bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
Infrared Spectra of the Azide Ion in Alkali-Halide Lattices
Authors: Bryant James I. , Turrell George C. 
Published: January 2005

The infrared-active vibrational frequencies of the azide ion as an impurity in KI, KBr, KCl, and NaCl lattices have been measured as functions of temperature. Samples were prepared using the pressed-disk technique. In several cases comparisons are made of the spectra of pressed disks with those of single-crystal samples grown from aqueous solutions. Identical frequency shifts with temperature and lattice in the two types of samples offer strong evidence of lattice intermixing (solid solution) in pressed disks.
A simple electrostatic model of impurity-ion—lattice interaction is presented. It is shown that inductive, Coulombic, and short-range forces all provide significant contributions to the lattice perturbation. The experimental data on the azide ion are used to make approximate calculations of the quadratic and cubic force constants for the hypothetical ``free'' azide ion and to provide tests of the electrostatic model being considered.
Kinetics of the Reaction of HI with Propylene
Authors: Bose A. N. , Benson Sidney W. 
Published: January 2005

The very slow gas phase reaction between HI and propylene has been observed to follow a second-order rate law near 230°C. The product is i-PrI with less than 0.1% of n-PrI produced initially. Above 270°C, the secondary production of C3H8 and I2 becomes important. The lower temperature data permit measurement of the equilibrium constant K2.1 for C3H6+HI⇌ lim 12i−C3H7I.The value at 238° is in excellent agreement with independent estimates of the thermodynamics for this reaction which give ΔH0=—20.6 kcal/mole, ΔS0=—34.1 cal/mole-°K, ΔCp0=—1.6 cal/mole-°K.
The rate data yield for the addition reaction (k2) logk2=−(23 400/4.575T)+7.89  (liters/mole−sec).The combination of k2 and K2.1 yield values for k1 in excellent agreement with the directly observed values by Jones and Ogg at 330°C. Independent observations on the 328°C pyrolysis of n-PrI show that appreciable isomerization to i-PrI takes place and that HI is an important intermediate.
Displacement of Photoelectrons and Positive Holes in Sheet Crystals of Silver Bromide as Shown by Development Techniques
Authors: Saunders V. I. , Tyler R. W. , West W. 
Published: January 2005

The mobility of electrons in unannealed, large, thin crystals of silver bromide made from the melt was measured from the displacement of latent-image centers formed by flash exposures synchronized with pulsed electric fields; an etching-development technique was used to locate the latent image as reduced silver. Similarly, the motion of positive holes in the crystals was determined by the hole-induced destruction of previously introduced latent-image centers or fog centers, which, on development, yielded a bleached image against a background of reduced silver. At 30°C, the electron mobility in these crystals was 66 cm2 V—1 sec—1, and their lifetime about 0.3 μsec; the mobility of the positive holes was 1.7 cm2 V—1 sec—1 and their lifetime in the undisturbed crystal was greater than 10 μsec.
Even in the absence of positive holes, the formation of latent image on a surface of silver bromide may be greatly facilitated by the presence of a sensitizer, such as silver sulfide. In such a case, silver sulfide appears to act as an electron trap or in some other way not associated with the capture of positive holes.
Multiple Reactions and the Vapor Transport of Solids
Authors: Mandel G. 
Published: January 2005

The method of Lever, which has enabled calculation of the steady-state diffusion limited rate of transport of solid for the case of a single chemical equilibrium, is generalized to include the situation in which several equilibria are simultaneously operating. This is accomplished for the case of N equilibria by the introduction of (N — 1) ``coupling parameters,'' so defined that the steady-state conditions become formally identical to those given previously. Following Lever, the results of these operations are combined with the usual thermodynamic relations for the temperature dependence of the equilibrium constants, finally resulting in a set of (N — 1) linear simultaneous equations in (N — 1) unknowns, the ``coupling parameters.'' These equations can be solved, in general, in terms of the ratios of (N — 1) dimensional determinants.
On the basis of the above, a straightforward procedure is devised for the calculation of the rate of transport of solid, based on knowledge of initial conditions as well as thermodynamic and diffusion coefficient data.
Motion in Polyethylene. II. Vibrations in Crystalline Polyethylene
Authors: Wunderlich Bernhard 
Published: January 2005

