bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Helium Buffer Gas Atoms on the Atomic Hydrogen Hyperfine Frequency
Authors: Clarke George A.
Published: January 2005

Calculations are made for the pressure, mass, and temperature dependence of the atomic hydrogen hyperfine frequency shift arising from the perturbing influence of helium buffer gas atoms. The calculated fractional pressure shift is found to be +1.73×10—9 mm Hg—1 compared with the experimental value of +3.7×10—9 mm Hg—1. From the standpoint of the calculation this discrepency may be related to a failure of the simple wave function employed to adequately characterize the unpaired electron spin density at the hydrogen nucleus. The results of the calculations for the temperature variation and mass dependence indicate that these are very small effects. The form of the mass dependent quantum statistical correction, used to elucidate the mass effect, suggests that the relatively large variations experimentally observed with other buffer gases, due to hydrogen isotope variation, are in error.

Finally, a calculation is made for the pressure shift from a kinetic theory point of view and the result obtained (+1.79×10—9 mm Hg—1) is in fair agreement with the above mentioned quantum statistical calculation.
Studies on the Alternant Molecular Orbital Method. I. General Energy Expression for an Alternant System with Closed-Shell Structure
Authors: Pauncz R. , de Heer J. , Lowdin P. O.
Published: January 2005

The alternant molecular orbital method is used to derive a general energy expression for an arbitrary alternant system with closed-shell structure. This expression exhibits a simple dependence on a single mixing parameter, minimization with respect to which yields the optimum energy. An analysis reveals the effectiveness of the method to depend on the relative magnitude of two quantities, one involving the one-electron operator energies and the other related to electron interaction integrals which connect the bonding with the antibonding orbitals from the simple ASMO scheme. Some comments on the method, in the light of the results obtained, are added.
Magnetic Properties of Hydrogen Fluoride. I. Rotational Moment
Authors: Das T. P. , Karplus Martin
Published: January 2005

A variation-perturbation formulation is presented for the calculation of the electronic contribution to the rotational energy and magnetic moment of a 1Σ molecule. An application of the method to a one-center single-configuration wave function for hydrogen fluoride is given and compared with a two-center function result. The calculated magnetic moment is found to be 0.9276 nuclear magnetons for the one-center function and 0.6354 nuclear magnetons for the two-center function in comparison with the experimental value of 0.7392 nuclear magnetons. Analysis of the results shows that the nuclear charges make the dominant contribution and that the electronic ``slippage'' is almost complete. Furthermore, the convergence of the variational expansion indicates that a significant improvement in the theoretical value probably requires refinements in the ground-state wave function.
Termination Products and Processes in the Pyrolysis of Dimethyl Ether
Authors: Anderson Kenneth H. , Benson Sidney W.
Published: January 2005

Termination processes in the pyrolysis of dimethyl ether studied by trace product analysis using gas—liquid chromatography revealed the presence of methyl ethyl ether, 1,2-dimethoxyethane, and methanol. These ethers had been predicted in the work of Benson and Jain by including CH3OCH2 as a chain terminator, and their identification is evidence for the reaction CH3OCH2→CH3+CH2O being an energy transfer process in its second-order region. Methanol was also predicted from the reactions of CH3O or CH2OH. Quantitative measurement of the trace termination products were made to obtain yields for MeOEt, Me2O, and C2H6, which could be used to calculate the rate constant ratio k2′/k2 for the attack by CH3 on MeOEt compared to Me2O. When the steady state is approached from both sides, k2′/k2 ranges from 4–12 and is greater than unity, as expected. A reasonable difference in activation energy of about 2–4 kcal is estimated for these reactions. However, the MeOEt gas chromatography peak was broad when resolved from Me2O resulting in loss of precision and together with the required estimates in the steady-state equation (7) severely limit the usefulness of trace termination product analysis in determining new rate constants. Ethane was measured and compared to a calculated steady-state value. Because of attack on the ethane and the disappearance of radicals by other termination processes the ratio of the Me2O decomposed to the C2H6 found is not as good a measure of the chain length as those calculated from the rate law.
Ultraviolet Spectra of Stilbene, p-Monohalogen Stilbenes, and Azobenzene and the trans to cis Photoisomerization Process
Authors: Dyck Rudolph H. , McClure Donald S.
Published: January 2005

In order to improve our understanding of the electronic states and photochemical reactions of stilbene, we have carried out a spectroscopic and photochemical investigation of stilbene, some substituted stilbenes, and azobenzene. High resolution absorption and fluorescence spectra of the singlet—singlet transition in dilute mixed crystal have been analyzed, and from them it is estimated that the potential barrier to trans-cis isomerization in the first excited singlet state is about 40 kcal/mole. The absorption spectrum of the first singlet—triplet transition has been observed by enhancement with a heavy atom solvent and is interpreted as showing that the central bond in the lowest triplet state has a very substantial barrier to rotation. An electronic energy level scheme for stilbene has been constructed by treating the molecule as one ethylene molecule interacting with two toluene molecules. This treatment suggests that as many as four triplet states may be of lower energy than the first excited singlet and would then be possible pathways for photoisomerization.

A study of the deactivation processes of photoexcited stilbene has included the temperature dependences of fluorescence and of isomerization efficiencies. The first showed an activated quenching process with a frequency factor of 1012, which makes it a less forbidden process than is common for singlet—triplet crossings. The second showed that the activated process has the major isomerization yield. In p-bromostilbene an unactivated process has the major isomerization yield, indicating that there is an atomic number effect on the rate of the unactivated process.

