bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonequilibrium Effects in Recombination—Dissociation Kinetics
Authors: Kolker H. J. 
Published: January 2005

It is well known that if a mixture of atoms and diatomic molecules are at thermodynamic equilibrium in a chemically inert, constant-temperature heat bath, the molecular internal degrees of freedom can be characterized by a Maxwell—Boltzmann or equilibrium distribution. If the temperature of this system is suddenly changed, atoms will start to recombine or molecules will start to dissociate in order to restore chemical equilibrium; however, the diatomic molecules will no longer have a Maxwell—Boltzmann distribution. The rate at which these internal energy levels approach equilibrium is influenced by the reaction velocity, the rate at which molecules are created or destroyed. Since it is relatively easy to dissociate highly excited molecules, the rate of reaction is coupled to the rate at which the internal degrees of freedom relax to an equilibrium or Maxwell—Boltzmann distribution.
It is very difficult to develop a theory of recombination—dissociation kinetics that explicitly accounts for the coupling of the rate of reaction to the rate of relaxation. Several theoretical techniques have been proposed for solving this problem; however there seem to be certain discrepancies in the theories that are based on these techniques. In the present study, an iterative perturbation procedure, which couples the rate of relaxation to the rate of reaction in a self-consistent manner, is used to derive a nonequilibrium theory of recombination—dissociation kinetics. One of the immediate advantages of this theory is that it includes many of the existing theories as special cases. This theory provides a way of predicting under what conditions it is possible to evaluate atomic recombination coefficients from a knowledge of the dissociation rate constant and the equilibrium constant for the reaction. For a nearest-neighbor transition model of a diatomic molecule, this theory also predicts that the atomic recombination coefficients should decrease as T−2 at sufficiently high temperatures.
Vibrational Relaxation of Deuterium by a Quantitative Schlieren Method
Authors: Kiefer John H. , Lutz Robert W. 
Published: January 2005

A quantitative schlieren method is described which uses photomultiplier detection of the deflection of a narrow gas-laser beam to obtain a close approximation to a point measure of density gradient. This method is very sensitive to rapid density changes (a gradient of 5×10−5 g/liter·mm can be detected in argon) and laboratory relaxation times as short as 0.2 μsec can be measured in the shock tube. The application of this technique to studies of vibrational relaxation is discussed in detail, and the method is compared with the integrated schlieren of Resler and Scheibe for this application.
This technique has been applied to a shock-tube study of the vibrational relaxation of mixtures of D2 in Ar with the results, in atmosphere·seconds, Pτ = (2.7±0.3)×10−10 exp[(110.5±1.5)/T⅓], (1100°—3000°K) for pure D2, and Pτ = (1.0±0.7) × 10−9 exp[(118±10)/T⅓], (1600°—3000°K) for D2 dilute in Ar. The experimental results are in serious disagreement with both the correlation scheme of Millikan and White and the SSH theory.
Effects of Charge Compensation on the Absorption Spectrum of Yb3+ in Cadmium Fluoride
Authors: Banks E. , Wagner P. 
Published: January 2005

The absorption spectrum of Yb3+ in CdF2 has been found to consist of two spectra which are distinguishable on the bases of differences in integrated absorption intensity, temperature dependence, and effects resulting from impurity compensation. One spectrum is similar to those observed for Yb3+ in yttrium gallium garnet and YbCl3·6H2O and is little affected by impurity compensation, nor does it exhibit any unusual temperature dependence. The other spectrum, which strongly resembles that for Yb3+ in aqueous solution, is markedly sensitive to both temperature and impurity compensation.
Optical correlations with the extent of impurity compensation and lattice parameter suggest that one of the spectra is due to an associative interaction between Yb3+ and interstitial F−, and that interstitial F− is removed in a quantitative manner by the impurity compensator Na+.
Alkali-Atom—Halogen-Molecule Reactions in Molecular Beams; The Spectator Stripping Model
Authors: Minturn Robert E. , Datz Sheldon , Becker Richard L. 
Published: January 2005

