bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissociation and Isomerization of Vibrationally Excited Species. II. Unimolecular Reaction Rate Theory and Its Application
Authors: Wieder Grace M. , Marcus R. A. 
Published: January 2005

Data on quasi-unimolecular reactions have usually been compared with theoretical equations based on classical treatments, because the expressions are simpler than those obtained on the basis of a quantum model. The quantum reformulation of the RRK theory in Part I is used to compute the pressure dependence of the rate constants and the limiting low-pressure rates for a variety of unimolecular reactions without employing adjustable parameters. An asymptotic expansion of the integral for the limiting low-pressure second-order rate constant provides a very simple expression for this quantity.
The errors inherent in corresponding classical calculations are estimated by comparing these results with those obtained from the theory in its classical limit. The error is temperature dependent and at low pressures increases from a factor of about three (under typical experimental conditions) for small reactants such as O3 and N2O to 105 or more for large molecules such as cyclopropane, C2H6, and N2O5. In most cases the rates calculated from the quantum form are in reasonable agreement with those obtained experimentally when all of the reactant oscillators are assumed effective in intramolecular energy transfer.
Electron Spin Resonance of Gamma-Irradiated Single Crystal of Acetyl-L-Glutamic Acid
Authors: Katayama Mikio 
Published: January 2005

The electron spin resonance spectra of gamma-irradiated single crystals of acetyl-L-glutamic acid have been measured at 9 and 23.4 kMc/sec for various orientations of the crystal in the external magnetic field.
From the analysis of the hyperfine interaction constants, the free radical produced immediately after the irradiation of acetyl-L-glutamic acid is thought to be[Complex chemical formula]However, this radical transforms to another more stable one in the half-life of three days. The structure of the stable free radical is inferred from the hyperfine structure of its electron spin resonance.
Structural and Magnetic Characteristics of TiFe2–ZrFe2 and ZrCo2–ZrFe2 Alloys
Authors: Piegger E. , Craig R. S. 
Published: January 2005

Structures and unit-cell dimensions for a number of alloys of TiFe2–ZrFe2 and of ZrCo2–ZrFe2 have been determined at room temperature, and the magnetic properties of alloys of the two systems have been investigated over a range of temperature extending from 4° to 650°K. Results for the TiFe2–ZrFe2 system show two terminal phases separated by a two-phase region extending from 56 to 85 mole % ZrFe2. TiFe2 behaves like a strongly paramagnetic substance with a susceptibility which is practically temperature independent, whereas ZrFe2 is ferromagnetic with a Curie temperature of 355°C. The effective moment per iron atom, obtained from the observed saturation magnetization at 4°K, is 1.62 μB. The reduced moment in both the TiFe2 and ZrFe2 phases compared to that for elemental iron is attributed to a transfer of charge from Ti or Zr to iron.
The ZrCo2–ZrFe2 alloys form a single phase system which approximately obeys Vegard's law. ZrCo2 is found to be fairly strongly paramagnetic at room temperature, while at low temperature it appears to be either very weakly ferromagnetic or paramagnetic with a susceptibility which is field dependent and shows saturation effects. As ZrCo2 is dissolved in ZrFe2, the shapes of the magnetization—temperature curves change in a way which indicates that the destruction of the ferromagnetism occurs over an unusually large temperature interval. This effect is attributed to microscopic variations in the molecular field in the solid solutions. The small values of the observed magnetic moments suggest that in these materials zirconium donates electrons to iron and cobalt. When Fe in ZrFe2 is progressively replaced by Co, the average moment of Co and Fe is observed to decrease initially and to reach a minimum at about 40 mole % ZrFe2.
Spectrum of N3— in Solution
Authors: Burak Itamar , Treinin Avner 
Published: January 2005

