bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear Magnetic Relaxation in Ionic Solution. I. Relaxation of 23Na in Aqueous Solutions of NaCl and NaClO4
Authors: Eisenstadt Maurice , Friedman Harold L. 
Published: January 2005

The relaxation time of the nuclei of sodium ions has been measured for aqueous solutions of sodium chloride and sodium perchlorate at 25°. The longitudinal and transverse relaxation times are equal and depend on solution composition according to the rate law T1−1=17.55+0.55cNaCl+11.95cNaClO4±0.30,with T1 in seconds and cX in moles of X per liter, for single and mixed electrolyte solutions at concentrations less than 1M. Deviations from the equation are small up to 3M total concentration, and also in D2O if the coefficients are first multiplied by the ratio of solvent viscosities.
The limiting value of T1 at low concentration agrees roughly with the calculation of the effect of fluctuating electric-field gradients due to reorientational Brownian motion of water molecules coordinated to the sodium ion, but there are some very uncertain factors in the calculation. The coefficients of the rate law may be related to the distance of closest approach of the ions in various ways, with the result that this distance is much smaller for Na+ClO−4 than for Na+Cl−.
Dielectric Relaxation in the Electric Double Layer
Authors: Bockris J. O'M. , Gileadi E. , Müller K. 
Published: January 2005

There are two groups of phenomena that can cause frequency dispersion of capacity and resistivity at a perfectly polarizable interface. The first comprises artifacts which lead to the observation of an apparent frequency dispersion: Of these, penetration of the electrolyte to shielded parts of the electrode and the resulting transmission line phenomena are discussed. The second group comprises processes which lead to an inherent frequency dispersion of the double-layer impedance: among these are, in particular, the relaxation phenomena of polar double-layer constituents.
Experimental results have been obtained for the interface: Hg (dropping) /6NHCl aq., in terms of parallel capacity, Cpd1, and resistivity, Rpd1, of the electric double layer as a function of frequency, v. These results are consistent with the occurrence of dielectric relaxation of the water dipoles adsorbed at the interface, and characterized by a certain distribution of relaxation times around τ0≃10−6 sec. The results are not consistent with the values ∂ lnRpd1/∂ lnv expected from the effect of a possible penetration of electrolyte into the capillary.
On the basis of a molecular model of the relaxation process, a rough estimate of the energy of activation for the process which results in a change of direction of the water dipole is made which is consistent with the mean relaxation time, τ0, estimated on the basis of the dielectric properties of double-layer water. It is shown that the frequency variation of the double-layer capacity is less than the detection limits of most ac bridges up to very high frequencies, as long as the high-atom polarization of water remains unchanged, and only dipole polarization is gradually reduced to zero with increase of frequency.
Study of CO Radicals on Magnesium Oxide with Electron Paramagnetic Resonance Techniques
Authors: Lunsford Jack H. , Jayne John P. 
Published: January 2005

It has been determined that a fraction of the carbon monoxide which is adsorbed on magnesium oxide is in a paramagnetic state. Magnesium oxide was degassed at 850°C and 10−5 Torr for 16 h, cooled to room temperature, and then exposed to 150 Torr of high-purity carbon monoxide. The resulting paramagnetic spectrum grew slowly for several weeks.
This paper describes the spectrum of the adsorbed CO radical (g∥=2.0021, g∂=2.0055, ax=27 G, ay=11 G, az=0 G), the probable type of site on which the molecule is adsorbed, its bonding, and the effect of evacuating at elevated temperatures.
Kinetics of Unimolecular Breakdown. I. The Formal Solution
Authors: Hall G. G. , Levine R. D. 
Published: January 2005

A quantum-mechanical discussion of the kinetics of unimolecular breakdown is presented using the Green's operator formalism. Experimentally, chemical reactions are characterized by their products and the theoretical discussion starts from this fact in an attempt to define the activated state. A scheme is indicated for the calculation of experimental results such as rate constants or yields of products. The concept of a natural line shape of a process is employed in discussing the separation of excitation and breakdown stages and the limitations on such a description are noted.
Applications are made to model theories of chemical reaction rates and to results of computer simulation studies.
Computer Calculations of Ion—Molecule Reactions
Authors: Wolf Fred A. 
Published: January 2005