Crossed-molecular-beam techniques have been used to study reactive collisions in some alkali-metal—halogen systems (Cs+Br2, K+I2, K+Br2, Rb+IBr). Both the absence of rainbow scattering in elastic-scattering distributions and the magnitude of the reactive collision yield suggest large reaction cross sections in the order of 100 Å2 for all the systems studied. The position and width of the angular distributions of alkali halide product molecules indicate forward scattering in the center-of-mass system with recoil energies close to zero.
These observations suggest a stripping mechanism for these reactions and a model, based upon the simplest possible stripping mechanism, has been proposed to explain the observations. This model, called spectator stripping, predicts the gross features of the distributions and leads to a prediction of the maximum intermolecular distance at which reaction can occur. This corresponds to a reaction cross section of approximately 100 Å2.
The effect of electron transfer from the alkali atom to the halogen molecule at large distances is shown to be almost equivalent to spectator stripping for these reactions if the vertical electron affinity of the halogen molecule is used. Even larger cross sections would be predicted if the adiabatic electron affinity were used; however, an evaluation of the probability of adiabatic adjustment of the halogen internuclear distances during the collision time appears to preclude this possibility.
Infrared-Reflection Spectra of Molten Fluoride Solutions: Nb (V) in KF:LiF
Authors: Fordyce J. Stuart , Baum Ruth L. 
Published: January 2005

Infrared-absorption spectra derived from reflectivity measurements over the range 4000 to 200 cm−1 have been obtained for KF:LiF melts containing Nb (V). The results show two strong bands at 315 and 555 cm−1 and a very sharp medium band at 250 cm−1 superimposed on the former. Comparison of these spectra with well-characterized solid compounds such as K2NbF7 demonstrate that the NbF7−2 complex ion is the predominant species in these melts.
The NbOF63— anion is shown to be the predominant species in melts containing hydrolyzed Nb (V).
Studies of Lithium Hydride Systems. III. Solid—Liquid Equilibrium in the Lithium Bromide—Lithium Hydride and Lithium Iodide—Lithium Hydride Systems
Authors: Johnson Carl E. , Wood Scott E. , Crouthamel Carl E. 
Published: January 2005

Thermal analysis has been used to determine the temperature—composition solid—liquid equilibrium diagrams for the two binary systems, LiBr–LiH and LiI–LiH. Both are simple eutectic systems with no experimental evidence for the formation of solid solutions. Eutectic compositions of 29.7 mole % lithium hydride, mp 453.3°C, and 23.5 mole % lithium hydride, mp 390.8°C, were observed for the bromide and iodide systems, respectively. The values of the chemical potential of each component have been calculated along the equilibrium curves where the solutions are saturated with respect to the pure solids.
The limiting slopes of the saturation curves are consistent with the interpretation that lithium bromide and lithium iodide both exist primarily as un-ionized dimers when dissolved in lithium hydride and that lithium hydride exists primarily as an un-ionized monomer when dissolved in either lithium halide.
High-Temperature Vapor-Pressure Studies of UO2 by the Effusion Method and Its Thermodynamic Interpretation
Authors: Ohse Roland W. 
Published: January 2005

A high-temperature effusion investigation under vacuum of the vapor pressure of UO2 is presented over the temperature range from 2200° to 2800°K. A least-square analysis of the experimental results yielded the equation logp (mm)=12.426–3.318(104/T).The latent heat of sublimation ΔH°298=148.6 kcal/mole was determined by applying the third-law method of thermodynamics. Blackbody hole readings, corrected for both the transmissivity of interposed windows and the cavity temperature, were checked by measuring the spectral emissivity of the optically smooth polished tungsten surface at 0.65 μ, which decreased from 0.44 at 2300°K to 0.416 at 2850°K.
Compatibility tests at 2800°K revealed no signs of a noticeable reaction between UO2 and the tungsten effusion cell.
Ionic Adsorption and Dissociation Cross Section for Nitrogen
Authors: Winters H. F. 
Published: January 2005

The adsorption of energetic N2+ ions on nickel and molybdenum surfaces has been investigated. Comparison of the sticking probabilities of N2+ and Ar+ as a function of ion energy indicates that the binding mechanism for these two gases is different. The experimental evidence suggests that the mechanism causing adsorption of N2+ may be dissociation upon collision with the surface and the subsequent adsorption of the resulting atomic nitrogen.
The total absolute dissociation cross section has also been measured in nitrogen for electron energies from 0 to 300 eV. The cross section has a maximum value of 2. 10−16 cm2 at an electron energy of about 90 eV.
Raman Spectral Studies of the Effects of Temperature on Water and Electrolyte Solutions
Authors: Walrafen G. E. 
Published: January 2005