The electronic absorption spectrum of N3— in solution was investigated. For this purpose environmental effects on this spectrum were studied, and the thermodynamic properties of the I2–N3— complex were determined. In the 190–300-mμ region the spectrum consists of at least three bands, designated by A, B, and C. Their identification is based on the comparison with the spectra of solid alkali azides. Band A which is of moderate intensity (ε∼400 liter mole—1 cm—1) appears at 230 mμ and is assigned to 1Δu←1Σg+ transition. Band B with λmax at about 200 mμ originates from a charge transfer to the solvent (CTTS). For Band C, the peak of which is at the vacuum uv, a 1Σu+ excited state is suggested.
The nature of the CTTS state of N3— is discussed and evidence is provided for the mixing of this state with the 1Δu state. The investigation of the CTTS band leads to a value for the electron-affinity E(N3)=81 kcal. One method for deriving this value is based entirely on solvent effects by means of a method which was recently developed. This method yields also an estimate of the crystallographic radius of the ion: R(N3—)∼1.92 Å.
Optical Studies of Anisotropic Color Centers in Germanium-Doped Quartz
Authors: Halperin A. , Ralph J. E. 
Published: January 2005

The optical absorption induced by x rays in germanium-doped quartz has been investigated using polarized light. The wavelength range was 220–800 mμ, and the behavior of the various bands was examined over the temperature range of 77°—600°K. Absorption bands polarized in parallel to the optical axis were observed at 250, 285, 296, 450, and about 620 mμ, and bands at 260, 272, 290, and 330 mμ were found to be polarized perpendicularly to the optical axis. The experiments also included a study of the optical bleaching of the bands and the effects of exchange of interstitial monovalent ions by electrical diffusion.
The results are discussed and correlated with results of electron paramagnetic resonance measurements carried out on the same specimens by J. H. Mackey.
Conformal Ionic Mixtures
Authors: Blander Milton , Yosim S. J. 
Published: January 2005

The excess free energy of mixing of molten reciprocal salt solutions (A+, B+, X—, Y—) has been calculated up to the second order by the perturbation method of Reiss, Katz, and Kleppa. The result is a power series containing integral powers of the ion fractions (concentrations). This demonstrates that mixtures of two salts of the same valence type cannot be considered as a mixture of a salt with a dielectric solvent.
The first term in the series is proportional to the free-energy change for the reaction AX+BY→AY+BX and is the same as the theory of Flood, Fo/rland, and Grjotheim. The results of the symmetric approximation based upon the quasilattice model are consistent with the first term and one of the second-order terms. The remaining second-order terms are related to the excess free energy of mixing in the binary systems AX—AY, BX—BY, AX—BX, AY—BY and are of a form first suggested by Fo/rland. This theory, thus, gives a relatively rigorous justification to aspects of previous theories of reciprocal salt solutions which were based upon restrictive models and assumptions.
Study of Moderately Rapid Chemical Exchange Reactions by Means of Nuclear Magnetic Double Resonance
Authors: Forsén Sture , Hoffman Ragnar A. 
Published: January 2005

A nuclear magnetic double-resonance method for the determination of chemical exchange rates has been developed. The method is applicable to systems in which a nuclear spin is reversibly transferred between two nonequivalent sites, A and B. The lifetime (τA) and spin—lattice relaxation time (T1A) in Site A are obtained through the study of the decay to a new equilibrium value of Signal A upon the sudden saturation of Signal B. The converse experiment permits the determination of τB and T1B. A number of data for cross checks are furthermore obtained through the study of the recovery of the signals upon the release of various combinations of saturating rf fields.
A simple theory based on the Bloch equations as modified by McConnell to incorporate the effects of chemical exchange is given. Experimental results on the hydroxyl proton exchange in the system salicylaldehyde and 2-hydroxyacetophenone are well described by this simple theory.
The present method, which can readily be extended to systems with several sites, offers a complement to the Gutowsky—Saika single-resonance method and is particularly suited to the study of exchange rates slower than those accessible by the single-resonance method.
600—Å Band of Helium
Authors: Tanaka Y. , Yoshino K. 
Published: January 2005

Using the third-order spectrum of a 3-m grazing incidence-type vacuum spectrograph, the 600-Å band of helium was studied in combination with an uncondensed discharge of helium operated at liquid-nitrogen temperature as well as at room temperature.
The 600-Å band is tentatively explained as originating in the transition, A 1Σu+—X 1Σg+ of He2, where the A state has a potential maximum and the molecule is formed at high vibration levels of the A state by a collision of two atoms, one normal (1s2 1S0) and one metastable state (1s2s 1S0), through the potential barrier.
The observed intensity enhancement of the neon line at 600.04 Å is also discussed with relation to the 600-Å band.
Structural Aspects of the Kinetics of Four-Center Reactions in the Vapor Phase
Authors: Benson Sidney W. , Bose A. N. 
Published: January 2005