A computer program has been developed which follows Light's phase-space theory of three-body ion—molecule reactions. The program predicts cross sections for 10 possible reaction branches as functions of the relative kinetic energy of the colliding particles in the range from thermal energies up to 20 eV. It also yields partial cross sections for the populations of the vibrational levels of the diatomic molecules in the product channel. Included in the results are reactions for the following ion—molecule pairs: [O++N2], [N++O2], [O+N2+], [He++N2], and [18O++O2]. The effects of varying the level of excitation, both vibrationally and electronically, of the reactants are presented. Increasing the excitation level always results in greater cross sections for reactions which are otherwise endothermic and slightly smaller cross sections for reactions which are otherwise exothermic.
All endothermic cross sections reach maximum values as functions of the barycentric kinetic energy of the reactants. All exothermic cross sections decrease with increasing barycentric kinetic energy at rates faster than predicted by the Gioumousis and Stevenson theory. This is due to the greater competition between the products for the available phase space which occurs at elevated energies. Good agreement is found between the theory and experiment in the high-energy region above 5 eV and in some cases throughout the whole energy range. Disagreement is most pronounced for low energies. It is felt that this indicates the presence of a small activation energy or, in the case where the products differ from the reactants by a charge transfer A++BC→A+BC+, the neglect of including resonance forces in the calculation.
Gas-Phase Radiolysis of Cyclobutane
Authors: Doepker R. D. , Ausloos P. 
Published: January 2005

The gas-phase radiolysis of cyclo-C4H8 and cyclo-C4D8 has been investigated in the presence of O2, NO, H2S, NH3, and several organic compounds. From the products formed, it could be inferred that the following fragmentation processes occur: C4H8+→C3H5++CH3,C4H8+→C2H4++C2H4,C4H8+→C2H5++C2H3,C4H8+→C3H4++CH4.At 20 Torr, the ion-pair yields which can be ascribed to some of these processes are lower than the corresponding ion-pair yields observed in the mass spectrometer at a pressure of 10−5 Torr.
When compounds such as NO (I.P.=9.25 eV) or (CH3)3N(I.P.=7.8 eV) are added to cyclobutane, butene (I.P.=9.13–9.58 eV) is a major product. On the other hand, when organic or inorganic compounds whose ionization energy is higher than that of butene are added to cyclobutane, the yield of butene is, in most cases, negligibly small. The formation of butene can be tentatively accounted for by a ring opening of the parent ion followed by charge transfer. On the basis of this mechanism, a minimum value of 0.42±0.02 can be ascribed to M(C4H8+)/N.
When an electrical field is applied in the saturation current region, during radiolysis of cyclobutane—NO mixtures, the yields of methane, ethane, and butene which have the parent ion or fragments thereof as precursors, remain unchanged. On the other hand, the yields of products such as ethylene, allene, acetylene, and 1,3-butadiene whose formation is, in part, attributed to the decomposition of neutral excited molecules, are seen to increase due to increased excitation by electron impact. In the absence of an electrical field, the number of neutral excited molecule decompositions per ion pair is estimated to be ≤0.65±0.05.
Role of Interaction Constants in Force-Constant Calculations
Authors: Lehmann Walter J. , Beckmann Leo , Gutjahr Liselotte 
Published: January 2005

The five in-plane vibrational frequencies of X2CO molecules are used to determine nine independent force constants of a general quadratic force field.
Instead of the usual arbitrary assumptions about the four supernumerary force constants (which four?), yielding simpler force fields, a minimum of very mild constraints was applied to the interaction constants (e.g., assumptions about some signs and the setting of reasonable limiting values). Some of these constraints in turn produced further constraints on the other force constants.
A specially designed analog computer allowed these calculations to be performed in a reasonable time. It was possible to vary continuously any of the force constants and to observe directly the effects on the frequencies and on the other force constants. Thus very quickly some ``feeling'' was developed for the molecule and the interrelation of the force constants.
The result then is not a unique set of force constants (which might be recorded in the literature with several decimals), but rather a nine-dimensional hypersurface of solutions, whereon each of the nine GFF constants occupies a range of values. For example, f(C=O) in Br2CO ranges from 12.9 to 14.2 mdyn/Å, and the C–Br stretch/opposite-angle interaction from −0.25 to −0.34 mdyn.
Ultraviolet Absorption and Excitation Spectrum of Ruby and Sapphire
Authors: Loh Eugene 
Published: January 2005

