bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Mass Spectra and Metastable Transitions of H2S, HDS, and D2S
Authors: Dibeler Vernon H. , Rosenstock H. M.
Published: January 2005

Mass spectra are reported for isotopic hydrogen sulfides. The occurrence of metastable transitions and the effect of isotopic substitution on their relative abundances are discussed. Appearance potentials are given for the molecule and fragment ions in H2S, the molecule ions of HDS and D2S, and the principal metastable transition in each species. The latter process is interpreted as resulting from electronic transitions rather than from vibrational relaxation processes.
Absorption and Emission Spectrum of CaF2:U3+ from 2.1 to 2.5 Microns
Authors: Meredith Robert E. , Jenney Joe A.
Published: January 2005

The emission and absorption of CaF2:U3+ has been scanned at 77° and 4.2°K and linewidths have been measured. The spectrum is interpreted as arising from ions perturbed by a weak tetragonal crystal field. Preliminary results of the Zeeman effect on the narrowest lines are presented.
Spin—Orbit Interactions in Molecular Radicals
Authors: Glarum Sivert H.
Published: January 2005

Contributions to the g-tensor and zero-field parameters arising from spin—orbit interactions are derived for molecular radicals. Calculations are made for CH3, NH2, and CH2, and where experimental data are available, agreement is satisfactory. Polynuclear radicals are qualitatively discussed.
Isotope Effects on Internal Frequencies in the Condensed Phase Resulting from Interactions with the Hindered Translations and Rotations. The Vapor Pressures of the Isotopic Ethylenes
Authors: Stern Marvin J. , Van Hook W. Alexander , Wolfsberg Max
Published: January 2005

Interaction of the hindered translations and rotations with the internal vibrations in the condensed phase leads to isotope-dependent shifts of the internal frequencies. This isotope dependence is a necessary consequence of the fact that the coordinates representing the translations and rotations of the molecule as a whole are, in general, isotope dependent. This external—internal interaction is investigated and the XH2 system is employed as a simple example to demonstrate the nature of the interaction. It is shown that the experimentally determined vapor pressures of the isotopic ethylenes may be rationalized when the external—internal interaction is taken into account. A force field based on a simple cell model for liquid ethylene is obtained which yields good agreement with the experimentally determined vapor-pressure isotope effects. The force field, while not unique, fits (and is in fact partially based on) other available data on liquid ethylene.
Statistical Mechanics of Nonspherical Molecules
Authors: Steele William A.
Published: January 2005

A general approach to the calculation of the properties of classical fluids made up of nonspherical molecules is discussed. It is assumed that the total interaction energy is a sum of pairwise interactions which are arbitrary functions of the molecular separations and orientations. The pairwise interaction energy, and the two-molecule correlation functions are written as series in the complete set of orthonormal functions of the molecular orientation angles, with coefficients which are functions of the distance of separation. Explicit expressions are given for the thermodynamic properties of these systems, and for the dielectric constant and rotational friction constant. Equations for the coefficients in the series for the pair correlation function are obtained by using a coupling parameter which determines the magnitude of the nonspherical part of the potential. Finally, it is shown that the number and kind of terms which appear in the series for the interaction energy and the pair correlation function are determined by the symmetry of the molecules. In this way, one can bring about a considerable reduction in the complexity inherent in the calculation of the ensemble average properties of molecules having arbitrary shapes.
Separation of Gas Mixtures in Supersonic Jets
Authors: Reis Victor H. , Fenn John B.
Published: January 2005

The supersonic jets resulting from the free expansion of nitrogen—hydrogen mixtures from small sonic nozzles were carefully studied by means of pressure and composition probing. The apparent concentration of heavy species in the core of the jet, originally observed by others, was confirmed. The mechanism by which this separation occurs is shown to be a consequence of the presence of the probe. The deceleration occasioned by the bow shock on the probe is suggested as the cause of the separation. The previously suggested mechanism of radial migration of light species from the jet axis does not seem to be applicable to the present results.
Dielectric Dispersion of a Polar—Nonpolar Liquid Mixture Near the Critical Solution Temperature
Authors: Quinn R. G. , Smyth C. P.
Published: January 2005

