ethyl formate reveals the presence of at least two rotational isomers. Both isomers have the ethyl group cis to the carbonyl oxygen atom but they differ in the orientation of the methyl group about the –CH2–O bond. The trans isomer has the conformation with the heavy-atom skeleton coplanar, while in the gauche isomer the methyl group is 95° out of the plane. The relative intensity measurements show the trans isomer to be lower in energy with the difference between the lowest states of the two isomers (gauche—trans) equal to 186±60 cal/mole. Five vibrationally excited states for the trans and one excited state of the gauche are assigned to the torsion about the –CH2–O bond. The relative intensities of these excited states and their rotational constants are used to derive, in the one-vibration approximation, the potential function for the internal rotation of the ethyl group. This potential function yields an estimated 1100±250 cal/mole for the trans—gauche potential barrier. The dipole moment of both isomers is calculated from Stark-effect measurements, yielding μ = 1.98±0.02 D for the trans and μ = 1.81±0.02 D for the gauche form.
Photochromism. II. Photochemistry of Salicylideneaniline
Authors: Ottolenghi Michael , McClure Donald S.
Published: January 2005

The processes following electronic excitation of salicylideneaniline include the photochemical formation of a colored orthoquinonelike molecule, phosphorescence, and several modes of radiationless decay back to the ground state. These pathways are examined in detail to learn the steric requirements, relative yields, temperature effects and the electronic states involved for each. It is shown that the photochemistry occurs from the lowest singlet (nπ*) level, and that phosphorescence (τ=80 μsec in EPA at 77°K) is in competition with it. An independent parallel radiationless process appears to lead from the lowest ππ* singlet to the lowest ππ* triplet. Evidence for the latter state is a metastable absorption at 5000 Å, τ=330 μsec in EPA at 77°K. The steric inhibition of the photochemistry was investigated by using a mixed crystal system, salicylideneaniline in dibenzyl.
Molecular Orbitals and Inner-Electron-Shell Chemical Shifts for Sulfur and Chlorine Oxy-anions
Authors: Manne Rolf
Published: January 2005

Approximate MO LCAO SCF calculations have been performed on the ions SO42−, S2O32−, SO32−, ClO4−, ClO3−, and ClO2−. The results are applied to a discussion of chemical effects in x-ray spectra and inner-shell photoelectron spectra. Good agreement is obtained with charge distributions estimated from shifts of the Kα12 emission line of sulfur and chlorine. The valence-electron molecular-orbital structure differs considerably from that obtained from Wolfsberg—Helmholz calculations and agrees with ESR measurements on SO4− and S2O3−.
Effects of Fluorescence and Energy Transfer in Polystyrene under Excitation in the Vacuum Ultraviolet
Authors: Leibowitz M. , Weinreb A.
Published: January 2005

The emission spectrum of solid polystyrene is investigated as a function of excitation wavelength in the region 2540–1216 Å, for various modes of preparation (solid machined disks, films, evaporation layers) and treatment (heating, polishing, etc.). A strong dependence of the spectral distribution on excitation wavelength is observed. Exciting radiation which is more strongly absorbed produces a fluorescence spectrum extending to longer wavelengths. A strong influence of the mode of preparation and treatment of the sample on the fluorescence spectrum is observed. The results are tentatively interpreted as representing the strong influence of the solid-state structure of the material on intermolecular interactions between segmers.