The absorption spectrum of thin samples of ruby with 0.5 to 0.005 wt. % of Cr2O3 has been measured up to 8.9 eV at room temperature with linearly polarized light. The spectrum shows an absorption peak at 7 eV followed by humps around 8 eV with absorption cross section and oscillator strength at the 7-eV peak ∼7×10−17 cm2 and ∼0.3, respectively. The absorption with E⊥c is generally larger than E| | c in the vacuum-uv region. The absorption between 6.8 and 8.6 eV is interpreted as a charge-transfer transition around the chromium ion because of its large oscillator strength and some similarity to the ultraviolet reflectance spectrum of Al2O3 crystal.
The excitation spectrum of ruby cubes with several chromium concentrations has been measured to 11 eV at room temperature with linearly polarized light. Structure and polarization effects corresponding to those of the absorption spectrum are observed. The quantum efficiency in the region 7 to 9 eV is comparable to that in the blue absorption band of ruby and is essentially concentration independent. Above 9 eV the relative quantum efficiency drops about two orders of magnitude and is concentration dependent, with low quantum efficiency for samples of low chromium concentration. Similar spectra on sapphire are also included for comparison.
Electronic Structure of Diatomic Molecules. III. A. Hartree—Fock Wavefunctions and Energy Quantities for N2(X1Σg+) and N2+(X2Σg+, A2Πu, B2Σu+) Molecular Ions
Authors: Cade Paul E. , Sales K. D. , Wahl Arnold C. 
Published: January 2005

The problem of the convergence of a sequence of Hartree—Fock—Roothaan wavefunctions and energy values to the true Hartree—Fock results is examined for N2(X1Σg+). This critical study is based on a hierarchy of Hartree—Fock—Roothaan wavefunctions which differ in the size and composition of the expansion basis set in terms of STO symmetry orbitals. The concluding basis set gives a total Hartree—Fock energy of −108.9956 hartree and Re(HF)=2.0132 bohr for N2(X1Σg+).
Results are also presented from direct calculations for three states of the N2+ molecular ion (X2Σg+, A2Πu, B2Σu+) which are also thought to be very close approximations to the true Hartree—Fock values. The results give EHF=−108.4079, −108.4320, and −108.2702 hartree and Re(HF)=2.0385, 2.134, and 1.934 bohr for the X2Σg+, A2Πu, and B2Σu+ states of N2+, respectively. Extensive calculations for various R values establish that the X2Σg+ and A2Πu states are reversed in order relative to experiment, a short-coming ascribed to the Hartree—Fock approximation.
Observation of Conformational Isomers of the Tetraisopropylnitrobenzene Anion Radical by Electron Spin Resonance Spectroscopy
Authors: McKinney Ted M. , Geske David H. 
Published: January 2005

The electron spin resonance spectrum of the anion radical obtained by electroreduction of 2,3,5,6-tetraisopropylnitrobenzene has been studied extensively. The spectrum is interpreted in terms of two discrete conformational isomers existing in thermodynamic equilibrium. The isomeric difference arises from concerted interaction of the ring substituents which allows the nitro group to assume two different angular orientations with respect to the plane of the ring. These orientations are manifested as two different 14N isotropic coupling constants. In acetonitrile solution these values are 23.6 and 22.0 G for the more- and less-twisted conformers, respectively. An apparent equilibrium constant for interconversion is defined and evaluated under a wide variety of solvent and temperature conditions. The free energy of conversion from the more- to the less-twisted conformation is estimated as ΔG298° = −5±1×102 cal mole−1 in acetonitrile. A necessary condition for the proposed equilibrium is that both species decay at the same rate and this condition is observed experimentally.
2,4,6-Tri-isopropylnitrobenzene anion radical was also studied. The nitrogen coupling constant was 20.6 G in acetonitrile, but no conformational isomerism was observed presumably because of the absence of buttressing 3,5-substituents.
Adsorption and Oxidation of Carbon Monoxide on Clean Films of Palladium and Nickel
Authors: Kawasaki Koji , Sugita Toshio , Ebisawa Shigeo 
Published: January 2005