Thus the direct isomerization in the first excited singlet or first excited triplet states has been ruled out; two other paths, one with a small activation energy and the other apparently a singlet to excited triplet crossing, have been found.
Electrical Properties of Chlorpromazine
Authors: Gutmann F. , Netschey A.
Published: January 2005

Chlorpromazine (10-dimethylaminopropyl phenothiazine) in the form of slabs cast from the melt is a semiconductor. The activation energy of conductivity has an average value of E=2.1 ev, referring to the equation σ=σ0 exp(—E/2kT), above a transition temperature of 32°C. There is no significant change of E upon fusion, its value remaining constant up to 80°C. The transition has been confirmed by thermal analysis, dielectric measurements, and by infrared spectroscopy. The spectra indicate that the side chain as well as the ring system are affected by the transition, which is believed to be due to an unfolding of the sidechain above a critical temperature, this causing a change in the micellar association of the substance. Values are reported, as functions of temperature, for the refractive index, the permittivity at 1 Mc/sec and at 1592 cps, the parallel ac conductivity and the loss tangent at the latter, lower, frequency. The substance is diamagnetic.
Vibrational Spectrum and Force Constants for Molybdenum Hexacarbonyl
Authors: Jones Llewellyn H.
Published: January 2005

The vibrational spectrum of molybdenum hexacarbonyl has been examined in greater detail than previously. Assignments of 12 of the 13 fundamental frequencies have been made. Approximate anharmonic corrections have been applied to the CO stretching vibrations. Force constants have been calculated using a resonance interaction valence force field [L. H. Jones, J. Mol. Spectroscopy 8, 105 (1962)]. The results are quite encouraging concerning the applicability of this force field.
Electronic Spectrum of Decaborane
Authors: Haaland Arne , Eberhardt W. H.
Published: January 2005

The near ultraviolet absorption spectrum of decaborane has been studied in the gas from 90° to 140°C, in solution in cyclohexane and acetonitrile at 25°C, and as single crystals at 4.2°K, and evidence found for one electronic transition with origin at 3.86±0.03 ev in the gas, 3.81±0.06 ev in cyclohexane, 4.00±0.06 ev in acetonitrile, and 3.850±0.001 ev in the crystal. The existence of another excited electronic state of slightly higher energy cannot be ruled out since the absorption due to transitions to this state might be concealed by that due to the 3.85 ev transition.

Assuming the absorption is due to one transition only, the transition moment and oscillator strength in cyclohexane are p2=0.21×10—16 cm2 and f=0.10, respectively. The shift of the spectrum towards the blue in the polar solvent acetonitrile relative to that in the nonpolar solvent cyclohexane indicates that the dipole moment of the excited state is less than that of the ground state.

The absorption of the crystal is completely polarized perpendicular to the crystal c axis and the twofold axis of the molecule. This result implies that the excited state of the free molecule is of either B1 or B2 symmetry and the transition is allowed. No structure was observed in the gas or solution spectra, but in the crystal the electronic transition is accompanied by three totally symmetric boron framework vibrations of the excited state with frequencies 425, 390, and 135 cm—1. A detailed discussion of the wave functions and energies of the optically excited crystal states indicates that the Davydov splitting should be too small to be observed under the experimental conditions.

The spectrum is entirely consistent with that expected from existent theories of the nature of electronic bonding in this molecule.
Paramagnetic Excitons in Solid Free Radicals
Authors: McConnell Harden M. , Lynden-Bell Ruth
Published: January 2005

It is suggested that the low-temperature paramagnetism of many aromatic free-radical solids may be due to triplet excitons, and that the formation of these exciton states rather than other low-temperature magnetic states is due to low-temperature crystal lattice structures that favor a singlet pairing of electrons on neighboring molecules. As an example it is shown that the paramagnetic resonance spectra of certain TCNQ charge-transfer complexes observed by Chesnut and Phillips may be interpreted in terms of triplet excitons.
Effect of Anharmonic Vibrations on the Bond Lengths of Polyatomic Molecules. II. Cubic Constants and Equilibrium Bond Lengths of Methane
Authors: Kuchitsu Kozo , Bartell L. S.
Published: January 2005

The method for estimating cubic potential constants described in the preceding paper is applied to tetrahedral molecules. A general expression for the cubic constants is obtained in a matrix form for which the elements are the elements of the L matrix and the force constants. By the use of the spectroscopic data of Jones and McDowell, the L matrix, the force constants, and the cubic constants are estimated for CH4 and CD4. A first-order perturbation calculation based on these cubic constants is made of root-mean-square amplitudes of vibration and of the effect of vibrations on mean values of internal coordinates and mean bond lengths rg. It leads to values for rg—re of 0.0221 for C–H (CH4) and 0.0164 A for C—D (CD4). An evaluation is made of the effect of common approximations in the calculation of amplitudes of vibration. The rotational constants, B0, for the ground vibrational state of CH4 and CD4 are also calculated according to the present model, using the method of Wilson and Howard. The results for r0—re are found to be 0.0090 A for C–H (CH4) and 0.0067 A for C—D (CD4). Experimental bond lengths derived from recent diffraction studies of rg and spectroscopic studies of r0 are compatible when viewed in the light of the above calculations, and indicate that the equilibrium lengths re of the C–H bond in CH4 and the C—D bond in CD4 are very nearly 1.085 A.
Theory of Hole Injection and Conductivity in Organic Materials
Authors: Kallmann Hartmut P. , Pope Martin
Published: January 2005