The fluorescent quantum yield of solid solutions of diphenyloxazole and of anthracene in polystyrene is investigated as a function of the excitation wavelength in the region 3164–584 Å. A strong variation of the quantum yield with excitation wavelength is observed. The results are interpreted in terms of a competition between solvent—solvent and solvent—solute interactions, the probability of each depending on excitation wavelength. The difference in behavior of solutions of PPO and solutions of anthracene is discussed.
Molecular Resonant Charge-Transfer Processes; H2+–H2 and N2+–N2
Authors: Leventhal J. J. , Moran T. F. , Friedman L.
Published: January 2005

A study has been made of the competition between exothermic ion—molecule reactions and resonant charge-transfer processes in collisions of diatomic molecule ions and their parent molecules; H2+–H2 and N2+–N2. Experimental values of resonant charge-transfer cross sections are shown to be smaller than values obtained from calculations using an impact parameter method. Much better agreement between experiment and theory is obtained if competition between ion—molecule reaction and charge transfer is assumed and experimental values of both channels of reaction are summed prior to comparison with theory. The mechanisms of the respective processes are illuminated by an examination of the velocity dependences of charge-transfer cross section for both diatomic systems. With H2+–H2 where reaction producing H3+ is a probable process, in low-velocity collisions, the velocity dependence of charge transfer is essentially that of collisions of ions with unperturbed rectilinear trajectories. In a similar low-energy region, N2+–N2 is not energetically capable of participating in ion—molecule reactions and the velocity dependence of charge-transfer cross section is steeper, characteristic of both orbiting collisions and the larger-impact-parameter rectilinear trajectory collisions. Experimental cross sections for charge transfer and ion or atom transfer reflect probability of reaction but their velocity dependences clearly isolate the range of impact parameters operative for the respective processes.
Fluorescence and Triplet State of Hexafluorobenzene
Authors: Phillips David
Published: January 2005

The photochemistry of hexafluorobenzene in the vapor phase has been studied to compare the heavy-atom substituted molecule with the unsubstituted molecule of the same symmetry. Results show that at all wavelengths below 2800 Å, absorption produces two excited singlet states, one of which is quickly equilibrated to a fluorescent state, the other more slowly. Some process occurs from the latter state with a rate such that collisional loss of energy is barely competitive. This process may be an isomerization. The use of the biacetyl sensitization and Cundall techniques at various wavelengths indicated that the lifetime of the hexafluorobenzene triplet was short, and of the order of 10−7 sec leading to difficulties in absolute measurement of the triplet-state yields. The quenching of biacetyl phosphorescence excited by 4358-Å radiation by hexafluorobenzene is observed, and the effect of exciting wavelength upon the fluorescence yields of hexafluorobenzene is discussed. A simple mechanism has been proposed and rate constants and quenching cross sections calculated.
NMR Studies of Single Crystal ND4Cl
Authors: Linzer Melvin , Forman Richard A.
Published: January 2005

The 2D and 14N NMR spectra in single crystals of ND4Cl have been studied from room temperature to −175°C. At high temperatures, motion of the ammonium ion narrows the NMR resonances and averages out both dipole—dipole and quadrupole interactions. As the temperature is lowered, a linewidth transition occurs and quadrupole splittings of the 2D spectrum appear. No splitting is found for the 14N spectrum in both NH4Cl and ND4Cl. From crystal rotation studies, the 2D quadrupole coupling is determined to be 180.1±1.0 kHz and the asymmetry parameter to be 0.00±0.01.
Pairwise Trapping of Dissimilar Radical Species and Radical Conversion in a Single Crystal of Monofluoroacetamide γ Irradiated at 77°K as Studied by Electron Spin Resonance
Authors: Iwasaki Machio , Toriyama Kazumi
Published: January 2005

This is the first report of the pairwise trapping of dissimilar radical species in irradiated crystals. Besides the isolated radical of ·CH2CONH2, a radical pair between ·CH2CONH2 and ·CHFCONH2 was found in a single crystal of CH2FCONH2, γ irradiated at 77°K. The paired radicals were formed with one specific orientation and separation which were the same as with the molecules in the undamaged crystal. The observed principal values of the D tensor due to the magnetic dipole interaction of the two unpaired electrons gave a mean distance between the paired radicals of 7.03 Å. The alignment of the paired radicals was also determined by the principal directions of the D tensor. Both the separation and the alignment of the paired radicals thus obtained are in very good agreement with those calculated from the structure of the mother crystal. Furthermore, on warming the crystals the isolated radical ·CH2CONH2 was quantitatively converted into the radical ·CHFCONH2 which is the same species as found in room-temperature irradiation. The pairwise trapping of dissimilar radicals and the radical conversion found must give important information in considering the primary process of the radiation-induced reaction.
Pople-like SCF—LCAO—MO Treatment of 77′,88′-Tetracyanoquinodimethan and Its Univalent Anion
Authors: Lowitz David A.
Published: January 2005