The data on the unimolecular elimination of HX from gas-phase alkyl halides (Cl, Br, I) are examined critically in terms of the recent and less controversial results on iodides. Despite difficulties in the bromide and chloride systems due to chains and surface effects, these systems all show the same effects of α and β substitution. Using available or estimated thermodynamic data for the elimination reaction, the rate constants for the bimolecular addition reactions (HX+olefin→RX) are evaluated. Here, for the exothermic direction, the regularities are even more striking. The activation energies decrease by about 5 kcal on going from HCl to HBr and by another 5 kcal going to HI. They also decrease by about 7 kcal for the substitution for H of an α-Me and by about 1–2 kcal on substitution of a β-Me group. An equally striking aspect of these substituent effects is the directive effect of the α-Me group in locating the X atom. In the iodide systems the selectivity is 1000:1 in favor of formation of the i-RI over n-RI. This is directly observed and for the RCl and RBr systems, the same order of magnitudes can be calculated from kelim and Keq.
It is shown that these data are compatible with a very polar transition state. Ion-pair transition states are shown to require too high activation energies. It is estimated that a ``semi-ion pair'' transition state in which the olefin and HX are each polarized by about ±½ε can give semiquantitative correlation of the data. Empirically, almost any electrical properties of the molecules plot very well against the observed activation energies for either common HX or common olefin.
It is shown also that the positive inductive property of the α-Me group can be understood in terms of a simple electrostation polarization effect.
Absolute Infrared Intensity Measurements in Thin Films. II. Solids Deposited on Halide Plates
Authors: Maeda S. , Thyagarajan G. , Schatz P. N. 
Published: January 2005

When a thin film of an absorbing substance is deposited on a halide plate, because of various reflection effects, the absorption coefficient measured experimentally in transmission will not correspond to the true absorption coefficient. This paper examines the relationship between this apparent absorption coefficient (α′) and the true absorption coefficient (α). Starting with a rigorous expression for the observed transmission, a relationship is established between α′ and α expressed as an infinite series in powers of d/λ (film thickness divided by wavelength). The result is valid for small d/λ. In the limit as d→0, a very simple relationship connects α and α′. For finite (but not too large) d, higher-order correction terms are derived.
The theory is applied to the data of Wieder and Dows on SF6(s) deposited on AgCl and to the data of Yamada and Person on CS2(s) deposited on AgCl. For comparison and to calculate the higher-order correction terms, the data are also fit and analyzed using the damped oscillator model (DOM). The DOM results agree well with the theory. A marked change in band shape due to reflection effects is predicted for the two SF6 fundamentals. Some general suggestions are made concerning experimental procedures. It seems likely that the methods developed in this work will permit reliable corrections for reflection effects in thin film absorption measurements.
In the final section, a rigorous method of treating the entire problem is outlined which is applicable, in principle, in all cases. This method depends on the fact that the transmission and phase shift can be related by a Kramers—Kronig-type dispersion relation. It is thus possible, in principle, to calculate α (and the refractive index) under any circumstances without any reference to a physical model. A preliminary application of this method to the SF6 data is presented.
Nuclear Magnetic Resonance Study of the Protolysis of Trimethylammonium Ion in Aqueous Solution—Order of the Reaction with Respect to Solvent
Authors: Luz Z. , Meiboom S. 
Published: January 2005

It was found previously that the proton-transfer reaction between trimethylammonium ion and trimethylamine in aqueous solution takes place via water. In the present investigation the number of water molecules involved in this reaction was determined. Proton exchange rates were determined from NMR measurements in trimethylamine—trimethylammonium chloride buffer solutions in O17-enriched water. It is concluded that one water molecule is involved in the transfer reaction.
In the appendix, theoretical equations are derived for the dependence of the observed spin-echo decay rate on the 180° pulse rate for the case of fast exchange.
Nuclear Pure Quadrupole Relaxation and Its Temperature Dependence in Solids
Authors: Woessner D. E. , Gutowsky H. S. 
Published: January 2005