Using the specific heats of completely crystalline polyethylene as a basis, the vibrational spectrum is discussed. The vibrational spectrum is found to consist of three completely separate parts. (A) The high-frequency CH2-stretching vibrations between 2850 and 2930 cm—1 which contribute little to the specific heat below 350°K. (B) The low-frequency optical vibrations between 720 and 1480 cm—1 which contribute above 150°K increasingly to the specific heat. (C) The acoustical vibrations which stretch from zero to approximately 500 cm—1 and are at 260°K to 90% excited. A and B are adequately known from infrared and Raman experiments. C can be approximated by a Tarasov-type treatment leading to θ temperatures of 123° and 540° for the three-dimensional and one-dimensional parts, respectively.
More detailed spectra are discussed, and a semiempirical best fit is given. The one-dimensional Debye function necessary for this discussion has been computed to five places and is tabulated in steps of hν/kT=0.01.
Adsorption of Hydrogen on a (110) Nickel Surface
Authors: Germer L. H. , MacRae A. U. 
Published: January 2005

Hydrogen adsorption at room temperature on a clean (110) surface of a nickel single crystal is accompanied by reconstructive rearrangement of the surface metal atoms to form a (2×1) surface structure. It is possible to remove this adsorbed hydrogen and obtain a planar surface by heating the crystal slightly above room temperature. A determination of the temperatures and equilibrium hydrogen pressures necessary to remove this adsorbed hydrogen yields an isosteric heat of adsorption of 1.2 eV.
Oxygen displaces the hydrogen in the (2×1) structure from the surface and results in the formation of the (1×2) structure characteristic of adsorbed oxygen. This oxygen can be removed from the surface, however, by heating the crystal to 200°C in hydrogen.
Classical Model for Vibrational and Rotational Excitation of Diatomic Molecules by Collision. II. Interaction with Arbitrary Potential Functions
Authors: Benson Sidney W. , Berend George C. , Wu James C. 
Published: January 2005

Two classical models for vibrational energy transfer between a diatomic harmonic oscillator A-B and an atom C are examined in detail. The first model corresponds to a harmonic repulsion between B and C with a smooth cutoff at zero interaction. It can be solved exactly. The second corresponds to a Morse-like potential between B and C. In this case, the orbits for colinear collisions are followed on a digital computer, and ΔEv the inelastic energy transfer is ``measured'' from this numerical solution for the equation of motion. The results can be transformed into probabilities by defining excitation as the condition: 2hν&gt;ΔEv≥hν. ΔEv is a strong function of the phase angle of the oscillator. The probability function for excitation is transformed into a rate constant by averaging over the temperature-dependent distribution functions for energies.
In contrast to other ``classical'' solutions, it is found that P, the probability of excitation (or de-excitation), has a nearly Arrhenius type of dependence on temperature. The activation energy of P is quadratically sensitive to the range of the repulsive interaction between B and C. This arises from the result that the excitation probability P(ER) goes very sharply to zero as ER, the relative collisional energy, approaches some small limiting value. This is in marked contrast to present theories for which P(ER) goes asymptotically to zero with ER.
Features of the classical model are discussed in some detail and comparisons are made with experimental data from shock tubes. Because of the extreme sensitivity of the model to the value for the range parameters, no absolute predictions of de-excitation probabilities are possible. However, it is possible to fit the temperature dependence reasonably well with physically acceptable Morse parameters.
ESR Investigation of Some Thiazine and Oxazine Dye Radicals
Authors: Heineken F. W. , Bruin M. , Bruin F. 
Published: January 2005

ESR spectra of semiquinone radicals, formed as intermediary reduction products in reversibly reducible thiazine and oxazine dyestuffs, have been investigated in acid as well as in alkaline solution.
In acid solutions at relatively high concentration of the dye the spectra consist of four lines. In alkaline solutions at high concentration there are three lines. At lower concentrations most spectra could be resolved further into many components.
A tentative interpretation of the spectra is given.
Effect of Added Quenchers in Organic Scintillator Solutions: Organometallics
Authors: Kropp John L. , Burton Milton 
Published: January 2005