Roothaan closed- and open-shell SCF—LCAO—MO calculations were carried out for 77′,88′-tetracyanoquinodimethan (TCNQ) and its univalent anion (TCNQ−), respectively. The dominant integrals were evaluated semiempirically in the manner of Pariser, Parr, McWeeny, and Peacock, including the approximation of total zero-differential overlap (TZDO). Singlet and triplet spectra for TCNQ0 and doublet and quartet spectra for TCNQ− were calculated by means of a configuration-interaction treatment involving singly excited states. Good correspondence was obtained with the experimental spectra. In addition, also in the TZDO approximation, we calculated the same spectra based on a semiempirical evaluation of the dominant integrals in the manner of Mataga, Nishimoto, Popkie, and Moffat. The two sets of theoretical spectra can be taken to correspond equally well with experiment. Charge density and spin density in TCNQ− based on an approximation to a projected UHF wavefunction following Amos and Snyder were obtained. Comparisons made with SCF, Hückel, and McLachlan spin-density values show the usual correspondence, and there is reasonable agreement with an experimental value of the spin density at the unsubstituted ring carbon. Bond lengths obtained from bond orders agree very well with the x-ray results of Fritchie and Arthur on Cs TCNQ, where they observed two species of TCNQ and assigned one as TCNQ0 and the other as TCNQ−.
Cyclotron Resonance in Gases. I. Atoms and Nonpolar Molecules
Authors: Tice Russell , Kivelson Daniel
Published: January 2005

The cross sections for the scattering of very low-energy electrons, i.e., room-temperature electrons, from N2 molecules have been measured as a function of electron velocity. The cross sections were determined by analyzing the widths and shapes of the cyclotron resonance absorption lines for electrons in an active nitrogen atmosphere. The electron-scattering cross sections for He, H2, D2, Ar, CH4, CD4, and CF4 have also been determined by analyzing the cyclotron resonance linewidths and shapes for electrons in a gaseous mixture of N2 and the other gas studied. The results agree reasonably well with those obtained by different techniques by other workers. No isotope effects were observed.
Paramagnetic Resonance of Gd3+-Doped La(NO3)3·6H2O and Nd(NO3)3·6H2O Single Crystals
Authors: Singh G. B. , Venkateswarlu Putcha
Published: January 2005

The paramagnetic resonance of Gd3+ in single crystals of La(NO3)3·6H2O and Nd(NO3)3·6H2O is studied at room temperature. A seven-line spectrum for H∥Z as well as for H ∥ X corresponding to ΔM = ±1 transitions, are observed in these crystals. The estimated zero-field splittings of Gd3+ in various single crystals studied by the authors are compared and discussed.
Kinetics of Anion Exchange between Methyl Mercuric Complexes
Authors: Simpson Richard B.
Published: January 2005

In the proton magnetic resonance spectrum of CH3HgBr or of CH3HgI, the satellites produced by 199Hg–H spin coupling are broader than in other methyl mercuric compounds. This broadening, formerly attributed to alkyl exchange, is better explained by fast relaxation of the 199Hg nuclear spin. The large quadrupole moments of bromine and iodine are probably responsible for the 199Hg relaxation.