The dielectric dispersion of the mixture nitrobenzene and 2,2,4-trimethylpentane has been measured at a single concentration over a temperature range from 40°C to the temperature of turbidity and at wavelengths of 575 m, 1.26, 3.22, and 10.0 cm. It was found that the dispersion can be characterized by a single relaxation time over most of the temperature range but that a distribution of relaxation times was necessary near the critical solution temperature. The distribution was also found to broaden as the temperature was lowered. The magnitude of the relaxation time was found to tend to a maximum value as the critical solution temperature was approached. The variations of the static dielectric constant and the density were also measured and found to exhibit the usual maxima. The data obtained are discussed in a qualitative manner in terms of cybotactic regions existing within the liquid and similarities between the dielectric and structural relaxation processes are pointed out.
Upper and Lower Bounds for Ground-State Second-Order Perturbation Energy
Authors: Prager Stephen , Hirschfelder Joseph O.
Published: January 2005

The first-order perturbation equation, using the Dalgarno—Lewis formulation, is arranged in a form analogous to the Poisson equation for the electrostatic potential produced by a charge distribution in a medium of variable dielectric constant. Thus, the Thomson and Dirichlet variational principles of electrostatics can be used to obtain approximate solutions to the first-order perturbation equation for systems in either the ground state or the lowest energy state of a given symmetry. The Thomson principle provides a useful lower bound to the second-order perturbation energy. The Dirichlet principle is derivable from the Rayleigh—Ritz or Hylleraas principles and gives an upper bound to the second-order energy. For excited states, the Sinanoğlu principle provides the upper bound. By optimizing the scaling of the trial perturbed wavefunction, the Hylleraas principle is presented in a somewhat improved form. As an example, the polarizability of atomic hydrogen is used to illustrate both the Thomson and Dirichlet principles and to place upper and lower bounds on the polarizability.
Molecular Orbital Study of the B 1Σu+ and 3Σu+ States of the Hydrogen Molecule
Authors: Taylor Howard S.
Published: January 2005

The molecular orbital method is applied to the calculation of the potential curve of the B 1Σu+ and of the 3Σu+ states of the hydrogen molecule. Results comparable to those obtained using much more complicated wavefunctions are obtained.
Transport in a Two-Component Square-Well Fluid
Authors: Naghizadeh Jamshid
Published: January 2005

Transport properties of a two-component dense square-well fluid are calculated with the assumption that local distribution functions are unperturbed by temperature and concentration gradients. The Onsager relations are found to be satisfied at high temperatures.
Spectra of Matrix-Isolated Water in the ``Pure Rotation'' Region
Authors: Robinson Dean W.
Published: January 2005

The infrared spectra of matrix-isolated water in neon, argon, krypton, and xenon solids near 4°K have been obtained between 29 and 60 cm—1. The few lines that are observed depend strongly on the matrix material and are in good agreement with lines in the v1 and v2 vibrational bands. This observation confirms the widely held belief that the fine structure in the near-infrared spectrum has a rotational or hindered-rotational origin.
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.
Diamagnetic Anisotropy Effects of C≡C and C≡N Bonds in Nuclear Magnetic Resonance Spectroscopy
Authors: Reddy G. S. , Goldstein J. H.
Published: January 2005

The previously reported empirical method for determining diamagnetic anisotropy contributions to chemical shifts in nuclear magnetic resonance spectroscopy, based upon a linear relationship between chemical shifts and C13–H coupling constants, has been applied to a series of compounds containing the C≡C and C≡N bonds. The anisotropy effects upon the protons in HC≡CH and HC≡N have been found to be 160 cps and 170 cps, both ±20 cps, respectively, corresponding to a value of Δχ = —16.5×10—6 cm3/mole for both bonds, if the centers of anisotropy are located at the midpoints of the bonds. These values account satisfactorily for the anisotropy effects on methyl and methylene protons in all acetylenic and nitrilic compounds studied. The value of Δχ for C≡C bond obtained by this procedure agrees well with the theoretical estimate of Pople. An attempt is made to separate the C–C σ-bond contribution from the total C≡C bond anisotropy and thus obtain the ring current effect in acetylene. The value thus obtained compares reasonably well with Pople's theoretical estimate.
Electronic Properties of a New Class of Highly Conductive Organic Solids
Authors: Siemons W. J. , Bierstedt P. E. , Kepler R. G.
Published: January 2005