The Cu63 and Cl35 pure quadrupole relaxation times have been measured by rf pulse techniques in cuprous oxide, paradichlorobenzene, 2,2-dichloropropane, t-butyl chloride, and methylene chloride at temperatures from 77°K to room temperature. The Cu63 T1 data agree with the ionic lattice model. The Cl35 T1 data for paradichlorobenzene agree with a torsional molecular-oscillator model. For 2,2-dichloropropane the Cl35 T1 values agree with a model based on field-gradient fluctuations produced by reorienting CH3 groups. The more complicated T1 temperature dependences observed in t-butyl chloride and methylene chloride appear to be the result of multiple thermal motions. The same can be said of our limited data on the Cl35 relaxation in 1,2-dichloroethane. No discernible difference was found for the relaxation times of the two Cl35 resonance lines in methyl chloroform at 77°K.
In general, the available proton T1 and linewidth data correlate well with our chlorine results; this agreement is discussed. The chlorine spin phase memory times are governed by the local magnetic fields except when decreased by spin—lattice lifetime broadening. The inverse linewidth parameters exhibit broadening by a distribution of field gradients. The fadeout of the Cl35 quadrupole resonance with increasing temperature in 2,2-dichloropropane is the result of T1 broadening, while in t-butyl chloride and methylene chloride it is produced by phase transitions.
The Bayer model for spin—lattice relaxation by molecular torsional oscillations is treated in some detail, including a new approach which dispenses with some of his simplifying assumptions. A brief analysis is given of T1 for the case in which field-gradient fluctuations are produced by random, large-angle reorientations of groups near to the relaxed nucleus. The theory is presented for a null method of measuring the pure quadrupole T1. The method, which was used in most of our measurements, is similar to the Carr—Purcell 180°—90° pulse method for measuring nuclear magnetic T1's.
``Bond-Orbital'' and ``Modified Electron-Pair'' Calculations on the Ammonia Molecule
Authors: Tsuchida Atsushi , Ohno Kimio 
Published: January 2005

Nonempirical calculations of the electronic structure of the ammonia molecule are carried out using a ``bond-orbital'' and a ``modified electron-pair'' function. The calculated binding energies are 0.348 a.u. (76% of the experimental value) and 0.381 a.u. (83%), respectively. The best theoretical value previously known was 0.378 a.u., the result of a self-consistent LCAO calculation including limited configuration interaction.
It is concluded that the ``modified electron-pair'' function is an adequate simple approximation, and the ``frozen core'' approximation employed in the calculation is satisfactory.
The dipole moment is also calculated, and reasonable agreement with the experimental value is obtained.
Thermodynamic Properties of CH4 and CD4. Interpretation of the Properties of the Solids
Authors: Colwell J. H. , Gill E. K. , Morrison J. A. 
Published: January 2005

The paper gives the results of calorimetric measurements of the heat capacities of solid and liquid CH4 and CD4, the heats of fusion of both substances and the heat of vaporization of CD4. The results for the solids, which extend from 2.3°K to the triple points, are analyzed in some detail.
In order to account for the apparent zero-point entropies of both CH4 and CD4 quantitatively, it is necessary to recognize the existence of different nuclear spin species (as with ortho and para hydrogen) and to say that, as T approaches 0°K, each species tends to occupy its lowest available molecular energy level. No conversion between the different species has been observed. The relevance of these findings to the usual applications of the third law of thermodynamics is discussed.
The thermal transitions which occur in solid CH4 and CD4 (as well as in the partially deuterated methanes) have also been examined and an attempt made to correlate the thermodynamic results with information derived from other experiments (e.g., spectroscopic, neutron scattering) and from theory. While correlations are possible, the fundamental causes of the transitions can still not be established.
Correlations among Electronic Transitions for Carbonyl and for Carboxyl in the Vacuum Ultraviolet
Authors: Barnes Edwin E. , Simpson William T. 
Published: January 2005