Anion exchange of various pairs of methyl mercuric compounds (studied by the line-shape method of Gutowsky and Holm) was too fast to measure unless cyanide was one of the anions. Rate constants and heats and entropies of activation for exchange of cyanide with hydroxide, chloride, sulfite, and thiosulfate were calculated assuming an anionic attack mechanism, e.g., CH3HgCN+X−=CH3HgX+CN−. For exchange of CH3HgCN with the hydroxide complex below pH 9 or with the mercaptoacetate complex, anionic attack seems inadequate to account for the rates, so direct reaction between CH3HgCN and the other methyl mercuric compound is postulated to occur at the high methyl mercuric concentrations used in NMR.
Electron Spin Resonance Studies of Ion-Pair Equilibria
Authors: Crowley Arthur , Hirota Noboru , Kreilick Robert
Published: January 2005

We have investigated the ESR spectra of the sodium anthracene and sodium 2, 6-di-t-butylnaphthalene anion radicals in a series of different solvents and a number of different temperatures. The sodium splitting, in both radicals, depends both on solvent and temperature. Changes in the sodium coupling constants, with these parameters, are explained by a model involving equilibria between different ion pairs. Equilibrium constants and enthalpy changes are calculated. The rate constants for interconversion of the two species are determined from changes in linewidths. Activation energies were obtained in some cases.
Optimized Molecular Orbital Wavefunctions for Methane Constructed from a Minimum Basis Set
Authors: Pitzer Russell M.
Published: January 2005

Molecular orbital wavefunctions are given for methane for three closely spaced values of the C–H distance near equilibrium. The basis set is a minimum set of Slater orbitals with optimized orbital exponents. The energies are less than 0.1 a.u. from estimated Hartree—Fock energies. Other properties of the molecule, including force constant, quadrupole coupling constant, and octopole moment are computed. Localized molecular orbitals have been determined for one case.
Influence of Finite Number of Chain Segments, Hydrodynamic Interaction, and Internal Viscosity on Intrinsic Birefringence and Viscosity of Polymer Solutions in an Oscillating Laminar Flow Field
Authors: Thurston G. B. , Peterlin A.
Published: January 2005

The theory for the frequency-dependent properties of dilute polymer solutions, i.e., flow birefringence, acoustic birefringence, and viscosity, has been developed by Peterlin using the Gaussian necklace model and incorporating the internal viscosity introduced by Cerf. The results of this theory are now examined particularly for the influence of molecular weight (number of Kuhn statistical segments in the model), hydrodynamic interaction, and internal viscosity as three independent parameters. The theoretical results are examined in detail for a wide variation of each of the parameters. It is found that while the frequency dependence of the magnitude and phase of the viscosity and the birefringence are greatly affected by all three parameters, the number of segments is capable of producing the greatest variation. The character of the frequency dependence of viscosity may be considerably different from that for birefringence depending upon the effect of the internal viscosity. The intrinsic flow birefringence and acoustic birefringence are shown to have identical frequency dependences, irrespective of the values of the three parameters.
Relativistic Crystal-Field Splitting of Mn2+
Authors: Van Heuvelen Alan
Published: January 2005

Relativistic effects described by Wybourne have been used to help explain the crystal-field splitting of the 6S5/2 ground state of Mn2+. The relativistic axial splitting has the correct sign and M dependence, and about one-half the magnitude of the axial splitting observed in most crystals containing Mn2+. The relativistic effects compare in magnitude to splittings predicted by other mechanisms. Other mechanisms require the use of unknown integrals, whereas the relativistic theory can be checked experimentally by optical and electron paramagnetic resonance techniques.
Isotope Effects on Metastable Transitions. II. CH3CD2CH3 and CD3CH2CD3
Authors: Lifshitz Chava , Shapiro Moshe
Published: January 2005