Quenching constants (γs and γx) are given for a variety of perphenyl metals (Si, Ge, Sn, Pb, Sb, and Hg) and for mercury dimethyl acting on benzene and cyclohexane solvents and p-terphenyl and DPA scintillators. Specific rates are calculated for the quenching processes and are found to break into the following classes: &lt;7×109 M—1 sec—1 corresponding to spin-perturbation-induced quenching (with a probability factor less than unity, according to Umberger—LaMer calculations) and ≧3×1010 M—1 sec—1 (exceeding such calculated values), corresponding to highly favored excitation-transfer processes. The latter high values can be explained in terms of the domain theory of liquid scintillator solutions. Specific rates in the intermediate range for GePh4, and perhaps for SiPh4, acting on solvents are consistent with resistance to high-energy irradiation and with the attendant probability that long-lived excited states of such quenchers actually transfer excitation to the scintillator.
Anomalously high quenching constants and specific rates for quenching (as well as an anomalous relationship between quenching constants for aerated and de-aerated solutions) in the case of cyclohexane suggest that a proper view of energy deposition should be an initial nonlocalized excitation of the system, followed by competitive localization of excitation in one of several particular species: i.e., cyclohexane (which may immediately decompose if an excited state is directly produced), quencher, or scintillator.
Nuclear Spin Relaxation in Liquid CHFCl2
Authors: Brown R. J. C. , Gutowsky H. S. , Shimomura K. 
Published: January 2005

Nuclear spin relaxation times have been measured for liquid CHFCl2, the values of T1H and T1F between 132° and 298°K at 27, 20 and 17 Mc, and T2H and T2F over the same temperature range at 20 Mc. The results of these measurements are discussed, and the following relaxation mechanisms are shown to be important: (a) intermolecular dipole—dipole interactions, including their effect upon the electronic, scalar coupling of the proton and fluorine nucleus, (b) the quadrupolar relaxation of the chlorine nuclei which are coupled to the proton and the fluorine nucleus by scalar couplings, and (c) the spin-rotation interaction between the fluorine nucleus and the reorientation of the molecule. It is noted that relaxation of the same type as mechanism (b) accounts for the relatively large natural linewidths and poorer resolution often found in spectra of heavier nuclei such as F and P, compared to spectra of protons in the same liquid compound.
The statistical assumptions of rotational Brownian motion of the molecule, in the liquid, when applied to the spin-rotation interaction, are found to predict the wrong temperature dependence of T1F at high temperatures. A transient rotation model is proposed in which the molecules ``jump'' from one orientation to another at random times; the spin-rotation interaction is assumed to operate during these ``jumps'' when the molecule is actually rotating. The statistical properties of such a model are calculated, and it is shown that T1F is predicted to have the correct temperature dependence. The model is compared with that developed by Johnson and Waugh for nuclear relaxation by the spin-rotation interaction in gases. The dipole—dipole and quadrupole interactions are discussed in detail, and a treatment of intermolecular dipole—dipole relaxation by Redfield's method is given, with results indicating that the electronic, scalar coupling of nuclei contributes to the inequality T2&lt;T1 often found in liquids.
Structure of Formaldoxime
Authors: Levine Ira N. 
Published: January 2005

The microwave spectra of cis-CHDNOH, trans-CHDNOH, C13H2NOH, CH2N15OH, and CH2NO18H were assigned. Together with the results of previous work on the normal species and CH2NOD, the data give the following planar structure for formaldoxime: bond lengths in Å; CHcis=1.085, CHtrans=1.086, C=N=1.276, NO=1.408, OH=0.956; bond angles; HcisCN 121°46′, HtransCN 115°33′, CNO 110°12′, NOH 102°41′.
The most significant feature of the structure is the difference between cis- and trans-HCN bond angles. This ``tilt'' of the methylene group appears to be too large to be attributed to steric repulsion. The C=N and N–O bond lengths are consistent with the Schomaker—Stevenson relation if allowance for resonance is made.
Magnetic Susceptibility of Diatomic Molecules
Authors: Karplus M. , Kolker H. J. 
Published: January 2005