Measurements of the electronic properties of a wide variety of organic salts formed from the anionradical of tetracyanoquinodimethan (TCNQ) and various cations have been made. The results indicate that in the highest conductivity salts, which have conductivities of the order of 100 Ω—1 cm—1, the electrons are degenerate as in a metal, but in the less conductive salts the conduction takes place by means of an activated process. It is not certain whether the carrier production or the carrier motion is activated.
Fluorescence of Europium Thenoyltrifluoroacetonate. II. Determination of Absolute Quantum Efficiency
Authors: Gudmundsen R. A. , Marsh O. J. , Matovich E.
Published: January 2005

The absolute quantum efficiency of the fluorescence of europium thenoyltrifluoroacetonate in acetone has been measured by a calorimetric method, and substantiated by comparing the output against that from acridone. The quantum efficiency of the fluorescence, which peaks at 6122 Å, from acetone solutions at 25°C is 0.56±0.08.
Calculation of Surface Distortion in an Alkali Halide Crystal Bounded by a Free {100} Face
Authors: Benson G. C. , Freeman P. I. , Dempsey E.
Published: January 2005

Previous calculations of the distortion in the outermost layer at a {100} face of an alkali halide hemicrystal with NaCl-type structure are extended to consider deformations occurring within the first n layers. The model permits the ions of the surface region to relax in a direction normal to the face and to be polarized by the local electric field; the equilibrium configuration is determined by minimizing the energy of the system. Results of numerical computations with n = 5 are presented for a number of alkali halides.
Classification of Rotational Energy Levels. II
Authors: Hougen Jon T.
Published: January 2005

The classification of rotational energy levels according to symmetry species of the full molecular point group, previously presented only for symmetric-top molecules, is extended to nonlinear molecules of any symmetry in states of any multiplicity. Selection rules for electric dipole transitions between the rovibronic levels thus classified are 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.
Domains in Liquid Crystals
Authors: Williams Richard
Published: January 2005

A regular domain pattern has been observed to form in nematic liquid crystals when an electric field is applied. The domains are visible in unpolarized light by either transmission or reflection. Both ac and dc fields produce similar domain patterns and these appear at a rather sharp threshold field of about 1000 V/cm. The general features of the phenomenon have been investigated. It is believed that the domains are due to ordering in the liquid of a kind which has not previously been recognized.
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.
Equation of State for Hard Spheres
Authors: Thiele Everett
Published: January 2005

Simple and exact expressions have been found for the compressibility and pressure equations of state predicted by the Percus—Yevick equation for hard spheres. The equations of state are in good agreement with the machine calculations of Wainwright and Alder, and Wood, Parker, and Jacobson.
Electronic Structure of LiH and Quadrupole Moment of Li7
Authors: Kahalas S. L. , Nesbet R. K.
Published: January 2005

Hartree—Fock self-consistent field calculations of the Roothaan (LCAO—MO) type have been carried out on an electronic computer for LiH using an extended set of basis functions. Configuration interaction calculations result in a total molecular energy of 99.3% and a dissociation energy of 89.3% of the experimental values. It is found that large contributions occur from pπ orbitals in configuration interaction. Using a general method developed in the present work, the electric-field gradient is calculated in LiH. With Klemperer, Gold, and Wharton's measurement of the LiH quadrupole coupling constant, the quadrupole moment of the Li7 nucleus is found to be —4.4×10—26 cm2. This sign is unambiguously determined to be negative, in agreement with theoretical predictions from nuclear models. The dipole moment of LiH is calculated to be —5.89 D, and the quadrupole coupling constant of deuterium in LiD is calculated to be 35.3 kc/sec.
Oscillators Perturbed by Gaussian Barriers
Authors: Chan Sunney I. , Stelman David
Published: January 2005

A simple method has been developed to generate the matrix elements of the operator exp (—βξ2) in the representation of the harmonic oscillator. These matrix elements are useful in double-minimum problems where the potential energy function may conveniently be represented by a perturbed harmonic oscillator with a Gaussian barrier. Some representative calculations involving such potential wells will also be presented.
``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.
Deuterium Isotope Effect on Glass Transformation Temperatures of Aqueous Inorganic Solutions
Authors: Shepley L. C. , Bestul A. B.
Published: January 2005