Metastable transitions were studied in the mass spectra of 2,2-dideuteropropane and 1,1,1,3,3,3-hexadeuteropropane in a sector mass spectrometer. The relative abundances of the various metastable ions at 70 eV were determined. Two parent-ion metastable transitions were studied carefully: the methane- and hydrogen-atom eliminations. The metastable transition at m/e=19.6, due to the elimination of CH4 from CH3CD2CH3+, is very abundant, amounting to 0.19% of the total ionization at 70 eV. No metastable transition was, however, observed for either of the methane eliminations (CD4 or CD3H) from CD3CH2CD3+. Similarly, no transition was observed for the CH3D elimination from CH3CD2CH3+. The transitions at m/e=48.1, due to H loss from CD3CH2CD3+, and at m/e=42.1 due to D loss from CH3CD2CH3+, were both observed. Reaction rate constants were determined for these transitions, as well as, for the transition due to D loss from perdeuterated propane. The results are discussed in terms of the quasiequilibrium theory of mass spectra.
Mechanism of the Diels—Alder Reactions of Butadiene
Authors: Benson Sidney W.
Published: January 2005

Kinetic data on the pyrolysis of 1,5-cycloöctadiene to give butadiene and 4-vinyl cyclohexene by parallel paths are analyzed and shown to be quantitatively consistent with a common biradical precursor, the octadien−2,6,-diyl−1,8 biradical. It is further shown that these data are in excellent agreement with independent studies of the reverse reactions; pyrolysis of 4-vinyl cyclohexene to butadiene and the dimerization of butadiene. A fourth study of the pyrolysis, in solution of 1,2-divinyl cyclobutane to give butadiene, 1,5-cycloöctadiene, 4-vinyl cyclohexene, and cis—trans isomerization is shown to fit the same scheme with only minor modifications in two of the rate constants. The analysis lends support to the 12.6-kcal assignment of the allyl stabilization energy. It also resolves an apparent anomaly in the rate parameters for the reverse Diels—Alder pyrolyses of cyclohexene, 3-methyl cyclohexene, and 4-vinyl cyclohexene.

Arrhenius parameters for all the elementary rate constants are assigned and shown to be reasonable compared to similar processes. Important rotation-controlled rates in the scheme are examined and conclusions drawn about the contributions of different rotomeric forms of the biradical.
Magnetothermodynamics of α-NiSO4·6H2O. I. Heat Capacity, Entropy, Magnetic Moment, and Internal Energy, from 0.4° to 4.2°K, with Fields 0–90 kG along the c Axis
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: January 2005

The heat capacity and magnetic moment of single-crystal α-NiSO4·6H2O have been measured over a range of about 0.4°—4.2°K in stabilized fields of 0–90 kG. The field was parallel to the c crystallographic axis of the 4-cm-diam spherical sample. Although magnetic saturation was not attained even at 90 kG and 0.4°K, there was essentially no temperature coefficient of the magnetic moment below 0.7°K at any field. The heat capacity approached zero for all fields except for a small calculable contribution due to nuclear polarization at high fields. At 90 kG it was found that the nuclear-spin heat capacity at 0.95°K and above was in general equilibrium. At 0.90°K equilibrium was quite slow indicating a rather rapid increase in relaxation time with decreasing temperature. Each heat capacity series provided a zero-entropy reference, above that due to nuclear spin. These references agreed with precise measurements of the temperature change with field on adiabatics joining the various isoerstedic heat capacity series. The entropy changes, in combination with the work and free energy of magnetization, enabled the evaluation of the changes of internal energy and enthalpy as a function of field and temperature. With very minor deviations it was found possible to represent the heat capacity data at all fields by means of three state Schottky functions. At zero field the two upper states are degenerate and are 4.74 cm−1 (13.55 cal/mole) above the ground state. The variation of the enthalpy of each of the individual levels with field is given. A detailed description of the magnetocalorimeter is included.
Electronic Structure and Ground-State Properties of Titanium Mononitride
Authors: Carlson K. Douglas , Claydon Charles R. , Moser Carl
Published: January 2005