All known intermolecular Raman bands of water, viz., the hydrogen-bond bending and stretching bands, and the librational bands, decrease rapidly in intensity with temperature rise. In contrast, the librational intensities of water in electrolyte solutions exhibit very small variations with temperature. The intensity decreases observed for pure water indicate that hydrogen bonds are broken by increase of temperature, but the near constancy observed for solutions indicates that primary hydration is not greatly affected, even at temperatures near the normal boiling points of some of the solutions studied.
Integrated Raman intensities of the hydrogen-bond-stretching vibrations of pure water at 152–175 cm−1 were redetermined in the temperature range of −6.0° to 94.7°C. The new intensity data, which are more accurate than the old [cf., J. Chem. Phys. 40, 3249 (1964)], yield the values ΔH°=5.6 kcal/mole and ΔS°≈19 cal/deg·mole for the process B→U, where B refers to water molecules which contribute intensity to the 152–175-cm−1 Raman band, and U refers to molecules which make very little or no contribution. Interpreted in terms of non hydrogen-bonded monomeric defects in a tetrahedral liquid lattice, the above ΔH° yields a value of 2.8 kcal/mole H bond in resonable agreement with Scatchard's value of 3.41 kcal/mole H bond. The value of ΔS° for the process B→U also leads to interesting comparisons with known entropies, but the calculated heat capacity of water is only in fair agreement with accepted values.
The observed insensitivity of the solution librational intensities to changes of temperature indicates that primary hydration is involved almost exclusively. This conclusion complements the previous observations involving linearity of librational intensity with electrolyte concentration [cf., J. Chem. Phys. 36, 1035 (1962)], since both observations can be explained by primary hydration.
In addition, molar librational intensities (obtained from the temperature studies) confirm the large anionic effects reported previously, with Br−&gt;Cl−, but they also indicate that the effects produced by NH4+ are much smaller than those arising from Li+, Na+, and K+. It is apparent, therefore, that at least some cationic effects can be observed in the Raman spectra.
Polarization Studies on Recombination Luminescence in a Rigid Organic Solution
Authors: McClain W. M. , Albrecht A. C. 
Published: January 2005

Polarized photoselection techniques are applied to stimulated recombination luminescence in a rigid organic solution at 77°K. Ionization with polarized ultraviolet light leads to an oriented sample of solute cation and electrons trapped in the matrix. Infrared light stimulates the recombination of the electrons with the oriented population of cations giving a recombination luminescence whose polarization characterizes the orientation of the cations.
Two interpenetrating populations of cations are produced sequentially using perpendicular polarization directions for the ionizing light. Recombination emission from the two populations may be distinguished by their differing polarization, and it is found that the electrons ejected in the ionization of one population do not recombine with the cations of the other.
These results are examined in some detail. It is concluded that in the majority of ionization and recombination events, each electron remains highly correlated with its site of origin.
Kinetics of Desorption of the β-Nitrogen States Chemisorbed on Tungsten
Authors: Madey T. E. , Yates John T. 
Published: January 2005

The kinetics of desorption of the strongly chemisorbed β1 and β2 nitrogen states on tungsten have been studied. Independent techniques of isotopic mixing and flash-filament desorption have been employed. The rate of production of 14N15N (g) from 14N2(g) and 15N2(g) in a steady-state flow experiment is completely accounted for by the kinetically determined rate of desorption from the chemisorbed layer. β1-nitrogen appears to desorb by first-order kinetics; β2-nitrogen desorbs in a complex manner with higher-order kinetics. The apparent β2 desorption order decreases markedly as temperature increases. A superposition of two or more unresolved substates in the β2 state is postulated. The temperature variation of desorption order can be accounted for by a lack of achievement of equilibrium between the spatially separate β2 substates during desorption at scan rates of 12.5°K/sec or greater.
Above 1500°K, where the steady-state coverage of nitrogen is very low, a sticking coefficient of less than 0.02 has been measured. The sticking coefficient is nearly constant in the range 1500°—1700°K and over a 25-fold pressure range.
Kinetics of Unimolecular Breakdown. II. Time-Dependent Theory
Authors: Levine R. D. 
Published: January 2005

The solution of the Schrödinger time-dependent equation is discussed in a form suitable for chemical kinetics. The evolution of the system is considered with respect to the simultaneous evolution of independent events and the sequence evolution of events.
The lifetime is defined as the average duration of an event. It is shown to be the inverse of the rate constant for the activated states. The distinction between unimolecular and bimolecular reactions is discussed and the realization of genuine termolecular processes is considered.
14N Hyperfine Structure in ESR Spectra of Heterocyclic Anions
Authors: Henning J. C. M. 
Published: January 2005