Three more or less structured bands (at 55, 60, and 68 kK in propionaldehyde) are located in compounds containing carbonyl. These bands are tentatively assigned, respectively, as n′→π; n→σ* (n→3s); and π→π*.
The π→π* is tentatively located in compounds containing carboxyl, e.g, at about 67 kK in formic acid and acetic acid, and is followed as it red shifts in methyl formate and finally to 58 kK in formamide. The band is considered as perturbed carbonyl with some charge transfer until the perturbation becomes too strong—as it evidently is in dimethyl formamide where the band comes at 51 kK. Here one sees (from the absence of a Brooker deviation) that the molecule must be regarded as allylic. Other bands in carboxyl are tentatively identified as being analogous to the 55- and 60-kK bands in propionaldehyde, though the possibility of a second π→π* absorption in the region studied cannot be ruled out. The spectra of formic acid and acetic acid dimer are presented and interpreted.
Diffusion of Three Ionic Species in Liquid Solution
Authors: Gose Earl E. 
Published: January 2005

The limiting expression for simple diffusion is Fick's first law, J=DdC/dx, which states that the flux of a diffusing component is proportional to its concentration gradient. The constant of proportionality is called the diffusivity, D. In real systems the diffusivity will not be precisely constant. When a diffusing solute dissociates completely to form two ions, electroneutrality demands that the ratio of concentrations of the two ions remain constant. Thus, the two ions must have the same ``effective'' diffusivity. The limiting expression for this case is the Nernst equation Ji=[D1D2(Z1−Z2)/(D2Z2−D1Z1)]/(dCi/dx),  i=1,2.
When three ions are present in the solution, for example if Na+ and Cl— were to diffuse into a solution of K+ and Cl—, the ratios of the ionic concentrations are no longer forced to remain constant. This additional degree of freedom allows the system to exhibit a much greater variety of behavior. For example, an ionic species may remain stagnant in the presence of a concentration gradient, and may even diffuse in a direction opposite to its concentration gradient.
This paper presents, for the first time, a solution to the general three-ion problem in closed form, without mathematical approximations. The physical assumptions made are the same as those implicit in the Nernst equation; i.e., the system must be very dilute in all three ions. The applications range from industrial corrosion problems to transport phenomena in living systems.
Thermoelectric Effect in Single-Crystal Cuprous Oxide at High Temperatures
Authors: Zirin Moshe H. , Trivich Dan 
Published: January 2005

The thermoelectric effect in single-crystal cuprous oxide, measured at temperatures of 500° to 1130°C and oxygen pressures P of 160 to 2×10—6 Torr, was found always to be positive, indicating that the material is a p-type semiconductor in these ranges of conditions.
Plots of the thermoelectric power Q vs 1/T at different constant oxygen pressures yield parallel straight lines with a slope of 0.75 V. Plots of Q vs logP are mostly straight lines with slopes approximating (—2.3k) / (8q), in which k is Boltzmann's constant and q is the electronic charge.
These results can be explained fairly satisfactorily in terms of a modified Wagner model for the defect structure of Cu2O and existing theories of the thermoelectric effect in semiconductors. It is assumed that the concentration of acceptors is a function of both the oxygen pressure and the temperature and that a gradient of acceptors exists along the temperature gradient. Thus, the model shows that the factor 8, originally obtained from conductivity measurements, should also be contained in the slope of Q vs logP. The slope of 0.75 V for the plot of Q vs 1/T can be related to the energy of creating an acceptor, i.e., a copper atom vacancy, plus the energy of ionizing this acceptor.
Emission Spectrum and Thermodynamic Properties of Gallium Monoxide
Authors: Raziunas Victor , Macur George J. , Katz Sidney 
Published: January 2005

The spectrum of the GaO molecule excited in the aureole of a dc arc has been investigated and previous assignments of the vibrational energy levels of the 2Σ+→X 2Σ+ transition have been re-evaluated. The splitting of bandheads noted by earlier writers has been attributed to the isotope shift. A rotational analysis of the O–O vibrational band has been carried out. The B0′ and B0″ values are 0.3861 and 0.4108 cm—1, respectively, corresponding to internuclear distances r0′=1.829 Å and r0″=1.773 Å.
The effects of the nonrigidity of the rotator have been observed. The difference in the spin splitting of rotational levels has been determined to be γ′—γ″=0.01808 cm—1. The spectroscopic constants determined in this study were used to calculate the thermodynamic functions up to 3000°K.