Electronic-band systems recently have been observed and attributed to the TiN and MoN molecules, but they have not been analyzed. This is the only available experimental evidence for the existence of nitride molecules of the transition elements, although oxide and halide molecules of these metals are well known and have been studied extensively. Approximate wavefunctions based on the matrix Hartree—Fock method of Roothaan have been calculated for TiN in this study to provide some information not otherwise available on the ground-state-term type and molecular properties of this molecule. It is found that TiN has a 2Σ+ ground state at re≃1.55 Å and a reasonable dissociation energy of about 5 eV. For thermodynamic reasons, however, gaseous TiN is unstable in equilibrium systems and absent in measurable concentrations.
Radiationless Transitions in Polyatomic Molecules. I. Calculation of Franck—Condon Factors
Authors: Siebrand W.
Published: January 2005

Radiationless transitions between two electronic states are studied for a system consisting of a polyatomic molecule in a medium where vibrational relaxation is rapid. The transition rate is then governed by a vibronic matrix element and a vibrational overlap factor. Only the latter, known as the Franck—Condon factor and denoted by F, is investigated in detail. For harmonic oscillators F derives from shifts in equilibrium distance (displacements) and shifts in frequency (distortions). It is shown that for radiationless transitions involving large energy gaps (E), F is dominated by distortions, whereas for optical transitions it is dominated by displacements of the oscillators. These distortions lead to an approximately exponential decrease of F with increasing E. An isotope rule for F is derived which is valid for both displaced and distorted oscillators provided E is not too small. Since all formulas are of the form F (E), where E is the principal variable, comparison with experiment is only possible for a class of related molecules. Within this class E should vary a great deal but all other parameters should either be constant or vary in a simple, systematic manner. The dependence of some of these parameters on the number of oscillators involved in the transition is examined. Finally the theory is extended to molecular crystals and the corresponding liquids. It is concluded that in these systems the rate constant of an intramolecular radiationless transition must be equal to or smaller than that in dilute solutions, except when excited dimers are present in the initial state.
O−17 Nuclear Magnetic Resonance of Manganese (III) Tris(Acetylacetonate)
Authors: Luz Z. , Silver B. L. , Fiat D.
Published: January 2005

The 17O NMR signal of manganese (III) tris(acetylacetonate) was studied in the temperature range 26°—83°. From the temperature dependence of the shift of this signal, a hyperfine interaction constant of 1.88 G is found. This result is used to estimate the covalent character of the σ metal—oxygen bond. An upper limit of 0.077 is found for the mixing coefficient of the oxygen 2s orbitals in the bonding molecular orbitals of the complex. The electron spin transverse relaxation time is estimated from the linewidths of the 1H and 17O resonances to be in the range 10−11 to 10−12 sec.
Energy Levels of Np3+ in LaBr3
Authors: Krupke William F. , Gruber John B.
Published: January 2005

The polarized absorption and emission spectra of single crystals of LaBr3 doped with nominally 0.15% and 0.75% 237Np have been recorded between 5000 and 25 000 cm−1 at temperatures of liquid helium and nitrogen. Fluorescence excitation spectra and both parallel and perpendicular Zeeman spectra were also recorded. Based on the number, polarization, and magnetic behavior of Stark components appearing in distinct groups, as well as on preliminary 5f-hydrogenic calculations, 14 absorption groups were identified as levels of the ground electronic configuration 5f4 of Np3+. The assumption of a pure 5f4 electronic configuration does not lead to a satisfactory interpretation of the spectrum; however, the inclusion of electrostatic configuration interaction permits a satisfactory fitting of the observed levels with an rms deviation in energy of 86.4 cm−1 using the parameters: E1=3394.3±29.1, E2=14.19±0.22, E3=317.5±1.9, ζ5f=1969.2±10.8, α=35.0±2.2, and β=−802.4±11.3 cm−1. Using 25 crystalline-field-split Stark components of the 5I4,5,6,7 levels of the ground multiplet, a first-order crystal-field perturbation calculation was performed. An rms deviation in energy of 8.0 cm−1 is obtained using the parameters: B20=−22.8±8, B40=−86.7±2.4, B60=−70.8±0.9, B66=+857.1±12.0 cm−1. The negative value obtained for B20 represents a crystal-field shielding in excess of 100% and is discussed in some detail. Parallel and perpendicular Zeeman interactions are also discussed in some detail.
Adsorption of CO on a Tungsten (100) Surface
Authors: Anderson J. , Estrup P. J.
Published: January 2005