A variation—perturbation method is presented for the calculation of the magnetic susceptibility tensor χ from a single-determinant ground-state wavefunction for a 1Σ molecule. The diamagnetic contribution χd is obtained directly by first-order perturbation theory and the paramagnetic contribution χp is determined by extremizing a functional corresponding to the second-order energy in an external magnetic field. By an appropriate choice of perturbation function and zero-order Hamiltonian, the functional is expressed in a relatively simple form requiring only one-electron matrix elements. The importance of employing Hartree—Fock functions as the zero-order solution is stressed and an analysis given of the order of the errors in the variation—perturbation treatment. Explicit comparisons of the present method with simplified forms of the variational procedure demonstrate that the neglect of electron exchange or use of an ``average'' perturbation function can introduce significant errors in the results.
Calculations are made of the magnetic susceptibility tensor for a series of diatomic molecues. Ransil's minimal basis set functions serve as unperturbed wavefunctions and a four-term polynomial is used to represent orbital perturbations in the second-order treatment. The values obtained for χd, χp, and χ of H2, Li2, N2, F2, LiH, HF, LiF, and CO are presented. Comparisons with the available magnetic data for these molecules demonstrates that the variation—perturbation method is a useful tool for ab initio susceptibility calculations. For the more difficult paramagnetic term χp, criteria for the convergence of the second-order energy are discussed and applied to the molecules considered. The magnetic anisotropy (Δχ=χ⊥—χ∥) is evaluated theoretically for hydrogen and found to be in reasonable agreement with experiment. The inaccuracies arising in Δχ values for more complex species (through differencing in a purely theoretical treatment) are overcome by the inclusion of rotational magnetic moment data to obtain relatively reliable results. To examine the effect of the vibrational state on the susceptibility of a molecule, an exploratory calculation is made for LiH, which demonstrates that small sut significant deviations from the equilibrium-distance value are to be expected. Finally, some indication is given of the additional experimental and theoretical work that is required in this field.
Molecular, Crystal, and Valence Structures of B18H22
Authors: Simpson Paul G. , Lipscomb William N. 
Published: January 2005

A three-dimensional x-ray diffraction study of single crystals has yielded the molecular structure of B18H22. The molecule is centrosymmetric, has six bridge H atoms, and has the geometry of two decaborane-14 cages sharing a common B9–B10 edge. The space group is Pccn, and there are four molecules in a unit cell having dimensions a=10.844, b=12.107, and c=10.803 Å.
The valence structure has been studied in the two-center and three-center resonance approximation, which is comparable in its predictions to the Hückel molecular orbital method in the other boron hydrides. The charge distribution in B18H22 has been obtained from an analysis of the 6506 resonance structures.
Shock-Wave Integrated Intensity Measurements of the 2.7-Micron CO2 Band between 1200° and 3000°K
Authors: Breeze J. C. , Ferriso C. C. 
Published: January 2005

A shock-wave technique is described which provides a means of measuring the infrared integrated intensity of molecular bands at elevated temperatures. The total band emission from the high-temperature gas region existing between the end plate of a shock tube and the reflected shock wave was measured using a rapid-response infrared detector. The total emission of the band is obtained as a function of pathlength as the reflected shock wave recedes from the end plate. The initial concentration, shock velocity, and reflected-shock pressure were measured and the final conditions of the test gas were calculated from the normal shock relations.
The method has been used to measure the absolute intensity of the 2.7 μ band of CO2 (ν1+ν3 and 2ν2+ν3) in the temperature region 1200° to 3000°K. The shock-heated samples were produced in a 4% CO2—96% Ar mixture using helium as a driver gas. To ensure adequate pressure broadening at high temperatures for this weak band and yet to remain within the optically thin region, the measurements were made at approximately 2.5-atm total pressure, 0.1-atm CO2 partial pressure, and CO2 optical path lengths up to a maximum of 0.8 cm·atm. The observed integrated band intensity of the 2.7-μ CO2 band increases by a factor of approximately 2.5 in going from 300° to 3000°K. This variation with temperature is discussed in terms of a simple harmonic-oscillator model.