Determinations have been made on the effect of deuterium substitution on the glass transformation temperatures (Tg) evaluated for aqueous solutions of about 15 wt. % HCl and SO3 by differential thermal-analysis measurements. Complete substitution of D2O as the solvent shifts Tg from 128.1° to 131.8°K for the HCl solution and from 143.7° to 146.3°K for the SO3 solution. This shift is linear with extent of D2O substitution. If it is assumed that the potential-energy barriers to configurational changes in the supercooled liquid are not altered by deuterium substitution, the above shifts can be interpreted as consistent with the proposition that the configurational changes which are immobilized when the solutions are cooled through the glass transformation involve simply the translation of single H2O or D2O groups. On the above basis, translational frequencies around 200 cm—1 observed by Raman spectroscopy in water correspond to potential-energy barriers around 2000 cal/mole. This is in rough agreement with hydrogen-bond energies, which are around 3000 cal/mole. This identification of the barriers with hydrogen bonds provides a reasonable support for assuming the barriers insensitive to deuterium substitution.
Variational Calculations of Some S States in Two-Electron Atoms
Authors: Perkins J. F.
Published: January 2005

Nonrelativistic energies of the 21S and 23S states of He, Li+, and Be++ and the 31S and 33S states of He and Li+ were calculated by the Rayleigh—Ritz variational method, using expansions in r1, r2, and r12 as originally employed by Coolidge and James. Mass polarization corrections and 〈δ(r2)〉 have also been evaluated. For states for which values of relativistic and electromagnetic shifts are available, the energies calculated with 31-term expansions, after correction for these shifts and for nuclear motion, differ from experimental values by about 2 or 3 cm—1 for singlet and about 0.4 cm—1 for triplet states. The relative effectiveness of expansions involving one, two, or three exponential parameters is discussed. A search was made for a bound 23S state of H— but no indication of the existence of such a state was found.
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.
Energy Dependence of Cross Sections for Ion—Molecule Reactions. Transfer of Hydrogen Atoms and Hydrogen Ions
Authors: Giese Clayton F. , Maier William B.
Published: January 2005

This report describes measurements of cross sections for ion—molecule reactions by use of a technique which involves preselection of the primary ion in terms of both mass and kinetic energy. Cross sections as functions of ion kinetic energy are given for the reactionsAr++D2→ArD++D,N2++D2→N2D++D,H2++H2→H3++H,D2++N2→N2D++D,H2++He→HeH++H,D2++Ar→ArD++D.The behavior of the cross sections for the first two of these reactions, which can be considered to involve hydrogen atom transfer, is strikingly different from that of the remaining four, which can be taken as cases of hydrogen ion transfer. The comparison with previous measurements shows fair agreement; however, agreement with existing theories is rather poor.
Vapor—Liquid Equilibria of Dilute Solutions of HT in e—H2 and DT in e—D2 from the Triple Points to the Critical Temperatures of the Solutions
Authors: Bigeleisen Jacob , Kerr Eugene C.
Published: January 2005

The liquid—vapor fractionation factors for dilute solutions of HT in e—H2 and DT in e—D2 have been measured over the temperature ranges 13.95°—30.26°K and 18.67°—32.48°K, respectively. At these temperatures the respective fractionation factors are 3.66, 1.24, 1.36, and 1.07. In all cases the heavy isotope concentrates in the liquid phase. The solutions obey Henry's law in the concentration range studied (1–2×10—8M). The fractionation factors vanish at the critical temperatures of the respective solvents. The differences in the partial molal heats of vaporization of the isotopes are functions of the temperature. It is shown conclusively that the fractionation factors for the HT—H2 mixtures are appreciably smaller (∼24%) than those to be expected for dilute mixtures of D2 in H2. The difference in behavior of HT from D2 is a manifestation of the effect of the molecular structure on the phase equilibrium properties of the liquid. The principal structural effect is shown, by comparison of the experimental data with theoretical calculations, to be a coupling of the molecular rotation with the hindered translation of the molecule in the liquid.
Indirect Detection of Weak or Hidden Nuclear Magnetic Resonance Signals
Authors: Freeman R. , Anderson W. A.
Published: January 2005