The adsorption and surface reaction of carbon monoxide and oxygen on clean films of palladium and nickel at room temperature at pressures in the range of 10−9−10−2 torr were studied by means of mass spectrometer and by measuring simultaneously electrical resistance.
CO preadsorbed on clean films of palladium and nickel reacted readily with gaseous O2 and no induction period was observed. Oxygen preadsorbed on palladium film immediately reacted with CO, but on nickel never reacted.
Some discrepancies between the results and those in the literature were discussed.
Intermolecular Obstruction in Rubber Elasticity Theory
Authors: Jackson Julius L. , Shen Mitchel C. , McQuarrie Donald A. 
Published: January 2005

The leading term of the equation of state of rubber relating elongation to stress may be obtained by treating the polymer chains in the rubber as independent and distributed according to the laws of Brownian motion. A great deal of theoretical work has been done on corrections to this simple picture, particularly in consideration of the finite extensibility of the chains and the network character of their connections.
In this paper we attempt to take into account the fact that in the rubber there is a high density of chains which causes mutual obstruction among the chain Brownian motions. In the unstrained, symmetric state the obstruction is isotropic; however, when the rubber is stretched, the degree of obstruction will be different in different directions. An equation is obtained for the dependence of free energy on this anisotropic effect. The theoretically derived stress—strain equation is compared with experimental results.
High-Temperature Equilibrium in the Germanium—Nickel System and the Dissociation Energy of GeNi
Authors: Kant Arthur 
Published: January 2005

The GeNi molecule has been shown to exist in the vapor phase over liquid solutions of germanium and nickel above 2000°K.
Using information derived from a combination of effusion and mass-spectrometric techniques, the energies and equilibrium constants of the gaseous reactions GeNi+Ge=Ge2+Ni and GeNi=Ge+Ni have been calculated. The values of the energy assuming a 1Σ ground state of GeNi are GeNi+Ge=Ge2+NiΔE0∘=1.6±4 kcal,GeNi=Ge+Ni  D0∘(GeNi)=66.4±4 kcal.
The dissociation energy of Ge2 was also determined and the value of D0°(Ge2) of 64.9±3 kcal confirms results obtained previously.
Structure of Cubic Ammonium Fluosilicate: Neutron-Diffraction and Neutron-Inelastic-Scattering Studies
Authors: Schlemper Elmer O. , Hamilton Walter C. , Rush J. J. 
Published: January 2005

The motion of the ammonium ion in the cubic phase of (NH4)2SiF6 has been investigated by the inelastic scattering of slow neutrons. The prominent feature of the neutron energy-gain spectrum is a moderately broad band peaked at 168±8 cm−1 with a shoulder at 305±25 cm−1. These are assigned to the 1–0 and 2–0 transitions of a rotational motion of the ammonium ion.
A precision refinement of single-crystal neuron-diffraction data has also been completed. There is a well-defined disorder of the ammonium groups. Although a model with a static threefold disorder, with each ⅓ hydrogen atom undergoing harmonic vibration gives a very satisfactory fit to the data, such a model is probably unrealistic in view of the fact that the disordered positions are only 0.75 Å apart. A more realistic model is one involving an ordered hydrogen atom undergoing thermal motion in a very anharmonic potential well. We propose a model in which the hydrogen atom is relatively free to move over a region of about 1 Å2 by small rotations of the ammonium ion but with a very high barrier toward a reorientation which involves an interchange of two hydrogen atoms. Such a model is an agreement with both the neutron-diffraction and the inelastic-scattering data.
The hydrogen-atom positions found in the diffraction study do not agree with those reported by Vainshtein on the basis of an analysis of the electron-diffraction data. The N–H bond length is not well defined because of the uncertainties regarding the thermal motion. An uncorrected mean atomic separation of 0.985 (σ=0.007) is obtained; the actual bond length is about 0.08 Å longer. The SiF62— ion is a regular octahedron with a corrected bond length Si–F=1.696 (σ=0.003).
Calculation of the Surface Tension of a Simple-Cubic Crystal According to Two Different Methods
Authors: Yun K. S. , Benson G. C. 
Published: January 2005