The relationship between current and applied voltage is calculated for a process in which a given number of charge carriers of one sign is injected into matter which contains only a negligible density of charges of the opposite sign. Diffusion effects are taken into account approximately. The current-voltage relationship depends strongly on the image force exerted on the injected carriers near the electrode. The calculated current-voltage curve agrees qualitatively with that observed in anthracene under light excitation. The voltage at which saturation is approached can be calculated and depends upon a recombination velocity of the injected charge with the injecting electrode, and upon the image force. Different saturation voltages for various electrodes can be explained by a difference in recombination velocities. The dependence of the saturation voltage upon the intensity of the saturation current is also explained. For anthracene, the recombination between holes and a water electrode is expressed as a velocity much greater than thermal velocities.
Electron Coupling of Nuclear Spins. VI. Relative Signs of JgemHH, JgHH, and JtHH in (2.2) Metacyclophane
Authors: Gutowsky H. S. , Juan Cynthia
Published: January 2005

The high-resolution proton magnetic resonance spectrum of the methylene groups in (2.2) metacyclophane has been observed at 60 and 15 Mc. In this compound, the C–CH2–CH2–C groups are fixed in position with the dihedral angle between alkyl C–C–C bonds slightly less than the symmetrical, staggered 60° and with little distortion from tetrahedral of the other bond angles in the group. Therefore, the HCCH coupling constants should be characteristic of ethanic trans and gauche orientations and the CH2 should be comparable with the geminal coupling in methane.

A complete analysis of the A2X2 and A2B2 type spectra, in combination with previous, unambiguous experimental findings that |JgemHH|≅|JtHH|>|JgHH|, leads to the following assignments in (2.2) metacyclophane: JtHH=±12.3,Jg′HH (the coupling of the ``central'' pair of gauche protons) =±3.2,JgemHH=∓12.0,and JgHH=±4.0,all±0.1 cps. The magnitudes of these constants agree well with previous valencebond calculations for CH4 and the ethanic HCCH group. However, the opposite signs found for the large trans and geminal constants disagrees with the theoretical prediction that both are positive. The observed difference in sign can not be attributed to substituent effects, angular distortions, or to motional averaging. It is concluded that one of the two sets of calculations is in error; the implications of this result are discussed.
Compressibility of Liquid Sodium—Potassium Alloys
Authors: Abowitz G. , Gordon R. B.
Published: January 2005

The velocity of sound has been measured in the sodium—potassium alloy system as a function of both composition and temperature. For each composition the velocity was found to be a linear function of the temperature. The behavior of the compressibility, because of the volume contraction on alloying, cannot be explained in terms of a free electron model. A possible explanation is that changes in the electronic charge density upon alloying gives rise to both the volume contraction and the slight positive deviation in the compressibility.
Vaporization of Ruthenium and Osmium
Authors: Panish Morton B. , Reif Liane
Published: January 2005

The vapor pressures of ruthenium and osmium have been determined by the use of Langmuir vaporization and Knudsen effusion techniques. The vapor pressure of ruthenium over the temperature range 2000° to 2500°K is represented by the equation logpmm=10.81–33480/T, and the vapor pressure of osmium over the temperature range of from 2300° to 2800°K by the equation logpmm=10.85–40950/T. Third-law analyses of the data yield the following heats of vaporization: ruthenium ΔH298∘=154.9±1.3 kcal/mole; osmium ΔH298∘=187.4±0.9 kcal/mole. Estimated boiling points for ruthenium and osmium are 4350°±100°K and 5300°±100°K, respectively.
Infrared Spectrum of Bromine Pentafluoride
Authors: McDowell Robin S. , Asprey Larned B.
Published: January 2005

The infrared spectrum of bromine pentafluoride has been observed in the region 4000–215 cm—1 with a resolution of 0.5–1.0 cm—1. All infrared-active fundamentals have been observed; these occur at 684, 584, and 370 cm—1 (A1) and 644, 415, and 245 cm—1 (E). The spectrum confirms the C4v (square pyramidal) structure. Corrections are given for the previously reported thermodynamic functions.
Excess Free Energies and Heats of Mixing in Certain Molten Salt Mixtures
Authors: Blander Milton
Published: January 2005

The third- and fourth-order terms of the perturbation theory of Reiss, Katz, and Kleppa for the excess free energies and heats of mixing of molten salts have been calculated for a particular choice of ``test salt.'' Up to the fourth order, the expressions have the form X1X2Pδ2+X1X2(X1−X2)Qδ3+(X1X2R+X1X2(X1−X2)2S)δ4+···,which is consistent with and rigorously justifies the concentration dependence of the observed heats of mixing of alkali nitrates. The equations can be derived for salts having a much more general cation—anion interaction potential than was stated by Reiss, Katz, and Kleppa.
Analysis of Complex NMR Spectra. An Iterative Method
Authors: Swalen J. D. , Reilly C. A.
Published: January 2005

A method for analyzing complex NMR spectra, which utilizes an iterative technique on the spin energy levels, is described. We show how the experimental energy levels and their errors are derived from the observed spectrum and the assignment of the various transitions. We discuss several techniques and methods that are helpful in obtaining this assignment. Sum rules for the energy levels and the intensities of the transitions, useful in the analysis, are also pointed out.