High-resolution nuclear magnetic resonance signals that may not be directly observable can be detected indirectly in a double-resonance experiment that applies a weak perturbing radio-frequency field to each hidden line in turn while recording the splitting produced on transitions of a second nucleus which is spin coupled to the first. The method is illustrated for the simplest model which may be regarded as typical, three weakly coupled spin-½ nuclei, and the importance of the ``common energy-level rule'' is emphasized. The example studied is the C13 spectrum of 1,1,2,2 tetrabromoethane and it is found that the three coupling constants J(HH), J(C13H) and J(C13CH) all have the same sign, presumably positive. The chemical shift of C13 in this compound has been related to the resonant frequency of protons in tetramethylsilane in the same applied field, with an accuracy of ±1 part in 108.
Melting and Polymorphism in SbCl3 and SbBr3
Authors: Bowles Billy F. , Scott Gene J. , Babb Stanley E.
Published: January 2005

The phase diagrams for SbCl3 and SbBr3 have been determined to 175°C and 30 kbar. Two new forms are reported in each substance, and their phase diagrams are very similar. These form another example of the approximate validity of the law of corresponding states for similar solids.
Absorption and Fluorescence Spectra of Er3+(4f11) in LaF3
Authors: Krupke William F. , Gruber John B.
Published: January 2005

The absorption, fluorescence, and excitation spectra of Er3+(4f11) in LaF3 have been investigated between 3500 and 10 000 Å. Based on an energy-level scheme consistent with all observed spectral lines, a number of states have been identified. The parameters giving the best over-all agreement between the predicted ``free-ion'' spectrum and the spectrum of Er3+ in LaF3 are F2=428.708 cm-1, F4=67.784 cm-1, F6=6.751 cm-1, and ζ=2389.60 cm-1. The average deviation for 11 of these levels is 35.3 cm-1. The possible use of Er3+ in LaF3 for the generation of coherent green light is also discussed.
Fluorescence Spectral Study of Wavelength Shifters for Scintillation Plastics
Authors: Sandler Stanley R. , Tsou K. C.
Published: January 2005

An investigation of the fluorescence spectra of a series of 1,3,5-triaryl-2-pyrazoline indicated that substituents in the 3-phenyl ring shifted the fluorescence emission wavelength linearly with Brown's σp+. On the basis of this evidence the excited state is thought to have a partial positive charge located on carbon-3 of the pyrazoline ring. The shift in the absorption spectral bands of 1,3,5-triphenyl-2-pyrazoline with concentration is presented as evidence of a dimer or an associated complex. The fluorescence quenching at higher concentrations may be due to the energy dissipating effect of the dimers or complexes. The high extinction coefficient of the uv maximum and yet the similarity of the fluorescence intensity of 4,4′-bis-[5-(1,3-diphenyl-2-pyrazolinyl)] benzene to 1,3,5-triphenyl-2-pyrazoline is explained on the basis of an internal quenching mechanism. The efficiency of these two compounds as wavelength shifters in plastic scintillators are approximately equal.
Statistical Mechanics of Cross-Linked Polymers: Formation of the Infinite Network
Authors: Brodowsky Horst , Prager Stephen
Published: January 2005

It is shown that cross links of infinite functionality in equilibrium with a solution of bifunctional monomer behave as particles interacting with a Debye—Hückel type of potential. Applying the Debye—Hückel theory to a fluid consisting of such particles leads to a condensation phenomenon which corresponds to gel formation.
Photolysis of Methane by Vacuum-Ultraviolet Light
Authors: Magee Ellington M.
Published: January 2005

Methane photolysis with light of wavelength down to 1050 Å has shown that product propane does not result from reaction of the ethane that is produced. The distribution of products is very similar to the distribution found in the radiolysis of methane. This result indicates that both photolysis and radiolysis of methane proceeds mainly by a free-radical process and/or by reactions of excited molecules, rather than by reactions of ions. A mechanism involving insertion of the ethylidene radical is proposed to account for the results.
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.
Natural Expansions of Exact Wavefunctions. III. The Helium-Atom Ground State
Authors: Davidson Ernest R.
Published: January 2005

A wavefunction similar to the Kinoshita function has been analyzed into natural orbitals. As it was for the hydrogen molecule, the first natural orbital for helium is very nearly the SCF function. The first three natural orbitals describe the atom quite well. These three terms give an energy of —2.8974 hartrees and an overlap with the exact wavefunction of 0.99979. Beyond these three terms, the natural expansion converges slowly with many terms required to even approximately fit the cusp in the correlation hole.
Crystal-Field Spectra of d3, d7 Ions. II. KCoF3, CoCl2, CoBr2, and CoWO4
Authors: Ferguson J. , Wood D. L. , Knox K.
Published: January 2005