The room-temperature adsorption of carbon monoxide on the (100) surface of tungsten has been studied using the techniques of low-energy electron diffraction, flash desorption, and work-function measurement.

CO is found to exist in two binding states whch have been labeled βL and βH and is desorbed from these two states at ∼1150° and ∼1380°K, respectively. At room temperature, CO appears to adsorb into the βL state, and is associated with a work-function increase Δφ which is approximately linear with coverage and amounts to +0.43 eV at saturation—a coverage of about 1.0×1015 molecules/cm2. CO in the βL states can be converted into the βH state by heating to 900°—1000°K. Associated with the latter is an ordered c(2×2) structure which, at maximum coverage—about 5.0×1014 molecules/cm2—exhibits a Δφ of −0.16 eV with respect to the clean surface.

Adsorption of CO to saturation on the c(2×2) structure appears to return the surface to a condition indistinguishable from that due to adsorption on the clean surface. A possible model for explaining this behavior is proposed.
Electric-Deflection Studies of the Geometry of Some Molecules Containing Cesium
Authors: Büchler Alfred , Stauffer James L. , Klemperer William
Published: January 2005

The deflection of molecular beams in an inhomogeneous electric field shows that the species Cs2O is polar and therefore nonlinear. The species Cs2SO4, Cs2O2, and Cs2(OH)2 are found to be nonpolar. H2SO4 is polar in agreement with the C2v heavy-atom structure deduced previously by Stafford and Chackalackal from infrared spectroscopy.
Hydrazine—Water System. III. Crystallization of the Monohydrate
Authors: McMillan J. A.
Published: January 2005

Incorporation of the coefficient of transmission for activation in the entropy term of Eyring's absolute rate equation as applied to crystallization leads to fictitious entropies whose knowledge permits one to decide between nucleation and dislocation-controlled growth. Application of such an approach to crystallization during warmup of supercooled mixtures of hydrazine and water is discussed in detail.
Infrared Spectrum of Germylacetylene
Authors: Lovejoy R. W. , Baker D. R.
Published: January 2005

Infrared grating spectra of gaseous GeH3CCH and GeD3CCH were obtained over the 4000-to−140-cm−1 region, and the fundamentals of both molecules were completely assigned using a C3v symmetry model. Q-branch structure was resolved for three of the five perpendicular bands of GeH3CCH, and values for all five Coriolis coupling constants were obtained from analysis or from the zeta sum rule. Anomalous band structure was observed for the C≡C stretching mode, similar to that reported for other monosubstituted acetylenes. A strong rotational perturbation was also observed in the degenerate GeH3 deformation mode which was interpreted as arising from a second-order Coriolis interaction.
Carrier Generation and Recombination in Anthracene
Authors: Silver M. , Sharma R.
Published: January 2005

The hole—electron recombination coefficient, 2–3×10−6 cm3/sec, in anthracene has been determined directly by observing the decay of photogenerated carriers as a function of time. From considerations of the magnitude of the recombination, it is concluded that carrier generation can be observed only after excitation to an almost free electron band above the lowest narrow tight-binding band.

The experimental data of Castro and Hornig, and Kearns, are analyzed in terms of band-to-band transitions to this upper band. From considerations of the wavelength dependence, autoionization of the Frenkel exciton levels at these energies is shown not to be important.