With the iterative procedure, which uses the eigenvectors of an approximate Hamiltonian, we then calculate the changes in the chemical shielding constants and the spin—spin coupling constants necessary to adjust the approximate energy levels toward the experimental ones. The probable errors in the derived magnetic parameters are also readily determined.
Trends in the Lattice ``Combination Bands'' of Zincblende-type Semiconductors
Authors: Keyes Robert W.
Published: January 2005

Well-known ideas suggest that the mass ratio of the constituents and the ionicity of a diatomic lattice will influence certain features of its vibrational spectrum: The splitting between the optical and acoustical branches increases with increasing mass ratio and the energy of the longitudinal optical branch is increased relative to that of the transverse optical branch by increasing ionicity. These effects are found to exist in the phonon frequencies which contribute to the lattice ``combination bands'' of zincblende-type semiconductors.
Statistical Thermodynamics of Polymer Solutions. III. The Second Virial Coefficient for Branched Star Molecules
Authors: Casassa Edward F.
Published: January 2005

The effect of branching on the osmotic second virial coefficient is calculated for a homogeneous solute of ``star'' molecules, each composed of a number of identical, flexible, linear, polymeric, chain elements joined together at one end through a common junction. The perturbation method of Zimm, familiar for linear chains, is generalized slightly to include the star molecule of arbitrary functionality. This calculation, applicable to thermodynamic interactions in poor solvents, is then combined with a method developed in the first paper of this series, to obtain an approximate theory for the virial coefficient in good solvents where thermodynamic interactions between solute molecules are large.
Radiation-Induced Free Radicals in Sulfur Compounds. ESR Studies in the Polycrystalline State
Authors: Henriksen Thormod
Published: January 2005

The secondary processes occurring in organic sulfur compounds, irradiated with ionizing radiation in the dry state, have been followed by ESR spectroscopy. Samples were irradiated in vacuum at 77°K and the ESR spectra recorded at this temperature before and after stepwise heat treatment at successively increasing temperatures.

The resonance spectra seem to indicate that after irradiation at 77°K, several kinds of ESR centers are formed. No or very few sulfur radicals seem to be formed at this temperature.

The results show that few secondary processes proceed efficiently in solids in the temperature range from 77° to about 110°K. Depending upon the compound, decay processes seem to dominate in the temperature range varying from about 110°K and up to about 250°K. Upon further heat treatment, secondary reactions take place which lead to the formation of sulfur radicals. The threshold temperature for these reactions is about 170°K for simple thiols and disulfides, 240°K for peptides like glutathione, and about 280°K for proteins. The formation of sulfur radicals is found to coincide with an increase in the total number of observable ESR centers. Thus, in the case of penicillamine, the number of unpaired spins observed after annealing to 295°K exceeds the initial value at 77°K by about 70%.

Evidence is presented that diffusion-controlled intermolecular reactions take place in irradiated solids, and it is suggested that the observed formation of sulfur radicals may in part be explained by such a mechanism.

The resonance pattern due to polyoriented radicals of the type R—CH2–S· (e.g., cysteine, cysteamine, glutathione, proteins) was found to exhibit a temperature dependent hyperfine splitting which is not found for radicals of the type R—CX2—S· (e.g., penicillamine). This observation supports the model for organic sulfur radicals proposed by Kurita and Gordy.
Polyhedral Clathrate Hydrates. IV. The Structure of the Tri n-Butyl Sulfonium Fluoride Hydrate
Authors: Jeffrey G. A. , McMullan R. K.
Published: January 2005

The preparation and crystal structure of (n-C4H9)3S+F—·20H2O is reported. This hydrate is isostructural with the chlorine gas hydrate, 6Cl2·46H2O, having a pseudo body-centered arrangement of H40O20 pentagonal dodecahedra in a cubic unit cell of approximately 12 Å edge. The cations occupy large voids formed by the tetrakaidecahedra in the structure and are statistically disordered. The water structure is distorted as compared with the idealized polyhedral framework and there is evidence that the pentagonal dodecahedra may be occupied by a water molecule or a fluoride ion.
Dissociation of Gaseous Diatomic Molecules. II. Effect of Anharmonicities
Authors: Light John C. , Arnstein Rodolphe
Published: January 2005

The classical adiabatic calculation of the rate of dissociation of diatomic molecules is extended to Morse potential oscillators in one-dimensional colinear collisions. The limits of error of the method are formulated and numerical calculations of the rates of dissociation of H2 in Xe and I2 in Ar are made assuming both the Morse and harmonic potentials. The harmonic results are in good agreement with experiment. Estimates of the errors involved show that the anharmonic results are not as reliable as the harmonic results. The distribution functions for a strongly interacting harmonic oscillator are also calculated.
Fluorescence Polarization of Some Porphyrins
Authors: Gouterman Martin , Stryer Lubert
Published: January 2005

Fluorescence-polarization data on porphyrins are reported. The results can be readily interpreted in terms of the theory of polarization spectroscopy and the theory of the electronic and vibrational structure of these molecules. It is shown how these two theories combine to interpret most of the data, but some anomalies remain. The results hint at the richness of data that may be expected from fluorescence-polarization experiments when techniques are developed further.
Spectrophotometric and Partition Methods of Determining Association Constants of 1 :1 Charge-Transfer Complexes
Authors: Hayman H. J. G.
Published: January 2005

The spectrophotometric method of determining the association constant of a complex AB when A, B, and the solvent have appreciable optical absorption is discussed, and the influence of the ratio of the concentrations of A and B examined. The formation of termolecular complexes such as A2B and of self-complexes such as A2 is found to affect the spectrophotometric method but not the partition method of determining association constants, whereas nonideality of the solutions affects both methods. The significance of the spectrophotometric method when applied to a completely general system including contact charge-transfer absorption is examined by means of Hill's statistical thermodynamic method of treating solutions. The results obtained are applied to three simple quasi-crystalline models.