ESR spectra of the anions of several aromatic heterocyclics, containing nitrogen, have been recorded with the object of correlating the observed nitrogen hyperfine splittings with the π-electron spin-density distributions.
As a result of this analysis it is found that the 14N hfs splitting constant (AN) depends not only on the π spin density at the nitrogen site (ρNπ) but also on the π spin densities at the nearest-neighbor carbon atoms (ρC1π and ρC2π, respectively).
If, to a first approximation, the relationship is written as AN=QNNNρNπ+QCCN(ρC1π+ρC2π),where C1 and C2 are the two nearest neighbors of N, the coupling factors QNNN and QCCN are found to be +19.1±1.7 and +9.1±1.7 G, respectively.
On the Kinetic Theory of Dense Fluids
Authors: Hurt Norman , Rice Stuart A. 
Published: January 2005

In this paper we analyze the Rice—Allnatt kinetic equations using a formal perturbation expansion in which the lifetime of dynamical coherence plays a fundamental role. It is shown that:
(a) In the limit of short dynamical coherence time, the Rice—Allnatt equations are a valid description of steady-state transport phenomena in a liquid,
(b) The Kirkwood time-smoothing hypothesis is a natural expression of the nature of the coherence time expansion,
(c) The use of a separable intermolecular potential, the instantaneous nature of rigid-core collisions, and the nature of time smoothing all have interesting consequences for the derivation of Markovian kinetic equations from the Liouville equation.
Chemisorption Studies of Nitrogen on Polycrystalline Tungsten
Authors: Hill M. P. , Lecchini S. M. A. , Pethica B. A. 
Published: January 2005

The effect of nitrogen adsorption on the thermionic emission from a polycrystalline tungsten ribbon has been measured in the accelerating region both at high and low applied fields. The results have yielded information on the behavior of the work function of (100) and (111) planes towards nitrogen adsorption.
The thermionic-emission data have been compared with average work-function changes measured using a diode operating in the space-charge-limited region.
The work-function data combined with adsorption kinetics and with thermionic-emission changes during desorption have confirmed that on chemisorption:
(i) (100) planes show a decrease in the work function and have a higher sticking probability and lower heat of adsorption than (111) planes.
(ii) Conversely, (111) planes show an increase in the work function and have a lower sticking probability than (100) planes. At high temperatures nitrogen desorbs preferentially from (111) planes, and moreover the order of desorption from the two planes is different.
An initial adsorption at coverages less than 4×1013 atom/cm2, occurring on highly reactive sites tentatively associated with defects and crystallite edges has been found to increase the work function.
Correlation of the C–H Stretching Force Constant with the Nuclear 13C–H Coupling Constant
Authors: Brown Theodore L. , Puckett Janice C. 
Published: January 2005

The characteristic CH3 stretching frequencies in a number of selected compounds in carbon tetrachloride solution have been measured and compared with the nuclear 13C–H scalar coupling constant, J. The correlation provides a basis for expressing the C–H stretching force constant Kr in terms of J. Using a modified valence-force-field potential function for the CH3 group, Kr=4.74+8.8×10−3 (J−125) mdyn/Å.
The orbital contributions to Kr have been examined theoretically. Variation in fractional s character in the carbon orbital to hydrogen does not, of itself, lead to a significant variation in Kr. The force constant increases with increasing ionic character in the C–H bond, rather than as a result of hybridization changes.
Thermoluminescence in Vitreous Sodium Silicate
Authors: Bettinali C. , Ferraresso G. 
Published: January 2005

Vitreous sodium silicate has two quite distinct thermoluminescence maxima between 20° and 250°C, each having its own spectral composition (about 420 and 515 mμ, respectively). The peaks have equal activation energies (about 0.8 eV). It seems likely that, between 20° and 250°C, the thermoluminescence emission model for vitreous sodium silicate is a recombination of electrons trapped in a single energy level, with centers that probably consist of positive holes having different capture cross sections.
For the low-temperature thermoluminescence, Kikuchi's suggestion appears to have been confirmed.
Ion—Molecule Reactions between H3+ and Saturated Hydrocarbons
Authors: Aquilanti V. , Volpi G. G. 
Published: January 2005