Theoretical considerations predict a very small quantum yield for the band-to-band transition. A small cross section is consistent with experiment.
Radiationless Paths in the Diazines
Authors: Cohen Beverly J. , Goodman Lionel
Published: January 2005

Fluorescence was observed from pyrazine, pyrimidine, and pyridazine and their substituted derivatives in both liquid and rigid solutions. The fluorescence was assigned as emission from the allowed singlet (n, π*) excited state. Fluorescence and phosphorescence quantum yields of pyrazine, pyrimidine, and pyridazine, their deuterated analogs, and their substituted derivatives were measured by comparison of their emission with a standard substance of known quantum yield. Intersystem crossing yields were measured by Stephenson and Hammond by a chemical quenching method. The results of these measurements are presented in Table I.

The rates of the radiationless processes, internal conversion, and intersystem crossing were calculated from the quantum-yield data. In all cases, internal conversion was found to have the fastest rate and was the process responsible for the weak fluorescence intensity in the diazines. From the deuteration and other substituent effects on the quantum yields, it was concluded that internal conversion proceeds from the allowed singlet excited (n, π*) state to a lower forbidden singlet excited (n, π*) state. Intersystem crossing between the lowest triplet state and the ground state of pyrazine and pyrimidine was found to be noncompetitive with the radiative rates. In the ortho-diazine, a different situation was observed to exist. In the latter case, deactivation of the triplet state was attributed to an intersystem crossing process to a low-lying excited singlet state. Intersystem crossing rates were shown to be largely dependent on factors other than the first-order electronic perturbation matrix element.
Calculation of Ionization Potential of Various Atoms
Authors: Iafrate Gerald J.
Published: January 2005

A calculation of the ionization potential of various atoms has been done by assuming a pseudocore potential in the form of a simple analytical expression. The results calculated by using the variational method on hydrogenlike orbitals are in reasonable agreement with the experimental values.
Paramagnetic Catalysis of the Ortho—Parahydrogen Conversion
Authors: Nielsen Svend E. , Dahler John S.
Published: January 2005

A theory is presented for the paramagnetic catalysis of ortho—para transitions in molecular hydrogen, deuterium, and tritium. The cause for reaction is taken to be an inhomogeneous magnetic field, orginating from a catalyst molecule and operative during the binary collisions of catalyst and reactant species. Formulas for the distorted wave approximation to the cross sections are presented, as are expressions for the specific rates of the associated thermal reactions. Exploratory calculations are performed for the oxygen catalyzed para (L=0)→ortho(L=1) transition in hydrogen. With the assumption of a hard-sphere interaction the rates calculated for 77.3° and for 86°K turn out to be only about 25% to 30% of the experimentally observed rates.
Crystal Vibrations of Polyethylene
Authors: Tasumi M. , Krimm S.
Published: January 2005

Several problems involving the internal and external vibrations of the polyethylene crystal have been studied. The splittings of some of the internal vibration bands arising from transition dipole coupling have been evaluated and found to have small but nonnegligible values as compared with the splittings calculated from the intermolecular H···H interaction potential. On the other hand, interactions between permanent CH2 dipole moments in different chains have been shown to make quite insignificant contributions to the translational lattice frequencies. The effects on the vibrational frequencies of cell contraction with decreasing temperature have been calculated, and the experimentally observed upward shift of a lattice frequency is found to be explainable primarily on this basis. The effect caused by the change of the setting angle of each chain in the unit cell has also been examined. The short-range H···H interaction force constants and the dispersion curves of normal and deuterated polyethylenes have been obtained.
Series Solutions and Rotationless States of the Vibrating Hydrogen Molecule Ion
Authors: Harriss Donald K.
Published: January 2005

The generalized series solution methods for nonseparable Hamiltonians proposed by Frost are investigated. It is shown that for the general case a solution is not possible without explicit evaluation of a minimum number of integrals. The B matrix method is shown to be equivalent to the use of the integral relations, J(f), developed in Hirschfelder's derivation of quantum-mechanical hypervirial theorems. The B matrix method is applied to vibrating H2+, HD+, and D2+.