The experimental fact that spectrophotometric association constants are usually smaller than those determined by the partition method is shown to indicate that the attractive forces causing the formation of 1:1 complexes are probably not completely saturated in these complexes. In particular, for the extreme case in which the tendency of one side of an aromatic compound to complex formation is not affected by complex formation on its other side, it is shown that the spectrophotometric association constant would have only half the value found by the partition method. The experimental values in the literature for the association constants of a number of alkyl naphthalene-picric acid complexes are in good agreement with this view.
Proton Magnetic Resonance Studies of Polycrystalline Uranium Oxide Hydrates. III. UO42H2O
Authors: Porte A. L. , Gutowsky H. S. , Boggs J. E.
Published: January 2005

The broad-line proton magnetic resonance spectrum of polycrystalline samples of the compound formulated empirically as UO42H2O has been investigated in the temperature range 77° to 356°K. Analyses of the absorption line shapes, and their derivatives, at 77° and 257°K, coupled with chemical analysis for peroxide oxygen, show that the compound is essentially the dihydrate of uranyl peroxide, UO2(O2)·2H2O. The sample investigated has about 1/12 of its protons in UOH or UOOH groups of a second component, possibly a hydroperoxide, UO(OH)3(OOH), or hydroxy peroxide, UO(OH)2(O2)·H2O. At temperatures between 125° and 210°K, the absorption of the OH protons in this component undergoes changes which are compatible with self-diffusion. The apparent activation energy for this motion is 2 kcal. The two component formulation of the ``compound'' accounts for most, if not all, of its complex chemical behavior.
Crystal Chemical Study of the Rare-Earth Iron Garnets
Authors: Espinosa G. P.
Published: January 2005

Crystallographic and preparative data are given for high-purity rare-earth iron garnets (R3Fe2Fe3O12 and {R3—xRx′}Fe2Fe3O12, where R and R′ are rare earths). Lattice constants are obtained for hypothetical La, Pr, and Nd iron garnets. Maxima have been found for amounts of Pr substitution in Sm, Gd, Y, and Lu iron garnets which in turn lead to a principal maximum lattice constant of 12.540 Å for any rare-earth iron garnet, in good agreement with 12.538 Å obtained by Geller, Williams, and Sherwood. The maximum for La substitution in YIG is also given. A plot of lattice constant vs atomic number shows some influence of crystal field on the trivalent rare-earth ions with nonspherical electron configuration superposed on the lanthanide contraction. The importance of the size difference of the dodecahedral rare-earth ions in the praseodymium-substituted rare-earth iron garnets with respect to the maximum attainable lattice constants is shown corroborating observations on the neodymium substituted rare earth iron garnets. A set of relative effective CN(12) trivalent rare earth radii is calculated from the rare-earth iron garnet lattice constants.
Photochemistry in the Photo-Ionization Region. I. Apparatus and Techniques
Authors: Back R. A. , Walker D. C.
Published: January 2005

An apparatus for the study of photochemistry in the extreme vacuum-ultraviolet is described. The light source and photolysis vessel were separated by a fast-flow separation system, so that no windows were needed. Using a microwave discharge in helium as the light source, photo-ionization in methane and the rare gases has been studied. By using a filter to attenuate the light intensity, it was possible to measure saturation ion currents in the spherical photolysis vessel, which also served as an ion-chamber. Ion currents up to 25 μA were obtained in methane, corresponding to a useful incident-light intensity of about 3×1014 photons/sec. This light is thought to be mostly the helium resonance line at 584 Å, strongly reversed. A ``background'' ion current was observed with only helium in the photolysis vessel, and has been tentatively attributed to electron emission from the collecting electrode induced by collision of metastable helium atoms.
Absorption and Fluorescence Spectra of Hexagonal SmCl3 and Their Zeeman Effects
Authors: Magno M. S. , Dieke G. H.
Published: January 2005

The absorption and fluorescence spectra of SmCl3 have been studied at 4°K and the Zeeman effects of many lines obtained in a magnetic field of 35 100 G. The lower group of levels obtained chiefly from the fluorescence spectrum can be unambiguously identified as the multiplet components of the 6H and 6F levels. The situation for the higher levels is confused.