The ion—molecule reactions of H3+ and D3+ with methane, ethane, propane, isobutane, and n-butane have been studied by high-pressure mass spectrometry, using an ion source which employs the beta rays of tritium as the ionizing medium.
The rate constants have been measured, and proton transfer has been shown to be the major mode of interaction. If not stabilized by collision, protonated methane and protonated ethane decompose by elimination of hydrogen, with a lifetime of the order of 1 and 10−1 μsec, respectively. Protonated propane and protonated butanes, which have not been detected as stable species at pressures as high as 0.3 torr, decompose by elimination of hydrogen or a smaller saturated hydrocarbon to give an alkyl carbonium ion. Some results concerning the reactivity of these alkyl ions with deuterium and the hydrocarbons are also reported.
Gas—Gas Equilibria
Authors: de Swaan Arons J. , Diepen G. A. M. 
Published: January 2005

This article deals with a remarkable phenomenon in chemical-phase theory, i.e., the limited mutual solubility of gases, which was predicted by van der Waals and first demonstrated by Krichevskii in the nitrogen—ammonia system. The phase behavior in question is characterized by a peculiar course of the critical locus in some systems for which the components have a considerable difference in volatility. Under special conditions such a system showing limited miscibility may also exhibit the barotropic phenomenon, i.e., the equilibrium phases change position in the gravitational field.
Using the conditions Temkin derived from van der Waals' applications of Korteweg's fold theory, we could predict that the helium—xenon system probably exhibits gas—gas equilibria. We have confirmed the predicted behavior by visual observations of phase transitions in helium—xenon up to 2000 atm and 65°C.
Ba(B0.5Ta0.5)O3 Ordered Perovskite-Type Compounds, Possible New Laser Host Materials
Authors: Galasso F. S. , Layden G. K. , Flinchbaugh D. E. 
Published: January 2005

The trivalent ions of Nd, Sm, and Yb were incorporated into powders of ordered perovskite-type compounds having the general formula Ba(B0.5Ta0.5)O3, where B is a trivalent rare-earth cation, In3+, Y3+, or Sc3+. Fluorescent lifetimes measured employing these materials indicate that the lifetimes for Nd3+ fluorescence are not as dependent on crystalline field as those for Cr3+ fluorescence. Of the Nd3+-doped phases studied, Ba(Gd0.48Nd0.02Ta0.5)O3 and Ba(Lu0.48Nd0.02Ta0.5)O3 were found to exhibit the longest lifetimes (800 and 850 μsec, respectively, at 77°K).
Preliminary studies show that single crystals of Ba(Y0.5Ta0.5)O3 can be grown from a B2O3 flux by slow cooling or by a modified Czochralski technique. Developing crystals of suitable quality for laser studies, however, requires further research.
Neutron-Scattering Study of Hindered Rotational Motions and Phase Transitions in Hexamethylbenzene
Authors: Rush J. J. , Taylor T. I. 
Published: January 2005

The low-frequency motions of solid hexamethylbenzene (HMB) have been investigated above and below its λ transition near 110°K by the energy-gain scattering of cold neutrons. Measurements were also obtained above and below the high-temperature phase transition near 383°K. At temperatures below the λ point the neutron spectra exhibit a band peaked at 137±5 cm−1, which is assigned to the 1→0 transitions of the torsional oscillations of the methyl groups. Above the transition this band is broadened considerably and its maximum is shifted down to 120±5 cm−1. These results show that the λ transition is associated with a small change in the forces hindering rotation of the methyl groups. Assuming a simple threefold cosine potential for the methyl groups, the torsional peaks are used to calculate ``average'' barriers to rotation above and below the λ transition of 1.07±0.09 and 1.35±0.10 kcal/mole, respectively. These barriers are considerably lower than a recent estimate of 3–8 kcal/mole from thermodynamic results. Moreover, the torsional bands and calculated barriers are also significantly lower than those obtained recently by the neutron technique for the methyl groups in o-xylene and durene (vtors≃170 cm−1, V3≃2 kcal/mole). This indicates a considerable difference between the potential experienced by a methyl group surrounded by two other methyl groups on the benzene ring and that experienced by two adjacent groups.
A second band with a maximum around 60 cm−1, which shows little change at the λ transition, is also observed in the low-temperature spectra and is attributed primarily to the over all librational motions of the HMB molecules. The spectra above and below the high-temperature transition show only small changes with the change in phase.