Detailed absorption spectra of crystals containing cobalt (II) in octahedral or slightly distorted octahedral sites are reported. Prime consideration has been given to the observation of the doublet states and the assignments are discussed in relation to a four-parameter crystal field theory (Dq, ζ, B, and C).
Absorption Coefficients of Xenon and Argon in the 600–1025 Å Wavelength Regions
Authors: Huffman R. E. , Tanaka Y. , Larrabee J. C.
Published: January 2005

Absorption coefficients of xenon and argon have been measured at wavelengths between the P322 ionization threshold (Xe, 1023 Å; Ar, 787 Å) and 600 Å. Similar measurements have recently been reported by us for krypton [Appl. Opt., September 1963]. A photoelectric scanning technique with a Hopfield helium continuum source as background was used at a bandwidth of 0.5 Å. The oscillator strengths of the auto-ionized lines which belong to the two overlapping series p6(1S0) —p5(2P½)ns′ and p6(1S0) —p5(2P½)nd′ and which occur between the P322 and 2P½ ionization limits were calculated from the measured absorption coefficient curve. The total oscillator strength was 0.60±25% for the first six Xe peaks and 0.011±25% for the first four Ar peaks. For xenon, the k value is 2100 cm—1±10% at the 2P½ threshold, and it drops smoothly to 1050 cm—1 at 600 Å. For argon, the k value is 930±10% at the 2P½ threshold, and the curve rises smoothly to 1200 cm—1 at 600 Å. In both cases, no lines or thresholds were observed at wavelengths shorter than the 2P½ threshold. Comparison is made with ionization efficiency data.
Energy Exchange between a Hot Tungsten Surface and Cold Gases
Authors: De Poorter Gerald L. , Searcy Alan W.
Published: January 2005

The exchange of energy between a tungsten filament heated at 1710° to 2500°K and cold helium, neon, argon, nitrogen, and carbon dioxide was studied at gas pressures from 0.1 to 10 μ Hg. The exchange of energy was found to be directly proportional to the gas pressure in the 1- to 10-μ range but essentially independent of the filament temperature. The results are interpreted in terms of a process in which the impinging gas molecules are first physically adsorbed, then heated until they gain sufficient thermal energy to overcome the attractive forces of the tungsten surface. On the average, the gas molecules then desorb at a critical temperature that is independent of the filament temperature. For the gases studied, the critical temperatures lie between 580° and 1070°K. Reaction efficiencies of oxygen and carbon dioxide were calculated from the irreversible change in the rate of power consumption of the filament produced by introduction of these gases.
Predissociation
Authors: Harris Robert A.
Published: January 2005

A general theory of predissociation is presented. Initial conditions are correctly taken into account. The wavefunction is obtained as a linear function of an external electric field. The linear absorption coefficient is written in terms of matrix elements describing the deviations from the Born—Oppenheimer approximation, from which the shapes of predissociating energy levels may be derived. Certain previous theories are shown to be limiting cases of the work described in this paper.
Radiative Transition Probabilities within 4fn Configurations: The Fluorescence Spectrum of Europium Ethylsulfate
Authors: Axe John D.
Published: January 2005

The relative intensities of the transitions occurring in the fluorescence spectrum of Eu(C2H5SO4)3·9H2O have been measured at 77° and 4°K. The strengths of both the ``forbidden'' electric dipole transitions and magnetic dipole transitions which were observed are compared to theoretical expressions and the results are discussed. The results are in reasonable agreement with recent phenomenological treatments of crystal-field-induced dipole radiation, and suggest that g-orbital configurational mixing contributes significantly to the process.
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.
Fluoride Interference Films on Uranium Dioxide. II. Kinetics of the Hydrofluorination Reaction
Authors: Ellis W. P. , Roberts B. W.
Published: January 2005