The splitting into Stark components of many of the levels could be determined with their symmetry and magnetic properties.
Effects of Intramolecular Electric Fields in Molecules: EQR Coupling Constants
Authors: Musher J. I.
Published: January 2005

The variation in EQR coupling constants in chloro-, bromo-, and iodobenzenes is interpreted in terms of intramolecular electric fields acting on the carbon—halogen bonds. The proportionality factors cX's, relating such shifts to the effective electric fields are determined for the three types of bonds. The cC1 for a carbon—chlorine bond agrees reasonably well with the value determined in experiments in external electric fields as long as the sign for the latter is chosen as positive. It is expected that further extensions of the method are possible.
Comparison of Radial Distribution Functions from Integral Equations and Monte Carlo
Authors: Broyles A. A. , Chung S. U. , Sahlin H. L.
Published: January 2005

The radial distribution functions g for a system of particles interacting with the Lennard-Jones 6–12 potential have been found by solving the Percus—Yevick (PY) equation, convolution approximation or hypernetted chain equation (CHNC), and the Born—Green—Yvon (BGY) equation, for four particle densities already investigated by Monte Carlo (MC) techniques by Wood and Parker. The thermodynamic quantities p/nkT, E/NkT, and nkTK have also been computed from the g's. A comparison shows that the PY quantities agree best with MC, CHNC quantities agree next best, and BGY agree most poorly, particularly at high densities. A comparison of nkTK computed by differentiating p/nkT and by direct integration involving g gives approximately consistent results for the PY g but not for the CHNC g. The asymptotic form of g for high densities for the PY and CHNC equations is found to agree with that obtained by Kirkwood.
On the Kinetic Theory of Dense Fluids. XIII. The Mobility of Negative Ions in Liquid Ar, Kr, Xe
Authors: Davis H. T. , Rice Stuart A. , Meyer Lothar
Published: January 2005

In this paper we report measurements of negative ion mobilities in liquid Ar, Kr, and Xe, and a comparison of the observations with the modern statistical theory of transport. It is tentatively suggested that the negative ion involved in these studies is O2—. Accepting this premise, quantitative agreement between theory and experiment is attained if the depth of the non-Coulomb portion of the potential well of the O2—–Ar interaction is a factor 3.4 greater than the depth of the O2–Ar potential well. Uncertainties in the calculation of the pair correlation function prevent confirmation of all details of the theory.
Nuclear Magnetic Double Resonance Spectra of Three Spin Systems
Authors: Rao B. D. Nageswara , Baldeschwieler John D.
Published: January 2005

The nuclear magnetic double resonance spectra of general three-spin systems are analyzed in detail by using a Hamiltonian that is made stationary by transformation to a rotating coordinate system, and by diagonalization of the complete Hamiltonian in the rotating frame. The double resonance spectra for ``field-sweep'' conditions are obtained from a plot of the ``frequency-sweep'' transition frequencies versus the frequency of the strong radio-frequency field. The double resonance spectra of the ring protons of 2-amino, 3-picoline are in close agreement with the results of the above analysis. It is also shown that the methyl protons in 2-amino, 3-picoline are coupled to the 4-proton.
Varying Orbital Exponents in Molecular Orbital Theory
Authors: Dehn James T.
Published: January 2005

By means of the variational principle a set of conditions is derived for the orbital exponents which minimize the energy in the LCAO form of molecular orbital theory, using Slater atomic orbitals. These equations are to be solved simultaneously with Roothaan's conditions for the best LCAO coefficients. The method is illustrated for the molecular ion H2+ and the molecule He2.
NMR Relaxation Times in Solid White Phosphorus: Diffusion and Rotation
Authors: Resing Henry A.
Published: January 2005

Nuclear magnetic resonance relaxation times have been measured for solid white phosphorus by spin-echo techniques. The diffusion coefficient calculated from T2 in the α phase can be represented as D=D0exp(−ΔH/RT),where D0=0.077±0.014 cm2/sec, and ΔH=12.1±0.1 kcal/mole. The correlation time for rotation calculated from T1 in the β phase can be represented by tc=t0exp(ΔH/RT),where t0=6.04×10—14 sec, and ΔH=4.02±0.02 kcal/mole. The distance between phosphorus atoms in the P4 molecule is found to be 2.24±0.03 Å from the value of T1 at the T1 minimum in the β phase.
Reaction Kinetics of a Long Chain Molecule
Authors: Keller Joseph B.
Published: January 2005

A long chain molecule is considered, of which each segment carries a reactive group. It is assumed that the reactivity of each group depends upon whether zero, one, or two of its nearest neighbors have reacted. The average fraction of reacted groups is determined as a function of time. This is done by first deriving appropriate equations to describe the kinetics and then solving these equations. The results are illustrated by a number of graphs which show the average fraction of reacted groups as a function of time for different ratios of the reactivities.
Pair Distribution in the Rigid-Sphere System by the Method of Particle Scaling
Authors: Helfand Eugene , Stillinger Frank H.
Published: January 2005

By use of the scale of interaction distance as a coupling constant, integral equations for the molecular distribution functions are derived and discussed with particular reference to the calculation of the pair distribution for rigid-sphere systems. It is shown that considerable improvement over the usual superposition approach results upon retention of the superficial form of the superposition approximation, but with a suitably defined effective local density. Specifically, the equation becomes exact over half the range of the coupling parameter. The fourth virial coefficient in the equation of state is correct in this theory, in comparison with an ordinary superposition value 61% low. Generalization of the effective density analysis to the case of arbitrary potentials is briefly discussed.
Effect of Oxygen on the Vapor Pressure of Uranium
Authors: Ackermann R. J. , Rauh E. G. , Thorn R. J.
Published: January 2005