A comparison is made of the surface tension of a simple-cubic crystal calculated according to two different methods: (i) from the variation of the surface free energy with surface area and (ii) from the surface-stress tensor.
A Lennard-Jones 12–6 potential is employed for the interaction between pairs of atoms and the effects of surface relaxation are investigated extensively. The numerical results show that the two surface tensions approach one another as the relaxation of the surface region of the crystal is extended further into the crystal.
Microwave Spectrum, Internal Barrier, Molecular Structure, and Dipole Moment of Disilanyl Fluoride
Authors: Cox A. Peter , Varma Ravi 
Published: January 2005

The microwave spectra of five isotopic species of disilanyl fluoride (Si2H5F) have been studied in the region 12–38 Gc/sec. Several of the ground-state transitions are split into doublets, some into triplets, due to the coupling of internal and over-all rotation. Analysis of the splittings gives a barrier value V3 = 1048±40 cal/mole.
Rotational constants have been determined for molecules containing silicon−28, −29, and −30 isotopes in each position and have been used to calculate the following structure:  Si–F=1.598±0.008 Å, Si–Si=2.332±0.005 Å, Si–H=1.483 (assumed), Si–H(F)=1.477 Å (assumed),∠HSiH=180∘20′ (assumed),  ∠HSiH(F)=110∘2′  (assumed),∠SiSiF=109∘30′±30′,∠SiSiH(F)=110∘22′±2∘.
Stark-effect measurements yield μA = 0.934 D, μB = 0.850 D, and a total dipole moment μ = 1.26±0.01 D inclined at an angle of 10° to the SiF bond.
Molecular Structure of (CF3)2PCl3: Infrared and Raman Spectra
Authors: Griffiths James E. , Beach Alexander L. 
Published: January 2005

The basic structure of (CF3)2PCl3 has been established from a study of its vibrational spectrum (D3h point group). The CF3 groups occupy axial positions in a trigonal bipyramidal framework, but no direct information is obtained concerning the heights of the barrier to internal rotation. Molecular models indicate strong F···Cl steric interference and suggest a high barrier, however.
All of the active fundamentals are assigned in the Raman (Δν=50–1500 cm−1) and infrared (ν=33–2000 cm−1) spectra. Gas, liquid, and solution spectra were recorded. Fundamental frequencies are: a1′=1173, 739, 366, 237; a2″=1184, 748, 447, 254; e′=1150, 589, 534, 335, 186, 89; e″=1193, 539, 304, and 202 cm−1.
Unlike CF3PCl4, the trichloro compound, (CF3)2PCl3, is quite stable at 40°C and to irradiation by 4358-Å Hg light.
Wavelength Dependence of the Quenching of Iodine Fluorescence
Authors: Steinfeld Jeffrey I. 
Published: January 2005

The variation of the quenching efficiency of various gases (He, Xe, NO, CO2, C2H4, C6H6, I2) with energy of excitation was measured for the iodine B→X fluorescence. The correlation of efficiency with the parameter αμ½, previously found, was confirmed over a range of vibrational states. States of v′≤7 appear to be ``unquenchable'', and a fluorescence stabilization effect appears as a departure from the Stern—Volmer law. This is attributed to the absence of repulsive electronic states below the seventh vibrational level of I2. Anomalously large quenching cross sections are found for several species (NO, CO2); however, there is no conclusive evidence for a complex formation mechanism.
Using these data, it was possible to locate approximately the repulsive states of I2 relative to the B state. The magnetic quenching rate can be computed to good accuracy from simple LCAO—MO wavefunctions, using first-order time-dependent perturbation theory. The collision-induced quenching can be completely explained on the basis of a van der Waals-type interaction.