In the temperature interval 200°—300°C optically isotropic uniformly colored interference films are formed on the flat, polished surfaces of fused uranium dioxide by reaction with anhydrous gaseous hydrogen fluoride. The kinetics were determined spectrophotometrically at eight temperatures for film thicknesses up to ¼ micron. In the pressure interval 20–53 cm Hg, the rate of film growth is diffusion controlled with the thickness proportional to the square root of both pressure of HF(g) and time. The proportionality constant is β=β0exp(−Q/RT)Å/(sec×cm Hg)12 in which β0=2.59×103 and Q=6930 cal/mole with a 90% confidence interval of ±140 cal/mole. From metallographic examinations it was concluded that the uranium tetrafluoride product is deposited at the film—UO2(s) interface.
Microwave Spectrum, Structure, and Dipole Moment of Silyl Acetylene
Authors: Muenter John S. , Laurie Victor W.
Published: January 2005

The microwave spectrum of silyl acetylene has been investigated in the region 8–36 kMc. The rotational constants for the isotopic species H3Si28C12≡C12H, H3Si29C12≡C12H, H3Si30C12≡C12H, H3Si28C13≡C12H, H3Si28C12≡C13H have been determined to be 4828.66, 4775.65, 4725.65, 4803.98, 4662.34 Mc/sec, respectively. From these data the structural parameters rSiC=1.826 Å and rCC=1.208 are determined. If rCH is assumed to be 1.056 Å then rSiH=1.455 Å, <HSiH=110.3°. The length of the SiC bond is definitely shortened by its location adjacent to the CC triple bond and there may be some lengthening of the CC bond. Measurement of the Stark effect leads to a dipole moment of 0.316 D.
Chemi-Ionization in Atomic O and N Mixtures
Authors: Gatz Carole R. , Young Robert A. , Sharpless Robert L.
Published: January 2005

Saturation current methods have been used to measure ion-production rates with and without the addition of a nonreactive quenching compound (N2O). These measurements strongly indicate that metastable molecules play a decisive role in chemi-ionization processes occurring in atomic O and N systems. Mobility measurements, derived from an analysis of transient currents resulting from pulsed operation of the ion-collection system, identify the predominant ion as NO+. No change in this mobility occurs from 0.6 to 100 msec after a pulsed clearing field has removed ions previously created. This and other observations indicate that NO+ is the initial ion formed by chemi-ionization processes. Only the reactions N+N+NO*→N2+NO++e and N2*+NO*→N2+NO++e are consistent with these observations.
Absorption Spectra of Polyatomic Molecules at High Temperatures. II. Benzene and Perfluorobenzene. Kinetics of the Pyrolysis of Benzene
Authors: Bauer S. H. , Aten C. F.
Published: January 2005

The near-ultraviolet absorption spectra of benzene and of hexafluorobenzene vapors were measured over the range 690° to 1900°K. The samples were diluted with argon (90%—99% of inert gas) and shock heated. Absorption coefficients were evaluated at a fixed frequency (Hg, λ2537) as a function of time after passage of the shock front [Iλ(t)], and as a function of wavelength at a fixed time interval [Iτ(λ)]. For temperatures below 1300°K for C6H6 and 1600°K for C6F6, absorptions were recorded prior to the occurrence of significant decomposition of the sample; above these temperatures values were deduced for benzene from measurements extrapolated to zero time.

Integrated absorption coefficients (f) for the 1B2u←1A1g transition were evaluated for the range in temperature given above and were compared with theoretical analyses of the effect of temperature on f numbers.

A mechanism for the pyrolysis of benzene is proposed which is compatible with flow experiments through tubes at 1500°K and the present shock-tube data.
Magnetic Characteristics of Dysprosium, Erbium, and Thulium Hydrides
Authors: Kubota Yoshio , Wallace W. E.
Published: January 2005

Magnetization—temperature data are presented for the hydrides DyH1.97 to DyH2.97, ErH1.96 to ErH3.02 and TmH1.99 to TmH2.95 and for the three parent metals. Of the 15 hydrides examined only the Dy hydrides exhibited magnetic ordering. These hydrides showed a Néel point at nearly the same temperature as that found earlier for HoH2, 8°K. The susceptibilities followed the Curie—Weiss law over most of the paramagnetic region with an effective moment nearly that of the free tripositive ion. Deviations from the Curie—Weiss law noted at low temperatures are attributed to crystal-field effects. The absence of magnetic ordering in the saturated hydrides is ascribed to the fact that these hydrides lack conduction electrons, which are essential for the magnetic coupling.