The published observations pertaining to the vapor pressure of uranium have been examined for consistencies. Since it was shown previously by Rauh and Thorn that oxygen suppresses the vapor pressure, the experiment by DeMaria, Burns, Drowart, and Inghram involving a mixture of uranium and aluminum oxide contained in a molybdenum effusion cell cannot yield the vapor pressure of pure uranium, but rather yields the individual partial pressures for the equilibrium U(Mo and O in solution)+UO2(s)=2UO(g),and a composition of the vapor which is approximately that of the monoxide. Using all the data one can construct a diagram schematically describing the effect of oxygen on the vapor pressure of uranium.
Paramagnetic Resonance Spectrum of Fe3+ in Guanidinium Aluminum Sulfate Hexahydrate
Authors: Brock E. G. , Stirpe D. , Hormats E. I.
Published: January 2005

The electron paramagnetic resonance spectrum of Fe3+ substituted for Al3+ in guanidinium aluminum sulfate hexahydrate, C(NH2)3Al(SO4)2·6H2O, was measured at X-band and K-band frequencies at room temperature and 77°K. The spectra were observed with the magnetic field parallel to the c axis, which is also the axis of distortion of the octahedra formed by the water molecules. Relative values only of the spin Hamiltonian parameters for an S=5/2 ion were determined; the fitting procedure gave D negative and a and F positive. For room temperature and type-II sites, the parameters in the spin Hamiltonian were calculated as; g=2.003, D=—0.17601 cm—1, a=0.020595 cm—1, and F=0.10047 cm—1. For type-I sites at room temperature; g=2.003, D=—0.18508 cm—1, a=0.021966 cm—1, and F=0.10530 cm—1. At 77°K for type-II sites; g=2.003, D=—0.18902 cm—1, a=0.053963 cm—1, and F=0.15203 cm—1. Type-I sites at 77°K gave g=2.003, D=—0.19506 cm—1, a=0.059302 cm—1, and F=0.16389 cm—1.
Atomic Electric Field Gradients of Five-Electron Ions
Authors: Platas Oscar R.
Published: January 2005

The electric field gradient (∂2V/∂Z2)atom has been evaluated for BI, CII, NIII, OIV, FV, NeVI with an open-configuration wavefunction for the 2P state. The fine structure splitting separation δ is calculated using the computed values of (∂2V/∂Z2)atom and the energy optimized orbital exponents for the 2p electron. The electric field gradient of BI agrees satisfactorily with the previous value obtained from the observed fine structure levels. The use of a relativistic correction on the fine structure which minimizes the error in comparison with the experiment is investigated.
ESR Studies of γ-Irradiated η-Octadecyl Disulfide
Authors: Truby Frank K. , MacCallum Crawford , Hesse James E.
Published: January 2005

Octadecyl disulfide irradiated at — 196°C in the absence of oxygen exhibits radicals reflecting breakage at the sulfur group to form RS·radicals as well as breakage in the alkyl group. During storage of the samples at from 0° to 40°C an increase in RS·concentration is observed while reduction of radicals in the alkyl group takes place. After initial rapid reactions occurring immediately after warm-up, a lower rate is observed for the increase in RS·content and decay of the radicals associated with the alkyl group. Both of these slower processes appear to occur as a result of a common reaction with an activation energy of about 13 kcal/mole. It is believed that this reaction involves the combination of a disulfide link with a radical in the alkyl group and occurs as a result of molecular diffusion in the crystalline material. Calculations based on a diffusion model yield theoretical curves which can be made to fit the experimental results within the limits of experimental error.
Photolysis of Aqueous Azide Solutions
Authors: Shinohara Kenichi , Shida Tadamasa , Saito Nobufusa
Published: January 2005

Azide ion solutions containing mercuric chloride were photolyzed with ultraviolet light from a mercuric arc. The products were nitrogen and mercurous azide, both of which were produced by a chain mechanism. Assumptions that the reaction is initiated by photochemical charge transfer from an azide ion to water and that the chain carriers are the lowest triplet state nitrogen molecule and the excited azide radical can account for the reaction of azide ion plus mercuric chloride system.

Based on the same assumption, the photolysis of pure azide ion and hydrogen azide solutions have been successfully reviewed.
Wide-Angle Scattering in Molecular Beams. The Rainbow Effect
Authors: Beck D.
Published: January 2005

Differential elastic scattering cross sections have been measured for collisions of potassium with krypton and hydrogen bromide at different energies in the thermal energy range. In all qualitative details the results can be explained assuming an interaction potential of type exp-6 (Buckingham). Rainbow scattering is observed and potential parameters are evaluated.

Even though several hundred partial waves contribute to the scattering the experimental evidence appears to indicate the need for the semiclassical rather than the classical treatment of wide-angle scattering in the region of the rainbow maximum.
Valence-Bond Structures and Matrix Elements for Any Multiplicity
Authors: Kellogg R. E.
Published: January 2005

A simple method of obtaining an independent set of valence-bond wavefunctions of any multiplicity and of evaluating the matrix elements is given.
The Measurement of Magnetic Induction in High Magnetic Fields at Low Temperatures. CoSO4·7H2O
Authors: Giauque W. F. , Hornung E. W. , Fisher R. A. , Brodale G. E.
Published: January 2005

A discussion of the potentiometric method of measuring magnetic induction has been given for isothermal, isentropic, and isoerstedic processes. The magnetic properties of CoSO4·7H2O have been investigated over the range 1.2° to 78°K and in fields up to 93 kgauss. Values of the differential isothermal magnetic susceptibility and intensity of magnetization as a function of field have been given. Within the limits of error, the system may be considered to consist of a major component which is a function of H/T, and a small temperature independent component with a negative field dependence. The entropy of magnetization calculated from the temperature coefficient of the magnetic work has been compared with the previously published directly determined values. The saturation value of powdered CoSO4·7H2O has been found to be 11800 gauss cm3 mole—1, and the Curie constant, Tχα,m(initial)=1.964 deg cm3 mole—1, each for the magnetic component which is a function of H/T. The temperature-independent susceptibility including diamagnetism has been represented by χβ,m=(0.0113—2.5×10—8 Hi) cm3 mole—1, with Hi in gauss. A correction has been applied to the earlier initial-susceptibility measurements of Fritz and Giauque and their results are in agreement with the present data within their limit of accuracy.
Paramagnetic Resonance of Glassy Mn(H2O)62+
Authors: Wakim Fahd G. , Nolle A. W.
Published: January 2005

The ESR absorption curve for the Mn2+ ion in an aqueous glass is structureless and almost symmetrical, with a width of 800 Oe between inflections. The theory of the Mn2+ spectrum in a single crystal with tetragonal symmetry can be related to this result by averaging over random orientations and choosing the value 300 Oe for the axial splitting parameter D.
Crystal Structure of CsMnF3
Authors: Zalkin Allan , Lee Kenneth , Templeton David H.
Published: January 2005

A single-crystal x-ray diffraction study shows that CsMnF3 has the hexagonal BaTiO3-type structure. The space group is P63/mmc. The unit cell with a=6.213 Å, c=15.074 Å contains six formula units. Each cesium atom has 12 fluorine neighbors at an average distance of 3.13 Å. One third of the manganese atoms occupy the centers of fluorine octahedra that share their corners with other octahedra as in the perovskite structure. The remaining two thirds of the manganese atoms are in distorted fluorine octahedra that each share one face and three corners with other octahedra; these manganese atoms are in pairs 3.00 Å apart. The average Mn–F distance in the octahedra is 2.13 Å.
Polarization of the Electret
Authors: Gross Bernhard , de Moraes R. J.
Published: January 2005

The internal charge distribution of the carnauba wax electret has been determined by a sectioning method: After polarization and cooling samples are cut into sections of different thickness. These are reheated and the ensuing discharge currents are measured. The total released charge, as determined by numerical integration of the corresponding current—time curve, gives the polarization of each section. A macroscopic space charge polarization would give charge values which, with decreasing thickness of sections, go to zero; a uniform volume polarization would give values which are independent of thickness. Measurements gave constant values and therefore prove the existence of a uniform volume polarization of the electret.
Effect of Molecular Shape on Nuclear Magnetic Relaxation
Authors: Shimizu Hiroshi
Published: January 2005

The dependence of magnetic relaxation processes upon molecular shape is examined by regarding the molecule as a rigid ellipsoidal body which shows anisotropic rotational and translational Brownian motions. The shape effects are examined based on particular mechanisms of relaxation: (1) intramolecular dipole—dipole interactions, (2) intermolecular dipole—dipole interactions, (3) anisotropic spin—spin couplings, (4) interactions of the nuclear moments with the local magnetic fields due to anisotropic shielding of the external field, and (5) electric quadrupole interactions. The relaxations caused by the first and second mechanisms are discussed in detail by taking a prolate spheroid as an example; the correlation time and the relaxation time are obtained as functions of the axial ratio. Saturations of multiple NMR lines are discussed; then, by taking the multiple lines of the three vinyl protons of acrylic acid as an example, the shape effect on the saturation, as well as an application of the saturation effects of multiplet lines to the assignment of a complex NMR spectrum, is discussed.
Determination of the Atomic Kinetics of the Freezing Process. I. Theory
Authors: Kramer J. J. , Tiller W. A.
Published: January 2005

A new method for determining the mechanisms and kinetics of atomic exchange across a liquid—solid interface during the freezing process is proposed and evaluated. The limitations of the method are entirely experimental, making the method effective only at freezing velocities less than 5×10—3 cm/sec.
Pressure Dependence of Fluorescence Spectra. IV. Effects of Vibrational Energy Transfer between Fluorescing Molecules
Authors: Davis Robert C. , Wilson David J.
Published: January 2005

Vibrational relaxation of a system of s-dimensional degenerate harmonic oscillators is investigated. The oscillators are impulsively excited and are then allowed to relax to thermal equilibrium by collisions with a heat bath and by transfer of vibrational quanta among themselves. The model is applicable to analysis of experimental data in which excited molecules are produced in concentrations not negligible in comparison to the concentration of heat-bath molecules.
Flash-Photolysis Studies of α- and γ-(2,4-Dinitrobenzyl)pyridine
Authors: Mosher Harry S. , Hardwick E. R. , Hur David Ben
Published: January 2005

From flash-photolysis experiments it has been determined that the blue, phototropically produced substance from α-(2,4-dinitrobenzyl)pyridine fades to the colorless form by at least two mechanisms. The rate of the slower process, which is controlling in neutral and slightly basic solution, is first order in the blue substance and is apparently independent of the nominal hydrogen-ion concentration. The faster process is rate controlling in the acidity range, [H+]=5×10—7 to at least 5×10—1, and follows a rate constant which is linear in [H+] over some 5 or 6 orders of magnitude, i.e., a half-life from ∼10 to ∼3.5×10—5 sec. Similar behavior is displayed by the γ isomer.

The large solvent dependence reported earlier is now ascribed to slight acid impurities in the sensitive 10—6—10—7[H+] range.

These and related findings are discussed in terms of possible structural and mechanistic details.